Beginner questions :)

[msacco]

Hi guys, sorry in advanced, but I might ask some really stupid questions.

So I recently got into AP, my gear is far from being good for it, I own a skywatcher 200p with EQ5 GOTO, and a canon EOS 6D DSLR camera(which is rather heavy).

So far I wasn't really able to get anything good due to technical issues, but now everything should be fine and I should be going to a dark site next week, I'd like to try capturing andromeda galaxy and maybe some planetry imaging.

Meanwhile, I had a chance to watch a few tutorials on image stacking/processing as I've never actually done it before(got my hands on raw andromeda photos), the thing is I'm not quite sure how to color is achieved eventually.

From tutorials I've read I understand that you should get the image with 3 colors(which is RGB ofc), is this what I'm missing? Do I also need to take photos of the RGB for the raw images as well to get color?

I've also seen many different values such as dark, flat, offset etc, can anyone give me a short summary of when do I pick each of them?

As far as I currently understand, this is everything I need from the beginning up to a complete processed image:

1. Take long exposure images of the target, the more the better.

2. Take pictures with RGB filters, 1 photo for each filter?

3. Then I stack up the unfiltered images to get a processed image.

4. When editing in photoshop/or any other program I also add each filter image as the colors for the image, and then modify it to reveal the correct colors of the image.

Is that correct? Anything I might be missing?

Sorry for all the awful questions, I'm just not 100% sure about the whole process. Thanks in advanced!!

[vlaiv]

You will be using DSLR camera.

When using DSLR / OSC (one shot color) cameras, you don't need additional RGB filters and workflow is just a bit slightly different in that case.

OSC sensors have something called Bayer matrix. This means that each adjacent group of 4 pixels (2x2 arrangement) has 1 "red" pixel, 1 "blue" pixel, and two "green" pixels. Each of these pixels have their own little integrated filter - either R, G or B.

Raw image taken with such camera is "mono" - meaning it only has one value per pixel (and not 3 values like RGB). To turn such image into RGB image you need to do something called debayering / demosaicing. Software handles that for you, but you need to tell it that you are working with bayer matrix RAW images rather than regular mono images. You also need to know bayer matrix order (I think that it is written in raw files for DSLR and you can get specs from camera vendor for astro OSC cameras). It will be something like R-G-G-B or similar (left to right, top then bottom row in 2x2 segment).

When working with DSLR camera, this would be your workflow:

1. Because your camera is not cooled, get some bias frames at the beginning.

Bias frames are just readout signal from camera sensor - that means minimum exposure time and no light, so cover scope and set to minimum exposure length.

2. Get some Dark frames before you start

Dark frames represent camera response to long exposure without any light - it just involves signal accumulated due to heat of sensor. It contains bias signal within (that is why we take bias separately so we can remove it later if it suits our purpose). Dark frames must be on same settings as lights and of same duration with scope covered - meaning no light is present. Bias frames need same ISO and other settings, covered scope and minimum exposure length

3. Do set of exposures on your object (same settings as darks, same exposure duration, but remember to uncover the scope )

4. Do another set of darks at the end. In principle you don't need to do this, but since you don't have set point cooling camera, and there will be temperature drop during the night, darks at the end of the session will be better match for light subs taken close to the end of the session. Most people don't bother with this and only take darks at the beginning or at the end of a session (some even don't bother with darks at all, but more on that later).

5. Take flats and flat darks. Flats are taken by various means - some people use dedicated flat boxes, some wait till dawn and point scope to the sky and cover it with white T-shirt or some other cloth to make field illumination even. Some use laptop screen held against the telescope. Point with flats is to give some sort of flat/uniform illumination inside telescope. You want your exposure to be such that there is no clipping in histogram and that histogram peak is somewhere between 2/3 and 3/4 (you are aiming for strong signal but no clipping and in linear region of sensor). Flats usually are very short exposures (sometimes as low as dozen of ms, sometimes up to 1-2 seconds, depends on camera and strength of flat source).

Flat darks are subs taken with exact same settings as flats except light is removed - you get them with your scope covered. They are used to calibrate flat frames.

6. After you have all the frames, you fire up stacking program, tell it about all the frames you have, select suitable options - like tell it that it is working with OSC bayer matrix and such and it will produce high dynamic range stack of your images, usually in either 16 or 32 bit.

If you load this result it will be color image, but you won't see almost anything in that image except few stars. This is because image is so high dynamic range and target is so dim that it hides in shadows. Next step is to "develop" your image - or do processing in your favorite image manipulation software. You load this image, and first thing you do is histogram stretch to bring signal that hides in shadows into view. This is delicate operation because there will be noise as well. You want to hit sweet spot between showing enough of signal while not showing too much of noise. Next you can do some color balancing, saturation, denoising, sharpening - what ever suits your fancy.

Now just few more pointers. There are couple of ways to do proper calibration. All other calibrations will not be "proper", but that does not mean that they can't work in particular cases. Main problem that you will face is the fact that you don't have set point cooling on your DSLR, so sensor temperature will change with ambient temperature (as imaging session lasts in to the night, ambient temperature will fall - this means check your focus from time to time, and also means that sensor temperature will change if you don't have set point cooling).

If you don't have matching darks, you can't do proper calibration. This includes temperature at which both lights and darks were taken needs to match. There is algorithmic way around this and it is called - dark frame optimization / scaling. Algorithm tries to match darks to lights by scaling them. This works fine in some cases, but for it to work you need bias frames. Bias signal does not depend on temperature and needs to be removed from darks before algorithm tries to scale them. Some sensors don't have usable bias and you can't use this algorithm with them. I think that most DSLRs have stable bias and you can use it.

Because of this issue with darks and temperature, some people choose not to use darks at all - they just use bias files to remove bias and count on the fact that dark current is uniform across the sensor (sensors with amp glow have non uniform dark current and amp glow will show in this case).

You can also skip flats - you run risk of dust bunnies or vignetting showing on your image. You can skip flat darks, but in that case, as well in case of not using dark frames you run a risk of flats over or under correcting.

How much of these problems will show if any, depends on particular camera and settings, so you will have to experiment, or take advice from someone who used/uses DSLR camera (I only do dedicated astro cameras, so can't give precise advice for DSLR cameras).

Hope this helps and answers your questions (and sorry if I just added confusion).

[bobro]

Great explanation from @vlaiv - first time I have understood the reason for taking bias frames.

[michael8554]

3 hours ago, vlaiv said:

You can also skip flats - you run risk of dust bunnies or vignetting showing on your image

Don't Flats help STOP dust bunnies and vignetting showing ?

Typing error ?

Michael

[Starwiz]

12 hours ago, msacco said:

1. Take long exposure images of the target, the more the better.

If you are not auto-guiding, then your exposure time will be limited before you start seeing star trails.   Maximum exposure length will depend on how good your mount is and how well it is polar aligned.  I can't say what it will be with your kit as I have the 200p on an NEQ6 mount.  Maybe someone else can comment?

So, you'll be better off taking a lot of shortish exposures, then stacking these.  I would experiment by taking different length subs, then examining these before you start your main imaging run.

You might want to start off as I did, by imaging some of the brighter DSOs, such as star clusters and planetary nebulae.

John

[vlaiv]

9 hours ago, michael8554 said:

Don't Flats help STOP dust bunnies and vignetting showing ?

Typing error ?

Michael

Don't think it is typing error - maybe error in expression, I meant to say:

You can also skip flats but THEN you run a risk of dust bunnies and vignetting showing in your images. I need to be more careful when phrasing a sentence

Thanks for pointing it out and good thing we made this clear for everyone else.

[msacco]

14 hours ago, vlaiv said:

You will be using DSLR camera.

When using DSLR / OSC (one shot color) cameras, you don't need additional RGB filters and workflow is just a bit slightly different in that case.

OSC sensors have something called Bayer matrix. This means that each adjacent group of 4 pixels (2x2 arrangement) has 1 "red" pixel, 1 "blue" pixel, and two "green" pixels. Each of these pixels have their own little integrated filter - either R, G or B.

Raw image taken with such camera is "mono" - meaning it only has one value per pixel (and not 3 values like RGB). To turn such image into RGB image you need to do something called debayering / demosaicing. Software handles that for you, but you need to tell it that you are working with bayer matrix RAW images rather than regular mono images. You also need to know bayer matrix order (I think that it is written in raw files for DSLR and you can get specs from camera vendor for astro OSC cameras). It will be something like R-G-G-B or similar (left to right, top then bottom row in 2x2 segment).

When working with DSLR camera, this would be your workflow:

1. Because your camera is not cooled, get some bias frames at the beginning.

Bias frames are just readout signal from camera sensor - that means minimum exposure time and no light, so cover scope and set to minimum exposure length.

2. Get some Dark frames before you start

Dark frames represent camera response to long exposure without any light - it just involves signal accumulated due to heat of sensor. It contains bias signal within (that is why we take bias separately so we can remove it later if it suits our purpose). Dark frames must be on same settings as lights and of same duration with scope covered - meaning no light is present. Bias frames need same ISO and other settings, covered scope and minimum exposure length

3. Do set of exposures on your object (same settings as darks, same exposure duration, but remember to uncover the scope )

4. Do another set of darks at the end. In principle you don't need to do this, but since you don't have set point cooling camera, and there will be temperature drop during the night, darks at the end of the session will be better match for light subs taken close to the end of the session. Most people don't bother with this and only take darks at the beginning or at the end of a session (some even don't bother with darks at all, but more on that later).

5. Take flats and flat darks. Flats are taken by various means - some people use dedicated flat boxes, some wait till dawn and point scope to the sky and cover it with white T-shirt or some other cloth to make field illumination even. Some use laptop screen held against the telescope. Point with flats is to give some sort of flat/uniform illumination inside telescope. You want your exposure to be such that there is no clipping in histogram and that histogram peak is somewhere between 2/3 and 3/4 (you are aiming for strong signal but no clipping and in linear region of sensor). Flats usually are very short exposures (sometimes as low as dozen of ms, sometimes up to 1-2 seconds, depends on camera and strength of flat source).

Flat darks are subs taken with exact same settings as flats except light is removed - you get them with your scope covered. They are used to calibrate flat frames.

6. After you have all the frames, you fire up stacking program, tell it about all the frames you have, select suitable options - like tell it that it is working with OSC bayer matrix and such and it will produce high dynamic range stack of your images, usually in either 16 or 32 bit.

If you load this result it will be color image, but you won't see almost anything in that image except few stars. This is because image is so high dynamic range and target is so dim that it hides in shadows. Next step is to "develop" your image - or do processing in your favorite image manipulation software. You load this image, and first thing you do is histogram stretch to bring signal that hides in shadows into view. This is delicate operation because there will be noise as well. You want to hit sweet spot between showing enough of signal while not showing too much of noise. Next you can do some color balancing, saturation, denoising, sharpening - what ever suits your fancy.

Now just few more pointers. There are couple of ways to do proper calibration. All other calibrations will not be "proper", but that does not mean that they can't work in particular cases. Main problem that you will face is the fact that you don't have set point cooling on your DSLR, so sensor temperature will change with ambient temperature (as imaging session lasts in to the night, ambient temperature will fall - this means check your focus from time to time, and also means that sensor temperature will change if you don't have set point cooling).

If you don't have matching darks, you can't do proper calibration. This includes temperature at which both lights and darks were taken needs to match. There is algorithmic way around this and it is called - dark frame optimization / scaling. Algorithm tries to match darks to lights by scaling them. This works fine in some cases, but for it to work you need bias frames. Bias signal does not depend on temperature and needs to be removed from darks before algorithm tries to scale them. Some sensors don't have usable bias and you can't use this algorithm with them. I think that most DSLRs have stable bias and you can use it.

Because of this issue with darks and temperature, some people choose not to use darks at all - they just use bias files to remove bias and count on the fact that dark current is uniform across the sensor (sensors with amp glow have non uniform dark current and amp glow will show in this case).

You can also skip flats - you run risk of dust bunnies or vignetting showing on your image. You can skip flat darks, but in that case, as well in case of not using dark frames you run a risk of flats over or under correcting.

How much of these problems will show if any, depends on particular camera and settings, so you will have to experiment, or take advice from someone who used/uses DSLR camera (I only do dedicated astro cameras, so can't give precise advice for DSLR cameras).

Hope this helps and answers your questions (and sorry if I just added confusion).

Wow, amazing explanation, thanks a lot for that! I had to read it a few times to stack(Ba Dum Tsss) and process all the information here. A few things I'm still find kinda confused about:

How do I take the bias frames before trying to even image my target? How do I know which ISO and exposure time to use? Same goes for dark frames.

The logical process to me would be setting everything up, trying to image the target, get all the settings correctly, and only then get all the bias and dark frames.

Also, how much frames do I approximately need to take for each one?

For example, let's say I have 20 light images, what is the image ratio for the other frames?

As for the colors, I'm still not quite sure I understood how it should work, I have the raw images of andromeda now, I believe that bias/dark/flats could improve the image further, but that doesn't seem to have any assistance color wise.

How do I go about getting color on the stacked image?

Thank you so much for the incredibly detailed answer again, it was very very useful, and helped me understand how I should get it started.

[carastro]

Quote

How do I take the bias frames before trying to even image my target?

Just set the camera to the shortest exposure it will take and put the lens cap on.  You don;t even have to have the camera attached to the scope.  You can keep these and just keep reusing them all the time you use this camera.

Quote

How do I know which ISO and exposure time to use? Same goes for dark frames.

Generally for a DSLR it is best to use 800iso, and if you were guiding on a better mount (I will come to that in a minute), you can do 5 minute exposures.  If you are not guiding you will get star trails and much depends on how good your PA is.  You will have to experiment and see how long you can image before you get star trails.

Dark Frames:  Generally these need doing each time you image as they need to be the same temperature as when the light frames were done for best results.  But don't waste good imaging time doing darks, do them when you have a cloud interruption, or While you are setting everything up or taking everything down.  

Number of exposures and Darks flats and Bias:

Number of light exposures will depend on how much you can manage to get done, as many as you can manage is the answer to that.  the more you have the smoother will be the finished result.

As regards number of dark, flats and Bias, Some people do loads, I never do much more than 15 of each regardless of number of exposures.

Flats: 

Vlaiv has described them well, but the length of exposure is very important, otherwise they won't do anything for your images if over exposed.  This can be tricky for a newbie but you need to get the histogram so it is 1/3 to less than half way accross from the left.  This will require some experimentation.  With my first DSLR I found if I set the camera to AV and 100ISO the camera would automatically take the correct flat, but this did not work with my 2nd DSLR unfortunately so I had to do it the hard way. 

Getting colour:

Nothing to do with the Darks flats and Lights, it is to do with your processing skills and how much colour there is in the target.  What software are you using for processing so we can offer advice?

Mount and telescope:

You have rather a large scope and heavy camera on too small a mount, and you will find great difficulty getting good results with this set up due to stability and possibly wind.  But you can use it to "cut your teeth" on imaging, but either you will have to use a smaller scope, or get a sturdier mount if you want to progress.  

Does your mount guide, as this will also be a big step forward enabling you to do longer exposures?

M31 Andromeda galaxy.  

This is a large target and too big for your FOV.  I would suggest you find something a bit smaller. unless you are happy to create a mosaic and do it in two halves, but this is not really something for a learner.

HTHs

Carole 

 

Edited July 21, 2019 by carastro

[vlaiv]

12 minutes ago, msacco said:

Wow, amazing explanation, thanks a lot for that! I had to read it a few times to stack(Ba Dum Tsss) and process all the information here. A few things I'm still find kinda confused about:

How do I take the bias frames before trying to even image my target? How do I know which ISO and exposure time to use? Same goes for dark frames.

The logical process to me would be setting everything up, trying to image the target, get all the settings correctly, and only then get all the bias and dark frames.

Also, how much frames do I approximately need to take for each one?

For example, let's say I have 20 light images, what is the image ratio for the other frames?

As for the colors, I'm still not quite sure I understood how it should work, I have the raw images of andromeda now, I believe that bias/dark/flats could improve the image further, but that doesn't seem to have any assistance color wise.

How do I go about getting color on the stacked image?

Thank you so much for the incredibly detailed answer again, it was very very useful, and helped me understand how I should get it started.

Astro photography is a bit different than regular photography in the way you treat your settings.

With regular photography you compose your shot, do metering, decide on F/stop, then see what sort of exposure do you need (to avoid or impart blur), set your ISO based on those two, etc ...

This is because you are taking single image, and you want to get it right in single image.

With AP you are stacking images, and you need to process your image to get meaningful result. This is because in AP you have enormous dynamic range in your image (or rather captured data). You can have as much as 10 mags of difference in stars in single image - that is x10000 light intensity.

That is why with AP you don't aim for "good exposure", you aim for good SNR, and you will adjust your exposure in post processing (think histogram manipulations to show what is in shadows in regular image - most of the stuff in AP is in shadows).

In AP with DSLR, ISO should be always set to one value (each camera has best ISO value for AP), and that is most often ISO800 (some have ISO400 as best, while others might be best at ISO1600). Do a search for your camera model to see if you can find recommended ISO value for AP. This means that ISO will be known in advance.

Same goes for exposure time - it is not governed by brightness of the target like in regular photography, it is dictated by other factors, and here is a short list of things that impact it:

- Go with longest exposure that you can manage

- You should take care not to saturate because of LP (light pollution) or to saturate parts of target. In general you can circumvent saturation of stars and bright target parts by using small set of short exposures at the end of session ("advanced" technique).

- Depending on your mount / guiding / polar alignment, mechanical issues are most likely to be limiting factor in how much you can expose for. Again this is something that you need to test. Start with fairly common exposure value for DSLR AP and build from there - 30 seconds. If your subs look ok - no star trailing, stars are tight and round, you can try to increase exposure length.

As for frame number - it is always better to have more. More of light frames, more of darks, more of bias, more of flats and flat darks .... At some point however you hit diminishing returns. We can sum things up by saying to improve things x2 you need x4 number of subs - and you can see how at some point you will hit "it does not make any sense to take more" . For example - you do total of 1h of imaging, so yes it is worth doing another 3h on the same night (provided you have time for it) to get twice better result. However, once you've done 4h for that evening, going for another x2 better result would mean three additional nights of imaging the same target - that means weather needs to cooperate, that means x3 additional setup times and doing exactly the same, etc, etc ... Yes, sometimes people are willing to spend 4 nights on one target, but for additional x2 of improvement you would need next 12 nights ... so there is a limit at some point, and that limit will be imposed by you.

As for other frames, again - depends on your budget, but get at least few dozen of each (20-30 up to 50 of each). Just as a reference, I'm a bit of nut case here, but I do couple of hundred of calibration frames each.

If you have some raw subs of Andromeda galaxy and want to get a grip on color in AP, then simply use data that you already have to learn. Stack those subs without any calibration frames - make sure you tell your stacking software to treat your RAWs as color (bayer matrix) images. This will produce color image - then import that image in some processing software (like PS or Gimp) and try to "expose" it properly - histogram stretch, apply some color correction and add some saturation. You should have color. You can always take stacked image and attach it here (maybe this thread or new one) and ask for help - people will process the image to show what you have captured (you will no doubt see different renditions of your data) and I'm sure they will explain how they got their results so you can try it yourself.

One important thing I missed in previous post - Flats need to be done without altering anything on your scope, so it is best to do it after lights while camera is still attached and you have not moved your focus. If you change something there is a good chance that you won't be able to get matching flats. Focus change, camera rotation, some dust settling or being dislodged - all of those can disrupt proper flat calibration.

 

[carastro]

Quote

One important thing I missed in previous post - Flats need to be done without altering anything on your scope, so it is best to do it after lights while camera is still attached and you have not moved your focus. If you change something there is a good chance that you won't be able to get matching flats. Focus change, camera rotation, some dust settling or being dislodged - all of those can disrupt proper flat calibration.

Oh yes, I also forgot to mention that, VERY IMPORTANT. 

Carole

Edited July 21, 2019 by carastro

[msacco]

1 hour ago, carastro said:

Just set the camera to the shortest exposure it will take and put the lens cap on.  You don;t even have to have the camera attached to the scope.  You can keep these and just keep reusing them all the time you use this camera.

Generally for a DSLR it is best to use 800iso, and if you were guiding on a better mount (I will come to that in a minute), you can do 5 minute exposures.  If you are not guiding you will get star trails and much depends on how good your PA is.  You will have to experiment and see how long you can image before you get star trails.

Dark Frames:  Generally these need doing each time you image as they need to be the same temperature as when the light frames were done for best results.  But don't waste good imaging time doing darks, do them when you have a cloud interruption, or While you are setting everything up or taking everything down.  

Number of exposures and Darks flats and Bias:

Number of light exposures will depend on how much you can manage to get done, as many as you can manage is the answer to that.  the more you have the smoother will be the finished result.

As regards number of dark, flats and Bias, Some people do loads, I never do much more than 15 of each regardless of number of exposures.

Getting colour:

Nothing to do with the Darks flats and Lights, it is to do with your processing skills and how much colour there is in the target.  What software are you using for processing so we can offer advice.

Mount and telescope:

You have rather a large scope and heavy camera on too small a mount, and you will find great difficulty getting good results with this set up due to stability and possibly wind.  Bit you can use it to "cut your teeth" on imaging, but either you will have to use a smaller scope, or getting a sturdier mount if you want to progress.  

Does your mount guide, as this will also be a big step forward enabling you to do longer exposures. 

M31 Andromeda galaxy.  

This is a large target and too big for your FOV.  I would suggest you find something a bit smaller. unless you are happy to create a mosaic and do it in two halves, but this is not really something for a learner.

HTHs

Carole 

 

 

 

 

Just to make sure I get this straight, for the bias frames I don't need to get it everytime? Like, I can simply take it right now and then always use it?

And for the dark frames, should I just take then with the lens cap on while I'm setting up all the equipment?

As for the mount, telescope and camera, as I stated above, I know it's rather heavy, I'm not expecting to get any amazing shots with it, but when and if I decide to get a different gear(whether it's a better mount of different tube) for AP, I'll have more knowledge I can use

Thanks for the great explanation! I will answer regarding the color processing below to both of you.

1 hour ago, vlaiv said:

Astro photography is a bit different than regular photography in the way you treat your settings.

With regular photography you compose your shot, do metering, decide on F/stop, then see what sort of exposure do you need (to avoid or impart blur), set your ISO based on those two, etc ...

This is because you are taking single image, and you want to get it right in single image.

With AP you are stacking images, and you need to process your image to get meaningful result. This is because in AP you have enormous dynamic range in your image (or rather captured data). You can have as much as 10 mags of difference in stars in single image - that is x10000 light intensity.

That is why with AP you don't aim for "good exposure", you aim for good SNR, and you will adjust your exposure in post processing (think histogram manipulations to show what is in shadows in regular image - most of the stuff in AP is in shadows).

In AP with DSLR, ISO should be always set to one value (each camera has best ISO value for AP), and that is most often ISO800 (some have ISO400 as best, while others might be best at ISO1600). Do a search for your camera model to see if you can find recommended ISO value for AP. This means that ISO will be known in advance.

Same goes for exposure time - it is not governed by brightness of the target like in regular photography, it is dictated by other factors, and here is a short list of things that impact it:

- Go with longest exposure that you can manage

- You should take care not to saturate because of LP (light pollution) or to saturate parts of target. In general you can circumvent saturation of stars and bright target parts by using small set of short exposures at the end of session ("advanced" technique).

- Depending on your mount / guiding / polar alignment, mechanical issues are most likely to be limiting factor in how much you can expose for. Again this is something that you need to test. Start with fairly common exposure value for DSLR AP and build from there - 30 seconds. If your subs look ok - no star trailing, stars are tight and round, you can try to increase exposure length.

As for frame number - it is always better to have more. More of light frames, more of darks, more of bias, more of flats and flat darks .... At some point however you hit diminishing returns. We can sum things up by saying to improve things x2 you need x4 number of subs - and you can see how at some point you will hit "it does not make any sense to take more" . For example - you do total of 1h of imaging, so yes it is worth doing another 3h on the same night (provided you have time for it) to get twice better result. However, once you've done 4h for that evening, going for another x2 better result would mean three additional nights of imaging the same target - that means weather needs to cooperate, that means x3 additional setup times and doing exactly the same, etc, etc ... Yes, sometimes people are willing to spend 4 nights on one target, but for additional x2 of improvement you would need next 12 nights ... so there is a limit at some point, and that limit will be imposed by you.

As for other frames, again - depends on your budget, but get at least few dozen of each (20-30 up to 50 of each). Just as a reference, I'm a bit of nut case here, but I do couple of hundred of calibration frames each.

If you have some raw subs of Andromeda galaxy and want to get a grip on color in AP, then simply use data that you already have to learn. Stack those subs without any calibration frames - make sure you tell your stacking software to treat your RAWs as color (bayer matrix) images. This will produce color image - then import that image in some processing software (like PS or Gimp) and try to "expose" it properly - histogram stretch, apply some color correction and add some saturation. You should have color. You can always take stacked image and attach it here (maybe this thread or new one) and ask for help - people will process the image to show what you have captured (you will no doubt see different renditions of your data) and I'm sure they will explain how they got their results so you can try it yourself.

One important thing I missed in previous post - Flats need to be done without altering anything on your scope, so it is best to do it after lights while camera is still attached and you have not moved your focus. If you change something there is a good chance that you won't be able to get matching flats. Focus change, camera rotation, some dust settling or being dislodged - all of those can disrupt proper flat calibration.

 

Once again, really great explanation, that's very very useful. I believe I'll pretty much just get how many frames I can get for each during my time period.

As for the image color processing, this is the final result of the image:

@All copyrights go to this guy: https://www.facebook.com/deddydayagmusicastronomypage/

He shared his RAW files, and I used Deep Sky Stacker to stack up the images, and this is the result:

In my opinion that still looks amazing, but I don't seem to get any color details here.

So should I get some color after stacking the images? Or would I get it only after some processing in photoshop/gimp? (I have both programs).

I believe it's probably something I'm missing in Deep Sky Stacker? Even though I did see something checked related to bayer matrix.

Just to point out, I'm not expecting to get any result close to that with my equipment.

Thanks again!

Edited July 21, 2019 by msacco

[vlaiv]

29 minutes ago, msacco said:

He shared his RAW files, and I used Deep Sky Stacker to stack up the images, and this is the result:

Let me get this straight, you used someone else's data to stack an image right?

Do you know what sort of raw data did you get from them? Raw subs? Already stacked image in LRGB? What sort of camera was that person using?

I would need a bit more info before I diagnose why you are getting B/W result. It is entirely possible that you applied wrong workflow based on their data, but we need to check that.

[msacco]

2 minutes ago, vlaiv said:

Let me get this straight, you used someone else's data to stack an image right?

Do you know what sort of raw data did you get from them? Raw subs? Already stacked image in LRGB? What sort of camera was that person using?

I would need a bit more info before I diagnose why you are getting B/W result. It is entirely possible that you applied wrong workflow based on their data, but we need to check that.

Maybe this would be of any use? https://www.astrobin.com/415559/?nc=user

When posting this image he also said: here are the RAW fits images of this image:

https://drive.google.com/drive/folders/1VgMbdtTBx4sEQuKP6iMWjYk4q8oK6uWE?fbclid=IwAR2nhiIGYdOed3km79F0BHDiDus1O1nHiGQ944-eHYFJrX2xfd7FKKoi6U0

So I simply downloaded all these images and stacked them up, from the data I could see that he's using ZWO 294, thought I don't really have more information.

[carastro]

This is a mono image, no wonder you are not getting any colour.  We had assumed you were trying to process data from your canon camera and not getting any colour.

He is probably using a mono camera and using filters and has given you just the luminance filter.  

This is what he says his filters were on Astrobin: Filters:Optolong Ha 7nm,  Optolong SII 6.5nm,  Optolong OIII 6.5nm

though I have to say I have never seen M31 done entirely in narrowband before.  I am sure he has simply added this to previous colour data. 

Have you taken any data with your own camera yet?

 

To explain to msacco.  If you are using a mono camera filters are used to produce colour, each of these sets are stacked separately and then combined in processing software to produce colour.  

You won't need to do this with a coloured camera. 

It would be a better exercise for you to stack and process some colour data from a DSLR camera if any-one was willing to offer some.  Or get some of your own. 

Carole 

 

Edited July 21, 2019 by carastro

[carastro]

Further puzzled as you say ............

Quote

 I could see that he's using ZWO 294,

But on the Astrobin link you provided it says Imaging camera:ASI294MC Pro

Carole 

[msacco]

4 minutes ago, carastro said:

This is a mono image, no wonder you are not getting any colour.  We had assumed you were trying to process data from your canon camera and not getting any colour.

He is probably using a mono camera and using filters and has given you just the luminance filter.  

This is what he says his filters were on Astrobin: Filters:Optolong Ha 7nm,  Optolong SII 6.5nm,  Optolong OIII 6.5nm

though I have to say I have never seen M31 done entirely in narrowband before.

Have you taken any data with your own camera yet?

Carole 

 

So to get color I'll also need the filtered images he was using I believe right?

Aight then, I have taken some planteray images with my DSLR, but nothing more than that yet.

I'll be going outside now, the skies doesn't look all that good tbh, but I'll give a shot with the lagoon nebula which should be fairly bright

Just now, carastro said:

Further puzzled as you say ............

But on the Astrobin link you provided it says Imaging camera:ASI294MC Pro

Carole 

Hmm isn't it a model by ZWO?

[carastro]

OK, I stand to be corrected on two things, yes it does look like this is the same ZWO camera, I was confused by the different prefix.

I also input your Model of DSLR camera and scope into a FOV software that I use (very useful called Imaging toolbox and Andromeda galaxy will fit into the FOV - JUST!!!

I don't think you should be trying to process data from a mono camera with filters at this stage, it is far too complex for a beginner who is not even going to be using a mono camera anyway.

I'll have a look in my archives and see if I have some very old DSLR data you can use.

Carole 

 

Edited July 22, 2019 by carastro

[alacant]

3 hours ago, msacco said:

he's using ZWO 294,

Hi. The images are in colour BUT the fits header is wrong. The debayer information is incorrect:

19:19:05: Conversion: processing...
19:19:05: Reading FITS: file frame_42.fits, 1 layer(s), 4144x2822 pixels
19:19:05: Bayer pattern found in header (BGGR) is different from Bayer pattern in settings (RGGB). Overriding settings.
19:19:05: Filter Pattern: BGGR
19:19:09: Saving FITS: file a_00001.fits, 3 layer(s), 4144x2822 pixels
19:19:09: Execution time: 4.01 s.

Cheers and HTH with the issue.

Edited July 21, 2019 by alacant

[vlaiv]

3 hours ago, msacco said:

Maybe this would be of any use? https://www.astrobin.com/415559/?nc=user

When posting this image he also said: here are the RAW fits images of this image:

https://drive.google.com/drive/folders/1VgMbdtTBx4sEQuKP6iMWjYk4q8oK6uWE?fbclid=IwAR2nhiIGYdOed3km79F0BHDiDus1O1nHiGQ944-eHYFJrX2xfd7FKKoi6U0

So I simply downloaded all these images and stacked them up, from the data I could see that he's using ZWO 294, thought I don't really have more information.

Ok, I see your point. This image has very low saturation for some reason. It can be processed, but it requires usage of more sophisticated tools (or quite a bit of fiddling with white balance and saturation in image processing).

Color is there but it is so low intensity that you need to do saturation quite a lot.

This is just a bit of fiddling around with saturation and levels in Gimp after stacking in DSS. In order to process image as this, you need to be able to wipe the background - there is quite a bit of LP gradient. You also need to do a proper white balance on the image as green is too strong, etc ...

I think above image posted on facebook was probably processed with PixInsight or similar tool which offers all of that functionality.

[vlaiv]

@alacant

This is quite confusing now, as ASI294 has RGGB bayer pattern according to ZWO website

Which means that it can be either RGGB or GBRG depending on software used (if it flips image upside / down - screen or image coordinate system).

Fits header gives wrong bayer pattern (but it does note that some software should use vertical reversed order).

[alacant]

4 hours ago, vlaiv said:

RGGB or GBRG

The OP's is neither... No idea!

Probably best to recommend taking some shots with the DSLR and forgetting the technicalities?

Cheers

Edited July 21, 2019 by alacant

[msacco]

Thanks for all the comments guys, actually, it really doesn't matter at all, since processing an image is also an important part of getting a result, I wanted to practice on that meanwhile, but the more important part is getting the shots with the camera, and that went so awful for me tonight, I didn't really get any result at all.

Since I didn't actually want to work on an object and only test, I didn't take bias,dark,flat frames, as I don't think it matters unless you actually manage to get an image, which is what I was trying to do tonight - with 0 success.

I'm not sure if that was my actual problem, but I simply didn't manage to get my prime focus unless I used a 2x barlow which sort of acted as an extension tube.

Still, even with 2x barlow I would expect to be able to get some images, even something extremely faint, but not really even that.

The main issue I encountered is that for a reason I thought I was imaging something, but ended up realizing I'm not actually imaging anything. For a reason when I took some photos, there was a red mark in the middle.

This is just one picture for example:

I'm not really sure why I received this reddish thing, at first I was quite exited, I was able to see some stars as well(not sure why I can't see it in the picture now tbh), but then I realized I'm not actually looking at anything(I thought I was on lagoon nebula), I randomly slewd my mount a bit then took another picture, and the results were pretty much the same.

I wonder what I was doing wrong..I wasn't in a light polluted area, not a really dark site either where you can easily see the milky way, but a place that should probably be dark enough, I was able to visually see M31(extremely fainted though).

Everything was set up correctly(PA, mount balance, etc). I should be going to a dark site this weekend, and I'd really want to manage to at least get just a slight glimpse of a dso.

I should have an extension tube so I'll be able to use it instead of using a barlow which sounds fairly bad to me, still, I wouldn't expect the barlow to screw up everything, and I don't think that was the issue today, still wonder what was.

Also, since I don't have a guide scope, what would be the easiest way to get focus?

Thanks!

BTW - have bought this: https://www.aliexpress.com/item/32857513893.html?spm=a2g0o.detail.1000014.41.b273b83f7PLzIc&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.13338.128357.000000000000000&scm_id=1007.13338.128357.000000000000000&scm-url=1007.13338.128357.000000000000000&pvid=0c229b61-471a-49b8-aa21-f8f49f8d6638

As I thought it might be very useful in order to get an accurate focus without having to mess around too much with too much extension vs too low extension, seems like with this I can pretty much get to the desired extension I need

Edited July 21, 2019 by msacco

[alacant]

13 hours ago, msacco said:

not really sure why I received this reddish thing

Hi

Am assuming sw200p and eos6D

This is what it looks like. No stars:(

The eos will come to focus with a a 200p with a few mm to spare when racked most of the way in. 

Perhaps best to start by removing the barlow, rack in the focuser -with the 6d attached- all the way toward the tube and point somewhere in Cygnus. Now very slowly rack out the focuser.

The telescope will only cover only a small central part of the 6d's sensor, so concentrate just on the centre of the field of view. Live view on your 'phone at iso 102400 is good for this. Keep racking outwards -very slowly- until you see stars. That's it.

13 hours ago, msacco said:

since I don't have a guide scope, what would be the easiest way to get focus?

I'm lost again now!

Cheers and HTH.

Edited July 22, 2019 by alacant

[Starwiz]

17 hours ago, msacco said:

Also, since I don't have a guide scope, what would be the easiest way to get focus?

You could always try some daytime experiments to get an idea where the focus is.

Point your scope at something on the horizon, then try focusing using live view.  With all the extra light, you shouldn't have a problem seeing something with live view.

Once, you've confirmed it can actually achieve focus, then try again on a clear night.

John

[msacco]

3 hours ago, alacant said:

Hi

Am assuming sw200p and eos6D

This is what it looks like. No stars:(

The eos will come to focus with a a 200p with a few mm to spare when racked most of the way in. 

Perhaps best to start by removing the barlow, rack in the focuser -with the 6d attached- all the way toward the tube and point somewhere in Cygnus. Now very slowly rack out the focuser.

The telescope will only cover only a small central part of the 6d's sensor, so concentrate just on the centre of the field of view. Live view on your 'phone at iso 102400 is good for this. Keep racking outwards -very slowly- until you see stars. That's it.

I'm lost again now!

Cheers and HTH.

I've found some new way to get prime focus which I didn't try, I'll give it another shot tonight.

One thing I forgot to mention, what I did was tracking saturn, then got the camera to focus, and then slewd(that's how you write it?) to M8, since the focus was locked, and I did seem to get some reddish thing in the middle, I actually thought that I was on the target, guess not.

Not sure if that happened due to focus issues, but I still can't understand the reason for the reddish thing in the middle, why would it happen at all?

Thanks! Will update more after tonight's 2nd attempt