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My first DS Image (Advice)


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not sure,

maybe I missed the advise I am willing to give as you had quite a lot already, but here are extra 2p from me :)

simply cut/3d print/or buy the Bahtinov mask.

I noticed your images got sharper and sharper, - so you are already getting towards correct focus,

but Bahtinov mask or just a simple Y mask will help a lot!

During post processing, learn to shrink stars a bit, - and do not over sharpen.

P.S.

really nice data for a start! :)

 

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Vlaiv that is a miraculous turn around for Pac man :D Thank you and good job! Happy I got useable data again, but it is an eye opener that I have a lot to learn in processing! I will invest in decent software soon, maybe give my Na and Pelican nebula a proper work over to see its true potential.

RolandKol, thank you for the tips and praise. Been a fun week. I have a mask that is built in to the cap of the telescope, and I am sure I am focusing correctly, I take my time to get even spacing between the spikes. I am looking forward to getting a dew heater for the telescope, I am wondering if that is impacting things. Next time I go out I will take an image of the focus spikes I shoot with and take a closer look.

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1 hour ago, vlaiv said:

Pacman data is actually quite nice if handled properly:

pacman.thumb.png.a19efba6e5db5806860dce6fc94821c4.png

Much less noisy than my processing. What software/workflow did you use, if I may ask?

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39 minutes ago, Iem1 said:

Vlaiv that is a miraculous turn around for Pac man :D Thank you and good job! Happy I got useable data again, but it is an eye opener that I have a lot to learn in processing! I will invest in decent software soon, maybe give my Na and Pelican nebula a proper work over to see its true potential.

RolandKol, thank you for the tips and praise. Been a fun week. I have a mask that is built in to the cap of the telescope, and I am sure I am focusing correctly, I take my time to get even spacing between the spikes. I am looking forward to getting a dew heater for the telescope, I am wondering if that is impacting things. Next time I go out I will take an image of the focus spikes I shoot with and take a closer look.

I have the same mask in the Z61, but I have not found it very useful. Although I position the spikes as they are meant to be, the stars never seem to be in focus when I look at the live view. So I end up focusing by zooming in the live view, which so far has been reasonably good. I assume that I'm doing something wrong with the Bahtinov mask, but I haven't found out what!

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22 minutes ago, Felias said:

I have the same mask in the Z61, but I have not found it very useful. Although I position the spikes as they are meant to be, the stars never seem to be in focus when I look at the live view. So I end up focusing by zooming in the live view, which so far has been reasonably good. I assume that I'm doing something wrong with the Bahtinov mask, but I haven't found out what!

Yeah I find the same with the Z73, the shapes it produces are not the best to work with. And I always rotate it and check again to be sure.

 With the mask on, I use x10 Zoom and then focus.

might look for another just to compare results 

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24 minutes ago, Felias said:

Much less noisy than my processing. What software/workflow did you use, if I may ask?

Gimp and ImageJ

In gimp I first loaded tiff and separated channels into mono images and saved them as fits format.

Then I loaded them into ImageJ where I did very small crop to remove stacking artifacts. Then I binned data x4 - as it was grossly over sampled to start with. That recovers much quite a bit of SNR.

Next step was background / gradient removal for each of channels (custom plugin for ImageJ that I wrote) and then I just made sure min / max values for each channel were the same (it's like normalizing to 0-1 range except I don't have to do that as Gimp will automatically do that when importing data - I just needed to make sure that color will be preserved and each channel image has same min and max value).

I then loaded images into Gimp, did RGB compose and three step levels stretch and a bit of wavelet denoising. Exported image as png

1 hour ago, Iem1 said:

maybe give my Na and Pelican nebula a proper work over to see its true potential.

I think that you missed focus by quite a bit in that image. Stars are huge and in fact - in blue channel stars are doughnuts rather than stars:

image.png.5229c5848f0f6ed009e726fbe7f9df2c.png

For that reason I needed to bin x6 and to sharpen things up on top of that in order to try to get decent looking stars.

In any case, here is the result:

GIMP-2_10.png.7d5b43cc9915cd634dc65f01140db725.png

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10 minutes ago, vlaiv said:

Gimp and ImageJ

In gimp I first loaded tiff and separated channels into mono images and saved them as fits format.

Then I loaded them into ImageJ where I did very small crop to remove stacking artifacts. Then I binned data x4 - as it was grossly over sampled to start with. That recovers much quite a bit of SNR.

Next step was background / gradient removal for each of channels (custom plugin for ImageJ that I wrote) and then I just made sure min / max values for each channel were the same (it's like normalizing to 0-1 range except I don't have to do that as Gimp will automatically do that when importing data - I just needed to make sure that color will be preserved and each channel image has same min and max value).

I then loaded images into Gimp, did RGB compose and three step levels stretch and a bit of wavelet denoising. Exported image as png

 

Thanks, very useful. I have only worked once or twice with separate channels, it seems that I'll have to try again. I tweaked my previous attempt, trying to reduce the noise and rethinking what I did for the contrast and the star reduction. Cosmetic changes really, and I didn't bother with the gradients since it takes me long to eliminate them, but it looks a bit better. It helps when you have a picture to follow as a model.

pacman-Edit3.thumb.jpg.284171d42975ef32248d29ca7d4e002a.jpg

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9 hours ago, vlaiv said:

Gimp and ImageJ

In gimp I first loaded tiff and separated channels into mono images and saved them as fits format.

Then I loaded them into ImageJ where I did very small crop to remove stacking artifacts. Then I binned data x4 - as it was grossly over sampled to start with. That recovers much quite a bit of SNR.

Next step was background / gradient removal for each of channels (custom plugin for ImageJ that I wrote) and then I just made sure min / max values for each channel were the same (it's like normalizing to 0-1 range except I don't have to do that as Gimp will automatically do that when importing data - I just needed to make sure that color will be preserved and each channel image has same min and max value).

I then loaded images into Gimp, did RGB compose and three step levels stretch and a bit of wavelet denoising. Exported image as png

I think that you missed focus by quite a bit in that image. Stars are huge and in fact - in blue channel stars are doughnuts rather than stars:

image.png.5229c5848f0f6ed009e726fbe7f9df2c.png

For that reason I needed to bin x6 and to sharpen things up on top of that in order to try to get decent looking stars.

In any case, here is the result:

GIMP-2_10.png.7d5b43cc9915cd634dc65f01140db725.png

That is a brilliant result! Looks a lot cleaner and sharper than my effort.

I am a complete beginner, sorry for the questions, but what do you mean by bin x6?

I tried to reduce star size a bit in GIMP by following a YouTube tutorial using the Tools > Colour select which forms a ring around most of the stars. Then using Growing and feathering before adjusting values and then editing the values in Filters > Distorts > Value propagate. But I found this process didn't seem to do anything.

I always thought the image looked a little hazy, but mostly chalked it up to dew, but if it's the focus then I am definitely going to look at getting a second mask as I feel like I am focusing well with my current mask, but the images disagree :D

thanks again for taking the time to help out 

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2 minutes ago, Iem1 said:

I am a complete beginner, sorry for the questions, but what do you mean by bin x6?

Binning is procedure where you take certain number of adjacent pixels and create one "large" pixel in their place.

Imagine you take every 2x2 pixels and sum / average their value and produce a single value in their place.

This does two things:

- it reduces pixel count of the image. If you start with say 5200px x 3600px image for example and bin x2, you'll end up with 2600px x 1800px image instead.

- it improves SNR. It's a bit like stacking, stacking also averages pixel values - but does it on pixels in successive images. Binning averages adjacent pixels on single image - but SNR improvement is the same.

If you end up over sampling your image, it is handy way to increase SNR without loosing detail. If image is over sampled in the first place - then you won't be loosing anything except pixel count. Over sampled means that you are using "too much zoom" for image sharpness - or more precisely, you are using too much pixels to capture what can be captured.

10 minutes ago, Iem1 said:

I tried to reduce star size a bit in GIMP by following a YouTube tutorial using the Tools > Colour select which forms a ring around most of the stars. Then using Growing and feathering before adjusting values and then editing the values in Filters > Distorts > Value propagate. But I found this process didn't seem to do anything.

I don't particularly like such techniques in images. I don't like to even sharpen image. If you get the sampling rate right - you'll match star size to pixels and there won't be a need to do any star reduction - stars will be small.

 

11 minutes ago, Iem1 said:

I always thought the image looked a little hazy, but mostly chalked it up to dew, but if it's the focus then I am definitely going to look at getting a second mask as I feel like I am focusing well with my current mask, but the images disagree

I don't like B masks either. Have two of them but they just gather dust. My preferred way of focusing is just by looking at the stars - I tweak the focus until stars are tightest. That might not be as practical with DSLR (I use computer and dedicated camera so it is easier to see stars on computer screen) - but why not give it a go using DSLR screen in live mode zoomed in?

In any case - that is something that you can try and maybe you'll find it easier and more precise than B-mask (if not, you can always revert back to B-mask, I'm sure that with practice one can be mastered as well).

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12 hours ago, Iem1 said:

Yeah I find the same with the Z73, the shapes it produces are not the best to work with. And I always rotate it and check again to be sure.

 With the mask on, I use x10 Zoom and then focus.

might look for another just to compare results 

It sounds like you checking LCD on the Canon while focusing...

If I am correct, 

try NINA or APT software, so you will have Live View on the Laptop with Bigger screen and proper Zoom, - software also has Bahtinov aids (focusing aids), which will give you some values of sharpness to support your viewing.

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27 minutes ago, RolandKol said:

It sounds like you checking LCD on the Canon while focusing...

If I am correct, 

try NINA or APT software, so you will have Live View on the Laptop with Bigger screen and proper Zoom, - software also has Bahtinov aids (focusing aids), which will give you some values of sharpness to support your viewing.

Yeah I use the live view, zoom in x10 and then adjust focus.

I do not currently use a laptop at all, the battery life on my laptop is absolutely horrendous and I do not have a portable power source ...I might still try with my laptop one night, see how long it holds up. I do not have guiding so it would presumably only be used to achieve a solid focus.

Related question, do you think I could find a dew heater that does not require a power bank? Perhaps one that plugs into the Sky guider pro? Or am I going to need a power bank for that anyway?

Thanks for the help :)

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18 hours ago, vlaiv said:

Gimp and ImageJ

 Then I binned data x4 - as it was grossly over sampled to start with

All very interesting ! I now have FiJi-ImageJ  and a whole new world to explore :)

What is the indication that it was over sampled ?

Thanks.

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2 hours ago, Malpi12 said:

What is the indication that it was over sampled ?

Best indication is to measure FWHM and average FWHM of stars in the image should be about x1.6 sampling rate (if you measure both in arc seconds per pixel - or simply FWHM should be ~1.6px if you measure both in pixels).

However, you can see it fairly easily by naked eye. Just do simple processing of the image and if your stars look like this at 100% zoom level:

image.png.455c645cc7d8ea38c175732baff20a51.png

Then you are hugely over sampled. You want your stars to be as small as possible when image is displayed at 100% zoom level - something like this:

image.png.a7a80de3615ef77449b6c4c436f4d3d9.png

or maybe like this:

image.png.5aec57177e8037c443987e4f65d5a4bd.png

Faintest stars should really be almost point like, and medium and brighter stars - maybe just 5-6 pixels across (if their FWHM is 1.6px then they can't be much larger in diameter when fully stretched).

Another way to test if your image is over sampled is to resample it to smaller size and then scale it back up to original size. If it shows same level of detail (just be careful - noise is not detail although our brain perceives noise as sharpness) - then you can use smaller resolution without loss of detail. For example - let's take first example and scale it down.

base.png.f7564789f6f93b356e94f6ab2173fe73.png

here is small version that I resized to only 25% of original image:

small.png.4fe65f22c62c47b329ebe04dede48ef2.png

When we scale that up back to 100% we get this:

resized.png.92ea88f1d918456b5a073a2ae17b9852.png

Original image is more aesthetically pleasing perhaps due to noise grain size (second one has lost detail in the noise and noise looks blurred) - but data is not lost - every single star / feature and its shape is the same in first and in second version.

This means that you don't need to waste pixels to record the data - you can do it with only 1/16th of pixels in this example (25% or 1/4 by width and same by height).

Note also that stars look much better in small version of the image - they look pin point-ish and much closer to other two examples that I gave as visual guide of proper sampling rate.

 

 

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On 22/07/2021 at 23:54, vlaiv said:

Gimp and ImageJ

In gimp I first loaded tiff and separated channels into mono images and saved them as fits format.

Then I loaded them into ImageJ where I did very small crop to remove stacking artifacts. Then I binned data x4 - as it was grossly over sampled to start with. That recovers much quite a bit of SNR.

Next step was background / gradient removal for each of channels (custom plugin for ImageJ that I wrote) and then I just made sure min / max values for each channel were the same (it's like normalizing to 0-1 range except I don't have to do that as Gimp will automatically do that when importing data - I just needed to make sure that color will be preserved and each channel image has same min and max value).

I then loaded images into Gimp, did RGB compose and three step levels stretch and a bit of wavelet denoising. Exported image as png

I think that you missed focus by quite a bit in that image. Stars are huge and in fact - in blue channel stars are doughnuts rather than stars:

image.png.5229c5848f0f6ed009e726fbe7f9df2c.png

For that reason I needed to bin x6 and to sharpen things up on top of that in order to try to get decent looking stars.

In any case, here is the result:

GIMP-2_10.png.7d5b43cc9915cd634dc65f01140db725.png

Hey buddy,

It's looking like I might be able to go out tonight and do some imaging. I am thinking of trying the NA and Pelican nebula again, though I highly doubt I will be able to frame up properly and combine data so I am just going for a fresh set. 

I am going to try get hand warmer strips as a make shift dew heater as I think dew my have impacted the sharpness and image detail, I was wondering if you had any other recommendations about changes to try improve the image quality.

I believe the original data was around 1.5 hrs of 2 minute exposures at ISO 800 

Any input from anyone welcome, cheers guys :)

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7 hours ago, Iem1 said:

Hey buddy,

It's looking like I might be able to go out tonight and do some imaging. I am thinking of trying the NA and Pelican nebula again, though I highly doubt I will be able to frame up properly and combine data so I am just going for a fresh set. 

I am going to try get hand warmer strips as a make shift dew heater as I think dew my have impacted the sharpness and image detail, I was wondering if you had any other recommendations about changes to try improve the image quality.

I believe the original data was around 1.5 hrs of 2 minute exposures at ISO 800 

Any input from anyone welcome, cheers guys :)

I'd say that you should focus on focus :D - try to get it spot on.

I'm not sure if DIY dew heater is a good idea (unless you know what you are doing). Too much heat will mess up your optics and focus again. With changing temperature - scope length changes (heat expansion / contraction) - and that shift focus position very slightly - but enough to throw focus off. Best conditions are stable conditions - if you can get dew heater to give stable temperature (no warm - but maybe 1-2C above ambient) - that would be ok.

Dew won't usually mess too much with sharpness. It will produce scatter around bright stars but sharpness will be ok. It will lower SNR though because it block light.

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Posted (edited)
16 hours ago, vlaiv said:

I'd say that you should focus on focus :D - try to get it spot on.

I'm not sure if DIY dew heater is a good idea (unless you know what you are doing). Too much heat will mess up your optics and focus again. With changing temperature - scope length changes (heat expansion / contraction) - and that shift focus position very slightly - but enough to throw focus off. Best conditions are stable conditions - if you can get dew heater to give stable temperature (no warm - but maybe 1-2C above ambient) - that would be ok.

Dew won't usually mess too much with sharpness. It will produce scatter around bright stars but sharpness will be ok. It will lower SNR though because it block light.

I tried to focus by x10 zoom on live view and making the star as small as possible and then checked with the mask, but they disagreed :D

The mask always has the same focus (47), but I do notice that the shape, the spikes, the mask produces on the star are not symmetrical. The spikes on one side of the star seems perfectly focused while the other is slightly off. I did take pictures but I had to clear card as I forgot from the last imaging session.

Last night was a bust anyway, I tried for the veil nebula. I checked framing on telescopius beforehand, but could never get more than a thin feint whisp in frame at any time..imaged for about 10 minutes before convincing myself I could frame it better, trying to do so, failing and then I just mucked about finding random objects to take test exposures to check framing for future projects :D  (The Whirlpool galaxy looks so tiny in my Z73 430mm :D)

I can't really complain, I did well the first 4-5 times of imaging in the last 7-10 days..i should expect at least one hiccup!

Going to get a proper dew heater and a second mask in before my next outing ..Looking forward to shooting on a moonless night, closer to winter, in true darkness!

In the meantime, time to practice editing everything I have in PS!

Thanks to everyone for all the advice and feedback, it has been absolutely crucial in developing the basics and I have had a blast this past week! 

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bahtinov's are specific to the aperture and FL of the lens, so worth checking that you've got right one for your Z73 ? jacktheprinter on ebay does a great job of doing custom ones for a tenner if not.

with bahtinov you are trying to get the straight line in the middle of the X. that's it - not trying to make the line or X sharp. If the line is in the middle, you are in focus. I know vlaiv isn't a fan, but for us mortals, I fond them invaluable unless I'm using autofocus on the asiairs.

unless you have a fancy WO perspex job, the cross patten can be pretty tiny, but same principle.

index.jpg

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