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Wish to clarify technical approach to both planetary/lunar, and deep sky imaging


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Dear all,

I wish to check with the many experienced people on this forum about how to approach the above two types of imaging.

Planetary/lunar

​I will be purchasing a Celestron 8" Schmidt Cassegrain with Advanced V mount next week all being well - am rely looking forward to lots of excellent astronomy :). After some easing I now realise that it is by virtue of their design, impossible to get a small FOV image of any planet, due to the large sensors of decent DSLRs - which I have been using until now. So I am keen on buying the Clelstron NexImage 5 CCD for these purposes. Already using the BBC SkyatNight's imaging simulator, the angular magnification of the image is amazing! I realise that a cheaper alternative is modified webcam etc. However I want a dedicate astronomical CCD, and I gather that the bundled iCap Celestron software is powerful but simple to use, and can adjust RGB etc. pre exposure/recording, and has the flexibly of going up to 5 MP frames (though stacking very few!!) Obviously it is considerably cheaper than other planetary CCDs, so I just wondered whether at this stage, if I need to fret about paying say £400 + for a top of the range CCD or is the NexImage more than good enough for a serious newcomer?

Deep sky

I understand that, following reading an excellent article on the BBC SKyatNight's website:

http://www.skyatnightmagazine.com/astrophotography-complete-guide/introducing-deep-sky-photography

my Nikon DSLR would actually be ideal for imaging these sorts of objects in the night sky? If so then I confident about trial and error with the various control, ISO, number of frames/each of exposure x seconds. I gather deepskystacker ought to be used instead of Registax 6 for deep sky objects? Finally "light/claibration/flat frames" is often mentioned during guides on this type of imaging. I have no idea what this means/what I need to do; could someone explain please?

Thanks for any help in advance.

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You say "Celestron NexImage 5 CCD", the Celestron NexImage 5 is a CMOS device, well according to the Celestreon site it is a CMOS.

Celestron

Then look at Specification.

Checked 3 of the familiar retailers and all say CMOS as well.

That, if it is correct, sort of negates the "However I want a dedicate astronomical CCD" aspect somewhat.

DSLR: Very often used but many use the Canon, not better or worse then the Nikon, just Canon supply a fair bit of support software and you can remove the IR filter (and replace it with another if you wish).

The IR filter starts to cut off tha around 650nm, that is where Ha is present and Ha is a fair component of nebula. In effect with the filter in place you are filtering out a lot of the wavelength you actually want. What the cut off characteristics of a Nikon are I have no idea. May be better or worse for AP.

One thing I will say is at a talk on AP the presenter was asked about getting improved images, they asked if the person used a DSLR and when the reply was Yes, they got told in simple terms that a DSLR is for holiday snaps not astrophotography.

The realistic approach is yes they will take some good astro images, but a person with a dedicated ccd for astro imaging will produce better images and more consistantly.

One concern on the S@N artical is that they manage to not specify what was used for the M13 cluster.

One the first Stargazing Live they showed an image of Jupiter they had taken and said that "you can get images like this."

What they did not point out was that they used a 150mm APM APO refractor and a cooled dedicated ccd. Now the refractor costs about £6000, and the camera I would guess at another £2000.

Not quite your £300 127 Mak and a webcam.

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You say "Celestron NexImage 5 CCD", the Celestron NexImage 5 is a CMOS device, well according to the Celestreon site it is a CMOS.

Celestron

Then look at Specification.

Checked 3 of the familiar retailers and all say CMOS as well.

That, if it is correct, sort of negates the "However I want a dedicate astronomical CCD" aspect somewhat.

DSLR: Very often used but many use the Canon, not better or worse then the Nikon, just Canon supply a fair bit of support software and you can remove the IR filter (and replace it with another if you wish).

The IR filter starts to cut off tha around 650nm, that is where Ha is present and Ha is a fair component of nebula. In effect with the filter in place you are filtering out a lot of the wavelength you actually want. What the cut off characteristics of a Nikon are I have no idea. May be better or worse for AP.

One thing I will say is at a talk on AP the presenter was asked about getting improved images, they asked if the person used a DSLR and when the reply was Yes, they got told in simple terms that a DSLR is for holiday snaps not astrophotography.

The realistic approach is yes they will take some good astro images, but a person with a dedicated ccd for astro imaging will produce better images and more consistantly.

One concern on the S@N artical is that they manage to not specify what was used for the M13 cluster.

One the first Stargazing Live they showed an image of Jupiter they had taken and said that "you can get images like this."

What they did not point out was that they used a 150mm APM APO refractor and a cooled dedicated ccd. Now the refractor costs about £6000, and the camera I would guess at another £2000.

Not quite your £300 127 Mak and a webcam.

Thanks for the reply. Although apart from correcting me on my slight mistake regarding the NexImage, you didn't seem to have made any comments about it's use? 

Apart from deepskystacker, is there any other specialist software I should be trying to use fro deep sky stuff?

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I do not own one so cannot comment on it's use.

Although why I would buy at £170+ what amounts to a 5Mp webcam I do not know.

Also it is less flexible then a webcam, at least on a webcam I could display the image on a laptop, I doubt the NI5 does that.

Concerning the software it is the same comment. There are a few free stacker packages so the Celestron one has little going for it. Other then filtering out the poor frames at the time of recording so keeping only good one it is just a webcam. The Meade imager did the same prefiltering a number of years ago. When you consider that the prefiltering takes time I cannot see the reason for it. That is likely the reason for the stacking of 5Mp frames taking so long.

Just get the .avi file then sit inside and let Registax or Sharpcap sort it out while having a coffee.

You can buy a 5Mp webcam for £40 then get the software free.

The NI5 is planetary only (webcam video) for another £70 I could get the AS 120MC that would fo planetary video and long exposure DSO, and also gives me a handfull of software.

I would say that it can only be used with the Celestron software so the possibility no flexibility to feed the frames into another package. Remember that Celestron will not update the software on a regular basis. What actually is provided could be 5 years old now and Registax and Sharpcap undergo regular updates to functionality. Although this time R6 looks less friendly then R5 was.

Now this is just from what I have read about.

The finding that it was CMOS took all of 30 seconds.

Puzzled by the original comment:

"Already using the BBC SkyatNight's imaging simulator, the angular magnification of the image is amazing."

Where does an imaging simulator come into it, remember it is a simulator and may not match what you get/see.

The image on the sensor is what it is and is created by the focal length of the scope and the subtended size of the object, you can add an additional chunk of optics (barlow) prior to the sensor to increase the final image size on the sensor.

A simulation is not a real situation, if it were people would die trying a flight simulator for the first time.

A simulator could magnify the image and morph it from what is on a webcam to what hubble could see. You however just get the webcam image.

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" Where does an imaging simulator come into it, remember it is a simulator and may not match what you get/see.

The image on the sensor is what it is and is created by the focal length of the scope and the subtended size of the object, you can add an additional chunk of optics (barlow) prior to the sensor to increase the final image size on the sensor.

 

A simulation is not a real situation, if it were people would die trying a flight simulator for the first time. 

 

A simulator could magnify the image and morph it from what is on a webcam to what hubble could see. You however just get the webcam image "

Sorry to shoot you down here but the simulator shows exactly what you will record/see with a given 'scope/camera , 'scope/eyepiece combination , it is the very highly regarded 12 Dimensional String software used by pretty much everyone wishing to calculate their FOV ...  :smiley:

http://www.12dstring.me.uk/fov.htm

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! I realise that a cheaper alternative is modified webcam etc. However I want a dedicate astronomical CCD, and I gather that the bundled iCap Celestron software is powerful but simple to use, and can adjust RGB etc. pre exposure/recording, and has the flexibly of going up to 5 MP frames (though stacking very few!!) Obviously it is considerably cheaper than other planetary CCDs, so I just wondered whether at this stage, if I need to fret about paying say £400 + for a top of the range CCD or is the NexImage more than good enough for a serious newcomer?

NexImage 5 is a cheap entry level sensor. It's not a magical "CCD" :) 5Mpix isn't really useful in planetary imaging (you would crop the frame when recording to like 500x500 or less), and for lunar full frame would be nice, but color sensors won't be as good as mono on Moon (you would have to use IR passing filter which with color camera will be less efficient).

The camera may be cheap. Depends how much you can spend. Most of the more addicted people use now ASI120MM or QHY5L-II as one of the best cameras (for planets, and moon, less for sun).

my Nikon DSLR would actually be ideal for imaging these sorts of objects in the night sky? If so then I confident about trial and error with the various control, ISO, number of frames/each of exposure x seconds. I gather deepskystacker ought to be used instead of Registax 6 for deep sky objects? Finally "light/claibration/flat frames" is often mentioned during guides on this type of imaging. I have no idea what this means/what I need to do; could someone explain please?

That depends. It can be good (for a start), especially if you will be able to control it from imaging software like APT or Nebulosity. DSLR are used in astrophotography (mostly Canons), but note that they aren't as good as dedicated DS cameras. Dark frames are taken with camera covered (no light) to capture sensor noise like hot pixel (which then can be removed from image). Flat frames are taken with the setup pointing at some evenly illuminated surface or not so bright sky. Those frames will catch the lower illumination in the corners as well as some dust/camera artifacts which also will be removed from the image to get a better end result :) Note that for DS imaging you need an EQ mount with good tracking and quite likely guiding setup as well.

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las

Dear all,

I wish to check with the many experienced people on this forum about how to approach the above two types of imaging.

Planetary/lunar

​I will be purchasing a Celestron 8" Schmidt Cassegrain with Advanced V mount next week all being well - am rely looking forward to lots of excellent astronomy :). After some easing I now realise that it is by virtue of their design, impossible to get a small FOV image of any planet, due to the large sensors of decent DSLRs - which I have been using until now. So I am keen on buying the Clelstron NexImage 5 CCD for these purposes. Already using the BBC SkyatNight's imaging simulator, the angular magnification of the image is amazing! I realise that a cheaper alternative is modified webcam etc. However I want a dedicate astronomical CCD, and I gather that the bundled iCap Celestron software is powerful but simple to use, and can adjust RGB etc. pre exposure/recording, and has the flexibly of going up to 5 MP frames (though stacking very few!!) Obviously it is considerably cheaper than other planetary CCDs, so I just wondered whether at this stage, if I need to fret about paying say £400 + for a top of the range CCD or is the NexImage more than good enough for a serious newcomer?

Deep sky

I understand that, following reading an excellent article on the BBC SKyatNight's website:

http://www.skyatnightmagazine.com/astrophotography-complete-guide/introducing-deep-sky-photography

my Nikon DSLR would actually be ideal for imaging these sorts of objects in the night sky? If so then I confident about trial and error with the various control, ISO, number of frames/each of exposure x seconds. I gather deepskystacker ought to be used instead of Registax 6 for deep sky objects? Finally "light/claibration/flat frames" is often mentioned during guides on this type of imaging. I have no idea what this means/what I need to do; could someone explain please?

Thanks for any help in advance.

You can get good results using the equipment that you have mentioned but you need to be realistic. Getting good images of the planets and DSOs as you see in mgazines or on the web takes a  lot of skill, patience, planning and know how as well as perseverance. You will gain all this in due time but do not expect to get Hubble Class images from the start.

Good luck and best wishes,

A.G

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" Concerning the software it is the same comment. There are a few free stacker packages so the Celestron one has little going for it. Other then filtering out the poor frames at the time of recording so keeping only good one it is just a webcam. The Meade imager did the same prefiltering a number of years ago. When you consider that the prefiltering takes time I cannot see the reason for it. That is likely the reason for the stacking of 5Mp frames taking so long.


 


You are falling foul of Celestron's poorly worded advertising here.


 


The camera does not 'filter out' any frames as it records , and nor did the Meade , they just stream AVIs onto your laptop.


 


It comes with a free copy of Registax thrown in with the package for stacking , it is this that "filters out" the bad frames


 


"Just get the .avi file then sit inside and let Registax or Sharpcap sort it out while having a coffee."


 


SharpCap is a capture software and has no part to play in AVI processing 


 


 


 


 


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I think that at f10 that scope will be a bit slow if you really want to do DSO imaging too. You could do some clusters but you will need much longer exposures so your guiding will need to be bang on. Something a bit faster might be a good compromise as you could still squeeze some planetary out of it with a decent barlow and a cheap webcam (Lifecam etc) but you could probably still do some decent DSO stuff with your Nikon. Use the field of view calculator to make sure your desired targets are not only taking up 3% of the chip size. Barlows can be employed but then the scope effectively becomes even slower and exposure times even longer.

As for a mount, if you want DSO imaging then watch out for the payload limit as you might need to factor in the weight of tube rings, mounting systems, guide scope, guide camera, filter wheel as well as your scope and DSLR. The maximum is, I believe, aimed at visual use. For imaging you can pretty much halve it as working near the limit will compromise accuracy.

This is a total minefield so get hold of Making Every Photon Count for more details on all this stuff before you buy anything, and have a word with the dudes at First Light Optics - they will steer you well and they know their stuff. And their prices are very competitive and their customer service is genuinely second to none in my experience.

Take your time and maybe find online the kind of pictures you want to take and start making lists of what equipment was used. You will be gutted if you buy a setup and find it will only do planetary/lunar. I compromised on portability and am now regretting it a little although I had a clear night last so I feel a bit better :)

cheers and keep asking questions!

Chris

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I think that at f10 that scope will be a bit slow if you really want to do DSO imaging too. You could do some clusters but you will need much longer exposures so your guiding will need to be bang on. Something a bit faster might be a good compromise as you could still squeeze some planetary out of it with a decent barlow and a cheap webcam (Lifecam etc) but you could probably still do some decent DSO stuff with your Nikon. Use the field of view calculator to make sure your desired targets are not only taking up 3% of the chip size. Barlows can be employed but then the scope effectively becomes even slower and exposure times even longer.

As for a mount, if you want DSO imaging then watch out for the payload limit as you might need to factor in the weight of tube rings, mounting systems, guide scope, guide camera, filter wheel as well as your scope and DSLR. The maximum is, I believe, aimed at visual use. For imaging you can pretty much halve it as working near the limit will compromise accuracy.

This is a total minefield so get hold of Making Every Photon Count for more details on all this stuff before you buy anything, and have a word with the dudes at First Light Optics - they will steer you well and they know their stuff. And their prices are very competitive and their customer service is genuinely second to none in my experience.

Take your time and maybe find online the kind of pictures you want to take and start making lists of what equipment was used. You will be gutted if you buy a setup and find it will only do planetary/lunar. I compromised on portability and am now regretting it a little although I had a clear night last so I feel a bit better :)

cheers and keep asking questions!

Chris

Thank you to the last four posters or your helpful advice. Thanks in particular for reassuring me Chris with: "keep asking questions!" I believe these forums serve keen newcomers (like me), as much as the seasoned pro's. Wouldn't be doing what I am by day without inquisitiveness! 

It's slightly off-putting when you get supposedly experienced forum members who lecture more than help! But generally I find stargazerslounge to be very good.

Thanks again all.

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Lights : these are the images you take of the object 

Darks : these are images you take with the telescope covered, we use these to capture noise the camera makes.

Bias / Flats : these images are of a white background, we tend to slip a white t-shirt over the top the we takes some pictures,

these images show spots of dirt and also the gradient ( slight changes graidents and viengeting (sp). 

now take all the light frames, and the dark and flat frames we subtract from the main lights ( computer does this for us)

what we get is a nice clean image devoid of most if not all errors like gradeints, and noise - viengneting.

if you have a DSLR stick with that, take pictures and learn to manipulate them, every picture needs adjustment.

and you need a lot of them.  most start with a webcam and/or a camera. most basic things can still give you an image.

astrophotography / imaging is NOT easy , its not a plug in record and yeah i haff awesome pictures.

its the 3hrs waiting for the computer to chug out that image then to find its no good, then another 3 hrs and an extra day messing around

then the extra two months going back to get more data to add to your picture to have that eyecandy facemelting picture of glory.

thats what i have learnt before even starting to try DSO imaging.

I have a webcam to but i dont like the planets , trying to image mars with a dslr you will need a few barlows just to make a dot.

a webcam does 100times that of the dslr. but my DSLR will capture DSO something the webcam will struggle with. 

I own a DSLR and its my most fave imaging device, its simple it was cheap being secondhand, and it does the job.

it works day and night, the major area is SOFTWARE, you need to be able to understand software.

i spend an hour or so watching youtube videos on Gimp image editing software, learning how it works and adjusts.

i also spent time watching videos on learning to stack with DSS and registax. 

I spent countless months playing with said software , lunar images are nice to test with learning how those sliders work and pop out details.

or how DSS would stack images and the differnet adjustments that could be used and the effects, it wastes away those raining nights and days.

I had all the Gear and No Idea, now i have half the gear and a good idea on how things work,

start cheap and simple then allow your knowledge and gear to grow

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Lights : these are the images you take of the object 

Darks : these are images you take with the telescope covered, we use these to capture noise the camera makes.

Bias / Flats : these images are of a white background, we tend to slip a white t-shirt over the top the we takes some pictures,

these images show spots of dirt and also the gradient ( slight changes graidents and viengeting (sp). 

now take all the light frames, and the dark and flat frames we subtract from the main lights ( computer does this for us)

what we get is a nice clean image devoid of most if not all errors like gradeints, and noise - viengneting.

if you have a DSLR stick with that, take pictures and learn to manipulate them, every picture needs adjustment.

and you need a lot of them.  most start with a webcam and/or a camera. most basic things can still give you an image.

astrophotography / imaging is NOT easy , its not a plug in record and yeah i haff awesome pictures.

its the 3hrs waiting for the computer to chug out that image then to find its no good, then another 3 hrs and an extra day messing around

then the extra two months going back to get more data to add to your picture to have that eyecandy facemelting picture of glory.

thats what i have learnt before even starting to try DSO imaging.

I have a webcam to but i dont like the planets , trying to image mars with a dslr you will need a few barlows just to make a dot.

a webcam does 100times that of the dslr. but my DSLR will capture DSO something the webcam will struggle with. 

I own a DSLR and its my most fave imaging device, its simple it was cheap being secondhand, and it does the job.

it works day and night, the major area is SOFTWARE, you need to be able to understand software.

i spend an hour or so watching youtube videos on Gimp image editing software, learning how it works and adjusts.

i also spent time watching videos on learning to stack with DSS and registax. 

I spent countless months playing with said software , lunar images are nice to test with learning how those sliders work and pop out details.

or how DSS would stack images and the differnet adjustments that could be used and the effects, it wastes away those raining nights and days.

I had all the Gear and No Idea, now i have half the gear and a good idea on how things work,

start cheap and simple then allow your knowledge and gear to grow

No. Bias are dark frames of the shortest duration the camera can take. They are taken with the lens covered. Their main use is in calibrating flats, which are indeed taken with the scope pointing at an even light source. Personally I have no other use for bias frames than this. Used in this way, bias frames can also be called 'darks for flats.' Without them, flats will over-correct your light frames.

I think that a good read-through of Steve's book Making Every Photon Count would be a great idea. It is very difficult for any of us to give you a quick over-view of what deep sky imaging entails because it is a long winded process! No one part of that process is particularly difficult or obscure but there are lots of parts to get right.

DSLR cameras can be used to create decent deep sky images but they are certainly not ideal. At very fast F ratios they can approach the quality of dedcated astro CCD cameras on some targets but very fast F ratios are very expensive and very tricky to tune. When DSLR enthusiasts object to this claim and link to a great image you'll usually see that it came from something like a Takahashi Epsilon at F2.8. This is not a 'normal' F ratio.

I hope I'm not 'lecturing.' I'm not sure how to distinguish advising from lecturing. Most of my living is derived from being an astrophotography 'provider' so I don't know where that places me!

Olly

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2266922474&k=Sc3kgzc

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 for another £70 I could get the AS 120MC that would fo planetary video and long exposure DSO

+1 for the ASI... but not for DSO, unless you consider a very noisy 10sec exposure long and like playing "join the dots" with the saturated pixels :)

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Dear All,

I am a good way into Making very photon count. Now being fairly confident with the theory behind the different pieces of equipment, I wish to ask:

since sampling rate = (206.265*pixel size)/focal length  [in microns and mm respectively],       

am I correct in saying that sampling rate is proportional to resolution, or is a lower arc second per pixel value better and getting a sharper/higher resolution image? I cannot conceptually decide which way round is better. 

I gather from the book that one should aim for a sampling rate of between 1 - 3 " per pixel? So a similar question is which end of this range one should try to be closer to, for a higher resolution image?

Also could someone confirm the focal ratio to exposure time relationship for me please; I understand it to be:

(assuming f/new < f/old, for a faster 'scope modification) :              ((f/new)/(f/old))^2 

e.g.  for the Celestron C8 SCT;          (6.3/10)^2 = 40% of previous exposure time needed?

Thanks in advance.

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For DS imaging or for planetary? DS imaging has that 1-3" sampling rule and alike, while planetary goes max scope resolution - like Nyquist criterion is handy for picking initial optimal-max f/ratio for given pixel size. For 3.75 pixels in ASI120 and others it's f/13.6 while efficient imaging may vary depending on object. Like Mars likes overscaling and even ~f/20 will look good without degradation in good conditions. Jupiter maybe, Saturn is dim and not that much fine-detailed and it likes lower f/ratios (like that theoretical or less). Lunar imaging may be spoiled by light diffraction so to limit it it's good to do images below optimal f/ratio, like f/10 so that diffraction won't be visible and every edge/crater will be edge sharp without ghostly diffraction.

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For deep sky imaging, you would probably want a fast scope with about 700mm focal length. And as pointed out above, you are going to need a guider, espcially with a long focal length. Again this takes alot of patience and passion and practice. PPP!

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