Mono or Colour?

[Jez]

I have pretty much decided on the equipment I want as a first time AP setup. (Thanks to some great feedback on this page).

i am still undecided whether to go Mono or Colour though with my first time dedicated camera?

Any advice would be greatly appreciated.

Thanks

Jez

[Tim]

What set up have you opted for Jez? That might have a bearing on the advice.

Also, what do you want to photograph? What are your average skies like? Do you get plenty of time under clear skies or does work etc get in the way? How is the light pollution where you live? Do you have much time available for processing your images?  What level of quality of astronomy image are you aspiring to? It is helpful to put some links to the type of results you hope to achieve if you can.

Whichever camera you choose, there will be some compromises to be made, but we can help you ensure that those compromises are the least worst for your circumstances.

Cheers

Tim

[ronin]

Very difficult, may be a case of what budget overall is there, big one will be the time available to you.

Mono will give the better results, as in effect for each "colour" all the pixels will be used. So a 10Mp camera uses all 10M on Red, then all on Green and then all 10M on Blue. So more data and a better final result. The negatives are that you will need the camera, then you will need a filter wheel, then you will need the filters. None of which are exactly inexpensive. The next problem is you need time. You need to collect the Red data, then you need to collect the Green data, then you need to collect the Blue data. So doing it "simply" you have to have 3 imaging sessions. What is the weather like in Swansea ? Lots of good clear nights ?

With a colour camera you basically lose the number of pixels, the mask means you have 3 colours at once so on a 10Mp camera I think about 30% are Red, 30% Blue and he rest Green - there is a bias towards Green on a DLR not sure if the same on a dedicated AP camera, have sort of assumed there still is.

So for Red and Blue you have about 3Mp, not the 10Mp of a mono. That is a big decrease. Where you "gain" is initially not needing a filter wheel and you gain on time. You get the whole lot in 1 session.

So maybe simplistic that is where the choices lie. On a colour camera the "key" bit seems to be the "O" in OSC = One.

Budget is simply the filter wheel and filters that you will need, but ultimately (not immediatly) you should get better images, in some instance much better but the "much" better may be a case of 5 to 10 years learning all the data collection and processing skills required. They do not appear overnight. I for one do not have the patience for mono.

Very likely it should be a progression of colour to mono, meaning both at some time. So you start on colour, learn all you can and when you cannot progress much further you enter the world of mono.

Myself I have already marked up the ASI 178 camera as a candidate for when I want to lose the DSLR and maybe try an AP camera, likely for convenience to be colour.

[Scott]

This is one of the most toxic subjects you'll find on the imaging forum. You will hear very strong technical arguments from mono users but at the end of the day it's what happens in practice that counts. I use mono coz my LP is pretty bad so I tend to shoot nb. For broadband under U.K. Skies I might be tempted to go for colour as you get all rgb with every frame. 

Enter Olly ?

[iapa]

3 hours ago, Jez said:

I have pretty much decided on the equipment I want as a first time AP setup. (Thanks to some great feedback on this page).

i am still undecided whether to go Mono or Colour though with my first time dedicated camera?

Any advice would be greatly appreciated.

Thanks

Jez

As @Tim says, if you can advise your chosen equipment and targets., we may be able to help match a camera.

It does depend a bit on the target, focal length of OTA. You'd not want a small pixel large sensor size on a long focal length tube on a smaller mount as guiding would be difficult. 

The diameter of the imaging circle, if small, on a large sensor may cause vignetting. Large diameter imaging circle with a small sensor would be wasting a lot of light.

@Scott has a valid point too. Mono v OSC is almost as bad as 'fracs vs Newt' discussions LOL

If you already had a DSLR use that for a while.

Edited June 15, 2017 by iapa

[tomato]

I started out on OSC simply because I wanted to start imaging and a second hand colour CCD came up on the classifieds before a colour one. I have enjoyed using it and particularly like the fact I can get a 'complete' image no matter how short my imaging session. 

However IMHO a OSC camera will struggle to deliver as 'good' an image as mono + filters due to the sensitivity reduction. 

I should get my mono camera and filters next week, it remains to be seen if the extra complexity (i.e. frustration) of achieving a complete image under U.K. skies will out weigh the improved quality of the end result, but the fun is in the trying!

[Astrosurf]

As has been said here, I started with a modded DSLR and then moved to my Atik mono. I don't have much staying power so don't have much time to gather enough colour in one night, so tend to have stuck with nebulae in Ha with the Atik. I'm impatient to get objects so haven't yet done separate nights for colour! That'll come next. I'm beginning to want to go back to my DSLR for colour as I get so much more time. Maybe not the clarity of detail but still quite a lot of data over at least two hours. I also find the processing with DSLR colour images much easier than the Ha/LRGB processing. I can't get rid of the turquoise colour in the latter! 

So of course it's up to you. Go straight in to the mono, filter wheel etc if you feel confident, or go to the modded DSLR route (or equivalent) to get your hand in.

Good luck!

Alexxx

[spillage]

You are not the only one in this dilemma. I have been using my canon dslr's for while now and would like to take the plunge into the money pit whirlpool of a dedicated camera.

I think osd will  be easier but I think after a while I would be wanting a mono and start to regret buying the osd. I also think to get the best out of it you will need a permanent pier for your mount to help go back on a different night to collect more data and just cannot see myself trying lrgb over several nights having to setup up polar align and take down every time. Although I must admit that I have given up at the moment with the dslr until my pier is complete.

 

[Jez]

Thanks for all the replies!

I am going to try and answer everyone with one answer as I'm away from home for a couple of days and only have access to my phone.

Equipment so far:

SW Eclipse 80ED Triplet

Advanced VX

im down to two options for autoguiding but have plenty of information on this so feel confident enough.

At the moment I live about two hundred metres away from the cities old observatory, however it is currently being converted into a cafe as the society couldn't afford the rent anymore (that's as far as I know).

The Astronomical Society are in the process of moving to a different part of the city that has great clear skies. So I have a places I can drive to within 15 minutes.

i also have an international dark sky reserve (Brecon Beacons) about 40 minutes drive from me.

i work for myself at home so am flexible on the time I work. I have a multiple monitor setup/Mac Pro so have the equipment/time to process.

i don't have a dslr, I thought about buying one but I wouldn't use it for anything apart from AP and that's why I started looking into CCD/CMOS.

i don't have any AS/processing experience but know I really want to get into it. I have been working abroad until recently but now that I'm home I think it's time to purchase the equipment.

I will be going to my local astronomical society stargazing nights when they start again but as I said above they are busy setting up the new location.

initially I was keen on the celestron nightscape 8300, more recently looking at the asi1600mm-cool.

however, like I've said I don't have any experience and obviously it's going to take time to learn so don't know if these are good for a first time  camera?

also I don't want to rock up the the stargazing night being the guy who has spent all this money just for the hell of it ? All the gear no idea!

i can afford these cameras but just don't know if they are best for my setup/learning curve.

now that you know about my setup hopefully it will be easier to recommend.

sorry if this reply is all over the place, I'm using my phone and it's not ideal!

thanks

Jez

 

[ollypenrice]

13 hours ago, ronin said:

Very difficult, may be a case of what budget overall is there, big one will be the time available to you.

Mono will give the better results, as in effect for each "colour" all the pixels will be used. So a 10Mp camera uses all 10M on Red, then all on Green and then all 10M on Blue. So more data and a better final result. The negatives are that you will need the camera, then you will need a filter wheel, then you will need the filters. None of which are exactly inexpensive. The next problem is you need time. You need to collect the Red data, then you need to collect the Green data, then you need to collect the Blue data. So doing it "simply" you have to have 3 imaging sessions. What is the weather like in Swansea ? Lots of good clear nights ?

With a colour camera you basically lose the number of pixels, the mask means you have 3 colours at once so on a 10Mp camera I think about 30% are Red, 30% Blue and he rest Green - there is a bias towards Green on a DLR not sure if the same on a dedicated AP camera, have sort of assumed there still is.

So for Red and Blue you have about 3Mp, not the 10Mp of a mono. That is a big decrease. Where you "gain" is initially not needing a filter wheel and you gain on time. You get the whole lot in 1 session.

So maybe simplistic that is where the choices lie. On a colour camera the "key" bit seems to be the "O" in OSC = One.

Budget is simply the filter wheel and filters that you will need, but ultimately (not immediatly) you should get better images, in some instance much better but the "much" better may be a case of 5 to 10 years learning all the data collection and processing skills required. They do not appear overnight. I for one do not have the patience for mono.

Very likely it should be a progression of colour to mono, meaning both at some time. So you start on colour, learn all you can and when you cannot progress much further you enter the world of mono.

Myself I have already marked up the ASI 178 camera as a candidate for when I want to lose the DSLR and maybe try an AP camera, likely for convenience to be colour.

Ronin, you trot out this answer every time anyone asks this question and, alas, I don't agree with much of it. Please give some thought to the following points.

1) Mono is more expensive, agreed.

2) The increase in resolution by using all the pixels in a mono is actually trivial. The debayering routines are very sophisticated and interpolate (make an educated guess) about the 'missing' information remarkably well. I advocate mono but not for reasons of resolution because I have found very little or no gain in resolution when using mono over OSC on the same make of chip in the same telescope. 

3) You do not need more time with a mono camera, you need less. An OSC camera shoots through colour filters all of the time so it can never capture more than a third of the incident light, ever, under any circumstances. However, when a mono camera is working in its luminance mode it is capturing all of the incident light  and obtaining a massive speed advantage over colour. This cannot be less than a 6 to 4 time advantage and can easily rise to being twice as fast. The LRGB system was invented to save time.

4) OSC cameras are filtered for daylight and have twice as many green filters as red and blue. This is entirely inappropriate for astrophotography and wastes more time.

5) OSC cameras use low grade absorption colour filters rather than high quality interferometric ones availble to mono imagers.

6) Mono cameras can capture narrowband efficiently, Ha opening up many nights of moonlight to the imager.

A while back I set myself the task of demonstrating the remarkable speed of the mono camera by doing a two hour Heart Nebula. This has just an hour of Ha and twenty minutes each of R, G and B. This was at a FL of 530mm and at F5. I do not believe I could have obtained this result, or anything remotely like it, from an OSC camera in the same telescope in two hours. At some point I'll do a fast LRGB image as well to make the same point. 

It's been argued that using colour filters adds to the complexity because you may have to refocus between colours. The other way to look at it is that non-parfocality does not come from the filters but from the optics, so at least you can refocus a mono but with an OSC some of your colour will always be out of focus.

The genuine reason for going for OSC is that it may be less frustrating in terms of capturing an incomplete data set. But mono is faster. It really is.

Olly

 

Edited June 15, 2017 by ollypenrice

[DaveS]

The biggest step-change in my imaging was when I went directly to a mono CCD from my DSLR, it really was a dramatic improvement. With our miserable weather, cantankerous moonlight, and lack  of astro-dark in summer the ability to capture H-alpha data under those conditions means that imaging is possible when a DSLR or OSC would just white (Or orange) out.

An example:

I captured this in under 80 min (It was actually about 78 min) in H-alpha when only the "skeleton" of Cygnus was visible, even Albireo was barely glimpsed, and the bight star (52 Cygni) was totally invisible.

Not quite the write-off I first thought, and I hope to be adding to it in due course.

[Guest Tuomo]

12 minutes ago, ollypenrice said:

Ronin, you trot out this answer every time anyone asks this question and, alas, I don't agree with much of it. Please give some thought to the following points.

1) Mono is more expensive, agreed.

2) The increase in resolution by using all the pixels in a mono is actually trivial. The debayering routines are very sophisticated and interpolate (make an educated guess) about the 'missing' information remarkably well. I advocate mono but not for reasons of resolution because I have found very little or no gain in resolution when using mono over OSC on the same make of chip in the same telescope. 

3) You do not need more time with a mono camera, you need less. An OSC camera shoots through colour filters all of the time so it can never capture more than a third of the incident light, ever, under any circumstances. However, when a mono camera is working in its luminance mode it is capturing all of the incident light  and obtaining a massive speed advantage over colour. This cannot be less than a 6 to 4 time advantage and can easily rise to being twice as fast. The LRGB system was invented to save time.

4) OSC cameras are filtered for daylight and have twice as many green filters as red and blue. This is entirely inappropriate for astrophotography and wastes more time.

5) OSC cameras use low grade absorption colour filters rather than high quality interferometric ones availble to mono imagers.

6) Mono cameras can capture narrowband efficiently, Ha opening up many nights of moonlight to the imager.

A while back I set myself the task of demonstrating the remarkable speed of the mono camera by doing a two hour Heart Nebula. This has just an hour of Ha and twenty minutes each of R, G and B. This was at a FL of 530mm and at F5. I do not believe I could have obtained this result, or anything remotely like it, from an OSC camera in the same telescope in two hours. At some point I'll do a fast LRGB image as well to make the same point. 

It's been argued that using colour filters adds to the complexity because you may have to refocus between colours. The other way to look at it is that non-parfocality does not come from the filters but from the optics, so you at least you can refocus a mono but with an OSC some of your colour will always be out of focus.

The genuine reason for going for OSC is that it may be less frustrating in terms of capturing an incomplete data set. But mono is faster. It really is.

Olly

 

Olly, I have read many times your same answer over and over again. I completely understand what you are trying to teach. I (and many others, I assume) would be really intrested with proper image comparison between OSC and lrgb image by you. That way we would see the difference. I think you would have the resources and proper skies for it....Dear santa.....:)

[brrttpaul]

I have to say I have gone from a OSC to a mono very recent , learning curve yes, regret it no, just in the narrowband alone it was worth it for me as i can image on a full moon, (is it just me or does anyone else notice that its only clear skies when the moon is near full? lol)

[Tim]

Jez, here's what I do, and the rationale behind it, it may help you.

At home, on the edge of a badly light polluted city in the heart of the midlands, I have an observatory with permanently mounted telescope and the opportunity to image the samd object for weeks on end if necessary with pixel perfect precision. Narrowband imaging is very important to me at home, and it opens up the opportunity of moonlit imaging. At home I use a MONO camera. Unless the desired target is something unusual, short lived, or generally requiring short time on target. These may be comets, asteroids, supernovae etc, in which case I use a OSC or DSLR camera. Downside of LRGB imaging is the hassle of calibrating four sets of images, including taking flats through each filter, for each session. This process I find fiddly, tedious, and time consuming. LRGB images take a lot longer to process than OSC, require more discipline, more knowledge, and MUCH more disk space. The tortoise OSC catches up with the mono hare here somewhat. There is nothing more precious than time......

When I travel to dark sky locations, with a portable setup, and limited consecutive nights on one target, I take advantage of the darker skies and use my OSC. This way, even if I only get clear enough skies for one 10 minute sub, I still have a reasonable, true colour record of the target in question. Typically, when I travel to star parties, when I go with a OSC I get more useable results than when I have taken a mono camera. I am lucky that my imaging scope of choice has excellent colour correction, which makes OSC imaging possible. This is the UK, dark, clear, transparent skies are rare. I like to have the right tool available as the conditions dictate, and this may be a mono or a colour camera. As mentioned previously, there are compromises. 

Aesthetically, colour images taken with a OSC camera always appear more "realistic", or natural to my eye. It is entirely possible, and is best practice, to calibrate RGB colour imaging by using a G2V star with similar colour to our sun. In many images however the colours can appear a little forced, although this is a personal opinion and preference.

I guess, what i'm getting at, is go for a mono camera, you'll need it in the UK. But if you can, get a colour camera too to really maximise your astro imaging potential.

Hope those ramblings help a bit.  As you can see, the answer to your question is, "it depends...."

Cheers

Tim

[rigradio]

Jez, you have to listen to me 
Why? Because....both of us:
- Have a baby sitting mount, AVX
- Use +/- 400mm small refractor
- Are a portable newbie imager

Suggestion:" Used cheap canon dslr + BYEOS"

If you are really really a newbie, the are many things you have to learn before you are ready for a mono camera. 
- Balance the mount (toward the telescope & 'little more heavy' east balancing)
- Precise polar alignment 
- Focusing
- Calibration frames
- Dithering
- Star alignment (ASPA)
- Plate solving
- Processing your data
- Bla bla bla...

Practice your polar alignment at the backyard. Try to get a precise PA within 30m
Here are the unguided images with AVX+AT65EDQ+60D -> 180sec & 300sec 

Now, you are ready to learn the auto guiding.
- Ascom, focusing, exposure, saturated star, min motion, aggressive, hysteresis, bla bla bla.....

Now, you are ready. Sell the dslr, purchase a mono camera, LRGB/NB filter, EFW.
Learn the auto focus, sho, hst hargb, lrgb, bla bla bla....

Then, you need more FL for galaxy, need a better mount to handle your bigger telescope, bla bla bla...

Regards,
Ketut

My ASI1600-MM cooled is on the way to Bali...wheeeeeeeeeee 

 

 

 

 

 

 

[ollypenrice]

9 hours ago, Tuomo said:

Olly, I have read many times your same answer over and over again. I completely understand what you are trying to teach. I (and many others, I assume) would be really intrested with proper image comparison between OSC and lrgb image by you. That way we would see the difference. I think you would have the resources and proper skies for it....Dear santa.....:)

I no longer have an OSC. When I did have mono and OSC versions of the Atik 4000 I did a direct shoot out and article for Astronomy Now. There was precious little difference between the final images but I was imaging M42, a bright target and one not needing Ha. The longer I kept the OSC the more frustrating I found it on faint targets. Tidal tails and extensions in galaxies just took forever and, in the end, I went to dual mono cameras.

Unlike Tim I never found OSC easier to process. Rather the reverse, in fact. But there are any number of reasons for this. I still think the double green is an issue for OSC in astronomy. However, Tim's point about 'getting something keepable' is a good one and is, as I said earlier, the real reason for using OSC if that's what you fancy. My real beef is with the speed claim.

Olly

[RichLD]

For me the pros for OSC are (in no particular order) size and weight, price, convenience and, in the field, ease of use (there's one less thing to go wrong as there's no filter wheel). As Olly has said before,  the speed of capture is technically faster with mono and filters and the processing for OSC can be a real pig IMHO.

I have 2 monos and 1 OSC. The OSC can take great shots in a very neat and tidy package (great for when I haul everything to a dark site, which is when the OSC comes into its own) but for every other situation the mono wins hands down.

Just my 2 cents 

HTH

Rich

 

[ollypenrice]

2 hours ago, rigradio said:

Jez, you have to listen to me 
Why? Because....both of us:
- Have a baby sitting mount, AVX
- Use +/- 400mm small refractor
- Are a portable newbie imager

Suggestion:" Used cheap canon dslr + BYEOS"

If you are really really a newbie, the are many things you have to learn before you are ready for a mono camera. 
- Balance the mount (toward the telescope & 'little more heavy' east balancing)
- Precise polar alignment 
- Focusing
- Calibration frames
- Dithering
- Star alignment (ASPA)
- Plate solving
- Processing your data
- Bla bla bla...

Practice your polar alignment at the backyard. Try to get a precise PA within 30m
Here are the unguided images with AVX+AT65EDQ+60D -> 180sec & 300sec 

Now, you are ready to learn the auto guiding.
- Ascom, focusing, exposure, saturated star, min motion, aggressive, hysteresis, bla bla bla.....

Now, you are ready. Sell the dslr, purchase a mono camera, LRGB/NB filter, EFW.
Learn the auto focus, sho, hst hargb, lrgb, bla bla bla....

Then, you need more FL for galaxy, need a better mount to handle your bigger telescope, bla bla bla...

Regards,
Ketut

My ASI1600-MM cooled is on the way to Bali...wheeeeeeeeeee 

 

 

 

 

 

 

I can't see why mono would be significantly harder. You just shoot through a red filter, then a green, then a blue, giving each image a name to identify the colour. 

Processing goes like this (in AstroArt for me.)

Stack the reds, the greens and the blues to make three images called Red, Green and Blue.

Go to Images, Align All, set to Translation and Rotation and click once.

Go to Colour, Trichromy, and put the red in the red box, the green in the green and the blue in the blue. Check Auto White Balance and click once. You now have an RGB image. At this point you will be in the same place as you would be with an OSC. Both will have gradients which need processing out. 

I often think that only people who haven't tried mono imaging think that it's difficult! I just don't think it is, though. 

Olly

Edited June 16, 2017 by ollypenrice

[rigradio]

1 hour ago, ollypenrice said:

I can't see why mono would be significantly harder. You just shoot through a red filter, then a green, then a blue, giving each image a name to identify the colour. 

Processing goes like this (in AstroArt for me.)

Stack the reds, the greens and the blues to make three images called Red, Green and Blue.

Go to Images, Align All, set to Translation and Rotation and click once.

Go to Colour, Trichromy, and put the red in the red box, the green in the green and the blue in the blue. Check Auto White Balance and click once. You now have an RGB image. At this point you will be in the same place as you would be with an OSC. Both will have gradients which need processing out. 

I often think that only people who haven't tried mono imaging think that it's difficult! I just don't think it is, though. 

Olly

For a person who really has never ever ever tried AP before, I think dslr will be easier for them to get started before they can shoot through lrgb filter properly.
Imagine a guy who doesn't even know how to ride a bicycle, wants to learn ride a motorbike. I will suggest him learn with Honda Scoopy (automatic) first, because there are basic things he needs to learn: balance, acceleration & break. After he get used to it, then he can tries to ride the superior Kawasaki Ninja with clutch

Ketut    

[spillage]

@Jez

I really would suggest that you try out the obvious processing programs available. pixinsight and startools not sure about astroart. pixinsight is a 30 day trial and startools is unlimited but without the function to save the final image.

 

Ask around and I am sure someone will be able to provide you with the data need to try processing. This will not only help you decide what software will suit you but also if you prefer mono or osc.

You can then make you mind up using advice here and experience of using the end data. Of course the cost of each may also be a factor.

[iapa]

18 minutes ago, rigradio said:

Imagine a guy who doesn't even know how to ride a bicycle, wants to learn ride a motorbike. I will suggest him learn with Honda Scoopy (automatic) first, because there are basic things he needs to learn: balance, acceleration & break. After he get used to it, then he can tries to ride the superior Kawasaki Ninja with clutch

Ketut    

hmmm, I learnt on a 250 Ymaha, then moved to a Road King when I passed my test 6 weeks later

I tend to try to run before walking

Digression 

[DaveS]

1 hour ago, rigradio said:

For a person who really has never ever ever tried AP before, I think dslr will be easier for them to get started before they can shoot through lrgb filter properly.
Imagine a guy who doesn't even know how to ride a bicycle, wants to learn ride a motorbike. I will suggest him learn with Honda Scoopy (automatic) first, because there are basic things he needs to learn: balance, acceleration & break. After he get used to it, then he can tries to ride the superior Kawasaki Ninja with clutch

Ketut    

Not the same at all really, since you're not risking injury or death (Unless a stupidly massive 'scope falls of the mount on top of you). It's a learning curve like any other, and if you move straight to Mono CCD / CMOS you won't have to un-learn any bad habits you might have picked up with a DSLR (I know. Been there, done that), and you won't have wasted any money down a blind alley.

As I've said above, if you run mono with filters then in H-alpha you can image when OSC or DSLR imaging is no-go. Lord knows we get few enough clear nights here without having to pass one up due to inadequate kit. NB will also cut through the all-to-pervasive LP we suffer from.

You don't have to buy a full house of NB filters either, H-alpha, Lum, RGB will fit in a 5-position wheel without breaking the bank (Unless you buy Astrodon ). With Astronomik you could use their CLS-CCD as a Luminance filter and they would all have the same thickness.

[ollypenrice]

8 hours ago, rigradio said:

For a person who really has never ever ever tried AP before, I think dslr will be easier for them to get started before they can shoot through lrgb filter properly.
Imagine a guy who doesn't even know how to ride a bicycle, wants to learn ride a motorbike. I will suggest him learn with Honda Scoopy (automatic) first, because there are basic things he needs to learn: balance, acceleration & break. After he get used to it, then he can tries to ride the superior Kawasaki Ninja with clutch

Ketut    

I'd agree with this if you didn't have to do so many work arounds to make DSLRs function for astronomy, for which they were not intended. I use Atik cameras and the user-friendly default software called Artemis Capture. It is designed for astronomy. It just plonks everything you need on one screen in front of you and off you go. You can, in luminance, pretty well guarantee that in a 5 second sub (maybe binned 2X2 or 3X3) you'll be able to see you target easily and frame it as you wish. You have a full width half max focus tool. You have cooling to control noise. In short you have the right tool for the job. I think DSLR astrophotography is obscure and confusing...

Olly

PS While working as a motorcycle instructor I once had a young lad turn up so I gave my usual introduction and then set him off for a gentle potter around the training circuit. He let the clutch in nicely enough but always keeled over shortly afterwards. I was stuck for a solution till it occurred to me to ask if he could ride a bike. He couldn't. Aha! After that I always made a point of asking but this had never come up once in my own instructor training.

Edited June 16, 2017 by ollypenrice

[toxic]

i would not go for a dslr and go  for the dedicated ccd/cmos as i went down that road my self but i didn't have the dslr modded as i use it for daytime photography.

i now have the atik 383l+ mono and it is so much easier to use in AP than a dslr even if you onl get a HA filter to start with.

you mention the celestron nightscape 8300 ,that is the same chip as the atik 383l but the nightscape only go's down to -20 ambient but the atik go's to -40 ambient i dont know anything about the nightscape aprt from the specs online but for £24 more i would go for the atik i have had mine for over 2 years and its a superb camera.

you cant really compare a dslr to an astro ccd/cmos camera but here is a comparison any way.

the first is a single 900 second exposure from the eos 1100D not modified unprocessed taken in 2014

the second is 3 x 300 second exposures 1 red - 1 green - 1 blue (dss to align and photoshop to combine) apart from that unprocessed taken 2015

 

[Stub Mandrel]

Here's an interesting graph for Canon 350D, 450D appears to be close, other cameras similar:

We forget that OSC bayer filters are NOT narrowband filters, instead they mimic our eyes, and with the IR cut filter removed they are even wider band.

Imagine you are imaging a lager Ha nebula with an astro-modded DSLR. Its maximum red sensitivity is pretty much lines up with Ha. Green registers about 1/6 of the Ha signal and blue approaching 1/10.

So sensitivity at Ha is about 1+1/6+1/6+1/10 = 1.4 times what it would be if it was just from the red pixels.

If you look across the graph adding up B+2xG+R for each wavelength - you will see sensitivity is rather more than the 1/4 you would expect.

Add in the recovered set from a decent debayering algorithm and I think the valid signal might be closer to the sensitivity of mono+filters than people expect.