DSLR, CCD Astrophotography quandary

[smr]

Hi all,

I've been into astrophotography for around 12-18 months now, starting off with a Star Adventurer and progressing onto my HEQ5, I am confident with my HEQ5, aligning and imaging etc. I haven't delved into auto guiding yet but that is next on my list (last night I connected and controlled my DSLR from my laptop for the first time using APT, which was great and I really enjoyed not having to use an intervalometer!)...

So that's pretty much where I am at with astrophotography now. The imaging I am interested in is all the beautiful DSOs rich in Ha, and the faint stuff, objects like the Jellyfish Nebula are a dream for me to image etc. but I've still plenty to delve into first such as the HH Nebula, therefore I think that a camera which can pick up plenty of Ha signal is the way forward. My current and only camera is my Canon 80D, unmodified.

As well as astrophotography my other passion is landscape photography. So I need an unmodified DSLR for this purpose. 

Ergo, what to do? As I need a DSLR for landscape there are a number of options to choose from; keep my Canon 80D as is, and invest in a second hand astromodified DSLR or go for an OSC CCD, or modify the 80D. The 80D is an almost ISO-less sensor which enables me to shoot at ISO 200 though, and if I were to go for say, a Canon 700D and have it modified or buy one already modded, I'd be losing that ISO 200 and have to shoot at ISO 1600 instead. I then might be thinking of how much better my images might look with my 80D if I had had it modified... But is that a problem when the SNR is improved by stacking anyway, cancelling out the noise? Or would I see better results stacking as many shots with my 80D at ISO 200? The point being, I am wondering whether to get my 80D modified, and then buy another 80D for around £600-700 new for landscape photography. Going for a full frame camera for landscape photography is an option too, but more expensive as I only have APS-C lenses. If I went for a 700D it looks likely to cost around £500 for a used, modified one.

Or do I spend a bit more and go for something like a ZWO ASI-294MC Pro (I'd probably want to go for a OSC camera due to clouds). This would mean having to save up for one, and during that time I'd have to stick with my unmodified 80D, but then I guess I do need time to get my head around autoguiding. I'd aim for around the Summer if I were to save up for a OSC camera. So long term budget wise I'd be willing to stretch to around £1k. 

I know it's a bit long winded but I've been thinking about posting this for a while now and would really appreciate some guidance. 

Joel

[Adreneline]

Hi Joel,

I made the move from dslr to ccd because (a) I didn't want to mod my 70D, and (b) I didn't like the way I would fetch it in after a night of imaging only to find it covered in dew and soaking wet. I also found noise to be quite problematic with the sensor frequently operating at around 30 degrees C.

I went down the CCD route, first buying an Atk414osc and then an Atik428ex mono. I still have both but as my interests now are more directed to nebula these days I rarely use the 414 osc. I use the 428 mainly with a Samyang 135mm and I've played around using the 414 with a Samyang 85mm - when the weather permits and Mr Moon isn't around. Both also get used with an SW-ED80DS and a WO-ZS71. 

Good luck with your deliberations.

Adrian

[michael.h.f.wilkinson]

I have an unmodded 80D for general photography, along with a slightly older 700D (also unmodded). For astro imaging I have been using a modded 550D which works very well indeed, but some experiments with my ASI178MM planetary camera on DSOs turned out some nice results, so now I am considering the ASI183MM-C Pro model (mono because I do have an electronic filter wheel), which could perform both DSO and planetary/lunar imaging neatly. The small pixels give a lot of image scale even on my 80mm F/6 reduced to F/4.8. You could perhaps consider the ASI183MC-C Pro instead, if you aim for OSC imaging.

[ollypenrice]

I strongly believe that if you're interested in, 'all the beautiful DSOs rich in Ha, and the faint stuff, objects like the Jellyfish Nebula...' then you should go for mono, CCD or CMOS. I know that being cut off after a short time by cloud is psychologically less frustrating with OSC but the net capture time needed for a given standard of image is always shorter with mono and sometimes much shorter. It is always shorter because the luminance captures all colours at one on all pixels and this is never possible with OSC. It is sometimes much shorter because Ha captured through a filter gives you just what the image needs and that's high contrast and clear structure in the gasses. There is more to this than 'Ha sensitivity.' I think this is the source of common misunderstanding. A mono camera with good Ha filter will capture Ha more quickly because a) all the pixels are used and b) because the dedicated Ha filter will be more sophisticated than the red filters on an OSC matrix. But what is also important is that which the filter excludes. The more exotic an Ha filter the more it blocks. And it is this which gives you the contrasts and structures you're looking for.

My standard supporting evidence is below. This is the Heart nebula shot in two hours. 20 mins per colour and 2x30 mins Ha. Atik 11000 mono. I do not believe that an OSC camera working at F5 could equal this. (It's not a great image but, hey, two hours and processed simply and quickly).

Or the Spaghetti nebula. On the left, OSC Atik 4000. On the right, same thing with Atik 4000 mono Ha data added...

And you can shoot Ha in the moonlight. (You can do so on an OSC as well but with only a quarter of your pixels operating.)

Olly

 

[wimvb]

1 hour ago, ollypenrice said:

The more exotic an Ha filter the more it blocks. And it is this which gives you the contrasts and structures you're looking for.

Which begs the question: which Ha filter was used for those two images?

Further I would like to add one more advantage that mono has: it's somewhat less sensitive to light pollution. RGB filters are generally designed with a slight overlap between blue and green (at the Oiii wavelength), and a gap at the Na/Hg wavelength. The latter improves performance for imaging in light pollution.

I went from unmodded dslr to mono cmos (with electronic filter wheel), and have not regretted it once. The efw allows me to rotate filters quickly, so even if it clouds over, I'll have a full dataset after each session.

[ollypenrice]

21 minutes ago, wimvb said:

Which begs the question: which Ha filter was used for those two images?

Further I would like to add one more advantage that mono has: it's somewhat less sensitive to light pollution. RGB filters are generally designed with a slight overlap between blue and green (at the Oiii wavelength), and a gap at the Na/Hg wavelength. The latter improves performance for imaging in light pollution.

I went from unmodded dslr to mono cmos (with electronic filter wheel), and have not regretted it once. The efw allows me to rotate filters quickly, so even if it clouds over, I'll have a full dataset after each session.

Astrondon 3nm for the Heart, Wim, and Baader 7nm for the Spaghetti.

Olly

[tomato]

As an illustration, below  is my early attempt with an Atik 314+OSC, on the Elephant’s Trunk Nebula, compare this with any mono narrow band image of this object, if it is contrast and detail your after, OSC will leave you disappointed. I was simply amazed at what a mono camera with a mid priced Ha filter can capture under a suburban sky.

[carastro]

Another one for the Mono route.  It definitely captures more data, and it is cooled as well, suppressing all that noise you get with an uncooled camera. 

I would not waste your time buying a 2nd DSLR, if you are going to have to buy so you can keep an unmodded DSLR then save up for a Cooled CCD or CMOS camera.

Learn guiding while you are saving up.  

Carole 

[dannybgoode]

Don’t forget how a Bayer filter works. Half the pixels on an OSC camera only capture Green and 25% each only capture Red and Blue. 

The software (either in camera for a D-SLR, mobile phone or whatever or the processing software on your computer for AP) then guesses the value of the missing two colours for each pixel based on the information from the surrounding pixels. This is know as de-bayering. 

If you use an Ha filter then only the red pixels will record anything at all so you’ll only be using 25% of the available pixels of the sensor with the software essentially guessing the rest of the values. 

With a mono sensor the camera records the true luminance value for each RGB and any other filter across the whole sensor and then software blends the channels. You gave 50% more true Green data and 75% more each true Blue and Red data. 

Hence more true detail and ultimately faster overall exposure time  

I’d love to see an OSC Astro camera based on Sigma’s Fovean sensor . That would be interesting...

[cjdawson]

I've got a 70d which I've had for a couple of years, it's unmodified and I love it for daytime, timelapse and everything photography.   There's no chance that I will be getting it modified, I find it too useful stock.   As for a second camera, I've make the leap over to a dedicated Astro cam.  In my case, I'm using a ZWO.    Which one?   Well currently I have the ASI290MM on the scope, but have just put in an order for an ASI1600MM Pro - cooled version.  I have very high hopes for this camera.