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DSLR to colour cooled CCD


jambouk

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Having now guided (first time last night), and realised the fundamentals are actually remarkably easy (using metaguide and a qhy5), I am wondering if there would be many benefits from swapping my unmodified Canon 6D (full frame) for a colour cooled CCD.

I'm really not keen on going mono with filters as hate, and am useless, at the processing side of things.

I presume I'd still use a light pollution filter with a colour CCD, and i've have to settle for a much smaller sensor unless i coughed up £4000.

Have others gone down this route? Were there significant improvements?

Thanks

James

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CCD is miles better than DSLR. Why mince words? The advantage diminishes once you get into ultra fast optics (Tak Epsilon etc) but these bring their own issues.

Is OSC easier to process? Not in my view. It may be quicker to pre-process (ie stack) but combining R, G and B involves the following, which even I can do;

Open R, G and B and the trichromy window. (I use AstroArt.) Put red in red, green in green, blue in blue and click auto white balance then click for RGB. There is your colour image.

By all means go for OSC but don't go for it for the wrong reasons. Easier processing would be the wrong reason - in my view. OSC captures the wrong colour balance by default. (It shoots 50% green and 25% each red and blue.) This is not optimal for astrophotography. It is a daylight solution. Nobody with a mono camera shoots twice as much green as red and blue. This would surely be potty?  http://stargazerslounge.com/topic/227656-the-mysteries-of-green/

Olly

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Thanks for the comments so far.

Does the red component of the bayer matrix in a OSC CCD block much hydrogen alpha?

Looking at older OSC CCDs like the atik 16ic, combined with the ED80, the combination frames various planetary nebula and clusters quite nicely.

James

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No, i wasn't thinking about using an Ha filter, i was just wondering if the bayer filter blocked or permitted Ha transmission.

Why do you say the 16ic isn't a dslr improvement? Because it's old and More modern sensors will have improved QE and better signal to noise, or because the chip is small?

When just comparing a dslr sensor to a OSC CCD sensor, what makes the CCD miles better?

James

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Using narrowband filters is possible, but you won't be using the full potential of them. H-alpha will be only on 25% pixels, O III would get the 50% green ones. It would be better to use a narrow UHC filter that passes O III and H-alpha at the same time (+ H-beta, S II maybe) for nebulae imaging, and broader (like CLS) for other objects.

16ic has a small sensor, and not very new one or that much sensitive. It works, but it's a very small color sensor. If it was mono - then it would have more advantages over the DSLR. Note that sensor used in QHY8 was in origin used in DSLR before CCD was replaced by better CMOS in those DSLRs. Big color sensors are as cheap as medium sized mono ones (or cheaper) as they get more non-specialized usage (so produced in bigger quantities). When comparing DSLR and the QHY8L equipped with a very similar equally big sensors you get the advantage of cooling, better electronics, and better shape/software for the dedicated camera. DSLR is hard to cool, has sometime non-optimal size when imaging, and the firmware, electronics wasn't optimized for long exposures and low noise.

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I don't know about the transmission in Ha of the red fiters on the popular Bayer matrices. It's a good question. However, I think that most of the damage to Ha is done by the DSLR filters in front of the Bayer matrix, which is why modding DSLRs works. It wouldn't work if the red Bayer filters had low Ha transmission of themselves.

For me the big 16ic negative (I've had both OSC and mono versions as guide cameras) would be the chip size. But DSLRs have advanced since then in terms of noise and sensitivity as well and even I, as an arch CCD enthusiast, would be tempted by a modern DSLR over a 16ic.

Why are CCDs miles better? They are more sensitive, they are cooled, they don't come with absurdly small pixels for astronomical purposes, they can (in mono format) be binned 2x2... It's a long list.

Olly

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

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Thanks again all. Really useful stuff.

Now i can guide, i need to give this dslr a good run for its money, before writing it off. It's got good QE for a dslr (47% i think), reasonably large pixels (6.5 microns), low read out noise, and a massive sensor.

I'll find out how much it would cost to get it modified to increase the Ha sensitivity.

I'll also investigate the optimum delay between subs to minimise heating effects, though i think the cmos sensors get heated throughout the sub, not just when its being read.

Thanks again.

James

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Why are CCDs miles better? They are more sensitive, they are cooled, they don't come with absurdly small pixels for astronomical purposes, they can (in mono format) be binned 2x2... It's a long list.

Olly

Well, there still are big pixels out there, but most of the market want's more resolution in a smaller form factor so small pixels dominate :( As for technical capabilities CMOS can be and sometimes are much better than a CCD due to easier and more flexible overall design. It's just they had to catch up with CCDs.

PS. I wonder what would happen if a SBIG, FLI or QSI would release a DS imaging camera with a big and good CMOS sensors? ;)

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In this geographically unfortunate zone, OSC seems the way to go, disatvantages are offset by having to shoot a lot less subs (e.g. not extra ones for Luminance, R, G, B).

Well, I often shoot only luminance or one narrowband with a mono camera. I rarely do color DS images, but still if doing LRGB type image time spent on color channels is much shorter due to having very good luminance. Color or mono sensors aren't that obvious in advantages and disadvantages.

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This is a combo of Atik16 osc (Olly's old camera) shots through a CLS-CCD filter combined with shots through a UHC-S filter-

M27_2hrs_uhc_40mins_lum_26may_01jun13_zp

Wow, Andy, I hadn't seen that one. What an absolute cracker, one of the best 16ic images I've seen - and there are some good ones.

Congratulations.

Olly

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You are meant to be all pitting me off a OSC camera :)

You are right to be doing this research but don't be put off buying a one shot colour camera, especially as you are UK based and, therefore, suffer from UK Sky Syndrome. A cooled one shot colour (OSC) CCD camera comes into its own when imaging time is at a premium because of unreliable sky conditions. I have no technical reason to doubt the argument that mono plus filters is 'quicker' than one shot colour but my own experience is that I can wring a more than acceptable colour image from little data from an OSC session cut short as so many are by the weather, whereas the same conditions make it very iffy to collect a full set from mono plus filters! If I could be fairly sure of another attempt to collect data the next night, I may feel differently but that just doesn't happen often in West Sussex .......

What I can tell you from a technical point of view is that mono plus filters opens up a host of exciting imaging opportunities in the form of higher resolution, no interpolation, narrowband imaging capabilities and, of course the ability to mix wideband (LRGB) and narrowband data together, all using a single camera.

If you want some examples of one shot colour imaging, have a look at some of my deep sky work using either an SXVF-H9C (my earlier images using s small sensor) or an SXVF-M25C (larger sensor) - please note that these are not prize-winning images, just examples of what can be done using a one shot colour camera under UK skies!

On my site, you will also see some images taken with a mono CCD camera with filters and there is the rub - both types most certainly have their place and I love'm both!!

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Really nice images. But both are relatively large sensors and not cheap.

Many of your OSC images are only 300 second subs - is there a reason you haven't used 600 second subs more commonly?

I do think I need to push the DSLR to its limit and hone some skills with it, before splashing out £3000 on a OSC CCD.

But thanks again for the input, really helpful to see what can be achieved.

James

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If you want color - then get QHY8L for £999. It's not that expensive yet it has a big DSLR-like sensor. Anything smaller and color looses on resale a lot... and it's small. Mono sensors get much more expensive with size. Things like Atik 314L+ are already quite expensive (£1035), yet it have 2/3" sensor and not APS-C size. But they can do narrowband and luminance with all pixesl. For short focal length refractors there are more entry level (yet still pixel rich) mono Atik 320E or maybe even 314E (but note the small sensor diagonals). For longer focal lengths there is Brighstar Mammut camera that can work as an entry-level model (less pixels, but bigger).

I often shoot with 3 min exposures as I don't gain anything by using longer exposures (noticeably). The signal is already above noise level (low noise camera) and by stacking more frames it seems to be easier to even out the background noise (plus I'm photographing from a city so very very weak parts of nebula or dust can't be caught at all usually).

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Many of your OSC images are only 300 second subs - is there a reason you haven't used 600 second subs more commonly?

It's a good question!!! The answer is historical (or actually, maybe that should be hysterical! :grin: ) - when I started out in deep sky imaging, 5 minutes was considered to be a good long exposure and I guess I got used to working with those sort of exposure lengths although I have, of course, taken much longer ones as well subsequently. However, there is a balance to get here, again (sorry to bang on about it) with relevance to the skies I get here in Sussex - more individual exposures leads to less 'noise' when stacked but, this does need to be tempered with obtaining enough detail in the data and 5 minutes has always worked well for me allowing me to collect sufficient colour to work on in post-processing with adequate detail and not too much damage from light pollution. Longer exposures (but still lots of them) would be better providing you can track well enough to avoid nasty star shapes. You'll note that I take 600 or longer exposures when I am using my QSI mono camera and narrowband filters.

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Again, useful comments.

I had seen the qhy. I guess I've just got size issues. Ny canon 6d is full frame (well nearly), so i had been looking at sensors in that size range. Again, i'll look on field of view calculator and see how the qhy8l sizes up.

James

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I'm just experimenting with cooling my 6D.

I've got an aluminium bar screwed into the tripod hole on the base of the camera, with some conducting tape between the bar and the body. I've currently got a small peltier and heat sink strapped onto the aluminum bar with elastic bands, and sheets of card to direct the vented gas away from the camera body.

Early results suggest the sensor peaks at 36 degrees after an hours run of 60 seconds subs with a 2 second gap without cooling (ambient temp in garage is about 18 degrees). With the peltier on, the sensor temperature appears to have settled at 26-27 degrees. I'm now going to do an hour of 10 minute subs and see what happens to the temperature. If it somehow keeps the sensor just 10 degrees above ambient compared to 20 degrees above ambient, I am going to have to think how to make this a more permanent set up for the 'field' and see if it helps. I'll report back.

James

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