CCD viable under UK skies?

[ollypenrice]

10x2 minutes? Well, I guess if you're going to go as short as that then literally the time taken to change the filters plays a part! To be honest I can't say much about 20 minute images because for me that isn't astrophotography. I'm most certainly not condemning anyone for whom it is, though. And, yes, it might be better to use OSC for a 20 minute image. I suppose that for a twenty minute image you wouldn't take flats at all, but it is true that OSC reduces the flats workload.

Once you start to take a more serious image, though, I don't think processing an OSC is much faster than processing an LRGB. It can be harder because, at least in my experience, OSC can be a bit fickle on some targets.

Olly

[earth titan]

If a CCD is more sensitive, are subs generally shorter? With my DSLR I currently use around 240 secs per sub so I'm interested what the equivalent would be.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[johnrt]

If a CCD is more sensitive, are subs generally shorter? With my DSLR I currently use around 240 secs per sub so I'm interested what the equivalent would be.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

As long as possible really until you start to see either l/p effects begin to ruin the background or saturation in either stars or of the target itself occurs. It also very much depends on the target, you most certainly wouldn't run the same exposure time on say M31 as you would M101. I usually set my minimum at 5 mins and work up from there dependent on target.

[Magnum]

I use a been using a OSC Starlight Xpress SXVF-h9c since October and am really getting to like this camera, which has the same Sony 285 sensor as the the Atik 314L.

This chip is a bit different to most OSC cameras in that its still very sensitive in all wavelengths, its is very low noise meaning I don't need to take darks, don't get me wrong you still get hot or warm pixels but the seem to disappear if a stack more than 30 subs with the SD mask algorithm, but if not it only takes a couple of minutes to manually remove them with the clone tool in the final stage of processing .

Here is the website that made me go for this camera, most of this chaps images were done with 4 min subs at f5, he just takes plenty of them.

http://www.heavenlyview.com/h9cnewimages.htm

Lee

[ollypenrice]

If a CCD is more sensitive, are subs generally shorter? With my DSLR I currently use around 240 secs per sub so I'm interested what the equivalent would be.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

No, because CCD is cooled and low in noise it can take longer subs. Longer subs produce far better results than short provided your sky allows them. 10x10 mins beats 20x5 mins.

Lee, if you used dithered guiding your hot pixels would vanish from smaller stacks. You could also make a bad pixel map by clipping 2000 ADU from a dark frame. This would just leave the hot pixels and a suitable routine (AstroArt 5) would remove them.

Olly

[russellhq]

My skies limit me to about 5 min subs with my DSLR and I would assume that a CCD would be limited even further due to it's increased sensitivity.

I'm probably missing something, but I don't think I would see a great benefit going down the CCD route?

[Gina]

Having used both DSLR and mono CCD I think the question is the wrong way round - it should say "Is a DSLR viable under UK skies?". The answer of course, is that both are viable but a mono CCD more so. The vastly higher sensitivity and absence of noise in the mono CCD means you need far less imaging time for a given picture quality. I feel well qualified to say this because I have striven to virtual lunacy to squeeze the absolute maximum out of a DSLR - taking what is arguably the best DSLR for AP, removing the red blocking filter and cooling it to -15C. Even with these mods the Atik 314L+ mono CCD beats it hands down and then some.

[opticalpath]

As I've progressed in the hobby, I realise that I get the greatest satisfaction now from quality, rather than quantity. If that means taking several nights to capture the data I need - perhaps spread over a period of time - so be it. When I started out, I wanted to capture as many objects as possible, usually several per night. I was satisfied with an image - any image. My objectives have changed now and I don't feel the same impatience. I enjoy the processing freedom that having plenty of good data gives you. So it's mono for me now.

OSC is certainly convenient - at the time of capture - but I don't believe it's any quicker in total time and effort in the production of a good quality image, and it's certainly not as flexible. IMO.

Adrian

[ollypenrice]

I think most of share Adrian's experience of wanting to spend longer on a target. Where OSC really suffers in on emission nebulae, where catching the Ha (which is often pretty much all there is) through a Bayer matrix is ludicrously inefficient since only one pixel in four is catching the data. It is obviously far faster to catch it with all the pixels. There are plenty of objects in which the colour really only does anything for the stars and here a short total exposure in RGB is a positive benefit because you retain colour in the cores rather than burning them to white. Then you go after the emission nebula all pixels blazing with an Ha filter.

This had precisely half an hour per channel in RGB and the rest was in Ha. Trying to get the signal through an OSC would have taken much longer. http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-pqmrgHC/0/X3/SH2%20129%20HaRGB%20-X3.jpg

Olly

[russellhq]

OK, maybe im missing something, but if I'm imaging from a heavily light polluted site e.g. a city centre, then wouldn't the extra sensitivity from a CCD over a DSLR just mean the LP would saturate the image quicker?

[ollypenrice]

OK, maybe im missing something, but if I'm imaging from a heavily light polluted site e.g. a city centre, then wouldn't the extra sensitivity from a CCD over a DSLR just mean the LP would saturate the image quicker?

I usually post from experience but here I can't because I have hardly any LP at all. However, astrophotography is all about signal to noise. Noise can be in-camera or it can be sky noise. In any event the better your S/N ratio the better your picture and that means CCD beats DSLR. In my opinion it beats it by a large margin, too. Above all, with a mono CCD you could image to your heart's content in narrowband and beat the LP almost entirely.

From LP narrowband is easiest, then Luminance and the worst hit is RGB. May of our guests shoot their NB at home, some get their Luminance at home as well, but all get their colour here for preference.

Olly

[russellhq]

... Above all, with a mono CCD you could image to your heart's content in narrowband and beat the LP almost entirely...

Very good point! I may have reason to buy one after all

[Naemeth]

Tom,

I guess what you've got to ask yourself is, after all this advice, is there anything stopping you getting a CCD? Is it the cost (which if you spread over many years of enjoyment isn't actually that high), or is it something else?

You're looking for an answer to the question of "is a CCD viable under UK skies", and I think the resounding answer is yes. (As long as you can afford it )

HTH

[ollypenrice]

If you're worried that CCD is somehow obscure and difficult - it isn't. It's very logical and systematic. I was learning my way round a cooled DSLR last night and I found that far harder.

Olly

[dph1nm]

10x10 mins beats 20x5 mins.

Only if the 5 min shot has a significant read-noise contribution. If we are considering areas with high light pollution this is almost certainly not the case.

OK, maybe im missing something, but if I'm imaging from a heavily light polluted site e.g. a city centre, then wouldn't the extra sensitivity from a CCD over a DSLR just mean the LP would saturate the image quicker?

Yes, so you do shorter exposures, which will still get you the same signal-to-noise. If you are dominated by sky noise there is no disadvantage to stacking more, shorter subs.

NigelM

[Fogboundturtle]

If you're worried that CCD is somehow obscure and difficult - it isn't. It's very logical and systematic. I was learning my way round a cooled DSLR last night and I found that far harder.

Olly

Yep. Today's software makes it so much easier to operate. the BC, Canada sky are very similar to UK. Last year we had 8 months of clouds. Yes. not a single day of clear night for 8 months.

[lukebl]

Out of interest, I've just been doing a test run for capturing tomorrow's flypast of Asteroid 2012 DA14, just using my 'bog-standard' ST80 guidescope (to get the widest possible field of view) and my SXVF-H9 cam (same mono sensor as the Atik 314).

Given the speed of the asteroid I've been experimenting with one-second exposures, and was amazed to note that I was capturing stars down to magnitude 14. I think that demonstrates why a mono CCD is worth having. Not sure that a OSC or DSLR could capture stars that faint with such a short exposure?

[Uranium235]

Out of interest, I've just been doing a test run for capturing tomorrow's flypast of Asteroid 2012 DA14, just using my 'bog-standard' ST80 guidescope (to get the widest possible field of view) and my SXVF-H9 cam (same mono sensor as the Atik 314).

Given the speed of the asteroid I've been experimenting with one-second exposures, and was amazed to note that I was capturing stars down to magnitude 14. I think that demonstrates why a mono CCD is worth having. Not sure that a OSC or DSLR could capture stars that faint with such a short exposure?

Interesting, I was wondering what exposure times to go for should it be clear tomorrow. Im hoping to point the mount to a predicted position and catch it as it whizzes through.

But as to the OP.... CCD every time in the UK, its the only way to get something fairly quickly. DSLR has it merits, but its the processing side that slightly does my head in - and unless you have tons of long subs or a fast scope, its a constant battle against noise.

[earth titan]

Okay!

I give in!

Seems as though the mono CCD is now on the shopping list. Plus filters plus filter wheel...

How much do you get for a kidney again?

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[opticalpath]

Only if the 5 min shot has a significant read-noise contribution. If we are considering areas with high light pollution this is almost certainly not the case.

Yes, so you do shorter exposures, which will still get you the same signal-to-noise. If you are dominated by sky noise there is no disadvantage to stacking more, shorter subs.

NigelM

Exactly! The difference in the skies at Olly's place in France and the typical suburban site in the UK is astonishing. In France, exposure times had to be more than 10x longer for me than at home to get anything close to the same background level. Where sky background is very low, other noise sources predominate and fewer, longer exposures are needed to minimise *total* noise. In a noisy sky, by contrast, sky background is far more significant than read noise, so in practice total S to N does not suffer so much if you expose a larger number of shorter exposures. However, in both cases a CCD astro camera will deliver cleaner images than a DSLR, with better S to N.

Adrian

[Komet]

I don't see it mentioned but if your filters are parfocal then as long as your capture program supports it (SGP does at least) you can rotate through the filters in sequence so you end up with a colour image every three exposures. I have started doing this recently to very good effect. This applies to both RGB and NB of course. I have used both DSLR (modded and unmodded) and a cooled CCD is both easier and way more sensitive.

Just recently I have been stuck with my DSLR as my IMG2Pro has had to go back to base for a repair. Its been awful without it .....

[Komet]

Would like to add to the above that in my opinion and experience the CCD is easier to use.

[ollypenrice]

Would like to add to the above that in my opinion and experience the CCD is easier to use.

In mine too. At one time I think I was the only person saying this so it's great to have a co-conspirator. DSLRs seem to be getting harder, too, as more automatic functions that you don't want need to be disabled. They are also getting far too many pixels! I think the perception is that we are familiar with DSLRs from the daytime and so CCD with 'all those filters' must be harder. However, with CCD you have all that you need and nothing you don't need, all laid out before you on the screen. I know I'm very familiar with it but in all the IT activity I do I know of nothing so nice to use as Artemis Capture, Atik's control software.

Scrolling LRGB has a lot going for it psychologically. Strictly though, at least on low targets, you should certainly shoot red and green low to the horizon and luminance and blue as high as possible.

Olly

[jezhughes]

In mine too. At one time I think I was the only person saying this so it's great to have a co-conspirator. DSLRs seem to be getting harder, too, as more automatic functions that you don't want need to be disabled. They are also getting far too many pixels! I think the perception is that we are familiar with DSLRs from the daytime and so CCD with 'all those filters' must be harder. However, with CCD you have all that you need and nothing you don't need, all laid out before you on the screen. I know I'm very familiar with it but in all the IT activity I do I know of nothing so nice to use as Artemis Capture, Atik's control software.

Scrolling LRGB has a lot going for it psychologically. Strictly though, at least on low targets, you should certainly shoot red and green low to the horizon and luminance and blue as high as possible.

Olly

I'd agree with that, i used to be intimidated by CCDs when i had a DSLR, but the flexibility and control you have over them is superior to a DSLR

[opticalpath]

I don't see it mentioned but if your filters are parfocal then as long as your capture program supports it (SGP does at least) you can rotate through the filters in sequence so you end up with a colour image every three exposures. I have started doing this recently to very good effect.

I work that way with my MN190: I focus on green and then can't find any better focus position for red and blue filters. However it seems not to be so with the same (parfocal) filters on my refractor and on a SCT ....... which I suppose are just not perfectly apochromatic: I can always improve focus a little between filters. The MN190 is very good in this respect.

Adrian