Long exposures with unmodded DSLR's

[Atmos]

As there are a good number of DSLR astrophotography enthusiasts on here, I figured this would be the best way to get an answer.

I have a Nikon D700 that I mostly use for daytime photography but I am wanting to do some wide fields with it now that I have a way of nicely connecting it to my old HEQ5. What I am wondering is, as it is uncooled, whether doing 5m exposures will be more problematic than it is worth.

I was doing some testing tonight and after some testing I have come to realise that I need to use my 50mm lens at F/7.1 to get reasonably good stars over the whole FX frame. Some back of the envelope calculations suggest that at this I am best using 300s (5 minute) exposures. I know that if I do not sufficiently get close to sky limited with my camera I get terrible banding that cannot be processed out so I do need to overwhelm it.

What I am curious about is whether the dark current (thermal) is going to start being more of a problem than I might imagine it to be?

[rustigsmed]

hi col,

i am pretty sure Richard M did a lot of testing on cooled vs uncooled dslrs.
a melbourne winter might help but i don't think it was too promising for uncooled dslrs past 2 or 3 minutes.

on a side note - if you have ever wondered what a 30 minute exposure of the helix looks like with a Ha filter on an uncooled dslr @25degs i have the answer here
https://www.flickr.com/photos/80336656@N07/21485020864/in/dateposted-public/lightbox/ ... very difficult to see the noise!! haha

[rmuhlack]

look here: http://www.iceinspace.com.au/forum/showthread.php?t=106775

[glend]

Forget 5 minute subs, even with winter weather the internal heat built up by the camera processor, sensor and battery (yes it gets hot too) will give you a mess of noise.
I agree two minutes is about all you can manage before the noise threshold gets too high, and really a long cool down pause would help as well, otherwise you build heat on heat and the images get worse and worse. This is why we use cold finger cooled dslrs, so the sensor can be held at 0C or lower. A battery eliminator adaptor also helps.
You can test yourself, just find a way to read the EXIF header temperature info on each image file, this will show you the processor temperature (as no dslr actually has a sensor temp probe), and you can watch it climb as you shoot a sequence of long subs.

[alocky]

I have plenty of examples using 10 minute subs on a D800 at 1600 ISO at 20 degrees plus that were fine after dark and bias calibration and stacking, and although the D810A is 'unmodified', it is considerably cleaner.
http://www.astrobin.com/24974/
Cheers,
Andrew.

[Camelopardalis]

I've done the vast majority of my DSO imaging with both unmodded and modded DSLRs. My cooling mod was only a recent addition to survive the QLD summer...

Down in your neck of the woods I'd expect 5 minute subs with your camera at a suitable ISO to be very effective. The Sony sensors in Nikons usually fare better than those in Canons.

I'd suggest favouring f-stop over stars though...you can always crop ;)

[Atmos]

May just have to max myself at the 120s mark.

That's a great shot considering the sheer lack of red that can get through.



Thanks Richard, only quickly glanced at it so far but it looks to be an interesting read.



This is pretty much where my concern was. Haven't ever noticed a temperature in the EXIF data but I'll check it out.



The D800 may be cleaner than the 700, not sure. I haven't been game to push mine over the 60s mark yet. Haven't shot darks either, so far I have used the mount PE as a kind of dithering and then with a lot of subs there is a decent regection. Should probably give darks a shot in the future :P



Crop... CROP... ;)

In saying that on my next dark sky trip I want to do some 30s shots at F/1.8 on NGC 5128 to see if I can detect the jets after 30m. Anything outside of the very centre will NEED to be cropped! :lol:

[alocky]

I guess the best news is that you won't break anything by trying it, and you may be pleasantly surprised at how long you can go with a DSLR. Especially in Vic - as long as your tracking is up to it, why not find out for yourself, verify the research, then post it here?
cheers,
Andrew.

[Atmos]

Very true Andrew, cannot break it by playing with settings :P My introduction into astrophotography was pretty much a QHY9 so I've only ever really worked with sensors at -20 - -35ºC :)

[DJT]

I use to run my DSLR between 10mins for OSC and 20 Minutes for NB clip in filters just for the hell of it at ISO between 400 and 800 from sunny Sydney. I found that using a mains power supply helped, avoiding the summer and doing proper calibration was a must. Whether I got any value out of subs that long for RGB I never knew, twas early days in the hobby, but given I had an LP clip in filter for OSC I figured why not.

[Camelopardalis]

:lol: maybe f/1.8 is too much to ask for, but many lenses, even kit lenses, can work pretty well f/4~f/5. Worth a try :shrug:

[Atmos]

It worked okay at F/4-5 and until I get under some dark skies it is a bit difficult to be certain about performance. I focused on a bright star in the sky and then moved it into a corner and decreased the F-Stop every image (1s) as it was just on a tripod. Watched that one star get better and felt reasonably happy at F/7.1 :)

At least with some time without the moon around I can see what it looks like with 60s subs at different ratios.

[andyc]

My experiences have been mostly quite favourable with my combination of ISO800 & 300s frames with an EOS 60D, no mods. I picked ISO800 after a bit of reading, and haven't varied it hugely over the past year or so, partly because the results seemed decent. Early tests didn't show a great change from 800 to 1600, and so I went with the better depth of the 800. I seemed to get better data off the 5min rather than 2-3min exposures. I've had issues on warm summer nights or on hazy nights, but most of the year, or mostly below 20C it seems fine, even for extended series of shots. My usual process would be 300s frames, 5s gap between frames. That includes pretty much all the images in this gallery (http://www.pbase.com/andycasely/deep_sky_astrophotos). I've had occasional issues with background grain, especially on warmer nights, and they are probably the ones where I should've shortened the exposure, but most nights it's OK. But I suspect it'll be different for different cameras, and there's probably better settings I should be using!:lol:

[Atmos]

Thanks for that Andy, during winter when the ambient temperature is around 2ºC sounds like it won't be a problem with a few minutes exposure.

[jenchris]

I foind my 450d ran at about 26c on extended exposures.
That was in summer when the air temp was about 23c
My friend ran his 700d at about 40c at the same time with similar exposures.
we both have battery eliminators. why they are so diffetent i don't know.
The noise produced on mine is processible with dark and other offset bias frames.
I don't use live view and keep my veiw screen turned off.

[RobF]

Give it a go Colin. You'll probably find you only start to run into trouble on dimmer objects as exposures get over 5mins.

For the popular brighter objects and widefield lenses, the humble un-modded DSLR can still produce wonderful images.

Of course, during winter you'll get an added suppression of noise, and hot summer evenings the opposite.