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Old 21-01-2009, 12:53 PM
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Max DSLR Exposure Time @ Dark Subtractions/Processing

I have a 350D, I haven't been able to find much information on the Max Exposure times a Canon DSLR is capable of?

Can an exposure go for more than 10mins? 15, 20 ? more.. ?

I gather that the other factors to be considered with will limit the exposure time of course will be: temp, ISO settings, LP, etc.

Assistance much appreciated. Cheers

Last edited by leinad; 21-01-2009 at 11:43 PM.
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Old 21-01-2009, 02:39 PM
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Max exposure time can be till your battery goes flat. But it will be hell noisy!
But with my 8" f/4.6 scope, I could get maybe 7 min @ iso800 before LP becomes a major issue. Your 8" f/6 newt would go maybe 12 min at the same iso.A lot will depend on your system speed and how much LP you have. (My LP is only minor) You also have to consider thermal noise in as well. As the longer the exposure the more noise you shall get, especially on the warmer nights, ICNR can remove most of it but it will still be noiser than shorter exposures.
The only way is to experiment and see how far you can go?
cheers Gary
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Old 21-01-2009, 02:58 PM
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Quote:
Originally Posted by Garyh View Post
Max exposure time can be till your battery goes flat. But it will be hell noisy!
But with my 8" f/4.6 scope, I could get maybe 7 min @ iso800 before LP becomes a major issue. Your 8" f/6 newt would go maybe 12 min at the same iso.A lot will depend on your system speed and how much LP you have. (My LP is only minor) You also have to consider thermal noise in as well. As the longer the exposure the more noise you shall get, especially on the warmer nights, ICNR can remove most of it but it will still be noiser than shorter exposures.
The only way is to experiment and see how far you can go?
cheers Gary
So under the right conditions and factors to consider, I could go for over 15mins If I wanted to . Hence 'bulb' ?

Has anyone gone for an exposure with a DSLR(350D variety) for 20mins or over?? I can't see any mention of people using greater than 10min exp.
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Old 21-01-2009, 03:43 PM
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AS Gary has just mentioned anything over 10-15 minutes would certainly be the limit, and also it depends how dark your sky is.

My Modded 5D will start to pick up LP at about 7-9 minutes, and ICNR dose help with this.

Leon

Last edited by leon; 21-01-2009 at 05:39 PM.
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Old 21-01-2009, 03:50 PM
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What's the longest exposure time someone has done with a DSLR ?
Google isn't helping me much in the way of posts mentioning this...
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Old 21-01-2009, 03:53 PM
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Experiment mate, that will give you the answer.

Leon
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Old 21-01-2009, 05:00 PM
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Leinad,
I use a Canon 20Da.
As Gary indicated it'll stay open pretty much as long as its powered but as Leon says, you'll have to experiment to see what becomes an acceptable level of thermal noise.

I have pushed my exposures to 20 and I think once to 30 minutes.

I have found that the best I get out of my camera, which has been a similar experience of a friend who uses a 350D is to aim for shots at ISO 800 between 8 min to 12 minutes.

I regularly take 15 min but if I can I try to aim for 8 to 12, seems to get me the best results without generating too much noise.

Incidentally, I use the plug in adapter instead of batteries as this is suppose to generate a bit less of the dreaded "burn mark" ni the lower right hand corner of the image.

I also no longer tend to shoot darks at all unless i really feel like it and have time to kill. Likewise, I never use ICNR, never (i di at first then stopped) If you are going to use dark frames, you're better off getting more light frames and then some darks.

The reason i dont use darks or dont worry as much about them anymore (i have a few master dark frames saved in a file I can refer t oif i really want to) is because of the great litle fature in DeepSkyStacker called cosmetics. Set it at 1 pix and 1% and it magically removes all noise without affecting the resolution/quality (trust me I'v conducted truckloads of tests on it)

Anyways,
hope this helps,

summary:
consider the power adapter for the Canon
use ISO800
aim for 8 to 12 min shots for faint DSOs (obviously less for very bright objects-seconds for the core of Orion M42 for example, a minute for globular clusters, etc.).
Get the free DeepSkyStacker to stack frames

most importantly, experiment and HAVE FUN!
That's what its all about!
cheers
frank
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Old 21-01-2009, 05:06 PM
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Quote:
Originally Posted by leon View Post
Experiment mate, that will give you the answer.

Leon
Hehe, I would, but I wanted to check with others first to save me the experimentation woes of pushing the limits to no return, and be wallet broke for ~$600.


Quote:
Originally Posted by spearo View Post
Leinad,
I use a Canon 20Da.
As Gary indicated it'll stay open pretty much as long as its powered but as Leon says, you'll have to experiment to see what becomes an acceptable level of thermal noise.

I have pushed my exposures to 20 and I think once to 30 minutes.

I have found that the best I get out of my camera, which has been a similar experience of a friend who uses a 350D is to aim for shots at ISO 800 between 8 min to 12 minutes.

I regularly take 15 min but if I can I try to aim for 8 to 12, seems to get me the best results without generating too much noise.

Incidentally, I use the plug in adapter instead of batteries as this is suppose to generate a bit less of the dreaded "burn mark" ni the lower right hand corner of the image.

I also no longer tend to shoot darks at all unless i really feel like it and have time to kill. Likewise, I never use ICNR, never (i di at first then stopped) If you are going to use dark frames, you're better off getting more light frames and then some darks.

The reason i dont use darks or dont worry as much about them anymore (i have a few master dark frames saved in a file I can refer t oif i really want to) is because of the great litle fature in DeepSkyStacker called cosmetics. Set it at 1 pix and 1% and it magically removes all noise without affecting the resolution/quality (trust me I'v conducted truckloads of tests on it)

Anyways,
hope this helps,

summary:
consider the power adapter for the Canon
use ISO800
aim for 8 to 12 min shots for faint DSOs (obviously less for very bright objects-seconds for the core of Orion M42 for example, a minute for globular clusters, etc.).
Get the free DeepSkyStacker to stack frames

most importantly, experiment and HAVE FUN!
That's what its all about!
cheers
frank
Thanks Frank!
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Old 21-01-2009, 05:09 PM
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After 2 minutes amp glow in the bottom right of the frame will start to creep in, this can be cropped out but as others have said noise gets gradually worse across the whole frame as time progresses. I generally do 5-6 minute frames with no big issues, in my case any longer and LP drowns everything out.
BTW I use a modified Canon 350D fitted with a CLS filter.
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Old 21-01-2009, 05:43 PM
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And to add to this always use ICNR, it makes a hell of a difference.

Leon
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Old 21-01-2009, 05:54 PM
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But with ICNR, if you're taking a 5 min frame, you have to wait another 5 mins for the in camera dark to be taken. Don't you? Very time wasting? I was recommended to turn ICNR off, take all the shots I want, then can put lens cap back on and take darks while I'm packing up gear.
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Old 21-01-2009, 06:02 PM
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Troy, I know where you are coming from, and I to find that it is very time consuming, but at the end of the day you know that all your dark's are matched, temperature wise to the lights they accompany.

It dose double your imaging run, and halves the exposures you can get in one night, but it is the better of many ways to do darks.

Leon
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Old 21-01-2009, 06:02 PM
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I gather it all depends Troy whether you're time constrained on the viewing night.

I havn't tried ICNR as yet, but for the meantime I find it more suited for my needs to take the manual darks after.

For instance, I'll take maybe 5 x 5min subs or 3-4 targets. Then take a roll of darks, and use the one run of darks for each batch of lights.

I'll have to experiment some time with ICNR.
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Old 21-01-2009, 06:41 PM
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Hi Frank,
I tried hot/cold pixel detection as you suggested, and results are attached.
I also included identically processed image, but with hot/cold pixel detection disabled.
Both attached images are crops from stacks of 2 frames, taken with INCR ON (that means, darks were taken automatically after each exposure and subtracted from image).
It seems the final image with hot/cold pixel detection is a bit blurred (the first one). Probably not important in most cases.
However, I agree that it is not necessary to have INCR ON, especially for longer exposures (I have it ON because those images were 1min exposures through 1000mm lens, so in this case it is not too time consuming..). The rationale for this is, darks are supposed to be used to remove hot and cold pixels, together with any constant features on the image. Noise, being random is dealt with by the greater number of light frames (by means of averaging).
The argument for INCR would be, darks are taken at roughly the same temperature (and they are really taken, and not forgotten like it happened to me in the past couple of times :-) )
Attached Thumbnails
Click for full-size image (Screen_02_ 2009-01-21 19.33.jpg)
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Click for full-size image (Screen_01_ 2009-01-21 19.33.jpg)
27.7 KB18 views

Last edited by bojan; 21-01-2009 at 07:30 PM.
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Old 21-01-2009, 08:44 PM
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Bojan,
Dont use the cold pixel removal, just the hot.
set it at 1pix and 1%
There is probably a limit too, the amount of noise is very intense on the second shot, I'd say that if there is that much noise then the exposure was probably a bit too long to begin with.

I've run stacks of tests, usually stacking 2 frames or 3 and the results using hot pixel cosmetics only is what wins the day.

I wouldn't use it if it blurred the final this much.

Using DDS I have also learned that it is best to NOT add the saturation, leave this for processing in PS and also flatten the curve a bit that DSS automatically generates. Using a sharp curve and the DSS saturation tends to add noise or highlights noise.

attached are samples of recent tests on Thor (yes I know I'm obsessed...) they were 2 frames of slightly too long duration I think 15 min at ISO 800(a fair amount of noise and vignetting etc)
On close inspection (onthe full versions, I couldn't find much if any blurring using just hot pixel cosmetix but the use of both hot AND cold made things a bit. I also allowed the push of noise through the use of DSS saturation (set at 20) for the purposes of the experiment.

Of course, what i normally do is stack lots of frames, i dont use the DSS saturation and I do quite a bit more processing in PS to remove gradient, adjust set black white points, high pass filter some sharpening and saturation amongst the basics.
Anyways,
hope this helps
frank
PS the files: the one that says "no cosme" is stacked as is no use of cosmetics, "cold n h" is the stack using hot and cold pixel removal (both set at 1pix 1%) and of course the one that says "cosmetix" is only using the hot pixel settings at 1pix, 1%.
Attached Thumbnails
Click for full-size image (thor-test-2-frames-cold-n-h.jpg)
196.3 KB42 views
Click for full-size image (thor-test-2-frames-cosmetix.jpg)
192.7 KB41 views
Click for full-size image (thor-test-2-frames-no-cosme.jpg)
196.6 KB38 views
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Old 21-01-2009, 08:47 PM
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They're not labelled very well, in the IIS display on the left hand corner: top is using hotn cold, middle just hot, bottom none
cheers
frank
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Old 21-01-2009, 10:02 PM
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Yes, hot only is better... see attachment. Even slight banding is reduced.
Obviously, far better results should follow use of larger number of frames (here I used only 2).
Normally, I never do anything else in DSS, post processing here was done in DPP and was quite aggressive, to exaggerate the result.
Attached Thumbnails
Click for full-size image (Screen_01_ 2009-01-21 22.47.jpg)
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Old 21-01-2009, 10:59 PM
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agree, and your result is consistent with mine, dark parts of the sky get dark, and typically nebula stays nice
cheers
that's what its all about
experimenting, having fun and sharing our experiences
frank


Quote:
Originally Posted by bojan View Post
Yes, hot only is better... see attachment. Even slight banding is reduced.
Obviously, far better results should follow use of larger number of frames (here I used only 2).
Normally, I never do anything else in DSS, post processing here was done in DPP and was quite aggressive, to exaggerate the result.
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Old 21-01-2009, 11:05 PM
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I never use ICNR. I don't know what algorithm is being used to subtract data. I rather trust in manual dark frames and the functions available to me in my pre-processing tool.

Regards,
Humayun
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Old 22-01-2009, 12:24 AM
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Thanks bojan and spearo for contributing to more of the processing side. Lots of valuable information
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