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  #21  
Old 22-12-2010, 05:23 PM
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Quote:
Originally Posted by dugnsuz View Post
I'm trying to match darks temperatures as closely as I can.
Thanks
Doug
If you're doing that then your images will benefit more from trying to do this. If you go through my gallery you should see all the 40D image present low noise. I used darks I took months and in some cases a year before and the dark subtraction was consitently good. Maybe it was an aberration.
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  #22  
Old 22-12-2010, 09:04 PM
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Depending on the camera darks may not be needed IMO (shoot me)

flats yes but must be good flats otherwise just don't work
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  #23  
Old 22-12-2010, 09:06 PM
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Trevor,

Show me a DSLR that doesn't need dark frames, and, I'll... something.

H
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  #24  
Old 22-12-2010, 09:17 PM
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IMO, on a bigger screen than my laptop (first post), the image without the darks (and flats) has tighter star images and a tad more detail - see core of the Tarantula. Sure the the "Darks/Flats" image has more contrast and at first glance looks more pleasing. But would be interesting to see what the image looks like with just the flats. Are you subtracting bias from the flats?
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  #25  
Old 22-12-2010, 09:35 PM
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Reading this thread I'm a little lost...

Seeing as I have limited experience here and for clarification. Is the use of libraries ok or is it better to shoot the darks, flats and biases during your session?

I was going to go exclusively with the library route, but now am unsure.

OIC!
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  #26  
Old 22-12-2010, 09:52 PM
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OICURMT,

The conventional way of imaging, if you don't own a Peltier-regulated CCD camera, is to take darks on the night of the misadventure.

You don't need bias/offset frames as that information is already contained within the darks. The only time these are potentially of any benefit is when you're scaling dark frames (that is, you try and subtract a 10 minute master dark frame from a 5 minute light exposure). Not sure why you'd do this and not just take dark frames on the night, itself.

What has worked for me over the years is to take a bunch before the imaging session, a bunch during a meridian flip, and a bunch afterwards.

As others have mentioned, their mileage varies.

I guess it just depends on how anal you are.

H
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  #27  
Old 22-12-2010, 09:55 PM
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Talking

Quote:
Originally Posted by Octane View Post
I guess it just depends on how anal you are.
I'm an engineer...

Thanks for your answer.

OIC!
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  #28  
Old 22-12-2010, 11:42 PM
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H, I was not referring to a DSLR as most are uncooled and produce noise depending on weather etc (all the best for the season by the way) although Doug may be moving into the CCD realm and my experience with the QHY8 is you can get noise free subs up too 10 minutes
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  #29  
Old 23-12-2010, 12:27 AM
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Quote:
Originally Posted by Octane View Post
OICURMT,

...You don't need bias/offset frames as that information is already contained within the darks. The only time these are potentially of any benefit is when you're scaling dark frames (that is, you try and subtract a 10 minute master dark frame from a 5 minute light exposure). Not sure why you'd do this and not just take dark frames on the night, itself...

H
Not quite sure about this and I'm no expert, but granted the dark frame has the bias error already in it, fine if you just subtract the darks. But if you use both darks and flats, as the flat frame has the bias error in it as well, aren't you going to subtract out the bias error twice (or at least a proportion of it) which will in fact be adding noise, unless you subtract the bias from the flats. Not quite sure how the various programs out there use the bias frames.
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  #30  
Old 23-12-2010, 08:07 AM
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Craig,

That's why we also take flat darks as well.

So, lights, darks, flat lights and flat darks.

H
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  #31  
Old 23-12-2010, 11:35 AM
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This image was processed with 'Flats only' on the 18x10min images.
I've added it to the original #1 post to compare the 3 files side by side.

Cheers
Doug

ps... and at last a High Res version
http://s327.photobucket.com/albums/k...urrent=23b.jpg
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Last edited by dugnsuz; 23-12-2010 at 01:21 PM.
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  #32  
Old 23-12-2010, 04:26 PM
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Quote:
Originally Posted by Octane View Post
Craig,

That's why we also take flat darks as well.

H
Umm, why?. Are your flat exposures more than a few seconds?.

Would be a worry, needing darks for a 2 second exposure
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  #33  
Old 23-12-2010, 04:41 PM
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Fred,

Whether the exposure is 1 second, or 600 seconds, there is always going to be some kind of dark noise present in the image.

And, if not, what's the harm? It's all part and parcel of calibration. It makes sense to me. Besides, how long does it take to run off 15-19 1-second flat dark frames? Not long. How long does it take to median combine them? Perhaps 10 seconds. No skin off my nose.

H
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  #34  
Old 23-12-2010, 04:46 PM
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Quote:
Originally Posted by Octane View Post
Fred,

Whether the exposure is 1 second, or 600 seconds, there is always going to be some kind of dark noise present in the image.

And, if not, what's the harm? It's all part and parcel of calibration. It makes sense to me. Besides, how long does it take to run off 15-19 1-second flat dark frames? Not long. How long does it take to median combine them? Perhaps 10 seconds. No skin off my nose.

H
Anyway, I like HDR, so there
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  #35  
Old 23-12-2010, 05:38 PM
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There's no accounting for taste.

H
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  #36  
Old 23-12-2010, 06:34 PM
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Hey Doug,

Really like the ""flats only" version - the best of the three IMO. Has tighter stars than the darks/flats version and more detail. It is also smoother than the darks/flats version, less 'mottled' looking in the darks.

Craig
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  #37  
Old 23-12-2010, 07:17 PM
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There's no accounting for taste.

H
I dont have any. I appreciate the work in expertly photoshoped-to-hell single shots to look-like-hdr pics and hdr done subtly to look like well ..hdr. Its the over done I dont like (as I suspect you dont). How you get the same result is interesting but ulimately futile.
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  #38  
Old 23-12-2010, 08:02 PM
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Hold on a second. That is a major insult.

My images, if you are referring to them, are not Photoshop'ed to hell and back.

Try taking photos at the right time of day with the appropriate hardware (polarisers, filters, lens and sensor) and anyone can do it.

Lastly, the type of imaging I engage in has been done for at least 35 years. HDR is a relatively recent gimmick which doesn't come anywhere near the single exposure method.

You can join me on a workshop in the new year if you like to see that it's possible.

Apologies for the diversion, Doug.

H
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  #39  
Old 24-12-2010, 10:31 AM
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Quote:
Originally Posted by dugnsuz View Post
This image was processed with 'Flats only' on the 18x10min images.
I've added it to the original #1 post to compare the 3 files side by side.
how much difference can you see on your computer at 100% when you flick the between the darks/no darks version?
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  #40  
Old 24-12-2010, 12:50 PM
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how much difference can you see on your computer at 100% when you flick the between the darks/no darks version?
Will try tonight Phil if Suz lets me near the computer on Xmas Eve!
Doug

EDIT: 100% crops added - not much between them apart from obvious processing differences
Left pic - Flats only
Right pic - Dark and Flats
Attached Thumbnails
Click for full-size image (flats-only-crop.jpg)
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Click for full-size image (Darks-Flats-crop.jpg)
195.5 KB15 views

Last edited by dugnsuz; 24-12-2010 at 06:36 PM.
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