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  #1  
Old 06-06-2008, 11:52 AM
TrevorW
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Darks, lights ,light darks, dark dark and the meaning of Life

Can anyone please explain to me these terms so a layman could understand and why you need to do these things to produce a good image.
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Old 06-06-2008, 12:24 PM
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lights = a normal exposure

darks = an exposure with the same settings as your lights but with the scope/lens cover on so basically all you are recording is the noise generated by the sensor without any light hitting the chip.

flats = exposing to an evenly illuminated light source across the entire telescope aperture to around 30% of your maximum pixel value (records dust/vignetting)

flat darks = if the exposure needed for flats is long enough you will need to take dark frames to be applied to them.

meaning of life, the answer is 42 (apparently)
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Old 06-06-2008, 12:27 PM
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Quote:
Originally Posted by monoxide View Post
meaning of life, the answer is 42 (apparently)
I don't know why that is, but it looks nice in binary. Add a leading 0 for best effect.

ps. thanks for the succinct explanation.
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Old 06-06-2008, 12:30 PM
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pps - what is a "sub"?
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Old 06-06-2008, 12:46 PM
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Ah I know that one, it is a boat that swims under the water.

leon
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Old 06-06-2008, 01:03 PM
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or some sort of sandwich thingie?


OK, I'll expand. I think it's an abbreviation for sub-frame, one of a number of frames which are put together (stacked?) to create a final image? Have I guessed right?
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Old 06-06-2008, 01:22 PM
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exactly
also its good to take the same amount of flats/darks/flat darks as lights
that way you get a better 'reading' of whats going on.

takes a lot of exposures for 1 image doesn't it
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Old 06-06-2008, 01:23 PM
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Ah I know that one, it is a boat that swims under the water.

leon

No, it's a bus admiring itself in the mirror!!!

Serious question!
Do flats have to be taken at same FL and f ratio as imaging run? I'm thinking about lens imaging here.
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Old 06-06-2008, 02:22 PM
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Quote:
Originally Posted by dugnsuz View Post

No, it's a bus admiring itself in the mirror!!!

Serious question!
Do flats have to be taken at same FL and f ratio as imaging run? I'm thinking about lens imaging here.
In answer to your question you may refer to Jim Solomon's Astrophotography Cookbook

Flat Darks- exactly same value ISO and Tv settings when collecting flat lights but with eyepiece cover and lens cap in place

I noticed that you are using a Pentax stD I have recently purchase the K100d super. What program do you use to stack photo's. Also is it a good idea to set ISO to 800 etc and do muliptle short shots

Last edited by TrevorW; 06-06-2008 at 02:36 PM.
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Old 06-06-2008, 03:27 PM
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I noticed that you are using a Pentax stD I have recently purchase the K100d super. What program do you use to stack photo's. Also is it a good idea to set ISO to 800 etc and do muliptle short shots
Cheers Trevor
Sold the ist-D a while back to fund the 40D purchase.
The pics in my gallery would have been stacked using either Registax (earliest widefield pics) and then Images Plus.
I found iso 400/800 to be good on the Pentax, but get as many subs as you can due to the noise generated!
Doug
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Old 06-06-2008, 03:44 PM
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I found iso 400/800 to be good on the Pentax, but get as many subs as you can due to the noise generated!
Doug[/quote]

The K100d has built in noise reduction and supports ISO up too 1600 or would this be way too much

Regards
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Old 06-06-2008, 04:41 PM
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Doug, if you shift your focus between taking your lights and taking your flats or rotate your camera or do anything that alters your imaging train, then your flats will be no good to you. They must be taken with the same imaging train/layout/orientation/dust (yep don't even blow the dust away ) as your lights.
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Old 06-06-2008, 04:48 PM
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Quote:
Originally Posted by TrevorW View Post
I found iso 400/800 to be good on the Pentax, but get as many subs as you can due to the noise generated!
Doug
The K100d has built in noise reduction and supports ISO up too 1600 or would this be way too much

Regards[/quote]

Not really too sure Trevor - there are a few devoted Pentax users on IIS.
Perhaps start a Pentax related thread?
I would just experiment with iso settings though Trevor.
You'll probably know quite quickly if the noise produced looks unacceptable.
I would add that the same rules apply to all astro dslrs (pentax, canon etc), take as many subs as possible of an image to obtain the best signal to noise ratio when stacked.
All the best
Doug
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Old 06-06-2008, 07:47 PM
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A bit of experimenting then is on the cards
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Old 06-06-2008, 08:57 PM
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Do you have autoguiding capability with your EQ5 mount Trevor?
If not is it driven in RA?

If polar aligned, a driven EQ5 will give you 30-60sec unguided exposure time. Probably closer to 30secs unless you're anal about the polar alignment!!

That will necessitate the need for multiple exposures.
If you have a Pentax remote shutter switch this is easy.
Set the camera to multiple exposure mode and the maximum exposure setting: 30secs. Put your remote switch into the hold mode - this will make the camera take one shot, do a dark then take another shot etc etc as long as the remote button is depressed.
Doug
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Old 07-06-2008, 04:34 PM
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Jeepers! I logged on to get some info about focal reducers and saw the subject of this thread (which made me laugh in empathy) and, of course, had to read the whole thing because I'm just learning about the subject. Now I'm too sleepy to look up focal reducers. LOL.

I love this place!!
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  #17  
Old 09-06-2008, 10:21 AM
TrevorW
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Welcome to America, it's gratifying too know we can help.

I'm not new to astronomy as a hobby but monetary restrictions have placed limitations on what I could do in the past but now I'm building up some modest equipment to try my hand seriously at astrophotography.

The advent of DSLR's and the like has widely opened this realm to the amateur in more ways than one.
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  #18  
Old 09-06-2008, 10:36 AM
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Quote:
Originally Posted by dugnsuz View Post
Serious question!
Do flats have to be taken at same FL and f ratio as imaging run? I'm thinking about lens imaging here.
Serious answer !: Yes
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