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Old 30-09-2009, 03:29 PM
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lesbehrens (Les)
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image question

hi. when i take a series of images and stack them to gether i notice that they are very noisy and have red banding at the bottom of the image. is this to to with how the images are stacked to gether or mabye to do with the camera?
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Old 30-09-2009, 03:37 PM
TrevorW
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Need more detail Les

camera (i assume the 450d) number of exposures, length, iso setting

what program are you stacking in

conditions when image taken
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Old 30-09-2009, 03:45 PM
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ok. i use a cannon 450D. exposure time can very from 30 sec to 10mins but this is still the outcome. i use deep sky stacker to stack them. i do use darks but the image seems less nosier if i dont use them. the iso used in thes images was 400. the images are taken in a darks site with little light around
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Old 30-09-2009, 03:52 PM
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Do you have ICNR turned off
Do you use a LP filter
Is the red appearing in the same spot on the final stacked images
also does it appear in the unstacked frames
do you use both darks and flats
is is more prevalent in the 10 minute exposures

Sorry just trying to narrow cover all options
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Old 30-09-2009, 03:53 PM
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Hi Les

How many darks are you using? are you using flats? is the colour in bands, or kinda round like look a faint hole in the middle of the image?
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Old 30-09-2009, 03:54 PM
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Could you maybe post a picture Les?
Ta.
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Old 30-09-2009, 03:55 PM
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lesbehrens (Les)
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Quote:
Originally Posted by TrevorW View Post
Do you have ICNR turned off
Do you use a LP filter
Is the red appearing in the same spot on the final stacked images
also does it appear in the unstacked frames
do you use both darks and flats
is is more prevalent in the 10 minute exposures

Sorry just trying to narrow cover all options

thats cool.
no filter
no flats
is not seen in the unstacked pics. alsways in the same area in the final image.
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Old 30-09-2009, 03:57 PM
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If you are taking darks after taking a series of images is there much of a temp change between lights and darks?
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Old 30-09-2009, 04:02 PM
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lesbehrens (Les)
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Quote:
Originally Posted by [1ponders] View Post
If you are taking darks after taking a series of images is there much of a temp change between lights and darks?

i take the darks after i have finished taking the light frames
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Old 30-09-2009, 04:12 PM
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If you take your first image and the temp is 24deg and when you take the last image the temp is 18deg then the last image will have half the dark current (noise) than the first. If you start taking darks then and by the time you finish taking the darks the temp is 12 deg then the last dark will have half the dark current than the first and only 1/4 the dark current the first light has. It is almost impossible to get accurate dark subtraction in this situation. Unfortunately this exact situation is not uncommon in SE Qld at this time of the year. You start taking images after twilight and finish taking darks 4 hours later.

I used to be a strong advocate for taking darks after lights. But I consistently get better result using ICNR now. If the temp is stable within a couple of deg then later darks can work well, otherwise I would strongly recommend using ICNR.

The biggest problem with ICNR is the loss of time collecting Lights. It takes two hours to collect an hours worth of lights. As with most things, its a trade off. If you have plenty of time then ICNR, if only a small window then darks later.

Mind you I'm not convinced that this is your problem, but trying this method may eliminate one factor that could be causing you issues.
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Old 30-09-2009, 04:14 PM
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Quote:
Originally Posted by jjjnettie View Post
Could you maybe post a picture Les?
Ta.
these are the images. the first is all stacked with darks 2nd lights staked only, 3rd one light frame ,4 dark frame
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Old 30-09-2009, 04:18 PM
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i used icnr before but this made no difference, just took longer.

Quote:
Originally Posted by [1ponders] View Post
If you take your first image and the temp is 24deg and when you take the last image the temp is 18deg then the last image will have half the dark current (noise) than the first. If you start taking darks then and by the time you finish taking the darks the temp is 12 deg then the last dark will have half the dark current than the first and only 1/4 the dark current the first light has. It is almost impossible to get accurate dark subtraction in this situation. Unfortunately this exact situation is not uncommon in SE Qld at this time of the year. You start taking images after twilight and finish taking darks 4 hours later.

I used to be a strong advocate for taking darks after lights. But I consistently get better result using ICNR now. If the temp is stable within a couple of deg then later darks can work well, otherwise I would strongly recommend using ICNR.

The biggest problem with ICNR is the loss of time collecting Lights. It takes two hours to collect an hours worth of lights. As with most things, its a trade off. If you have plenty of time then ICNR, if only a small window then darks later.

Mind you I'm not convinced that this is your problem, but trying this method may eliminate one factor that could be causing you issues.
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Old 30-09-2009, 04:20 PM
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It has to do with the settings in DSS don't you think?
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Old 30-09-2009, 04:20 PM
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Could it be AMP glow I've heard of this happening but not seen it myself

the third image doesn't look too bad

someone said that the more darks to lights the better
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Old 30-09-2009, 04:24 PM
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lesbehrens (Les)
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Quote:
Originally Posted by jjjnettie View Post
It has to do with the settings in DSS don't you think?
i have played around with this but similar outcomes. i mite need someone with a bit of experience to help out with the settings ?
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Old 30-09-2009, 04:26 PM
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Its not amp glow and it's not dark subtraction. To me that looks like its been way over stretched. We need to know what settings you are using in DSS and what post processing you are doing.
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Old 30-09-2009, 04:26 PM
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Quote:
Originally Posted by TrevorW View Post
Could it be AMP glow I've heard of this happening but not seen it myself

the third image doesn't look too bad

someone said that the more darks to lights the better
what is amp glow? i have once used more dark to light but the final pic looked very green
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Old 30-09-2009, 04:29 PM
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What format are you recording your images in RAW or jpeg? Are you stacking RAW. To me it looks like information is being deleted during the stacking process.
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Old 30-09-2009, 04:32 PM
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lesbehrens (Les)
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Quote:
Originally Posted by [1ponders] View Post
Its not amp glow and it's not dark subtraction. To me that looks like its been way over stretched. We need to know what settings you are using in DSS and what post processing you are doing.
setting i use are:
standard mode - align rgb channels
light - median
dark flat bias median
alignment - auto
i am use ing RAW
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Old 30-09-2009, 04:36 PM
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Les, as asked previously, how many dark frames?
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