Stripes in picture

[supernova1965]

This is a Zoom and crop around the coalsack of a picture I took showing downward stripes what causes this is it LP or something else

[renormalised]

Most likely thermal noise. Maybe some LP. What did you take the piccies with??. What were the exp lengths, ISO etc etc.

[supernova1965]

Nikon D200 Apeture 3.5 18mm ISO 1600 15sec x 30 exposures stacked in DSS
There was a fair bit of Light Polution

[jjjnettie]

Carboni Actions have a quick fix for this sort of noise. Very handy to have.

[TheDecepticon]

You may want to calibrate your images with dark, flats and bias frames.:)

[supernova1965]

It has a dark but I have no idea what a flat and or bias frame is.

JJJ I looked up Carboni Actions and google says you need PP I only have Gimp

Thanks all

Warren

[renormalised]

Flat frames, or flat field frames, are just frames that create a flat field of intensity across the pic, so that any imperfections in the pics you take (like dust bunnies etc) that are represented by changes in intensity can be accounted for. One way to make a flat is to take a white T-shirt and stretch it across the front of your scope and then take pics of the T-shirt framed against an evenly illuminated background...like the evening sky at zenith. They have to be of the same length as your light subs (pics).

Bias frames are frames that account for electrical bias in the CCD chips. That's basically an electrical charge that occurs in the chip when no light is striking the surface of the chip. Bias frames can by just snapshots because the bias will be present in the pics no matter the exp' length.

[supernova1965]

Thanks Carl,

:thumbsup:

So if I am taking flats with just the camera do I put a white shirt on the lens:question:

[irwjager]

Hi Warren,

Since you have StarTools, there's a new Banding reduction tool (similar to Noel's actions) as of 1.1. See if that helps at all?

Cheers,

[supernova1965]

Would you believe Ivo I forgot I had Startools:doh:Thanks for the tip

[renormalised]

Just stretch the T-shirt over the front of the scope and secure it whilst you're taking the flats.

With a lens on a camera, you do much the same. Might be better to cut the T-shirt to size and secure with a rubber band.

You can also buy illuminated panels for taking flats, which are better than the T-shirt method. Plus, there's the ol' light box method as well.

[jjjnettie]

You can also use Al's Virtual Light Box.
http://www.iceinspace.com.au/files.html
it's down the bottom, "VLB"