Flat Help

[astro mick]

Hi.

I,m seeing a strange effect when applying my Flats to an image.The Flats seem to do the job(ie. Remove the artifacts)but i am left with slightly sunken depressions of the artifacts.

Any idea whats going on.

Cheers.

Mick.

[Spikey]

Mick, could you supply more information about the flats and maybe post an example of your problem?

What camera setup are you using? how are you taking your flats? flat exposure times etc..

[Dave Smith]

My first thought would be that there has been a slight movement between taking the lights and the flats. An example would be useful.

Dave

[astro mick]

Hi Guys.

OK.im using a 80mm ED Refractor F7.5,attached to this is a Filter Wheel,and a MX716 ccd Camera.

I take my lights as normal,but tend to take the flats at a later date.

I am using a Gerd Neuman Panel screen to take the Flats.

I didnt think the orientation of the scope matterd for Flats,so i point the scope Horizontal,and take Flats to about half the saturation level of the camera.

I take seperate Flats for each LRGB Fliter.

Usual around 2-3 secs.

I,ve posted a Master Luminance Flat taken at 1x1,and a Flat taken through the Red Filter at 2x2.

The masters were made up of 15 Flats.

Unfortunately the images have,nt come out well here,

Please have a look.

Mick.

[Dave Smith]

Taking the flats at a later date may well be the problem. Especially if you have moved the filter wheel. Ideally, the flats for each colour should be taken before anything is moved.

One thing puzzles me and it may just be the way you have prepared your images for presentation here, but here is a comparison between your first flat and a recent one of mine (reduced in size) but both stretched. This may be nothing to do with the problem - maybe someone else can advise?

Your flat is very pixelated and only has 3 or 4 levels of brightness???

Dave

[astro mick]

Hi Dave.

The thing is i dont disturb the set up of the scope,as its in an observatory.

Just point it in a horizontal position to take the flat.

Here is an image of my flat again,hopefully a bit better.

Mick.

Flat.tif

[Dave Smith]

That one is fine - so nothing to do with that.

All I can suggest is take the flats before moving the filter wheel - sorry no other ideas.

Dave

[astro mick]

Ok Dave thanks.

I,ll try sort it.

Mick.