Dss flats problem

[icpass]

Why cant i make flats work in Dss.

Im using a modded dslr and a light box,my flats look good to me problem is when i put it all together in Dss they dont seem to work and im still left with artifacts in the image.

I have attached a flat image,am i doing something wrong this is now becoming a major headache for me .

Ian

[jgs001]

I'm not sure I've done this right, but looking at the histogram on my puter, it looks overexposed. How are you taking the flats ? What settings on the camera ?

[icpass]

John

They were taken in av mode the master flat i have looks good too

[icpass]

Taken with a light box and white t shirt stretched over ,i have attached master flat from dss

[jgs001]

Have you got any exposure compensation set on the camera ? that will affect the exposure levels... other than that... sorry I just don't know... It'll need someone more familiar with flats I'm afraid. What it would be a good thing to do... post up the end result pic... as that may give a clue as the problems.

[dmahon]

Why can you see all the pixels in the master?

[icpass]

I think its where i reduced the size of the image so much,was 80mb

[icpass]

Actally im not sure,just looked at the original master and i think it could be the tee shirt fabric.

[Paxo]

All the particles on your flat look very sharp (in focus) have you altered the focus between taking your deep sky images and taking your flats.

Steve

[icpass]

Nope focus stays the same!!

[Paxo]

There doesn't seem to be any gradient on the flats towards the corners which I would expect to see with a larger chipped camera, they may well be saturated as John has already suggested.

Steve

[icpass]

I think it would help if i new what i was looking for!!

[jgs001]

If you put your SLR into Av mode, (assuming it's a Canon) on the rear display (xxxd models, not sure where it is on the xxd and higher models) there's an exposure scale from -2 to +2, where is the little vertical bar indicating... ? I suspect it's not under the 0 point.

[icpass]

John,it was at zero just been trying again this time watching the histogram and varying the exp

[jgs001]

ok, that means no exposure compensation... good start. Av mode, normally, for me puts the histogram peak on about the 75% mark on the graph, although I did have one really weird night, where something got the exposure values all wrong... I ended up binning the flats as the image was much better without them.

Looking at the histogram for the first image you posted on my laptop, it's hard against the right hand edge...

[icpass]

So where would the ideal histogram lie,i will post latest attempt

[jgs001]

I'm not sure these are ideal, but they work for me...

The flat itself

The histogram from that (as shown in GIMP)

Here's the histogram of your image (also from GIMP) as posted at the top

Hth...