Rings in my Flats again

[leon]

Hi Guys, some of you may have read my earlier post about concentric rings in my flats after processing them in Image Plus.

I was determined to get to the bottom of this, but to no avail.

I even built a light box, which I might add works very well, so I thought i would give these flats another go.

I have two Canon 5D's, one modded and one not modded, so I thought that i would see if there was a difference, both took 19 exposures at the same ISO and at the same exposure length, under the exact same conditions.

However after converting Raws to 16 bit Tiff, and combineing two sets of frames from either camera the results were the same, still got those rings in the final image of both cameras, so at least it is not the hardware.

So I'm at a lose of what the problem is, if in fact it is a problem, as the appearance of the combined images has no effect on the final light image.

Any suggestions would be helpful, thank you.

Leon

[rat156]

Hi Leon,

Can you post a pic so we can see?

Cheers
Stuart

[leon]

Yes Stuart I can, but they look as they did when I posted some in the previous post regarding this strange effect.

When the original images are captured they are normal, and very light in colour, however once converted to tiff's and combined in Image Plus they tak on this very dark nature and the rings appear.

Leon.

One Image is with the unmodded camera and the other with the nodded unit

[Tandum (Robin)]

Leon, have you tried taking flats with a canon lens attached to see the result? That would eliminate a scope problem...

[leon]

Robin I have actually the result is the same.

Now just for the hell of it i took those exact raw flats and converted them to Tiff's in Canon Photo Professional soft ware and then combined them in Image plus, and the results are different again.

This program is not related to Image Plus, and obviously sees the process different.
Image below is a combined set of 19 raw flats processed in DPP.

Leon

[Tandum (Robin)]

That attachment shows me rings on my laptop, which is outside, but I don;t see rings here on this machine indoors. This machine has a much larger Samsung monitor on it. But it's a jpg and I just thought what I was seeing on the laptop was from compression. Why not grab a free copy of deep sky stacker and see if it does it. You might have to actually process something to make it go but once done it will leave a master flat in the flat directory.

[edit]
I just checked the master flats from 25 I made yesterday and I see rings in it. But, drop it into Ps and adjust levels and the rings go. I think it's a monitor phenomenon. Our 8bit monitors can't display this stuff properly.

[leon]

Robin I am starting to think that as well, and I do have Deep Sky Stacker, things seem to be the same as with the others.

I don't think it is Camera or capture related, and the software seems to be doing what it is supposed to as well, so eliminating these things all that is left it maybe the screen displays.

I know mine is pretty bright, I do that on purpose, and if i drop the brightness the rings tend to deminish quite a bit.

It dose not seem to effect the final light image though.

glade you have seen some rings as well Robin, I thought it was just me giong mad.

leon

[Tandum (Robin)]

Yep I agree, our monitors can't display the levels in the gradient properly.

[Doug]

Leon those images look perfectly normal. They are a 'light map' of your optical system. That is what you want a flat for, or did I miss something???
Doug

[Doug]

Leon monitors do differ in gamma response etc. So do imaging programs.
I do not have imaging plus so I can not point specifically to any parameter option that might or might not be present there. With MaxDslr, when converting to Tiff there is some scope for control of 'stretch' and a few other things that happen during conversion.

One ultra simple test you can do is to look at your dark frames. You can play around with stretching to go from black to grey/white and see if those rings are there as well; if they are, then it is s/w related; if they are not then it is light related. and if Light related then it is nothing more than a light signature whether this monitor displays it and that monitor does not:another issue.
cheers,
Doug

[leon]

Thanks Doug, I will give your suggestion a try, I would like to find out if this is in fact a problem.

Leon