Iv'e Had a Flat Day

[leon]

Hi Guys, as the heading may suggest i have not personally had a flat day, but have had a day sorting out this continuing saga of rings in my flats.

Some of you may have seen my earlier posts on this subject, of rings in my flats, so I promise this is the last I will speak of it.

I spent most of Sunday morning taking flats through my new light box, which i might add, works a treat, no more waiting for the right light etc.

I have tried every possible combination, of exposure times, histogram read outs, with filters, and without filters, and so on.

Image Plus, gives about 10 different ways of combining the converted 16 bit Ti'ff's, and I tried them all to see it i would make any difference in the final combined master flat, it did not.

So my conclusion is, what I see in the final image is supposed to be there, and is and image of my optical train as the camera sees it.

I have two options, and that is not to bother with flats, or accept that the flats that I'm getting are correct.

I am going with the later, as there is no more test I can do, and each test has the same out come anyway, so I conclude that it is correct.

What do you guys think on the subject, yea, I know you are probably sick of hearing about it, but I would be interested in you opinions.

Thanks, Leon

[Doug]

Leon I have said all that I think is needed, but please allow me this one question.

What do you, or did you expect a flat frame to look like in the first place?
I know that expectations unfulfilled can be a huge disappointment sometimes,

doug

[leon]

Doug, good question, and no mate, I'm not disappointed at all, I just wondered why they had those lovely concentric rings in them.

To perfectly honest I didn't really know what to expect, however, having said that I did think that the master flat after conversion and combining would stay the same colour as the original raw frames taken.

It did surprise me to see them come out of the processing sequence as very dark nearly black appearance, but I presume this is normal.

Doug you must understand, I have not done this sort of stuff for all that long, but am still learning every day, this certainly has been an interesting episode, and that is good, as I have learned something, I think.

As said earlier Doug, there is no apparent problem applying these flats to the lights, and the final image is fine.

So I will accept that this is how it is supposed to be, unless told other wise.

Thanks.


Leon

[Tandum (Robin)]

My master flats look darker to me that the individual flats, see attached. Even though you could get them both looking the same in photoshop, they both hold the same numbers, which should represent the gradient across the optics, so they should both do the same job. I see rings in my master flat here, but I'll bet it's a monitor thing not a data thing.

[Doug]

Ahh! Leon there is a can of worms if ever there was one.
Colour!!
When a raw Flat frame is subtracted from a Raw Light Frame, the colour balance of the resultant calibrated light frame will be influenced by the colour (off whiteness) of the Flat frame. That is true as far as it goes. I have been given to understand that with Images Plus (Remember I don't have that!) converts flat frames to grey scale thereby eliminating colour bias from the flat field light source. If all this is true (Which it is not with MaxDslr), then you should never be deal;ing with anything other than a Raw Flat frame ie. before debayering.
HTH,
Doug

[leon]

Robin Thanks for the two images you have posted, it dose make me feel better to see those rings in your images as well, I do feel better now.

Doug it is true that Image Plus converts to gray scale, I do know this, and I do use Raw Flat frames before the processing.

Many thanks for your patience, and sorting out this problem for me, which in the end is not really a problem, but the normal end result, but I now know this.

Leon