DUAL BAND FILTER OSC FLATS

Malcolm Park

Adam,

may I ask for your opinion please? And I may be out in left field on this.

I have a difficult situation with my OSC dual band flats. 

I'll attach the flat histogram.

The way I read this, each "hump" is one of the three primary colours which seems to indicate that the R, G and B components (as determined by the L-Ultimate filter) are all exposing differently in the flat. Am I wrong?

And so when it comes to applying the flat, the distribution of intensities varies.

I've attached the calibrated master light, OSC with dual band HA/O3 filter. 

Is this a common outcome?

I am having a devil of a time getting this gradient out, any suggestions on how to deal with this? 

I re-shot my flats, no change.

This does not happen with the unfiltered OSC data.

thanks,

Malcolm 

BlockHead

Yes, of course. Consider broadband imaging- your light source is certainly not going to emit light equally in each color and your sensor isn't going to detect light equally in each wavelength/color and your filters do not transmit light quality at whatever color that permit to pass. So RGB values will not be anywhere near equal.

This isn't a source of flat field problems. 

The image you are showing me is using a flat that is not calibrated correctly.

You think the problem deals with flats. 

I think the problem is biases, darks, or lack thereof.

Are you also asking this identical question elsewhere?

-the Blockhead

Malcolm Park

What an odd question, thats the second or third time you have asked me that. No. I am relying exclusively on you for guidance. Are you under the impression that I am?

I think it would be rude to disrespect you that way frankly, although there are probably some that do it.

You wouldnt ask if they werent. I assume.  

Anyway, I assumed that as a subscriber I am entitled to ask for help.

Forgive me if this is incorrect. 

I'll check on the flat calibration files. 

thanks

BlockHead

I will answer as many questions from members as quickly as I can. 

Yes, there does appear to be an element of polling for answers from other sources by some members. I honestly can't keep track- but I am interested in making the heartbeats I spend in answering questions be for the members as a coherent story as possible. I appreciate you get that. Thanks.

-the Blockhead

Malcolm Park

I looked at the light subframes and the gradient is extreme, so I looked at the date and these were shot during 100% full moon. 

I'm going to re-shoot. 

Malcolm Park

I'd say that it was the moon. These are UNCALIBRATED.

Moonless on left, full moon on right. 

as usual, user error ;) 

BlockHead

Oh..I see. Yes, if the field is illuminated strongly that can happen. 

Assuming you took these data in some kind of sequence you can see the effect of moonlight on the data by blinking the images. 

-the Blockhead