Help with odd master lights after WBPP

Hi

Maybe, if red and green frames were taken before the blue ones, there was some kind of ligth pollution affecting those first frames. The flats doesn´t seem to be bad, so the reason for the gradients must be in the lights themselves.

Anyway, have you tried to stack the frames using, for instance, DSS? just to discard any possible problem from WBPP configuration, which sometimes can be tricky.

HTH

Carlos

In addition to the above, check for light leaks or reflections in your environment.  It does not look like sky produced light as it is too sharp and consistent between the two filters.  Your flats look fine.

Show us uncalibrated light frames - some R, G and B
Also you should check process twice - maybe you did calibration twice on some frames.

Hi,
Can you let us know what camera you used?
I can assume a CMOS of some sort.   You have a master dark, flats and flat darks.   I assume the flat darks were exposed at the same temp and exposure length as your flats.  Is there a reason you used a bias?   Bias are only used to scale dark frames and its more of a ccd thing.  If you have a matching master dark for your exposure times and temp, no need for a bias.   This looks like a calibration problem but as was mentioned would like to see a uncalibrated Red and Green.  Also can you  take a screen shot of your WBPP setup?

Thanks all for the replies. I'll try and summarize and later today provide some uncalibrated lights. The camera is a QHY268M and I'm using Astrodon LRGB filters in the QHY3M wheel on an AG Optical 14.5" iDK (with shroud). The darks were taken at the temp and duration of the lights and the exact same calibration masters (except flats of course) were used for all three master lights so the blue, which came out okay, would have been effected as well if it was related to the darks or bias frames (at least that is what I assume would be the case).

I didn't notice anything unusual about the individual light frames in terms of a gradient but perhaps it is so light that it doesn't clearly show but when stacked it adds up enough to cause this problem. I'll try excessive stretching of the red and green individual frames to see if I can find anything.

I tried a simple GraXpert run using the newer AI version script in PI and it removed much of the gradient but nowhere near all of it.

Yeah, I would agree Linwood. The thing is, I've successfully used these filters previously without this issue and I haven't touched my set up (it's all in my backyard roll-off) so not sure how suddenly I have a light leak issue. Not saying it isn't, just hard to explain how it suddenly could be. Again, I'll do an extreme stretch on some individual frames to see if anything shows up.

I had a light leak once in an unexpected way - the power supplies' red face happened to be pointing near the tripod, and when the OTA was pointed high in the sky, the red light was going in a crack between the camera and its mount (a tilt cage was involved as well).  Upon checking I found leaks around the OAG to EFW attachment as well, but the light had to be coming basically sideways to get in.

The obvious fix was turning the power supplies around, but a lot of electrical tape also now protects those paths from (say) neighbor flood lights or other sideways sources of light.

My point is that the leak could only occur in certain positions. which is one possible explanation for not showing up in flats. 

I've also had leaks in darks I didn't expect, which can make quite an impact as well.  I now do all the darks inside a fridge with the door shut (thus proving the age old mystery of whether the light really does go off). 

Murphy is very creative in how he can screw up the best of plans.

And light leaks would show pretty strongly in darks. 

Clearly you have a mystery and need to dig more at the uncalibrated everything, and the calibrated outputs - some where in there is a discrepancy.

Hi Jeffrey,
I has a similar problem recently when setting up a new OTA - although my problem was not being able to balance out vignetting in the corners, rather than a gradient as is evident in your red/green masters - but this might provide a clue …

Your flats are very slightly offset - the vignetting is not symmetrical, which suggests your camera is not in the optical centre of your OTA.

Did you by any chance do a meridian flip between capturing the blues and the red/greens ?
Did you take the flats on the same night as your lights - before or after imaging ?
What happens when you stack your lights without the flats ?

I solved my problem by dividing the uncalibrated light by the flat in Affinity photo, and moving the flat around until the image balanced - which confirmed that the issue was a problem with alignment between the flats and the lights. Then I replaced the coupling ring between my camera and OTA, and the problem went away.

I hope that helps

Cheers,

Gary

Very interesting …

My first suspect would be your flats - they are not symmetrical - something that has caused me a lot of grief in the past.

It would be pretty easy to confirm whether they're contributing to the problem - what happens if you stack your lights using an identical process, but without calibration frames - do you still see the gradient ?

Cheers,

Gary

Was that last posting a calibrated light?  Have you blinked through all the lights (in a bad stack) to make sure they all look similar, and in particular are they all reasonably centered?  One possible cause is if some of the imaging occurred with the frame shifted up (relative to the masters you show).  Star align would shift those up leaving no data in the bottom, which depending on stacking could show as too dark, or too light from noise.

Interesting, if that's the whole frame there's no visible vignetting on it despite the flats showing quite a bit.   Not that that is relevant, just surprised. 

I am out of ideas.  Get the Sherlock hat on and a magnifying glass and solve the mystery, inquiring readers now want to know!