Dodgy data diagnosis - large circles of light

[rnobleeddy]

Got a mono camera + filter wheel + filters and just about happy with it - except I appear to have introduced some weird reflection or stray light source that's bright enough to show up on the lights if they're stretched in just the right way. Fortunately(?) it's also present on the flats and so calibrates out to some extent, but does lead to noticeable residual noise in the S data which prevents the S data being pushed too strongly when processing.

I've got some time later so I'll try attacking the problem systematically, but wondering if anyone has seen something similar before? 

Kit is, from OTA on : 130PDS, Baader MPCC v2, varilock spacer, baader filters in a QHYCFW2-M-UltraSlim, QHY163M. Flats are taken with an old samsung table - has worked well in the past.

My hypothesis is that this must be caused by light (as the dark is clean), and is happening before the filter, because it appears to be present on all the filters, but is much stronger on Ha. It looks pretty central so I'm betting against dirt? I haven't necessarily got the CC spacing correctly yet but I don't expect that should cause this kind of issue?

 

Ha flat

O flat

S flat

Stretched single dark frame (300s)

 

Stretched single light (not sure if this will be easy to see - but the circle is there)

Stretched stacked/calibrated S data (the H data calibrate well, the O data somewhere in-between)

 

Edited January 16, 2021 by rnobleeddy

[david_taurus83]

How far from the sensor are the filters? Are they 1.25 mounted?

[rnobleeddy]

8 minutes ago, david_taurus83 said:

How far from the sensor are the filters? Are they 1.25 mounted?

Filters are 36mm unmounted.

It's 25mm from the sensor to the front of the EFW body - I'd guess the filters may be around 15mm or so. AFAIK the only control I have over this is by changing the way the camera connects to the EFW - it appears to come with 2 different adapters.

Edited January 16, 2021 by rnobleeddy

[rnobleeddy]

Despite finding a massive finger mark on the coma corrector, cleaning did nothing. 

I realized I can't easily remove the CC as I won't be able to refocus in the house.

However, I did discover I don't see the issue on luminance/colour flats.

Some additional screen grabs are below - looks like it's only a serious issue on Ha and S filters, but it's slightly offset for S. 

I've also attached the final processed image - it's my first attempt at narrowband so whilst I'm sure there's a lot to improve, I'm generally happy.

Perhaps I can just live with it calibrating it out?

 

 

Luminance

Red

 

Ha

 

O

 

 

S