Bad vignetting in spite of using flats

[headdown]

Hello did,

The red arc is still a mystery to me though.  Any LP from the RV would have been very diffuse, and in no way bright enough to cause a lens flare.  When I stretch the image to extremes I can see that there is a second, fainter red arch that mimics the one that is visible here.  What I find puzzling is that the arch looks the color of hydrogen.  Do lens flares come in that flavor?  I have never seen a lens flare that color, or that "soft" looking.  But then again, my experience with lens flare is very limited.  If there is someone more knowledgeable than I about lens flare that could enlighten me on this it would be appreciated.  Is a double soft red arc that is shaped like a double rainbow possible or common with a lens flare?  The other mystery is, there is no bright star just our of the frame.  So if it is a lens flare, what is causing it?  And if it is not a lens flare, what is it? 

Dean

[dld]

Hello Dean and sorry for the late reply,

I only use unmodified dslr cameras and lenses so I don't have experience with spacers, flatteners or filters/filterwheels which as far as I can understand, they may introduce internal reflections. The red arcs may be due to the lights of a passing car or any red light/led which accidentally was in the vicinity of the telescope aperture.

[headdown]

Hi did,

I am late with my reply too, so no problem. 

And I use a Hutech modded Canon 6D, and the only thing in the optical train is my OAG.  This system hasn't changed in a while, so I doubt if these red arcs are related to any kind of internal reflections, or I should have seen them before.  They couldn't be car lights because I was out in the desert with no traffic.  And that might affect a frame of two if it happened, but would have shown up in Blink. 
And the lower left corner of the frame where the red arcs appear is not any brighter than the rest, as it would likely be if there was a bright light or star just out of the frame causing a lens flare of some sort.  There is a star in that direction, but it is more than a full 6D frame width away.  See attached.

Dean

[GregW]

Occam's razor at work

[dld]

Hello again,

please take a look at the following thread:

https://pixinsight.com/forum/index.php?topic=13226

for a discussion on similar nuisances.