My images have recently developed a strange artefact that I can't explain. I'm getting the vertical band down the middle of the Master Light from Pixinsight (60 x 180 sec, IR/UV cut filter, WO Zenithstar81 with matching field flattener, ZWO 294MC Pro camera). The following image is from one night, but I've processed 2 other nights on the same target and I'm getting the same effect.
Here is the master flat - the faintly darker area matches the artefact in the Master light:
Here is the Pixinsight high rejection map of the Master Light (the double area is because half the images in the Master were obtained after the meridian flip):
The next images are close ups of the affected area on individual subframes, nos. 1, 2, 5, 10 and 20 in the sequence of shots. The speckling is visibly decreasing so by about sub 20 it's not visible. When I watch each sub appear on the ASIAir after each exposure is completed, I can see that the artefact - which on screen looks like a muddy brown stain - decreases from sub to sub.
I've carefully checked all the optical surfaces and nothing untoward is visible. I'm convinced it's not the scope as when I rotate the optical train the artefact stays in the same spot. It also appears whatever filter, or blank spot, is chosen on the filter wheel.
I just don't understand what's causing this or its behaviour. It can't be light pollution as I saw the same thing a month or two ago when I was shooting from a different location. Nothing has changed in my setup, and a few weeks ago I was able to shoot a different target over 4 consecutive nights without a problem.
Any guidance and solutions would be appreciated.
Frank
Here is the master flat - the faintly darker area matches the artefact in the Master light:
Here is the Pixinsight high rejection map of the Master Light (the double area is because half the images in the Master were obtained after the meridian flip):
The next images are close ups of the affected area on individual subframes, nos. 1, 2, 5, 10 and 20 in the sequence of shots. The speckling is visibly decreasing so by about sub 20 it's not visible. When I watch each sub appear on the ASIAir after each exposure is completed, I can see that the artefact - which on screen looks like a muddy brown stain - decreases from sub to sub.
I've carefully checked all the optical surfaces and nothing untoward is visible. I'm convinced it's not the scope as when I rotate the optical train the artefact stays in the same spot. It also appears whatever filter, or blank spot, is chosen on the filter wheel.
I just don't understand what's causing this or its behaviour. It can't be light pollution as I saw the same thing a month or two ago when I was shooting from a different location. Nothing has changed in my setup, and a few weeks ago I was able to shoot a different target over 4 consecutive nights without a problem.
Any guidance and solutions would be appreciated.
Frank
