Banding when imaging from one filter position in ZWO EFW

[Mark Jo]

I have been imaging with a ZWO EAF and not had any issues until a few weeks ago added a new filter and also removed the existing hydrogen filter to remove some dust. 

After refitting the Hydrogen filter there was a band across the image as if there was cloud in the image, (there were no clouds).

removed filter and refitted same as before.

Contacted Astronomik to see if there was problem with the filter - they advised that appeared may not be fitted correctly.

after moving filters to different positions can confirm is not issue with the filter but appear to happen with all in the 2nd position in wheel, the orientation of band is always the same and I am unable to see any problems with how the filter is fitted after multiple attempts.

I have included some images  as example

[jacko61]

Maybe light leaking into the filter wheel?

Graeme

[wimvb]

I agree, either light leak or a reflection. Take an image withe the lens cap / telescope cover lock on and take a few images. One image with the suspected slot and one each with the two neughbouring slots. Do you have a manual or an electronic filter wheel?

[Mark Jo]

it is a ZWO electronic  7 position 36 mm filter wheel and the filters Astronomik 36mm unthreaded.

I have tested again covering the telescope objective and could see light in the position 2 but also the 1st and third positions.

I removed the camera from the telescope capped the the nose piece and covered filter wheel with heavy cloth and the stray light disappeared.

have taken everything apart and reassembled but the only thing that appears to make any difference is putting duct tape around the join of the filter wheel and spacer for back focus. There was no problem with this before so not sure what changed.

any spacers came with the filter wheel or camera.

is there any  better solution than tape?

 

[wimvb]

Efw's should be light tight, unlike manual wheels which have an openi g to turn the wheel. I find it strange that th leak is external (spacer) yet only affects a few positions. I would expect an external leak to affect all filter positions. So, you need to find out what is special about position 2. Have you ever dropped or bumped the fw, causing something to bend or go out of alignment? Are ther any reflecting spots (paint worn off?) near position 2?

I would probably disassemble the optical train and inspect each part. What you also can do is put the camera in streaming mode, and look at the stream while changing filter positions. If you do the streaming in a dark room, you can move a dimmed light around the setup to find the exact location of the leak. Third, you can replace the spacer (never mind which length you replace it with, this is only for testing) and check if it is the spacer that is the culprit. Although, I doubt it will be because, as I wrote, this should affect all filter positions.

Does duct tape completely remove the light leak, or just make it less obvious? You could try black electrical tape, which may keep more light out. Of course it's always better to fix the cause of the problem.