Filter vignetting

[jiberjaber]

Help! What have I done wrong to get vignetting this bad? I've double checked that the filters are as close to the camera as can be, camera is asi16000, filters are ZWO unmounted 31mm... (since the photo of the EFW, I've flipped a few of the filters to the right direction so the a/r coating is in the right place) - vignetting wasn't this bad when it was just the DSLR and the flattener.

Any pointers welcome please!

[symmetal]

I originally used the original Zwo 31mm unmounted filters in the EFW Mini filter wheel with the ASI1600 and had to use masks over the filter edges to avoid excessive reflections. This made the filters only slightly larger than the 1.25" mounted so in the end swapped them out for Baader 1.25" filters. There is no noticeable difference in vignetting between the two types and in both cases is only slight.

Your images look highly stretched and black crushed so it's hard to say what they are really like. Do you have an unstretched example from the 1600 to post?

Alan

[vlaiv]

That might not be bad as it looks - it really depends on how much you stretch it. Can you post single fits for one filter for inspection so we can see actual values in that flat?

For example:

These two are the same master flat - but stretched differently - in fact, light loss is only about 20% at extreme corners.

[tomato]

I agree, but if they have been stretched a lot wouldn’t the dust motes be more visible? Unless of course, your imaging train is dust free?

[jiberjaber]

4 hours ago, vlaiv said:

That might not be bad as it looks - it really depends on how much you stretch it. Can you post single fits for one filter for inspection so we can see actual values in that flat?

For example:

These two are the same master flat - but stretched differently - in fact, light loss is only about 20% at extreme corners.

Hopefully this will work, some are masters, others not as I haven't built them yet

masterFlat-BINNING_1-FILTER_Luminance.fit masterFlat-BINNING_1-FILTER_Red.fit masterFlat-BINNING_1-FILTER_Blue.fit masterFlat-BINNING_1-FILTER_Green.fit masterFlat-BINNING_1-FILTER_H_Alpha.fit Flat_NoFilter_0.242_secs_2020-05-28T16-52-54_001.fits Flat_OIII_0.879_secs_2020-05-28T17-05-10_001.fits Flat_SII_0.750_secs_2020-05-28T17-04-50_001.fits

[vlaiv]

Yes, of course

I just downloaded the first one - it has about 86.5% light level due to vignetting in the corners - so 15% light loss, not that much at all.

[jiberjaber]

Thanks - I guess I was expecting less as I think I had less with the DSLR and going for the larger filters, from what I read, would have no effect on the vignetting.