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| I have uneven vignetting on my 130D and always assumed it was normal for this scope. It seems to calibrate out but maybe I have a bad eye for imperfections. What does the calibrated frame look like? |
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I've messed around a lot with various positions in the last few months so it's hard to find a good example (plus I mercilessly delete old data). A current configuration looked a lot like this after calibration: The overall gradient is probably from LP. You can see the incorrected edge on the right which I drew on to highlight. This didn't start happening until I switched to a mono camera, so I assume there's some constriction occurring somewhere from the M54 to M42 adapters.  |
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| Ok. Yeah I don’t get a pattern like that on my frames. Maybe the M42 connections are the culprit? I briefly used an M42-threaded FW with my 130D and had myriad problems that I never quite nailed down, but they all went away once I made everything M48 or M54. I’ve just assumed since then that M42 and T2 does not jive with the Epsilon scopes. |
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| What's curious is that I can push the sensor away from the hard vignetting section using the octopi and it looks fine - but then I'm contending with bad stars on that side which never seem to go away. |
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| If you can't correct it with the right flat master then it is a light leak. |
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What's curious is that I can push the sensor away from the hard vignetting section using the octopi and it looks fine - but then I'm contending with bad stars on that side which never seem to go away. You can ONLY center your chip using vignetting as a guide if the vignetting is centered within your optical axis. In your case it is not, so when you move the chip to even out the vignetting you are introducing field curvature on one side of your frame. If you want to center your chip for the scope, which will give you symmetry with field curvature even though vignetting is not even... remove everything from your inage train and only have the octopi and camera installed. Take a flat frame and center the chip using vignetting as a guide. Then reassemble and don't touch those centering screws. Your asymmetric vignetting is caused by something else. Either a poorly machined adapter or most likely, your filters are not centering well. Regarding the problem with flats not correcting perfectly, you may have an adapter that is a little shiny on the inside. Take off your image train (leave the corrector on the scope) with the red filter in front of the chip. Hold it at an angle and look into the image train. If you see any blue reflecting off of the edge of an adapter this is a problem. You need to flock or replace the adapter with something that is not shiny. Flats will not correct for these kinds of internal reflections. |
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Unfortunately my octopi only has an interface for attaching to a filter wheel; doing tests that are just coma corrector - octopi - camera aren't possible. The Asymmetrical vignetting I thought was a filter issue - when I switched to a mono camera I to deal with poor, intermediate filter centering but that's been fixed. Something I haven't explicitly tested is seeing if increasing the space between the filter wheel and camera via the octopi makes it worse - not that I could fix it without purchasing different equipment. The flat correction and the asymmetrical vignetting are connected, the corner with the mechanical (Optical??) vignetting is the corner that doesn't have the good correction. |
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Unfortunately my octopi only has an interface for attaching to a filter wheel; doing tests that are just coma corrector - octopi - camera aren't possible. You could remove your filter carousel and shoot through the filter wheel too. I doubt the filter wheel housing opening is decentered. |
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1.51
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I realized I had empty filter wheel spot I could test in the wheel and shot a quick skyflat through one of those. You can see the decrease in hard vignetting on the right on the empty spot vs a Lum filter on the left. I also measured the filter depth and came up with about 8.5mm and measured the clear aperture of the ZWO filter wheel to be about 34mm; Adding in the 17.5mm focal flange of the risingcam 571 + another .3 for the octopu and you get a amount that the filter suitabilty guide says needs more than 34mm of clear aperture. so I guess buyer beware for this combination. |
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2.71
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I get uneven vignetting with the 130D with or without a filter wheel. Even when I used the 268C with the filter screwed directly in front of the sensor, I got the same vignetting pattern I get now. Mine looks similar to yours but the darker side is on the right of the image rather than the left. This is a flat I just took with the 2600MC, filter mounted in a ZWO filter drawer with M54 spacers and gender changer.  Flats taken through my 268M and CFW3L with 2" filters have the same pattern as above. The ones from my 268C looked a little different but still clearly had the right side darker. The only thing in common between all three setups is the M54 gender changer. Oh and I don’t really have any major issues with field distortion as long as I keep my spacing right and avoid creating any obvious sources of tilt (like pairing the very heavy CFW3L with the Blue Fireball rotator). |
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| The uneven vignetting is due to the secondary dot not being perfectly positioned. I'm referring to the change in intensity in the right corners - the top right and bottom right basically have a "faster" vignetting and I suspect it is in fact due to the focal flange distance of the risingcam 571 and the smaller clear aperture of the 36mm filters when using the filter masks/filters. |
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| Ah, ok. I should have read your post more carefully. |
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| whoops that was dumb |
