I just got my C8-A in with the Celestron
My image train currently is a WOAs for the vignetting, that's pretty common. A reducer can only produce an illuminated spot that is equal to the clear aperture of the reducer multiplied by it's reduction factor. So for the .63 reduction, and the 41mm aperture of the reducer, that results in a spot 25.83mm in size. That's a tad smaller than an APS-C sensor. So there will be vignetting for any sensor with a diagonal measurement that's close to 25.83mm.
So here're my questions.
Do I need 55mm, 85mm or 105mm? With extension tubes I already have on hand, I can add up to another 52.5mm. That would take it to about 100mm total so I would need another 5mm
I also read that bringing the camera closer to the reducer decreases the reduction factor. Based on what I read above, that would be beneficial by creating a larger image circle. I would need to move inward until the reduction factor is .67. to cover the T2i 's sensor? Does decreasing the distance from the sensor to the camera actually reduce the reduction multiplier? My brain says yes as I visualize the camera moving inward in the light path, however, my brain has been known to be wrong. I'm more than willing to experiment with shooting different back focus lengths, experimenting is half the fun, if that is even a possibility.
As always, thanks for any input, good, bad or indifferent!
Clear Skies,
Chris