Quote:
Originally Posted by JA
Hi Adam,
Depending on which flavour of Skywatcher ED 80mm you are using: "Espirit 80ED", Blackdiamond ED80 / "80 EVOSTAR ED" it may have an image circle that doesn't support full-frame sensors like your Canon 5D. The specs for the Espirit 80ED say that it has a 33mm image circle, well short of the minimum 43.3mm image circle required for full frame. The other 80ED models I mentioned, I checked their specs and they do not specify the image circle size, BUT they do say that they work well with APSc sized sensors and don't mention full-frame, so I suspect they too may also fall short of the 43mm required for full frame. It's not entirely clear in their specs. It's something to consider as a reducer will only make it worse (use even less of the full-frame sensor) and a flattener may well be a moot point if the sensor diagonal isn't filled and you are seeing the extreme edges of the (say 33mm) image field and all the aberrations and light fall off associated with the extremes. It might be OK to have a 33mm or so image circle on an APSc sized sensor (28.3mm diagonal), but not OK on a Full-frame sized sensor (43.3mm diagonal), unless of course you are prepared to crop out heavily as you will see the edge aberrations and see extreme vignetting.
I can't be certain which model ED80 (which?) you have of those listed, but it would pay to know its image circle diameter from specs (or measurement) in consideration of its use with a full-frame camera. I believe that is the central issue you should consider in deciding what you'd like to do next.
Best
JA
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Hi JA
Good point! I've got the EVOSTAR 80ED. I can't find any specs on the image circle, how do I measure it manually?
Thanks for raising this issue!
Adam