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Old 13-03-2012, 07:34 AM
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Phil Hart
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Phil Hart is offline
Join Date: Jan 2007
Location: Mount Glasgow (central Vic)
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Originally Posted by Martin Pugh View Post
Hi everyone
I posted the full FITS because I assumed that if people wanted to assess the image, an uncompressed image is the way to go, rather than a JPG.

Anyway - I guess the point I am making here, is that I dont believe I would get dissimilar results with the $380 85mm lens I first bought, and that I did not expect to go these lengths with a $1600 L lens. My next trial will be just that - I will take an image with the 85mm lens, stopped down appropriately, and compare those results. Really, at this stage, I think the differences will be negligble. We shall see.

The other point I was making is that I seem to have got fairly good stars across the field at f4.5 with the ST8300, so I expected similar results by using the lens at f4.5 on the 550D. This was not the case.

Tilt? Even if it is in the ST8300 - Cant do anything about that. I tried to measure with a caliper the depth of the SBIG Canon lens adapter, and was fairly satisfied that the measurements were very close. I am not ruling the adapter out though.

One question I have though - if I gently rock the lens, I can hear the lens elements moving about slightly - is this normal?

hi Martin

85mm is a little less demanding than 50mm, but broadly I would say you are right.. any high quality prime lens at f4.5 should be delivering pretty good results.

I'm with bojan.. this result is pretty impressive though. I wouldn't be able to beat that image quality at 100% scale with any combination i've used either. I'd say my 50mm f1.4 lens might be a close match but i can't use it with my mono sensor (and i know there's tilt in mine which would kill it).

Not entirely unusual to feel a small amount of movement in the lens (but it shouldn't rattle when you shake it ). Hard to say whether it is a problem or not from here.. i've got some lenses that have that slightly loose feeling but no issue as far as i can tell.

Can you send us a sample from the 550D.. f4.5 and maybe even something wider if you have it. Full res JPG more than sufficient for judging image/optical quality in this case. Perhaps a different story if you were trying to gauge noise peformance etc.

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