takumar disappointment

[alacant]

Hi everyone. After good experiences with my 135 and 200 takumars I was let down by this 28mm. This is a corner enlargement from at f5.6. Maybe I just got a bad one? Any ideas? Must I close the aperture more I wonder? TIA and clear skies.

[happy-kat]

Are all four corners the same

[Knight of Clear Skies]

That doesn't look great, have you tried the thirds focusing technique?

[alacant]

Hi. It's worse in the corner I posted. Here's a light frame:

https://drive.google.com/open?id=0B_uUt0LyuuEdR2ZoS1RlV3VqdzQ

 

[alacant]

I don't think it's focus as the stars toward the centre of the field are circular. But yes, I had the moon and later vega half way to the edge on a diagonal sort of thing in APT zoom before I recomposed. Not easy to focus a 28mm I'm finding. Infinity is just before I hit the hard stop, with a tiny turn back out again [1]. I'll try again whilst I still have the moon as a bahtinov doesn't work. Thanks for the heads up.

[1] Better this than my 135 which was the other side. I had to dismantle and turn the focus ring to get beyond the stop.

[alacant]

Hi everyone. It seems that the canon to takumar lenses should have the adaptor without the flange which compresses the auto-pin. The confirmation came in this article. You can see light between the adaptor and the  [**edit] camera lens body on the diameter where the pin is located  -lucky I didn't over-tighten I suppose. So, either I file a mm or so off the pin, a notch in the adaptor or wait for the flange-less version to arrive. HTH.