First results with Pentax SMC K 135mm f2.5

Started Jul 23, 2013 | Discussions thread
OP kitsios_spyros Senior Member • Posts: 2,580
Re: First results with Pentax SMC K 135mm f2.5

Thank you for you response to the aperture issue. I would not post about this today, but since you ask, I'll try to describe it. Sorry that I use other's photos.

Closing the aperture blades the shape is like in the picture of this review of the SMC Takumar M42 variant

4th photo

so, neither a cyrcle nor an octagone with clear angles. Look at the point where one aperture touches the next one, if it is not clear from my decription. This shape is from f4 to f8, if i remember correctly, and is actually better defined as an octagone as I open the aperture from closed to wide open.

So this might be normal for this lens design. Please verify.

What puzzles me is that the aperture at the two or three last f stops is not normal. It is a little stretched. If i try to normalize the octagone I will get an egg shape that a round one. I have not tested the last f stops yet but specular highlights look ok from f2.5 to f8, but maybe not perfect, just a little stretched. Sorry but I don't have samples with me.

I'll try Miles Green's tip to see I the lens needs some work out. But I feel like I should have been informed by the seller about this. It seems like a problem than a characteristic of the lens design. Any thoughts?

I'll post samples as soon as I can.

Kind Regards,


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