75MM Takumar Corner Sharpness

nightfly · 10-29-2009, 07:13 PM

I recently acquired a 75mm f/4.5 SMC Takumar and have been shooting with it for about a month. I noticed that the corners were a little soft and that stopping down does not help much. Is this normal or do I have a bad copy? I hear it is one of the sharpest. Indeed it is very sharp other than the extreme corners.

Any feedback is appreciated.

This is a 100% crop of a Provia 100F transparency (corner only) scanned at 1200PPI. The lens was stopped down to f/11

*Wheatfield* · 10-29-2009, 09:37 PM

Yup, it's a little soft in the corners and it can be made to flare most gloriously.
Learn to frame a little loose with it and avoid having the sun in front of the lens and you'll be fine

nightfly · 10-30-2009, 04:56 AM

Originally Posted by Wheatfield

Yup, it's a little soft in the corners and it can be made to flare most gloriously.
Learn to frame a little loose with it and avoid having the sun in front of the lens and you'll be fine

Thanks, the lens is a beauty and works great other than the extreme corner sharpness which I thought would improve with smaller apertures. The lens review database had two reviews and mentioned nothing of this effect.

Thanks again.

tuco · 10-30-2009, 11:12 AM

A little soft? That is hugely soft in the RH corner. Now is that a focus issue? I'd think you should shoot a brick wall on a tripod with mirror lockup and have a look.

nightfly · 10-30-2009, 12:46 PM

Originally Posted by tuco

A little soft? That is hugely soft in the RH corner. Now is that a focus issue? I'd think you should shoot a brick wall on a tripod with mirror lockup and have a look.

All four corners exhibit the same softness. The center to just before the corners is perfectly sharp. I usue this lens for astrophotography, the ultimate test for sharpness and focus. The same results. Stars are sharp, except for the extreme corners.

Example: 75mm - 45 minute exposure, f/5.6 Centuria Pro 400

tuco · 10-30-2009, 01:36 PM

Gee, I guess if you are use to looking at the cosmos you'd spot a soft conner. But it all looks the same to me.

nightfly · 10-30-2009, 04:03 PM

The lens aberrations are less at infinity, lucky me

tuco · 10-30-2009, 04:31 PM

Oh, you missed a dust spec in the upper, RH area. ;-)

nightfly · 10-30-2009, 04:57 PM

I was going to post a close up of a corner on this shot, but Centuria is pretty grainy stuff. It's hard to see the softness or the dust specs

desertscape · 10-30-2009, 05:53 PM

I use this lens mostly between f/8 and f/22. It is possibly the sharpest lens in the P67 line up, especially at f/11. Have never seen any softness but then again, I don't use it wide open.

nightfly · 10-30-2009, 08:13 PM

Originally Posted by desertscape

I use this lens mostly between f/8 and f/22. It is possibly the sharpest lens in the P67 line up, especially at f/11. Have never seen any softness but then again, I don't use it wide open.

I agree it is very sharp and I'm liking it very much. The softness is ONLY in the last 2mm of the film corners. My original post showed the corner softness at f/11. It seems I have this at every f/stop. I figured it would get better by f/8. I may pick up another copy to see what's going on.

Thank you all for replying.

desertscape · 10-31-2009, 11:42 AM

You say it has this softness at every f-stop in the corners. Of the seven aberrations, only lateral chromatic and distortion are not affected by the diaphragm . Your softness does not seem to be either of those. So edge softness should be reduced when stopping down. What is going on with your 75mm is odd. Curvature of field(an aberration) is not flattened by the diaphragm but is masked by the increased depth of focus when stopping down and has the appearance of being reduced. So your corner softness is not from curvature of field.

nightfly · 10-31-2009, 05:08 PM

Originally Posted by desertscape

You say it has this softness at every f-stop in the corners. Of the seven aberrations, only lateral chromatic and distortion are not affected by the diaphragm . Your softness does not seem to be either of those. So edge softness should be reduced when stopping down. What is going on with your 75mm is odd. Curvature of field(an aberration) is not flattened by the diaphragm but is masked by the increased depth of focus when stopping down and has the appearance of being reduced. So your corner softness is not from curvature of field.

The problem does appear worse when the corner features foreground landscape. It might be that the corners themselves, featuring closer objects are simply not in focus. Indeed the problem is still apparent, but much less so when the corners feature objects at infinity. I will play around with close focus with objects at a uniform distance, like a brick wall. Thanks much for the great information.

Oh yea, I have the 35mm f/3.5 SMC Takumar for my spotmatic, it's basically the same lens design and I have never noted this effect.