Will an oblong aperture opening affect image?

[ethirtym]

First off I am new to LF and this forum, so hello all! Now my question:

I bought a used 75mm schneider super angulon w/ copal 0 and received it in the mail today. I soon noticed that the aperture, when stopped down to F32 or F45, does not form a circular shape but more of a football shape. The opening is probably 1.3x, maybe 1.4x wider in one direction. At least one or two of the blades is a bit out of alignment. Otherwise the aperture blades move smoothly and by F22 or F16 the aperture looks to be round. So I'm wondering if this flaw would:
1. affect bokeh
2. affect flare shooting into the sun
3. create measurable distortion or
4. make the light falloff football shaped

The seller was not aware of this flaw and is willing to accept a return for refund. The lens otherwise seems to be an ok value so I'm soliciting your advice. The lens would be used in part for architectural interiors and I want to be able to use F45 to increase DOF (in spite of diffraction) and for long exposures.

Thanks!

[Archphoto]

You don't have to use f:45 for interiors, I have been using a 75mm SA for 20 odd years at f:22 and had allway's good results.
Make one or two shots at f:22 and give it a close look, if you like the results, keep it.
Sometimes this "football" shape happens, the problem is with the shutter, it was never designed to be realy used at f:45.
The only time you might need f:45 is with a studio flash if you have too much light and can not turn the power-ouput of the flash down.

It will affect your bokeh a tad, but it will not make your light falloff any diferent.

Peter

[Eric Woodbury]

Similar to a cat's eye. It will give you slightly more depth of field in the short axis than the long. More diffraction in the short than the long, etc. Probably not noticeable.

[Gem Singer]

If the shutter doesn't allow the aperture to remain as a round shape all the way to f64, there is defect somewhere in the aperture blade mechanism. It probably can be repaired by a skilled tech.

I would return the lens to the seller, or perhaps he/she would be willing to negotiate the price to cover the cost of the repair.

The defect probably will not noticeably affect the image quality, but it will affect the resale value of the lens.

[ethirtym]

Thanks for the quick responses. I'm still putting together my system and don't have a camera yet to test the lens. Your thoughts on the probable effects all make sense to me and will help me make a decision. Elsewhere it seems that most recommend entirely avoiding F45 for 4x5. Please keep the comments coming if you have any additional thoughts.

[Gem Singer]

More than likely the aperture opening is also oblong shape at wider apertures, but it's not that noticeable.

However, it probably will be noticeable on the out of focus areas of an enlarged print.

[GPS]

If the f32 and f45 aperture is up to 1.4x wider on two sides of the diameter then the physical aperture does not correspond to the correct f number and can influence your exposure values.

[Chuck Pere]

I'd return it. Why start off with a possible lens problem? Lot's of good working lenses out there. One less thing to consider when you are troubleshooting the weird problems that always happen when you are starting out.

[Bob Salomon]

Beyond f16 you will degrade the image due to diffraction. At f32 and beyond you are well into diffraction.

[JOSEPH ANDERSON]

I Had The Same Problem With A Longer Lens. As Time Went On It Got Worse.
The Same Could Happen To Your Shutter. I'm Not Saying It Will But It Could.
Perhaps You Should Return It.
Good Luck Joe A

[cowanw]

Similar to a cat's eye. It will give you slightly more depth of field in the short axis than the long. More diffraction in the short than the long, etc. Probably not noticeable.

This caught my eye.
If a point is less in focus because it is on a long axis of another point, is it not on a short axis of its own. And isn't the first point short axis point on the long axis of another point? And so on and so on.
I am not sure DOF has to do with aperture shape.
But then the older I get, the less sure I get of anything.
Regards
Bill

[ethirtym]

What a range of responses! I should add that the aperture is never 100% regular shaped, even opened up, but the irregularity becomes much less noticeable. I agree that there would be a certain inaccuracy in exposure, mostly when stopped down.

I am going to try to test the lens today. I am guessing any bokeh will be in the abnormal shape when stopped down. I am thinking I'll take some exposures at more normal f8 thru f22 settings and then a couple at f32 and f45.

If it doesn't work out I guess I'll be looking for another; I'll have to wait to get upgraded to the For Sale section here... Any ideas on a good/fair price for a used but modern 75mm SA in EX condition? I might even get a vintage one if I can find a nice example.

[GPS]

What a range of responses! I should add that the aperture is never 100% regular shaped, even opened up, but the irregularity becomes much less noticeable. I agree that there would be a certain inaccuracy in exposure, mostly when stopped down.

....

The aperture is normally 100% regular. Pentagons, sexagons, oktagons etc. are all "regular shaped"...;) Good luck in your looking for a normally functioning lens!

[ethirtym]

Right - I was just concerned with the irregular shaped example that I currently possess! :)


The aperture is normally 100% regular. Pentagons, sexagons, oktagons etc. are all "regular shaped"...;) Good luck in your looking for a normally functioning lens!