topic SEL50F18 aperture is not round? in Alpha & NEX interchangeable lens cameras

SEL50F18 aperture is not round?

blaz07 — Thu, 22 Mar 2018 09:35:01 GMT

Hello,

I have question for sony fast lens users, is my aperture normal (not perfect 'rounded')?

This is at F11, but noticed at F9 - F22. Lens is Sony 50mm F1.8.

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IamNic — Thu, 22 Mar 2018 21:23:06 GMT

Hi @blaz07,

that is completly normal.

Less expensive lenses have less blades (usually 5) and more expensive lenses have more blades (usually 9).

The more iris blades the mechanical iris consists of, the more round the hole is when you close it.

- Nic

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blaz07 — Fri, 23 Mar 2018 15:29:34 GMT

Hi, I know what you mean. My aperture have 7 blades, and 'rounded' with 7 blades is for me what you see on left picture. My aperture is like what you see on right picture - all 7 blades are not alligned in circle. Is this normal?

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IamNic — Fri, 23 Mar 2018 17:37:05 GMT

Hi @blaz07,

I can't quite see any misalignement on the first image.

Could you please shoot an image of a single lightsource and adjust the focus so the bokeh-shape shows up on the image?

- Nic

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blaz07 — Sat, 24 Mar 2018 19:35:58 GMT

What do you think? This kind of misalignment is affect photo quality or just bokeh quality? Thank you for help.

PS: it is not a big misalignment, but is noticable when you look into lens. If anyone have this lens, could you look into the lens and close aperture between cca F9 - F18. Anyone notice the same? If it is normal, then ok. This is my first prime fast lens with F1.8 and i don't know what is accaptable error.

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IamNic — Sun, 25 Mar 2018 11:12:18 GMT

Hi @blaz07,

sorry again, yet I am not seing a misalignement - at least not as extreme as you illustrated it with your graphic.

To me the Bokeh shape looks (near) perfect, so unless there are any effects visible on the images which indicate a defect of the lens, I would say it is good to go.

- Nic

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blaz07 — Mon, 26 Mar 2018 14:45:18 GMT

It's really not extreme, of course. But if you look precisely, it is visbible.

Ok, if you think this is normal, then OK. I will pay attention on other new fast lenses in shops, I'm just curious

Thank you for help.

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TLysholm — Sun, 01 Apr 2018 13:22:11 GMT

I think you're just missing the fact that yours is not hexagonal but heptagonal, and not a skewed hexagonal as you're implying it looks like. (Your drawing is also wrong, showing two hexagonals while you're talking about 7 aperture blades.) That's why it doesn't look like the image you're using for reference. That has 6 aperture blades and yours has 7. Actually making the bokeh balls more round than those produced by the 6 aperture blades.

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blaz07 — Mon, 02 Apr 2018 08:16:19 GMT

Yes I know that my aperture has 7 blades and it is not possible to be rounded. I know that 7 blades are better than 6, 9 is better then 8. I just illustrated what I see in my aperture (sorry for picture with 6 blades, I did not pay attention to that). I mean alligned in round shape, not round hole.

I mean not perfect round in way, if you look lenght of each side, I will try to illustrate on next picture.

Must be a=b=c=d=e=f=g?

If you draw a circle over the blades, you will get ellipse.

It is not matter how many blades you have, 6, 7, 9, if you draw a cirle over the hole, you must get a perfect circle. This is what i mean. If some missalligment is normal, okay, so my aperture is perfect and normal. I'm just asking because this is my first fast lens with so big apperture Iand I noticed that

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TLysholm — Mon, 02 Apr 2018 08:36:16 GMT

Ahh, yes I see what you mean. But you gotta take the picture straight on (perpendicular) not to get a skewed view. It's geometry, and you can't distort the perspective and expect any degree of accuracy. You're looking through a lens element(!) so you have to be straight on. I'm not saying that it's not misaligned at all, but looking at it from an angle through a lens is prone to distort what you see. Look at that last image again and note how what should be a circular edge to the entire iris (all the aperture blades) has an oval shape. (Not including the shadow cast. You can see the edge of the iris taking an oval shape even just in the lit area.

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blaz07 — Mon, 09 Apr 2018 19:25:16 GMT

Yes, picture is from an angle, but no matter from what angle I look into lens, the same side (blade) is longer (of course distortion must be taken into account).

Last week I check some new lenses in photo store and also other lenses have that kind of missaligment. Even expensive Zeiss F1.8. I think this is normal on fast big apertures.

If you have that kind of lens, look closely and pay attention at small aperture values (F11, F16, F22).

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TLysholm — Tue, 10 Apr 2018 23:41:13 GMT

I think it's perfectly normal. I have six lenses here right now, vintage and modern (Yashica, Sigma, Sony including the FE50/f1.8), and none of them are 100% perfectly aligned. So don't sweat it. I'm sure it's all fine. I haven't noticed anything irregular in my photos. Even now that I know, I don't see it in the bokeh stopped down. Maybe very high end lenses have perfectly aligned blades ..? I don't know.

Maybe what you can take away from this is that now you know, and you know there's a sort of acceptable margin. Maybe they simply have to make the blades a little bit "loose" like that. After all the blades have to work for many years and open and close a million times. Having a tight and snug fit would maybe wear them quickly. I dunno, I'm just riffin' here ... but as long as they keep working and I can't tell in my photos, I'm fine.

Anyways, know I've checked.

EDIT: I just grabbed this screenshot from a video review of the Sigma 50mm/1.4 Art lens. Same thing.

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blaz07 — Wed, 11 Apr 2018 14:54:57 GMT

Yes, this is normal. Maybe is for some reason (for long time working), maybe because is difficult to allign this small parts. Great, now we all know something new bokeh is great, and the lens (Sony SEL50F18) is just perfect, have very sharp images and I love it. If I compare kit lens vs this prime lens..it is almost unbeliaveble difference

Thank you for all answers.