SEL50F18 aperture is not round?

[blaz07]

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.

[IamNic]

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

[blaz07]

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?

[IamNic]

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

[blaz07]

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.

[IamNic · Accepted solution]

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

[blaz07]

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.

[TLysholm]

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.

[blaz07]

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

[TLysholm]

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.