[stoppingdown]

Yesterday I tested my SEL1670Z against the full sun of the middle of the day (more or less). It's not a typical kind of shot I take   but as I noted problems even when shooting the sun near the sunset (more typical kind of shot), I wanted to study better the phenomenon.

 

In short, the sun looks as the worst problem of this lens: you can play around with various focals and apertures, and some heavy artefacts (typically green blobs) are always here. In the worst cases they are huge and ruin the photo. In just a few cases I managed to make them small as in the picture, and in this form they could be easily fixed in pp. 

 

What puzzles me is the diagonal upper-left -> lower-right bright streak around the sun. I mean, I know that sun produces streaks with many lenses and it's normal. But so far I've seen more regularly distributed streaks (some even pleasing), not a fixed one, always at the same angle, wherever the sun in the frame is (other artefacts, such as green blobs, move around).

 

In my optics ignorance, I'm curious about what is the cause of such an artefact and why it is always in the same position; I would have said that moving the sun around the lens it should have rotated and even got to be in a specular layout.

 

Thanks.

[Brightcolours]

The sun "star" "rays" are caused by corners in the aperture shape. Your aperture will have uneven aperture blade shapes, causing one corner to produce a longer, more "focussed" sun star ray in both directions. Probably when you change the size of the aperture, you will see that stronger "ray" rotate, as the aperture rotates.

[stoppingdown]

It doesn't, that's why I'm curious. The previous image was shot at f/4, but the angle didn't change at f/5.6, f/6.3 and f/8. Only the strength of the streak and the extension changed.

I've added a second attachment shot at f/8.

[Brightcolours]

Then the aperture shape does not turn while going through that aperture range. Lens dependent, how the shape "moves".

[stoppingdown]

Thanks. Further questions... Is it a thing that can be commonly found in lenses? Do you think it is because of a precise design of the blades (maybe because it makes something simpler) and they just didn't think of this consequence? Could be it defined a design defect in some way?

[stoppingdown]

Sorry, another question, stepping back: but at full aperture, shouldn't the blades fully retract so the resulting diaphragm is perfectly round?

[Brightcolours]

I don't know if a not perfectly aligned aperture blade shape is a production defect, I guess if it is by design it is a sloppy aperture design. About the blades retracting not fully, is that through the whole focal range? I have seen at least two lenses of which the edges of the blades were still visible when at max. aperture, but I do not know if it is normal for your lens type.

http://www.slrclub.com/bbs/vx2.php?id=sl...asc&no=360

All images I see from the lens appear to have a closed aperture, I guess Sony E lenses close down when not mounted.