Comparing Fish-Eyes : Rokinon 7.5mm vs Zuiko 8mm (FOV and look)

Started Jan 25, 2013 | Discussions thread
micksh6
micksh6 Senior Member • Posts: 2,613
Re: Rokinon infinity focus?

Anders W wrote:

micksh6 wrote:

Anders W wrote:

micksh6 wrote:

Anders W wrote:

micksh6 wrote:

Anders W wrote:

James Pilcher wrote:

I read early-on that the Rokinon, despite being a manual focus lens, does not stop at infinity focus; it goes a bit further. The implication is that you must actively focus on infinity instead of employing the useful MF technique of just turning the focus ring toward infinity until it stops.

Is this true? Comments?

Yes, it is true. See here. On the other hand, for reasons explained in that post, I have no difficulties setting infinity focus expediently anyway.

Yes, it goes a bit beyond infinity. And, the amount may vary from body to body. What's worse is I think distance scale shifts a bit over time.

I got Rokinon version last spring and I used it on E-P3 and E-PM1. Focus could go past infinity but it was less than 1mm on distance scale. It was noticeable at F3.5 aperture, but not at F5.6 (sharpest aperture of this lens). Since I mostly used F5.6 outdoors when I needed infinity I didn't bother to adjust focus.

But, for indoor use I scratched a mark on distance scale with a knife; the mark corresponded to 1 meter focus distance. That worked fine for months.
Now I noticed that the focus shifted on E-P3 by about 1mm - I have to focus closer to 0.25mm mark if I want to focus at 1 meter. Infinity is closer by almost 2mm now and F5.6 aperture doesn't make infinity sharp.

That's on old E-P3 that I had since its introduction. On newer body, E-PL5, the marks are closer to real focus distances, but also a little bit off from what they were months ago. And I don't think lens mount on E-P3 has worn out. First, there aren't major signs of wear. Second, I have MD to m4/3 adapter that didn't allow my Minolta 50mm F1.4 to focus to infinity by very small margin 1.5 year ago. It still doesn't allow infinity by about the same margin. So, I think, the body is the same but focus scale shifted a bit after 9 months.

Bottom line - test Samyang fisheye with your bodies periodically.

Sounds weird. Never heard of a lens that did that without being exposed to external physical damage. Do you know of any other example than this one and/or do you have an idea of what might be going on?

No. It could be my mistake, of course. AFAIK the lens wasn't hit, but I have a small son who could access the lens, so, who knows. The lens is fine, I just need to keep in mind new distance scale.

Anyway, it's one thing to check for manual lens.

It seems unlikely that the lens would have suffered any damage from rough handling that a) wasn't visible on the outside and b) didn't manifest itself optically in other ways than a change of ininfity focus. One thought that came to mind after I posted is that the external focus ring might have slipped slightly compared to some inner ring that is actually adjusting the focus. But if so, the infinity mark on the focus ring should be located differently compared to the white reference dot than was originally the case. On my copy the infinity mark is located as shown on this image

http://www.estiasis.com/totalid/lens/samyang/75mm-f35-umc-fisheye-lens-mft

when I hit the hard stop (i.e., slightly to the left of the middle of the white dot).

From what I see on this picture, on my lens I can rotate top focusing ring slightly to the left from what is shown to hit a hard stop, maybe a half of millimeter. Hard to tell exactly.

It looks like my focusing ring is a bit slipped. There is no backlash, though. So, focusing ring is still reliable, just distance scale is a little bit shifted.

Yes, could be that the focus ring has slipped just a little bit at some point although it remains fixed at its current position. If I try to be as precise as possible, the infinity mark on my copy (i.e., the end of the "inverted" L) is just at the left edge of the white dot, but I have no way of telling whether that location varies slightly from one copy of the lens to another.

On my lens the end of the top inverted "L" seems to be just at the left edge of the white dot, exactly as you describe it.
I still think the focusing position has shifted a little bit over time, but I don't know where in lens it happened. The lens works fine, so I don't worry about it for now.

 micksh6's gear list:micksh6's gear list
Olympus PEN E-PL5 Olympus E-M1 Olympus M.Zuiko Digital ED 9-18mm F4.0-5.6 Panasonic Leica Summilux DG 25mm F1.4 Olympus M.Zuiko Digital ED 40-150mm 1:4-5.6 R +6 more
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