[turbo_bird]

Hello, last night was the first time I've really been able to try out my latest lens, a Rokinon 14 f2.8, at night. I've tried it out a bit in daylight to get familiar with how it handles and make sure it will focus to infinity, and it seems good. Infinity focus looks to be roughly halfway between the 3m mark and the infinitely mark and all seemed well. Last night I was out in roughly freezing temperatures trying to take pictures of the milky way, and found that the sharpest focus I could get on the stars was with the focus ring turned all the way to the infinity stop, and it still wasn't as sharp as I expected based on my daytime results. Has anyone else noticed issues like this, or am I doing something wrong here? I'm using a K3, and trying to focus using live view magnified on stars and other distant light sources.
Kristian

[Wingincamera]

I have this lens and while I find my copy very sharp, the focus marks on the lens body were way off. There is an instruction somewhere on how to correct the marks. What I did was apply some graffers tape over the original marks and then set the camera/lens on a tripod and take focus readings from a few feet in front of the lens and toward infinity and made my own marks. But I found that if I align my 8-foot alignment mark then everything from within a few feet to infinity was in focus. This was on a KP. Hope this helps.

[Kwong]

I have this lens and while I find my copy very sharp, the focus marks on the lens body were way off. There is an instruction somewhere on how to correct the marks. What I did was apply some graffers tape over the original marks and then set the camera/lens on a tripod and take focus readings from a few feet in front of the lens and toward infinity and made my own marks. But I found that if I align my 8-foot alignment mark then everything from within a few feet to infinity was in focus. This was on a KP. Hope this helps.

Perhaps this link will help.

Calibrate the focus ring of the Samyang 14mm F2.8 | DSLR Astrophotography

[Pål Jensen]

This is normal for all lenses (and cameras as well). Thats why telephotos focus past infinity....

[stevebrot]

Perhaps this link will help.

Calibrate the focus ring of the Samyang 14mm F2.8 | DSLR Astrophotography

I have done that procedure and should note that the ring it says to move was taped in place on my copy and that moving it resulted in the tape breaking and the ring being free to move, secured only by the rubber grip. I was eventually able to tape the ring back down and use the adjustment window to calibrate the focus scale to 1 meter, which also resulted in usable focus for very far objects.

Of course, what worked for me, may not work well for others...YMMV.

As noted above, focus drift with dropping temperature is not unexpected.


Steve

[turbo_bird]

Thanks everyone. I was expecting some focus change with temperature, just not as much as it ended up being with a roughly 15° C temperature change. I'll have to play with it a bit more I guess, and see if I actually had it focused to infinity in my daytime shots. It looked like it based on a treeline a mile or so away, but I guess that's hard to judge with this wide a lens. Hopefully with warmer weather I won't have this issue at night, and when winter comes again I can try it in the cold with daylight. That would make things easier to see.
Kristian

[DeKay]

I had the same lens hit the back stop before infinity was reached. As it was still under warranty, it was sent back to Samyang for recalibration and now infinity is dead bang on the infinity mark.

[niels hansen]

I have done that procedure and should note that the ring it says to move was taped in place on my copy and that moving it resulted in the tape breaking and the ring being free to move, secured only by the rubber grip. I was eventually able to tape the ring back down and use the adjustment window to calibrate the focus scale to 1 meter, which also resulted in usable focus for very far objects.

Of course, what worked for me, may not work well for others...YMMV.

As noted above, focus drift with dropping temperature is not unexpected.


Steve

As noted above, focus drift with dropping temperature is not unexpected.

Is it possible that cold related focus shift also affects AF

[turbo_bird]

As with many things in life, the issue was the loose screw behind the camera. When I thought I had this lens focused at infinity in the daytime, I didn't. Tried the 3.5m and infinity thing out on my deck after work today, and now I've got it so it goes just a bit past infinity focus sitting on my deck at 12°C. The distance scale is nowhere near accurate, but it at least goes to infinity and beyond. I scouted out another spot for hopefully a decent milky way picture on my dirtbike today, and might try again tomorrow morning before work. Thanks for the help guys.

Previous travel stop.


Focused at infinity now.


I might try to get the focus scale lined up better with the markings if it bugs me, but that can wait for when I have more time. I don't generally do hyperfocal focusing, but I can see it being useful having an accurate distance scale with this wide of a lens.
Kristian

[turbo_bird]

I think I'm figuring this lens out a bit now. I was having trouble with getting any sort of consistent focus with it, and noticed that most of the lens seemed to move more than expected when it was on the camera. I pulled the focus scale back and noticed 3 holes that looked like they should have set screws in them to hold the lens at the same relative position in front of the sensor. Holding it on a table with the front facing down, I was able to move the lens mount up and down probably 1/32" in relation to the rest element, so I threaded the holes and put some tiny set screws in them. It's much better now, and doesn't move at all. I should have taken pictures I guess. If I end up trying to adjust the distance scale in the near future I'll add a couple here.
Kristian