14mm Rokinon (Samyang) won't focus at infinity

[Leo.G (Leo)]

I have the non AF Nikon version of a Rokinon 14mm F2.8-ED lens, it's a fantastic lens for shooting the Milky Way on my old Nikon D80. It also produces great images when I use an adapter and fit it onto an original Canon 5D I was loaned but I can't for the life of me get it correctly focused on my Nikon D810.
It seems like the focus ring just doesn't go far enough to obtain focus.
I had the identical problem with the first Rokinon lens I purchased but it was returned and reissued immediately and no problems achieving focus until trying it on my D810.


It's the most frustrating thing, especially since we've had so much rain over the past few years and now outside temps are below zero and the skies are clear (locally) it just won't focus.
It seems like I have to go beyond where the focus ring locks at infinity. I even thought if I could get a minute spacer between the camera and lens it may be fine but I have to check if the lens moves closer or further from the sensor at infinity, I can't remember.



I've searched online in the past and just can't find any reference to a strip down to rectify the problem. I believe I found such a video for the 85mm Rokinon but not the 35mm or the 14mm.


I also have the 35mm F1.4 I purchased used and was assured focus was fine, it's not, it's the same on any camera. I can stop it down and achieve focus but that defies the point of having an F1.4 lens.


In just remembering that fact I didn't think to try stopping the 14mm down and seeing if it will focus, I'm such an IDIOT!


I'd love to see a video or any information in relation to stripping the lens down and fixing it for good if anyone has any idea where I may find such information?

[bojan]

Originally Posted by Leo.G

.... I believe I found such a video for the 85mm Rokinon..

The approach is probably the same or similar...
Try Youtube (correct search keyword is essential...), maybe someone did this and post the info.
I would risk and try removing screws at the camera end.. then again, my short focus FD Canon lenses should be opened from the front end (retaining ring) to get access to focusing mechanism.

[Leo.G (Leo)]

Thank you but I soon found with the one video I found on the 85mm the lens construction was very different to the 35mm when I stripped it to try and fix it.
I haven't searched for the 14mm since I got it replaced under warranty, only the 35mm but I have just searched and found mention numerous times but haven't yet checked if any of the discussions show the fix or point to a video which does. I'll go have a look now though.


I would have thought since it focuses on the DX format D80 and the FX format Canon 5D (with adapter which may make the difference) it should focus on the D810 but no matter what I do and how long I spend playing with the focus the stars are very out of focus. At first I was blaming star drift as the problem but even a 10 second exposure produces the same results so it's definitely a focus thing.


Using live view I've done everything and at high magnification levels I get a lot of noise, much like a grainy video stream and it's terribly hard to pick what's in focus, even using the moon.

[bojan]

It is possible that you have some flaring as well, so try to stop it down one or two stops.

You should try focusing with Bahtinov mask (it is easy to cut it out of black paper, using scalpel and ruler), it will then be quite obvious what is the problem - If the focus ring does not go far enough or it passes the sweet spot (in which case you have flaring and stopping down should help)

[Leo.G (Leo)]

Stopping it down defeats the purpose of finding infinity at F2.8 where I want to use the lens. That's the exact issue I have with the 35mm, it will focus nicely on infinity stopped down at night but not at f1.4 where I want to use the lens.
The Rokinon and Samyang (same lens) are notorious for this but when focused they are an amazing lens when you take price into consideration.



I have a couple of Bahtinov masks but they are both too large to keep on the lens. I have read/seen somewhere a wire strainer works on lenses, I have a few of those in different sizes. I'd try tonight but our skies have clouded over and we're apparently expecting snow tonight/tomorrow.
I did find a lot of information which never used to be available for the adjustment.


Strangely enough on the DX Nikon and the FX Canon infinity is just near the mark, close enough to be able to find but playing around outside with distant houses it's showing infinity focus is at 2 metres. That doesn't seem right to me but it won't make a difference until I try on the night sky.
Plus zooming on an image enough to try and see focus at a distance of maybe 100 or so feet the image just pixelates so I'm still confused.
I do know infinity focus on the land and infinity focus on the night sky are two different things.
I'll have to wait till the sky clears again I think.

[JA]

Originally Posted by Leo.G

Thank you but I soon found with the one video I found on the 85mm the lens construction was very different to the 35mm when I stripped it to try and fix it.
I haven't searched for the 14mm since I got it replaced under warranty, only the 35mm but I have just searched and found mention numerous times but haven't yet checked if any of the discussions show the fix or point to a video which does. I'll go have a look now though.


I would have thought since it focuses on the DX format D80 and the FX format Canon 5D (with adapter which may make the difference) it should focus on the D810 but no matter what I do and how long I spend playing with the focus the stars are very out of focus. At first I was blaming star drift as the problem but even a 10 second exposure produces the same results so it's definitely a focus thing.

If your 14mm lens reaches infinity focus and gave nice sharp stars on the DX Nikon D80 it should also reach similar infinity focus on the FX Nikon D810 as they are both Nikon F-mount cameras and both have the same nominal flange focal distance of 46.5mm. Perhaps your D810 has been modified or has had a sensor change and requires adjustment{?} of the flange focal distance, or maybe it's an unfortunate stack up of tolerances between the cameras and lens.

Originally Posted by Leo.G

Using live view I've done everything and at high magnification levels I get a lot of noise, much like a grainy video stream and it's terribly hard to pick what's in focus, even using the moon.

Using live view is a good first option to get in the zone, but if you want to check focus more critically take a test image and zoom in.

The moon is about 1/2 a degree wide and shooting a 14mm focal length on full frame should result in an image scale around 60 to 70 arc seconds/pixel, so the Moon should be some 25 to 30 pixels wide so should be able to be discerned, depending on the screen resolution on the D810 and the image resolution you are shooting in. Perhaps instead of using the magnify feature within live view you could try an optical magnifier of some type and experiment with ISO to try and get a bright live view image.

Best
JA

[Leo.G (Leo)]

Thanks JA!
I thought the focal point should be the same between the D80 and the D810.
As for modification, both cameras were purchased used so I wouldn't know, the D810 more recently.


Quick edit I'm using live view/mirror lock up mode to alleviate a typical slightly clunky D810 mirror and an intervalometer to avoid shutter shake on a sturdy tripod so they aren't part of my issue mistaking vibration/shift/blur for focus.
And another two characters ".." so the edit will accept the change, that's confusing?
I know, I can't count.



I've looked at a video, adjusted a ring but poor eye sight doesn't help.
I tend to take a couple of snaps and run inside and shove the CF card into my computer to check the focus on my 27" monitor, it's so much easier than the small screen on the D810 (small for my eyes) and the viewfinder, that's like trying to discover a distant galaxy through a pin hole camera, lol.
Of course now that I've started playing with the ring inside the lens which changes the focus the weather has turned sour with expected snow today/tonight.
If nothing else it's good sleeping weather and I've decide after being awaken early by a neighbour wanting a lift (after less than 2 hours sleep), I'm going back to bed, it's a problem for another day.


Though I have thought about putting a series of red marker spots around the perimeter of the focus ring at equal distances and shoot an image at each spot as I change through the focus range and take an equivalent number of images as red spots then compare them on the computer until I find the best (right or nearest) focal point. Then it appears to be a simple matter of changing the focus ring marker to represent focus at infinity so I don't have to play around and guess in the dark (according to a video I saw).


All of my other lenses (mostly genuine Nikon) focus at infinity exactly at the infinity mark, right in the middle of the twisted 8. This makes focusing easy, even with a few lenses with the capacity to go to infinity and beyond (Buzz Lightyear?), it's still easy to set exact focus in the house before I venture out into our cold nights (below zero currently).
I just have to remember to put my heater band on the lens because fog and ice doesn't help with focusing, or image quality.


I guess I should be happy because it's been so long since we've even had clear skies with the constant rain for way too long.