I recently picked up a pair of Samyang 14mm f2.8 lenses for shooting startrails on my older cameras. The quality control on these isn’t great, but if you manage to get a good copy it’s performs well for astro.
One of mine doesn’t quite reach infinity focus, it hits the focus stop just short of infinity, leaving distant object soft at f2.8. Because I’m using this only for startrails that isn’t a problem, as I prefer to have the trails slightly defocused for a smoother look. When stopped down it brings everything into sharp focus.
My second lens is badly de-centered, there’s no easy fix for this so it’s going back to B&H, I’ve head of some people going through 5 or more copies before they find a good one, shipping to and from Australia adds up pretty quick so I think I’ll just give up on Samyang and maybe go for a Sigma 14-24 instead.
One thing I noticed on both of the Samyangs was the position of the focus ring was way off, the image below shows the position of the distance scale when both lenses are focused to infinity (or in the case of the one on the left, almost at infinity).
To fix this you’ll need a small flathead screwdriver and your camera body.
Mount the lens on your camera and focus on a distant object to find infinity focus, take note of the position of the focus ring, try not to move the ring at all during the next steps. (You can use sticky tape to hold it in place while removing the rubber grip).
Remove the rubber grip, you might need to stick something under it to get it started, or sometimes you can just get it off my moving it around with your fingers. You can remove it from the lens or just slide it down far enough that you can see the distance marker.
There are 3 small flathead screws on the focus ring, loosen these screws but don’t completely remove them, this will disengage the outer focus ring from the internal focusing mechanism.
With the 3 screws loosened you should be able to move the outer focus ring independently of the internal focusing ring (the silver piece circled in green below). Sometimes the outer ring can be a bit sticky and move the internal ring as you turn it. If this happens it’s best to tighten up the 3 screws and mount the lens on your camera to find infinity focus once again, you can then use the screwdriver to hold the internal ring in place while you move the external ring, position it so that the indicator points to the infinity marking on the distance scale.
Tighten up the 3 screws and mount the lens on your camera, focus to infinity and check the position of the distance scale, you might have to loosen the screws and make some further adjustments to get it just right.
Once your happy with the position of the distance scale slide the rubber grip back on.
If you are using a Nikon check the position of the aperture ring on the lens, it needs to be at f22 or your camera will report an error. I bumped mine just enough to get an error when moving the rubber grip around.