Help with testing sharpness/focus of Samyang 12mm for landscape astrophotography

Started 6 months ago | Discussions thread
W5JCK
W5JCK Veteran Member • Posts: 3,838
Re: Help with testing sharpness/focus of Samyang 12mm for landscape astrophotography

MartStokeley wrote:

Hi brains trust,

I recently picked up a Samyang 12mm (APS-C) due to much fanfare and have now had the chance to try to shoot with it a few times. With previous lenses I have always found that I can focus beyond infinity, however with this one it appears that infinity is right at the end of the focal rotation - or that perhaps it does not even quite reach infinity because stars don't seem as sharp as they should anywhere along the focal range.

I've attached two images to demonstrate (please let me know if these cannot be zoomed in on for proper inspection) the first with the new Samyang and the second with my 16-55mm 2.8 which I feel achieves more accurate infinity focus.

Keen to hear any thoughts from others about whether I'm being too much of a stickler or there is actually an issue here. Also keen to hear from any Samyang 12mm users as to where you've found infinity focus to be on your lens (i.e., the very end of the range or somewhere before).

Cheers!

Are you focusing by eyesight, or just trying to use the infinity mark on the lens. You need to zoom in and use your eyes to get a good, sharp focus.

Wide open general yields softer focus. We often have to stop down a lens one or two stops from wide open.

The Samyang/Rokinon 12mm f/2 is capable of fairly sharp focus on my Sony a6000. With different cameras YMMV. Also, Samyang is not known for the best quality control. These are less expensive lenses after all.

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Best Regards,
Jack
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Sony RX100M3, a6000, and a7

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