mainebrien

Hope some smart person out there can help. My MANUAL IRIX 15mm f2.4 has a special infinity focus stop (click) and it works great on Nikon D750 for night sky pinpoint stars. However, when I switch that lens with the same settings to Nikon D850, the photo is blurry. I've run the test several times with the same results.

I'm thinking it must be some setting on the D850 that needs to be changed. The D850 is set to Manual mode.

Any thoughts out there among the mentally gifted?

Thanks,
Brien

rmalarz Loc: Tempe, Arizona

You might try to let the camera know what lens you're using. Look for the "non-CPU Lens Data" section of the setup menu. Then enter the information about the lens as required.
--Bob

mainebrien

Thanks, I'll try it.

photoman43

I have the 11mm Irix lens that I use on my Nikon DSLRs. . Make sure you download the Extended User Manual from Irix and read it carefully. This waring appears on page 6 of my manual.

CAUTION: Do not turn the focus lock ring out of the center marker
or use excessive force. This may damage the locking mechanism
of the focus ring as well as make it more difficult to release
the focus ring lock.

One thing I would try is to make sure the focus lock is NOT set when you add the lens to a body. While I found nothing in the manual about this, for focus lock to work correctly, it might have to be set after the lens is mounted.

If the aperture is set higher than f 16, you may get image softness due to diffraction.

https://irixlens.com/new/wp-content/uploads/2020/12/Irix_15mm_F2.4_Extended-User-Manual_v2.0.pdf

Check out all of the details about focus ring and calibration.

MJPerini

Modern lenses for digital cameras don't have infinity stops, and the answer I got from Canon was it was for temperature related issues, (sometimes a point 'past' a normal infinity mark is required)
I do not know if this could contribute to your problem , ( it may be totally unrelated). The other thing to watch out for is the rear element touching the sensor. ( I would hope that is not possible) These are just FYI I am not sure either will be helpful.
Good Luck

selmslie Loc: Fernandina Beach, FL, USA

When I started to use non-Nikon* manual focus lenses on my Z7 I discovered that I could not rely on the hard stop for infinity focus. Lenses that seemed to work on a 24MP camera did not focus at the hard stop on the 45.7MP sensor. It turns out that they were not in focus at 24MP either but I just had not noticed it.

Fortunately they all focus properly a tiny bit closer. I need to magnify the image on the LCD to get this right.

On your D850 you should be able to do the same by displaying the mage in Live View magnified to the maximum.

* The same thing happens with older manual focus Nikon lenses.

mainebrien

I'll try it, thanks!

selmslie Loc: Fernandina Beach, FL, USA

I should have mentioned that I focus with the lens wide open and then close it down to shoot.

A very wide angle lens makes this more difficult because the DOF is so deep.

Stopping down doesn't cause the focus to shift but it spreads the sharpness out towards the corners. I can see sharpness start to drop off at around f/8.

mainebrien

Got it, thanks.