So I bought a Kood slimline clear filter to protect the front element of my 500 f5.6PF.
I had some issues with getting the lens to focus sharply, but Tom Hogan's method using auto fine tune was great.
I was still not convinced that the focus was sharp, but the weather's been really crap here recently & not good light. On Sunday I took some pictures of a Little Egret on a canal & even as I pressed & held the back focus button, I could see in the viewfinder of my D850 that it was way off focus. So I took the filter off & reshot from the same position. Lo & behold it was fine! Distance was about 30-40m
Why would a clear filter affect the ability to focus?
And in case you want to know, yes it was fitted correctly & screwed right in.
And no, it wasn't fitted when I did the AF fine-tune.
Anything to do with the PF element?
Comments
I tried it over the weekend (still lousy light), and when I look at the images at 100% on ViewNX they still look 'unclear'. Maybe rather than a focussing problem, the filter softens the image?
Also, the lens seems to hunt with the filter in place - it focuses when I hit the AF-button, then jumps off & then back on again
Once I had a D7000 with a 24-200mm with a clear filter. It focused in front of the object. I had the camera and lens controlled by Nikon but they found no fault. I removed the filter and the problem disappeared. From that day I have never had any filter on my lenses.
The front glass on Nikon lenses are extremely durable. Have never had any issue with not "protecting" the lens other than using the lens hood.
And on a birding holiday recently I found a similar thing when trying to shoot AF through a car windscreen.
It seems that my 500PF doesn't like anything in front of it!