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Kowa Prominar 16H wont' focus wide open!


dhessel
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I am new here and want to say hello before getting into it.

 

I've just got my Kowa shooting on a Mark II and I cannot get it to focus wide open or anywhere near wide open. I can only get soft focus at f6.3 and higher. I have tried it on several lenses including a Canon 85 mm 1.8 and all show the same problem. If I get something focus as close a possible the defocused parts of the image that are beyond the focal point appear to be skewed to the left. I am wondering if maybe the optics are out of alignment a little bit. I had a giant ISCO projection lens that displayed similar artifacts and the front and back lenses were slightly off, visually it doesn't look like the Kowa is and I can look through the back of it and it looks sharp to my eyes. Any advice on what might be going wrong?

 

Thanks.

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It appears so, I disassembled the lens so I could adjust the focus and rotate the front element independent of the rear. Doing so I was able to get near perfect focus using my 85 mm at 1.8. At this point I am not sure if its an issue with just the rear or the front since the front appears to have more than 1 piece of glass. Can anyone confirm if that is the case with the front piece. Thanks.

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Your problem is that the front and rear glass elements are not aligned  to each other properly. It is enough to adjust only the front part or only the back. I don't have a kowa but it looks as simple as a Sankor or Sun so there should be only 2 glass groups. I had the same problem with my sun and adjusting the front glass (rotating it so that the image was sharp) solved it. You can usually use a caliper to rotate glass elements.

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Thanks for the advice, this one is a little trickier. Some I have done have some screws that you loosen and then you can rotate the rear element. This one has a tube that wont allow them to rotate independently. Looks like I may have to rotate the rear glass. It appears to be mounted on a threaded ring with 2 notches in it, any advice on how to rotate that? 

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