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02-02-2018, 05:25 PM   #1
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Focusing issue with Pentax 645N

Hello, I'm a newbie to shooting pictures with a Pentax film camera--and so far, I love it, and am happy that it is my first medium format camera. It is really fun to shoot pictures with it.
Today I got my first roll of film processed and discovered that some pictures are a bit out of focus. And since I know that my 75mm manual focus lens is (apparently) pretty sharp, I should assume I'm just not experienced with focusing with this camera.
Here is the issue--with other film SLRs or RFs that I've used before, there was a sort of line or 'box' in the middle of the viewfinder that basicaly tells me if I'm perfectly in focus. But for Pentax 645N, there's only a circle in the middle of the viewfinder, and I find that it is rather for framing, not focusing, and in order to focus, I need to 'eye-ball' it.
I've been googling for a while to learn what I need to do, and apparently there is an adjustable diopter which I found on my camera, but have no idea how to use it. I even went to Ken Rockwell's website and he says for manual focus "Look at the screen, or look for the in-focus dot at the bottom. Slide the power switch to the middle position, and the beeper goes off when you're in focus" and I don't see any dot or hear any beep at all.
Please help this newbie out...
Thank you for reading.

02-02-2018, 11:31 PM   #2
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For the viewfinder diopter: In good light focus manually as usual with the lens. Then slowly change the diopter while looking thru the view finder. The view finder will eventually get worse, so then change it back the other direction. Somewhere you will find it looks sharpest to your shooting eye. Once that is set, there is no need to change it unless your eyesight or vision changes in a few years.

Sorry but my 645N is at work right now and I canʻt verify this but....I do not believe that what Ken Rockwell describes would work with a manual focus lens. If it did, you have to press the shutter release button slightly while focusing. When the phase detect of the AF system confirms youʻre in focus, a little hexagon appears in the bottom of the viewfinder.

You can also set the camera to have an audio beep, and it would beep when it is confirming focus. Again, this requires you to hold down the shutter release button half way while focusing....and may not work on manual focus lenses. (I have both the 75mm AF and MF version of the 645 and have never tried to use the AF on the 645 or the MF on the 645N).

Hereʻs a link to the 645N ownerʻs manual, and page 56 seems to agree that you need an AF lens to get the MF focus assist to work:

Last edited by Alex645; 02-03-2018 at 12:10 AM. Reason: ownerʻs manual
02-05-2018, 01:39 PM   #3
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In my experience as long as the lens is an "A" lens designed for the P645 or P645N then the green focusing hexagonal will light up when you have the lens in focus and yes there is an beep as well but it is hardly necessary as the green "dot" shows up well in the viewfinder The correct focus does not rely on you using the correct dioptre in the eyepiece. That for the benefit of your eyesight and not the camera's eyesight


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