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01-29-2016, 07:33 PM   #1
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90mm 2.8 D FA 645 Macro Focus Hunting Issue

Hey all, good evening and happy Friday. I have a question re: this lens on a 645z with the latest firmware.

Has anyone experienced extreme focus hunting or it not locking focus right way?

I own many of the older FA 645 lenses and today while on a shoot for a client I had this lens and my 35mm and the 90mm was constantly hunting while the 35mm was locking focus immediately on the same subject in the same environment under the exact same lighting conditions on auto focus.

Am just wondering if the lens is the issue. As there aren't a lot of owners who have written about it online, I figured I would tap the knowledge base here.

Thanks all.

01-29-2016, 09:22 PM   #2
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You didn't, by any chance, have a Lee filter holder on it at the time did you? I have found that mine actually prevents the lens from quite focusing to infinity (needs a spacer) and the AF tends to hunt while it tries to focus. Unlikely, but you never know! (For now, I solve it by stopping down so the slight gap to infinity is taken up by the DoF)
01-30-2016, 05:21 AM   #3
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I think all macro lenses are prone to more 'hunting' due to focus range. Did you limit the focus range using the switch. Re nd filter holders I agree with Ed. My solution is to unscrew the holder by two revolutions and then infinity focus is achievable, but with a less secure filter mounted.
01-30-2016, 05:33 AM   #4
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A good solution except when you are using a big stopper (or other really dark ND) where you are trying hard to avoid light leaks. Maybe it's still light tight screwed on less tightly, but I would worry...

Looking into spacers! With a lens than long, there must be some leeway before vignetting occurs.

Not that this might be the issue in the OP, but could be!

01-30-2016, 05:53 AM - 1 Like   #5
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QuoteOriginally posted by Ed Hurst Quote
A good solution except when you are using a big stopper (or other really dark ND) where you are trying hard to avoid light leaks. Maybe it's still light tight screwed on less tightly, but I would worry...
Ed no light leaks from two revolutions in my experience, but I couldn't say that it isn't dependent on the manufacturing tolerance of both the lens and the holder. Maybe I am just fortunate in this regard. I hope the OP finds a solution to his issue an I will stop going on about another issue now.
01-30-2016, 06:16 AM   #6
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Ed/Unkipunki thanks so much for the feedback! I've tried both limit and full and the hunting is slightly better when limited. Just figured that as this is one of Pentax's newest lenses made specifically for the 645Z that hunting wouldn't be an issue. Of the few reviews that I did find some said that the focus was zippy.

Also, I had no filter on the lens.
01-30-2016, 04:52 PM   #7
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I tried a 90 once and yeah it hunted. Very similar to the 55mm in that regards.

Pretty disappointing for such a expensive lens. Amazing optics though.
01-31-2016, 09:54 PM   #8
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I've used my 90 for a year and very satisfied with it. No hunting issue. It's the best optic I've ever used, period.

You need to understand that this is a macro lens. All macro lens has greater focus throw. For example, a Canon 100mm 2.8 L Macro will not focus as fast as a 100mm f2 USM, even it's an L lens.

02-17-2016, 09:22 AM   #9
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Brelip did you compare it to the 75 and 150?
I own this 2 and thinking about getting the 90mm because I can use it more open and have shake reduction.
I do portrait and fashion, and would like to do more with contious light. So I need quite fast shutter speeds.Worry a bit of the shallow depth of field though, because I really need the eyes sharp.
I shot all side by side already in the studio. f11 did not show to much differences between them. And at f5.6 shallow depth of field was kind of a limiting factor.
In general colors and contrast is very nice on the 90mm.
02-17-2016, 08:19 PM   #10
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QuoteOriginally posted by Toni999 Quote
Brelip did you compare it to the 75 and 150?
I own this 2 and thinking about getting the 90mm because I can use it more open and have shake reduction.
I do portrait and fashion, and would like to do more with contious light. So I need quite fast shutter speeds.Worry a bit of the shallow depth of field though, because I really need the eyes sharp.
I shot all side by side already in the studio. f11 did not show to much differences between them. And at f5.6 shallow depth of field was kind of a limiting factor.
In general colors and contrast is very nice on the 90mm.
I dont think I've ever taken a shot with 90mm at narrower than f5.6. I generally handhold for all my portraits and SR definitely helps. I love the creamy bokeh from the 90mm. 150mm is also very nice, but 75mm is not as nice IMO. I cannot speak to results at f11, but at wide apertures, 90mm is razor sharp.
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