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04-28-2015, 02:03 PM   #1
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645 120mm A Macro - Aperture for Infinity?

Hi everyone, I'm wondering what sort of aperture one needs for corner to corner sharpness with the manual focus 120mm A Macro on a 645 digital for distant scenes, because I am thinking of buying a used one. From previous experience (like with the Olympus OM 50mm f3.5 macro) many old school macro lenses require a lot more stopping down than regular tele lenses for distant subjects. Is it the case with this lens too?

How would you compare the performance of this lens with the 150mm f3.5 A for landscape use. I'm looking to use the lens in a typical tele way on a 645Z, so mostly distant vistas. I am wondering if the 150mm will need less stopping down at distance.

Any help is appreciated!

04-28-2015, 03:16 PM   #2
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The timing of your question was pretty good. I recently picked up an A 120 and am taking it on a hike to a spot where I'll have clear views of distant vistas this evening. I'll pick a spot at infinity and shoot it at several apertures (say 4, 5.6, 8, 11, 16) and post the results so you can see first hand.
04-28-2015, 07:44 PM   #3
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I use my FA120mm the 645Z for distant vista's. Generally between f8-f11. I found it to be critically sharp, I also found that even just a hair off and the slightest bump on the focus ring to make a soft image.
04-28-2015, 08:09 PM - 1 Like   #4
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Here's some shots taken at infinity, on tripod, 2s timer. It was pretty windy so I was pressing down on the trips base to try to dampen things. All shots straight RAW conversions, no editing. 1st is at f4 with each subsequent shot stopped down 1 full stop. I usually shoot this one between f8 and f16.

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04-28-2015, 10:41 PM   #5
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All Pentax macros for the 645 have "floating elements" which means that the lens elements change internal spacing as you focus to optimize the lens design for the distance you are focused on. I thought the 120A lens I used to have was great at all lens openings (it was stolen or I would still have it). Of course almost all lenses perform better stopped down a stop or two. It has already been mentioned that stability is important. My Gitzo tripod had a loose rivet and made my Pentax 400 look unsharp. I fixed the looseness and all of a sudden my lens got way sharper.
04-29-2015, 03:53 AM   #6
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If the A120 and A150mm 3.5 are anything at all similar to the FA120 and FA150mm 2.8 (my samples at least), the 150mm should have better corners by f/8, but I've tested this by shooting a chart, so in practice you may not notice the difference at all.
04-29-2015, 04:01 PM   #7
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Thanks for posting. I tend to like f11 with no need to go to f16.
04-30-2015, 10:41 AM   #8
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Original Poster
Thanks everyone - very helpful.

06-11-2015, 09:01 PM - 1 Like   #9
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I've been waiting a while for a chance to use the 120mm Macro at infinity so that I could participate in this thread.


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