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11-06-2013, 04:11 AM   #1
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Is This Normal for a Pentax M 50mm 1.7?


I bought an SMC Pentax M 50mm 1.7 (advertised as near mint) off ebay a few weeks ago to experiment with on my Canon 600D via an adapter. I checked it over when I got it and immediately noticed something I wasn't expecting. At larger apertures the iris has a kind of 'step' shape instead of being hexagonal (see picture below). The effect of this could be seen in some quick test pictures I took - I could see some out-of-focus lights/highlights taking on this shape instead of being round or hexagonal as I am used to seeing.

Can anyone confirm whether this is normal or whether I may have received a dud lens?



11-06-2013, 06:57 AM   #2
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yes, this is a characteristic of this lens.
11-06-2013, 07:00 AM   #3
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Mine looks like that at f2 or f2.8, but it's gone at f1.7 and less noticeable the more you stop down.
11-06-2013, 07:18 AM   #4
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OK thanks. I guess I was expecting a bit too much from a relatively cheap lens. Interestingly though even something like the Pentacon 50mm 1.8 MC M42 looks much smoother in comparison despite costing less:

(From Wikipedia)

11-06-2013, 09:40 AM   #5
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QuoteOriginally posted by Digitalis Quote
yes, this is a characteristic of this lens.
There you go, panic yee not.

All is well in the camp.
11-06-2013, 09:49 AM   #6
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That is probably the only negative aspect of an otherwise stellar lens.
11-06-2013, 10:22 AM   #7

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As an aside, the Pentacon 50/1.8 is the same lens as the older Meyer-Optik Oreston 50/1.8 and were kit lenses for old Prakticas. The build quality wasn't so great with either version, and not as sharp or contrasty as the Pentax, but still one of my favorite fast 50s. Has a certain character...
11-06-2013, 11:54 AM   #8
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My M 50mm f1.7 does the exact same thing.

11-06-2013, 12:19 PM   #9
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Same for M, A and F series. You could avoid all apertures wider than f4 except for f1.7.

11-06-2013, 12:34 PM   #10
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Thanks guys, I feel better knowing that I haven't been ripped off or anything.

@Just1MoreDave: I spent ages searching Google trying to find an image like that to check against! All the images I've seen either show the lens wide open or stopped right down.

Actually I see now that I should have read the reviews on this site properly. The bokeh issue is illustrated here perfectly: SMC Pentax-M 50mm F1.7 Review #3432

Oh well, it's still a nice lens, hopefully I'll get some use out of it.
11-07-2013, 04:01 PM   #11
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Welcome to the forum, I'm struggling to work out why you'd buy a 30+yr old Pentax lens for a Canon when the much more suitable/usable EF50/1.8ii is relatively cheap. However, welcome to the world of Pentax SMC lenses, the M50/1.7 is very underrated and more than capable of being used wide open.

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