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10-07-2013, 06:11 PM   #1
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Newbie question - Asahi Pentax SMC 50mm f/2 vs 1:1.7


I am sure this will seem like a silly question, but I'm pretty new to D/SLRs and am still trying to wrap my head around how everything interacts with everything else - aperture, shutter speed, ISO, etc.

I have a K30 (just the 18-55mm DAL kit) and picked up a few lenses on eBay, including a Pentax SMC 50mm f/2. I really like it and have gotten what to me are great photos with good bokeh, and I thought it would likely be the lens that stayed on my camera the most.

Then earlier today I was at my local thrift store and apparently a Pentax user had donated some of their old kit. I made the mistake of buying a Vivitar 28-200mm lens that I thought would fit but doesn't (it's a PK-R and has a flange that doesn't let it seat correctly), and an ME that had a Pentax/Asahi SMC 50mm 1:1.7 on it. I bought it just for that lens.

My question is, what is the functional difference between the two SMC 50mm lenses? I understand that the aperture is wider; so am I better off with this lens, or does it depend on what I'm shooting? Is there enough of a difference that I should keep both 50mm lenses?

My plan now is to put the Vivitar on the ME and put it up on eBay to cover the cost of the 50mm lens. If there's no advantage to keeping the 50mm f/2, I would add that in too.

Any thoughts or advice would be appreciated. Thanks!


10-07-2013, 06:24 PM   #2
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The 50/1.7 is a better optical design than the 50/2.

So theoretically the 50/1.7 should be better at ƒ/2 than the 50/2. The sweet spot for both lenses is around ƒ/8.
10-07-2013, 06:27 PM   #3
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10-07-2013, 06:31 PM   #4
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The wisdom now by post M-ers is that the 1:1.7 will be unconditionally better than the 1:2.
However, these are old, I would examine them both carefully for clean glass and snappy close-down and no sign of ham handed repair attempts.
Then take test shots under various lighting.

Particularly, take photos (no filters) into the low sun at various angles, and compare flare.
i found this is the best test of old lenses for deterioration etc.
Better, in my experience to have an excellent copy of a mediocre lens than a deteriorated copy of an excellent lens.

Good Luck !

10-07-2013, 09:22 PM   #5
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Two might be handy if you had one dedicated to an unusual setup, like a reversing ring. The M50/1.7 is better but this difference is not huge. It will be sharper at apertures wider than f8, usually on the edges and sides. But a lot of photos at those apertures have out-of-focus areas so the sharpness difference is immaterial. The wider aperture used to be really important but newer sensors make it less necessary.

Some versions of the M50/2 are built cheaper but honestly you can't tell, and the cheaper versions hold up just fine.

You should be able to modify the Vivitar's flange to fit your K30.

This is with an M50/2 at f2:

10-07-2013, 09:57 PM   #6
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Thanks for all the input As it happens, dogs are one of my most frequently captured subjects (I have 3 dogs... oh, and some kids).

I took this yesterday with the f/2 at the dog park.

Mr. Growley HATES the K30 (probably because of the spot meter and shutter sound) but the fact that I was able to get this shot of him was worth the price of the f/2 right there.

I'll play around with the 1.7 and see which one I like better.. maybe I will keep both.. though I am afraid, knowing me, of winding up with stacks of lenses!
10-07-2013, 10:59 PM   #7
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Just as an aside, the zoom lens can be made to fit, there is a slight mod to the flange that protects the aperture lever that is too big. Also be aware of the Ricoh pin. It can get caught in the AF drive and lock the lens un-intentionally on the body. Do a search on the Ricoh pin I. The lens forum for learning how to deal with it.

As for the difference between an F1.7 and F2 lens. The F2 lens was the basic kit lens, the faster lens was an upgrade. Both are quite capable lenses, and the condition will drive the final quality more than any optical differences
10-08-2013, 06:24 AM   #8
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QuoteOriginally posted by Coelli Quote
I'll play around with the 1.7 and see which one I like better.. maybe I will keep both.. though I am afraid, knowing me, of winding up with stacks of lenses!
You don't have LBA until you have 5 50mm lenses...

Just remove the flange from the Vivitar. There are 4 small screws that hold it on. They look like #00 Philips head, but they are JIS so be careful not to strip them.

10-08-2013, 09:08 AM   #9
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I have a 50mm f1.7 and a couple of f2 versions, not to mention a couple of f1.4...

forget about the 1.4 for now, I find the f1.7 to be better by far than both the f2 versions. I tried them a couple of months ago, and all at f8, the f1.7 lens was sharper every time than the f2 lenses. I tried one of them all day and never did get anything quite as sharp as I get all the time with the f1.7, which I used this morning. Still haven't transferred those to the computer to see what they really look like, but I'm expecting some nice shots of fall flowers covered in dew...

Tried some similar shots of spring flowers and dew, never did get the tiny dewdrops to come out as sharp as I can almost always get them with the 1.7 or 1.4. The f2 lenses do ok, and I had no complaints with film, but now with digital, which shows even slightly out of focus a lot better, the difference is very noticeable. If you got a good copy of the f2 lens, you may be happy with it. I tried out a A series f2 version a while back and liked it pretty well, but had to return it, since it was a part of an online auction buy with a defective 300mm Lentar that had fungus they didn't tell me about...sure wanted to keep it though...

Try out both for a while, don't make a decision based on just a couple of days of use. Get really familiar with them, use each quite a lot, be especially critical of your focus, I usually stick to apertures around f8 most of the time for the sharpest performance, and they can also do a good job as wide as f4. I rarely go wider than f4 though, sharpness tends to suffer. But give them both a thorough chance before making a decision on getting rid of one. I'd probably just keep both and carry on...
10-08-2013, 10:32 AM   #10
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Cool, thanks, you guys are right - I should just keep playing with both of them and see for myself. I'm really, really trying not to wind up with a ton of lenses I don't use since I tend to be a collector and packrat, and that could get very expensive very fast. I like the older manual lenses so far though. They feel good and I like the fine control (with autofocus I feel kind of out of control). They're heavier (the Owen 135 is a little brick), but they don't feel flimsy like the kit lens does or the freebie Sigma 28-80mm AF lens an eBay seller threw in (not that I wasn't grateful she did!).

Still, last night I inventoried everything on the kitchen table and my boyfriend's eyes boggled a little at how many lenses managed to just magically show up so far...

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