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02-18-2022, 03:21 PM   #1
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SMC Pentax 55mm F/1.8 or Pentax-A 50mm SMC 1:1.7

I know it's probably a very close call, but which lens would you say is optically best?
Being 1.7 and an A, the 50mm 1.7 seems to be the obvious choice, but the 1.8 seems to have a legendary status upon reading its reviews & about it.

Which would you buy if you could buy only one of them?
Any other comments are welcome please - especially if you have used/owned both of them...

Thanks,

Michael


Last edited by Michael Piziak; 02-18-2022 at 03:49 PM.
02-18-2022, 03:56 PM   #2
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I own both and for practical purposes there is nothing to choose between the two. The K lens is more substantial, has no plastic, but lacks the auto exposure capabilities of the A

I think they are the same optically...ie 6/5 .... perhaps someone else can confirm.
02-18-2022, 03:59 PM   #3
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QuoteOriginally posted by pschlute Quote
I own both and for practical purposes there is nothing to choose between the two. The K lens is more substantial, has no plastic, but lacks the auto exposure capabilities of the A

I think they are the same optically...ie 6/5 .... perhaps someone else can confirm.
Since they are both k lens, your answer somewhat confuses me.... They both have the metal mount too. From your answer, do you lean toward the choice of the 1.7 A lens?

Thanks for your reply!

Michael
02-18-2022, 05:09 PM   #4
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QuoteOriginally posted by Michael Piziak Quote
Since they are both k lens, your answer somewhat confuses me.... They both have the metal mount too. From your answer, do you lean toward the choice of the 1.7 A lens?
The A series lenses have a focus ring which is plastic rather than rubber. It does not to my mind feel as substantial as the K and M series lenses. The rest of the construction is metal.

They are I believe identical in optical design. The speed difference is tiny. The A lens is more flexible because you can use it it in the auto modes on a modern DSLR. If you use the A lens, do not move the aperture ring off the A setting, the A 50mm 1.7 has a habit of the ring sticking if you do so.

02-18-2022, 05:15 PM   #5
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The 1.8 is a K series lens and the 1.7 is a KA series lens which means the A lens is more useful on DSLRs as you are not restricted to M mode. The optical formula for both looks identical but the SMC coating won't be identical, it improved steadily over the years.
02-18-2022, 05:30 PM   #6
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QuoteOriginally posted by steephill Quote
The 1.8 is a K series lens and the 1.7 is a KA series lens which means the A lens is more useful on DSLRs as you are not restricted to M mode. The optical formula for both looks identical but the SMC coating won't be identical, it improved steadily over the years.
For these two lens in particular, the coating is pretty much identical, right? (both being smc of a similar era)...(?)

Last edited by Michael Piziak; 02-18-2022 at 05:41 PM.
02-18-2022, 06:23 PM   #7
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I would take the "A" advantages, definitely. I have the "F" version of the 50mm f/1.7 which is an AF lens and probably the same formula as the "A" version you indicate here, which was made before AF became available. Mine was my first AF lens and also has the "A" setting on the lens ring. Mine has shown exceptional imaging capabilities, being able to yield very good results even at wide open aperture. I got it new with my first AF camera body, the SF-!n way back around 1990, after shooting with the Pentax ME Super for some 8 years, and before that with a Vivitar SLR for 6 years.

The coatings will be quite the same between mine and the "A" version.


Last edited by mikesbike; 02-18-2022 at 06:30 PM.
02-18-2022, 07:17 PM   #8
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With a little diligence, you should be able to get both of these for (well?) under $100 total on eBay.

Get 'em and try 'em. If you don't like either one, you can probably sell it/them for about what you paid.
02-18-2022, 07:38 PM   #9
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The two are not the same optically...The Pentax-K is a carryover of the SMC/S-M-C Takumar 55/1.8 design while the Pentax-A 50/1.7 carries on the optics of the Pentax-M 50/1.7. I own both and prefer the Pentax-K 55/1.8 over the Pentax-A 50/1.7, mostly on account of build. Optically, the A 50/1.7 should perform as well as the highly-regarded M 50/1.7, a lens that "lives" on my go-to Ricoh XR-2S.


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02-19-2022, 06:04 AM   #10
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QuoteOriginally posted by Michael Piziak Quote
For these two lens in particular, the coating is pretty much identical, right? (both being smc of a similar era)...(?)
not sure when " improvements " happened

but similar era ???


QuoteQuote:
Production Years
1984 to 1989
SMC Pentax-A 50mm F1.7 Reviews - A Prime Lenses - Pentax Lens Reviews & Lens Database


QuoteQuote:
Production Years
1975 to 1977
SMC Pentax 55mm F1.8 Reviews - K Prime Lenses - Pentax Lens Reviews & Lens Database
02-19-2022, 06:51 AM   #11
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The K55 1.8 is, in my opinion, optically better. As mentioned in an earlier post, it carries over the glass and coatings of even earlier Takumar lenses. The extra green button step to meter is a bit of a pain and does take away from my overall experience with this lens. The A1.8 doesn't require this, just focus and shoot in A mode.
02-19-2022, 07:42 AM   #12
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I would think if you had 10 each and ordered them from best to worst, the order would resemble 20 coin flips. The plastic aperture ring being cracked would probably skew more "a" series to the lower end though.
02-19-2022, 09:25 AM   #13
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I have both as well and would pick the K55/1.8 every day of the week. While optically they are both very close, the K55/1.8 is way better built and the handling is also better. The A50/1.7 has a plastic aperture ring assembly and is a disaster waiting to happen. If you want a 50/1.7 then pick the M or F version instead of the A Series.

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02-19-2022, 10:08 AM   #14
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The A has a little plastic spring underneath the aperture ring that tends to break after all the years - an easy(ish) fix, but keep it in mind when shopping.
02-19-2022, 03:38 PM   #15
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QuoteOriginally posted by Wasp Quote
The A has a little plastic spring underneath the aperture ring that tends to break after all the years - an easy(ish) fix, but keep it in mind when shopping.
"The A has a little plastic spring underneath the aperture ring that tends to break after all the years - an easy(ish) fix...". Well, easy-ish if you don't have sausage fingers like me. My A50/1.7 suffered from the stuck aperture ring too, so I thought I would give fixing it a go following the directions found here. I fixed the loose spring all right, but everything went sideways when it came time to put the lens back together. Now it's junk. gofour3 is right: M or F, avoid the A.

Last edited by erichope; 02-19-2022 at 04:21 PM.
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