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11-14-2018, 12:45 PM   #1
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M vs A 50/1.7

Am I correct in thinking that the M and A versions of the 50mm f1.7 have the same optical formula? Any other reason to get an M vs an A in 50/1.7?

11-14-2018, 12:52 PM - 3 Likes   #2
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the biggest issue with the A version was the cheap build-quality of the aperture ring...

granted, if you leave it in the "A" position, it's a moot point...
11-14-2018, 01:00 PM - 1 Like   #3
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QuoteOriginally posted by pepperberry farm Quote
the biggest issue with the A version was the cheap build-quality of the aperture ring...

granted, if you leave it in the "A" position, it's a moot point...
Thanks, I didn't realize that the aperture ring was an issue. Good to know.
11-14-2018, 01:18 PM - 1 Like   #4
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QuoteOriginally posted by Docrwm Quote
Thanks, I didn't realize that the aperture ring was an issue. Good to know.
read the reviews here; I sold my copy after buying an A50/1.4, but the 1.7 had the typical graunch in the aperture ring...

11-14-2018, 01:33 PM - 2 Likes   #5
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I'm pretty sure they share the same optical formula - I have both and they render almost identically. The M has better build quality, but you will need to use green-button (stopdown) metering in M mode, where the A can use all modes. The M is also limited to center-weighted metering IIRC, where the A can use all metering modes. Reports suggest the A has a weak/poorly made aperture ring although I've personally not experienced any problems. Just leave it in A and don't worry about it. My M and A50s see about equal use depending on my mood that day.
11-14-2018, 01:36 PM - 2 Likes   #6
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QuoteOriginally posted by Docrwm Quote
Thanks, I didn't realize that the aperture ring was an issue. Good to know.
The aperture ring weakness is part of K-mount lore and is a permanent mark on the A-series' generally very good to excellent build quality. My A 50/1.7's ring works, but is very rough and I expect it will fail completely at some point, so I leave it on the "A" setting.

Optically, I consider it equivalent to my M 50/1.7, though will confess to never actually having done a 1-on-1 comparison.


Steve
11-14-2018, 02:21 PM - 2 Likes   #7
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Thanks folks. Based on this input I won an "A" auction instead of an "M" auction and came out cheaper too!
11-14-2018, 03:00 PM   #8
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I love the build feel of the M series over the A. Even my A 50 1.4 feels cheaper than any of my M lenses.

11-14-2018, 03:18 PM   #9
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Aperture ring lore

I have used my M 50 1.7 lens since I bought it in the 70ís and there are firm clicks between stops. I have never heard about a problem before and Iím not going to worry about it now. The reason I like M over A is because I like picking the aperture instead of letting the camera do it automatically. I feel more in control of the outcome especially when it becomes a 35 mm equivalent of a 70 mm lens, perfect for portraits.
11-14-2018, 04:45 PM - 1 Like   #10
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I have both versions, although, as Steve, I’ve never done a 1 on 1 comparison but consider them optically equivalent.

My A version usually gets used in the A position, which I suspect most of them did throughout their life. The only real difference I feel between the aperture rings is the A version is a bit harder to turn. I suspect this is because it hasn’t been turned with regularity. It’s not difficult to remove the aperture ring to re-lubricate it, which has been done by several members.
11-14-2018, 05:54 PM - 1 Like   #11
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QuoteOriginally posted by Docrwm Quote
Thanks folks. Based on this input I won an "A" auction instead of an "M" auction and came out cheaper too!
Good for you! Actually, having the "A" feature is an advantage in many ways. The better action of the "M" version aperture ring is moot, because it is completely unnecessary to take the ring off of "A". In fact not only is there no advantage, there are many disadvantages. Of course as most of us know, there are many control features and other camera features not available when using the ring. But also, electronic control of aperture via the camera body has its own advantages. I have the "F" version, which has AF and also the "A" setting on the ring. From the specs, the "M", the "A", the "F", and the "FA" all seem to have the same optical formula.

---------- Post added 11-14-18 at 06:13 PM ----------

QuoteOriginally posted by clem Quote
I have used my M 50 1.7 lens since I bought it in the 70’s and there are firm clicks between stops. I have never heard about a problem before and I’m not going to worry about it now. The reason I like M over A is because I like picking the aperture instead of letting the camera do it automatically. I feel more in control of the outcome especially when it becomes a 35 mm equivalent of a 70 mm lens, perfect for portraits.
When not using the aperture ring, but having the "A" setting, with a camera body having electronic control of aperture via on-body controls, you can still select your apertures manually instead of the camera doing the selecting. Newer lenses don't even have an aperture ring at all. This came about back in the film era. Electronic implementation controlling aperture proved to have better exposure accuracy at certain settings, in the case of many camera bodies, over mechanical aperture control. Even true where the body could function either way. Back then, test reviews of both camera bodies and lenses often included exposure accuracy.

Your 50mm equivalent is more like a 75mm lens with a Pentax DSLR having the APS-C format. Actually, if I remember right, with Pentax it is 1.53 x which would put it at 76.5, quite close to the FA 77mm Limited on a 35mm film body.

In addition, when using a variable-aperture zoom lens, which most are, with the mechanical control, the aperture value will actually change as the lens is zoomed, no matter where you set your aperture. if you set f/5.6 it might well become f/9.5 or even f/11! With the electronic control, however, if you select f/5.6 it will stay at that value even when the lens is zoomed, unless the lens's wide open maximum is not that wide, like f/6.3 at the long end. Of course, if shooting in Av mode, the camera will alter shutter speed to preserve the exposure value, but that may not be what you'd rather have. Electronic control is even more advantageous in manual mode, so you don't have to continuously manually compensate for such change as you zoom.

Last edited by mikesbike; 11-14-2018 at 06:28 PM.
11-14-2018, 07:18 PM - 2 Likes   #12
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QuoteOriginally posted by mikesbike Quote
Electronic control is even more advantageous in manual mode, so you don't ave to continuously manually compensate for such change as you zoom.
You used the term "electronic control" several times. FWIW, there is only one lens in the history of the K-mount that supports electronic aperture control. That is the DA 55-300/4.5-6.3 with KAF4 mount where there is no physical control/actuator coupling with the camera. Control on that lens is "by wire". All others have purely mechanical control, either through an aperture ring or by the body through the actuator coupling.**

There are many advantages to using lenses supporting body-controlled aperture (you listed most) and also a few distinct disadvantages when lacks the option of a functioning aperture ring. Examples include (most) extension tubes, non-compliant tele-converters (do any support KAF4?), macro with reversed lens, mirrorless and other other adaptations, and (of course) all bellows. There are always workarounds, of course, and sometimes those require purchase of a lens with an aperture ring. Last, but not least is backward compatibility to one's favorite K-mount film camera.

A working aperture ring is a nice thing to have.


Steve


(...are we far enough off-topic yet?)


* Pentax jargon for body control of the aperture for exposure or DOF preview. This is to differentiate from "Automatic Aperture Actuation" (aka "auto aperture"), a completely different lens feature.

** The better K-mount adapters for mirrorless cameras actually provide an aperture ring that mechanically couples to lenses lacking such.
11-14-2018, 07:31 PM   #13
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QuoteOriginally posted by stevebrot Quote
...........A working aperture ring is a nice thing to have.
So, in a nutshell: An aperture ring is a beautiful thing.
11-14-2018, 11:46 PM - 2 Likes   #14
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I have both and have had multiple copies of both. The aperture ring of the A series is prone to failure, becoming rough and gritty to use and maybe even jamming the whole mechanism at some point. In my experience the A series is slightly sharper wide open than the M but despite that I usually go for the M because it's more pleasant to use due to it's superior build quality and I don't have to worry that it might break down on me. I use them on both film and digital so I need a working aperture ring on the lenses. As has already been said, if you're going to use it only on digital and without reversing it or using any extension tubes or anything, then you can leave an A lens in the A position and you won't have any problems.
11-15-2018, 02:21 AM   #15
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QuoteOriginally posted by paulh Quote
I'm pretty sure they share the same optical formula - I have both and they render almost identically. The M has better build quality, but you will need to use green-button (stopdown) metering in M mode, where the A can use all modes. The M is also limited to center-weighted metering IIRC, where the A can use all metering modes. Reports suggest the A has a weak/poorly made aperture ring although I've personally not experienced any problems. Just leave it in A and don't worry about it. My M and A50s see about equal use depending on my mood that day.
YOUR ANSWER is the Best, not sure why it should matter anyhow if the aperture is set in the A position as it should be>
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