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12-09-2015, 10:09 AM   #16
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QuoteOriginally posted by jkomp316 Quote
its interesting; many people prefer A series for aperture control or m42 for lack of lever. yet i always get pushback when i suggest modifying an M series to operate in the same manner as an m42. the new china 85mm K lenses don't even have levers.
Since you always get push back, you might want to consider that the M42 experience may not be as great as you might think. I have about a dozen M42 lenses, but when they are on any of my K-mount cameras, it is for their optical characteristics, not for the ease of use. When presented with a K-mount equivalent (e.g. Super-Tak 55/1.8 vs. Pentax-K 55/1.8), the K-mount wins hands down simply because I get full-open focus without having to fiddle with the aperture ring in between shots. IMHO, automatic aperture actuation was the best thing to happen to SLR photography since the invention of the pentaprism.

As for the new China 85mm (Zhong Yi Mitakon 85/1.2?), the lack of aperture coupling and click stops is an indication of the intended market (video, to facilitate aperture-pull) and the desire for production cost savings. I don't believe that usability for still photography was a design goal.


Steve

12-09-2015, 11:35 AM   #17
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QuoteOriginally posted by elementdtlop Quote
so an M lens will automatically open/close the aperture like an A lens based on what you set the aperture to but it just won't automatically adjust aperture to compensate for exposure or meter i guess is the terminology? like an A lens? i never knew that. if thats not what this "trick" is bypassing I'm missing something.
I believe your understanding is correct. Just in case, I am wrong, the comparison between a K/M-series lens and an A-series (and newer) lens goes like this (please forgive my being pedantic):
  • Almost all K-mount lenses feature automatic aperture actuation (traditionally referred to as "auto" aperture). The exceptions are bellows, some ultra-teles, tilt-shift, and certain specialty optics. This is the feature that automatically closes and opens the iris diaphragm before and after the exposure. The aperture is intended to stay wide open except during exposure.
  • All K-mount lenses, with the exception of those lacking an aperture ring, have a "hidden" coupler that signals the position of the aperture ring to the body. This feature makes open-aperture metering in M mode and aperture-priority exposure automation (Av mode) possible on most legacy film cameras. All Pentax dSLR bodies lack support for the hidden coupler with the result that open-aperture metering with those cameras is not possible.
  • A-series and newer lenses generally have "A" contacts on the mount, which allow automatic aperture control. This is the official Pentax term for allowing aperture selection from the camera body instead of the aperture ring. This is the feature that makes P, Sv, Tv, and TAv modes possible.
  • The "M Trick" involves backing the actuator lever on the lens away from the coupling on the body such that the lens is always stopped down (fully "manual" aperture)
Having a fully manual aperture is preferred by some users. The most common use is shooting in Av mode. Since the lens is always stopped down, the body will continuously vary the shutter speed according to the light present in the frame. In practice, you stop down until you see the shutter speed you want. This is good except that manual focus with a stopped-down lens is not advisable, so the aperture must be opened/closed between each exposure for most subjects hand-held. Another common use case is for video with a "de-clicked" aperture ring where aperture-pull is being used.

QuoteOriginally posted by elementdtlop Quote
timing may be bad for your searches purposes because I've come across a bunch of m 50 1.7's usually they go for around 20-30$ at most id say on eBay. the a 50 1.7's usually go for like 30-40$. i bought and sold an A 50 1.7 in great shape (wife's stepdad happened to have one too that he gave me) for about 30$ in both cases.
My timing may very well have been off. To be honest, I was surprised that KEH had no K-mount fast 50s in stock and doubly surprised to see that eBay had almost no M 50/1.7 lenses. As for the pricing, I have noticed an upward trend in the last few years when doing price checks for inquiries on this site. Historically there has been a good selection on eBay with v. good to exc M 50/1.7 being available for about $35-$45 with good examples in the $25-$30 bracket. That is no longer the case, at least not in terms of asking price. If you recently sold an A 50/1.7 in decent condition for $30, you made for a happy buyer. I don't recall seeing any for under $50 yesterday on eBay, with most being at $65 and above.

Steve
12-09-2015, 10:23 PM   #18
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QuoteOriginally posted by stevebrot Quote
I believe your understanding is correct. Just in case, I am wrong, the comparison between a K/M-series lens and an A-series (and newer) lens goes like this (please forgive my being pedantic):
  • Almost all K-mount lenses feature automatic aperture actuation (traditionally referred to as "auto" aperture). The exceptions are bellows, some ultra-teles, tilt-shift, and certain specialty optics. This is the feature that automatically closes and opens the iris diaphragm before and after the exposure. The aperture is intended to stay wide open except during exposure.
  • All K-mount lenses, with the exception of those lacking an aperture ring, have a "hidden" coupler that signals the position of the aperture ring to the body. This feature makes open-aperture metering in M mode and aperture-priority exposure automation (Av mode) possible on most legacy film cameras. All Pentax dSLR bodies lack support for the hidden coupler with the result that open-aperture metering with those cameras is not possible.
  • A-series and newer lenses generally have "A" contacts on the mount, which allow automatic aperture control. This is the official Pentax term for allowing aperture selection from the camera body instead of the aperture ring. This is the feature that makes P, Sv, Tv, and TAv modes possible.
  • The "M Trick" involves backing the actuator lever on the lens away from the coupling on the body such that the lens is always stopped down (fully "manual" aperture)
Having a fully manual aperture is preferred by some users. The most common use is shooting in Av mode. Since the lens is always stopped down, the body will continuously vary the shutter speed according to the light present in the frame. In practice, you stop down until you see the shutter speed you want. This is good except that manual focus with a stopped-down lens is not advisable, so the aperture must be opened/closed between each exposure for most subjects hand-held. Another common use case is for video with a "de-clicked" aperture ring where aperture-pull is being used.



My timing may very well have been off. To be honest, I was surprised that KEH had no K-mount fast 50s in stock and doubly surprised to see that eBay had almost no M 50/1.7 lenses. As for the pricing, I have noticed an upward trend in the last few years when doing price checks for inquiries on this site. Historically there has been a good selection on eBay with v. good to exc M 50/1.7 being available for about $35-$45 with good examples in the $25-$30 bracket. That is no longer the case, at least not in terms of asking price. If you recently sold an A 50/1.7 in decent condition for $30, you made for a happy buyer. I don't recall seeing any for under $50 yesterday on eBay, with most being at $65 and above.

Steve

Thanks Steve. Excellent technical summary in an easy to understand language.
Regarding the price, I am going to check out some Pawn Shops during Xmas break. May be I get lucky in finding another Pentax-A 50mm f1.2 at a better price for my daughter.
12-10-2015, 04:22 AM   #19
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filling the viewfinder with light isnt a problem until after f5.6. this is the kit lens fastest speed at 55mm... 90% of my shots with any fast 50mm are at f5.6 or below. i see no need for a stop down lever here and having to spam the green button before each exposure is disruptive to workflow.

12-10-2015, 05:01 AM   #20
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I really think it is a waste of time and trouble for the M trick. This was posted years ago by someone who drilled secondary holes in the lens to prevent it from falling off, but I don't see the point of it.

When looking at manual lenses there are two real camps. Those who like K&M series lenses because you have open aperture focusing, and those who like M42 lenses because you have the availability of AV metering.

For me, I find if you meter on something close to mid grey, Paved road, tree trunk, block wall etc, and leave it until your lighting changes , shooting in manual is no big deal. We al shot this way for years with film,mwhich is much less forgiving than digital.
12-10-2015, 11:48 AM   #21
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QuoteOriginally posted by Lowell Goudge Quote
I really think it is a waste of time and trouble for the M trick. This was posted years ago by someone who drilled secondary holes in the lens to prevent it from falling off, but I don't see the point of it.

When looking at manual lenses there are two real camps. Those who like K&M series lenses because you have open aperture focusing, and those who like M42 lenses because you have the availability of AV metering.

For me, I find if you meter on something close to mid grey, Paved road, tree trunk, block wall etc, and leave it until your lighting changes , shooting in manual is no big deal. We al shot this way for years with film,mwhich is much less forgiving than digital.
Yes no retakes on films.
12-10-2015, 12:43 PM   #22
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I just thought of a use for the M trick. My Kiron 24mm f2 lens has oily aperture blades, again. I can use it without fixing it.
12-11-2015, 12:34 PM   #23
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QuoteQuote:

My timing may very well have been off. To be honest, I was surprised that KEH had no K-mount fast 50s in stock and doubly surprised to see that eBay had almost no M 50/1.7 lenses. As for the pricing, I have noticed an upward trend in the last few years when doing price checks for inquiries on this site. Historically there has been a good selection on eBay with v. good to exc M 50/1.7 being available for about $35-$45 with good examples in the $25-$30 bracket. That is no longer the case, at least not in terms of asking price. If you recently sold an A 50/1.7 in decent condition for $30, you made for a happy buyer. I don't recall seeing any for under $50 yesterday on eBay, with most being at $65 and above.

Steve
i bought mine this time of year in 2014 for 30+shipping and sold it in summer 2015 for 30+shipping so its not a matter of timing. if you watch auctions you'll see where they actually sell at. just because they are posted at that price doesn't mean they sell. those are the probably ones that haven't sold with those buy it nows at those prices bc most aren't dumb enough to pay that much. as a reference point, I've seen the 10-17's auctions sell for like 250-280 but the buy it now prices are usually at like 300-350 for used ones. if you watch the auctions you see where they actually sell at.

---------- Post added 12-11-15 at 02:37 PM ----------

QuoteOriginally posted by Just1MoreDave Quote
I just thought of a use for the M trick. My Kiron 24mm f2 lens has oily aperture blades, again. I can use it without fixing it.
i avoided the kiron made vivitar 28's because of that. thats a really good idea. you could probably get those really cheap when they have that issue. my A setting komine is still really nice but the kirons are usually like 10$ cheaper.

12-11-2015, 04:36 PM   #24
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QuoteOriginally posted by jkomp316 Quote
filling the viewfinder with light isnt a problem
I guess it depends on the definition of "problem". Stopping the lens down increases DOF as well as dims the viewfinder. At apertures f/4 and wider there is little difference when using the stock focus screen (focus sensitivity of about f/4 due to brightness optimization). At narrower than f/4 the ability to detect OOF is significantly degraded regardless of viewfinder image brightness. When using an aftermarket screen, the implications are much more severe. Most microprism focus aids black out at about f/5.6 and even the best split-image screens are struggling at f/8. The highly-regarded Canon S-type matte has too little contrast at narrower than f/4 to be usable at those apertures.

For focus confirm (green hexagon), sensor beam-splitter black-out is a problem at narrower apertures. Hint: There is a reason why no Pentax AF lens features a maximum aperture narrower than f/6.3. This also happens regardless of the amount of light that strikes the sensor. Basically, precision and ability to detect OOF degrades, but is helped somewhat by increased DOF. This may be fine for snapshots, but not good enough for serious work, IMHO.

Edit: The paragraph above may be somewhat difficult to understand. There are a fair number of articles and discussions on the Web regarding aperture limitations with PDAF. I have found the Flash animation on the Stanford University Web site to be very helpful (also very cool) when figuring out how PDAF works. From the diagram it is obvious that there are physical limits (both wide and narrow) for exit pupil size, beyond which performance will degrade.

http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.html


Steve

Last edited by stevebrot; 12-11-2015 at 05:22 PM.
12-11-2015, 04:40 PM   #25
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QuoteOriginally posted by Just1MoreDave Quote
I just thought of a use for the M trick. My Kiron 24mm f2 lens has oily aperture blades, again. I can use it without fixing it.
I will have to add that one to my mental list of use cases


Steve
12-11-2015, 04:57 PM   #26
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QuoteOriginally posted by elementdtlop Quote
just because they are posted at that price doesn't mean they sell
I saw no auctions, just buy-it-now. As I noted in a previous comment, that surprised me, though only a little.

I mentioned price and rarity data merely because those were both cited as reasons why munging an M/K-series lens is not big deal. What is not as well appreciated, particularly in regards to the M/K-series fast 50s (M 50/2 excluded) is that they were among the best quality (build and optical) lenses available at the time at their respective maximum apertures. Those qualities continue to be true to this day. With the possible exception of modern lenses selling for many thousands of dollars, the vintage Pentax product holds its own quite nicely. Given that, I don't know of too many people who would grind the rear off a 70s-era Summicron 50/2 just to fit it to a particular modern body and I don't see why anyone would do the equivalent to a M 50/1.7 whose performance is only a small notch below the Leitz product.

In my mind, a neutered K-mount lens has parts value only at resale. Just, my opinion...


Steve

Last edited by stevebrot; 12-11-2015 at 05:23 PM.
12-11-2015, 07:36 PM   #27
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QuoteOriginally posted by stevebrot Quote
In my mind, a neutered K-mount lens has parts value only at resale. Just, my opinion..
People grip about the K-mount being crippled on Pentax DSLRs. So why cripple the lens too? A mutilated K-mount lens has little value for most Pentax SLR and DSLR users. Maybe some Canon user would buy it, I sure wouldn't.
12-11-2015, 09:05 PM   #28
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the lens is already crippled by todays standards. why live with crippled metering as well?
12-12-2015, 05:21 PM   #29
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QuoteOriginally posted by jkomp316 Quote
the lens is already crippled by todays standards. why live with crippled metering as well?
From your avatar photo (hammer next to smashed lens), your values are, well, pretty obvious. As we both noted several times in comments above our opinions differ in that my take (colored by almost 40 year shooting K-mount glass and over 45 years shooting M42) is that the lens is perfectly functional to its original design and that chopping is a rather crude way to make it into something that is definitively crippled, though with dubious utility.

As for "crippled" metering...have you checked the accuracy of the stop-down metering on your camera (K-r?) lately?

BTW...I reviewed a few of your earlier posts on this same topic and from them, it appeared you that you had settled on drilling a second lock hole (a less destructive option) and was happy with that solution. Would you care to share what changed your mind?


Steve
12-12-2015, 09:27 PM   #30
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QuoteOriginally posted by stevebrot Quote
Would you care to share what changed your mind?
I can give you an entire story. My first dSLR was the ist DS and 50mm M series f1.4 my first decent lens. My best shots with it came in Av mode with one hand on the focus ring and the other on the shutter. This offered the least distractions for me to immerse myself in the shot. I really liked the depth of field work but had a hard time with how shallow f1.4 is wide open.

Frustrated by the manual mode requiring the green button I wanted a way to shoot Av around f2.8. I tried the hole method but ended up filling it back in with JB weld because I didn't like the less confident snap onto the body. I really thought hard about modifying the body to not engage the stop down lever... I settled on modifying the lens instead as it only cost $50 on eBay.

I tried the Takumar 50 but disliked the yellowing and couldn't find a reasonably priced 8 element version that wasn't worn out. My viewpoint was further reinforced by the fact that every Takumar lens is missing this stop down lever anyway. I don't shoot film and I know people who have/do will disagree with my approach, but is has helped me capture better shots and it works well for me in practice.

Majority of my work beyond f4 I am shooting at infinity anyway. This opened up an entire new realm of disassembling lenses and adjusting the infinity stop as most are off as well. The avatar pic is from a cheapo zoom that had cemented separation. I have since learned and fixed a prime with this issue using mineral oil instead of cement. Anyway, this forum is great for information and I have learned quite a bit in the past years. Cheers!
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