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02-02-2018, 09:09 AM   #1
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Mamiya / Sekor SX 55mm f/1.8 - adapter advice?

Hello, could you recommend adapters for this lens to fit to a K-Mount?

02-02-2018, 10:30 AM   #2
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Moved to new thread (you'll get more answers this way )...
02-02-2018, 03:28 PM - 2 Likes   #3
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Welcome to the Pentax Forums!

The M/S SX lenses have three compatibility issues. Those are:
  • A fairly deep "lip" or overhang on the rear of the aperture ring. The lip interferes with a proper seating of the lens flange to the mount face on the body. As a result, infinity focus is compromised as well as aperture ring function.
  • There is an index "pin" just inside the "lip" that may foul the cutouts on non-flanged adapters
  • AFAIK, the SX lenses have no Auto/Manual switch to allow for manual aperture operation (required for adapted lenses on K-mount bodies)
Remedies include:
  • Grinding/sanding down the aperture ring "lip" so that the lens may seat properly
  • Removal of the index pin (may require partial disassembly)
  • Rigging the actuator pin so that it is always depressed making the lens aperture fully manual (may require partial disassembly)
There may be other approaches as well to each of the concerns. With any luck those forum members who have converted SX lenses will drop in on this thread with what has worked for them. Once modified, the lens should adapt the same as other M42 lenses.

In regards to adapters, the fall into two broad categories:
  • Flanged adapters that engage the face of the K-mount with a broad flange. This type is safe and easy to use, though with the loss of infinity focus.
  • Infinity focus adapters that fit entirely within the throat of the K-mount allowing the mount face on the lens to engage the body flange directly. The genuine Pentax-brand adapter is of this type. This type allows infinity focus.
Conventional advice on this site is a strong recommendation of the genuine Pentax adapter. It simply works without tools or risk of becoming stuck in the mount, but with the penalty of a fairly high price. While exceptions do exist, most third-party infinity-focus adapters carry a very high risk of becoming stuck in the mount of the host camera. A stuck adapter may be very difficult to remove and in worst case, might require use of a Dremel or similar cutting tool. This is the voice of experience speaking.

That being said, there are many members of Pentax Forums that successfully and happily use third-party adapters.* Their solution is to remove the retention spring from the adapter such that it no longer will lock in the mount. Most of the third-party adapters are machined such that they offer adequate resistance to keep the lens from rotating off during normal operation.**

I hope all of the above does not discourage you from using and enjoying your lens. From all reports, the SX-series Mamiya/Sekor lenses are quite good and worth using.


Steve

* Unfortunately, it may be difficult to tell the difference between a genuine Pentax adapter and a good fake. What's more, name brand (Fotodiox, Bower, Dot-Line, etc.) is no indication of quality or source.

** The genuine adapter fits loosely in the K-mount, slightly below the mount face, such that as the lens is screwed on the face of the lens mount engages the face of the K-mount with the adapter being drawn up against the (spring-loaded) body tangs to secure the lens to the body. The third-party adapters do not operate in this manner.

Last edited by stevebrot; 02-03-2018 at 04:50 PM. Reason: grammar
02-03-2018, 11:47 AM   #4
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I'm not sure if the M/S SX Mamiya/Sekor has the same issue w/ the pin as my Yashica DS-M 50mm f1.4 lens, but the option I found is the M42 > K mount adaptor with an inner flange. The inner flange presses down the pin without needing to do anything to the lens. Here's the one at Adorama.

02-03-2018, 02:40 PM   #5
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QuoteOriginally posted by mgvh Quote
I'm not sure if the M/S SX Mamiya/Sekor has the same issue w/ the pin as my Yashica DS-M 50mm f1.4 lens, but the option I found is the M42 > K mount adaptor with an inner flange. The inner flange presses down the pin without needing to do anything to the lens. Here's the one at Adorama.
Just a point of caution:

Different lenses require different levels of depression of the diaphragm pin in order to fully close to the selected aperture. The inner flanged adapter I own works fine with some lenses, but doesn't depress the pin far enough on others... so when an aperture of, say, f/8 is selected, the lens may only be stopping down to f/5.6 (for example). It's worth checking this with your own adapter and lenses to ensure you're not experiencing the same thing. It can be remedied by placing a thin metal or hard nylon washer (or two) on top of the flange before fitting the lens, but finding such a washer is easier said than done. For that reason, I've ended up carrying out reversible modifications to most of the auto M42 lenses I own.
02-03-2018, 06:07 PM   #6
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QuoteOriginally posted by BigMackCam Quote
Just a point of caution:

Different lenses require different levels of depression of the diaphragm pin in order to fully close to the selected aperture. The inner flanged adapter I own works fine with some lenses, but doesn't depress the pin far enough on others... so when an aperture of, say, f/8 is selected, the lens may only be stopping down to f/5.6 (for example). It's worth checking this with your own adapter and lenses to ensure you're not experiencing the same thing. It can be remedied by placing a thin metal or hard nylon washer (or two) on top of the flange before fitting the lens, but finding such a washer is easier said than done. For that reason, I've ended up carrying out reversible modifications to most of the auto M42 lenses I own.
Exactly. You'll see on my review of the lens that I needed to cut out a plastic washer from a credit card to make it work properly.
02-06-2018, 05:00 AM   #7
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Thank you everyone for the input and helpful suggestions. Only recently gotten into dabbling with the classic lens market, and it's a steep learning curve. This instance is most frustrating, as the front/rear elements are very pristine, given the price I paid. I purchased a Pentax smc 55mm for about the same money, that is hazed/dusted enough to show in photos. Strange racket, methinks
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