[redrockcoulee]

Does your M42/K adapter have a wide flange? That type does not allow infinity focus. The reason is that M42 and K-mount have the same registration distance to the mount face. To get infinity focus you will need an adapter that fits fully within the mount such as the genuine Pentax adapter in the photo below:



The genuine Pentax adapter is strongly recommended over similar-looking brand-x product due to the tendency of the latter to become stuck on the camera. Brand-X may be used if the retention spring is removed. This leaves the adapter free to rotate in the mount, but many users on this site find that to be an acceptable compromise.


Steve

My Pentax brand adapter usually gets stuck onto my camera. 😑

[stevebrot]

My Pentax brand adapter usually gets stuck onto my camera. ��

I have heard of that, though it usually requires damage to the spring on the genuine adapter and/or the spring-metal catch in the mount. Either can happen if excessive torque is applied in the counter-clockwise direction with the adapter in the mount or if someone has manually bent the retention spring at some point. Damage to one or more of the bayonet tangs might also cause the adapter to jam. The key is that the adapter is supposed to fit fairly loose in the mount when a lens is not attached and should rotate into position when inserting with little resistance or drama.

I have also heard (recently on this site) of adapters being inserted inverted into the mount (hard to do, but possible) and becoming stuck as well as lenses that can be successfully mounted when attached to the lens, but cannot be unscrewed to removed due to a projection on the lens barrel interfering with the body.


Steve

[redrockcoulee]

I have heard of that, though it usually requires damage to the spring on the genuine adapter and/or the spring-metal catch in the mount. Either can happen if excessive torque is applied in the counter-clockwise direction with the adapter in the mount or if someone has manually bent the retention spring at some point. Damage to one or more of the bayonet tangs might also cause the adapter to jam. The key is that the adapter is supposed to fit fairly loose in the mount when a lens is not attached and should rotate into position when inserting with little resistance or drama.

I have also heard (recently on this site) of adapters being inserted inverted into the mount (hard to do, but possible) and becoming stuck as well as lenses that can be successfully mounted when attached to the lens, but cannot be unscrewed to removed due to a projection on the lens barrel interfering with the body.


Steve

Thanks, it is the adapter as multiple cameras have been tried. Good thing only one screw mount lens

[Bui]

Stopping down to f/8 shouldn't be necessary. What you are doing there is expanding the depth of field to the point htat it includes infinity, but you should be able to capture infinity in focus even at 1.4.

Here's a thread showing disassambly of this lens:

https://www.pentaxforums.com/forums/114-maintenance-repair-articles/208537-su...ssasembly.html

You are only interested in the first three photos.

First, remove the name ring using a rubber tool and turning counter clockwise.

Then remove the screws holding the front barrel in place

This exposes the three screws holding the focus ring, which has the infinity stop on it, to the inner focusing helicoid.

The easiest way is to mount your camera to a tripod, put it on live view, and point it at a very distant object, and set the focus ring to infinity.. Loosen but do not remove the three screws on the helicoid. This will allow the outer focus ring to rotate freely. Rotate it back a bit and tighten one of the screws. Now turn the focus ring until the very distant object just comes into focus. Loosen the screw you tightened, rotate the ring back to infinity, and tighten the screw back down. Check to make sure infinity is correct, and repeat if necessary. Once you are sure it is correct, reassemble the barrel and name ring, and you are done.

With practice, the whole process only takes a couple of minutes. The photos above show a Super Takumar, which has flat head screws.

Since yours is an SMC, it is likely to have JIS screws, which are easier to work with, but which require a special driver. You can find JIS drivers cheaply on Amazon, eBay, etc. Regular Phillips drivers run the risk of stripping the screw head, since they have a differently angled tip.

Thank you. Sound like an excellent way of fixing it, and also would be nice to have infinity focus at large aperture. However that would require an amount if courage, I will see if I can do that (I already broke some toys of my daughter trying to fix them)

I will tell you if I make it

[Bui]

This seems too be a little bit more complicated than I thought. I couldn't even removed the front name ring in the 1st step, it was too stubborn. I had to wait until weekend to try some other methods with success. Now I'm stuck again and need your advice.

Reading disassembling guide from your link and some others, I expected to see some screws just under the name ring, however that is not the case. There were indeed 3 screws I can see, but they are very deep and narrow cleft. I also notice the ring holding the glasses has two "split". I attach a photo here. Now before I go on blindly and break this beauty of a lens, I would like to ask you:

- In red, the 2 "split": do they have a function and do I have to do anything with them?

- In green: or I just need to find a very tiny yet long screwdriver to try to unscrew them, ignoring the split?

Thank you very much in advance for your help. Best.

Edited: this one is the S-M-C 135 3.5 not the S-M-C 50 1.4

[Jonathan Mac]

The 50/1.4 is good but not as good as it's reputation suggests and it's not worth the high price it usually sells for. If you want a very good quality 50-ish lens in M42 mount I'd suggest the Takumar 55mm f/1.8 or f/2 (they have the same optics) - they're just as good as the 50/1.4 except in sheer speed and sell for around a third of what the 50/1.4 does. I recommend selling the 50/1.4 and buying a 55/1.8.

However, the M 50/1.7 is just as good as the Takumar 55/1.8 so if you don't need both then stick with what you have.

[Bui]

I'm liking my 50 1.4 more and more, but yeah with my limited experience I can not tell to what degree of greatness it is. Perhaps it is not worth the >100$ price but I paid 1/3 of that amount for it so I'm not rushing. I will try to find a cheap 55 to see if it is as good as you advised :-)