[lotech]

Hi there, here is my 2cents...

I am using the K3, and I play with m42 lenses, Russian made mostly as they are low cost but not 'cheap', I always have problem with the adapter, those 'flush fitting' adapter that allows infinity focusing is hard to install and remove, quite trouble when I need to change lenses in middle of shoot, so I decided to stick with the non flush type, but I only able to do close focusing then, there is exception with mirror lenses, as they focus pass infinity (compensate for temperature change), more than enough to offset the adapter thickness.

Just recently I pick up a Jupiter 37A, which is a very sharp 135mm lens, with non flush fitting adapter I can only focus to about 20m, after looking at the inside of the lens I found a simple way to push the 'infinity lock' further, and this is completely reversible, but by doing so the focus scale will become out of line, I think that wouldn't be a problem, as we will focus by eye or use AF assist anyway !

Here is how to do it 'at your own risk !'

Simply remove the m42 mounting at the back of lens which locked by 3 screws, after that you will see two L-bracket at the sides of the lens assembly, they are used to limit the optical block from completely unscrew from the lens body. Remove only the 4 screws that holding the L-brackets, then turn the focus to the far end, so that the L-brackets shifted by one hole, that little adjustment moves the optical block further to the focal plane, thus bring the lens into near infinity focus. Put back only one screw at both L-brackets, or you can drill holes for the other screws but not necessary, put back the m42 mounting that's all !



I am still looking for ways to adjust my Mir 1B, Pentacon 30mm/3.5 and Pentacon 135mm/2.8 any idea ??

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[elektrolitr]

I corrected the infinity position another way, which is even simpler and 100% reversible (providing you haven't lost the shims)

I'll use photos made by Шпигель from russian Pentax forum to describe:

First of all, remove the mount by unscrewing three screws

Lens will look like that:


Unscrew the nut marked "2"

Next, take the lens at the front end with one hand and near the rear end with other hand and simply pull around: the lens will disintegrate into two halves and several smallish details:



As you can see, there are several shims (marked by red on the left) and stopper pin (marked by red on the right)

The pin itself (to the right side of the lens)


My particular lens had 2 0.5mm aluminum shims and 3 or 4 0.1mm brass shims. Each lens can have different number of shims. I removed one alu and 3 brass shims which made 0.8 mm correction to compensate for my particular adapter.

The only difficulty when assembling the lens is to put the stopper pin into it's place. I put the lens unit on the table, placed the pin into it's hole, put the helicoid block over and rotated until pin went into place.

It's possible that your lens doesn't have enough shims to remove, but it's worth to try this method before making more radical ajustments.

[lotech]

Thanks for the tip, I think this way you can keep the focus scale align

[elektrolitr]

Yes, that way the focal scale isn't affected.

[IgorZ]

What kind of adapter are you using? I haven't noticed infinity focus problem with my Jupiter 37

[elektrolitr]

Just like topic starter, I use adapter like that:



I have separate adapter for each my m42 lens, which all are infinity-corrected. These adapters are always on the lens. In fact, these lenses became K-mount lenses, they just do not have aperture coupling (which is good, because I don't need to use green button for stop-down metering).