Carl Zeiss Jena 2.8 135mm MC Infinity Focus

[cuivenion]

I have recently bought this lens and a Praktica B adapter for use with a Canon 500D. It won't reach infinity focus even though the adapter is supposed to allow this. The vendor has offered a refund but I'm wondering if the lens is at fault. Is it possible to adjust the infinity focus on this lens and if so how?

[cuivenion]

This is Vega as close to infinity as I can get:

[michael.h.f.wilkinson]

Odd. I have several Contax lenses with adapters for Canon EOS which reach infinity without issue in non-modded cameras. As a M42 threaded lens can be adapted to C/Y mount and reach infinity, it should be possible to reach infinity with an adapter from M42 to EOS mount. However, in my modded camera I think I need to insert e.g. a CLS or clear clip filter in order to reach infinity focus. Maybe that is the problem

[ronin]

I suspect the problem is the adaptor as it must add even a small amount of distance to the mechanics. So I can see why it will not manage it. I assume that closer things do come into focus. Equally they usually build the lens with additional travel beyond the infinity position. In which case a converter simply eats into that buffer.

I do like the image of Vega, think it is great. Even if not as it should be.

Not sure if the lens can be adjusted to achieve focus with the adaptor, actually doubt it can, as it is not a simple case of moving the location of a single lens location.

Is the converter the only one available? If there are alternatives I would spend an evening on google searching out all comments.

[cuivenion]

Hi Michael, thanks for the reply. My 500D is unmodded. This is a Praktica B lens not M42. As far as I can tell I'm running out of focus moving in towards the camera. Addiing a filter would move the lens out and make the problem worse wouldn't it?

[cuivenion]

2 minutes ago, ronin said:

I suspect the problem is the adaptor as it must add even a small amount of distance to the mechanics. So I can see why it will not manage it. I assume that closer things do come into focus. Equally they usually build the lens with additional travel beyond the infinity position. In which case a converter simply eats into that buffer.

I do like the image of Vega, think it is great. Even if not as it should be.

Not sure if the lens can be adjusted to achieve focus with the adaptor, actually doubt it can, as it is not a simple case of moving the location of a single lens location.

Is the converter the only one available? If there are alternatives I would spend an evening on google searching out all comments.

Hi Ronin, yes closer objects do come into focus and the adapter does add distance. There are adapters that have a lens to change the infinity focus position, but they are very expensive and the lens is not always good quality. I have read that sometimes the infinity focus in lenses changes over time and needs recalibrating. I was hoping someone could point me in the right direction.

[michael.h.f.wilkinson]

10 minutes ago, cuivenion said:

Hi Michael, thanks for the reply. My 500D is unmodded. This is a Praktica B lens not M42. As far as I can tell I'm running out of focus moving in towards the camera. Addiing a filter would move the lens out and make the problem worse wouldn't it?

A glass clip filter does not change the mechanical light path (distance between lens and chip or film plane), but can shorten the effective optical light path by about 1/3rd of the physical thickness of the glass. I found that my Contax lenses did not quite come to infinity focus in the modded camera, although they did in its non-modded twin. Inserting the clip filter sorted this.

[michael.h.f.wilkinson]

17 minutes ago, ronin said:

I suspect the problem is the adaptor as it must add even a small amount of distance to the mechanics. So I can see why it will not manage it. I assume that closer things do come into focus. Equally they usually build the lens with additional travel beyond the infinity position. In which case a converter simply eats into that buffer.

I do like the image of Vega, think it is great. Even if not as it should be.

Not sure if the lens can be adjusted to achieve focus with the adaptor, actually doubt it can, as it is not a simple case of moving the location of a single lens location.

Is the converter the only one available? If there are alternatives I would spend an evening on google searching out all comments.

Adding distance is not a problem as long as the flange to film (or chip) distance in the lens mount is larger than that of the (fairly short) flange to chip distance in the EOS

[cuivenion]

It's looking like it might be best for me to sell it, and stick to M42 lenses. The clip filter costs about twice what the lens cost.

[michael.h.f.wilkinson]

Various sources suggest infinity focus should be possible. Maybe there is an issue with the lens

[cuivenion]

Just now, michael.h.f.wilkinson said:

Various sources suggest infinity focus should be possible. Maybe there is an issue with the lens

Thats what I was thinking, I have no idea how to adjust the infinity focus for this lens though. I've read it can be done on other lenses. I've googled this quite a bit but I keep getting hits for the M42 3.5 lens.

[Alien 13]

There is sometimes adjustment screws that set the end stop under the rubber grip, I know some of my M42 lenses had to be tweaked to get infinity focus.

Alan

[cuivenion]

7 minutes ago, Alien 13 said:

There is sometimes adjustment screws that set the end stop under the rubber grip, I know some of my M42 lenses had to be tweaked to get infinity focus.

Alan

Thanks there are four philips head screw I can see when I turn the focus. There's three larger and one tiny one. Not sure how to proceed though, I don't want to wreck the lens.

[Knight of Clear Skies]

Just to add to the above, my modded 1100D will reach infinity focus with a large number of lenses as it was re-shimmed for this purpose. Many modded cameras aren't re-shimmed when modded, so may only be suitable for use with a telescope or lenses with plenty of travel past infinity, such as modern auto-focus lenses.

I've also found that some adapters are thicker than others.

48 minutes ago, michael.h.f.wilkinson said:

A glass clip filter does not change the mechanical light path (distance between lens and chip or film plane), but can shorten the effective optical light path by about 1/3rd of the physical thickness of the glass. I found that my Contax lenses did not quite come to infinity focus in the modded camera, although they did in its non-modded twin. Inserting the clip filter sorted this.

Thanks for clearing this up, there has been a lot of confusion in the past about whether a clip-in filter can help lenses reach focus.

[cuivenion]

I think I may have sorted it out. There are three screws on the focus indicator ring (the one with the focus range in feet and infinity). when I loosened them I could move this around and the focus now seems to go slightly past infinity. Just what I want. Much easer than I was expecting to be honest. I'll have to test on Vega again or the moon if I get a chance.

[Knight of Clear Skies]

Good to hear. I have a couple lenses I'd like to adjust so I could use them on one of two cameras, but have always been a bit scared to do so.

[cuivenion]

Here we go, this is focus at the infinity stop now:

And this is a few millimeters before the stop:

So hopefully I'll be able to get stars and the moon in focus now. The images were resized to 1280x960 for the net.

[Alien 13]

54 minutes ago, Knight of Clear Skies said:

Good to hear. I have a couple lenses I'd like to adjust so I could use them on one of two cameras, but have always been a bit scared to do so.

You are normally ok provided you loosen screws and do not remove them. I have found though that a lot of M42 lenses never seat fully on the adapter and you can gain a mill or so by slightly filling away the inner rim of the adapter (use a cheap one).

Alan 

[cuivenion]

On 7/12/2017 at 16:22, Alien 13 said:

You are normally ok provided you loosen screws and do not remove them. I have found though that a lot of M42 lenses never seat fully on the adapter and you can gain a mill or so by slightly filling away the inner rim of the adapter (use a cheap one).

Alan 

Just to add that with my lens I loosened the screws moved the ring and then tightened them again once the ring was in position. I gather it can be more complex for other lenses though.

[Alien 13]

5 minutes ago, cuivenion said:

Just to add that with my lens I loosened the screws moved the ring and then tightened them again once the ring was in position. I gather it can be more compex for other lenses though.

The adjustment does seem to vary a lot between lens types and manufacturers some are easy others virtually impossible. With the lenses I have managed to set I have them just past the infinity setting so that you can still see slightly unfocused stars in live view, go too far and they disappear.

Alan

[MARS1960]

I had one of those lenses, infinity is achievable providing you can find a thin enough adapter, there was only one company i found that that did the correct adapter for my canon.

[cuivenion]

7 hours ago, MARS1960 said:

I had one of those lenses, infinity is achievable providing you can find a thin enough adapter, there was only one company i found that that did the correct adapter for my canon.

It's sorted now, I tested it the other night. It's slightly over focused at infinity and stars come into focus just before the stop.