Focus question Elmarit -M 90

[Julius Bjornsson]

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Hi there,

 

I just got a 90 mm Elmarit f 2.8. used. As I am no expert on used lenses I gambled with this one and as it looked very good and I could not see any scratches or dust inside or anything I bought it. But now I am not sure if it works ok as I am having trouble focusing it and suspect that it has some backfocus, although I am having no trouble with my other three lenses. ( 28 Elmarit-M asp, 50 Summicron and 35 Voigtlander P-II).

 

The focus point appears to be behind where I am focusing on the 90 i.e. further away, I suppose this is the so called backfocusing.

 

So here come my questions.

 

1. Is it possible that this one lens (the 90 Elmarit) has backfocus when the others I have do not?

 

2. What procedure can I use to be certain of this, i.e. how should I test for this in a reliable way.

 

3. What aperture should I be using, it appears to me that the lens is best at f. 8.0 or below but that could be because that gives a longer DOF and is a little strange as I have read somewhere that this lens should be best at f 4.0.

 

Any recommendations greatly appreciated.

 

JKB

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[marknorton]

Are you using a focus magnifier? This is recommended for lenses of 50mm and up.

[Julius Bjornsson]

Yes I am using the 1.25 magnifier. But I must admit my glasses need updating too.

[Philippe D.]

Hi Julius,

Is it possible that this one lens (the 90 Elmarit) has backfocus when the others I have do not?

Or your M8 have BF, like many other.

And you see this stronger with a tele lens.

I had it with Cron 90AA, Lux 75, and in some extend with a Lux 50 too.

Self made cure on body.

[luigi bertolotti]

Hi Julius,

I also have an old 90 2,8 (maybe not exactly like yours... it's a Tele Elmarit, not an Elmarit) and is the only lens that gives me some focusing issue (for instance, the Tele Elmar 135 is all OK). It happens at short distances (< 3 meters about) and I attach a typical example; I was at 1,5 meters about, f4, and focused on the center of the rightmost mushroom :

 

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Enlarging, it's clear that focusing is better at a lower distance than the theoric one...I'd say 4 or 5 centimeters (I was in angled position respect to the soil)

 

 

I decided that... doesn't hurt too much most of the times... I simply try to shot with this lens a bit closed... at f8 I do not note focusing issues; it's a very old lens... and I do not chase for extra aperture on a 90... and I will read with attention the tests on the new Summarit when it will arrive.

[luigi bertolotti]

Sorry, I cropped but did not enlarge ... seem to me is clear anyway what I mean.

[Julius Bjornsson]

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ok so how do I do a simple test for backfocusing in order to determine if I need to send the camera in for adjustment? Luigi, my problem appears to be the opposite of yours, my focus point seems to be behind (further away) where I am focusing, not in front as in your example.

 

JKB

[kahner]

I'm not a very friend of testcharts, but it is a way to find out if there is anything going wrong.

An explanation and the chart at the last but one side can be found here.

OK its an explanation for SLRs, but its possible to take the test for Rangefinders, too.

 

Ralph

[Julius Bjornsson]

I'm not a very friend of testcharts, but it is a way to find out if there is anything going wrong.

An explanation and the chart at the last but one side can be found here.

OK its an explanation for SLRs, but its possible to take the test for Rangefinders, too.

 

Ralph

 

Thanks I will try this and let you know.

 

JKB

[garygsandhu]

Try focusing on the same point from infinity and from near, without rocking the focusing ring back and forth, and see if that makes a difference.

[Julius Bjornsson]

Hi all and again thanks for all the advice. I have now experimented a little with the testchart and find that my camera has slight backfocus which is not a problem with all my lenses, except the 90. There I have to stop down and/or take great care if at higher apertures with a narrow DOF. So I will give this a try for some days, but if I do not get used to this the camera might have to be sent in for adjustment.

 

Thanks again,

 

JKB

[carstenw]

You might want to try tweaking the rangefinder wheel, if you are comfortable with this type of adjustment. Use a 2mm Allen key to very slightly turn the wheel in both directions until the backfocus with the 90 is gone. It is quite possible that the 90 is the only lens which will focus differently, the others being more tolerant, and you could save yourself a trip to Solms. If it doesn't fix it, you lost nothing.

[Julius Bjornsson]

You might want to try tweaking the rangefinder wheel, if you are comfortable with this type of adjustment. Use a 2mm Allen key to very slightly turn the wheel in both directions until the backfocus with the 90 is gone. It is quite possible that the 90 is the only lens which will focus differently, the others being more tolerant, and you could save yourself a trip to Solms. If it doesn't fix it, you lost nothing.

 

Thanks Carsten, this is exactly what I have been doing now for the last 2 hours, tweaking, running outside to check infinity, shooting the test chart, adjusting, running outside. etc. BTW my wife came to me after an hour of this and asked me if anything was wrong, and why I was running outside all the time, if I was ok or what. She had never seen behavior like this on a sunday morning. LOL.

 

But I think I have got it now, the rangefinder appears to be correct at infinity, but there still remains a very slight backfocus at the biggest aperture on the 90. But I will contine testing this and doing very small adjustments. I find that you have to be very careful in adjusting as the smallest movement of the adjusting screw will have an effect. Hopefully I can avoid the Solms trip, would hate to be without my camera for the time that takes.

[luigi bertolotti]

You might want to try tweaking the rangefinder wheel, if you are comfortable with this type of adjustment. Use a 2mm Allen key to very slightly turn the wheel in both directions until the backfocus with the 90 is gone. It is quite possible that the 90 is the only lens which will focus differently, the others being more tolerant, and you could save yourself a trip to Solms. If it doesn't fix it, you lost nothing.

 

Carsten, you've convinced me to try the test and, above all, to take on the Allen key and operating on the RF wheel... brrr.. in 25 years of RF Leicas I NEVER dared to touch a delicate screw... Just a final question before I try... is there any risk one gets fooled at all ? I mean, are you SURE that if I get some confusing result (to say, OK the 90 but that 135 less good than before, the 50 OOF... I fear these instances...) you can revert to "all as before" simply positioning the wheel to the initial setting ?

Thanks in advance... I already saved, time ago, the posted pics which detailed the operation.

[Julius Bjornsson]

Ok guys, now I am having problems with this procedure. I am tweaking with the allen key and the problem is that when I get the 90 right, the 50 does not appear to go all the way to infinity. So I adjust for the 50 and then the 90 is out of adjustment at infinity. When the rangefinder shows correct focus the lens is out of focus and vice versa. So please some good advice, I have already been at this for a few hours and am getting very frustrated with this.

 

JKB

[Etruscello]

Julius --

I have the same problem with my 90 Cron. I chose not to fiddle with the M8 body. I use what I call my "smidge-to-the-right" technique. Reset your M8 to its original position and try the following. Focus your 90 as you normally would. Then, turn the focus ring to the right just a smidge (toward the shutter button for closer focus). If you don't understand my technical term "smidge," it means the smallest amount you can turn under your fingers muscular control. That'll be about 1 mm. You'll be surprised how well this seemingly imprecise method works. (Relax about it -- don't try to make it exactly 1 mm.)

Try it by taking a portrait (self in mirror is OK). Focus on the eye lashes. Take the first image with normal focus. Take a second image with just a smidge of a turn to the right. The second image will be just the one you wanted from your 90.

If this doesn't work for you, send the lens to Leica or DAG for back-focus adjustment. That's better than playing with the M8. That way, your perfect lenses won't be effected. Just work on the back-focused lenses. By the way, your 90 probably works fine on a film M. Film has greater flatness tolerances than a sensor. Good luck. Tom P.

[Etruscello]

PS

To be clearer:

My 90 has a back-focus problem. If your's is a front focus problem -- use the smidge-to-the-left technique (not right). Good luck.

[Jamie Roberts]

Julius,

 

The problem is you don't know if your 90 was in spec when you started messing with the rangefinder.

 

Personally, if I had one lens that was off and the rest were ok, I'd be getting that lens adjusted, not the camera.

 

I don't know what other lenses you have, but if the 50 is the newest etc... then adjust for that one and make sure your other lenses are all ok up close and at infinity.

 

Then get some one good to look at the 90.

 

You can drive yourself nuts with the allen key In my case, all my lenses were backfocussing about 2 inches up close; the allen key fixed them but I still had to have a 75 Lux adjusted for back focus.

 

The technician--who is exceptionally good btw--said my new (used) mint 75 lux could not acheive infinity focus. So he fixed it

 

(that's Gerry at Kindermann Canada, folks. Cost about $75 to fix).

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[Julius Bjornsson]

Julius,

 

The problem is you don't know if your 90 was in spec when you started messing with the rangefinder.

 

Personally, if I had one lens that was off and the rest were ok, I'd be getting that lens adjusted, not the camera.

 

I don't know what other lenses you have, but if the 50 is the newest etc... then adjust for that one and make sure your other lenses are all ok up close and at infinity.

 

Then get some one good to look at the 90.

 

You can drive yourself nuts with the allen key In my case, all my lenses were backfocussing about 2 inches up close; the allen key fixed them but I still had to have a 75 Lux adjusted for back focus.

 

The technician--who is exceptionally good btw--said my new (used) mint 75 lux could not acheive infinity focus. So he fixed it

 

(that's Gerry at Kindermann Canada, folks. Cost about $75 to fix).

 

Thanks this is the situation now, I have adjusted for all the other lenses and they are ok and the 90 is backfocusing. Have to get that fixed. You are also right, this was almost driving me nuts, so I stopping now with most of my lenses ok.

 

Thanks for all the advice.

 

JKB

[Etruscello]

Julius,

Before you have the 90 fixed, try my smidge-to-the-right method (post above). I'm curiuos if it works as well for you as for me. Tom P.