Front focus question --

rfaspen

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OK, I've been using my film Ms and M8 happily for a while, but for reasons due to crop factor, I got an M9. I will let go of the M8 soon...but....

The M9 has serious focusing issues. After a lot of frustrating "testing", I find that nearly all of my lenses focus farther out than my subject (that which I focus on in the rangefinder). The worst offender is my favorite lens -- v4 summicron 50/2. However, almost all of my lenses exhibit this behaviour to some extent. Although my Canon LTM 50/1.4 (adapted to M) is almost spot on, odd.

All of my lenses focus quite well on the M8 and film Ms (including the Canon 50/1.4). So, I'm guessing a rangefinder problem in the M9. I don't know why the Canon works in the M8 and M9.

*My question: What does it mean if my lenses front focus more at farther subject distances than at close distance? For example, my summicron front focuses about 1 to 2 inches beyond the subject when the subject is at 1m from the camera. The same summicron front focuses 2 to 10 feet when my subject (that I focus on in the rangefinder) is at 30 feet. I'm hoping this behaviour provides some hint at exactly what is wrong with the rangefinder mechanism in the M9.

In addition, with most of my lenses I cannot get the rangefinder to reach infinity. In other words, I rotate the lens focus all the way to infinity (as marked on the lens), but the rangefinder images don't reach coincidence. The greatest difference between lens infinity and image non-coincidence happens with my summicron. For some reason I fully reach coincidence at infinity with my Elmarit 90 (old version). All of my other lenses are somewhere in between.

Other lenses in this case are M-Rokkor 90, Biogon 35/2, Canon 50/1.4, Canon 50/1.8, CV 35/2.5, and I guess that's all I've tested so far.
 
Hi, i think you have to adjust the RF in your M9, with little allen wrench you can doi it easily. It´s far easier than changing a flat tire.
 
I'm coming to that conclusion (I need to adjust the RF mechanism).

***I'm just wondering what the pattern of increasing front focus with increasing camera-to-subject distance indicates? Is this an expected pattern if I have a mis-adjusted RF mechanism? ***

In other words, is this the symptom of a typical need for adjustment, or is it some perplexing pattern that indicates something way more wrong than a simple RF misadjustment?

I might not be describing the pattern well....I'm also not sure if "front focusing" is the correct term -- when I focus on a subject, the actual focus is always further out, the amount that its further out increases as my subject distance increases. When I focus on somthing 20 meters away, the actual plane of focus is almost 25 meters away. When I focus on something only 1 meter away, the actual plane of focus s about 1.04 meters out -- another 4 cm farther than I was focusing.

Needless to say, its frustrating when I can't focus correctly. My M8 was always perfect. With the sonnar, I had a predictable back focus, but that's something else entirely...
 
I believe you're describing back focus. The actual point of focus is behind the subject. If it was front focus, it would be in front of the subject. I.e. if you focused on someone's eyes but the actual point in focus in the image is the tip of their nose...

My experience has been that it's typically non-linear, where it's minimal at near distances but more noticeable at far distances.
 
First is to align RF, then you may perform some tests with a ruler.
Focus shift is something that non aspherical fast lenses have.

Good luck
 
The M9 has serious focusing issues. After a lot of frustrating "testing", I find that nearly all of my lenses focus farther out than my subject (that which I focus on in the rangefinder).

As mentioned earlier, that's back focus.

In addition, with most of my lenses I cannot get the rangefinder to reach infinity.

An RF patch that falls short of correctly overlapping at infinity will cause back focus. So assuming the rangefinders in your M8 and film M rangefinders reach infinity with each of your lenses, the problem is definitely the M9. Time to send it in for an RF adjustment.

Focus shift is something that non aspherical fast lenses have.

And aspherical fast lenses too!
 
An RF patch that falls short of correctly overlapping at infinity will cause back focus.

I had the similar problem with M4-2 (RF patch not correctly overlapping at infinity) but it was front-focus in my case.

I think with respect to correct RF patch overlapping at infinity there are two possibilities, either the moving patch does not fully reach the fixed patch or there is some kind of over traveling, means the moving patch travels farther than the fixed patch.
 
I think with respect to correct RF patch overlapping at infinity there are two possibilities

Yep, agreed!

either the moving patch does not fully reach the fixed patch

By "falls short", I meant this first possibility which is what I understood the OP to mean with his comment "with most of my lenses I cannot get the rangefinder to reach infinity".
 
Yes, the moving patch never fully reaches and coincides with the fixed patch. It comes closer or not depending on the lens that's mounted.

I suspect I need to adjust my infinity rangefinder adjustment. Directions to be found here and elsewhere, but I need to know if I'm experiencing front-focus or back-focus. I'm definitely confused as to which is which.

Thanks for everyone's comments.
 
Think about it like this: If the Rf patch doesn't reach infinity, every time that you focus, you have to "over focus" for the patch to coincide. Meaning you make the lens shorter than it should be. Meaning it will back-focus, I.e. focus behind the subject.

So, your back-focus observation is consistent with the patch never overlapping at infinity. Pick your favorite lens with most shallow DOF and align the patch at infinity - best with a magnifier if you have. Focus on a star at night, for instance.

Lens compatibility on digital Leicas is a myth. Most LTM lenses focus differently than M lenses, Canon different from Nikkors, Leica lenses different from CV lenses, etc., and god knows who adjusted a used lens before you bought it on eBay.

So you either make sure that your favorite lens focuses right and get to know how to adjust other lenses in use, or calibrate all your lenses.

Roland.
 
Yes, the moving patch never fully reaches and coincides with the fixed patch. It comes closer or not depending on the lens that's mounted.

I suspect I need to adjust my infinity rangefinder adjustment. Directions to be found here and elsewhere, but I need to know if I'm experiencing front-focus or back-focus. I'm definitely confused as to which is which.

Thanks for everyone's comments.

just think where is the shot actually in focus behind or infront of where you focused with the rangefinder. back or front focusing.
I adjusted my M9 myself biased to shooting at about 2-3 meters, my most used lens is a 35mm summicron so even if the RF is off further away I would never notice and by happy coincidence all my lenses focus spot on. Its not difficult to do but its also not expensive to get a good local repairman to adjust.
 
Stand at a 45 degree angle to a bookcase and focus on one of the book spines. You'll quickly realize what front and back focus means by seeing where the focus falls on the neighboring books, i.e in back of or in front of the book you focussed on.
 
Thanks everyone. I learned something and have a strategy I will implement later today. I'll report success or....the need for another strategy.
 
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