Focus shift through apertures

[danedit28]

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Brand new 50mm Summicron on brand new Leica M-P.

 

At f/2, the 50mm is spot-on focus through the rangefinder. At f/2.8, f/4 and beyond, the focus through the rangefinder is back-focusing.

 

I can confirm this through the LiveView with focus assist. I'm aiming a ruler angled away toward infinity and at f/2, LiveView matches the rangefinder focus spot-on. As I roll through the aperture ring on the Summicron, I can see the focal plane shift back up to about a full half-inch and the LiveView focus no longer matches the rangefinder.

 

What could explain this? Is it the lens or the camera or both?

 

Thanks in advance for your thoughts,

-dan

[TomB_tx]

Nearly all "fast" lenses have some amount of focus shift as stopped down, if you look closely enough. I have versions I-IV Summicrons, and testing on tripod on M9 to look for this, they all show it, but I've used some since 1969 and never found it to be a problem in actual use.

The models I have from the 1950s -70s came set to be spot-on at about f2.8, so shifted slightly in both directions, instead of all in one direction. I believe that was intentional by Leica.

I don't have the new APO Summicron Asph, but every 50 of f2 and faster I've tested of every make I have (including SLR Canon, Nikon, Pentax, Minolta, etc.) shows the same effect to some extent.

I quit worrying about it.

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[danedit28]

I'm sorry I cannot accept this as a standard, but it appears from reading through the extensive threads on this site that this is a common observation. F/2 is good, and everything else goes to sh*t.

 

Given the situation, how do you get accurate rangefinder focus at f/4 on a 50mm Summicron? My shots are coming out back-focused and I feel like I didn't experience this issue when I used to shoot with a 50mm Summilux.

Edited September 25, 2014 by danedit28

[jaapv]

Which 50 Summilux? All but the asph shift more than the Summicron does.

It is rare to see a complaint about focus shift on a Summicron. But yes, there is a minimal amount.

[Photomek]

A few months ago I've bought a used Summicron-M 2/35 Asph with the serial number 406xxxx and after some use I've found out, that it has considerable focus shift from f/2.8 up to f/8. I've send the lens to Leica and after an in-depth examination they have confirmed the problem. A week later I've got my adjusted lens back and now it's focusing fine at all apertures. I had to pay nothing.

[-Lss-]

As I roll through the aperture ring on the Summicron, I can see the focal plane shift back up to about a full half-inch and the LiveView focus no longer matches the rangefinder.

 

What could explain this? Is it the lens or the camera or both?

Your thread title 'Focus shift through apertures' is the explanation. There is nothing wrong with your camera. The culprit is your lens, but there is nothing wrong with that either. It's not a "bad sample" issue.

 

Focus shift happens, because the rays of light traveling through the lens at various distances from the optical axis converge at somewhat different focal points (spherical aberration). When you change the size of the aperture, you cut some of those rays of light (from the periphery). What is in focus is basically the greatest sum of converging light rays. When the aperture blocks some of the rays, and the number of rays you consider in said sum therefore decreases, the resulting point of focus will be slightly different. Thus, you observe a focus shift.

[Lieberman]

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My Apo-Summicron 2,0/75 had been adjustend two times by Leica because of backfocus problems.

The problem was and - unfortunately still is - that there is no backfocus at close distances but backfocus increases by longer distance and is biggest at infinity. This is very aweseome because I thought that it should not be there at all due to incasing depth of field. Cam somebody explain this? Please exuse my bad English.

[thighslapper]

If you look carefully with this (and similar lenses) you usually notice that the 'front' end of the in focus area moves backwards much less than the 'rear' end of the in focus limit .....

 

If the Rangefinder is adjusted correctly .... and the lens is within spec, the movement of this band of 'in focus' will still include the focus point, although the shift will move it within the band itself..... if you are lucky ..... and not all lens/camera combos can be adjusted to do this ...... I have adjusted my M so that the Nocti 0.9f works fine ..... but because the inevitable small tolerances between lenses the likelihood if having several working like this is remote ....

 

Also ...... with the Noctilux in particular, the shift is much more marked a close range .... and tends to diminish dramatically when used at 2m+ .......

 

How often are you going to use this lens wide open at 0.7m ?

 

If the lens is ok at distance ....... RF images and infinity stop coincide and image is sharp .... and near focus is ok when compared to the LV image at 1-1.5m or so then I might be inclined to live with it.

 

The 50/1.4 is difficult to calibrate correctly due to the floating elements and there are often complaints about it being out of spec. You really need a dealer or someone with another lens to compare to tell if it is RF adjustment or the lens that is out. From what you are describing I suspect it is the Rangefinder near calibration that is out .... and that the lenses natural focus shift is allowing you to use it wide open with no problem ..... in reality it should be the reverse......

 

The 75/2 is a b*gger too...... both to adjust ...... and the focus shift wide open makes it iffy to use close-up wide open..... I have to remember to focus on a point a bit in front of the target ..... or use the EVF. Mine took 3 trips to Solms/Wetzlar before it came back ok.

 

ps. with some of the Zeiss lenses you can specify whether you want focus adjusted for wide open use or 2.8 .... either way you have to compensate for focus shift some of the time ...

Edited September 25, 2014 by thighslapper

[250swb]

I feel like I didn't experience this issue when I used to shoot with a 50mm Summilux.

 

I don't find all that much, if any, focus shift with my Summicron but how it is perceived and how acceptable you find it can vary with type of photo and whether the subject is far enough away for DOF to cover any shift. Close up subject matter can cause all sorts of problems when focus shift is added on top of the basic inaccuracy of focusing and reframing and the extremely narrow DOF. But it would be worth getting your lens checked if other lenses work accurately on your camera, it is possible to get sharp images even though the rangefinder system is a compromise when these traits rear their ugly head.

 

Steve

[danedit28]

To clarify, this issue is most evident with this brand new 50mm Summicron f/2 11826 (pre-APO).

 

At f/2 at about one meter, the rangefinder and LV agree. As I turn the aperture ring to f/2.8, the complete focal window now falls back behind my rangefinder focus point. I can no longer use the rangefinder to focus at close distance. I would be ok if the front range of the focal window stayed on the focal point while at f/2.8 but it is not and by f/4 the focal range is completely beyond my RF point.

 

EDIT:

I just did a much better test with tripod, eyepiece magnifier and bright lights on my ruler. My 35mm Summicron and 21mm SE are precisely centered and match on both the RF and the LV. The 50mm Summicron, however, is offset back across the RF point. This tells me that the M-P is ok and the 50mm should get sent back for a replacement.

 

Thanks for everyone's feedback thus far. It's been very interesting to read about the natural focus shift within a lens but it also confirms that a focus shift should at least stay on point within reason on the RF.

Edited September 25, 2014 by danedit28

[stallus]

Just to let you know:

I had the exact same problem with a 50mm summicron (early 1980).

The lens design is still the same since 1979!

I send the lens to leica service and let it adjusted for perfect focus at f 2.8

Now this lens is usable from f2.8 to f 16

 

For f 2.0 I have to compensate the resulting frontfocus now. With a little practice this could be done.

 

regards

 

Reiner

[lct]

Never got the least focus shift at f/2 (?) or f/2.8 on a 50/2 v4 or v5 so far. A bit around f/4 perhaps but it is hard to detect anyway. Here a v5 at f/4 and f/5.6. I would rather check if the camera or the lens needs a good CLA. FWIW.

- f/4.0 (6 MB file)

- f/5.6 (6 MB file)

[k-hawinkler]

Never got the least focus shift at f/2 (?) or f/2.8 on a 50/2 v4 or v5 so far. A bit around f/4 perhaps but it is hard to detect anyway. Here a v5 at f/4 and f/5.6. I would rather check if the camera or the lens needs a good CLA. FWIW.

- f/4.0 (6 MB file)

- f/5.6 (6 MB file)

 

Thanks. OT: What's the object next to the lens and its purpose? TIA.

[jip]

Again people complaining about shit they shouldn't be complain about when they use their common sense. 'Oh but I bought Leica so I feel fooled because Leica is perfection right?!' Go back to your CaNikon if the increase in quality isn't high/big enough.

 

I get sick of people complaining about stuff you can read about before you buy it.

 

Lenses have focus shifts, lenses do breath when you focus them, lenses have all sorts of shit you wouldn't like sometimes. Thats just the way lenses work...

 

Just my few annoyed cents.

Edited October 2, 2014 by jip

[lct]

Thanks. OT: What's the object next to the lens and its purpose? TIA.

A cooking timer for my barbecue but don't repeat it please . Just a reference to visualize DoF.

[danedit28]

Leica Summicron-M 50mm f/2 - Review / Test Report - Analysis

 

This website shows pretty much the exact shift that I experienced. At f/2, you can accurately focus through the RF. So my question remains, how on earth can you focus through the RF at f/2.8, f/4 and beyond? All of the focal planes at those apertures do not match the RF.

 

This all started when I noticed that all of my photos at f/4 and even f/5.6 were soft and clearly back-focusing.

Edited October 4, 2014 by danedit28

[danedit28]

Again people complaining about shit they shouldn't be complain about when they use their common sense. 'Oh but I bought Leica so I feel fooled because Leica is perfection right?!' Go back to your CaNikon if the increase in quality isn't high/big enough.

 

I get sick of people complaining about stuff you can read about before you buy it.

 

Lenses have focus shifts, lenses do breath when you focus them, lenses have all sorts of shit you wouldn't like sometimes. Thats just the way lenses work...

 

Just my few annoyed cents.

 

You sound like a lot of fun. Thanks for your informative contribution but I was shooting with a Summilux for four years and now I have a Summicron and I'm having trouble trying to find out how to focus a lens where all but one aperture setting give you out-of-focus pictures.

[aesop]

Again people complaining about shit they shouldn't be complain about when they use their common sense. 'Oh but I bought Leica so I feel fooled because Leica is perfection right?!' Go back to your CaNikon if the increase in quality isn't high/big enough.

 

I get sick of people complaining about stuff you can read about before you buy it.

 

Lenses have focus shifts, lenses do breath when you focus them, lenses have all sorts of shit you wouldn't like sometimes. Thats just the way lenses work...

 

Just my few annoyed cents.

 

 

 

...you really didn't have to comment, jip, particularly as you had little or no value to add to the discourse. I am not entirely sure what your intention was, but you came across as intentionally rude and foul-mouthed. No, it is not acceptable. Just so we are clear, nobody has the right to address a fellow member like you just did. And it matters not if you were "annoyed".

 

This is a civilised place - please leave your baggage at the door when you come in. Thanks.

[lct]

Leica Summicron-M 50mm f/2 - Review / Test Report - Analysis. This website shows pretty much the exact shift that I experienced. At f/2, you can accurately focus through the RF. So my question remains, how on earth can you focus through the RF at f/2.8, f/4 and beyond?

Yes and how could i do it since i purchased my 50/2 v4 in 1981 and my v5 in 2012? Because i don't use rulers to avoid paranoia and because my lenses are well calibrated first of all. Reviews are what they are, they depend on the sample tested which may be a workhorse lent to several reviewers. If you want to avoid front or back focus problems at the pixel peeping level, the best way is to use your lens on a mirrorless camera or with the EVF (or the LCD) of the M240. You don't even need to have your lens calibrated then. But if you want to use it with a rangefinder, a good calibration is needed and it may be that your lens and/or body are not perfect from this standpoint.

Edited October 4, 2014 by lct

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Hallo,

Look here: Leica M

[jip]

My apologies I was in a rather cranky mood that day...

 

I've got a 50mm summicron-m latest spherical version, and have noticed the focus shift, but barely! So I can't understand the real problem with real world shooting.

 

Also I only feel it is obvious from 2.8-4 not at 5.6 anymore. If you want to shoot at 2.8-4 just focus on the nose and the eyes will be sharp for example.

 

Again please accept my apologies since normally I don't post foul comments like that and I feel ashamed I lowered myself to the level where I did. It wasn't honestly meant very aggressive or anything but it sure came out that way.