Lens or camera calibration (M6)

[bryanfowler]

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Hi folks.

First, I know one answer is to send in a camera for calibration. My question is about process.

How are lenses and camera bodies calibrated? I know there's a small wheel in the body that can be adjusted so when the lens distance is at say, 5ft, an opject at 5ft in the viewfinder is matched up. 

My question is about that process. For film, would you do this calibration, then take some photos and develop them and then adjust accordingly? 

[Jewl]

It could also be the lens or both! For me, my M11 had a front focus issue at infinity. The body was properly calibrated so they needed to adjust the lens accordingly. 

[250swb]

6 hours ago, bryanfowler said:

 

My question is about that process. For film, would you do this calibration, then take some photos and develop them and then adjust accordingly? 

I take it to mean you want to adjust the body so the lens will focus accurately but you should only do that if you know for sure the lens is 100% ok. You have to be careful in knowing which is at fault because if you adjusted the lens it may not work with other bodies, and if you adjust the body it may not work with other lenses, which would be a very bad idea. The first thing to do is find out which is out of tolerance as @Jewl describes, then you can either send the lens to a technician or with more confidence adjust the body to be accurate with a lens you know to be accurate itself. If you sent the lens and body to a good technician they would do it the Leica way and adjust each of them separately.

[TomB_tx]

To keep lenses interchangeable bodies and lenses are each adjusted separately to standards. However, adjustments always have some acceptable tolerance, so if a body is at one end of tolerance and a lens at the opposite end they can be mismatched. So some technicians will want the body and lenses so they can check for this. They still don't adjust a body to a lens, but use the check to go back to the standards and adjust to a better part of the tolerance band.

I recently checked a checked focus on a number of lenses on my M10: some had slight front focus, some slight back focus, and my Summarit 50 & 35 2.5 matched exactly. The rest were fine for normal use, but explains why I get such good results on the Summarits. Since the lenses vary both sides of tolerance I'd say the body is fine. If I adjusted the body to be perfect with a lens that was at one end of tolerance, lenses at the other end would be farther off with that body adjustment.

My recently bought used M6 (1997) had been dropped and back focused on all lenses. I found its infinity setting had slipped, and reset the infinity focus (on a very distant object) and now it is fine.

[bryanfowler]

thanks for all the great info guys. Matches what I was thinking too.

So hypothetically, I could take my M10, and SL2-2 put each of my M lenses on them and with live view get a feel if 3ft on the barrel is 3ft of actual focus. Then take the lens that is the best in spec on both of those, and match it with the reticle (the square) in the M6 and I will likely be in a safe ballpark? 

If I had more time I'd send this to someone for the work, but we leave for a vacation in 4 days. 😃 ... . oh.. hypothetically of course.

[spydrxx]

Just be aware that the distance indication on lens barrels isn't exact. It is really much more useful for DOF guidance than exact measurement. Having said that, I always test my lenses against the barrel indications and they are usually very, very close.

[TomB_tx]

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Best is to set lens at its infinity stop and find a pole or similar VERY far away (or use the moon) and adjust the roller for coincidence at infinity. That usually corrects all distances. If not, there is another adjustment for "span" to get both infinity and close calibrated.

Unlike many dSLR lenses most M lenses have a solid stop at infinity, which is more reliable than the distance markings.

[250swb]

On 12/4/2024 at 2:01 PM, bryanfowler said:

 

So hypothetically, I could take my M10, and SL2-2 put each of my M lenses on them and with live view get a feel if 3ft on the barrel is 3ft of actual focus. Then take the lens that is the best in spec on both of those, and match it with the reticle (the square) in the M6 and I will likely be in a safe ballpark? 

 

I'm not sure what a 'feel' is if you are calibrating  a lens or body. What is wrong with working with 'facts' instead of 'feel'?

[TomB_tx]

Adjusting the camera for infinity is the best starting point as mentioned above. But to check overall focus at close distances forget about the lens distance markings - just focus and look for the sharpest focus on a test chart on the resulting pictures. Here's an example of a Nokton 50 @1.5 tested at about 5 ft, on an M6 where I had just started adjusting the infinity setting. Use the finest grain film you can find (this is Ilford PanF 50 ISO) and develop for fine grain - don't worry about tonal range, contrast, etc - you are just looking for the best focal plane. This is a common focus chart off the Web. With the camera firmly tripod mounted and level, tape the chart to a wall so the center is at lens height, with the camera pointed at center from 45 degrees to the side. 5 ft works well, as it is away from focus limits like most pictures will be. Focus the Rangefinder on the heavy line in the center.  This image is just off a flatbed scanner - adequate to see best focus place. Check how the focus fades in both directions to judge if sharpest is close to the center line. This is a strong crop, as the 50 FOV is MUCH wider than the paper target.

Usually a slight front focus wide open is good, as focus tends to shift to the rear as you stop down, (You can test for shift the same way.)

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Since I bulk-load B&W and process at home, I went through several trials as I tweaked and checked focus at infinity, then tried the chart as close distance, etc.

 

 

[TomB_tx]

Just for comparison - the focus test above using M6 & film does evaluate the RF accuracy at close distance, but with quick scanning the image isn't impressive. Here's a repeat of that test of accuracy using my M10 (original factory calibration from 2016) and a new Nokton 50 1.5 ii that I just got this week. Digital makes such lens tests fast and clearer to interpret. I think the M6 used above needs a tiny tweak yet on infinity setting, but is certainly good enough for most work.

I continue to be impressed with the quality of Voigtlander production and lens calibration.

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[bryanfowler]

Thanks everyone for the posts. Lots of great info here.

Right now here's my situation. Leaving in the morning on a trip. taking about 10 rolls of film, M6, LS2s with M adapter, and a handful of M lenses. Leica and Voit branded.

There's really no time for shoot a roll then develop it. to see if stuff is in focus. So I checked 3 of the lenses I have at 5ft and 10ft (I will likely go back and check infinity today). I used the M10-p (not going on trip) on Live view to see how far off the markings were from the lenses, they felt very close. As you said, it's more for DOF and not like cinema lenses accurate to the inch marking which I'm used to using.

With 3 lenses looking very close on the M10-p, I put them all on the M6 (same tripod and focus chart location) and adjusted rangefinder one small bump to the right to make the square(s) line up

Does that sound like the best thing I can do without the option of running a roll through, or sending off to someone? It feeeeeeels like that would work for me.