Focus nightmare. HELP. Advice needed

[leicamr]

Advertisement (gone after registration)

Last week I discovered that my 75 f2 and 90 f2 lenses are perfectly focussed from minimum focus distances up to about 7 to10 metres. At 25 metres a serious back focus problem is observed. Using a 28 f2 and a 50 f1.4 ASPH I cannot detect any focus issues at any distances. With previous M cameras I have known that if the focus is accurate at minimum focus distances then it will be fine over the rest of the range.

 

I will be taking the M8 and the 75 & 90 lenes for a checkup.

 

Mark

[Advertisement]

The Leica Q3 is available for pre-order at B&H Photo Video and Adorama

[fotografr]

The 6/2007, August, issue of LFI has a good article, "Sense and Sensuality," p 42, that talks about the focus shift issue. Leica lenses are set to focus at maximum aperture and some will vary either way as the lens is stopped down. Suggest reading the article for a better understanding.

M

 

I was just going to mention that, but you saved me the trouble. Basically, M lenses have focus shift and it is much more noticeable with a digital camera than it is with film. Part of this might be that we don't blow our film images up 200% to examine individual specks of grain. You won't see it as clearly with the wide lenses due to increased DOF, but with lenses like the Noctilux, particularly at wide apertures, it becomes quite obvious.

[AtelierM]

Brent et. al.,

The article [in the current LFI] is fairly in depth and too long for me to really do justice in trying to explain all the factors/issues, but the main ones I remember are that aspherical lenses can help correct focus shift, but because they also help other issues [such as keeping the lenses compact], they cannot completely eliminate the problem. However, in combination with a floating element they can further reduce the problem. Their later designs with both, such as the APO Summicron-M 75mm f/2 ASPH and Summilux-M 50mm f/1.4 ASPH should not have this issue. The article did mention that the Summilux-M 35mm f/1.4 ASPH has received complaints. I think this preceeded the other lenses. There are other factors that involve the placement of lens elements, quality control/adjustment, etc.

 

I hope this helps.

Mikeual

[carstenw]

The LFI articles somewhat understates the real problem, unfortunately. I normally support what they write, but this particular article was not very fair to the people who have had real problems.

[AtelierM]

Carsten,

I'm still learning--have a long way to go with my M8 and lenses. At least the LFI article is a start for someone to understand what the issues may be, and go from there. Are you aware of other references that cover this issue that might help? I don't seem to recall any books written about Leica M photography addressing this issue. Regardless, this Forum has been a help to me in that context.

Mikeual

[carstenw]

I've got a few M books, but none really touch on this topic as this forum has. There have been lots of threads here on this topic, so I would start by searching here and reading some of these. The bottom line is that the film Ms had a level of forgiveness with slight tolerance problems which the M8 doesn't. Most of the problems can be solved by tuning the M8's rangefinder, but some require lens modifications. Leica has been very forthcoming with this, so patience is the main thing you need.

[pelikan1931]

Advertisement (gone after registration)

you know now why Leica has cut the production of summilux and summicron, and has moved its resources to producing summarits.

 

the company simply can't afford to fine tune every lens and body they sell for free.

 

i don't know if a full frame sensor will be more tolerant to this issue with its increased dof.

 

 

my approach is to tune the body to work with f1.4 or above lens myself, or to buy a second M8.

 

nikon/canon DSLR all have the same front/back focus problems, at least for M8 you can try compensate yourself.

 

[AtelierM]

I recently sent in a lens [50mm] for adjustment--the bright squares in the rangefinder would never converge at infinity, like if the stop at infinity was not there and it could be turned a little further it would focus. Images at close range, when the rangefinder was in alignment, were not in focus. My 75mm is the opposite--I must back off from infinity for the bright squares to align, but the image there and any other distance are dead on in focus. The latter makes me focus more carefully/I can live with that issue as the lens is used more for close macro/portraits.

 

Can someone clarify the terms back focus and front focus?

 

Thanks,

Mikeual [Michael]

[thai.charlie]

Curious, how many are you using a 1.25x viewfinder magnifier? I'm using one (Leica's), and I STILL find it difficult to judge "fusion" within the rangefinder patch when focusing my Noctilux. I tend to look for fusing catchlights in subject's eyeballs, since that is easy to see if they come together or not. But I still think mine is slightly backfocusing (I haven't done any scientific tripod mounted test chart pictures yet).

 

I pretty much leave my 1.25x magnifier on the camera all the time, but then again my setup is pretty much my 21mm Elmarit (for which I use an aux finder) and a 50mm lens.

 

IMO Coming from the Epson RD-1 (which I had a 1.3 magnifier permanently affixed) I still felt that the M8, even though with its extended RF baselength, was still a challenge to focus a fast 50 wide open without a magnifying aid. Perhaps after my Noctilux is calibrated I will feel differently.

[carstenw]

I use the 1.25x loupe, and with or without I rarely have problems. Note that my rangefinder patch was initially out vertically, and I didn't realise this until I tested it on a star in the nightsky, and the star never met itself. When I tuned that, focusing got much easier.