90cron backfocusing (and noct)

[jackal]

Advertisement (gone after registration)

now ive tried my 90 cron (pre-asph) extensively on my m7 and m8 i now know that it backfocuses terribly on the m8 and is spot on on the m7

 

ignore any doubts about methodology... i have verified this time and time again by taking a series of images and noting that the one perfectly in focus is the shot when i focused the subject then wound the ring massivly clockwise so that the images in the viewfinder were very obviously split and a long way apart

 

i also noticed this with my noctilux when focusing 8m or more.. this isnt usually a problem because i rarely use my noctilux at F1 and 8m+

 

so question is what do i do ? does the m8 need checking ? The 90 cron is fine on the M7, absolutely spot on

[carstenw]

I think you have too few data points. Drop by a Leica dealer and try a few other lenses, to be sure. In this you could leave out the M7 and deduce its state once you know what is going on with the M8.

[jackal]

nope.... the 90 cron backfocuses by a mile

thats all I/you need to know

 

i also dont need to try out other lenses, i have enough of them already myself

 

so what needs to be adjusted, presumably the M8

and can it actually be remedied ?

[glenerrolrd]

nope.... the 90 cron backfocuses by a mile

thats all I/you need to know

 

i also dont need to try out other lenses, i have enough of them already myself

 

so what needs to be adjusted, presumably the M8

and can it actually be remedied ?

Actually you could benefit by trying your 90 on another M8 . If you get similar results its your lens.

[Guest guy_mancuso]

Richard you need to do the process of elimination to see which one is off. sure you can adjust the M8 for the 90 but the other 5 lenses you have maybe off, so that won't work. So you have to do some testing to find the culprit If you have a 75, 50 35 that are dead on than the 90 may need the work. i would run some simple tests and see who is the culprit if it is the camera you may adjust the focusing cam to the 90mm than check your other lenses and if all lenses are firing on all clyinders than case closed but if the 90mm is off by a country mile than it just needs to be adjusted or shimmed. a second M8 is good for confirming your results.

[billh]

I looked at the People section in your web site, and the plane of focus is perfect in them. I had the same problem, but Leica (finally) adjusted the M8, and now the lenses either are spot on, or very close. It renders the M8 useless when you know the focus will be off. Plan on losing it for 6 weeks or so, unless they have caught up a good bit. I did send my 50 ASPH in with the camera. You may want to do that with the lenses which are giving you problems. Whatever they did to the M8 cured the back focusing with the other lenses too, except for the APO135 f3.4. I simply don’t use that lens because I know the focus will be off.

 

(To be a bit more specific, all of my lenses except the APO 75 back focused - the 50s, Noctilux and ASPH, were particularly bad). The M8 is at fault, and it seems to be a very common problem.

[lars_bergquist]

Advertisement (gone after registration)

You should read the latest issue of the LFI, where an article has info on the problem, and why it is more noticeable with the M8 than on film. It is not the camera's fault, it is fast lenses that show aperture difference (focus shift when stopping down) due to residual spherical aberration. The 50 and 75 ASPH. do NOT show it because their floating elements control spherical aberration close up. This agrees with the results of my testing. Don't make sweeping statements until you have boned up on elementary optical theory, and (pardon me for saying this) on your rangefinder focusing practice.

 

The old man from the Age of the Brilliant Finder

[Paul Hart]

i rarely use my noctilux at F1

 

But that's what it exists for!

 

A 6 week trip to Uncle Ernst sorted mine and will probably sort yours too.

[stunsworth]

Paul, what's actually written is "i rarely use my noctilux at F1 and 8m+" - my italics. My interpretation is that the lens is used at F1, but in general close up.

[jackal]

It is not the camera's fault, it is fast lenses that show aperture difference (focus shift when stopping down) due to residual spherical aberration. The 50 and 75 ASPH. do NOT show it because their floating elements control spherical aberration close up. This agrees with the results of my testing. Don't make sweeping statements until you have boned up on elementary optical theory, and (pardon me for saying this) on your rangefinder focusing practice.

 

The old man from the Age of the Brilliant Finder

 

 

utter nonsense in my case I am afraid

[jackal]

I looked at the People section in your web site, and the plane of focus is perfect in them.

 

 

almost every single picture there is taken with the noctilux at F1 not the 90 (take note paul hart)

[cocker]

utter nonsense in my case I am afraid

 

And you want people to help you?

[jackal]

Actually you could benefit by trying your 90 on another M8 . If you get similar results its your lens.

 

 

good idea, thanks, i will try that asap

[jackal]

And you want people to help you?

 

 

 

certainly

 

and also, i don't expect to be "ticked" off and treated like a schoolboy, especially by someone who hasn't read the thread properly:

 

 

 

(see: "Don't make sweeping statements until you have boned up on elementary optical theory")

[wattsy]

Don't make sweeping statements until you have boned up on elementary optical theory, and (pardon me for saying this) on your rangefinder focusing practice.

 

The original poster is referring to problems with backfocus. This is not the same issue as focus shift.

[jackal]

The original poster is referring to problems with backfocus. This is not the same issue as focus shift.

 

thanks ian

at least there's one sane person how has read this thread

[carstenw]

Richard, you have kind of pre-diagnosed the problem and laid out all the conclusions, but then you don't want to take the last step. Anytime anyone says that you should check something, you say no, you have already checked everything. I have two thoughts here: 1) you are not writing enough information here for us to independently come to the same conclusion, and 2) why don't you make the logical conclusion yourself, if you are so sure, and send in the M8?

 

Personally, from what you have written, I think that there are too few datapoints. First of all, how many lenses do you have, what are they, and how do the other lenses behave? This would be important extra information which you didn't list. Secondly, You talk about the Noctilux at 8+m, but not about up close. What does the Noctilux do up close on the M8?

 

The facts are not unambiguous. If the M8 is off in the entire range with the 90, then how can it focus up close with the Noctilux (at least that is how the situation sounds)? If the M7 is perfect, how come your two lenses behave differently on the M8? Something is not right here. Please post all the facts, and then maybe it can be deduced what is going on, but not with what you have posted here.

 

If we take what you wrote, then the 90 backfocuses massively on the M8. Okay, send them both in together. When they come back, you can test the M7 and know what is going on there. Or, send everything in, since something is really weird with your facts.

[jackal]

Richard, you have kind of pre-diagnosed the problem and laid out all the conclusions, but then you don't want to take the last step. Anytime anyone says that you should check something, you say no, you have already checked everything. I have two thoughts here: 1) you are not writing enough information here for us to independently come to the same conclusion, and 2) why don't you make the logical conclusion yourself, if you are so sure, and send in the M8?

 

Personally, from what you have written, I think that there are too few datapoints. First of all, how many lenses do you have, what are they, and how do the other lenses behave? This would be important extra information which you didn't list. Secondly, You talk about the Noctilux at 8+m, but not about up close. What does the Noctilux do up close on the M8?

 

The facts are not unambiguous. If the M8 is off in the entire range with the 90, then how can it focus up close with the Noctilux (at least that is how the situation sounds)? If the M7 is perfect, how come your two lenses behave differently on the M8? Something is not right here. Please post all the facts, and then maybe it can be deduced what is going on, but not with what you have posted here.

 

If we take what you wrote, then the 90 backfocuses massively on the M8. Okay, send them both in together. When they come back, you can test the M7 and know what is going on there. Or, send everything in, since something is really weird with your facts.

 

 

 

carsten, noct is fine up close

never had a problem with it, all my pictures at F1 are bang on

 

all my other lenses focus perfectly (28ultron, 28 elmarit, wate, 12mm, 35 lux, 25mm zeiss) although i admit that I don't have many longer focal length lenses but the 35 lux at 1.4 should in theory show up a problem on the M8 but its spot on every time no matter what the distance

 

i agree something is not right, hence why i posted. The 90 is so off. Focusing on something say 5m away, to get it in focus on the m8 i'm telling you the 2 images in the viewfinder are so far apart off its untrue. On the M7 its bang on though... i shot close up and far away with a roll of delta100 last week and its all hunky dory.

 

maybe my m8 only starts to have a problem at long focal lengths. At 50mm you are starting to see it with longer distances by remember 90 i almost double the noct so teh problem is way way more pronounced.

 

I am open to suggestions and I think someones idea of taking teh M8 to a shop and testing it with say a 75 and another 90 is a great idea. That will quickly rule out my 90 (or not as the case may be). I have a sneaking suspicion its something to do with M8 though because i remember onc etrying a 75lux out in a shop and the focus seemed a bit odd then although i couldnt be 100% certain because I was in a shop and not concentrating that much.

[carstenw]

If all your other lenses are good, but start to be off at distance, then it sounds like the near-far balance is off in the M8. If the 90 Cron backfocuses everywhere, and the Noctilux only at distance (like your 50, and perhaps 35 Lux wide open), then the 90 is also off, because it should be working up close, like the others. If the M7 works with the 90, then it is also off.

 

You see what I mean, it is almost impossible to make proper conclusions with so many unknowns. You need a critical (90 Cron, Noctilux, 75 Lux, 75 Cron) known-good lens or camera to decide what is off. If you take your Noctilux and 90 Cron and M8 to the store, and try your lenses on another M8, and a known-good lens on your M8, I guess you can quickly decide what is going on.

 

It sounds like the M8 is off anyway, so I think I would send the M8, 90 Cron and Noctilux away to be set up together. Once those all work, everything else should fall into place, being so much less critical.

[Advertisement]

Hallo,

Look here: Leica M

[lars_bergquist]

Richard: Aperture difference (focus shift when stopping down) caused by spherical aberration is a known optical phenomenon. This is not nonsense. The explanation that the M8 is more sensitive to this because the shift of the true focal plane is not hidden in the depths of a film emulsion with a thickness of several tens of microns, is not nonsense either. Your response ("nonsense!") is however distinctly nonsensical – it does not contribute to a factual discussion. Don't scream, argue.

 

Ian: A lens (and for that matter, a rangefinder) may be mechanically incorrectly adjusted for focus. That is one thing. It has nothing to do with optical aperture difference. In that you are right. But what are we discussing? How are people using the exceedingly loose term 'backfocus'? Does it mean that the point of best focus (smallest circle of confusion) is right on at 1.4 or 2 and shifts outwards when the lens is stopped down? In that case we are talking of aperture difference/focus shift. But if it means that focus is off at any or all apertures, or that the customer is dissatisfied with the results, then we are talking of something altogether different. In that case it is meaningful to send the offending lens (NOT the camera unless you have specific reasons to suspect the rangefinder) in for re-calibration.

 

The LFI article told me – as I hadn't known because I have not worked with Zeiss lenses for the last sixty years – that Zeiss, unlike Leica, do not adjust lens focus to be spot on at the widest aperture. Instead, they are said to adjust at least close focus to the smallest average circle of confusion at several apertures, in order to even out the effects of the focus shift. If this is true, then it must mean that focus of high speed Zeiss lenses must be slightly off at full aperture – a claim that I presume will be vehemently denied from some quarters. Still, there is a legitimate argument for this kind of policy, if we assume, not unreasonably, that people do stop down for better depth of field at close focusing distances. I admit that I do.

 

Finally, my aside that it is good to abstain from generalizations until we have defined our terms and tightened our testing procedures – and preferably done a statistical analysis of the data points – was not directed at anybody particular. This sort of things is what scientists do, and pseudo-scientists do not. There is definitely too little fact and too much religious sentiment in certain arguments here.

 

The old man from the Age of Logic