Guest mc_k Posted June 22, 2010 Share #21 Posted June 22, 2010 Advertisement (gone after registration) ...focal length shift when focussing from close to infinity. I'm still confused about this. If the lens focuses as a unit, the angular field changes, but is it correct to say the focal length changes ??? Link to post Share on other sites More sharing options...
Advertisement Posted June 22, 2010 Posted June 22, 2010 Hi Guest mc_k, Take a look here M9 viewfinder-lens not accurate. I'm sure you'll find what you were looking for!
jaapv Posted June 22, 2010 Share #22 Posted June 22, 2010 Yes, because it actually does. The distance to the plane of focus, that being the focal length, changes. Of course the angle of view changes as a direct function of the focal length. It even holds true for an internally focussing lens because the virtual point of focus changes its distance to the plane of focus. Link to post Share on other sites More sharing options...
Guest mc_k Posted June 22, 2010 Share #23 Posted June 22, 2010 ...28mm...At infinity setting the error is approximately 7.3% where did this info come from?...it seems high, or a % of area Link to post Share on other sites More sharing options...
Guest mc_k Posted June 22, 2010 Share #24 Posted June 22, 2010 ...Leica has experimented with the framing in their digital Ms: in the M8, the lines were set to frame precisely at each lens's minimum focus distance (which made for very loose pictures at long distances); they changed that to a standard "correct for subjects at 2 meters with any lens" with the M8.2 (or upgraded lines) - which was still a bit loose at long distances and ran the risk of unintentional cropping at .7 meters; in the M9 they have compromised on "correct for subjects at 1 meter with any lens"... thanks, this is an interesting summary. Link to post Share on other sites More sharing options...
adan Posted June 22, 2010 Share #25 Posted June 22, 2010 Well, I would quibble with jaap - the focal length of a lens is defined as the distance over which COLLIMATED OR PARALLEL light rays are brought to a focus. Since only light rays coming from an infinitely distant subject point will be truly parallel, the focal length can only be defined when focused at infinity. Focal length - Wikipedia, the free encyclopedia The distance from the lens (or in real-world lenses the lens's rear nodal point) to the image plane for focused subjects closer than infinity is related to focal length by a function (see link), but it is not THE focal length. BTW - from the M9 instruction manual, p.131 (English): Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/124289-m9-viewfinder-lens-not-accurate/?do=findComment&comment=1359230'>More sharing options...
earleygallery Posted June 23, 2010 Share #26 Posted June 23, 2010 I think the lense is including too much in the frame because it has too many letters in the name. Link to post Share on other sites More sharing options...
hoppyman Posted June 23, 2010 Share #27 Posted June 23, 2010 Advertisement (gone after registration) where did this info come from?...it seems high, or a % of area I got the exact figures for the M9 and MP from their respective instruction books Link to post Share on other sites More sharing options...
Guest mc_k Posted June 23, 2010 Share #28 Posted June 23, 2010 I got the exact figures for the M9 and MP from their respective instruction books thanks, it's the "7.3%" that I can't find in the M9 manual Link to post Share on other sites More sharing options...
Guest mc_k Posted June 23, 2010 Share #29 Posted June 23, 2010 ...The distance to the plane of focus, that being the focal length, changes... yeah, I think this is the "image distance" in the lens formula, not the focal length. (as pointed out.) Link to post Share on other sites More sharing options...
hoppyman Posted June 23, 2010 Share #30 Posted June 23, 2010 thanks, it's the "7.3%" that I can't find in the M9 manual Well the exact figure is a very insignicant issue in practical use of course and we all learn to adjust for the limitations in use. Personally I actually preferred the 2 metre decision implemented with the M8.2, but it's no biggie since we were long accustomed to the previous arrangements prior to the M8. Remembering that the quoted error is only the worst case and is where the error is less likely to be significant at all regarding critical framing. Obviously Leica Camera did their sums before deciding on the current set up. The OP noticed the discrepancy but has now found that one of his 35mm lenses brings up the wrong frame-lines. Here's the M9 instruction manual quote for the detail oriented "Matching of viewfinder and actual picture The size of the bright-line frame corresponds exactly to the sensor size of approx. 23.9 x 35.8mm at a setting distance of 1 meter. At infinity setting, depending on the focal length, approx. 7.3% (28mm) to 18% (135mm) more is recorded by the sensor than indicated by the corresponding bright-line frame and slightly less for shorter distance settings than 1m." Link to post Share on other sites More sharing options...
Anguish Posted June 23, 2010 Share #31 Posted June 23, 2010 I vote for Steve's "250swb" answer - that the lens is being over-rotated with a finger on the lens release button, allowing the wrong frame to come up in the viewfinder. This was a technique proposed for use with a combination on the M8, if I remember correctly, and it was useful there. Did you try this, Wil? Link to post Share on other sites More sharing options...
gib_robinson Posted June 23, 2010 Share #32 Posted June 23, 2010 Geoff, Thanks for citing the M9 manual. I have been somewhat disconcerted by what I think is about a 10% discrepancy (more image than frame) with my 35mm 'cron. Your citation makes it seem close to what I should expect at infinity. --Gib Link to post Share on other sites More sharing options...
Guest mc_k Posted June 23, 2010 Share #33 Posted June 23, 2010 ... Here's the M9 instruction manual quote for the detail oriented ... thanks! I don't think the error is significant either, but the details are interesting for their own sake. The catch-22 is you need the details to prove they're not significant. I can't get the same figures as in the manual. You should be able to calculate the maximum error from the focal length and the frameline "exact distance" (1m in this case). Link to post Share on other sites More sharing options...
hoppyman Posted June 23, 2010 Share #34 Posted June 23, 2010 I can see that it's vexing you. Still, time spent re-reading your manual is not wasted I presume that Leica Camera is referring to area and they do say approximate. Probably the quoted number of frame widths is more useful. Now look through your finder repeatedly and see what variance is caused by eye position! If you really need that kind of precision at infinity then the LCD preview will solve the issue for you. That particular info is at the back in the Technical data section. Page 175 in the printed version. Page 89 of 92 in the PDF if you download the manual Honestly I really doubt that you can determine anything practically useful unless it's simply technical curiosity. You aren't an engineer by any chance? Link to post Share on other sites More sharing options...
thrid Posted June 23, 2010 Share #35 Posted June 23, 2010 My M9 viewfinder with the 35mm f1.4 Summilux does not give me an accurate representation of the image I capture. When I compose in the viewfinder using the bright-lines the resulting image I get is much larger than what is indicated by about 25% and is not at all what is indicated in the viewfinders "bright-line" frame. I have been using Leica M's for over 40 years now and have never seen anything like this. Hope someone can help. Wil Tifft 25% sounds excessive. It shoudl be about 15% at infinity with the M9 finder The M9 framelines mask is set up to indicate what you will get at 1 meter. Focused at infinity you should see about 15% more on your negative. Keep in mind that this is a rangefinder, not an SLR. You will get 'reasonably' accurate framing and nothing more. The Leica rangefinder (RF) compensates for parallax errors in X and Y (left/right up/down), but does not compensate for the change that occurs in lens magnification, when you focus from the close up to infinity. That is what you are seeing. Count yourself lucky that you are shooting an M9. M6 and newer bodies are equipped with a .7 m framelines mask that makes pretty much anything longer than 35mm (50mm and up) very inaccurate. Link to post Share on other sites More sharing options...
Guest mc_k Posted June 24, 2010 Share #36 Posted June 24, 2010 I can see that it's vexing you. Still, time spent re-reading your manual is not wasted I presume that Leica Camera is referring to area and they do say approximate. Probably the quoted number of frame widths is more useful. Now look through your finder repeatedly and see what variance is caused by eye position! If you really need that kind of precision at infinity then the LCD preview will solve the issue for you.That particular info is at the back in the Technical data section. Page 175 in the printed version. Page 89 of 92 in the PDF if you download the manual Honestly I really doubt that you can determine anything practically useful unless it's simply technical curiosity. You aren't an engineer by any chance? no I'm in the math dept. Thanks for the page reference...maybe you are right and the Leica figures are supposed to be % of area. In that case, for the M8 Leica states 7.3% max. error @ 28mm and 18% @ 135mm (I got 9% and 21%); for the M9 Leica states 9% @ 28mm and 23% @ 90mm (I got 6% and 21%). No doubt I'm wrong, and I'll have to measure to see. Again, I'm sure you're right it's not a real issue, but something like reframing or uncorrected parallax has the same kind of details, and I also use cameras that don't have the LCD or the parallax correction... so I got interested in these kind of errors. Thanks. Link to post Share on other sites More sharing options...
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