lct Posted April 2, 2012 Share #21 Â Posted April 2, 2012 Advertisement (gone after registration) It is just an application of the formula b = e*f2/k*z where b is the critical baselength, e the visual acuity (0.0003 at approx. 1 arcmin), f the focal length, k the aperture and z the circle of confusion (0.030mm for FF, 0.0226mm for the M8). Link to post Share on other sites More sharing options...
Advertisement Posted April 2, 2012 Posted April 2, 2012 Hi lct, Take a look here Leica Elmarit M-90 User/owner. I'm sure you'll find what you were looking for!
jaapv Posted April 2, 2012 Share #22 Â Posted April 2, 2012 These charts and figures about "critical base length" have taken on a life of their own. Originally published as a comparison value between an rangefinder system and an SLR system with focussing wedge, specifically Leica R screens, they have transmogrified into "possible or impossible to focus" charts, which is fundamentally incorrect. Â For instance, if one creates a similar chart for an SLR, a 28 mm lens can have (depending on the configuration of the microprisms or focussing wedge) an effective measuring base of less than 10 mm. Yet nobody in his right mind would present that as proof that it is impossible to focus a 28 on an SLR. Link to post Share on other sites More sharing options...
lct Posted April 2, 2012 Share #23 Â Posted April 2, 2012 I don't understand what you mean here. How do you value the critical baselength of a reflex camera? Link to post Share on other sites More sharing options...
jaapv Posted April 2, 2012 Share #24 Â Posted April 2, 2012 Read up in Gunther Osterloh. He has all the relevant calculations in his Leica M book.Too long for a post. Link to post Share on other sites More sharing options...
lct Posted April 2, 2012 Share #25 Â Posted April 2, 2012 I don't have this book sorry. Perhaps you could explain me how comparing critical to effective baselength of a reflex camera? Just curious as i did not know that such a comparo was even possible. Link to post Share on other sites More sharing options...
Lord Fluff Posted April 2, 2012 Share #26 Â Posted April 2, 2012 At full aperture, 90/2.8 is more demanding DoF wise than 50/1. Â I can't make sense of this assertion. Link to post Share on other sites More sharing options...
jaapv Posted April 2, 2012 Share #27  Posted April 2, 2012 Advertisement (gone after registration) I don't have this book sorry. Perhaps you could explain me how comparing critical to effective baselength of a reflex camera? Just curious as i did not know that such a comparo was even possible. I really must refer you to pp 42-47 and fig 32 of Gunther Osterloh’s Advanced Photo School, English edition ISBN 1-57990-637-0. Link to post Share on other sites More sharing options...
farnz Posted April 2, 2012 Share #28  Posted April 2, 2012 LCT is correct on the basis of Leica's own published lens data. The depths of field are as follows at each distance setting:  ................90/2.8........|..........50/1.0 ------------------------------------------------------ 1.0 m:.......20 mm.......|..........23 mm  1.2 m:.......29 mm.......|..........34 mm  2.0 m:.......84 mm.......|..........95 mm  3.0 m:......194 mm......|..........216 mm   Pete. Link to post Share on other sites More sharing options...
vk2109 Posted April 2, 2012 Author Share #29  Posted April 2, 2012 LCT is correct on the basis of Leica's own published lens data. The depths of field are as follows at each distance setting: ................90/2.8........|..........50/1.0 ------------------------------------------------------ 1.0 m:.......20 mm.......|..........23 mm  1.2 m:.......29 mm.......|..........34 mm  2.0 m:.......84 mm.......|..........95 mm  3.0 m:......194 mm......|..........216 mm   Pete.  True but one more thing to taken into account is that using 50mm and 90mm naturally you won't be thinking of using the same distance setting ...if 1m @90mm , you may be 0.7-0.9@50mm... Link to post Share on other sites More sharing options...
farnz Posted April 2, 2012 Share #30 Â Posted April 2, 2012 True but one more thing to taken into account is that using 50mm and 90mm naturally you won't be thinking of using the same distance setting ...if 1m @90mm , you may be 0.7-0.9@50mm... Hmmm ... that might be difficult since the 50/1.0 doesn't focus closer than 1 meter. Â Point taken but LCT only mentioned wide open, he didn't specify the same coverage area. Â Pete. Link to post Share on other sites More sharing options...
lct Posted April 3, 2012 Share #31  Posted April 3, 2012 Yes at same subject distance of course, how could we compare otherwise? Those who don't like formulas might wish to use DoF calculators instead. They say the same in color. Online Depth of Field Calculator 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/175876-leica-elmarit-m-90-userowner/?do=findComment&comment=1971656'>More sharing options...
Double Negative Posted April 3, 2012 Share #32 Â Posted April 3, 2012 The 90 Summicron and 75 Summilux have even thinner DoF (assuming 2m wide open). Link to post Share on other sites More sharing options...
Lord Fluff Posted April 3, 2012 Share #33 Â Posted April 3, 2012 Yes at same subject distance of course, how could we compare otherwise? Â Indeed, and that's where things change. I was thinking along the lines of 'for a given' purpose - a portrait for example, the classic narrow DOF situation. Â A comparison that somehow worked in coverage would be interesting to compare. Link to post Share on other sites More sharing options...
philipus Posted April 3, 2012 Share #34 Â Posted April 3, 2012 do your eyes get tired faster with this lens ? I feel like it's way demanding more in terms of focusing than a 50lux at 1.4 ? Â It must be due your concentrating a lot on the RF patch. I have noticed a similar feeling myself. In my case it is due to sometimes missing the sweet spot and then having to focus back and forth until I obtain sharp focus with my M6. It doesn't tire my eyes, though, as much as annoy me. I have found that my Elmarit-M is easier to focus than the 50 asph in this respect. Â I have concluded that this has nothing to do with my eyes but with my interaction with the focusing ring. Both lenses's rings are equally easy to turn but I focus better with the 90. I assume this is due to a slight difference in focus throw. Â LTM lenses with long focus throw are a different story. Link to post Share on other sites More sharing options...
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