ChiILX1 Posted July 20, 2011 Share #1 Posted July 20, 2011 Advertisement (gone after registration) The idea of collapsibility begs the question of varying focal lengths. While my 90mm elmar collapsible does not allow for focusing while collapsed, my 50mm collapsible summicron does. I don't have a digital M and don't want to waste film figuring this out- can you take focused pictures with the lens collapsed and if so, what's the rough equivalent focal length? Thanks. Link to post Share on other sites More sharing options...
Advertisement Posted July 20, 2011 Posted July 20, 2011 Hi ChiILX1, Take a look here Collapsible lenses- varying focal lengths?. I'm sure you'll find what you were looking for!
pop Posted July 20, 2011 Share #2 Posted July 20, 2011 "To focus" means to position the lens at a distance from the film such that the image of the desired spot of your subject lies exactly on the film. "Collapsing" the lens just moves the whole assembly into the camera. In the collapsed state the lens is closer to the film than its focal length. Since the images of everything are farther from the lens than its focal length, that implies that the images of everything are behind the film. It is not possible for a lens to produce a sharp image while collapsed into the camera. Link to post Share on other sites More sharing options...
250swb Posted July 20, 2011 Share #3 Posted July 20, 2011 The idea of collapsibility begs the question of varying focal lengths. While my 90mm elmar collapsible does not allow for focusing while collapsed, my 50mm collapsible summicron does. I don't have a digital M and don't want to waste film figuring this out- can you take focused pictures with the lens collapsed and if so, what's the rough equivalent focal length? Thanks. No, collapsing the lens is only a means to make it smaller in the camera bag or coat pocket or case. To make a photograph you need to extend it and focus. Steve Link to post Share on other sites More sharing options...
luigi bertolotti Posted July 20, 2011 Share #4 Posted July 20, 2011 To be strictly precise... you can use an Elmar 50 or 90 collapsed and focus....... mounting it on Bellows+Visoflex with sufficient bellows extension... , and of course is always a 50 or 90 mm lens (*), used as a macro unit. (*) nominal focal length : in macro usage the real FL is longer, the real angle of view smaller. Link to post Share on other sites More sharing options...
christer Posted July 20, 2011 Share #5 Posted July 20, 2011 ...... I don't have a digital M and don't want to waste film figuring this out- can you take focused pictures with the lens collapsed and if so, what's the rough equivalent focal length? Thanks. I suggest you spend a few pennies on film and make one single shot with the lens collapsed. The film frame will not be wasted as you will gain personal experience, an invaluable asset. Link to post Share on other sites More sharing options...
gyoung Posted July 21, 2011 Share #6 Posted July 21, 2011 maybe a simple book on optics, to gain an understanding of focal length, focus, nodal point, register, etc. Gerry Link to post Share on other sites More sharing options...
Xmas Posted July 21, 2011 Share #7 Posted July 21, 2011 Advertisement (gone after registration) Hi The rule you should observe is Mount and unmount the lens extended & locked, otherwise you risk damage to camera throat, e.g. rangefinder follower arm or removal of matt black paint. The first would be well expensive... Noel Link to post Share on other sites More sharing options...
adan Posted July 21, 2011 Share #8 Posted July 21, 2011 You basic misconception is that the focal length of a lens can somehow be changed by where you choose to put the whole lens. The focal length is a fixed quantity of the glass bits and their position relative to one another, not where you choose to put them as a unit. To change the focal length, you'd have to be able open up the lens and move the individual elements around, spacing them closer or further apart (as a zoom lens does). Without doing that, you have a "50mm" lens, whether it is collapsed, uncollapsed, or mounted on a bellows 3 feet from the film. Moving the whole lens controls "focus" - moving the separate bits of glass can vary "focal length" - but those are two different things. Can you take focused pictures with the lens collapsed? Sort of, up to a very limited point. Set the lens to "infinity" on the scale, collapse the lens 2mm, turn the focus ring to move the glass back out 2mm - and you'll be focused at infinity again. (Although the RF will not be in sync with the lens, so you'll have to find a subject you KNOW is at effective infinity - 150 feet or more away). But the focus ring will only allow you to do this for about 5mm - collapsed more than that, you can't get back to infinity. You are focused "beyond infinity" - so only Buzz Lightyear will be able to interpret the blur you'll get. So to answer your final question(s) - to a limited extent (and not with the lens fully collapsed); and "50mm". Link to post Share on other sites More sharing options...
jaapv Posted July 21, 2011 Share #9 Posted July 21, 2011 The idea of collapsibility begs the question of varying focal lengths. While my 90mm elmar collapsible does not allow for focusing while collapsed, my 50mm collapsible summicron does. I don't have a digital M and don't want to waste film figuring this out- can you take focused pictures with the lens collapsed and if so, what's the rough equivalent focal length? Thanks. Additional to everything said, DON'T collapse the old 90 Elmar on an M8 or M9 ! To stop myth-forming - the new 90 Macro is fine. Link to post Share on other sites More sharing options...
Xmas Posted July 22, 2011 Share #10 Posted July 22, 2011 Hi I'd not feel too bad about the zoom lens suggestion, many zoom lenses are (Cooke) triplet deravatives with variable separation between the three groups. Noel Link to post Share on other sites More sharing options...
tobey bilek Posted July 22, 2011 Share #11 Posted July 22, 2011 Obviously no. Link to post Share on other sites More sharing options...
ChiILX1 Posted July 22, 2011 Author Share #12 Posted July 22, 2011 I suggest you spend a few pennies on film and make one single shot with the lens collapsed.The film frame will not be wasted as you will gain personal experience, an invaluable asset. I guess I was hoping to see someone post a couple pics taken collapsed on their digital M. Link to post Share on other sites More sharing options...
earleygallery Posted July 22, 2011 Share #13 Posted July 22, 2011 I guess I was hoping to see someone post a couple pics taken collapsed on their digital M. Why? All you'll get is a VERY out of focus photo, possibly circular in shape. Link to post Share on other sites More sharing options...
ChiILX1 Posted July 22, 2011 Author Share #14 Posted July 22, 2011 Why? All you'll get is a VERY out of focus photo, possibly circular in shape. Now I know that but when I posted this topic and was thinking to see samples I didn't. Link to post Share on other sites More sharing options...
adan Posted July 23, 2011 Share #15 Posted July 23, 2011 Something interesting happens... I stopped by the shop today and realized we had an old collapsible 50 f/3.5 on display, so did the experiment. Top pic, lens extended and focused normally Middle pic, lens collapsed most of the way (not sure how far an Elmar f/3.5 could be collapsed safely on the M9, so about 4mm short of being fully collapsed) - aperture at f/3.5 Bottom picture, lens collapsed the same amount, but stopped down to f/22. The field of view DOES change to a wider view (except for the vignetting) - because the tiny aperture begins to act as a pinhole camera of "focal length" about 35-40mm. Exactly opposite to a lens, a pinhole's "focal length" is, in fact, determined soley by the distance between it and the sensor/film. The image would probably be slightly LESS blurry (and the vignetting would be less) if the defocused glass were removed from the equation. Link to post Share on other sites More sharing options...
adan Posted July 23, 2011 Share #16 Posted July 23, 2011 Ooops correction - the above images show the 50 uncollapsed, and collapsed at f/8 and f/22. This new image below was the shot collapsed and at f/3.5 Link to post Share on other sites More sharing options...
earleygallery Posted July 23, 2011 Share #17 Posted July 23, 2011 Andy, I'm not sure the field of view has changed, rather you're seeing the 'margin' of area that the lens covers beyond the 35mm full frame ? Link to post Share on other sites More sharing options...
luigi bertolotti Posted July 23, 2011 Share #18 Posted July 23, 2011 Something interesting happens... Bottom picture, lens collapsed the same amount, but stopped down to f/22. The field of view DOES change to a wider view (except for the vignetting) - because the tiny aperture begins to act as a pinhole camera of "focal length" about 35-40mm. ---- . That's exactly what does happen : apart the vignetting due to the tube, in practice you are using a 30-40mm lens, with its proper angle of view, which happens to be "wrongly built" as a 50mm... Just for fun... optical cells of the Elmar 50 and 35 aren't so different... a good craftman could try to mount the optical cell of the Elmar 35 into a Elmar 50 body, collapse it partially... and would obtain an identical image, with correct focus... Link to post Share on other sites More sharing options...
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