peterb Posted September 21, 2006 Share #1 Posted September 21, 2006 Advertisement (gone after registration) Focal length multiplication aside and, forgetting any lenses SPECIFICALLY designed for digital (like the new f4 Tri-Elmar), when you mount an existing f2.8 lens designed for the 35mm M on the digital M8 will it still be an f2.8 lens? Or will a Summicron suddenly become a Summilux or, instead, turn into an Elmarit? Or, will it become something in between them? Just curious. Peter Link to post Share on other sites More sharing options...
Advertisement Posted September 21, 2006 Posted September 21, 2006 Hi peterb, Take a look here Digital focal length question.... I'm sure you'll find what you were looking for!
wmyowell Posted September 21, 2006 Share #2 Posted September 21, 2006 The focal length of the lens isn't changed, just the amount of its "image circle" that is captured on the digital sensor. What confuses some is the concept of "35mm equivilent". The Digilux 2 uses this on the zoom ring. Personally, since it attempts to match the field of view with that of the cameras which we are all familiar, I find it more useful than 7mm or some such. The F stop is an expression of the ratio of the lens diameter to the focal length of a lens. Thus a 50mm lens set at F2 has a lens diameter of 25mm, or 1/2 of 50 mm. Bill Yowell Link to post Share on other sites More sharing options...
gravastar Posted September 21, 2006 Share #3 Posted September 21, 2006 Aperture and focal length of a lens remains the same regardless of the sensor size. The ratio (f number) doesn't change. So your f1.0 Noctilux etc. remains f1.0. What you may find different when working near full aperture is that the image gives the impression of being slightly brighter because the light fall off in the corners won't be so severe. Bob. Bill answered while I was typing Link to post Share on other sites More sharing options...
gepetto Posted September 21, 2006 Share #4 Posted September 21, 2006 The F stop is an expression of the ratio of the lens diameter to the focal length of a lens. Thus a 50mm lens set at F2 has a lens diameter of 25mm, or 1/2 of 50 mm. I think the key to Peter's question is in what Bill has said. The focal length of the lens to it's assigned F stops is in relation to 35mm film. A 50mm lens for film does not have a 50mm focal length while using an APS-C sized sensor. With a 1.33x crop factor a 50mm lens used for film has a 66.5mm focal length. The same lens at F2 the aperture will remain having a 25mm opening which is no longer half of the focal length. What this translates into is greater depth of field. At least that is how I am seeing it per Bill's definition. Link to post Share on other sites More sharing options...
kobold Posted September 21, 2006 Share #5 Posted September 21, 2006 The original poster was asking about whether the wide open marked ƒ stop changes when a lens designed and named for 35mm photography is used on a crop frame camera. AFAIK, it doesn't. And gepetto's point re. DOF is spot on, in my experience (and the main reason I still favour the 5D). Anyone else? Link to post Share on other sites More sharing options...
lct Posted September 21, 2006 Share #6 Posted September 21, 2006 ...The F stop is an expression of the ratio of the lens diameter to the focal length of a lens. Thus a 50mm lens set at F2 has a lens diameter of 25mm, or 1/2 of 50 mm... Agree of course. Hi Bill, nice to 'see' you again! Link to post Share on other sites More sharing options...
kobold Posted September 21, 2006 Share #7 Posted September 21, 2006 Advertisement (gone after registration) I was referring to the amount of light that the lens transmits, rather than the theoretical calculation of the ƒ stop. As far as I know, when you use an ƒ2 lens on a crop frame camera, it transmits the same amount of light as when it's fitted to a FF camera, and I assumed that was what the original poster was asking about. It's been a long day, and I might have missed the point, of course. Cheers to all, Kit Link to post Share on other sites More sharing options...
TimF Posted September 21, 2006 Share #8 Posted September 21, 2006 With a 1.33x crop factor a 50mm lens used for film has a 66.5mm focal length. The same lens at F2 the aperture will remain having a 25mm opening which is no longer half of the focal length. That's not true. The focal length remains 50mm irrespective of the size of the image recording area. On a reduced frame digital sensor you will only see the area that equates to a 66mm focal length on a full frame 35mm camera, but with the depth of field of a 50mm rather than that of the shorter lens. The outcome, a slight increase in DoF, is as you say, but the reason given as to why is not. Cheers! Link to post Share on other sites More sharing options...
cbretteville Posted September 21, 2006 Share #9 Posted September 21, 2006 The lens' focal length remains the same regarless of the size of the size of the image capturing 'device'. As this is true it also must be true that the f-stops do not change as they are a fraction of the lens' focal length. Original shot, 35mm Summicron at f2.0: [ATTACH]9443[/ATTACH] Same shot cropped by a factor of 1.33 (i.e., digital zoom by Photoshop). [ATTACH]9444[/ATTACH] To get this FOV on film I'd have to use, from the same shooting position, a lens with a focal length of 35.0x1.33=46.55mm. As the DOF of the image cast by the 35mm lens is the same whether it projecrts on a full format frame of film or a cropped censor we get the apperance of a larger DOF as the FOV is equivalent to that of a 46.55mm lens which would have a shallower DOF had it been used on full format film. - Carl Link to post Share on other sites More sharing options...
gduveen Posted September 21, 2006 Share #10 Posted September 21, 2006 There is a fine discussion of these questions in the LFI for April 2006 (Issue 3/2006) which emphasises the field angle of a lens and interprets this in relation to both film and digital media, and showing the relationship between them. Gerard Link to post Share on other sites More sharing options...
albertwang Posted September 21, 2006 Share #11 Posted September 21, 2006 the same whether it projecrts on a full format frame of film or a cropped censor we get the apperance of a larger DOF as the FOV is equivalent to that of a 46.55mm lens which would have a shallower DOF had it been used on full format film. - Carl But do appearances count? The depth of field may seem increased in length in the picture but that doesn't change the actual physical distance that the objects are in the focus. Cropping only simply zaps away elements but doesn't transform the object relation to each other in the physical sense (oops, did I sound like Wittgenstein?). Link to post Share on other sites More sharing options...
comapedrosa Posted September 21, 2006 Share #12 Posted September 21, 2006 What about long noses?? Building on the discussion above, here's a question I've been wondering about and was expecting more complains about than what I've read: We've established that on a non-FF camera we'll basically get a crop of the FOV we're used to. Hence, if I use a 35mm on my M8, I get the "FOV" I was used to w/ a 50mm on my M7. BUT, the 35mm has a (very) different perspective from the 50mm (it creates "longer noses" - the same way a longer focal flattens the perspective). Now, since my non-FF sensor only performs a crop, what I get with my 35mm on the M8 is "long nose" perspective but with a 50mm FOV. That animal is pretty different from either the 35mm or the 50mm on FF. Is this something people have noticed/complained about? (of course, in most parts of Asia, most of us would be considered long noses no matter what the lens ) Link to post Share on other sites More sharing options...
wmyowell Posted September 21, 2006 Share #13 Posted September 21, 2006 A 35mm lens does not have a "different perspecitve" from a 50, 200 or 20mm lens. The difference in perspective that you are observing is due to the fact that you shoot from a closer position with the 35mm lens that you do with a 50mm. Thus, the distance from the tip of your model's nose to that model's cheek is a larger percentage of the distance from which you are shooting. This increases the apparent size of the nose. If you shoot from the same position, there will be no difference in perspective, only more of your subject will be recorded on the film/sensor. Bill Yowell Link to post Share on other sites More sharing options...
comapedrosa Posted September 21, 2006 Share #14 Posted September 21, 2006 ooops, thank you Bill! I feel very dumb all of the sudden... Link to post Share on other sites More sharing options...
Riley Posted September 22, 2006 Share #15 Posted September 22, 2006 Most of you might remember Andy Piper's review of the Digilux 2, for tired minds you can find it here: Leica Digilux 2 Review I direct your attention to the para on "The Lens" in which Mr Piper says and I quote "The Vario-Summicron “shoots” wider than its “28-90mm” rating. The focal lengths are accurate if you crop the Digilux’s 4:3 “ideal” format to the shape of a 35mm frame. But if you use the entire Digilux image, the results look more like 8x10’s (A4s) cropped from a 24-75mm zoom." I have always been very puzzled by this, as even the diagram included did nothing to clarify the issue in my mind. Is there anyone here who would care to canvas an opinion on this? And given it is wider than its focal length, exactly how wide is the lens? Riley Link to post Share on other sites More sharing options...
TimF Posted September 22, 2006 Share #16 Posted September 22, 2006 exactly how wide is the lens? Why, 28mm of course (though given that its a zoom, the true focal length may not be exactly that as advertised at either end). Its just that the differing 4/3rds image format gives a look not entirely consistent with the well-known 2:3 35mm format until the image is cropped to shape as Andy stated. The same is true with other fomats when compared with 35mm,which is why so-called equivalency between an angle of view for a medium or large format lens can only ever be approximated to that on a 35mm camera. Link to post Share on other sites More sharing options...
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