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Photo Forum / Film Photography / Medium format / May 2005Lens lengths MF vs 35mm
Ok, I am a dummy, but an 80mm for 6x6 is a standard lens, no? Is there a rule of thumb to think of a MF lens and it's 35mm counterpart? Is a 80mm on 6x6 the same as a 50mm on 35mm? What is the 6x6 equivalent of a 90mm on 35mm? satbunny a écrit : > Ok, I am a dummy, but an 80mm for 6x6 is a standard lens, no? > Is there a rule of thumb to think of a MF lens and it's 35mm > counterpart? The rule of thumb is to consider that a "normal" lens has a focal length equal to the diagonal of the negative. With a 6x6 negative (in fact 56x56mm) this length is 56x1.4=78.4 mm, hence the "normal" lens of 80mm. This diagonal is roughly 50mm (more like 43mm) on a 24x36 negative. > Is a 80mm on 6x6 the same as a 50mm on 35mm? What is the 6x6 equivalent > of a 90mm on 35mm? It would be something like a 60mm. It is especially weird to make strict equivalences between 6x6 and 24x36 lenses as the negative proportions (1:1 vs 2:3) are so different.  SignatureVincent Becker Photographies et appareils anciens - Photography and classic cameras <URL:http://www.lumieresenboite.com> > > Is a 80mm on 6x6 the same as a 50mm on 35mm? What is the 6x6 equivalent > > of a 90mm on 35mm? > > It would be something like a 60mm. More like 150 mm. ;-) > It is especially weird to make strict > equivalences between 6x6 and 24x36 lenses as the negative proportions > (1:1 vs 2:3) are so different. That's right. Yet a simple rule is to multiply any 35 mm format focal length by 1.6 to get the 'equivalent' 6x6 format focal length. >>It would be something like a 60mm. > More like 150 mm. > ;-) Ah, yes, I made the conversion in the wrong way :-) SignatureVincent Becker Photographie et appareils anciens - Photography and classic cameras http://www.lumieresenboite.com Contact direct : http://www.lumieresenboite.com/contact.php > It is especially weird to make > strict equivalences between 6x6 and 24x36 lenses as the negative > proportions (1:1 vs 2:3) are so different. The negative proportions are unimportant. What *is* important is the size of the circle covered by the lens. -- dadiOH ____________________________ dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico > > It is especially weird to make > > strict equivalences between 6x6 and 24x36 lenses as the negative > > proportions (1:1 vs 2:3) are so different. > > The negative proportions are unimportant. What *is* important is the > size of the circle covered by the lens. On the contrary. The *horizontal* angle of view is what people use as a reference to know how wide a lens is, how much will fit in the picture. Lens and camera manufactures however provide us with data about the *diagonal* angle of view. When two formats are different in aspect ratio, comparing lenses by diagonal angle of view will give the wrong impression. And that is happening here too. The 80 mm lens on 6x6 and the 50 mm lens on 35 mm format have similar diagonal angles of view. But their horizontal angles of view differ more. So the usual fixed factor conversion, "6x6" = 1.6 * "35 mm format", is nice, but not accurate. It can be very important to know that, because the two formats differ in aspect ratio, you can't get as much in the picture using a 40 mm lens on 6x6 as you can using a 25 mm lens on 35 mm format. (Unless you have acquired the habit of composing diagonally, of course. ;-)) Many the people who have though about buying, or even bought, a Hasselblad Super Wide, believing that it is as "super wide" as the super wide lenses found in 35 mm format. And going by the simple conversion, the 38 mm should be as wide as a 24 mm lens on 35 mm format. But in real life (and despite its diagonal angle of view of just about 90 degrees, competing even with 21-22 mm lenses on 35 mm format), it's just a bit wider than a 28 mm lens on 35 mm format. Different negative proportions, you see... The circle covered is of no importance whatsoever as long as it covers the entire format. And that of all 6x6 lenses and 35 mm format lenses do. ;-) >>> It is especially weird to make >>> strict equivalences between 6x6 and 24x36 lenses as the negative [quoted text clipped - 9 lines] > Lens and camera manufactures however provide us with data about the > *diagonal* angle of view. Yeah, you are right because the diagonal defines the diameter of the *circle* covered by the lens. -- dadiOH ____________________________ dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico > > The *horizontal* angle of view is what people use as a reference to > > know how wide a lens is, how much will fit in the picture. [quoted text clipped - 3 lines] > Yeah, you are right because the diagonal defines the diameter of the > *circle* covered by the lens. It doesn't. That circle may be 2 feet in diameter, even when the format itself may be a tiny 24 x 36 mm. It most likely will not, but there it is: the circle is of no (!) importance, as long as it is large enough to cover the frame. Or how would you say 'oversized circle of coverage' lenses, a.k.a. shift lenses, compare to other lenses? Where would the size of the circle it can cover lead you? And how do you propose to 'fix' it so that what they actually produce on film is not at odds with what your 'circle of coverage' comparison methiod would lead us believe? ;-) Just keep it simple, forget about circles and keep to the frame dimensions. The angle of view, both vertically, horizontally, and diagonally) is determined by focal length and the *frame* dimensions. The aspect ratio of the frame therefor *is* important, the circle covered *is not*. Unless, of course, you want to talk about lenses that do not cover a given format. My opinion about such lenses is simple: if you can find any, avoid them. >>> The *horizontal* angle of view is what people use as a reference to >>> know how wide a lens is, how much will fit in the picture. [quoted text clipped - 10 lines] > It most likely will not, but there it is: the circle is of no (!) > importance, as long as it is large enough to cover the frame. OK, circle minimally necessary to cover the format used then. SignaturedadiOH ____________________________ dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico > OK, circle minimally necessary to cover the format used then. This is called "diagonal" by some weird people :-) SignatureVincent Becker Photographies et appareils anciens - Photography and classic cameras <URL:http://www.lumieresenboite.com> Recently, dadiOH <dadiOH@wherever.com> posted: >>> The negative proportions are unimportant. What *is* important is >>> the size of the circle covered by the lens. [quoted text clipped - 8 lines] > Yeah, you are right because the diagonal defines the diameter of the > *circle* covered by the lens. Hopefully, not. One could expect serious vignetting and possibly other distortions in the corners of the frame of such lenses. Typically, the circle covered by the lens at the focal plane is larger than the frame mask. Neil > The negative proportions are unimportant. What *is* important is the > size of the circle covered by the lens. I don't think so. For example, a 80mm lens on a 6x6 camera will have the horizontal angle of view of a 50mm on a 24x36 camera, but the vertical angle of view of a 35mm, whatever the circle covered by the lens. SignatureVincent Becker Photographies et appareils anciens - Photography and classic cameras <URL:http://www.lumieresenboite.com> > Ok, I am a dummy, but an 80mm for 6x6 is a standard lens, no? > Is there a rule of thumb to think of a MF lens and it's 35mm > counterpart? > Is a 80mm on 6x6 the same as a 50mm on 35mm? What is the 6x6 equivalent > of a 90mm on 35mm? Multiply by 8/5 (1.6) to get the 120 equivalent. Thanks, so the conversion from 35mm to 6x6 is the same as from the APS-C digital sensors to 35mm! > Thanks, so the conversion from 35mm to 6x6 is the same as from the > APS-C digital sensors to 35mm! Only coincidentally. > Only coincidentally. That's funny anyway :-) SignatureVincent Becker Photographies et appareils anciens - Photography and classic cameras <URL:http://www.lumieresenboite.com> > Ok, I am a dummy, but an 80mm for 6x6 is a standard lens, no? > Is there a rule of thumb to think of a MF lens and it's 35mm > counterpart? > Is a 80mm on 6x6 the same as a 50mm on 35mm? It is a bit longer, see below. ________________ > What is the 6x6 > equivalent of a 90mm on 35mm? 135 mm. See below _________________ A 35mm lens has to cover a circle with a diameter of at least 1.5". To determine the 35mm equivalent for any other film size, use a ratio where "FS" = the longest dimension of the film... 1.5:50::FS:x In your example, "FS" = 2.25 so... 1.5:50::2.25:x so "X" = 75mm A generic formula to get any image size/focal length equivalency would be... IS1:FL1::IS2:FL2 -- dadiOH ____________________________ dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico > A 35mm lens has to cover a circle with a diameter of at least 1.5". > To determine the 35mm equivalent for any other film size, use a ratio [quoted text clipped - 8 lines] > be... > IS1:FL1::IS2:FL2 Correction: The "longest dimension of the film" should be the diameter of the circle needed to cover same which means that it should be the diagonal of the frame. -- dadiOH ____________________________ dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico > Correction: > The "longest dimension of the film" should be the diameter of the > circle needed to cover same which means that it should be the diagonal > of the frame. There we are. So scrap that talk about circles, talk about the actual frame dimensions. So you too want to compare formats by their diagonal angles of view? And say too that the frame proportions do not matter? Hmm... Don't. ;-) |
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