pjdilip Posted August 9, 2012 Share Posted August 9, 2012 <p>Hi friends, I thought I understood enough about lens focal lengths and stuff like that, but of late have started feeling inadequate in this aspect (maybe approaching senior status!). <br>Firstly, why do people insist on multiplying fl numbers on smaller frame cameras (DX in Nikon)? As far as I can tell, a small frame camera just cuts out more of the surround, but thee size of the image remains the same. People go so far as to say that using a smaller format actually lengthens thee fl! That's just bs, isn't it, since you could always crop out any excess surround from thee larger format image as well? Does the multiplier effect actually make the same lens behave like a longer one on the smaller format, does it have shallower depth of field or smaller aperture for example?<br>Secondly, I wonder whether I really understand the perspective angle (pun intended)... does it change the relative sizes of the foreground subject versus the background subject, for instance, as a real change in fl would? How about the compression effect of long fl or the flattening achieved by wide lenses? I would assume that no such effects accompany the so-called increase in fl on the smaller format?<br>I know I should be reading up some basic tech stuff... but I'm interested here in the popular perceptions...</p> Link to comment Share on other sites More sharing options...
SCL Posted August 9, 2012 Share Posted August 9, 2012 <p>Forget popular perceptions and go with facts. There are lots of threads on this subject here on PN, some pretty convoluted. So my suggestion is to forgo the technical details and think of crop sensors doing just that...cropping a portion of the full frame sensor, and then enlarging the cropped area to the equivalent viewing space you would see with a full frame sensor. The subject will appear larger than it would with a full frame sensor. The laws of physics don't change because of the size of the sensor you are using....a 100mm focal length lens is still 100mm regardless of what sensor it is attached to, and it doesn't magically become something else. Rather than get wound up on DOF and perspective, I'll leave that for another respondee...but once again it has been covered ad nauseam here and on most other photo sites.</p> Link to comment Share on other sites More sharing options...
frank_skomial Posted August 9, 2012 Share Posted August 9, 2012 <p><a href="../beginner-photography-questions-forum/00ah0n">http://www.photo.net/beginner-photography-questions-forum/00ah0n</a></p> <p> </p> Link to comment Share on other sites More sharing options...
pjdilip Posted August 9, 2012 Author Share Posted August 9, 2012 Ok... using the same lens on a full-frame camera versus a small-frame is simple, it just drops out the surround. What about using a large-format lens on a smaller format camera, say a large format lens on a 35mm SLR camera? Is a 100mm large format lens going to do the exact same thing as a 100mm 35mm lens on the SLR? Or will it be like a 250mm SLR lens? Would enlarger lenses act the same way? Sorry to ask these trivial questions... I will do the reference work, promise! Link to comment Share on other sites More sharing options...
steve_levine Posted August 9, 2012 Share Posted August 9, 2012 <p>Yes a 100MM lens is the same on any format.<br> Focal length is a constant factor. What changes with format is angle of view and depth of field.</p> Link to comment Share on other sites More sharing options...
JDMvW Posted August 9, 2012 Share Posted August 9, 2012 <p>recent thread - http://www.photo.net/nikon-camera-forum/00afAG<br> The whole multiplier idea is simply a curse from old film shooters to confuse people who have never used a film camera in their life.</p> <p>My advice, forget about it. Only the sensor size is different. The lens is simply whatever focal length it really is. </p> Link to comment Share on other sites More sharing options...
Matt Laur Posted August 9, 2012 Share Posted August 9, 2012 <p>But using a smaller sensor doesn't just drop off some of the image. If you cropped the file that comes out of a larger camera, you're throwing away a lot of the data you've got. A sensor engineered to be smaller may make some compromises (more noise in low light, for example), but you're <em>keeping all the data</em>. That's a very important distinction. <br /><br />As I'm doing some side-bar testing of a D3200 right now, I can tell you that 24mp in that smaller format sensor (APS-C) is a lot less expensive that using a D800's 36mp and cropping it down to 24mp to achieve the same framing. It matters.</p> Link to comment Share on other sites More sharing options...
GerrySiegel Posted August 9, 2012 Share Posted August 9, 2012 <p>It is easier to explain with diagrams, but I won't bother because others have done this so many times and done quitewell. A 100 mm lens can be a big fat 100mm lens or a small one, depending on the sensor size field it must cover but the FL is always 100mm blessedly same. It will still capture the same light rays of its focal length to fill the frame that lens is built for. Crop factor or field of view equivalence using the old double frame 35mm is just a <em>rough</em> equivalent to give you a mental idea of how one format relates to another. (Movie 35mm-single 35mm- frames probably also had a known crop factor compared to still Leica photography on a set or the director's view gadget... <br> (It is easy to get confused with all the sensor sizes, I was no exception in that at first, almost like always mentally converting metric length to inches and getting stuck at times.)<br> If you get to look at the lens in finder you can see what 1.6 or 2X looks like with different FL optics. And how DOF remains tied to focal length as well. It is not that tough to get when you see the diagrams.</p> Link to comment Share on other sites More sharing options...
James G. Dainis Posted August 10, 2012 Share Posted August 10, 2012 Probably because cameras no longer come with a "normal" lens. When 35mm cameras came with a normal 50mm lens, people knew that 80mm was mild telephoto and 35mm was mild wide angle. If DX cameras came with a normal 35mm lens, they would know that 50mm is mild telephoto and 24mm was mild wide angle. An 80mm lens is a normal lens for a medium format camera. The 80mm image circle falls fully on the film diameter. Put an 80mm lens on a 35mm camera (or FX) and a 36 x 24mm section is cropped out of that 80mm image circle. The 35mm camera is a crop camera. Anytime you use a larger focal length than the normal focal length for that camera, be it DX, 35mm, MF or LF format, you are cropping. James G. Dainis Link to comment Share on other sites More sharing options...
pjdilip Posted August 10, 2012 Author Share Posted August 10, 2012 <p>Thanks for thee responses and the links. appreciate Matt's point in favour of small sensor... usually it's the other way round!<br> One disadvantage in small sensors I can see is that it makes it more difficult to produce the typical telephoto effect, separation of foreground and blurring the back (and achieving a pleasing bokeh?), because we're using shorter telephoto focal lengths ... we would have to compensate that by using larger apertures., giving less depth of focus for the main subject.. a concern for bird and flower photographers. With larger sensors, we can make do with slower lenses and still achieve the background blur... cheaper, lighter, presumably higher optical quality for the same price? That would actually go counter to the usual telephoto advantage of small sensors people cite usually.<br> Any advantage in small format from the framing aspect is, if I understand, mainly to do with the smaller frame size, which of course could be achieved on the large format too simply by cropping out at the time of printing. I appreciate the price differential referred to by Matt. Since now pixels are being packed more densely, I guess it makes sense to use shorter telephotos to achieve the same effect on the small sensor, with the same megapixels thanks to technology!<br> The advantages would appear the other way round for wide angle users for landscapes: we need wider lenses for small format to encompass the same scene, probably leading to higher design problems, higher lens cost etc. But that would be offset by using smaller apertures for a given effect (the opposite of telephoto, where we want to pick off or isolate a subject).<br> The fate of telephoto landscape users would be hung somewhere inbetween? It boggles the mind ... thanks all!</p> Link to comment Share on other sites More sharing options...
pjdilip Posted August 10, 2012 Author Share Posted August 10, 2012 <p>Sorry for the Biblical tone in thee post... dodgy keyboard!</p> Link to comment Share on other sites More sharing options...
bebu_lamar Posted August 10, 2012 Share Posted August 10, 2012 <p>The confusion about this subject is about manufacturers as well as many people taking the 35mm as standard. There were many formats before digital and nobody was talking about multiplier and such. They just know that each format need different focal length.</p> Link to comment Share on other sites More sharing options...
bebu_lamar Posted August 10, 2012 Share Posted August 10, 2012 <p>The smaller format does have more depth of field than the larger format. A 200mm lens on a DX camera focused at the same distance would have more DOF than a 300mm on an FX camera. However, a 200mm at the same distance would have less DOF than a 200mm on an FX camera.</p> Link to comment Share on other sites More sharing options...
scott_ferris Posted August 10, 2012 Share Posted August 10, 2012 Dilip, You are confusing compression and perspective with focal length, they are not related. The only thing that creates perspective is position. If you use a 200mm lens on your crop camera to frame your subject, and a 300mm on a ff camera to get the same framing from the same place your perspective, and compression, are the same. A 200 f2.8 is cheaper than a 300 f4 and that is what you would need for equivalence. Of course when you start to get longer lenses the prices to maintain equivalence gets very expensive! The "telephoto" effect does not work to the numbers, or even close to the numbers, bigger pixels are much better than smaller pixels, add in the iso crop factor and the tele effect is even less true. Link to comment Share on other sites More sharing options...
pjdilip Posted August 10, 2012 Author Share Posted August 10, 2012 <p>Alas... I don't have no FF digital camera to experiment ... and it looks like I shall have to take up a much deeper study to understand this! Looking forward to more good stuff... </p> Link to comment Share on other sites More sharing options...
scott_ferris Posted August 11, 2012 Share Posted August 11, 2012 Dilip, This article might help. http://www.josephjamesphotography.com/equivalence/ Link to comment Share on other sites More sharing options...
pjdilip Posted August 11, 2012 Author Share Posted August 11, 2012 <p>Hi Scott, thanks .. looks like a great site, my weekend cup is full!</p> Link to comment Share on other sites More sharing options...
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