psss Posted October 29, 2015 Share #21 Posted October 29, 2015 Advertisement (gone after registration) Thank you. THAT is an answer, and I do apologize for the inconvenience that may cause this forum to reply -again- to an obviously dealt with topic. no need for you to apologize, it is a valid question, the discussions surrounding it turned into something completely different..... Link to post Share on other sites More sharing options...
Advertisement Posted October 29, 2015 Posted October 29, 2015 Hi psss, Take a look here What's this "crop factor" (OT from Leica SL sensor). I'm sure you'll find what you were looking for!
IkarusJohn Posted October 29, 2015 Share #22 Posted October 29, 2015 no need for you to apologize, it is a valid question, the discussions surrounding it turned into something completely different..... Joking aside, what Michael was saying and what caused the confusion is that a 70mm lens is a 70mm lens, regardless of the sensor size. That means that the S 70mm lens will give the same field of view on the SL sensor as a 70mm lens designed for either the SL or M camera. Those lenses would just be smaller than the S lens. However, the image on the S camera using the S 70mm lens will be larger by a factor if 1.25 than the image on the SL camera using the same 70mm S lens. Cheers John Link to post Share on other sites More sharing options...
mjh Posted October 29, 2015 Share #23 Posted October 29, 2015 What do you mean the crop factor is 1.25? That when you use an S lens on the SL, the crop factor is 1.25. The field of view of that lens on the SL is equivalent to that of a lens with 1.25x the focal length on the S. Between MF and FF, the notion of a crop factor works in just the same way as it does between FF and APS-C or MFT. A 70mm S lens used on the SL will give the same field of view as any other 70mm lens will do, no crop factor needs to be applied. You could say the same about an FF lens used on an APS-C camera, still the notion of ‘crop factor’ is applied and appears to be useful. Link to post Share on other sites More sharing options...
psss Posted October 29, 2015 Share #24 Posted October 29, 2015 That when you use an S lens on the SL, the crop factor is 1.25. The field of view of that lens on the SL is equivalent to that of a lens with 1.25x the focal length on the S. Between MF and FF, the notion of a crop factor works in just the same way as it does between FF and APS-C or MFT. You could say the same about an FF lens used on an APS-C camera, still the notion of ‘crop factor’ is applied and appears to be useful. this is what i was referring to as the joke... the 70mm S lens just happens to cover a larger area.....almost no lens ONLY covers the sensor it is made for....think of a T/S lens....let's say a 90mm....it covers a much larger area then a "normal" 90mm so you can "move around" within that area (which is pretty much what T/S is) but it still is a 90mm lens..... the reason we talk about crop factors when using a 90mm on a smaller sensor is that FF is what we are comparing focal lengths to....a 90mm on a smaller sensor will still be a 90 but the angle will be like a ....135 (1.5 crop).... Link to post Share on other sites More sharing options...
CheshireCat Posted October 29, 2015 Share #25 Posted October 29, 2015 All these posts about the crop factor, are introducing a big crap factor into this discussion. Link to post Share on other sites More sharing options...
CheshireCat Posted October 29, 2015 Share #26 Posted October 29, 2015 However, the image on the S camera using the S 70mm lens will be larger by a factor if 1.25 than the image on the SL camera using the same 70mm S lens. The images projected by that 70mm lens inside the S and the SL are exactly the same. The only difference is that the S has a physically bigger sensor than the SL, hence it will capture a bigger angle (FOV) than the SL sensor. I often hear sentences like "a 70mm lens captures a diagonal angle of 35 degrees". But this is simply not true. A 70mm lens can capture a much bigger or smaller angle than 35 degrees, depending on its size and design. What is true, is that a full-frame sensor using any 70mm lens will capture an angle of 35 degrees (on the frame diagonal)... provided the lens projects a big enough circle (i.e. provided the lens itself captures at least 35 degrees). So, the big 70mm Leica S lens projects a big circle that is much more than 35 degrees, but the small SL sensor will only capture the center part of the big circle, equivalent to 35 degrees. Instead, the bigger S sensor does capture a bigger part of the circle. How bigger ? Linearly, 1.25 times bigger. See ? The crop factor has nothing to do with the FL. It just happens that if you multiply the FL by the crop factor, the math works for the FOV... but not for many other lens properties. Link to post Share on other sites More sharing options...
Daedalus2000 Posted October 29, 2015 Author Share #27 Posted October 29, 2015 Advertisement (gone after registration) That when you use an S lens on the SL, the crop factor is 1.25. The field of view of that lens on the SL is equivalent to that of a lens with 1.25x the focal length on the S. Between MF and FF, the notion of a crop factor works in just the same way as it does between FF and APS-C or MFT. You could say the same about an FF lens used on an APS-C camera, still the notion of ‘crop factor’ is applied and appears to be useful. What you say is correct of course, but I think the confusion has arisen because you and others used your own definition of a crop factor that uses the S sensor as the reference and not the usual 35mm full frame sensor as a reference that is commonly used. If we agree on the reference sensor I think this discusssion can stop! :-) Link to post Share on other sites More sharing options...
mgrayson3 Posted October 29, 2015 Share #28 Posted October 29, 2015 It helps, as a starting point, to know what combination of settings leads to "the same" picture from two cameras of different size. Then you can see the effect of something like moving a lens from one camera to another by seeing how much that move differs from the neutral settings. Suppose I want to take the "same" picture with two cameras, but Camera 1 has a sensor "c" times the size of Camera 2. Think c<1 so that we can use terms like "larger" and "smaller". To get the same FoV, I need Focal Length 1 to be c times Focal Length 2. To get the same motion blur or lack thereof, I need Shutter Speed 1 to equal Shutter Speed 2. To get the same DoF, I need the f-number of Aperture 1 to be c times that of Aperture 2 (this is somewhat counterintuitive, but you can either work through the math or do some ray tracing - see below). And by "same DoF", I mean that the same OOF point will make a circle of the same diameter in the final print or screen view from either camera - the photos will look the same without microscopic examination. Note that this means the physical size of the opening of the lens needs to be the same for both Cameras! But, and this is the part where most such discussions go off the rails, the larger Aperture 1 with the same Shutter Speed would overexpose the image, so ISO 1 needs to also be c times ISO 2. It's an amazingly tractable problem that causes no end of argument. Of course, color filter array and lens design and resolution differences will still make the pictures slightly different, but not glaringly so, as changes in focal length, aperture, or shutter speed would. --Matt Appendix: Why DoF is larger for a smaller sensor at the same aperture. There are two opposing forces. The smaller sensor (again, I'm thinking c<1 here) needs to be magnified more to make the final image, and that scales an OOF disk by 1/c, but the size of the OOF disk on the smaller sensor scales by c^2. One factor of c comes from the smaller physical aperture - f number is a ratio, and the smaller focal length leads to a smaller opening. And the other factor of c comes from the shorter distance between the rear node and the sensor - the light rays have less chance to diverge and cause the disk. The net effect in the final image, without changing Aperture 1, is an OOF disk c times as large as the one from Camera 2. Fun Fact: Suppose I'm focused on a person and there is a small light in the distance over their shoulder. How large is the OOF disk made by that light? Take the physical aperture of your lens at its current f-stop and place a disk of that size on the person's shoulder. That's how the distant light will look! Link to post Share on other sites More sharing options...
mjh Posted October 29, 2015 Share #29 Posted October 29, 2015 What you say is correct of course, but I think the confusion has arisen because you and others used your own definition of a crop factor that uses the S sensor as the reference and not the usual 35mm full frame sensor as a reference that is commonly used. If we agree on the reference sensor I think this discusssion can stop! :-) Indeed the notion of a crop factor is meaningless without a reference. But then the obvious and thus default reference is the image format the lens in question was designed for, which for S lenses would be 45 x 30 mm. If you took 36 x 24 mm as a universal reference the S would have a crop factor of 0.8 but crop factors < 1.0 don’t make much sense. Link to post Share on other sites More sharing options...
dupiastko Posted October 29, 2015 Share #30 Posted October 29, 2015 I guess all that crop talk supposed to derail the conversation about the terrible sensor quality in the new SL, right? Link to post Share on other sites More sharing options...
CheshireCat Posted October 29, 2015 Share #31 Posted October 29, 2015 Indeed the notion of a crop factor is meaningless without a reference. But then the obvious and thus default reference is the image format the lens in question was designed for, which for S lenses would be 45 x 30 mm. If you took 36 x 24 mm as a universal reference the S would have a crop factor of 0.8 but crop factors < 1.0 don’t make much sense. If it is not specified, the reference is to a 36x24 (i.e. full frame 35mm) sensor. So yes, the S has a 0.8 factor, and it makes perfect sense. Link to post Share on other sites More sharing options...
pop Posted October 29, 2015 Share #32 Posted October 29, 2015 If it is not specified, the reference is to a 36x24 (i.e. full frame 35mm) sensor. (...) If it is not specified, it is not specified. Link to post Share on other sites More sharing options...
lct Posted October 29, 2015 Share #33 Posted October 29, 2015 Both M8 and Hasselblads would have a 1.3x crop factor then... Don't call it "crop" factor if you wish but if the M8 has 1.3x, the 'blad has 0.7x and the S 0.8x in my book. Link to post Share on other sites More sharing options...
Daedalus2000 Posted October 29, 2015 Author Share #34 Posted October 29, 2015 If it is not specified, it is not specified. Come one, this is a serious forum, let's have some meaningful discussions and let's avoid this effort to redefine things to suit ourselves. Please read this: https://en.wikipedia.org/wiki/Crop_factor First sentence for those who do not want to read it: The terms crop factor and focal length multiplier were coined in recent years in an attempt to help 35 mm film format SLR photographers understand how their existing ranges of lenses would perform on newly introduced DSLR cameras which had sensors smaller than the 35 mm film format BTW, It would be interesting to know what is the crop factor of a T lens on the SL camera... Let's see how many different answers we get to this... :-) Link to post Share on other sites More sharing options...
pop Posted October 30, 2015 Share #35 Posted October 30, 2015 Come one, this is a serious forum, let's have some meaningful discussions and let's avoid this effort to redefine things to suit ourselves. Please read this: https://en.wikipedia.org/wiki/Crop_factor First sentence for those who do not want to read it: The terms crop factor and focal length multiplier were coined in recent years in an attempt to help 35 mm film format SLR photographers understand how their existing ranges of lenses would perform on newly introduced DSLR cameras which had sensors smaller than the 35 mm film format (...) Yes, indeed, and the article in the Wikipedia then goes on: most often, this term is applied to digital cameras, relative to 35 mm film format as a reference In the case under discussion here, however, someone asked how his existing MF lens would perform on a FF camera, in which case Michael's use of the cropping factor was consistent with normal use. Actually, the whole discussion about the use of the "crop factor" was quite superfluous as it ought to be a known fact that the sensor in S type cameras is larger than the sensor in the SL. No confusion about the direction of the cropping formula is really possible, this being a serious forum. Link to post Share on other sites More sharing options...
CheshireCat Posted October 30, 2015 Share #36 Posted October 30, 2015 If it is not specified, it is not specified. If you were right (and you are not), then people should specify it before posting BS. As you know, multiplying an unspecified number by a factor leads to an amazingly-unspecified result Link to post Share on other sites More sharing options...
dupiastko Posted October 30, 2015 Share #37 Posted October 30, 2015 god this is hopeless... Link to post Share on other sites More sharing options...
pop Posted October 30, 2015 Share #38 Posted October 30, 2015 This was the original question What happens (crop ratio) when you attach a S lens to the SL body? ... and this is the answer I believe we are discussing here. The crop factor is 1.25. The use case is not the same as the Wikipedia article mentions as the most usual one. The question clearly asked for the crop ratio when using an S lens on an SL body and not a FF lens on a body with a sensor of any other size. Michael's answer just as clearly says that the particular configuration under question yields a crop factor of 1.25. There really is no reason to presume that the answer related to lenses built to any other sensor sizes or to any camera but the SL. Michael's answer is consistent with normal use of the term "crop factor". It is also consistent with the cited Wikipedia article for those who think that when it's written in the Wikipedia it must be true. More importantly, the member who has asked the question has received and understood the answer. CheshireCat: You know perfectly well that you are not to insult other members. Calling Michael's well formulated reply in answer to a well formulated question "BS" may be acceptable where you live; it is not here. Link to post Share on other sites More sharing options...
lct Posted October 30, 2015 Share #39 Posted October 30, 2015 Why doing simple when one can do complicated... Just kidding . I'm no techie folks but when we want to know the equiv. FoV of a lens we multiply its focal length by 1.3 on the M8 and by 0.8 on the S don't we? Same when one calculates the circle of confusion. We take the 24x36mm value and we divide it by the same factors. Link to post Share on other sites More sharing options...
pop Posted October 30, 2015 Share #40 Posted October 30, 2015 Why doing simple when one can do complicated... Just kidding . I'm no techie folks but when we want to know the equiv. FoV of a lens we multiply its focal length by 1.3 on the M8 and by 0.8 on the S don't we? Same when one calculates the circle of confusion. We take the 24x36mm value and we divide it by the same factors. Yes, but only when you want to compare the FOV of the lens when used on a FF camera with the FOV that lens yields with another image size. The question which led to the discussion here explicitly was about the FOV of a lens made for the S when used on the SL. Link to post Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.