 Apryl D. Deeter |
the Conversion factor-HELP! I am trying to move from serious hobbiest/amateur to establishing a business, building a portfolio, etc. & am looking into buying a few new lenses. I thought I was ready to get the new lenses I have been reading about, researching, that will fit for the work I want to do, but now I am hearing about the conversion rate for non-full frame cameras. I am using a Nikon D80. Do I now have to start over on considering what size lenses I should purchase??? I have been somewhat confused up to this point, now beginning to feel completely confused!Can anyone help me? Thanks guys!
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
How are you confused about the narrower field of view when you're using a camera that has that? The narrower field of view doesn't really make a lenses act like a different focal length as some describe it to be. It means the outside portion of the normal sized frame is no longer included. This usually gets in the way with wide angle lenses where people want to use wide angles when standing very close to the subject. The field of view would require you to back up to get the same scope. And in some situations, that would result in somebody stepping in front of you and blocking you shot because you had to back up to get wide enough. Or there's not enough space to back up. Now whatever it is that you plan on shooting, whether you need to choose different lenses or just back up I can't tell you for sure.
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Apryl D. Deeter |
Ok, I may sound completely stupid, but I went from using a film SLR to digital without knowing that this is how most digital cameras are (narrower field of view). I honestly don't understand it. I just don't want to go further without knowing if this is going to affect any new purchases I make-I honestly didn't know it would make a differenceion the way you shoot. I am planning on photographing mostly children, families, etc. natural light photography, lots of close ups, etc. Could you explain further for me?
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Jon Close |
It makes no difference in the way you shoot. You simply need a different range of lens focal lengths than you're used to with 35mm film. Just as the range of lenses used with medium format cameras is different than needed with 35mm. Where you may have used a 19mm-35mm wide-angle zoom on the film SLR, to get the same range of field of view on the D80 you'd need a 12mm-24mm zoom on the D80. To get the utility of a 28-105 normal zoom on the 35mm film camera, the D80 would need a 18mm-70mm zoom.
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
In practical uses though, say you already had your portrait studio and you switch to a digital camera. You already have your finite working space, so if you were not able to move back to get the same field of view as before, then yes you may need to buy different lenses. But to use the zoom lens example, to fill the frame with the 28-105 you would need to shoot at 70mm instead of 105mm, while standing at the same spot as you were used to. As to the reason for the narrower view, the sensors are expensive and to keep the price down they are smaller than the normal film area. Therefore, the viewfinder and the area inside the camera body are smaller to match the size of the sensor.
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Alan N. Marcus |
Hi Apryl, The camera lens projects a miniature image of the outside world onto the surface of the light sensitive chip inside the camera. A “normal” focal length lens mimics the human eye as to angle of view. We humans see an angle of about equal to 53°. What focal length lens will be considered normal? Opticians tell us that when we mount a lens with a focal length that nearly matches the diagonal measure of the chip, the view seen by the camera mimics the human condition and this is said to be normal. This is also true for a film camera. A longer than normal focal length lens, when mounted, imparts a more magnified view. As a result, the angle of view seen by the camera is reduced. A shorter focal length lens yields even more petite view (less magnification) this causes the angle of view to be quite wide. A 35mm film camera utilizes a film frame that measures 24mm height x 36mm length. The diagonal of this rectangle is 43.3mm. Opticians normally mount a 50mm lens as this is a handy rounding up of the diagonal measure. Longer lenses are considered telephoto and shorter wide angle, for this film size. Consider that most lenses used on a 35mm camera would fall in the wide angle range if fitted to a view type camera using 4” x 5" film this is true because the diagonal measure and thus what is normal for this giant camera is a lens with a focal length of about 6 ½“ or 165mm. What I am trying to convey is “what is normal and telephoto and wide-angle is a function of the size of the imaging media. Now your camera spots a chip that measures 15.8mm x 23.6mm. Thus the diagonal measure is 28.28mm. Thus for your camera a 28mm is normal and shorter lenses falls in the wide-angle grouping and longer falls in the telephoto. Incidentally a good starting point for a portrait lens is about 2.5 times the diagonal. Thus for a 35mm this works out to 105mm. For your camera; its 28 x 2.5 = 70mm. What is this conversion factor thing? For most, the 35mm film camera experience is most vivid. Plus most with a collection of old lenses have a gadget bags filled to the brim with lenses designed for the 35mm film camera. How to convert? Again diagonal measure to the rescue (maybe if you are a math lover) . Your camera diagonal 28.28 divide by the 35mm camera diagonal 43.3 = about 0.66 or stated another way about 66%. Some like the inverse better 43.3 divide by 28.28 = about 1.5 (150%) or a factor of 1.5. What do we do with this conversion factor? Say you are told a 105mm makes a perfect portrait lens (35mm thinking). What would a perfect portrait lens be for your camera? 105 divide by 1.5 = 70 or 105 times 66% = 70mm. See how that works. Now go forth with your new found knowledge and convert away. Alan Marcus (know to be a photo math kook i.e. crazy)
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Craig m. Zacarelli |
your subject will be the same size but will appear to take up more of the frame. take a 4x6 photo taken with a 35MM camera and then cut it down 1.6X (off the edges) and theres your print from a crop sensor camera.
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Lawana Miljenovich |
you guys are awesome! Who knew we had to use math for photography. I'm SO incredibly new to photography it hurts so this info helped me out so much. I don't currently own a DSLR (Sony F828) but am in the process of buying a Canon 40d. But I'm doing my research first. So what your saying is... and pardon my ignorance.. but if we're digital, and have lenses designed for digital cameras we don't have to worry about conversion once we know what the diagonal is to figure out our normal lens? Which according to this would be about a 70mm?? The sensor size is 22.2 x 14.8 mm ... can't use my fingers to figure out the diagonal so I'm going to guess... And Craig Z, does what I see in my LCD live view.. does that also need to be considered as "cropped" when I compose my photograph?? I take a lot of close-ups, portraits and the like so I never factor that in. Did I read that right or am I way out in the parking lot of the ball park... way over in the dark spooky part? *sigh* I have a long way to go... :(
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Alan N. Marcus |
Hi Lawana, Most photographers and their teachers / instructors received their basics using the 35mm film camera. Additionally many of these people have gadget bags filled to the brim with used but good 35mm film camera lenses. Conversion factors are a helpful way for these folks to relate one format to another. It will get worse because digital technology advances day-by-day and the sensor sizes will get smaller and smaller. Eventually the 35mm with all accessories will make lovely viewing at the museum along side a display of Civil War medical tools. Your sensor 14.8mm x 22.2mm has a diagonal measure of 26.7mm. This is the measurement you are asking for. So we could say your camera if fitted with a 25mm focal length lens will yield a normal angle of view. The conversion factor for this camera is 1.6 or looking at this from the other direction, your chip is about 60% of the size of a standard 35mm film frame. We can calculate the ideal portrait lens for this chip as we know this to be about 2.5 times the diagonal so this figures out to be about 65mm. Most teachers and books tell us a 105mm is best for portraits with a 35mm film camera so 60% of that value is 63mm. See how that works? Now don’t get carried away by this old fool (me) and my math. It’s nice to know these facts but they seldom does this knowledgemake a big difference in the real world of photography. Photography is both art and science. My world was the science of photography (I am retired) and I am awful when it comes to picture taking. Alan Marcus (dispenses boring and sometimes questionable facts)
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Lawana Miljenovich |
Well I appreciate your "boring and sometimes questionable facts" It's taught me enough to be dangerous which is usually pretty much what this brain can handle on any given subject. I'll be seeing you around this site I'm sure as I'll be shooting out lots more questions. I'll try to search the site as I'm sure many of my questions have been asked before. Thanks again.
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