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05/10/2006 02:55:05 AM · #1 |
I have been trying to figure this one out. My camera, like many DSLRs has a 1.5x crop factor as the sensor is smaller than 35mm film. Does this mean that to get "normal" perspective I should still use a 50mm lens or that I should be using a 50/1.5 = 33mm lens or some other number.
At 33mm the frame coverage is the same as 50mm on a 35mm SLR but I'm not sure the perspective is the same. Anyone know? |
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05/10/2006 03:04:06 AM · #2 |
the crop factor of 1.5 means whatever lens u get, u multiply it by 1.5.
Like a 500mm lens on your camera means 500x1.5=750mm, so that means you get a 750mm in 35mm(film) equivalent in focal length using that same lens |
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05/10/2006 03:15:42 AM · #3 |
I'm not sure of what you mean by perspective. To me, you change the perspective by changing the angle or position of the camera.
If you are talking about field of view, then yeah, you are right. |
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05/10/2006 12:21:56 PM · #4 |
Originally posted by gbautista87:
I'm not sure of what you mean by perspective. To me, you change the perspective by changing the angle or position of the camera.
If you are talking about field of view, then yeah, you are right. |
Perspective shows the apparent depth (3d dimension) in photos. Clasic examples are train tracks appearing to converge, a line of telephone poles getting smaller in the distance, etc. See //www.dpchallenge.com/challenge_results.php?CHALLENGE_ID=377 for examples.
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05/10/2006 12:25:54 PM · #5 |
A 'normal' lens is the diagonal of the film/sensor measurement.
50mm on a full frame/35mm is the corner to corner measure. So get the measurements of your sensor and take the diagonal and there ya go. Same thing for bigger film like medium format where 90mm is the normal lens (i think it's 90, depends on what film format i suppose, i am not a MF guy)
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05/10/2006 12:30:39 PM · #6 |
Originally posted by crayon:
the crop factor of 1.5 means whatever lens u get, u multiply it by 1.5.
Like a 500mm lens on your camera means 500x1.5=750mm, so that means you get a 750mm in 35mm(film) equivalent in focal length using that same lens |
That's not exactly how I understand it. What I have read says that that 500mm lens in a 1.5 sensor will give you the field of view of a 750mm lens, but will not give you the magnification of the 750. In other words, it would be as if you cropped a portion of the image off, hence the term "crop factor".
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05/10/2006 12:47:03 PM · #7 |
Originally posted by Leok:
I have been trying to figure this one out. My camera, like many DSLRs has a 1.5x crop factor as the sensor is smaller than 35mm film. Does this mean that to get "normal" perspective I should still use a 50mm lens or that I should be using a 50/1.5 = 33mm lens or some other number.
At 33mm the frame coverage is the same as 50mm on a 35mm SLR but I'm not sure the perspective is the same. Anyone know? |
Perspective is determined by where your camera is in relation to your subject. If you use a 50mm on a FF sensor, and a 30mm on a 1.6 crop, you will get about the same framing if you stand at the same point. You will also get the same perspecitve.
If you use a 50mm lens on both FF and 1.6 crop cameras, and frame your shot the same, same, you will have different perspective because you will have to stand about 1.6 times further away with the croped sensor camera. |
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05/10/2006 02:09:42 PM · #8 |
Originally posted by dpdave:
Originally posted by crayon:
the crop factor of 1.5 means whatever lens u get, u multiply it by 1.5.
Like a 500mm lens on your camera means 500x1.5=750mm, so that means you get a 750mm in 35mm(film) equivalent in focal length using that same lens |
That's not exactly how I understand it. What I have read says that that 500mm lens in a 1.5 sensor will give you the field of view of a 750mm lens, but will not give you the magnification of the 750. In other words, it would be as if you cropped a portion of the image off, hence the term "crop factor". |
Magnification is a myth, using the word just confuses the issue. Want proof? Just look at binoculars, which use both magnification and field of view in their nomenclature.
Here's the bottom line: If you set your camera on a tripod with a WA lens and shoot a picture, then swap out to a 200mm lens and shoot a picture, without changing the camera's position at all; and THEN if you crop the WA picture to show the same area of the subject as the 200mm does, and put the pictures side-by-side, they will be absolutely identical if you disregard the greater "granularity" of the heavily-cropped image when it's blown up to match.
So "magnification" IS "crop", plain and simple, as far as we are concerned. But it's a bad word to use in the normal photographic context. We should reserve it for extreme macro usage, where 1:1 = life-size and 2:1 is 2x magnification. And THIS is regardless of the sensor: it just means that a centimeter-diameter object will be a centimeter at 1:1 and 2 centimeters (larger than life size) at 2:1 on the sensor. and this is true even if the magnification is so great it actually crops the object on the sensor.
This issue of "perspective" is entirely controlled by the relationship of the objects in the image to each other. The earlier exercise, with WA and 200mm, proves that. So, if you want to call the image delivered by a 50mm lens on a 35mm camera a "normal perspective" (The actual diagonal of 35mm film is around 43mm, sot hat would be "true" normal), you are basically saying "this field of view and this relationship of objects to each other most closely represents the way my eyes see the scene". Personally, I'd call that a "normal field of view".
In any case, for any given film/sensor size, the "normal" lens is indeed the lens of which the focal length most closely matches the diagonal of the sensor/film. That's something like a 35mm lens on a Canon 20D, and what it means is that if you set up a tripod and shoot with a 5D (FF camera)/50mm lens, then mount the 20D/35mm combo, those images will match each other very closely.
R.
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05/10/2006 02:14:57 PM · #9 |
Yeah, what Bear said. I wanted to say it, but I knew he'd be along and tell it so much more clearly :-)
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05/10/2006 02:27:18 PM · #10 |
Yep, sure can't really add a lot ot Robert's excellent response. Bottom line, yes, to get the same angle of view, and thus the same relationship of objects in the foreground to background, use a lens that reflects the sensor size in your cam. For 1.6-crop (Canon) cams, that's about 28mm if you go by the "sensor diagonal rule" or 31mm if you go in relation to 50mm as "standard on a FF body"." For Nikon (1.5-crop), the numbers are 33mm and 29mm.
Most other cameras are close to either the Canon or Nikon sensor size, with the exception of a few that are 2.0-crop. For 2.0-crop cams, the numbers are 22mm and 25mm.
Message edited by author 2006-05-10 14:29:26.
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05/10/2006 06:30:57 PM · #11 |
Thanks for your responses everyone, and especially Robert (Bear_Music) for your lengthy explanation. That is what I originally thought, but then I started to have doubts, and got myself all confused.
Your example of the WA v.s. 200mm lens is excellent. Its not the lens that gives perspective then, but the distance to subject. The lens just "crops" the view for you. Never though about it that way but it makes sense (now).
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05/10/2006 06:34:37 PM · #12 |
Originally posted by Leok:
Thanks for your responses everyone, and especially Robert (Bear_Music) for your lengthy explanation. That is what I originally thought, but then I started to have doubts, and got myself all confused.
Your example of the WA v.s. 200mm lens is excellent. Its not the lens that gives perspective then, but the distance to subject. The lens just "crops" the view for you. Never though about it that way but it makes sense (now). |
de nada, amigo.
R.
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