I've a question about the crop factor of 1.6 translating a 200 mm lens into a 320 mm lens. Is this increased zoom seen in the viewfinder or only by the sensor? The reason I ask is because in an SLR, the image in the viewfinder does not have anything to do with the sensor (correct?)
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Implications of crop factor
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John Harvie
Well-known member
You don't have to consider the "crop" factor when composing your pictures in the viewfinder.
John
John
Gary Rodgers
Veteran Member
a crop factor does not translate a 200mm lens into a 320mm lens. The physics of the 200mm lens still applies (for depth of field, etc.). All that happens is the "extra" image that surrounds the sensor is lopped off - this "extra" is there because your standard 35mm lens is projecting a circle large enough to encircle a 35mm film frame. The sensors are generally smaller than the 35mm film frame. A 5D/1Ds sensor (full frame) is larger than a 1D sensor (1.3 crop) which is larger than a 10/20/30/40d frame (1.6 crop).
When you look through the viewfinder of your SLR, what you see is what you get (ok, most viewfinders are 95% of what you get)...
Gary
When you look through the viewfinder of your SLR, what you see is what you get (ok, most viewfinders are 95% of what you get)...
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Gary
The viewfinder is close to 100% of what the sensor sees. It does not show you the full frame 35mm view.
With a 200mm lens (for example) you get a field of view of a 320mm lens, but the DOF of a 200mm. What this means in practice, is that you get a deeper DOF (more things in focus) for the same field of view as a full frame camera.
With a 200mm lens (for example) you get a field of view of a 320mm lens, but the DOF of a 200mm. What this means in practice, is that you get a deeper DOF (more things in focus) for the same field of view as a full frame camera.
Karl Gnter Wnsch
Veteran Member
It's not increasing the focal length, you get a more narrower field of view (that's why it's called a crop factor, it's the same as if you took some scissors and cropped your film frame) and yes the viewfinder will show the corresponding frame of the cropped frame - otherwise you'd get a wrong impression of your capture...
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regards
Karl Günter Wünsch
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Actually, I disagree with this.
Let's take two cameras for example, the 40D (1.6x) and the 5D (FF).
Using the same lens, looking at the same subject the same distance away, the subject will fill more of the frame on a 40D compared to a 5D.
Because the 5D has lower sensor density than a 40D (or even a 30D), if you crop the 5D image, you will end up with less pixels (details) in the subject compared to your 40D image.
The 1DsIII has about the same sensor density as a 30D. So you will capture the same amount of detail with a 1DsIII compared to a 30D - but you will also capture a lot more of the surrounding (a wider view).
Haggis
Member
With the 40D for example, what you see through the viewfinder is 95% of the area recorded by the sensor. If you use liveview you see 100%.
severoon
Veteran Member
Actually, you're comparing apples to oranges here. These two cameras are of different generations--the comparison of 5D to 30D is more informative for this discussion.
Using the same focal length, the subject will fill more of the frame on the 30D compared to a 5D. That is: the angle of view will be larger on the 5D.
The 5D and 30D have the exact same density of photosites on their sensors. The 5D sensor is physically larger than the 30D's, therefore it has more photosites and produces images with more pixels (higher resolution).
If you take an image on the 5D and crop off the edges, you will have exactly the same image as produced by the 30D. Same resolution, same data, same everything. (Obviously the sensors aren't exactly the same, the meters in the cameras are probably slightly different, etc, etc--but you get the point.)
severoon
Veteran Member
The answer to your question is easily understood if you think about the construction of the camera for a bit.
The lens throws an image circle onto the back plane of the camera, where the sensor resides. The part of the image circle that is cast over the sensor is what can be recorded in the form of an image.
An EF lens casts an image circle big enough to cover a 35mm film frame, a "full-frame" sensor such as that in the 5D. An EF-S ("S" stands for "short-back") lens does not--if you could somehow mount an EF-S lens on a 5D, the corners of the sensor would not be covered by the image circle. The only difference between an EF lens and an EF-S lens is that an EF-S lens can be made smaller and lighter because it is allowed to cast a smaller image circle. There is no other difference in terms of the photographic properties of the lens. In other words, 35mm focal length on an EF-S lens is the same as 35mm focal length on an EF lens--if these two lenses are mounted on the same camera body and set to 35mm, they will produce the same image on that particular body.
Now what if we hold the lens constant (an EF lens set to 35mm) and vary the body so that one is FF and the other is APS-C? In that case, just imagine what's going on inside the camera. On the FF body, the sensor is bigger and covers more of the image circle, capturing a wider angle of view. On an APS-C sensor, the sensor is smaller and captures only the center part of the image circle.
So, if you take an image on a FF body and crop off the sides, you have the exact same image that would be captured on an APS-C sensor. Simple as that. If you print an image captured on a FF sensor at 8"x12" and then crop it down, you'll end up with a smaller image (6"x9"? That's not exactly right, but let's say 6x9) covering a smaller angle of view. If you took the same shot with an APS-C sensor with the same lens at the same focal length and printed at 6"x9", you'd have exactly the same thing as the cropped FF shot.
Here's where the problem comes in: most photographers don't do this . Most photographers do not accept this comparison because they want to know: if I take two shots, one on a FF camera and one on an APS-C camera--same lens, same focal length, same aperture--and print both at 8"x12", what am I gonna get?
Well, the same rules above apply. If you take the FF shot, print at 8"x12", then crop off the sides down to 6"x9", you have the same image as the APS-C camera. Now, if you blow that image up to 8"x12", you can imagine how it will compare to the original FF shot. DoF will apparently decrease (even though it didn't really decrease) because you blew up the image. I say it apparently increased without really increasing because, if you enlarge any photo, whether taken on a FF camera, APS-C, medium format--whatever--you're not changing the DoF. However, things that were out of the focal plane that seem sharp on a small image will show as blurry on an enlargement. Many photographers mistakenly conflate apparent decreases in DoF with real decreases in DoF (even though they'd never make the same mistake when simply making an enlargement).
I won't get into the viewfinder here b/c I think this is more relevant to your question. I'll only say: the viewfinder is essentially a crop of the image captured by the sensor, same as the APS-C sensor is a crop of the FF sensor. If viewfinder coverage is 100%, then it's a 100% crop (no crop at all). If your viewfinder provides 95% coverage, then you're looking at a 95% crop of the final image when peering through the viewfinder.
The lens throws an image circle onto the back plane of the camera, where the sensor resides. The part of the image circle that is cast over the sensor is what can be recorded in the form of an image.
An EF lens casts an image circle big enough to cover a 35mm film frame, a "full-frame" sensor such as that in the 5D. An EF-S ("S" stands for "short-back") lens does not--if you could somehow mount an EF-S lens on a 5D, the corners of the sensor would not be covered by the image circle. The only difference between an EF lens and an EF-S lens is that an EF-S lens can be made smaller and lighter because it is allowed to cast a smaller image circle. There is no other difference in terms of the photographic properties of the lens. In other words, 35mm focal length on an EF-S lens is the same as 35mm focal length on an EF lens--if these two lenses are mounted on the same camera body and set to 35mm, they will produce the same image on that particular body.
Now what if we hold the lens constant (an EF lens set to 35mm) and vary the body so that one is FF and the other is APS-C? In that case, just imagine what's going on inside the camera. On the FF body, the sensor is bigger and covers more of the image circle, capturing a wider angle of view. On an APS-C sensor, the sensor is smaller and captures only the center part of the image circle.
So, if you take an image on a FF body and crop off the sides, you have the exact same image that would be captured on an APS-C sensor. Simple as that. If you print an image captured on a FF sensor at 8"x12" and then crop it down, you'll end up with a smaller image (6"x9"? That's not exactly right, but let's say 6x9) covering a smaller angle of view. If you took the same shot with an APS-C sensor with the same lens at the same focal length and printed at 6"x9", you'd have exactly the same thing as the cropped FF shot.
Here's where the problem comes in: most photographers don't do this . Most photographers do not accept this comparison because they want to know: if I take two shots, one on a FF camera and one on an APS-C camera--same lens, same focal length, same aperture--and print both at 8"x12", what am I gonna get?
Well, the same rules above apply. If you take the FF shot, print at 8"x12", then crop off the sides down to 6"x9", you have the same image as the APS-C camera. Now, if you blow that image up to 8"x12", you can imagine how it will compare to the original FF shot. DoF will apparently decrease (even though it didn't really decrease) because you blew up the image. I say it apparently increased without really increasing because, if you enlarge any photo, whether taken on a FF camera, APS-C, medium format--whatever--you're not changing the DoF. However, things that were out of the focal plane that seem sharp on a small image will show as blurry on an enlargement. Many photographers mistakenly conflate apparent decreases in DoF with real decreases in DoF (even though they'd never make the same mistake when simply making an enlargement).
I won't get into the viewfinder here b/c I think this is more relevant to your question. I'll only say: the viewfinder is essentially a crop of the image captured by the sensor, same as the APS-C sensor is a crop of the FF sensor. If viewfinder coverage is 100%, then it's a 100% crop (no crop at all). If your viewfinder provides 95% coverage, then you're looking at a 95% crop of the final image when peering through the viewfinder.
BadtzMaru
Veteran Member
In the viewfinder the level of magnification is the same, this does not rely on the sensor for anything but the size of the mirror/viewfinder.
dwalby
Veteran Member
the 10D/20D/30D/40D all put more pixels in the same image area compared to the 5D cropped to the 1.6x viewing area, so they are all generally regarded to have 'more reach'. The original claim that the image is the same in both cases, with the same number of pixels, is wrong.
The 200mm lens mounted to a 1.6x body will provide the same field of view as a 320mm lens mounted to a 1.0x body. If you try to use the same 200mm lens on both bodies, then crop the 5D to the same 320mm field of view as the 1.6x body, you will have less pixels in the 5D crop.
The 200mm lens mounted to a 1.6x body will provide the same field of view as a 320mm lens mounted to a 1.0x body. If you try to use the same 200mm lens on both bodies, then crop the 5D to the same 320mm field of view as the 1.6x body, you will have less pixels in the 5D crop.
Doug Kerr
Veteran Member
Hi,
In normal SLRs, the image seen in the viewfinder corresponds (almost) exactly with what is captured on the film or the digital sensor, for whatever lens is in place. (This is one of the main reasons we use the SLR architecture.)
The reason I say almost is that normally, the image seen in the viewfinder is cropped slightly from what is captured by the film or sensor (typically to about 95% of the width and height). This is so that, if the registration of the captured and finder images is not perfect (and that can well be due to small errors in mirror alignment), there will never be anything seen in the finder that does not make it into the image.
Thus, whatever effect the sensor size has on the field of view achieved with a certain lens focal length, then result (subject to that small wrinkle) I mentioned will be seen in the finder.
--
Best regards,
Doug
Visit The Pumpkin, a library of my technical articles on photography, optics, and other topics:
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'Make everything as simple as possible, but no simpler.'
Oh, quite the opposite.
In normal SLRs, the image seen in the viewfinder corresponds (almost) exactly with what is captured on the film or the digital sensor, for whatever lens is in place. (This is one of the main reasons we use the SLR architecture.)
The reason I say almost is that normally, the image seen in the viewfinder is cropped slightly from what is captured by the film or sensor (typically to about 95% of the width and height). This is so that, if the registration of the captured and finder images is not perfect (and that can well be due to small errors in mirror alignment), there will never be anything seen in the finder that does not make it into the image.
Thus, whatever effect the sensor size has on the field of view achieved with a certain lens focal length, then result (subject to that small wrinkle) I mentioned will be seen in the finder.
--
Best regards,
Doug
Visit The Pumpkin, a library of my technical articles on photography, optics, and other topics:
http://doug.kerr.home.att.net/pumpkin
'Make everything as simple as possible, but no simpler.'
Not sure what you mean. I refer to your comment:
That's what I disagree with. It most definitely helps. With a 1.6x crop camera, not only does your bird / athlete fill more of the frame, it will have more pixels (= detail) as well.
Or, as another poster puts it in another thread some time ago, you get "more pixels per bird" with a crop sensor camera compared to a full frame camera of the same generation.
If I understand what all of you are saying, a lot of folks multiply 1.6 by the focal length of the lens - but that does not mean that the lens gives me greater magnification or get me closer to the object. That is interesting and makes sense.
And small sensor dSLRs only crop out areas that the sensor cannot see. It does not increase the focal length (and its depth of field characteriestics). It only changes the field of view to make it APPEARS as if it were shot with a longer lens, but it is simply cropped what a 35mm/FF/film lens would see.
altair8800
Veteran Member
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You should read both comments by LennyL again. He explained it correctly, but you came to the wrong conclusion.
Dan
Your logic in the paragraph below seems to make a lot of sense. Then in that case when I use a 50 mm lens with a FF or crop frame camera, the magnication of the object stays the same, just that with the FF, I have more of the surroundings of the object. Very, very interesting indeed - thanks!
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