I've heard several people mention that the effective FL of a lens on an APS-C body is actually not the same FOV as a longer lens on a FF body. For example a 100mm lens on a 7D and a 160mm lens on a 5D (I'm not sure that one exists, but....).
Could you post comparison pictures taken with a shorter lens on an APS-C body, and also pictures taken with a FF body using a lens whose FL is equal to the effective FL of the APS-C setup? I don't have a FF body, so I can't try it myself.
I'm especially interested in photos taken with a 300mm on an APS-C body and with a 500mm lens (close enough to {300mm*1.6}) on a FF body, though I would still be interested in shorter FL comparisons as well.
1. The field of view of the 50mm focal length on a 1.6x cropped sensor camera is the same as the field of view from a 80mm lens on a full frame body. This relationship works and accurately gives you a piece of information that may be important to those who have to consider the functional use of particular focal lengths on the two formats.
I think this is your main concern - so you don't need to see pictures. You can simply do the calculation in the way that I believe you already understand. The 300mm lens on the cropped sensor body will give you the same angle of view that a 480mm focal length would provide on full-frame.
There are other issues that may or may not concern you when you compare formats. They are probably not a big concern to the majority of people who choose to shoot with a cropped sensor body. They might include:
2. There are differences in depth of field. The usual - and reasonable - statement that you'll get more DOF at a given aperture on a smaller format is a useful one to keep in mind. Simple formulas that attempt to quantify the difference are often not as accurate as one might think - there are multiple issues to consider.
3. The point at which diffraction blur may become an issue in photographs made with the two formats can differ if you consider making prints of the same size from the two sytems. Basically, you'll see diffraction blur sooner as you stop down when you use a smaller format. (But if you never make largish prints this may not be an issue to you at all.)
4. The larger format is capable of capturing more detail given lenses that produce similar resolution. One way to think of it: lens resolution can be described in terms of line pairs per millimeter (lp/mm). There are "more millimeters to hold line pairs" when the format is larger. You can also think of this as more line-pairs per picture width.
Photon wrote:
...I have a comparison of three camera formats
Good examples.
You might want to check the first image, though. It is captioned "Canon G10 [APS-C], 7.6 X 5.7 mm sensor."
A 7.6mm X 5.7mm sensor is not APS-C.
APS-C sensors range from 22.2 X 14.8 (Canon) to 23.6 X 15.7 (Nikon, Sony, Pentax, etc.). Then there's Canon's APS-H @ 28.7 X 19 (larger than APS-C), and the Four-Thirds system @ 17.3 X 13 (smaller than APS-C). All of these named formats offer sensor areas of 225 square millimetres or greater. At 43 square millimetres, the G10's sensor area and that of similar compacts pales by comparison.
I noticed that about G10 also. What is the definition of APS-C? I haven't found one solid format size, such as in 35mm FF. APS-C sensor crops vary from 1.5x-1.7x (Sigma). Is APS-C a sensor whose size is +225 mm2, as mentioned above?
It does not matter what size of sensor you use , you have to remember that the true MM of your lens remains the same.
eg the 300 mentioned above does NOT become a 480 (500) 2.8 on a Crop. Yes its FOV is the same as a 500 (ish) but its still a 300mm lens.
This is more pronounced when you come down to those P&S that have "500mm" lenses. They dont they have a 20 something mm lens cropped on a tiny sensor.
Also if you want to get a much more accurate equivelent then you have to multiply the fstop by 1.6 also.
EG the 17-55 2.8 is not a crop version of the 24-70 2.8 (nearest). if you multiply the f number by 1.6 you increase the fnumber by 1 1/2 stops (close enough) so its really a 27-88 4.8 . This will give you a much more accurate view on how much DOF you will get at any given FOV if you were to stand side by side a crop cam and a FF cam
Although, keep in mind that what Ian is talking about applies only to DOF -- just because the 17-55 in on APS-C it doesn't make it as "slow" as an f/4.8 lens. I think he was clear in what he was saying, buts just to be sure
Paul
Talking about equivalent fields of view, equivalent f-stops, and so on is interesting to me from a purely academic standpoint, but I really think the best route for most folk when it comes to actually taking a picture is to just forget about it and simply learn by doing what look a given focal length gives on a given body.
If one's prior experience was only with view cameras, the 35mm "full frame" equivalent wouldn't provide useful information, nor would it for those who have only previously used P&S compacts.
Want to know what FOV and DOF you get with a 135mm lens on a 7D? Look in the viewfinder!
Thanks for the comments and examples everyone. It is really interesting that while the FOV changes on the 50D, the DOF doesn't.
I am not as interested in DOF as FOV, though it is cool to see how DOF changes on crop cameras. Also, it wouldn't be possible to get a 500mm f/2.8, unless you paid 30k. An APS-C camera seems like a great alternative. But then again, if you have a 500mm f/4 on a FF body, you could use higher ISOs to compensate. It goes in circles....
Dpic_arctic wrote:
Thanks for the comments and examples everyone. It is really interesting that while the FOV changes on the 50D, the DOF doesn't.
Ian.Dobinson wrote:
Thats because it can't. For the DOF to change you either have to move closer/further from the subject or change focal length.
What those 2 crop sensor images are basicly just crops of the FF FOV but with more pixels crammed into the smaller space
APS-C seems like a decent compromise for those who don't have the money available to spend on a 35mm system. It's not like having a 6x crop sensor on a 100mm lens. The size of my 40D's pixels is equal to the size of the pixels on the 1D IV (APS-H) and almost as large as the 1Ds III. So they really aren't that crammed. The 7D is a different matter....it mas the highest pixel density of any other EOS DSLR.
by crammed I was only saying that in those examples as it went down the page the amount of pixels for any given are went up. I was not saying anything about them being too crammed.
I agree that the 1.6 crop seems to be a good compomise. I doubt tht any time soon I will get a FF camera and definatly not another 1.3 crop (I had a mk1 1D for a while)
I like my 40D very much but could see the next upgrade being a 7D
so the same can be said about 1.4x and 2.0x TCs...FOV wise
to me 1.6 crop is like a 1.6x TC if there was one
to me 1.3 crop is like a 1.3x TC if there was one
so I cant really understand why the confusion around this issue
digitalbug30d wrote:
so the same can be said about 1.4x and 2.0x TCs...FOV wise
to me 1.6 crop is like a 1.6x TC if there was one
to me 1.3 crop is like a 1.3x TC if there was one
so I cant really understand why the confusion around this issue
The difference is that a teleconverter does change the actual focal length of the lens.
so if a FF cam was shot at point A with a crop cam also shot with the same lens from point A (same distance) but obvious framing difference. would both cams have the same depth of field. the way i understood is that ff is able to achieve shallower dof because it can shoot closer with the same framing as a crop cam given the same lenses. is this right or not?
rogie wrote:
so if a FF cam was shot at point A with a crop cam also shot with the same lens from point A (same distance) but obvious framing difference. would both cams have the same depth of field.
According to an online DOF calculator, they would have different depths of field due to the difference in the size of their circles of confusion, the phenomenon that affects perception of focus.
For example:
Given a 200mm lens at f/16 focused at 30 feet:
Mounted on the 5D Mark II it has a DOF of 2.91 feet in front of the plane of focus and 3.61 feet behind the plane of focus, and a total DOF of 6.51 feet (rounding errors evident).
Mounted on the 50D it has a DOF of 1.91 feet in front of the plane of focus and 2.19 feet behind the plane of focus, and a total DOF of 4.1 feet.
rogie wrote:
so if a FF cam was shot at point A with a crop cam also shot with the same lens from point A (same distance) but obvious framing difference. would both cams have the same depth of field. the way i understood is that ff is able to achieve shallower dof because it can shoot closer with the same framing as a crop cam given the same lenses. is this right or not?
No, in this case the DOF will be smaller for the crop camera. The subject will appear larger using the crop camera. The magnification is higher, thus the DOF is less. If you cropped the FF shot however, to the same FOV, and then made identical sized prints, the DOF would be the same.
