More lens confusion

Chance White said:
Okay... so I thought I understood this, now I don't...

Is it all about relativism? What I mean is, most films are shot S35 which is inclusive of the 1.6 crop, which means most of us are used to seeing 28mm look like it does in a film, which has a 1.6 crop. So if you are doing cinematic work, a 28mm lens will look EXACTLY like it should look, how you've seen it in motion pictures, and you don't need to worry about crop factors... is this correct?

The only way you notice it is if you are familiar with photography where FULL FRAME lenses are more prevalent...

The more this is explained it seems the more people become confused. I definitely think there should be a FAQ or sticky.
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Relativism and inclusive of 1.6 crop and 28mm looking like 28mm? Oh boy. Have no idea about that.

Several things are confusing about the topic in general. There are two types of lenses in essence. Those designed for full frame and those designed for cropped frame and the manufacturers either don't say at all which lens is which or give a random designation like ES...or is it EF? Oh never mind! And there's confusion about the designation of 1.6x which makes it sound like there's magnification involved, and there isn't any magnification, there's cropping. So my 75mm lens is really 125mm, except not the magnification of 125, the cropping of 125!
 
By the way, just to make this clear once again, motion picture film cinematography is NOT full frame these days. "Full frame" refers to a frame size of 36mm by 24mm. This is only possible when running a filmstrip horizontally. Only VistaVision and IMAX run film this way. In standard motion picture cameras, the frame size is reduced by the areas reserved for sprocket holes and the sound track. The maximum frame width is a hair under 25mm. That would be the Super 35 format. Standard 35mm motion picture film is actually only about 22mm wide, which is almost exactly the same as Canon's APS-C implementation.
 
ydgmdlu said:
You only have to worry about crop factors if you're working with two different image formats. Are you also doing full-frame still photography?

Otherwise, simply forget about crop factors and learn what angles of view you get with each focal length on a given image format (in this case, APS-C).
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Yes but the problem is a full frame 70-200mm on the 7d isn't really a 70-200, it's a 70-200 with a field of view of 112-320. I don't see how we can ignore crop factor if we're at all interested in getting FF glass.
 
Regarding relativism...

Unless one has experience using a Full Frame sensor (as on the 5D MKII), they have no schema or perception of what any focal length lens should look like on a full frame sensor. More specifically, they do not have a mental conception of there being any connection between the numerical digits of focal length, and the specific field of view provided by a lens with that focal length.

Someone shooting on a film camera doesn't have any understanding of what a 28mm lens looks like on a full frame camera. Their camera isn't full frame! They only know what a 28mm looks like on their camera. They never bother with any magical numbers to try and get their image, they just pick the lens that best fits the shot they want based on their experience.

I will know what a 28mm looks like on my 7D because I have never shot on a full frame camera. I don't have any conceptions about what a 28mm is "supposed" to look like. It just is what it is.

Someone used to shooting on a 5D MKII knows what a 28mm lens looks like on a full frame camera. When they step down to a crop sensor (such as APS-C) they will either a) need to simply get used to what the lenses look like on that camera or b) make a conversion using a crop factor to help pick the right lens.

What ydgmdlu has said is correct: If you know what the lenses look like on your camera, you can forget about all this crop nonsense. There is no need to "translate" to another sensor size unless you need to get exactly the same shot using two cameras of two different sensor sizes.
 
I like this terminology (embracing subjectivity and relativistic claims):

  • Wide
  • Normal
  • Tele
 
Lucian said:
Relativism and inclusive of 1.6 crop
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Crop factor is inherently relativistic. It's relative to whatever format is being used as the frame of reference. The 1.6x crop is only meaningful when you're thinking in terms of full frame. If you don't think that way, then you don't worry about crop factor.

and 28mm looking like 28mm?
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You've taken that out of context. He was saying that a 28mm lens mounted on a 35mm motion picture film camera will give you the same field of view (essentially the same look) as when you take that same lens and mount it on the 7D. Please parse this sentence carefully.

There are two types of lenses in essence. Those designed for full frame and those designed for cropped frame
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I've explained the differences between them. I've tried to be as clear as possible. If you still don't understand, then take a few moments to read and think carefully.

and the manufacturers either don't say at all which lens is which
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Here's the rule of thumb that will save you the headache: When a manufacture says that a lens is "designed for digital cameras," then nine times out of ten, it means that it was designed for APS-C.

or give a random designation like ES...or is it EF? Oh never mind!
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It's not a random designation. EF refers to lenses designed for Canon full-frame cameras. EF-S refers to lenses designed for Canon APS-C cameras. Google/Wikipedia search will tell you all about it.

So my 75mm lens is really 125mm, except not the magnification of 125, the cropping of 125!
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Crop factor only has to do with field of view. That's the only thing that you should be thinking. Don't think in terms of "x is really y." That's not how it works.

You still have not answered my question. Is full-frame still photography your background or not?
 
Lucian said:
Yes but the problem is a full frame 70-200mm on the 7d isn't really a 70-200, it's a 70-200 with a field of view of 112-320. I don't see how we can ignore crop factor if we're at all interested in getting FF glass.
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Lets keep it simple and talk about primes. Take a 50mm f/1.4 prime lens. That's a good pretty common lens, especially if you are going for low-light shooting.


First things first - focal lengths (i.e. XXmm) are constants. A 50mm is always a 50mm because the focal length is a measurement of how strongly the lens converges or diverges light. No matter what, the lens will always do the same thing. Always.

That 50mm lens will always project the same image at some focal point - in this instance, where the sensor is when the lens is attached to the camera. Put that same lens on a full frame camera and the image is projected exactly as it would be on an APS-H, APS-C, 2/3", or 1/3". Heck, if you take the lens off the camera, it is still projecting that image - its just not projecting it onto anything!

The problem comes when the sensor size changes. Here's a picture to help.

sensorsandlenses.jpg


1. Let's say this is an APS-C sized sensor (the black square) and an EF-S lens (designed to fit the sensor). The EF-S lens projects an image circle (red) to fit the sensor - it leaves a little bit of room, but comes pretty close to being a perfect fit.

2. This is the same APS-C sensor, but with a lens designed for a smaller sensor - say 4/3". The image circle (red) doesn't cover the sensor! This makes vignetting occur - black areas on the border of the image because there isn't anything for the sensor to see there.

3. This is the same APS-C sensor, but with a full frame lens on it. Notice that the image circle (red) is larger than the sensor! That is because it is meant to fit a Full Frame sensor. So what does this mean? The image being projected by the lens is not entirely seen by the sensor - some parts are left out. This does not magnify the image at all, it simply "crops" it, or cuts off the sides. Because you are losing part of what the lens is projecting, the FOV is decreased.
 
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Lucian said:
Yes but the problem is a full frame 70-200mm on the 7d isn't really a 70-200, it's a 70-200 with a field of view of 112-320.
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That is correct. And if you buy a 70-200mm APS-C lens, then it STILL has a field of view (on an APS-C camera) of a 112-320mm lens on full-frame camera.

I don't see how we can ignore crop factor if we're at all interested in getting FF glass.
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Why are you buying FF glass?
 
Michael Olsen said:
Regarding relativism...


What ydgmdlu has said is correct: If you know what the lenses look like on your camera, you can forget about all this crop nonsense. There is no need to "translate" to another sensor size unless you need to get exactly the same shot using two cameras of two different sensor sizes.
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Okay I understand this, but! I do have a some APS-C lenses for my Canon 40d so if I start buying FF lenses, to avoid FOV redundancy, doesn't it behoove me to know the 1.6 crop factor of the FF lens?
 
ydgmdlu said:
That is correct. And if you buy a 70-200mm APS-C lens, then it STILL has a field of view (on an APS-C camera) of a 112-320mm lens on full-frame camera.

Why are you buying FF glass?
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All the teles I've been looking at seem to be FF.
 
Lucian said:
Okay I understand this, but! I do have a some APS-C lenses for my Canon 40d so if I start buying FF lenses, to avoid FOV redundancy, doesn't it behoove me to know the 1.6 crop factor of the FF lens?
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Think of it this way. If you own a 28mm lens, that has a FOV on the 7D equivalent to that of 44.8mm lens on a 5D. However, it does NOT have the magnification of a 44.8mm lens.

In other words, your lenses don't magnify more just because the sensor is smaller than full frame. If you need a 200mm lens, buy a 200mm lens regardless of sensor size. The only thing that will be effected is the field of view.

Another way to look at it...

Say I have a set of lenses 12mm, 28mm, 85mm. They are all EF-S (i.e. made for APS-C sensor cameras). I need to fill my gap of a 50mm lens. I can buy either a 50mm EF or a 50mm EF-S lens and the camera will capture the same image. The only thing is that the EF could be used on cameras with larger sensors later.
 
Lucian said:
Okay I understand this, but! I do have a some APS-C lenses for my Canon 40d so if I start buying FF lenses, to avoid FOV redundancy, doesn't it behoove me to know the 1.6 crop factor of the FF lens?
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Not unless you're using to working with full-frame photography. So please clarify for us: Is your default frame of reference full frame or APS-C? Because if it's APS-C, then stop worrying about crop factor. Don't even think about it, because it doesn't even apply to you.

The only thing that should enter your mind when you buy FF glass is, "Oh good, I can use this on FF cameras later."
 
ydgmdlu said:
stop worrying about crop factor. Don't even think about it, because it doesn't even apply to you.
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As I type this, I'm tattooing that on my forehead, backwards, so I can see it in the mirror every night when I brush my teeth.
 
The problem is that people say "just multiply the focal length" and leave out the fact that the crop only impacts field of view.

This leads people to think: I need a lens that magnifies 16x. But I have a 1.6x camera, so I only need to buy a lens that magnifies 10x.

That's dead wrong.

Taking a 100mm lens and sticking it on a camera with a teeny tiny sensor will NOT make it a 1000000mm lens that acts like a telescope. The moon won't get any closer. The camera will simply just have a really really small field of view because it is just cutting out a tiny little square in the middle of that image and throwing the rest away.
 
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