Canon EF 28mm f1.8 vs Canon EF 50mm f1.4

[ydgmdlu]

Not to nitpick, but they are not exactly the same. Nikon DX crop factor is 1.5x; Canon EF-S is 1.6x.

No, you're confused. He was referring to the fact that a Canon APS-C DSLR would have exactly the same sensor size as the 7D and therefore would work better for tests in the camera store. He knew full well that Nikon DX is a different size than Canon APS-C.

 

[tnle2]

No, you're confused. He was referring to the fact that a Canon APS-C DSLR would have exactly the same sensor size as the 7D and therefore would work better for tests in the camera store. He knew full well that Nikon DX is a different size than Canon APS-C.

LOL, this thread's confusion quotient is through the roof!!

 

[SPZ]

Alright, here's my take on this. Maybe I'm wrong.

The confusion here is on the numbers. a 28mm Canon Aps-C lens is an 28mm lens in the 7D. A Canon 28mm full frame lens field of view in a Canon Aps-c camera, which includes a 7D, is equivalent to a 50 mm APS-C lens.

From what I understood, its all a matter of what a sensor "sees":

A full frame sensor is bigger, so it needs bigger lens to cover it. An aps-c sensor is smaller than a full frame sensor, which requires smaller lens to cover it. If you put a lens designed for a full frame camera in an APS-C camera, the sensor will not see the full lens wide, but the middle of the said lens. That's what people mean with the "crop factor".

 

[ydgmdlu]

a 28mm Canon Aps-C lens is an 28mm lens in the 7D. A Canon 28mm full frame lens field of view in a Canon Aps-c camera, which includes a 7D, is equivalent to a 50 mm APS-C lens.

This wording, while technically correct, is also potentially confusing. Your second sentence here, without careful parsing, would seem to suggest that a 28mm FF lens is equivalent to a 50mm APS-C lens, which is not true.

All 28mm lenses on the 7D (or any other APS-C camera) look essentially the same. That's all that you need to know. The only meaningful difference between a lens designed for FF and one designed for APS-C is the size of the image circle. But that only matters if you're thinking about sharing lenses between FF and APS-C cameras. (Although to be even more technically precise, lenses designed for larger formats may have lower resolution, not that it really matters for our purposes.)

A full frame sensor is bigger, so it needs bigger lens to cover it.

Technically, a bigger sensor needs a bigger image circle. The physical size of the lens has little to do with the size of the image circle, per se.

If you put a lens designed for a full frame camera in an APS-C camera, the sensor will not see the full lens wide, but the middle of the said lens. That's what people mean with the "crop factor".

This is technically correct, but again, if you want a more complete and accurate understanding of the issue, you have to realize that a lens with the same focal length but a smaller image circle essentially does the cropping of the image for you, instead of leaving the cropping up to the sensor. The reason why lens makers design special lenses for smaller image formats is because the lenses can be made smaller, and therefore more efficient, for the smaller image circle. This results in cost savings. A 17-50mm F2.8 lens for an APS-C camera is much more efficient than a 17-50mm F2.8 lens for a full frame camera, and therefore it is much less expensive. FF zoom lenses in that focal length range with such a big constant aperture are actually very rare (I haven't found any) and very expensive.

 

[ydgmdlu]

A Canon 28mm full frame lens field of view in a Canon Aps-c camera, which includes a 7D, is equivalent to a 50 mm APS-C lens.

Actually, upon closer inspection, this isn't right. And actually, I'm not even sure what you mean. Your sentence is very confusing.

To obtain the same FOV as a 28mm lens on full-frame camera, you need a 17.5mm lens for your APS-C camera. The FOV of a 50mm APS-C lens is the same as 80mm on a full-frame camera.

A 28mm lens on an APS-C camera will have the same FOV as as a 45mm (not quite 50mm) lens on a full-frame camera.

 

[SPZ]

Actually, upon closer inspection, this isn't right. And actually, I'm not even sure what you mean. Your sentence is very confusing.

To obtain the same FOV as a 28mm lens on full-frame camera, you need a 17.5mm lens for your APS-C camera. The FOV of a 50mm APS-C lens is the same as 80mm on a full-frame camera.

A 28mm lens on an APS-C camera will have the same FOV as as a 45mm (not quite 50mm) lens on a full-frame camera.

Man, you're just trying to read too much into what I said. Yes, if I was to be precise, 28mm Full Frame lens ona a 7d would not have precisely the field of view of a 50mm Aps-c lens, but of a 45mm one.

You are the one that are confusing everyhting. Look, I tried to write in a way someone not tech savy could understand that if you buy a FULL FRAME 28mm lens, you would not get a 28mm Field of view in an APS-C camera.

I believe that what I said in the previous post is easily understandable, and I stand by it.

Was it the most technically precise in wording? Not at all. But does it put the things into perspective? I believe so. Anyway, everyone is free to understand what they want. I'm surelly more than clear what FF lenses I need for a 7D as well as what APS-C lenses I will buy and how to look for them.

Personally I will get anything above 28mm APS-C F.O.V in Full Frame lenses. The only APS-C lenses I'm buying will be Wide and Ultra Wides.

 

[ydgmdlu]

Trying to read too closely am I? I'm just taking at face value what your words plainly say.

28mm full frame lens field of view

A 28mm lens on a full frame camera provides a wide field of view. That's simply what it means. The problem with the first part of your sentence is the phrase "full frame lens field of view." What did you intend that to mean? Because, at face value, it would appear to refer to the FOV of a given focal length as it applies to a full frame camera.

in a Canon Aps-c camera, which includes a 7D,

A 28mm lens on an APS-C camera provides a normal FOV. That's simply what it means. When you say "full frame field of view in a Canon APS-C camera," do you mean that you are trying to achieve a full-frame FOV with an APS-C camera? If that's the case, then the first half of your sentence is saying that you're trying to achieve a wide-angle lens's FOV with an APS-C camera, which doesn't seem to be what you really mean.

is equivalent to a 50 mm APS-C lens.

A 50mm APS-C lens is a short telephoto. That's simply what it means. Did you intend to say that 50mm as in the normal FOV for full frame? When someone buys a 50mm lens that is designed for APS-C cameras, he/she should already know that it's a short telephoto, if he/she is familiar with APS-C cameras.

I'm not trying to talk in "tech savvy" terms. I'm trying to talk in precise, non-confusing terms. You're the one who's using confusing terminology. See, this is the reason why I and the others were talking about moving away from numbers and crop factor when talking about lenses. xbourque's little chart is the most useful thing in this thread. If everyone just learns and remembers that, there will be no more confusion and no more need to talk about crop factors or FF vs. APS-C.

The clearest wording that I can imagine for conveying what you originally intended to say would be:

A 28mm full frame lens on an APS-C camera (such as the 7D) will provide a normal FOV, basically the same result as a 50mm lens on full frame camera.

 

[mhood]

OK...duh...I just got the 28mm 1.8 USM (normal) and the 50mm 1.4 USM (short telephoto). What prime do I get next for my wide? I'm not interested in a fisheye...they make me sea sick.

 

[J Davis]

I said DX because most of my glass is nikon so I'm thinking nikon, you can get a aps-c canon if you want.
My point is you can do it yourself

 

[PaPa]

kk, so basically: If i use my nikon D lenses ( full frame ) i will be dealing with a crop factor of 1.6, thus although a 35mm lens full frame will still be a 35mm lens on the 7D, i will have a 1.6 crop factor giving me roughly the field of view ( once cropped ) of a 56 mm lens.

But

If you purchase a aps-c lens, with a smaller circle, then will a 24mm aps-c lens give me the same width of image on a 7d as a 24mm full frame lens would give on a 5D ?

Thus, if we need wide lenses, should we just purchase an aps-c lens and forget trying to get ultra wide full frame primes?

 

[mhood]

ultra wide full frame primes?

I'm too confused to answer (my guess is "no"...APS-C lenses offer no wider FOV than FF lenses do) but I would sure like to know which ultra wide (or even plain old wide) full frame primes you are referring to.

 

[SPZ]

kk, so basically: If i use my nikon D lenses ( full frame ) i will be dealing with a crop factor of 1.6, thus although a 35mm lens full frame will still be a 35mm lens on the 7D, i will have a 1.6 crop factor giving me roughly the field of view ( once cropped ) of a 56 mm lens.

But

If you purchase a aps-c lens, with a smaller circle, then will a 24mm aps-c lens give me the same width of image on a 7d as a 24mm full frame lens would give on a 5D ?

Thus, if we need wide lenses, should we just purchase an aps-c lens and forget trying to get ultra wide full frame primes?

Exactly. That's what I'm going to do: get APS-C wides and ultra wides.

EDIT- as for anything else, I will buy full frame, either second hand or new. Eventually we'll be getting a full frame camera with 1080p 25/24p or more, and having full frame lenses is a way to be future proof, at the same time preserving compatibility with APS-C cameras and FUll frame cameras.

 

[Michael Olsen]

Lots of confusion here. Images help.

Saying a 35 is like 50 is confusing because (for our purposes) its really only the FOV that is affected.

None of this is to scale or meant to be real world, it's just illustrative.

Imagine this image as a whole. It's a red box with a black box inside it. The Full Frame sensor has the same lens as the s35. The Full Frame sensor will have a wider FOV - it can see the whole image at once. The s35, however, has a smaller FOV and can only see the black box. In order to view the red box as well, the camera would have to be moved backwards or a different (wider) lens attached.

Here's a more real world example.

Again, both our FF and s35 cameras are in the same position using the same lens taking a picture of the same subject. The FF can see everything - the s35 can only see the portion within the red outline. The FF has a wider FOV and can see everything - the s35 has a smaller FOV and can see a smaller portion of the image. There is no extra magnification provided by using the same lens on a smaller sensor (i.e. a 100mm lens won't project the image of a 160mm lens, but will project a 100mm image with a tighter field of view.

To extend this concept, a 2/3" sensor would see an even smaller area of the image using the same lens because it is even smaller than s35 (significantly so).

Here's what happens with lenses.

Lets say that all of these sensors (the darker regions) are the same size - which they are. Lets call them APS-C.

Lets say that the size of the image circle projected by the lens (the red region) may vary.

No. 1 - This is an APS-C sensor with a lens made to fit - the image circle completely covers the sensor, but there is not a whole lot of wasted space.

No. 2 - This is an APS-C sensor with a lens made to fit a smaller sensor - the image circle does not cover the sensor, leaving areas of the sensor that do not record an image. This is how one gets real optical vignetting.

No. 3 - This is an APS-C sensor with a lens made to fit a larger sensor (say FF) - the image circle more than covers the sensor, meaning that the image is being cropped in camera. In other words, the sensor is too small to effectively see all that the lens is projecting. This is what happens when using a FF lens on the 7D - some of the image collected and projected by the lens is simply lost. There is no extra magnification; a 100mm lens won't give you the image of a 160mm even though there is a 1.6 crop factor. You will simply get a 100mm image with the FOV of a 160mm. This is also why FF lenses may be used on APS-C cameras, but APS-C lenses may not be used on FF cameras: the FF lens projects an image larger than necessary, while the APS-C lens would project one much smaller than needed to cover the sensor. (In fact, using a FF lens on an S35 sensor may produce a sharper image because the central area of lenses generally resolves better than the edges.)

A 100mm lens always projects the same image no matter what camera you put it on. The size of the sensor in the camera simply determines what area of the image is recorded or not.

This is why, to people who have always shot on s35, none of this "crop" and "its like XXmm on a Full Frame" makes sense. To them, a 28mm has always projected an image they've associated with 28mm - there was no reason to deal with crops and shifts in FOVs. A 28 is a 28 is a 28. They don't go through any conversion process thinking: "Okay, I want this to have 50mm FOV, but that's on a Full Frame...So I need to divide and do math and end up with a 31.25...which doesn't exist!? What do I do?!" They just know what they want it to look like on their camera - they may pick up a 28 and take a couple steps forward, or a 35 and jump back.

I hope I got all that right. :beer:

 

[SPZ]

Excelent post Michael. I think this clears everyone's doubts.

 

[tnle2]

If you purchase a aps-c lens, with a smaller circle, then will a 24mm aps-c lens give me the same width of image on a 7d as a 24mm full frame lens would give on a 5D ?

No, the image width will not be the same.

Here's another way to understand it:

1. What you're really interested in is the angle of view that you are recording. A "normal" lens covers an angle of about 46°. A wide-angle lens covers 70° to 90° or more for an ultra-wide angle lens.
2. Focal length by itself does not determine the angle of view. Focal length is a physical characteristic of a lens and is the same no matter what camera you put it on. This is what some people are saying but it's confusing others because focal length is not the same thing as angle of view. Angle of view is what you're really interested in.
3. Angle of view is determined mathematically by two things: focal length and the image format dimensions (the sensor size). If you want to maintain the same angle of view and you changed one of those two things, then the other variable has to change too. In this case, the relationship is proportional. So if the sensor size is smaller, the focal length must decrease to maintain the same angle of view.

A fourth thing that is adding confusion is the size of the image circle.

• The image circle is the size of the image that a lens projects onto the sensor. Lenses are designed to have an image circle that is just big enough to cover the sensor they are designed to be used with.

APS-C specific lenses like EF-S, DX, etc. have a smaller image circle than FF lenses because they only cover the smaller APS-C sensor size. Manufacturers came up with these lenses so that the lenses could be smaller, lighter and somewhat less expensive than FF lenses. The effect of a smaller image circle was illustrated by Michael Olsen above.

All you really need to know is that the angle of view is mathematically determined by two things: focal length and the image format dimensions (sensor size). If you know the width and height of a sensor you can calculate the angle of view for a given focal length here: http://imaginatorium.org/stuff/angle.htm

References:

http://photo.net/learn/fov/
http://en.wikipedia.org/wiki/Angle_of_view
http://www.toyoview.com/LensSelection/lensselect.html

 

[PaPa]

Right, so if i buy a 24mm aps-c lens for the 7D, will it give me the same field of view as a 24mm (full frame slr lens) on the 5D ?

i.e. does the smaller projected circle of the aps-c lens squeeze all the image into a smaller circle, or does it just get rid of the extra space that would otherwise be used by a non aps-c lens?

 

[mhood]

No...Yes... Would an old EF 20mm 2.8 USM be considered "wide" on a 7D?

 

[tnle2]

Right, so if i buy a 24mm aps-c lens for the 7D, will it give me the same field of view as a 24mm (full frame slr lens) on the 5D ?

No, it won't have the same field of view. A 24mm (regardless if it's an APS-C lens or a FF lens) on a 7D will have less field of view than a 24mm FF on a 5D.

i.e. does the smaller projected circle of the aps-c lens squeeze all the image into a smaller circle, or does it just get rid of the extra space that would otherwise be used by a non aps-c lens?

An APS-C lens is not squeezing the image. It's just getting rid of the extra space that a FF lens would normally have.

No...Yes... Would an old EF 20mm 2.8 USM be considered "wide" on a 7D?

20mm on a 7D would be somewhat wide. The diagonal angle of view is about 68°.

 

[PaPa]

Awsome, thanks Tim.

So basically, whichever way i go about it, if i want to get a full frame field of view of a 24mm lens, i would need to pick up something roughly around 16mm keeping the crop factor in mind, be it full frame slr lens or aps-c.

Correct?

 

[tnle2]

So basically, whichever way i go about it, if i want to get a full frame field of view of a 24mm lens, i would need to pick up something roughly around 16mm keeping the crop factor in mind, be it full frame slr lens or aps-c.

Correct?

Correct!

16mm on the 7D will give you a diagonal angle of view of 80°. That's pretty darn wide (but not yet ultrawide).