Beginner APC-S /Full frame lens question

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Simon
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#1
Good morning,

Would someone be kind enough to explain as I can't seem to get my head around it? If a Canon 24-105mm EF full frame lens is fitted to a cropped sensor body, would that be the same as a 38-168mm lens made for a cropped sensor body? ie would the field of view be the same with a FF lens set at 24mm as it is with an cropped sensor lens set at 38mm? Does that make sense?

Many thanks
Simon
 
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Kev
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#2
No and Yes!
The focal length of a lens does not depend on the camera, so a 24-105 is always a 24-105 and a 38-168 is always a 38-168, it is a property of the lens not the camera.
The field of view of the same lens fitted to a full frame sensor will be greater that the field of view on a cropped sensor, you see less of the view on a cropped sensor so you appear to be "zoomed" in a bit.
It may be easier if you imagine a full frame sensor with an image on it, then imagine a piece of card with a rectangular hole in it placed over the sensor to crop the image.
The terms full frame and cropped may make things easier for us oldies who grew up with 35mm but if you have a cropped sensor just think about the field of view and don't try to convert. Real oldies who used plate cameras would say that what we call full frame cameras are actually cropped!
 
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Jonathan
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#3
... a 38-168mm lens made for a cropped sensor body? ...
Just to note that lenses made specifically for cropped sensor bodies have their focal lengths stated in the same way as lenses made for full frame bodies (since they are the same, as Kev explained above).
So the EF-S 24 2.8 STM AND the EF 24 2.8 IS USM will BOTH provide the same field of view on a cropped sensor body (1.6 * 24 = 38.4).
 
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#4
So, does that mean that at 24mm, the FF lens would be giving the same field of view as a cropped lens at 15mm? (24 divided by 1.6 = 15)
 
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#5
So, does that mean that at 24mm, the FF lens would be giving the same field of view as a cropped lens at 15mm? (24 divided by 1.6 = 15)
Yes - (on Canon, anyway, Sony and Nikon cropped sensors are a little larger than those used by Canon, and have a 1.5x crop factor, rather than 1.6).

Edit: Re-read, and realised what I said was misleading.

You will get the same field of view from a FF 24mm lens on a FF body, as you would from a 15mm lens (FF or 'Crop'), on a Crop body.
 
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Alan
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#7
So, does that mean that at 24mm, the FF lens would be giving the same field of view as a cropped lens at 15mm? (24 divided by 1.6 = 15)
Just a quick note as I've found the replies confusing...

24mm on a 35mm/ff camera = 24mm FoV.
15mm on an APS-C camera = 15 x 1.6 = 24mm.
24mm on APS-C camera = 24 x 1.6 = 38mm.
 
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Tom
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#8
Good morning,

Would someone be kind enough to explain as I can't seem to get my head around it? If a Canon 24-105mm EF full frame lens is fitted to a cropped sensor body, would that be the same as a 38-168mm lens made for a cropped sensor body? ie would the field of view be the same with a FF lens set at 24mm as it is with an cropped sensor lens set at 38mm? Does that make sense?

Many thanks
Simon
What has been said about is very much true.

But in simple terms, yes 24-105 on ff would effectively be a 38-168 on a crop camera.

If you wanted to replicate a real 24-105 ff fl you’d need a crop lens of 16-70mm or so.
 
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Dominic
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#9
For me, who's never had a ff camera, a 24-105 on my camera is what it is (if you can see what I mean). I have nothing to compare it to, so i have a pretty good idea of what all my lenses will give me. I don't compare what the field of view a lens will look like on ff, because I haven't got one.
 
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#11
For me, who's never had a ff camera, a 24-105 on my camera is what it is (if you can see what I mean). I have nothing to compare it to, so i have a pretty good idea of what all my lenses will give me. I don't compare what the field of view a lens will look like on ff, because I haven't got one.
The reason I was asking is, I currently have an 18-135mm IS STM, if I were to up grade the lens, I was wondering what the equivalent "L" lens would be.
Just wondering, that's all.

Simon
 
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#12
The reason I was asking is, I currently have an 18-135mm IS STM, if I were to up grade the lens, I was wondering what the equivalent "L" lens would be.
Just wondering, that's all.

Simon
Sorry not having a go, just my thoughts on how I look at it :)
 
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#13
The reason I was asking is, I currently have an 18-135mm IS STM, if I were to up grade the lens, I was wondering what the equivalent "L" lens would be.
Just wondering, that's all.

Simon
18-135mm is the full frame focal length range, so you would want an 18-135mm L if such a thing existed.
 
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#15
I don't understand, could you explain this please?
The focal length of a lens is always described as it relates to a 35mm (full frame) camera even if the lens is not suitable for a full frame camera.

Your 18-135 is designed for an APS-C camera because it only projects enough light to cover an APS-C sensor, you could use it on a full frame camera but there would be large areas of black around the edges, like this https://images.app.goo.gl/E3QABzqvoxUcEAR7A

If you want a “better” lens for your camera while still keeping the 18-135 focal range then you are going to struggle. 18-135 is going to be a compromise, especially at the wide and far zoom ends - obviously it might not be an issue depending on what you are shooting and what you do with the resulting images

Most lens manufacturers have something like an 18-135 because it’s a good walking around lens.

If you want L lenses then you’ll probably need to replace the 18-135 with a 16-35mm, a 24-70 and a 70-200.
 
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#17
Is there a difference in the glass used to make the STM lenses and the USM lenses? I'm trying to find an answer on Google but it all seems a bit vague.
 
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#18
Is there a difference in the glass used to make the STM lenses and the USM lenses? I'm trying to find an answer on Google but it all seems a bit vague.
That’s going to depend on the lens.

USM/STM refers to the autofocus motors, STM is newer than USM - it’s quieter so great for video work and it’s also faster.

Here is a review of the 18-135 STM

View: https://youtu.be/_j7hQ17G_uk


It’s not just the glass used, potentially the coatings could be improved as well
 
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#19
Just a quick note as I've found the replies confusing...

24mm on a 35mm/ff camera = 24mm FoV.
15mm on an APS-C camera = 15 x 1.6 = 24mm.
24mm on APS-C camera = 24 x 1.6 = 38mm.
To be pedantic, you cannot measure a field of view in mm, you measure it in degrees. This is where all the confusion with crop factors comes from, trying to measure field of view in mm.
 
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#20
The focal length of a lens is always described as it relates to a 35mm (full frame) camera even if the lens is not suitable for a full frame camera.
The focal length of a lens is quoted as it relates to itself, not to a 35mm camera. The camera the lens is attached to does not affect the focal length. A 50mm lens is 50mm focal length if it is a telescope lens, a binocular lens, a microscope lens or a camera lens. The focal length is a property of the glass and nothing else - not the mount, not the camera, not the use.
 
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Phil
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#21
The reason I was asking is, I currently have an 18-135mm IS STM, if I were to up grade the lens, I was wondering what the equivalent "L" lens would be.
Just wondering, that's all.

Simon
The simplest and most useful answer is that there isn't one.
The best quality standard zoom you'll get for your crop camera is the 17-55 2.8 - but it's not quite as wide and nowhere near as long. OTOH it is faster (both in aperture and focus motor, and the IQ is better).
The 24-105 will be not as wide but will be longer, but you'll also need a wider lens if you use the wide end a lot.

It comes down to your use - if you're generally at the wider end of your 18-135, then the 16-35L is the best buy, if you're mostly at 18-55 then the 17-55 EFS is the one to go for, if you're at the longer end a lot, then you might want the 24-105 or something longer.

The easiest way to get 'quality' though is to buy a couple of prime lenses - the 135mm f2 is sublime if you often find yourself at the long end of your zoom.
 

StewartR

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#23
Wow. I think this thread has the highest proportion of confusion and bad information that I've seen in a long time. Why do people jump in to try to explain crop factors when they clearly don't understand it themselves?

For the OP, here [link] is an explanation of the crop factor concept that I wrote for another thread last week.
 
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#24
To be pedantic, you cannot measure a field of view in mm, you measure it in degrees. This is where all the confusion with crop factors comes from, trying to measure field of view in mm.
yes yes yes but saying this just confuses newbies. Just look at the replies in this thread... IMO as clear as mud and adding nothing but the potential for even more confusion.

The op asked a relatively simple comparative question and IMO we don't need post after post of in depth nit picking. Just a simple easy to understand answer.
 

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#25
The op asked a relatively simple comparative question and IMO we don't need post after post of in depth nit picking. Just a simple easy to understand answer.
Unfortunately the first person to answer the question got it completely wrong. He said "No and Yes!" when it should have been "No and No", and it all went downhill from there.
 
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#26
The reason I was asking is, I currently have an 18-135mm IS STM, if I were to up grade the lens, I was wondering what the equivalent "L" lens would be.
Just wondering, that's all.

Simon
400mm 2.8 L mk3 would be about right.
 
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#30
yes yes yes but saying this just confuses newbies. Just look at the replies in this thread... IMO as clear as mud and adding nothing but the potential for even more confusion.

The op asked a relatively simple comparative question and IMO we don't need post after post of in depth nit picking. Just a simple easy to understand answer.
Unfortunately you failed drastically!
I would say just quoting mm is what causes the confusion, it's clear enough once you understand, but the field of view bit needs to be stressed not ignored..

Your statement :
' 24mm on a 35mm/ff camera = 24mm FoV.
15mm on an APS-C camera = 15 x 1.6 = 24mm.
24mm on APS-C camera = 24 x 1.6 = 38mm.'

needed the 'FoV' on the latter two at the very least, and really should have been 'FF equivalent FoV' on both.
 
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#31
Your 18-135 is designed for an APS-C camera because it only projects enough light to cover an APS-C sensor, you could use it on a full frame camera but there would be large areas of black around the edges, like this https://images.app.goo.gl/E3QABzqvoxUcEAR7A
YOU MOST DEFINITELY CANNOT USE A LENS DESIGNED FOR AN APS-C CAMERA ON A FF CAMERA!

The back of the lens projects further into the FF camera and will hit the mirror as it comes up probably ruining it!

EXTREMELY BAD ADVICE!
 
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#32
YOU MOST DEFINITELY CANNOT USE A LENS DESIGNED FOR AN APS-C CAMERA ON A FF CAMERA!

The back of the lens projects further into the FF camera and will hit the mirror as it comes up probably ruining it!

EXTREMELY BAD ADVICE!
Note: This does depend on the brand of camera.
The Sony / Minolta A-Mount cameras did allow you to mount APS-C lenses on FF bodies, as the lens designs avoided elements projecting back into the body by any significant distance. The FF A-Mount bodies would also detect an APS-C lens, and automatically switch to an APS-C crop mode (with smaller file size).
 

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#33
YOU MOST DEFINITELY CANNOT USE A LENS DESIGNED FOR AN APS-C CAMERA ON A FF CAMERA!

The back of the lens projects further into the FF camera and will hit the mirror as it comes up probably ruining it!

EXTREMELY BAD ADVICE!
This is not universally true. It depends on the brand of camera and/or lens.

You really should try to get your facts straight before SHOUTING like this.
Or better still, avoid confusing the beginners and leave it to people who do know what they're talking about.

@Faldrax says it is possible, and safe, with the Sony/Minolta A-mount. (I don't have any knowledge on that mount so I'll defer to him.)

It is definitely possible, and safe, with the Nikon F-mount. Nikon FX cameras can automatically detect DX lenses and switch to DX crop mode.

It is definitely possible, and safe, with the Canon EF-mount and many third-party lenses. All the Sigma DC lenses and Tokina DX lenses which I've come across can be mounted on Canon full frame cameras, though the image may not fill the frame. Note however that I haven't tested every third-party lens so there may be some which can't be mounted safely.

It is not possible with the Canon EF-mount and Canon EF-S lenses. The mounts are subtly different and you simply cannot mount an EF-S lens on a full-frame camera.

So to summarise, in most cases you can use a lens designed for an APS-C camera on a full-frame camera. In some cases you can't because it just doesn't fit, but there's no danger of breaking anything. It's possible that there might be some third-party lenses which will mount but would not be safe to do so, but I haven't come across any and I think there probably aren't any.
 
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#34
This is not universally true. It depends on the brand of camera and/or lens.

You really should try to get your facts straight before SHOUTING like this.
Or better still, avoid confusing the beginners and leave it to people who do know what they're talking about.

@Faldrax says it is possible, and safe, with the Sony/Minolta A-mount. (I don't have any knowledge on that mount so I'll defer to him.)

It is definitely possible, and safe, with the Nikon F-mount. Nikon FX cameras can automatically detect DX lenses and switch to DX crop mode.

It is definitely possible, and safe, with the Canon EF-mount and many third-party lenses. All the Sigma DC lenses and Tokina DX lenses which I've come across can be mounted on Canon full frame cameras, though the image may not fill the frame. Note however that I haven't tested every third-party lens so there may be some which can't be mounted safely.

It is not possible with the Canon EF-mount and Canon EF-S lenses. The mounts are subtly different and you simply cannot mount an EF-S lens on a full-frame camera.

So to summarise, in most cases you can use a lens designed for an APS-C camera on a full-frame camera. In some cases you can't because it just doesn't fit, but there's no danger of breaking anything. It's possible that there might be some third-party lenses which will mount but would not be safe to do so, but I haven't come across any and I think there probably aren't any.
Of course it's also OK with all mirrorless cameras...
Many of the lenses I have don't protrude at the back at all, some (especially longer focal lengths) are deeply recessed.

Caution is always sensible when adapting lenses not designed to be used on your camera, but lenses that will do damage are fairly rare - usually manufactures ensure they won't mount directly if damage is possible...
 
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#35
I APOLOGISE - you are all quite right - you cannot fit an EF-S lens to a FF body or to an APS-H body.

I was confused because Andrew said you could and I am sure that I saw a warning about this years ago.

But I have now confirmed this on my own cameras.

And obviously you cannot damage the mirror on a mirrorless camera!
 
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