Canon L on a 20d

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Am I right in thinking most Canon L glass will not have the focal length stated due to the cropped sensor on the 20D?
( I take it say a L F4 17 - 40 will effectively be a 27 - 64mm lens? )
 
I make that about right:thumbs:
 
Focal length will not change but the field of view will. A 17-40 is the same focal length on any sensor.
 
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I think your calculations aren't far wrong :)

A common wide angle lens on a crop sensor tends to be;
10-24mm then 17-55mm

On a full frame;
17-40mm then 24-70
 
jmsjabb said:
Am I right in thinking most Canon L glass will not have the focal length stated due to the cropped sensor on the 20D?
( I take it say a L F4 17 - 40 will effectively be a 27 - 64mm lens? )
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Correct, don't worry about people banding around different terminology, as far as you're concerned if you're used to a 35mm film camera, the lens will be an effective 27-64mm lens, which is a good range :)
 
Depends which camera you have , a Full frame camera will be 17 -40 and a cropped sensor will be x1.6 27.2 - 64
 
So, as I am hopelessly lost with this, will I loose width of shot at 17mm compared to my 18mm lens designed for the cropped sensor? ( Sigma DC lens )
 
Made for APS-C lenses like sigma's DC or Canon's EF-S are not exempt - the difference is that these lenses only project a circle of light big enough for a cropped sensor - so 17mm EF is the same as 17mm DC or EF-S (just the later won't work on a full frame body). So you won't loose any width with either lens on a crop. You'll only loose length if you mount a 17mm lens on a FF body.
 
Greenninja said:
Made for APS-C lenses like sigma's DC or Canon's EF-S are not exempt - the difference is that these lenses only project a circle of light big enough for a cropped sensor - so 17mm EF is the same as 17mm DC or EF-S (just the later won't work on a full frame body). So you won't loose any width with either lens on a crop. You'll only loose length if you mount a 17mm lens on a FF body.
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The tool dogfish suggested shows it will crop, if I select a Canon EFS lens, the picture is cropped.
Is this a mistake on the tool?
 
I don't think that things have been stated very clearly so far, I'll have a go.

Lenses are desribed as a zoom length such as 17-40mm and whatever camera you fit them to the lenses remain the same, they are what they are, eg. 17-40mm.

However...when you mount the lens on an APS-C camera all you see is a "crop" from the centre of the image because the camera sensor is smaller than a full frame sensor. The "crop factor" for Canon APS-C cameras is x 1.6 so a 17-40mm becomes effectively 27-64mm because all we see is the centre portion of the image.

EF-S lenses and small sensor lenses made by Sigma and the rest are exactly the same. They are what they are, eg 18-50mm, but all we see is the centre portion of the image so when fitting these lenses to an APS-C camera we must always multiply the zoom length by 1.6 if we want to relate them to the field of view a lens of their zoom length would give on full frame.

Lenses like Canon EF-S and Sigma DC are designed for smaller sensors than full frame and give an image that wont completely cover a full frame sensor so if you tried to use one on a full frame camera you'd get vignetting.

I hope that's clear.
 
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jmsjabb said:
The tool dogfish suggested shows it will crop, if I select a Canon EFS lens, the picture is cropped.
Is this a mistake on the tool?
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Its not the lens that causes a different field of view its the size of the sensor in the body - a 24-70mm L EF would be exactly the same as a 24-70 EFS (if they did one) when mounted on a crop body.
 
I think I am getting this.
So, if I had a EFS lens and shot at 17mm and then a L lens, non EFS and again shot at 17mm, would the images be the same on paper?
So, in reality, my 17mm lens is, printed image, the equivalent of a 27mm film or non cropped body
 
jmsjabb said:
I think I am getting this.
So, if I had a EFS lens and shot at 17mm and then a L lens, non EFS and again shot at 17mm, would the images be the same on paper?
So, in reality, my 17mm lens is, printed image, the equivalent of a 27mm film or non cropped body
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yes.

Just an FYI: unless you need the weathersealing and outstanding build quality, don't get a 17-40 for a crop body - there are better options out there. 17-40 is really intended to be used as a wide angle zoom on a full frame body, and believe me when I say it does that very well. For crop bodies there are lenses that go just as wide (17mm), but go longer (up to 50 or 55mm), f/2.8 as opposed to f/4 and some even have IS.
 
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Yes, the lens is what it is, it's the sensor size that gives you a crop factor so an EF-S lens and an EF lens of the same zoom length give the same effect, x 1.6.

You can use EF-S and EF on something like a 7D but you can't really use EF-S on a 5D without big problems.
 
Thanks guys. seems I may need to go for a wide lens to add to say a 24 - something
 
Last ( silly? ) question.
What is the point then of the EFS lens? What benefit do I get by having them?
 
jmsjabb said:
Last ( silly? ) question.
What is the point then of the EFS lens? What benefit do I get by having them?
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It's not a silly question at all, and there are lots of benefits.

Basically, at shortish focal lengths it is optically quite hard to get a lens to project a large enough image circle to cover a full frame sensor. That is the point behind the advice above not to get a 17-40L for a crop format camera.

When designers are released from the constraints of full frame and only have to cover the smaller crop format sensor, they can do much more. Take the 17-40L for example, which is about as good as it gets for full frame. Compare that spec to the EF-S 17-55 which not only has significantly greater range, but is a whole stop faster at f/2.8 vs f/4 (that is quite a big deal optically) and it also has IS. It is a bit more expensive, but it is also exceptionally sharp. No full frame lens can get down to 10mm focal length at all, yet crop format specific lenses do it easily.

There are loads of similar examples in the wide to semi-wide range but the optical benefits quickly run out above 50-60mm which is why there are no EF-S lenses from Canon that start at longer than this, and likewise no Nikon DX either.

In a nutshell, if you fit a wide or standard-ish focal length EF/FX lens to a crop format camera, you will have a restricted spec and will also be paying for format coverage that you can never use.

Some people say don't buy crop format lenses because you won't be able to use them on full frame, but that is poor advice IMHO. Because:
a) while shooting on crop format you are not making the most of your money,
b) most people never move to full frame anyway,
c) if you do change then your EF lenses will behave completely differently so you'll have to replace them anyway to get the field of view you want back,
d) you can sell on good quality branded lenses on here very easily for good money. In fact if you buy used in the first place, you might well lose nothing. Certainly the price is small compared to what you'll get for your old camera, plus the high cost of buying a new full framer.
 
Some very good points raised there by Richard (HoppyUK)
My goal of L lenses for a 40D may be under review once I've given it all some more thought.
Back to the drawing board it is then.
 
While hoppy makes a good post most of it becomes irrelevant if you want a constant aperture lens, as the only constant aperture EF-S lens is the 17-55mm f2.8 IS USM, all others are EF fit so you will be forced down that route anyway if you go Canon.
 
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But why restrict yourself to Canon lenses? Why not just buy the best lens at the zoom length you are interested in?
 
jmsjabb said:
Am I right in thinking most Canon L glass will not have the focal length stated due to the cropped sensor on the 20D?
( I take it say a L F4 17 - 40 will effectively be a 27 - 64mm lens? )
Click to expand...

Not most but ALL lens will not be as stated but you have to do the 1.6 X what ever the lens is this is EF-S and EF lens
 
woof woof said:
But why restrict yourself to Canon lenses? Why not just buy the best lens at the zoom length you are interested in?
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I can only think of one good reason, and that's environmental sealing. None of the third parties offer it. Apart from that you just spend more wonga!
 
Dogfish_magnet said:
While hoppy makes a good post most of it becomes irrelevant if you want a constant aperture lens, as the only constant aperture EF-S lens is the 17-55mm f2.8 IS USM, all others are EF fit so you will be forced down that route anyway if you go Canon.
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What is the big benefit of a constant aperture? It's only constant at lowest f/number anyway. What difference does it make?
 
HoppyUK said:
What is the big benefit of a constant aperture? It's only constant at lowest f/number anyway. What difference does it make?
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As you know it helps focus in low light - regardless of the aperture selected, a f2.8 lens or faster coupled with the center focus point has greater focus accuracy (not sure if that s true on XXXD bodies) and it also helps when you want shallow DOF, you can use a tele converter without losing auto focus and you can use a EG focusing screen to help improve your manual focusing skills.
 
Dogfish_magnet said:
As you know it helps focus in low light - regardless of the aperture selected, a f2.8 lens or faster coupled with the center focus point has greater focus accuracy (not sure if that s true on XXXD bodies) and it also helps when you want shallow DOF, you can use a tele converter without losing auto focus and you can use a EG focusing screen to help improve your manual focusing skills.
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Those are the (marginal) benefits of a low f/2.8 aperture (which very few zooms have anyway) not of a constant f/number.
 
Chaps, to a layman, this is getting confusing!
OK, please recommend ma a lens to replace my Sigma, which it has been suggested is a soft lens and I think I need IS of some sort.
Thanks
 
jmsjabb said:
Chaps, to a layman, this is getting confusing!
OK, please recommend ma a lens to replace my Sigma, which it has been suggested is a soft lens and I think I need IS of some sort.
Thanks
Click to expand...

Unless you are unhappy with your Sigma, there is no need to replace it.
 
HoppyUK said:
Those are the (marginal) benefits of a low f/2.8 aperture (which very few zooms have anyway) not of a constant f/number.
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OK i forgot it was you - i should have stated

While hoppy makes a good post most of it becomes irrelevant if you want a constant aperture f2.8 lens, as the only constant F2.8 aperture EF-S lens is the 17-55mm f2.8 IS USM, all others are EF fit so you will be forced down that route anyway if you go Canon

Canon EF 16-35mm f2.8L USM mkII
Canon EF 24-70mm f2.8L USM
Canon EF 70-200mm f2.8L USM
Canon EF 70-200mm f2.8L IS USM
 
he is questioning why you want a constant aperture f/2.8 lens I think.

personally I love constant aperture, as I hate the viewfinder darkening as I zoom in. It also means that if you zoom the metering doesn't need to be retaken.
 
jmsjabb said:
Chaps, to a layman, this is getting confusing!
OK, please recommend ma a lens to replace my Sigma, which it has been suggested is a soft lens and I think I need IS of some sort.
Thanks
Click to expand...

Your lens is probably soft if you take a image with the lens wide open. Use AV to set the aperture. If you stop down the aperture an f-stops or 2 the images will sharpen up. Does depend what shutter speed the camera sets and the conditions you're taking the photo in.
 
OK, sorry, I missed a bit on this thread.
I suffer shaky hands and am looking at better glass / IS lenses to help me out. The sigma being soft to start with, coupled with my shake is not working for me.
 
Dogfish_magnet said:
OK i forgot it was you - i should have stated

While hoppy makes a good post most of it becomes irrelevant if you want a constant aperture f2.8 lens, as the only constant F2.8 aperture EF-S lens is the 17-55mm f2.8 IS USM, all others are EF fit so you will be forced down that route anyway if you go Canon

Canon EF 16-35mm f2.8L USM mkII
Canon EF 24-70mm f2.8L USM
Canon EF 70-200mm f2.8L USM
Canon EF 70-200mm f2.8L IS USM
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And the cheapest of those lenses is over £1,000. Most EF-S lenses are two or three hundred quid, with the most expensive being the 17-55 at £800, and that is also f/2.8. 60mm macro is also f/2.8.

trencheel303 said:
he is questioning why you want a constant aperture f/2.8 lens I think.

personally I love constant aperture, as I hate the viewfinder darkening as I zoom in. It also means that if you zoom the metering doesn't need to be retaken.
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I was questioning the benefit of a constant maximum aperture, as originaly stated, not necessarily f/2.8.

And you only have to adjust the exposure if you are shooting at that maximum aperture - all other f/numbers are always constant.
 
jmsjabb said:
OK, sorry, I missed a bit on this thread.
I suffer shaky hands and am looking at better glass / IS lenses to help me out. The sigma being soft to start with, coupled with my shake is not working for me.
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Its probably soft because of the setting your using to take the image, especially if the shutter speed is slow and your handholding.

It would be probably better to post some examples of why you think your lens is soft. I don't think you've mention which lens is causing you problems either.
 
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