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jim kelly
Guest
I assume that a EF-S 17-40 on a 20D would yeild 17-40 focal range and not 20 somthing by 50 something ??
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Jim
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Jim
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mdebrieder
Senior Member
and FOV FF = 1.6x FOV 20D
that is why the new 17-85 becomes like the standard approx: 28-135
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that is why the new 17-85 becomes like the standard approx: 28-135
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jacuff
Member
Nope, it would still be 27.2 - 64mm equivalent. EF-S lenses get closer to the sensor, allowing the wider angle of view, but are still affected by the crop factor.
To be technically correct, the focal length does not multiply. The cropping factor imposed by the smaller sensor yields a field of view similar to that of a larger focal length lens.
The EF-S lenses are marked with 35mm equivalent markings so photographers experienced with full-frame 35mm measurements can do the conversion math easier. eg. The numbers all mean the same (each 50mm is 1x)
By that I mean: An EF lens of, say, 17mm has an "apparent focal length" of 27.2 on a 1.6x crop camera. To maintain a consistant math conversion across all Canon lenses, Canon chose to mark the EF-S lenses using the same 35mm equivalent measurements.
So, you still multiply by 1.6 even when using an EF-S lens.
If I understood your question correctly then I believe this answer will help.
dpreview & pbase supporter
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The EF-S lenses are marked with 35mm equivalent markings so photographers experienced with full-frame 35mm measurements can do the conversion math easier. eg. The numbers all mean the same (each 50mm is 1x)
By that I mean: An EF lens of, say, 17mm has an "apparent focal length" of 27.2 on a 1.6x crop camera. To maintain a consistant math conversion across all Canon lenses, Canon chose to mark the EF-S lenses using the same 35mm equivalent measurements.
So, you still multiply by 1.6 even when using an EF-S lens.
If I understood your question correctly then I believe this answer will help.
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dpreview & pbase supporter
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Forget the "crop factor" or "magnification factor" or whatever it's called at any point in time. That's a crutch for old 35mm dogs who can't walk and chew gum at the same time.
The normal lens for what Canon calls "APS-C" format is 28mm (about). Anything longer than that is longer, anything shorter is shorter. Relate to 28mm as the starting point and don't worry about what it is in 24x36mm format terms.
Photographers who work with both 35mm and medium format aren't wondering what the "crop factor" is when they shift between cameras.
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RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'
They are marked with their true focal lengths, not with "35mm equivalent markings."
If you buy a medium format camera, you'll find that lens marked in the same millimeters that 35mm cameras use--there is no difference. In fact, you can mount Pentax medium format lenses on Pentax 35mm cameras, and you'll find that 80mm is still 80mm, regardless which camera format it's on.
There is no other way EF-S lenses should be marked.
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RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'
Martin Eager
Leading Member
You can't forget it. SLR lenses are marked and sold with focal lengths which correspond to 35mm film. But until all DSLRs are full frame (35mm equivalent) then we'll have to keep multiplying the focal length by the crop factor to gain an understanding of what field of view to expect.
DSLR users on the other hand ARE. At least until crop factors go away.
To answer the original poster's question, you do need to multiply the 17-85 by 1.6x to get it's 35mm equivalent when used on the 300D/10D/20D. So that works out at 27-136 equivalent.
Martin
Ah, I misspoke. I should have not implied the markings were modified to be 35mm equivalent -- just that they are marked 35mm, and that the same math applies.
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dpreview & pbase supporter
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They are marked and sold with the actual focal length. The camera you place in on does not change the focal length. The crop factor comes in because you are only using part of the image.
Rich
SLR lenses are marked and sold with focal
Rich
SLR lenses are marked and sold with focal
G. Rightmyer
Well-known member
I'm not sure what you mean by saying you are only using part of the image. You are using the full image on your sensor unless you are using a digital zoom which does in fact crop the number of pixels you are using in the camera just like you would cropping in photoshop otherwise the only thing that is actually cropped is the field of view when you are not using a full frame sensor. I understand what Martin is saying and agree with him.
Steve Farley
Well-known member
The markings don't actually "correspond to 35mm film". As stated earlier focal length is focal length, it doesn't matter what the sensor size is.
The problem is that we have become used to using focal length to describe Angle of View which is of coarse inversely proportional to focal length. With a fixed sensor size i.e. 35mm film focal length accurately decribes AOV.
However AOV is also inversely proportional to sensor size so a conversion will always be required.
Steve
The problem is that we have become used to using focal length to describe Angle of View which is of coarse inversely proportional to focal length. With a fixed sensor size i.e. 35mm film focal length accurately decribes AOV.
However AOV is also inversely proportional to sensor size so a conversion will always be required.
Steve
Let's pretend for a moment we're on the Pentax forum. Pentax makes both 35mm cameras, 45x60mm cameras, 60x70mm cameras, and APS-C digital cameras. They also have adapters so that the 35mm and APS-C cameras can take the lenses of the larger format cameras.
So let's say a Pentax 35mm owner mounts an 80mm focal length, 60x70mm format lens on his camera. That lens casts an image circle of at least 92mm. That is far greater than the diagonal of the 24x36mm format of the 35mm camera. So the 35mm camera is only using "part of the image" that the lens is casting.
One could say there is a "crop factor" between the coverage of that lens on the 35mm compared to the coverage of that lens on the medium format camera. But nobody ever does because nobody ever cares. What is a normal focal length on a medium format camera is a telephoto on a 35mm camera--but the 35mm camera user doesn't care what it does on a medium format camera.
Notice that the focal length never changes, regardless what camera it's on.
Canon presents us with a similar situation with regard to APS-C cameras. They (now) have their own series of lenses--EF-S. But it just so happens that we can mount the lenses designed for larger format on them as well. As a matter of fact, there are even adapters to mount medium format German lenses on a Canon 20D.
We can mount a 300mm f2.8 Sonnar on a 20D. What's the "crop factor" going from 6x6 to APS-C? Do we care? All we have to know is the relationship between the "normal" lens for APS-C (27mm) and the lens we are contemplating. The coverage of the lens on any other format is irrelevant.
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RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'
My point is that if he isn't even a 35mm camera user, he shouldn't be made to care.
And if he is a 35mm camera user (just like current 35mm camera users who also use larger formats) he still shouldn't care.
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RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'
As you know, in the 35mm world we are accustomed to each 50mm being approx. 1x in power. A 200mm telephone is approx. 4x. A 25mm wide angle is approx. 0.5x.
Each of these focal lengths yield a consistent resulting image on the 35mm (24x36) frame. Since lenses are marked in focal length (and not by degrees of FOV) then photographers have long associated -- and are accustomed to -- relating angle of coverage by using the focal length.
When a photographer begins using a 1.6x crop camera with his existing arsenal of 35mm lenses (or purchasing a new 35mm lens) he must choose a lens based on, among other things, the resulting image.
Although the focal length of the lens doesn't change, the FOV captured DOES change. And since we choose FOV based on focal length, then it's important to understand the impact caused by a 1.6x crop camera.
This is precisely why it's imporatant to know the crop factor. It DOES MATTER that the photograph understand the crop factor -- if for no other reason than to select a lens that will yield the FOV that he wants for a particular shot.
If the shooter is using a 1.6x crop camera and wants a FOV equivalent to what a 28mm lens would produce on a FF camera, then he needs to know that a 17 or 18mm lens is required. We all know what focal length we need to obtain a certain FOV for a 35mm full frame capture -- years of experience has taught us that. It will take some time before (my brain, at least) photographers can say "A 17mm lens will capture the FOV I want for this shot" and have it apply to his 1.6x crop digicam.
If it's unimporant to you, then that's fine. But it IS important to a great many photographers, which is why there's so much discussion about it.
dpreview & pbase supporter
http://www.pbase.com/digirob
Each of these focal lengths yield a consistent resulting image on the 35mm (24x36) frame. Since lenses are marked in focal length (and not by degrees of FOV) then photographers have long associated -- and are accustomed to -- relating angle of coverage by using the focal length.
When a photographer begins using a 1.6x crop camera with his existing arsenal of 35mm lenses (or purchasing a new 35mm lens) he must choose a lens based on, among other things, the resulting image.
Although the focal length of the lens doesn't change, the FOV captured DOES change. And since we choose FOV based on focal length, then it's important to understand the impact caused by a 1.6x crop camera.
This is precisely why it's imporatant to know the crop factor. It DOES MATTER that the photograph understand the crop factor -- if for no other reason than to select a lens that will yield the FOV that he wants for a particular shot.
If the shooter is using a 1.6x crop camera and wants a FOV equivalent to what a 28mm lens would produce on a FF camera, then he needs to know that a 17 or 18mm lens is required. We all know what focal length we need to obtain a certain FOV for a 35mm full frame capture -- years of experience has taught us that. It will take some time before (my brain, at least) photographers can say "A 17mm lens will capture the FOV I want for this shot" and have it apply to his 1.6x crop digicam.
If it's unimporant to you, then that's fine. But it IS important to a great many photographers, which is why there's so much discussion about it.
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David Kieltyka
Veteran Member
You're stuck in 35mm-centric thinking. But the photographic world doesn't revolve around the 35mm format. It's just one format out of many. If you don't own a 35mm camera there is absolutely NO reason for you to care about "crop factor" or "35mm equivalent." Learn the way your lenses behave in the format(s) you ARE using and you'll be all set. What you describe is like trying to speak German fluently by translating everything you hear, read & speak into English first. Forget about English and learn to think in German.
-Dave-
So why does that same photographer not have any trouble with the concept that on his 6x6 camera, 50mm is a wide angle and 80mm is normal without conjuring up "crop factors"?
In the APS-C format, 27mm is normal. A 50mm is almost 2x normal. A 14mm is about 0.5x. What is so difficult to understand about that without reference to the 24x36mm format?
Why clutter up the mind of someone who has never even shot 24x36mm format with references to the 24x36mm format? Why insist that it's necessary for his mind to be so cluttered?
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RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'
For someone whose never shot 35mm then yes, I agree, let's not clutter the mind with what it "would have been like on a 35mm".
But I've shot 35mm film for probably 30 years now. I've shot digital (with 1.6x crop) for about one year. My previous digitals had not interchangable lenses, so lens selection was moot.
For me, and apparently many others, it DOES make a difference. Why else is there so much discussion on the matter????
For the record, I am becoming accustomed to selecting a lens based on the FOV it will produce on my 1.6x crop camera. But it TAKES TIME.
It's the same reason the US hasn't adopted the metric system in everyday public life. When it's 100 deg F outside, I know it's HOT. When it's 40 deg F outside, I know I need a jacket.
When my wife wants to bake a cake, she sets the oven to 350 deg F.
But if our thermometers were all calibrated in Celsius beginning tomorrow, you'd have a lot of confused people.
The point is simply that many people who have years of history and expectation of the FOV produced by a lens with focal lendth x on a 35mm camera will continue to associate that FOV with focal lenght x -- and will need to do the cropping-math to quickly arrive at the correct lens for a cropping sensor.
Besides, what the hell difference does it make to you???
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dpreview & pbase supporter
http://www.pbase.com/digirob
But I've shot 35mm film for probably 30 years now. I've shot digital (with 1.6x crop) for about one year. My previous digitals had not interchangable lenses, so lens selection was moot.
For me, and apparently many others, it DOES make a difference. Why else is there so much discussion on the matter????
For the record, I am becoming accustomed to selecting a lens based on the FOV it will produce on my 1.6x crop camera. But it TAKES TIME.
It's the same reason the US hasn't adopted the metric system in everyday public life. When it's 100 deg F outside, I know it's HOT. When it's 40 deg F outside, I know I need a jacket.
When my wife wants to bake a cake, she sets the oven to 350 deg F.
But if our thermometers were all calibrated in Celsius beginning tomorrow, you'd have a lot of confused people.
The point is simply that many people who have years of history and expectation of the FOV produced by a lens with focal lendth x on a 35mm camera will continue to associate that FOV with focal lenght x -- and will need to do the cropping-math to quickly arrive at the correct lens for a cropping sensor.
Besides, what the hell difference does it make to you???
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dpreview & pbase supporter
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grsharp
Member
Now here's a question I've been thinking about...if you do consider the "crop factor" between the various formats, do you get the same amount of telephoto "compression"?
For instance, if I photograph a landscape scene with a 35mm film camera and a 300mm lens, the image will be compressed, distances between objects will appear smaller, and small hills will appear higher. If you consider the 1.6x crop factor of my D60, a 190mm lens will have an apparent field of view of about 300mm as compared to 35mm film format, but will it compress the scene as much as a 300mm lens on a 35mm film camera? I sold all my 35mm film equipment when I switched to digital, so I haven't been able to compare the two.
Thanks,
Gerald Sharp
For instance, if I photograph a landscape scene with a 35mm film camera and a 300mm lens, the image will be compressed, distances between objects will appear smaller, and small hills will appear higher. If you consider the 1.6x crop factor of my D60, a 190mm lens will have an apparent field of view of about 300mm as compared to 35mm film format, but will it compress the scene as much as a 300mm lens on a 35mm film camera? I sold all my 35mm film equipment when I switched to digital, so I haven't been able to compare the two.
Thanks,
Gerald Sharp
No. The compression will be the same as on a 35mm full frame. That's because the optics are the same.
It's called "crop factor" because the result is the same as you'd get if you cropped the image in Photoshop.
dpreview & pbase supporter
http://www.pbase.com/digirob
It's called "crop factor" because the result is the same as you'd get if you cropped the image in Photoshop.
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GraphikEdition
Forum Enthusiast
The format is different so we should stop comparing it to something that is entirely different. Well we could if there werent 1.6, 1.3, 1.5,2 and whatever other FOV's out there in the world of dSLRs!!!
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