Whats the difference?

I think, but could be very wrong that the 12-24 will work on a full frame sensor too, where as I dont think the 10-20 will.
 
^^^ you are indeed correct mate. As such, the 10-20, having been designed for cropped sensors actually reproduces 10mm. If you put the 12-24 on a cropped sensor, you will get 1.5 or 1.6 times the focal length.
 
As such, the 10-20, having been designed for cropped sensors actually reproduces 10mm. If you put the 12-24 on a cropped sensor, you will get 1.5 or 1.6 times the focal length.
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Focal length is focal length regardless of the sensor size of the camera. Either lens will produce the same image on a crop camera if set to the same focal length.

From what I've seen on here, the image quality of the 10-20 might be a little better as it doesn't have to produce the larger image circle for FF bodies.

I have the 12-24 but if I didn't need it for a 1.3 crop and ff body, I'd have the 10-20.
 
dazzajl said:
Either lens will produce the same image on a crop camera if set to the same focal length.
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Are you sure about that? If you set both the 20mm, the 12-24 will have a larger image spot size than the 10-20mm. Surely the resulting photos will have different fields of view?
 
Are you sure about that?
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Yup. :)

If you put both lenses on a 10D with a 1.6 crop sensor and set them to 20mm, the images will be the same. (Assuming the 20mm setting really is 20mm on both lenses. Lots of zooms don't always give the focal length they say are set at).

The difference will be a much larger amount image overspilling the sensor with the 12-24.
 
So then why do manufacturers of lenses that are full frame give equivalent focal lengths for when the lens is used on cameras with crop sensors? Because if the resulting image FOV is the same, it seems completly pointless to quote the altered effective focal lengths?
 
The field of view would be different if you took one lens and used it on two cameras with different sized sensors. It would be the same if you took two different zooms and used them at the same focal length on one camera.

...... really. ;)
 
dazzajl said:
The field of view would be different if you took one lens and used it on two cameras with different sized sensors.
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That's what I been trying to say. I probably worded it wrong to begin with :/

I'm having the same convo on IRC with robmiller and he says the same as you. Just something in my brain is not clicking. This link states:

http://www.kenrockwell.com/tech/crop-factor.htm

[FONT=Arial, Helvetica, sans-serif]"A 100mm lens on a 1.5x factor camera shows the same area of view that a 150mm lens would show on a 35mm film or full-frame camera."

So, if you put the "150mm" lens on a cropped sensor, that link is essentially saying that when the same 150mm lens is put on a FF sensor, the image FOV would be different?
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Sorry, I'll shut up :D I believe what you are saying mate, as I say, just something in my head not clicking :/

Shall we get back on topic? :bonk:
 
Wasn't that supposed to be my turn? :thinking: ;)

I understand the not clicking bit, I'm there often enough. :D

It's one of those things you need to not think about it for a while and then come back to it with a different head on. It's one of photography's many simple truths that's hard to explain simply.

Someone clever will though.
 
Matt

I have the 10-20. Infact, I think you had a play with it!

Give me a shout if you want another look. I've used both the 12-24 and the 10-20, and I ended up buying the latter.

:)
 
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