Bit of ignorance

Forgive me for being a behind on things but this is why i joined the forum

I have just bought a 7D to replace my ageing 450D and was looking at lens options.
Question that i have is - i know all about the crop factor when using EF full frame lenses but do Canon use the correct focal length on an EFS lens ie is a fifty a fifty in real tems or atually an 80?
Really want that ideal walk around lens as a basis and change my existing lenses to match with the higher quality of the 7D.
A nice red stripe is of course always an option - the dragon keeps saying i should make more of my hobby, so who am i to argue?

All lenses show the full frame focal length (even ef-s lenses), so you always have to take into account the crop factor

Yes the focal length of a lens doesn't change be it EF of EF-S but on the crop a 100mm EF and EF-S will effectively become equivalent to 160mm.

You see i was thinking Canon would have common sense and adjust it for the type of lens.
Least that makes my decision on a new lens a bit simpler now i know the focal lengths i've been using already

MarkB 65 said:

You see i was thinking Canon would have common sense and adjust it for the type of lens.
Least that makes my decision on a new lens a bit simpler now i know the focal lengths i've been using already

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Not really as all focal lengths should always be listed relative to eachother. At the end of the day the focal length is the focal length. If they didn't it would be more confusing. Crop body owners would have ef and efs lenses that would overlap focal ranges but offer completely different focal lengths on the body and everytime you considered a lens you'd have to do the maths.

With them all relative to eachother, you know an efs 10-22 is significantly wider than the ef 16-35 on your body. If the efs lens had the converted focal length on it it would look, on face value, to offer an almost identical focal range even though on a crop, the focal ranges are massively different.

So as Canon (and all the other manufacturers) have it, it makes more common sense as it is!

If you are looking for a 50mm equivalent lens then you will want something between 28mm to 35mm. My personal favourite lens is the sigma 30mm f1:4

MarkB 65 said:

You see i was thinking Canon would have common sense and adjust it for the type of lens.

Click to expand...

It's not common sense to change the FL at all. The focal length of a lens is completely independent of the sensor it is used with. What changes when you change sensors is the field of view as you are sampling more or less of the focal plane of the length.

What changes between EF and EF-S lenses is the size of the image circle they can create at the focal plane. Physically, you can't use them on a full frame camera because they would interfere with the mirror mechanism, but if you could (you can on the equivalent Nikon) it would only expose the centre portion of the sensor.

Smaller and smaller sensors need shorter and shorter lenses to produce the same field of view. For example, my Panasonic TZ3 has the following printed on it 3.3-4.9/4.6-46. It's a 10x zoom and the focal length is 4.6mm to 46mm. If I could use that on a full frame (which patently I couldn't as it's designed for a small sensor) it would still be a 4.6-46mm lens. When it's on the TZ3 though, the 4.6mm lens gives it the same field of view as a 28mm lens would on a wide angle.

Bottom line, lenses don't change focal lengths, what changes is the field of view when you change sensors.

arad85 said:

It's not common sense to change the FL at all. ....

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That post was probably the clearest explanation of this issue that I've ever seen. Well done Andy.

My post maybe wasnt as concise as maybe it should of been.... I am new to all this after all!

thanks for all the replies though- have definately found the answer i needed