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Focal Length Multiplier 1.6x and zoom lens

Matthew Koslow , Mar 23, 2006; 08:34 p.m.

Please help me understand how my choice of lens should be affected by the 1,6x Focal Length Multiplier. I am switching from my beloved 35mm ELAN 7 to the 20D and deciding on a lens. Street photography is my favorite followed by landscapes a distant second.


Mark U , Mar 23, 2006; 09:01 p.m.

Divide your favourite 35mm focal lengths by 1.6 to get the same angle of view on a 20D. If you want the same narrow depth of field capabilites shooting wide open, you should be looking for lenses that are 1 1/3 stops faster than your 35mm ones. You will find that diffraction limits sharpness at wider apertures too - if f/16 is your diffraction tolerance on full frame, you'll get a similar effect at f/10 on the 20D.

Bob Atkins has a nice discussion of the consequences for depth of field here:


Robert Hall , Mar 23, 2006; 09:03 p.m.

My suggestion is to buy the 17-85 lens made for it, the EFS lens. There are two others, a macro and a super wide angle EFS lens. I would not buy the macro unless I were into that, rather I would try the other macros which work just as well unless you are very technical. The 17-85 is a great (!) lens. Get the wide angle only if that is something you will use. I would think it would be great for street work. If you have not got the 20D (It is to be replaced soon), consider the 5D if you have the $$. However, the magnification factor with the 20D can be an asset with longer lenses and the macros. The 20D is a fabulous camera that will be around for 3 or 4 more years, an eternity for digital cameras. My guess is that you will not miss film once you make the transition.

Mendel Leisk , Mar 23, 2006; 11:27 p.m.

Coming at it a different directions, a 50mm lens will behave like an 80mm lens (50x1.6) on a 1.6 crop body. Telephotos get more so, wide angles become narrower. So telephotos tend to benefit, wide angles suffer, and there's a sort-of vacuum as far as "standard" (50mm) lens equivelant. Canon's 35mm f2.0 is a cheap contender for the latter role, but...

Then there is the issue of 1.6 crop purpose built lens, that are not compatible with regular film canon bodies, or full frame dslr's.

Here's an interesting site with some info on that subject, plus an exhaustive rundown of all the canon lens:


Fwiw, I have a 20D with the following canon lens:

10-22 (only fits crop bodies) (very sweet wide angle!)

24-70 (std zoom range, not quite enough wide)

70-200 f2.8 (IS version)

The 24-70 is my main lens, and is a good starting point with that body, though it could double as a dumbbell. Alternatives I would consider to the 24-70:

17-85 (only fits crop bodies)


17-55 f2.8 (also only fits crop bodies?)

Robin Sibson , Mar 24, 2006; 02:55 a.m.

The 17~85 is a versatile lens of reasonably good quality, but is rather slow espacially at the long end. The new 17~55 (equivalent angle of view is 27~88 on FF) is expected to turn out to be of high quality, and has constant f/2.8 aperture, but of course it has a more limited range than the 17~85 and is going to be quite expensive. I don't know what the requirements of 'street photography' are, but I would guess that a fairly fast lens is a help, and this might be a good choice for you.

I use the 10~22 plus 24~105 combination, which suits me very well and delivers excellent image quality. You get a 10.5 to 1 zoom range with only a negligible gap (equivalent to 16~168 on FF). The only real downside is that it involves changing lenses at around the FF equivalent of 35mm, and of course the 24~105 is only f/4 - but I have fast primes for when I need them.

andy Van Eynde , Mar 24, 2006; 03:12 a.m.

Also use a 20d and :

EF-s 17-85 IS USM - EF 70-200 F4L - EF 50 f1.8

some other good sites :



Ben Anderson , Mar 24, 2006; 03:20 a.m.

Reading the addendum on Bobs digital DoF article it states that for hyperfocal settings about 1.5 stops less should be used on crop bodies, is this also true of the markings on EF-S lenses (what little markings there are) or has this been taken into account by Canon already since the lenses are designed for cropped sensors?

Mark U , Mar 24, 2006; 08:26 p.m.

No EF-S lens has any DOF markings. They all have extremely short focus throws too - so really, you have to depend on AF if you want to focus with (hyperfocal) depth of field in mind.

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