"Normal" lens for 1.6x crop factor?

fatsheep · Jan 14, 2008

DSLR and 35 mm SLR seem to use the same lenses yet DSLR cameras have crop factors (like 1.6x in the rebel's case). So your "normal" 50 mm lens is going to end up being a moderate 80 mm telephoto on a DSLR right (50 * 1.6 = 80)?

If a "normal" lens ends up being a telephoto, do you have to employ a wide-angle lens to get a "normal"? If you have to go to wide-angle lens to get a "normal" focal length then do you have to go to a fish-eye lens to get wide-angle-like focal length?

I'm a bit confused here...

Explanations are more than welcome. Thanks in advance,

- sheep

Sideburns · Jan 14, 2008

The only problem with a 50mm becoming an 80mm is that it still has the same distortion as the 50mm.

Say you use a 35mm...that's a bit closer when cropped...but it is wider, and may make the people look fatter. Even though you get the field of view of an almost normal lens.

Mav · Jan 14, 2008

Yep. On 1.5x Nikon DSLRs the 35mm f/2 is what a lot of people use for a "normal" walkaround lens, although it was originally designed as a slight wideangle for 35mm film bodies. The widest angle lens I've seen for Canon 1.6x DSLRs is the EF-S 10-22mm which is equivalent to 16mm on a full-frame body. That's pretty darned wide with about a 100 degree angle of view or thereabouts. 14 or even 12mm on a full frame body will still end up being a lot wider, though. Sigma just came out with a fisheye lens for Nikon/Canon 1.5x/1.6x bodies that will give a 160 degree horizontal field of view and a 180 degree diagonal field of view on Nikons, and just a tad less than that on Canons. But you're correct in your idea that you could also use a full frame 15/16mm fisheye on a crop body, but it won't be as wide as the fisheyes that are designed for crop bodies. Not sure which would be wider, a 15/16mm fisheye on a crop body, or a 10mm rectilinear lens. The angle of view formulas that apply to rectilinear lenses don't apply to fisheyes. I'm sure if you Google around that somebody has tried it and you might be able to figure it out. BTW I think Canon also has a 28mm f/2.8 prime lens that might give a bit more normal view on a 1.6x body, but it's not quite as quick as the 35mm f/2.

Ls3D · Jan 14, 2008

In a related thought, does the 1.6 conversion factor apply to cannon's EFS lenses?

-S

Josh66 · Jan 14, 2008

Ls3D said:
In a related thought, does the 1.6 conversion factor apply to cannon's EFS lenses?

-S

I've always wondered about that too. Since they know it's going on a crop body, is 18-55 really 18-55, or is it 28-85?

Peanuts · Jan 14, 2008

I imagine an 18-55mm is perceived to be a 28-85mm. I can't imagine the confusion they would introduce by stating the 'real' focal length.

omardxb · Jan 15, 2008

Interesting enquiry and comments, it's true, the 18-55mm is actually a 28-85 lens, but for easiness sake (And marketing purposes probably)
they still call them 18-55

ghpham · Jan 15, 2008

hhmm...interesting discussion. The thing that's really confusing to me is the crop factor. Does it really mean "telephoto" or is it because the pictures got cropped, that it actually give you the feel of "telephoto" over the 35mm frame?

Mav · Jan 15, 2008

The focal length of the lens is the focal length of the lens, which never changes. The only thing that changes is the angle of view, which varies depending on the sensor size. A bigger sensor will see wider. Hence to get the same angle of view as 28mm on a full-frame digital or 35mm film, you need an 18mm lens on a 1.6x cropped DSLR to make up for the smaller sensor that doesn't see as wide.

jstuedle · Jan 15, 2008

omardxb said:
Interesting enquiry and comments, it's true, the 18-55mm is actually a 28-85 lens, but for easiness sake (And marketing purposes probably)
they still call them 18-55

They are marked what they are. A 18-55mm lens is a 18-55 focal length no matter the crop factor. The crop factor makes it "look" like a 28-85 as compared to the full frame 35mm film or sensor camera. It's strictly a "field of view" issue. It's no marketing, it is what it is. (no I'm starting to sound like Bill Clinton, gotta work on that) Look at your point and shoot camera. It might have a lens marked 4mm-13.5mm that looks like a 35-115mm lens on a full frame 35mm camera. They just have a similar field of view, but the P&S does in fact have a 4-13.5mm lens.

Tighearnach · Jan 15, 2008

Now im confused!

An 18-55mm EF-S lens for Canon is 18-55 yes but it is made specifically for a cropped sensor camera therefore it wont work on a full frame camera therefore it is not really 18-55 but 28-88....?????

Yes? No?

Big Mike · Jan 15, 2008

An 18-55mm EF-S lens for Canon is 18-55 yes but it is made specifically for a cropped sensor camera therefore it wont work on a full frame camera therefore it is not really 18-55 but 28-88....?????

Yes? No?

NO
Mav and jstuedle are correct. The focal length listed on the lens is the actual focal length. If it says 18-55mm, then that is the actual focal length.

Look at the EF 17-40mm lens, for example. It will fit both full frame (or 35mm film) and 'crop factor' cameras. The field of view (FOV) will be different though, depending on the camera it's mounted on. So it's not the lens that's different, it's the camera.

The same thing applies of EF-S lenses. They aren't any different...18mm is still a very short focal length...but because the camera 'crops' the image, the FOV is narrower than it would be on a full frame camera.

EF-S lenses are actually different from EF lenses. They will only be used on crop cameras, so they don't need as big of an image circle. Also, the rear element protrudes farther into the camera body, which is the main reason you can't/don't use them on full frame bodies....because the rear element would interfere with the movement of the mirror.

Just to say it again. The crop factor is a function of the camera...not the lens.

fatsheep · Jan 15, 2008

This makes more sense now. A 50 mm lens will have less FOV on a crop factor camera than on a 35 mm but the image has the same distortion properties. So a fish-eye lens will still have the same distortion, just less FOV on a crop factor camera.

Thanks for the explanations,

- sheep

Big Mike · Jan 15, 2008

So a fish-eye lens will still have the same distortion, just less FOV on a crop factor camera.

That's correct.
However, remember that with a fish-eye...there is more distortion at the edges than in the middle...so while you do get that distorted look...a fair amount of it will be cropped off of the edges (when using a full frame fish-eye on a crop body).

fatsheep · Jan 15, 2008

Big Mike said:
That's correct.
However, remember that with a fish-eye...there is more distortion at the edges than in the middle...so while you do get that distorted look...a fair amount of it will be cropped off of the edges (when using a full frame fish-eye on a crop body).

Ack... I'm not going to be buying a fish-eye lens in the near future but that doesn't sound too great for DSLR users. I've heard of full frame DSLRs but they are usually extremely expensive right?