• Wondering which camera, gear, computer, or software to buy? Ask in our Gear Guide.

Crop senser and 'made for' aps-c lens

Something that's been bugging me for a while but would like to know the definitive answer from someones big brain if possible...

I've a Canon 550D and a canon 50mm... so actual lens length is 80mm when calculated with the sensor crop right??

Also got a Sigma 30mm... which i read somewhere is built for APS-C crop sensor so.....

Is that a genuine 30mmm on the canon 550D or is it a 48mm

If it's the former... when using the online DOF calc.. could you just enter 5D instead of 550D as Camera type to avoid the 1.6x
 
DOF has to do with sensor size too, not just focal length, so no, enter in your crop factor.

Even if a lens is "made for" a crop sensor (like an EF-S) lens it's focal length remains true. The saying that a 50mm is really an 80mm for a crop is more or less a misnomer. A 50mm is always a 50mm, but if you're used to using a full frame sensor (or 35mm still film) then a 50mm on a crop sensor will feel and show as much as an 80mm would on a full frame. The DOF will be different though.
 
A lens is a lens is a lens.

When we talk about equivalent focal lengths we're really comparing the field of view, i.e. how wide an angle we can look at through the lens.

When calculating depth of field, you should use the sensor size and actual focal length of the lens - after all, crop factor is just an arbitrary number we use for comparison's sake (we could just as easily compare all sensor sizes to Super 8 or 120 medium format).
 
problem with that ^^^ is that your in one of those theory meets reality issues. In CG the camera is ALL theory, no reality, so you need to assure that that reality and the theory of CG camera line up. You should be able to devise or find some calibration technique that will let you set up a scene in the real world, import that into your CG world and line the camera and views up..

There are ways to film a yard stick to measure the actual FOV of your shot.

This may all be moot, as a 3d camera solve is solving positional information of your shot in the real world, so the biggest issue will be DOF, which is probably something you play by ear (eye) anyway..

EDIT: I relay have no idea what I'm talking about here..
 
A lens is a lens is a lens.

When we talk about equivalent focal lengths we're really comparing the field of view, i.e. how wide an angle we can look at through the lens.

When calculating depth of field, you should use the sensor size and actual focal length of the lens - after all, crop factor is just an arbitrary number we use for comparison's sake (we could just as easily compare all sensor sizes to Super 8 or 120 medium format).

This.

The crop affects your fov. It does not turn a 50mm into another focal length.
 
With the recent proliferation of sensor sizes on removable lens cameras, maybe it's time we start thinking in terms of field of view (FOV) as a reference for lenses rather than just mm.

180º is fisheye, 100º is an ultrawide, 75º is wide, 40º is 'normal', 24º is a portrait and 10º or less is a telephoto - no matter what the sensor size.

It makes a lot more sense to say a 50mm lens has a 40º FOV on FF35, 16º on APS-C, and 8º on S16 than to say "it's a 50mm on a FF, but an 80mm on APS-C and 150mm on S16, even though it's really just a 50mm on all of them but those are the approximate cropped equivalents..."
 
With the recent proliferation of sensor sizes on removable lens cameras, maybe it's time we start thinking in terms of field of view (FOV) as a reference for lenses rather than just mm.

Several of the larger lens sellers on Ebay have started including FOV comparison images with the rest of the tech specs. To me, it's much more useful than the whole crop-factor multipliers jiggled with various mounts. I dig it.

.
 
I think it's very easy to get confused on this subject. When I switched to DSLR, it was a huge headache for me. ShockingMind, forgive me for assuming, but since you're asking this question I'm thinking you don't come from a photography background.

And that is really the only instance in which crop-factor, and conversion of equivalent focal lengths (for field of view), comes into play. Somebody who is experienced with 35mm photography has a certain image in mind, when they hear focal lengths. But if they put that same lens on a camera with crop-factor, the image is literally going to be cropped. As has been mentioned above, they'll get the same magnification, same depth of field, but the top, bottom, and sides are gonna be cut off.

Which means that if this person with a background in photography wants a particular field of view, while working on a crop-sensor camera, they have to do some quick mental math to choose the correct lens, and it won't be the one that they would've instinctually went for.

So let me ask you this -- if you don't come from a photography background, and therefore don't have these preconceived ideas of how a certain lens should look, why does the crop factor matter to you? It doesn't.

It matters only in the sense that you need to be aware of what's going on, so that when you're working with someone who comes from a photography background, you'll be able to stay on the same page as them, and know what things are going through their brains.

But you? Shooting your own stuff? Pay it no mind. Feel free to become accustomed to the different looks of your camera. There's no need for you to do any conversion-math for how a lens might have looked on a full-frame camera.

And to that end, I really like what ItDonnedOnMe says about referring to types of shots, instead of just focal lengths.

Which, by the way, 35mm cameras for filmmaking do not work the same as 35mm for photography. They do not shoot "full frame". I think it can be argued that crop-sensor cameras actually come much closer to replicating the "filmic" look than does any full-frame camera.
 
I shouldn't have mentioned the DOF calc as I think I've confused you guys (and probably myself!)

Peter The Great - Thanks you answered by question about whether its "really" a 30mm

Cracker Funk - No not a photgrapher, but the information (numbers) is used to create various bits of 3D Camera solving/mapping I'm playing with so it's useful to know what the numbers mean. I'm not bothered about how they effect the image but how they effect a computer program interpreting that image... which is why I asked if the 30mm was really 30mm... hope that makes sense... :/

WheatGrinder - You confirmed what I suspected... "just use yr eyes to see if its right, no easy method" :)

Cheers all!!!
 
One reason to care about sensor size, is that its hard to find a large FOV in a fast lens. Fast and wide is the expensive end of the scale. If your sensor is smaller this requires even shorter focal length lenses to get a big FOV. sigh.. $$$$

That said, my pennies are going for a BMPC after I see some footage on vimeo!
 
Back
Top