A question about APS-C lenses

[Joshim]

Hi everyone, I've just recently started really getting into this DPS site and love it!

I have a question about APS-C lenses used on APS-C sensors that I am hoping someone can clear up for me: If you use an APS-C lens on an APS-C sensor camera, do the focal lengths stay the same as listed on the lens? Or do they still have to be multiplied by the crop factor of the sensor?

I know that using a full-frame lens on an APS-C sensor changes the focal length listed on the lens by 1.6 or whatever the sensor is, but what about when using a lens made for your specific sensor? Would a 17mm APS-C prime actually be 17mm on a cropped sensor?

The reason I am asking is because I'm in the process of debating whether to dish out the extra cash and buy a full-frame camera or a cheaper cropped one and stick with their lens offerings... Of course, that's just one of the details I'm pondering ^^

I'd appreciate all the input! Thanks!

[Japaslavian]

If I'm understanding your question correctly, yes it would be the stated focal length.
For instance my 10-22mm is a crop body lens is actually 10mm on my crop body camera, but it is theoretically about 16-35mm if you were to be able to put in on a full frame camera (which you can't but that is about the equivalent)

[Joshim]

Thanks, Japaslavian! You understood my question clearly.

Now to debating the other factors in my contemplation... ^^

[inkista]

Focal lengths do not change due to sensor size. A 10mm lens on full frame is still a 10mm lens on a crop body. Focal length is a physical property of the lens. What changes is the field of view: a 10mm lens on a crop-body will have the same field of view as a 16mm lens on a full-frame. It's not a focal length multiplier; it's a crop factor.

[Joshim]

Oooh, that makes perfect sense! So even if I use an APS-C lens on an crop-sensor, it wouldn't be the same as using a full frame lens and sensor combination at the same focal length?

I'm really debating getting a full-frame DSLR (maybe a used 5D?) over updating my current APS-C type camera due to that factor and the lower noise at higher ISO's. I'm currently using a Pentax *ist DS which I've had since it first came out, but am wanting to upgrade...

Thanks for the info!

[OsmosisStudios]

I think youre slightly confused.

If I mount my 18-70 onto my D80, it gives me the same field of view as a 27-105. So, if I were to mount a 27-105 lens onto a full-frame body, then the lenses would "see" the same thing.

In much the same way, if I use a lens at 200mm on my D80 (equiv: 300) and a 300mm lens on a full frame, they'll "see" the same thing.

[Joshim]

I mean, I totally understand that concept.

But then, there comes into play the fact that there are lenses made specifically for full-frames and lenses that are made specifically for APS-C sensors. Take for example Pentax, they make a lot of APS-C type lenses specifically for their DSLR's.

If the APS-C type lenses' designated focal lengths still have to be multiplied by the crop factor, what are the differences between APS-C lenses and full-frame lenses?

That's what I'm wondering. I hope I'm clearing my own question up.

[inkista]

The main difference between crop-body lenses and full-frame lenses is the size of the image circle they project onto the image plane of the camera, and how far away from the image plane the lens sits. APS-C lenses are designed to sit closer to the sensor, and project a smaller image circle. If you mount an APS-C lens onto a full-frame body, you will get vignetting (dark corners), because the image circle that's designed to cover a crop-body sensor won't be large enough to cover a full-frame sensor or a frame of 35mm film.

With Pentax, unless you're also shooting with a film body, you typically don't have to worry about any of this, since none of their digital SLR bodies are full-frame.

[wal]

hello,

I've got the same confusion here. Now, I have an APS-C frame(EOS 450d), and even if i upgrade, i'll just go for a EOS50 / EOS40... technically speaking,... I'll be using an APS-C size all the way.

Now, In my case, do i need to browse prices or crack my head figuring out which full size lense (EF range) to get, or just focus my attention and my limited budget on the EF-S lenses..?.

I mean, why the need to get a big one, if i'm only using small sensor and it can't see the whole image anyway, of course you can get a teleconverter/ extension (correct me if i'm wrong, i'm not familiar with tech term), but that will still add to the cost, am I right.?

Help me please,

Thanks,
wal..

[RexK_Cozumel]

Originally Posted by wal

hello,

I've got the same confusion here. Now, I have an APS-C frame(EOS 450d), and even if i upgrade, i'll just go for a EOS50 / EOS40... technically speaking,... I'll be using an APS-C size all the way.

Now, In my case, do i need to browse prices or crack my head figuring out which full size lense (EF range) to get, or just focus my attention and my limited budget on the EF-S lenses..?.

I mean, why the need to get a big one, if i'm only using small sensor and it can't see the whole image anyway, of course you can get a teleconverter/ extension (correct me if i'm wrong, i'm not familiar with tech term), but that will still add to the cost, am I right.?

Help me please,

Thanks,
wal..

If you are ever planning on moving to a full frame camera then you will need to get EF glass since EF-S lenses do not work on full frame bodies. That is a major downer with Canon. A teleconverter just multiplies the focal length of the lens by whatever the teleconverter is. So a 2 x would double the focal length. Extension tubes just allow you to focus on an object that is closer. Mainly used for macro work.