Question about APS-C Lenses

[Chuck Spaulding]

I just purchased the Tamron AF17-50MM f/2.8 and the Tokina 11-16MM f/2.8, in the description for these lenses at B&H it says that they were specifically designed for cameras like the 7D and are not meant to be used with full frame sensor cameras.

Does this mean that these lenses are as advertised, 11-16MM and 17-50MM respectfully? Or do I still have to multiply by 1.6?

[Dick Mays]

The numbers are the actual focal length ofthe lens. But since the 7D has a smaller sensor, the field of view (can be expressed as an horizonal and vertical angle) is smaller than with a full frame sensor. So the 50mm would give approx the same field of view as an 80mm on a 5D. The EFS lens can be made cheaper than a full frame ES lens, because it only has to image on a smaller sensor. There would be major vignetting if the lens were to be used on a full frame sensor.

[Chuck Spaulding]

I Kind of thought that was the answer but I was hoping it wasn't.

Since you can't really use this lens on a full frame ES Camera you'd think they might have created a"true" 17-50MM. Bummer.

Thanks

[Paul Cronin]

Chuck how do you like the Tokina 11-16MM f/2.8?

[Jean-Philippe Archibald]

Chuck, the lens is a true 17-50mm. It's just the sensor behind that is smaller. A focal length is a focal length, no matters what the sensor is used.

[Chris Hurd]

Originally Posted by Chuck Spaulding

...you'd think they might have created a "true" 17-50MM. Bummer.

Originally Posted by Jean-Philippe Archibald

Chuck, the lens is a true 17-50mm... A focal length is a focal length, no matters what the sensor is used.

Yes, it is indeed a "true" 17-50mm, that's why they call it that -- because that's exactly what its focal length is. You still have to do the 1.6x conversion math if you want to know what the full-frame equivalent field of view is.

[Liam Hall]

Focal length has nothing to do with the image circle a lens projects, it's just the distance from the centre of the lens lens to the film plane/sensor when the lens is focused at infinity.

[Chuck Spaulding]

Originally Posted by Paul Cronin

Chuck how do you like the Tokina 11-16MM f/2.8?

Hi Paul, I have not received the Tokina yet, it was out of stock at B&H.

The Tamron is a nice lens for the price, solid and really smooth focus.

I have the SP AF 17-50mm f/2.8 XR Di II LD Aspherical [IF] Autofocus Lens, it does not have any kind of image stabilization, it was $449.

They also have the SP AF 17-50mm f/2.8 XR Di-II VC LD Aspherical (IF) Lens, [VC' stands for Vibration Control and costs $624.

Is the image quality the same? Is VC Vibration Control the same as Image Stabilization? Does it work well with video. The stabilization in the kit lens works very well for shooting video. Is the VC worth an additional $175?

[Paul Cronin]

Thanks Chuck,

I think I might stick with Canon glass.

[Dick Mays]

Originally Posted by Liam Hall

Focal length has nothing to do with the image circle a lens projects, it's just the distance from the centre of the lens lens to the film plane/sensor when the lens is focused at infinity.

Liam,

Chuck asked if the focal length mean the same thing as with a FullFrame sensor, but also wanted to understand what was meant for a lens "Specifically designed" for the APS-C sensor size. You are correct, that the size of the image circle has nothing to do with focal length, but it has everything to do with a lens carrying the EFS designation.

The EFS lens can be designed to image a smaller circle, all other things being equal, you can get equivalent optical properties for a bit less than an equivalent EF lens.

[Chris Hurd]

For those who want to know, the "S" in EF-S stands for Short back-focus, which is a physical design element at the rear of the lens that makes the overall length and bulk of the lens barrel shorter, lighter and considerably less expensive than a full-frame (traditional 35mm) lens design. Unfortunately these physical changes also make an EF-S lens incompatible with Full-Frame or APS-H cameras, but that is the trade-off with the EF-S design; it's meant only for Canon APS-C cameras. There is no other difference, and some EF-S lenses (specifically the EF-S 17-55mm f/2.8 IS USM) are practically "L series" quality, even though they'll never bear the "L" designation officially.

[Liam Hall]

Originally Posted by Dick Mays

Liam,

Chuck asked if the focal length mean the same thing as with a FullFrame sensor, but also wanted to understand what was meant for a lens "Specifically designed" for the APS-C sensor size. You are correct, that the size of the image circle has nothing to do with focal length, but it has everything to do with a lens carrying the EFS designation.

The EFS lens can be designed to image a smaller circle, all other things being equal, you can get equivalent optical properties for a bit less than an equivalent EF lens.

Yes, I understand all of that Dick, I was just adding my comment to yours and Chris's.

Many people get confused about focal length and I just thought a little definition would be helpful. It always seems to be focal length, depth of field and angle of view that trip people up and there really is no reason for it to be so misleading. I think the use of terms like "crop factor" and "focal length equivalent" whilst helpful to some aren't very helpful to others, particularly those that have never used a 135 format camera.

If manufacturers/retailers wish to compare lenses designed for different formats I wish they would use the term "angle of view" and publish the size of image circle. Then we'd all know if it covered the sensor or not and whether it would be wide, close or whatever.

[Jay Houser]

Paul:

I was lucky enough to find a Tokina 11-16mm in stock at my local store.

It is sharp, great build quality, constant aperture. Love the push/pull manual/auto focus.

It is the only non Canon and the only EF-S lens I own.

A lot of people must share my opinion - it's out of stock at many sources, often.

[Paul Cronin]

Thanks Jay I will be looking for a wider lens next week for the 7d and if I can find 11-16 2.8 I might just go for it.

Well after looking around that is fast for the price and how wide it goes. Thanks Guys