Question about EF lens opposed to EF-S lens

[ednorm]

My question is this, does a lens designed for smaller sensor on the aps camera like my 7d still have the crop factor? I know that on my camera an EF lens used has the crop factor thing where they say a 50 mm is similiar to a 75 mm, I beleive. Several manufacturers have lenses like tamrons DI II lens which says its made for smaller sensors, and their regular DI for full frames, similiar to canon EF and their EF-S line. Will you have the crop factor regardless if the lens is made especially for smaller senors or not, is the only disadvantage of owning a one of these lens designed for the smaller senors be the inability to use the lens if you upgrade to a full frame. A simple, yes its going to have the crop factor, or no its not if it is especially designed for smaller sensor cameras is what I am asking as most stuff you find is more confusing than helpful.

ed

[V8Demon]

Yes, it still has the crop factor. In order to mount an EF-S lens on a full frame you have a little work cut out for you.

Read more about it here: Flickr: Discussing Lemons into Lemonade: The 10-22 'EF-S' on a 1D... in Canon DSLR User Group

[inkista]

Slight correction: that's not mounting the 10-22 on a full frame. That's mounting the 10-22 on a APS-H (1.3x crop) body. The 1D is 1.3x; the 1Ds is 1x.

ednorm: Yes, all lenses, whether they're designed for crop or full frame, when you put them on a crop body will "have the crop factor". The lens's focal length is a physical characteristic of the lens, which doesn't change depending on the size of the sensor mounted behind it. A 50mm lens on a full frame is also a 50mm lens on a crop body. What changes is the angle of view (scene coverage) you'll see with the same lens on the different formats. But lenses don't actually change their focal length on different formats.

P&S cameras also have a crop factor, if you stop to think about it. Something like a Canon SX130IS is speced as having 28-336mm reach, but what's printed on the front of the lens (and its actual focal length) is 5.0-60mm. The sensor in the SX130IS is so small, it has a 5.6x crop factor.

[tlake55]

Simplified...you can use an EF lens on either a "crop" body (small sensor) or a "full frame" body, you can only use an EF-S lens on a "crop" body (small sensor)...so if you think you will ever upgrade to a "full frame" body you would want to purchase the EF lenses because you could use them on both kinds of cameras

[tlake55]

Originally Posted by tlake55

Simplified...you can use an EF lens on either a "crop" body (small sensor) or a "full frame" body, you can only use an EF-S lens on a "crop" body (small sensor)...so if you think you will ever upgrade to a "full frame" body you would want to purchase the EF lenses because you could use them on both kinds of cameras

...not sure if this helps or not, good luck

[benchdog]

Does an EF-S offer any advantage over an EF lens on a "crop" body camera?

[inkista]

Originally Posted by benchdog

Does an EF-S offer any advantage over an EF lens on a "crop" body camera?

Yes. The EF-S lenses are lighter, smaller, and can be a much newer optical design. And because they're smaller (smaller image circle to project) and can be made sharper without resorting to exotic glass elements, they often cost far less than a similarly spec'ed lens that has to cover the much larger full-frame sensor.

One of the big "hidden" costs in moving to a full-frame dSLR is that of replacing a crop-body ultrawide lens. While a Canon EF-S 10-22 ultrawide lens is only about $700, the Canon EF 16-35 f/2.8L II USM is more than twice that. And Sigma, Tamron, and Tokina don't really make full-frame counterparts to the 16-35L.

One example of EF-S vs. EF design. Let's look at the basic macro lenses.

Here are the MTF charts for the EF-S 60/2.8 macro ($400), and the EF 100/2.8 (non-L) macro ($530) and the 100/2.8L IS Macro ($950). EF-S 60 on the left, 100 non-L in the middle, 100L on the right. All three are damn sharp lenses and terrific performers.



Now, I'm not going to give you the full spiel on what MTF charts mean, but essentially speaking, the closer the chart is to a flat line at the top of the chart (at "1"), the sharper the lens is. The black lines indicate wide-open performance, the blue ones f/8 performance. The left edge is at the center of the frame , the right edge is at the corner of the frame. Note the advantage that only having to go out to 13mm buys the EF-S lens. Thick lines are more about contrast, thin lines are more about resolution.

The crop-body 60mm Macro, while cheaper than both lenses, is actually performing closer to the L than the non-L. The L is the newest design and costs more than twice the EF-S, but performance wise, the EF-S lens isn't far behind (in terms of sharpness). That's the EF-S advantage.

[Doug Pardee]

Originally Posted by benchdog

Does an EF-S offer any advantage over an EF lens on a "crop" body camera?

The short answer is: affordable wide-angle.

Cameras with smaller sensors need shorter focal lengths to achieve a particular field of view than cameras with larger sensors do. For a 35mm film camera, 50mm is commonly considered a "normal" lens, but to get the same field of view on a "1.6x" camera you need a 32mm lens. A 28mm lens on a 35mm film camera is commonly considered a "wide-angle" lens, but to get the same field of view on a "1.6x" camera you need an 18mm lens.

The problem starts here: the small-sensor camera is designed to be able to work with lenses designed for the large-sensor cameras. So, the lens mount flange has to be the same distance from the imaging plane (film or sensor). For Canon EOS, that distance is 44mm. That means that it's physically impossible to create a simple Gaussian lens with less than a 44mm focal length without having it protrude back into the mirror cavity.

The almost universal solution is: wide-angle SLR lenses aren't simple Gaussian. They include a set of lens elements called a "retrofocal group". This group of lens elements allows the lens to be physically located farther from the imaging plane than its focal length. (By the way, its opposite number is the "telephoto group", which allows a 600mm lens to be less than 556mm long. That's 600-44, in case you didn't figure that out.)

The problem with retrofocal groups is: they're darned hard to make both cheaply and well. A retrofocal group will shrink the image coming out the back of the lens, and the more it has to shrink the image, the harder it is to get good results all the way to the edges of the imaging plane. Bottom line: the shorter the focal length, the stronger the retrofocal group has to be and the more you're going to have to pay for the lens.

How EF-S helps: an EF-S lens is only used on cameras with smaller sensors. The retrofocal group still has to shrink the image as much, but nobody gives a hoot how good the results are beyond the edges of the smaller sensor. The retrofocal group can be made simpler and cheaper.

Another way that EF-S helps: Since the lens doesn't need to capture such a wide angle of view, it can be made with a smaller objective (front element), which generally means that the entire lens is smaller and lighter. This isn't an issue with long focal lengths, where the size of the objective is controlled by focal length and minimum f-number.

Another, mainly theoretical, way that EF-S helps: the cameras with smaller sensors also have smaller mirrors, so when their mirrors swing up they don't reach as far forward as mirrors on the large-sensor cameras. The EF-S specification allows the lens to protrude about 3 mm into the lens cavity. So a wide-angle lens could be designed to be mounted 41 mm from the sensor, which means that the retrofocal group doesn't have to be so powerful. Which again means that the retrofocal group can be made simpler and less expensively. In practice, few EF-S lenses take advantage of this.

Anyway, you'll notice that there are no EF-S lenses that have a minimum focal length above 60mm. There's no point. The EF-S advantage is at short focal lengths.

Unrelated to any of the above: since EF-S zoom lenses can only be mounted on small-sensor cameras, they're designed to have focal length ranges that are appropriate for small-sensor cameras. The 18-55 "kit" lens commonly used on "crop" DSLRs would be a fairly odd focal-length range for a non-crop camera. Similarly, the 28-90 lens from a 35mm SLR would be an odd focal-length range for a "crop" DSLR.