EF-S (or Digital Only) Long Tele-Zooms - why don't they exist?

By making the image circle of the lens smaller - just lighting up the smaller sensor - a lens of a fixed physical size would project more concentrated light on the sensor. At the same time, the "crop factor" will disapear, so a 300mm lens will cover as much angle as on a ff body.

PWM2

If I understand what you are saying, if we took a 300mm f4 for instance, and adjusted the optics so that it's image circle was only big enough to cover a crop sensor (keeping the physical lens size the same) we would be able to basically make that a faster aperture lens?

If that's what you are saying, that was my though all along - you would be able to concentrate the light from a standard lens more in order to get a higher aperture without needing a bigger physical lens. I'm no physics/optics expert, but that would seem to make some sense to me. But maybe optically you just can't do this due to angle of incidence of the light onto the sensor when you try to do this "condensing" of the light.

But the other thing I think I am getting from your post is that in doing the above, you remove the "crop" factor. Hence a 300mm f4 lens, with some optics adjustment could produce a 300mm f2.8 lens (or something better than f4) that is crop only, but you would have to market it as a 180mm lens because it would not be the equivalent of putting a FF 300mm lens on a crop body.

Now it makes sense why there are digital only 50-150 lenses at 2.8. This is the equivalent of 80-240 f2.8 and can be had for about $600. In comparison a 70-200 f2.8 lens is $800 minimum. That solves the riddle for me. They basically DO make the 70-200 f2.8 for crop bodies - and they do it at a cheaper price as I would have expected. They just don't "yet" make any long primes, which may just be becaue they don't think there is a market for it, and the benefit of putting the existing FF teles on crop bodies gives amazing length, they know people will buy them for crop anyway.

Layston wrote in post #3388057
But the other thing I think I am getting from your post is that in doing the above, you remove the "crop" factor. Hence a 300mm f4 lens, with some optics adjustment could produce a 300mm f2.8 lens (or something better than f4) that is crop only, but you would have to market it as a 180mm lens because it would not be the equivalent of putting a FF 300mm lens on a crop body.

"Crop factor" is not something that you can add to or remove from a lens. The "crop factor" is merely a number to compare the field of view of a particular focal length used on different format cameras. By "format", I am referring to the size of the film frame or digital sensor of a particular camera.

Please read this thread (from the stickies) to understand the "crop factor" thing.

They dont make them because they would not be worth it to develope them anyways. Besides SIGMA has the 50-150 Telephoto lens that on a crop body is a 70-200. That is the best you'll ever get because there is no point, people want White lenses not over priced EFs digital only lenses.

I understand (without going and reading) that "crop factor" is a term refering to how by using a smaller sensor (APS-C) than a standard FF sensor you end up with a longer effective focal length. But I disagree with your statement. By changing the optics of a lens so that it directs a smaller image circle, you have effectively made that lens a "crop factor" lens.

So why did Canon make the 17-55 EF-S? Is this not an overpriced EF-S lens? I know the
argument for this lens is that a "high quality wide angle zoom" was needed. But I'll turn that back around and say, that if they could make a cheaper fast aperture zoom for APS-C format cameras, I think it would sell fine.

cjm - by looking at your listed lenses you seem to be an L coholic. I don't think everyone wants to spend that kind of money on their lens collections, so I would disagree with your statement. I wish I had the kind of money that is tied up in your collection, but I don't. And as it is, I have made the decision to buy only FF compatible lenses. So for me this whole thread is just conjecture and contemplation.

I still think my point is valid, but let me now rephrase it with better wording because people here seme to be obsessed with terminology rather that understanding the spirit of the discussion.

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If I were to take a lens designed for a full frame camera and were able to modify the internal optics such that it projected a smaller image circle that was APS-C format compatible, you should be able to get a lens that would have a faster/bigger aperture (lower f-stop number) while maintaining the exact same atual field of view when projected on the sensor. This means in practicality that the tele lens would not gain the 1.6X gain in focal length increase that we are used to on APS-C sensor cameras.

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As a side note, I understand that we can't magically "get more light" out of a lens. But by redirecting the amount of light needed for a larger format's sensor are down to a smaller area means more concentration of the light.

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pwm2 wrote in post #3387848
By making the image circle of the lens smaller - just lighting up the smaller sensor - a lens of a fixed physical size would project more concentrated light on the sensor. At the same time, the "crop factor" will disapear, so a 300mm lens will cover as much angle as on a ff body.

No, this is optically impossible. You cannot just "concentrate the light" from a lens by forcing the light into a smaller area without changing the focal length of a lens. You can only create more light at the plane of the sensor by increasing the aperture. I guess a manufacturer could design a "wide-converter" to reduce the size of the image circle a lens projects onto the sensor plane. Sort of opposite a telelconverter. A ".67x wide-converter", however, would have the effect of shortening the focal length of the lens to which it is attached by 2/3. For example, a 300mm f 4 lens with a "wide-converter" attached would become a 200mm f 2.7 lens. The light is "concentrated" but only by changing the focal length of the lens. There is no free lunch in optics.

The Canon EFS lens mount just places the back of the lens closer to the sensor plane making it easier to design wide-angle lenses that do not require the extent of retro focus design as would be required by a wide-angle lens designed for 35mm film cameras. (This is also why they only fit 1.6x crop factor bodies. The mirror design of a 1.6x crop factor body has been changed to keep from hitting the back of the lens.) Also, the EFS lens mount simply masks off the image circle to just cover the area of a 1.6x crop factor sensor.

If you start with a "full-size" 300/4 and modify it to reduce the image circle by a factor of 1.6, you would get a 188/2.5 lens. It would not work on a ff body, because it doesn't project an image on the full sensor. On a 1.6x camera, it will give a "virtual" focal length of 300mm, but since the physical lens is now only 188mm, it will have the DOF of a 188mm lens.

Basically, the modification would be the same as if someone produced a 0.625x TC. The historical reason why there haven't been any TC with a magnification less than 1, is that a normal lens (when used with a ff body) doesn't have enough image circle. You would get black corners. Hence, the normal way of getting a wider angle has been to add extra lenses on the other end of the lens - something that is regularly done with P/S cameras.

The lens will be just as expensive and large as the original lens - the trade will be zoom for light sensitivity.
Pro:
- better wide angle
- less autofocus problems (because of larger DOF)
Con:
- less zoom angle
- harder to isolate target from background

But if you are happy with the viewing angle of a 300mm lens (as seen on a ff body), the lens makers can make smaller and cheaper lenses for APS-style cameras. A 188/4 can most definitely be built smaller and cheaper than a 188/2.5 (or a 300/4) lens.

This is the reason for the puny "28-200" lenses on P/S cameras. If you start with a 5mm sensor, you can make a very small lens and still get the zoom range of a real 28-200 lens with a reasonable aperture. There are of course problems with the concept:
- Noise because sensor pixels are small
- Noise because little light is captured for each pixel
- A DOF that lets you capture dust on the front lens
- ...

Your original question was if long tele-zooms exists specifically for APS sensors. I don't know. There is no reason why they could not exists. The lenses I know exists are for example the Sigma 55-200 DC and the Tamron 55-200 Di II. They are significantly cheaper and smaller than ff lenses with similar zoom range and aperture.

oldsquawk wrote in post #3391007
No, this is optically impossible. You cannot just "concentrate the light" from a lens by forcing the light into a smaller area without changing the focal length of a lens. You can only create more light at the plane of the sensor by increasing the aperture. I guess a manufacturer could design a "wide-converter" to reduce the size of the image circle a lens projects onto the sensor plane. Sort of opposite a telelconverter. A ".67x wide-converter", however, would have the effect of shortening the focal length of the lens to which it is attached by 2/3. For example, a 300mm f 4 lens with a "wide-converter" attached would become a 200mm f 2.7 lens. The light is "concentrated" but only by changing the focal length of the lens. There is no free lunch in optics.

Correct! The viewing angle will look like a 300mm lens on a ff body, but the actual lens will be 188mm.

pwm2 wrote in post #3391035
Correct! The viewing angle will look like a 300mm lens on a ff body, but the actual lens will be 188mm.

I think I was typing while you were posting! If you want the focal length equivalent of a 300mm f 2.8 lens on a 1.6 crop factor body buy a Canon 200mm f 2.8 lens. If you want a "true" 300mm f 2.8 lens you'll have to buy the 300mm f 2.8L IS lens. No other way around it.

I pressed post, and 5 seconds later got a mail that the thread was updated

Press Release: For Immediate Release

LAKE CARP FACTOR, OY: Cannot Camera Inc today announced the launch of a brand new supertelephoto lens designed for crop factor users. Joe Fishmouth, spokesman for Cannot Inc. unveiled the tiny little supertelephoto to an audience of industry professionals and reporters "all wielding ancient and out of date designs that were not specifically optimized for digital" according to Mr. Fishmouth. "Gone are the days of large, heavy super telephoto lenses for crop cameras. We have designed a brand new 200mm f/2.8 lens that weighs only 700gm compared to the many pounds of the nearest competitor. Its red ring represents quality, white paint attracts the opposite sex and fingerprints, and the huge weight reduction was only possible because we took into account the crop factor for reduced frame users. Because of the crop factor, this revolutionary new lens has the field of view of a 300/2.8 lens of competitors yet weighs much less. To boot, this new product will be priced at a much more affordable $1999 compared to $4000 of the nearest competitor."

When interviewed by our photojournalist that this lens seemed to be remarkably similar to the black EF 200mm f/2.8 USM already on the market, Mr. Fishmouth declared that the only similarities were cosmetic. However, earlier our reporters had noticed employees of Cannot Camera with buckets of white paint, and the new 'prototype' lens appeared to smell strongly of volatile organic compounds. When quizzed as to whether Cannot Camera had simply re-painted their main competitor's full-frame-compatible 200mm prime lens offering in white and repackaged it at a much higher price, Mr. Fishmouth became extremely defensive. His discomfort was not helped any by the fact that discarded red-and-white "EF 200mm lens" boxes were found stuffed into a dumpster outside the conference center.

Inquiries are continuing.


(the above press release is a parody. All names and places are completely fictitous. If you want a 300mm FOV on a crop camera just go and buy a 200/2.8 lens. Intended for humor value only. All resemblances to actual people, organizations, companies or products is entirely coincidental. May cause excessive flatulence. Do not drive and operate heavy machinery while under the influence. See your proctologist if symptoms continue.)

Lightstream wrote in post #3391090
Press Release: For Immediate Release

Inquiries are continuing.


(the above press release is a parody. All names and places are completely fictitous. If you want a 300mm FOV on a crop camera just go and buy a 200/2.8 lens. Intended for humor value only. All resemblances to actual people, organizations, companies or products is entirely coincidental. May cause excessive flatulence. Do not drive and operate heavy machinery while under the influence. See your proctologist if symptoms continue.)

funniest post I've read today

You are missing the fact that a ff lens is projecting more than half the light outside the sensor.

pwm2 wrote in post #3391134
You are missing the fact that a ff lens is projecting more than half the light outside the sensor.

So what?

If I want a 70-200 f/2.8L IS zoom, there's no way that making a different version of it (that has a projected image only large enough to cover an APS-C sensor) is going to be any less expensive if everything else is the same - the optical quality, physical build, etc. I don't think anybody would choose to buy the one that is limited to the APS-C format bodies when the currently available lens works just fine on APS-C cameras as well as film cameras (or the larger digital formats that use EF mounts).