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Why are Telephoto lens not so good?

Sol Campbell , Dec 08, 2000; 09:26 p.m.

Hi,

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I have seen many posts here saying, don't get a tele lens. That if you have the bellows draw, get a long lens as opposed to a telephoto lens. That tele lenses aren't as sharp or good as non-tele lenses of the same focal length.

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But why? In 35mm, the big glass of Canon and Nikon are the finest. According to tests they beat all other types of lenses. They are as good wide open as stopped down. I am refering to lenses like the 200/1.8, 300/2.8 and 600/4.

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In fact according to "photodo" the best lens they have ever tested is the Canon 200/1.8. And all the other big glass are pretty much runners up.

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So why is it in large format tele lenses are so down played?

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Thanks!

Responses


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Quang-Tuan Luong , Dec 08, 2000; 09:54 p.m.

Regardless of the sharpness issue, a telephoto lens is significantly larger and heavier, and have a much smaller image circle. Compare for example a Fuji 450 with a Nikkor T 500. The fact that the nodal point is way outside could also make movements less intuitive.

David Goldfarb , Dec 09, 2000; 12:08 a.m.

Also, on 35mm cameras, there is considerable advantage to being able to have a shorter barrel if there is a possibility that you might want to hand-hold the camera or use it on a monopod. Older long lenses for 35mm were not necessarily telephoto designs. The early Canons came in two pieces and the 1000mm lens was really 1000mm long (minus the 40mm or so from the flange to the film plane).

William Levitt , Dec 09, 2000; 04:03 a.m.

There are some positive aspects to telephoto lenses as well. For a camera with limited bellows draw, a true telephoto lens will allow it's use where another lens of equal photo length will exceed the bellow draw capabilities of the camera.

Ellis Vener , Dec 09, 2000; 03:55 p.m.

Telephoto lenses for large format are larger, heavier, more expensive and project a much smaller image circle than lenses of more standard design and identical focal length, and they are not as well corrected forfocusing distances closer than near infinity. <P> The telephoto lenses start to come into their own when you get into the 500mm and longer focal lengths, but it doesn't make much sense to get a 270 or 360mm telephoto when there are several excellent 300mm lenses, like the NIkon 300mm ƒ/9 M-Nikkor, availible at good prices.

Staffan Johansson , Dec 09, 2000; 04:35 p.m.

Tele lenses for large format are "true telephoto" designs i.e. they have a much shorter draw than their focal length indicates. This is achieved by first creating an image and then enlarge this image by a rear, negative lens group. It is similar to a true "Galilean binocular", the first telescope ever invented. This enlargement of the first picture "dilutes" and thereby makes less sharp the first image created by the real image-forming lens group. The same thing is used in astronomical observations and is called "Barlow lens", offering larger magnification but lower resolution. The advantage: less draw and higher magnification. The disadvantage: less performance.

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If you have the draw, my recommendation is to use a low-priced copy lens of long focal lenght such as Apo Ronar or Claron. They have a small aperture but are critically sharp at all scales down to 1:1 (provided you have THAT draw!).

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Regards Staffan Johansson

Sol Campbell , Dec 10, 2000; 01:17 p.m.

Staffan,

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Your explaination makes sense. But still it does not explain why in 35mm telephoto lenses are the cream of the crop. Even more so when you consider the small negative size. You would expect every flaw to be magnified proportionally.

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One question about the G-Clarons and Apo-Ronars. These are the classic "process" lens designs. They are optimized for 1:1. Then why don't Schneider and Rodenstock call them Macro lenses? On the contrary each has its own line of Macro lenses which are different from the G-Clarons and Apo-Ronars!

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Thanks.

Robert A. Zeichner , Dec 10, 2000; 02:12 p.m.

The fact that there are so many good telephoto lenses for 35mm cameras should not come as a surprise. First of all, for the format to make any sense, lightweight, compact lenses are a must. Otherwise, why record an image on such a small area of film if you need to lug around 40 lbs. of equipment. Secondly, it is not nearly as challenging to design and manufacture good performing telephotos as it is to build good quality retrofocus lenses. The latter do kind of the opposite of a telephoto, which is necessary for instant return mirrors to have room to flip up and down in an SLR. These wide angles are the real challenge!

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But, back to telephotos. One reason these lenses look good has a great deal to do with the shallow depth of field one experiences when shooting a distant subject with a long lens of any type. Because the background is many times, out of focus by intent, the focused part of the image appears very sharp by comparison to the blurred background. Helping that along is the issue of scale. Because tele shots tend to be comprised of simpler subject matter, with far less "information" than you might encounter when shooting a vast expanse with a wide angle lens, even slightly less than tack sharp elements take on an acceptable appearance of sharpness. Any long lens is also much easier to focus accurately for that reasen. If you were to make direct comparisons between standard long focal length lenses and telephotos, no doubt you could see a difference but, would you be willing to carry the extra weight and a more stable tripod to be able to use them on small format hand cameras? A friend of mine who is somewhat of a lens expert, has built some adapters to allow the affixing of a 35mm Leica RF camera to the back of his view camera. By use of a Visoflex viewing device, he has been able to make some spectacular images with a host of Apo Artars, Apo Raptars, Dagors, Commercial Extars and the like. Imagine a 24" Apo Artar on your Leica! Is this practical? I doubt it.

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But, addressing your original querry about why telephotos are not the best way to go on a large format camera, my answer is: Like all options, what makes sense for the type of work you do and the techniques you use should dictate your decision. A tele may be just fine for you. Consider the pros and cons. Telephotos have shorter bellows draw requirements. They also have smaller image circles. When you tilt or swing the lens, you will experience the odd effects of the nodal point being out in front of the lens. If you want to do close up work, you will have to apply an exit pupil factor once the image on film exceeds 1/10th of the object's actual size. Is any of this going to matter? If you shoot landscapes from great distances and have rear tilt and swing on your camera, maybe not. I had a Fuji 300 T on my Horseman 45FA and it worked very well. I've likewise heard very good reports about the Nikons. I use a camera with longer bellows now and so employ lenses that will work on my 8x10 as well. The graphic arts lenses, BTW are wonderful at infinity. The Macro label associated with some lenses may be more of a warning that these lenses won't cover the intended format at infinity!

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That was probably more of an answer than you were looking for and I apologize if I've repeated a number of other respondants comments, but I hope it helps in some way.

Glenn Kroeger , Dec 10, 2000; 07:39 p.m.

Sol:

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I am not convinced that the best teles are worst than the best long focus lenses any more. If you check out Chris Perez's tests, a Fuji 300T was nearly identical to 2 Nikkor 300Ms. Similarly, Nikkor 360 and 500 bracketed the performance of 2 Fuji 450Cs. MTF curves from Schneider show the Apo-Tele-Xenar performing as well as the 300 Apo- Ronar in the center of the field, with the Apo-Tele-Xenar having a somewhat smaller image circle but more even performance to the corners. So, everything said above about coverage, weight and weirdness of nodal plane position is true, but pure optical performance of some of these lenses is quite good. If you want the "reach" of a long lens without the hassles of very long extensions (wind etc.) they seem like a perfectly reasonable choice if you can live with their limitations. I suspect a lot of the reputation is due to older design teles from the 50's and 60's designed for press work.

Sol Campbell , Dec 10, 2000; 09:01 p.m.

Glen,

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Thanks for your post. One of the reasons I posted this question was because from my own experience I found the contrary. One of my best performing lens is a telephoto. It is the new Apo Tele Xenar Compact 400mm from Schneider. It is awesome even when used wide open at f5.6.

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So I don't know why they are regarded as being inferior.

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Thanks.


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