Tele vs. lens of Equal focal length

[avid]

Can someone kindly tell me what to expect from a tele lens vs a non-

tele lens of an equal focal length (aside from the obvious, of

course). Are tele lenses just as sharp? Are they heavier? Anything to

keep in mind while employing movements or focussing with a tele?

Aside from a difference in bellows draw, what would be different

between, say, a Tele 270mm and a regular 270mm lens? Thanks.

[kbreak]

I don't do 4x5, I don't even do 35 anymore.

I've been digitized.

 

Just out of curiosity, how do two lenses of identical focal length not both be "tele"?

Assuming they are both covering the same diameter circle of view....

 

umm.

[scott bacon]

Its hard to answer your questions in broad terms. It really depends on the specific tele lens in question and which lens of "normal" design you're comparing it with. That being said... Tele design lenses are generally larger and heavier. Some of the older tele lenses will not have today's modern multicoatings, for example the Schneider Tele-Xenars. This means they may be more prone to flare, but are not necessarily "less sharp." I have a Tele-Xenar 300mm f/5.5 from the 50s that I'm quite happy with (besides the size and weight). There are several modern teles that are multicoated and regarded quite well, performance-wise. For example, the Nikkor 360T.

[scott bacon]

Kevin, large format lenses with a tele design require less bellows extension than the focal length to focus at infinity. For example, a normal design 300mm requires 300mm of bellows draw to focus at infinity. A Schneider Tele-Xenar 300mm only requires 220mm of bellow draw to focus at infinity. This is allows the use of longer focal length lenses on field cameras with limited bellows draw.

[kelly_flanigan1]

The "non-tele versions" are sometimes faster in speed. Here I have a 300mm F4.5 Xenar; and a 210mm F3.5 Xenar in non tele versions. One can focus at infinity with each on a speed Graphic; and the 210mm F3.5 will focus decently close too.

[michael_briggs2]

The term "telephoto" is frequently misused to mean any lens with a long focal length (for the format), which results in confusion when the term is correctly used. A telephoto lens requires significantly less extension than is focal length to focus on infinity.

 

The reduction in extension is given by the Flange Focal Length (FFD), which is the distance from the back of the shutter (which is the same as the front of the lensboard) to the image when the lens is focused on infinity. Typically the FFD of a telephoto design is about 70% of the focal length. A view camera can focus a lens on infinity if the FFD is less than the maximum extension of the camera. To be able to focus closer, reasonable distances, a rough rule of thumb is that the maximum extension of the camera should be about 10% of the focal length more than

FFD of the lens.

 

By definition of the focal length, when focused on infinity, the rear principle point is still one focal length in front of the image. So the rear princple point is about 30% of the focal length in front of the lensboard. These means that if your camera has an axis tilt on the front standard, you won't get axis tilts when you tilt a telephoto lens. The image will rise or fall a bit when you do a front tilt, requiring fall or rise to restore the composition -- a slight inconvenience.

 

Generally telephoto lenses are heavier and have less coverage than non-telephoto lenses of the same focal length.

 

My advice is to buy a telephoto lens only if your camera can't focus a regular lens of the desired focal length, or if your camera isn't rigid at that extension.

 

There are comments on specific telephoto lenses in the archives of the forum. Some users have reported some telephoto lenses to be less sharp than non-telephoto lenses, others have reported their telephoto lenses to be sharp. Using really long focal length lenses demands a very sturdy camera and tripod, or perhaps even two tripods.

[ronald_moravec1]

Tele designs only get the shorter draw advantage at infinity. After that, if you need 4 inches more to get th ten feet, you will still need four inches more.

 

The image circle is smaller usually.

 

The nodal point is way in front of the lens board causing weird tilting and swing focus error corrections.

 

Newer teles are much improved.

[michael_briggs2]

<p>For any object distance, a telephoto lens needs less extension than a regular lens of the same focal length. Of course, both types of lenses need more extension to focus closer than infinity.</p>

 

<p>Here is a specific comparison:</p>

 

<p>The 600 mm f12 Fuji-T has a FFD of 384 mm, a circle of coverage of 260 mm diameter, uses a Copal 1 and weighs 980 g.</p>

 

<p>The 600 mm f11.5 Fuji-C has a FFD of 573 mm, a circle of coverage of 620 mm, and despite using a large Copal 3 shutter weighs less, 600 g.</p>

 

<p>To be able to focus on infinity, a camera needs 384 mm of extension for the Fuji-T and 573 mm for the Fuji-C.</p>

 

<p>To focus on an object at 15 meters, both lenses need 25 mm additional extension: 409 mm for the Fuji-T and 598 mm for the Fuji-C. So both lenses need the same amount of additional extension to focus to the same closer subject distance, but the telephoto always needs less extension to focus on a subject at any particular distance.</p>

 

<p>The image / object distance calculations are done using the basic equation of optics. See, for example, the Lens Tutorial at <a href="http://www.photo.net/learn/optics/lensTutorial">http://www.photo.net/learn/optics/lensTutorial</a>.

To use the equation, for effective image distance is the physical extension plus the difference between the focal length of the lens and the Flange Focal Distance (FFD). This increases the effective image distance Si for telephoto lenses.</p>

 

 

<p>For a camera with 18 inches / 450 mm maximum extension, the 600 mm Fuji-T could be focused on objects at 15 meters (and even objects as close as 6 meters), but the Fuji-C couldn't be focused on any object. The 600 mm Fuji-T has plenty of coverage for 4x5, while the 600 mm Fuji-C has plenty of coverage for 11x14.</p>

[r_hofland]

Quote: "Just out of curiosity, how do two lenses of identical focal length not both be "tele"? Assuming they are both covering the same diameter circle of view....umm."

 

Ponder using a 300mm Symmar on your 35mm camera and ask yourself if that is really still a "telephoto". Indeed, as others point out the telephoto design is in fact an optical trick used to reduce the back-focus distance. Image if the optical focal center in those fancy high speed 300mm telephotos by Canon and Nikon had to extend out 12 inches just to get to infinity focus, and even father for closeups!

 

There are also enhancements to the image because of the telephoto design since the gathered photons are concentrated and thus optically better corrected.

[neal_shields]

There is no free lunch in design.

 

To make a telephoto lens the lens designer has to bend the light more and probably add more elements.

 

No doubt some non-telephoto lenses are not as good as some telephoto but I can't see how a telephoto can be as good a lens as if it wasn't.

[kbreak]

Thanks!

 

I did not know this stuff!

 

*files away to memory*

[colin carron]

I think if you use the older Tele-Xenar design you will find it will be outperformed by the equivalent non-tele design. I use both the 270mmf5.5 tele-xenar and the convertible Symmar 150f5.6 / 265f12. The Symmar is sharper but of course you need the full extension and the aperture is smaller(=darker screen). Incidentally the Tele-Xenar is a 4 element design and the non-tele non-convertible symmar of the same effective focal length is 6 elements. A converted symmar uses 3 elements - not that this is terribly significant by itself.

 

I use the Tele-Xenar because it is a much handier lens to carry around and use but there is a bit of compromise with sharpness. The Tele- lenses also tend to be older and in general the newer the lens the better it performs as manufacturers improved quality control ver time.

 

The movements available with the tele-xenar (old type) is quite a bit smaller than the equivalent non-tele lens. Also notice that the Tele-Arton design is designed for 6x9 and only the longer focal lengths cover 4x5 and then only just. You will sometimes see them advertised on ebay stating that they cover 4x5 but that is not always the case.

[avid]

Thanks everyone for enlightening me (and Kevin) about the tele designs in LF use. I know now what to expect. Of interest to me are two of the newer designs, namely the Schneider APO Tele-Xenar 400mm Compact (FFD of approximately 285mm) and the Fujinon Tele 400mm (the FFD should agree with my Ebony 45S' 270mm+90mm Extender back). I imagine the movement will work somewhat like a base-tilt (or worse) than the axis-tilt that I am so used to. Ultimately, because of the fact there is no way around it due to FFD, something will have to give and hopefully I will end up being extremely pleased or pissed with the performance. I will find out soon.

Obliged to everyone that answered.

[r_hofland]

Quote: "No doubt some non-telephoto lenses are not as good as some telephoto but I can't see how a telephoto can be as good a lens as if it wasn't."

 

The wonderful apochromatic telephotos that came out in the 1980's, the Canon 300 FD 2.8 L in particular, were amazingly sharp even when compared to high quality "normal" lenses of that era.

 

I'm certain the latest "apo" telephotos for veiw cameras are equally wonderful although they may not quite match the nominal resolutions of the latest "digital" lenses of equivilant focal length. However, ponder the functional resolution in the same image area of the two designs and perhaps you'll find that the telephotos are indeed superior, maybe even far superior.