[pure-silver] Re: Slightly OT: Large format telephoto
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 18 Feb 2010 08:43:42 -0800
----- Original Message -----
From: "Joseph O'Neil" <joneil@xxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, February 15, 2010 6:59 AM
Subject: [pure-silver] Re: Slightly OT: Large format
telephoto
On 2/15/2010 9:50 AM, pdesmidt tds.net wrote:
I miss Steve Grimes. He was always incredibly helpful.
If I could send work his way, I did. These days, though,
it often isn't as practical to mount old process lenses
in shutters. Sure, if you have some decent shutters
sitting around, the price isn't too bad, but new shutters
have gotten very expensive. One can buy a Sinar behind
the lens shutter for the cost of one new Copal 3 shutter.
The Sinar shutter will allow you to use as many barrel
lenses as you like, assuming you really need a shutter in
the first place. With 8x10 at least one can often do
without. In any case, while you can get some very high
focal length process lenses, I doubt that many of them
are telephoto.
Mostly a lurker here, but a couple of thoughts. I used
4x5 and 8x10, and I use both process lenses - some with
shuttes, some not with shutters such as apo-ronars, red
dot artars and g-clarons, and I do have one true, 4x5
telephoto - the Wollensak tele-raptar. I forget the
exact focal length, but it works out to about 360mm on 4x5
There are several differences, but one of the mian
ones is that on a true "tele" lens for LF, you do nto need
as much focus travel. for example, on my 4x5 Tachihara or
my crown graphic, my 270mm g-claron has to rack all the
way out to almost the limit of the bellows to focus,
whereas with the tele-raptor, which is actually almost
100mm longer, it goes out only about 2/3rds trhe way.
The drawback is that compared to F9 process lenses,
"tele" lenses tend to be much heavier, and you need a much
more robust camea. So my Crown graphic or my Zone field
camera will handle the tele-ratpor, but the front standard
on my Tachihara is way too light to handle it.
So if backpacking and light weight is the most important
thing, go the F9 process lenses, but if you are driving,a
nd just walking a little, you ay like the tele lens.
One last bit, on *some* process lenses, not all, the
image circle is bigger than on tele - lenses. This is
mostly true for the g-clarons, but the image circle on my
apo-ronar and my RD artar is not all that big
jeo
A couple of things: First, the distance a lens moves
from infinity focus to a closer subject is strictly a
function of focal length, it is the same for a lens whether
its a standard lens or a telephoto. The telephoto lens has
the advantage that the rear principal point is displaced in
space so that it appears further away from the image plane.
That is, the back of the lens can be closer to the film for
the same infinity focus. However, the distance the lens
moves to focus more closely is exactly the same as for a
standard lens.
Process lenses are designed for optimum correction at
equal subject and image distances. The Apochromatic Artar
and similar lenses are of a type known as a Dialyte, these
have unusually stable corrections with change in distance
plus they are relatively simple, slow lenses with limited
coverage. All of which tends to reduce the loss of
correction. The Artar works quite well at infinity when
stopped down a little particularly if you are not using the
full field. The Dialyte has a rather small image circle
which does not get much larger as the lens is stopped down.
I don't remember if the G-Claron is a Plasmat type, but
think so. Plasmats have inherently larger coverage than a
Dialyte although the process versions have less coverage
than general use lenses. Many view camera lenses are
Plasmats, the Schneider f/5.6 Symmar and Rodenstock Sirronar
being examples. The Plasmat was derived from the Dagor by
splitting the inner element from the cemented triplet in
each cell and air spacing it. The advantage is that the
Plasmat has much better correction for spherical aberration
than the Dagor. It retains the Dagor's property of being
essentially a wide angle lens.
One advantage of using these long lenses rather than a
telephoto is that they have less lateral color and less
geometrical distortion both of which are minimized by the
symmetrical construction even when used at infinity focus.
Both aberrations are correctable in telephoto lenses but the
lack of symmetry makes it hard to do so.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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