Re:LF focusing

[Jim Brick <jim@brick.org>]

At 06:41 PM 10/29/97 +0000, you wrote:
>>I'm trying to learn how to use a Linhof V but I'm having trouble with
>ground glass focusing.  Rewgards to all.  edwardk9@umcc.umich.edu
>

Ed,

I use a BOSScreen on my Linhof Technika. It is made from two very thin
layers of optical glass with a very very thin layer of wax & paraffine in
between the two pieces of glass. It is absolutely smooth and grainless.
What you are focussing on is truly the image, not the fresnel or other
light gathering aids. The focussed image is crisp and sharp. You also need
a good loupe. I use (and recommend) a Schneider 6x ASPH but there are many
good loupes available. Use 4x to 6x, good dark cloth, good loupe, and a
good ground glass is probably all you need. You may also need a pair of
extra strong reading glasses. I had my optometrist make a pair of glasses
for me that had a focus plane of six inches. With these, I can see clearly
to compose while under the dark cloth. I take them off and then focus with
the loupe. One other thing, I'm 59 and even though I have 20/15 vision, and
need reading glasses (my arms are not long enough), I found that I could
not effectively use the small aperture LF lenses. The wider the lens, the
larger the max aperture I need. My 75mm is a f/4.5 . I tried an f/8 90mm
but it was too dark. If I buy a 90, it will have to be at least f/5.6,
preferably f/4.5 . My 120mm, 180mm, and 240mm are all f/5.6 . Longer lenses
will have smaller max apertures but that's OK.

Bromwell (in Pittsburgh) distributes BOSSscreens, they're made in Holland,
$165, (412) 321-4118

Good luck,

Jim