In a discussion on the previous list, I speculated that the more
elements in a lens, the more likely there would be less variance in the
population of that lens, since to make it work in the first place you
would need greater tolerances than lenses with fewer elements. I
believe that I remember that Don Lopp concurred with this hypothesis (a
rarity to say the least!). In practice has anyone had difficulty
matching seven-element lenses? I'm trying to match a pair of wide
angle seven-element lenses and I'd like to get an idea of how difficult
it might be.
Thank you,
Steve

Steve

> In a discussion on the previous list, I speculated that the more
> elements in a lens, the more likely there would be less variance in
> the population of that lens, since to make it work in the first place
> you would need greater tolerances than lenses with fewer elements.

This is a false premise. Multi lens elements can have fl's that vary
considerably, say ± 5% in fl. This is very common. If a multi lens
element had very tight tolerances, the lenses would cost 5x the price.
The opposite premise is true in camera lenses... the more elements, the
less the tolerances, otherwise the design is not affordable. And by
affordable, I mean under $1k, not under $100.


I used to be involved with a user group on the Seitz 220VR round shot (a
rotational camera). The cameras brain-box needs to know the exact fl of
the lens being used, as it uses this value in its calculations for
rotational speed to prevent distortion. The camera has a unique
procedure to determine the accurate fl, although you burn a lot of film
testing. I once saw a chart of users test results from Nikon, Mamiya,
Leica, Hasselblad lenses. For a given nominal fl, such as 80mm, the
"true fl's" varied from 70 - 85mm. There is no benefit of a camera
lenses fl being exact for 2d photographers. (hence the term "nominal"
fl) Forcing the fl to be exact would add tremendously to the cost of the
lens, with no apparent benefits to photographers. (except for stereo
photographers) So overall, it's a crap shoot. Certain lens designs allow
fl's to vary considerably, while a few designs have much tighter fl
outcomes. An example is the mamiya 7 lenses, the few I tested, all were
within a few % of each other - sufficient for many users.

> I'm trying to match a pair of wide angle seven-element lenses and I'd
> like to get an idea of how difficult it might be.
>

I currently buy Schneider Digitar lenses direct from Germany. Digitar
lenses are the highest quality lenses they have ever made. To achieve a
matched pair, within a fl deviation I provide them (<1%) ....they often
go through 50 lenses to produce ONE matched pair... I pay them $250 to
"match" the lenses. I have waited up to 8 months to get a matched pair -
for a given fl.

Bill

Steve,

This depends on what lenses you are referring to. Mamiya TLR lenses
have a reasonably good match between the taking and viewing lenses. If
you are looking for 3 lenses (one for the viewer), buy two pairs and
you should get reasonably close.

Incidentally, if anyone is thinking of buying 55mm lenses for their
3DWorld camera, I have 3 I may be willing to sell. I had origianlly
hoped to machine completed units for use with the camera, but the deal
fell through. I made one set for myself but am not planning on making
any more, so if somebody wants to make their own board, barrels and
linkage, I have the lenses.

Please contact me offlist if interested.

Sam

--- In MF3D-group@yahoogroups.com, "coronet3d" wrote:
>
> In a discussion on the previous list, I speculated that the more
> elements in a lens, the more likely there would be less variance in the
> population of that lens, since to make it work in the first place you
> would need greater tolerances than lenses with fewer elements. I
> believe that I remember that Don Lopp concurred with this hypothesis (a
> rarity to say the least!). In practice has anyone had difficulty
> matching seven-element lenses? I'm trying to match a pair of wide
> angle seven-element lenses and I'd like to get an idea of how difficult
> it might be.
> Thank you,
> Steve
>

--- In MF3D-group@yahoogroups.com, "Sam Smith" wrote:

> I had origianlly hoped to machine completed units for use with the
> camera, but the deal fell through.

Sam,
I had been thinking about your actualized concept of replacing the
80mm lenses with 55mm lenses on the 3D World camera and was wondering,
based on my very simple manipulation of the inter-ocular distance
charts, that perhaps the distance between the lenses should be doubled
for wide angle lenses (e.g. 45mm to 55mm). Possibly the camera should
use an alternating frame system a la the Verascope F40?
Steve