[MF3D.FORUM:46] Re: Apparent image size, MF verus

[Alan Lewis <3-d@xxxxxxxx>]

Paul Talbot wrote:

> > 2) A full frame 35mm slide in a 50mm lens viewer (ortho)
> 
> I think you are assuming the full frame 35mm camera has a
> 50mm shooting lens when you call the 50mm viewing lens
> "ortho."  My chart used the FL of the Red Button viewer,
> which is probably what most people use to view full frame
> stereo images.  These images might be shot with twinned
> point and shoots with 35mm lenses, or an RBT with 35-70mm
> zoom lenses, or a variety of options in between.

Yes, that's what I was assuming.  I was first trying to sort out the
immersive effect (apparent image size) vs. format size.  So I chose a
common starting point for all formats to be fair.
What happened is that I realized that it is not really the format size
that makes for an immersive feel, it is only the apparent image size.  I
know this sounds so easy to figure out, but I (like others) never really
could quantify whether the format size made the most difference or
whether the magnification did.  

I can say now that magnification plays the larger role, and your format
choice will be guided by grain size and viewer lens choices.


> With the Red Button lenses the extra width of full frame seems
> roughly equivalent to the extra height of MF.

Kind of. It is very hard to get a full frame image in the Red Button
that is sharp from edge to edge, especially with eyeglasses.  (BTW: my
observations are based upon wearing eyeglasses, the most restrictive
situation).
So the ability to get 44mm f.l. lenses that will actually cover the
format size is the issue with the Red Button.  The lost "height" in the
rectangular format can play a factor in the immersive feel.
I do have a full frame Realist viewer, and I will say that without
eyeglasses it does have a very nice image, sort of immersive.  So I'm
not negative on that combination.  It isn't very forgiving though for
eyeglasses and eye spacing that is non-average.
I'll go out on a limb and say that if one could get a 35mm f.l. Realist
viewer with large enough dia. lenses to cover the full square realist
format that it will have a more immersive feel to it than the full frame
in a 44mm f.l. viewer.

> 
> > As you go to larger film formats you should also match your viewing lens
> > to the camera lens.  So merely moving to a larger format does not
> > guarantee a larger image, it depends on what lenses you are using.  As
> > you move to larger formats than 6x6 (6x9 would be a larger format for
> > this discussion) you need a different viewer design, and should use a
> > longer f.l. lens.
> 
> But if you have an 80mm lens on your 6x7 or 6x9 camera, then
> the roughly 80mm FL of the SaturnSlide is "ortho" for those
> images.

Yes, that is true.  But the practicality of image coverage then comes
into play.  You can get an 80mm f.l. lens to cover a 6x6 image, but it
won't fully cover a 6x7 or 6x9.  So this brings in the issue of
compromise.  If one is willing to give up full image coverage (corner to
corner) and be satisfied with edge to edge coverage at the best (if
that) then they will get a more immersive feel.
But a 6x9 will not fit into a parallel view design viewer (without
mirrors).

It seems to me that less than full coverage isn't too great a
compromise.
I have a (experimental) focal length combination in my latest viewer
design (posted earlier on this list) that is approx. 58 to 60mm using
triple achromatic lenses.  I was originally doing this for the panoramic
format mount.  It works well for coverage of the panoramic mount, makes
the image look just like sitting in a movie theater watching a
Super-Panavision movie.  But not much height, so not much immersion.

With a Spicer mount (King Inn size) 6x6 it will cover just about edge to
edge.  It is really just a round image that fills the entire view.  Now
you do really get a feeling of immersion with this.  The height of the
image is as important as the width to get this feeling.

When you view the world you are sensing both width and height.  Walking
into a wide room with a high ceiling does give a person a different
feeling than the same room with a low ceiling.

The lack of full image coverage plays a role in the immersive feel
(something observed by others on this and Photo-3d).  If you get rid of
the stereo window then you can uncover a larger film width to view.  You
will also get rid of conflicting visual clues due to the window.

Viewing with a window is preferred by some, and others don't mind the
lack of any visible window at all.  (I'm not saying you should set a bad
window and try to view it, that is not right at all!).

It appears that for 6x6 King Inn mount images that you will need a f.l.
of approx. 60mm to start getting an immersive feel.  You should use 60mm
lenses on the camera to keep the perspective correct.
This of course means lots of glass in your lenses, and lots of $$$. Also
remember that edge sharpness may fall off a bit no matter how good your
lenses are.

I'm not sure I see any advantage to going to larger formats in this
case.  The grain is not an issue for me on 6x6 images.

> >
> > I did some calculations similar to Pauls', then tested some of them out
> > with real viewers (I have lots of viewers).
> >
> > I assumed for fair comparison's sake that all calculations would be
> > based upon the full format size (not mount mask size)
> 
> That makes a big difference!  The standard MF mounts crop out
> a lot of image area!

Yes, that's one of my observations.  It is not the film format size as
much as the realized mount mask size that affects the image size.  In
6x6 stereo we could get a larger image by trying to eliminate the causes
of masking down.  Current cameras limit this, so the real change would
have to be a correct camera design.  A correct MF camera design sets a
proper window and has accurate vertical alignment.  Then we could use
larger mask openings.  I wouldn't fault the format size as much as our
equipment.

-- 
Alan Lewis  
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