P3D my 2 cents worth on adjusting projectors

[Project3D@xxxxxxx]

In a message dated 30/06/98 18:59:52 GMT, Paul Talbot wrote:

<< Bob Aldridge wrote:
 
 > major adjustments may be needed where the chips are not at the same
 > height [snip] with the projector adjusted so the homologues are level
 > - the apertures will not be, will probably ghost, and will certainly
 > float.
 
 This is a very significant point that deserves to be emphasized, IMO!!
 Just today I was reading Ferwerda's comments that vertical misalignment
 cannot be corrected through projection adjustment.  I didn't understand
 why and the text did not explain, but Bob's point makes it clear...you
 are trading off one artifact of poor alignment for another.
 
 If you believe in projector adjustment to cure alignment errors, please
 go back and read the above two paragraphs again!>>

At last, I've written something that has been clearly understood!
 
<< (Snipped, then:)

 CanterMike@xxxxxxx wrote:
 
 > The only presentations I have ever seen
 > that could be viewed comfortably with no adjustment have, without
 > exception, been the work of individual artists who had complete
 > control over the mounts and mounting.  Once the projector was aligned
 > for the first slide, the rest of the show was faultless.  As soon as
 > any other photographers slide was projected, some adjustment had to
 > be made.
 
 Can you give examples and explain what adjustments were necessary,
 and why (i.e., what made the slides unviewable, and how did adjustment
 improve the situation without introducing other artifacts?)  I have
 seen several projected showings of mixed slides with no adjustment,
 including a PSA "Hall of Fame" collections, and never experienced any
 discomfort.  Being relatively new to viewing stereo projection, I
 may have overlooked some technical shortcomings to which you could
 be alluding, but did not experience anything that made any images
 "unviewable." >>

The classic example where projector adjustment would be needed is where a
complete slide mount does not sit level in the projector gate. Here, adjusting
the vertical will not only level the homologues in the scene, but also level
the frames... And this, of course, is why one has to make gentle vertical
adjustments in mixed author shows. If it's done well, the audience will be
virtually unaware of the adjustment. Heavy handed, and it's a disaster. 

If the authors of these slides took their own slides and put them into their
own AV show, they would probably do a bit of "shimming" (sticking tape to the
top of the slide, so when it's dropped upside down into the projector it lands
level). Unfortunately, if you project with a different type of projector, the
shims may be in the wrong place, so the slide does not land level. Hence the
need for gentle virtical adjustment.

Bob Aldridge
Stereoscopic Society Projectionist 


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