I think I might have had one LED that had what I would call "peaks and dips." It was a defective LED...like part of it wasn't working.

As to the hot spot in the middle...I have yet to find a lens system that did not exhibit this, from my early days in photography up to the present day.

Here is some information to chew on though. Lets say the Cat. 566 film is flawed and it has louder tones recorded in the middle. I have no problem with the idea that it is flawed. After all, we have now ripped into Cat. 69T, 69P and Cat. 97 so why should Cat. 566 be blessed? But ok, for the sake of argument (and I love those) it is flawed....

...How would you explain that moving the just the cell will cause the hot spot to move? The LED to the film relationship hasn't changed, the lens to film hasn't changed, the slit to cell hasn't changed...only the cell to the lens. Either the cell's sensitivity isn't uniform or the lens isn't.

Instead of throwing up your theories and even the science, play with some Cat. 566 and set up a reader system...compare your results to using Cat. 97 (or other methods). And I mean REALLY play with it...see how it reacts to an LED that is off on it's azimuth, move the LED laterally and vertically, move the cell about. Then take two fresh systems, set up one my way, one the way you have been doing and compare the speed and accuracy of each. If done properly, both systems should agree with each other if both are valid.

In my opinion, Cat. 566 tells you what you need to know (LED position, rotation) in a visually easy to read sort of way. Now a difference I may have is that I use the ABACUS ARTA-600 scope attachment for my RTA so the 6 bands show even the slightest change, unlike LED based analyzers...Also the R2 can be used though there is a delay between action and response.

When using Component Engineering systems (which I use for the vast majority of my retrofits and all Century/Simplex 35 installations) you want to ensure you don't "crowd" the digital LED's space so making sure you are as far inboard without compromising the analog scaning is very important. Cat. 566 lets me do this easily.

Steve

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"Old projectionists never die, they just changeover!"

Moving the cell off-centre, even by a tiny amount will cause one side of the soundtrack to fall off the end of the cell, so I don't quite follow what you are getting at. But I will take your advice and do some comprehensive tests under lab conditions with Cat566 and we will see what comes up.

BTW I prefer to stick with the science, hokus-pokus and witchcraft are not within my area of expertise. Naah... just kidding, of course they are.

Lets say the MIDDLE bands on Cat. 566 are higher than the outer ones...When you move the cell with respect to the lens, the high bands move with the movement of the cell.

Lets call the bands looking from left to right 1, 2, 3, 4, 5, 6 (6 bands total)

Now lets say that band 4 is 1 dB higher than the rest. Now I shift the cell with respect to the film and I find that band 3 is 1dB higher than the rest (ignoring what happens on band 6 for the moment)...why would the high band shift if it wasn't a lens hot spot issue?

Also, the slit/cell is wider than the soundtrack. Both Kelmar and Component Engineering (an I would guess the rest) have to mask off the ends of their slits. CE hand paints them, Kelmar has a mask they set up to have them painted....depending on how well the mask was set up or how well the guy/gal dabbed the slit, is how much over you get.

Steve

AFAIK the cells used by CE and Kelmar are made for Dolby by the one company and are the correct width for the soundtrack at a specific focal length. I have not seen any with the ends masked but I have not pulled too many apart so I take your word for it that at least some have been treated in this way. This would mean that the focal length of the lens/tube assembly was made too short for the width of the cell, either deliberately for reasons of mechanical restraints in a particular projector or by accident. It would also result in the height of the slit being greater than necessary, resulting in reduced HF capability.

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935