Film-Tech Forum ARCHIVE: Vertical Lamphouse Lamp Alingment

This is topic Vertical Lamphouse Lamp Alingment in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Demetris Thoupis (Member # 833) on 09-17-2003, 12:03 PM:

Hello All,
I've been called to a local cinema to change a cracked mirror to a new one on a vertical lamphouse (PREVOST) although I do not recall the model of the lamphouse. The new mirror was far too large for the lamphouse and after hours of struggling I decided not to put it since it did not fit but put back the old cracked one which, when I removed it, broke into two pieces. The final picture quality is not the best. Now my question is: There are alen screws inside which can be accessed with a long alen key from the back of the projector for up-down and left-right mirror alignment. BUT. To align the distance between the mirror and the lamphouse and the distance between the mirror and the apperture plate has to be done from the inside and each time I had to turn off the lamphouse and let it cool down until I tried different positions to realign it. Can someone help as to what distance should be kept from the mirror to the apperture plate and what distance should be kept from the mirro to the lamp?
Thanks in advance.
Demetris

Posted by Gordon McLeod (Member # 33) on 09-17-2003, 10:19 PM:

Scarry as it sounds there are several lamphouse that you need to initially align with the door open

Posted by Christos Mitsakis (Member # 143) on 09-18-2003, 05:56 AM:

Dimitris,
What is the focal length of the new mirror you have.
You can do bulk alignement first by placing the mirror at the specified distance from the film gate using a simple measure.

Christos.

Posted by Demetris Thoupis (Member # 833) on 09-18-2003, 12:31 PM:

Dear Christo,
As I have mentioned, the new mirror cannot fit in the lamphouse. It is too big. I don't know the information you request. Are there any formulaes or something?

Posted by Christos Mitsakis (Member # 143) on 09-19-2003, 09:39 AM:

Do you know the origin of the mirror? By saying it is a large one, I assume it comes from a carbon arc lamphouse.
In any case look at the back of the mirror, there should be a sticker, ususlly of the brand (and or not the Serial No.)followed by two numbers, a small and a large one. Mirrors are eliptical designs and as every elipse have two centers, or here two focal points. The small number (in mm) is the one point where the lamp should be from the center of the mirror. The large one (again in mm) is the other center or the distance to the gate from the center of the mirror where the beam is focused. If you're lacking these info, well, you have to improvise. Start by trying to compare the mirror with another one of known focal length and place it with aproximation. Patience is a substantial factor.
I hope this helps.

Christos

Posted by Demetris Thoupis (Member # 833) on 09-19-2003, 03:39 PM:

Dear Christo,
Thank you very very much for your valuable information. Now the only thing I have to do is find out a way to fit the damn thing in the lamphouse!!!! Maybe I could use longer wires for top and bottom lamp connections so that the wires will not touch the mirror. Again thank you. I will let you know of the outcome.
Demetris

Posted by Gordon McLeod (Member # 33) on 09-20-2003, 08:55 PM:

First you seem to ignore the most vital point you have the wrong part so don't waste your time trying to make it fit
Order the right part number and fit that in place
If the original part is unavaiable from the manufacturer (and verify that by contacting prevost directly) then a new lamphouse is the option