|
Author
|
Topic: Buzz track & Azimuth 16mm Opt test loops
|
|
|
|
|
|
|
|
|
|
|
|
|
David Fouracre
Expert Film Handler
Posts: 123
From: Staffordshire, United Kingdom
Registered: Aug 2013
|
posted August 21, 2016 05:23 AM
Kevin,
I thank you for the PM and have replied.
Adjustment of the sound lens is made more fiddly due to lack of finger grip area on the lens itself. Without the special tool, I have found that a 16mm i/d open grommet will provide additional grip to the lens, but with the limited access area, makes alignment still very difficult.
I have been surprised, at the variation of track responses, both from differing prints, and also differing track formats.
In the absence of proper alignment film, I have found that the
testing with variable density track instead of "area" gives a better indication of azimuth. This seems particularly so with 35mm track alignment.I have experienced the odd print with a track that is definately "off azimuth", due to perhaps, poor lab equipment calibration.
Again Kevin, I thank you!
David
| IP: Logged
|
|
|
|
|
|
|
|
|
|
David Fouracre
Expert Film Handler
Posts: 123
From: Staffordshire, United Kingdom
Registered: Aug 2013
|
posted August 29, 2016 09:40 AM
Whilst awaiting the arrival of my replacement optical lens, I decided to test two other 16mm machines that I had preciously "aligned by ear", and had considered the sound to be ok.
Having now received two sound test films: Buzz track (for centering and frequency track for azimuth settings), I decided to re-test those two projectors.
I was VERY surprised to realise that my previous "by ear" alignment was far from optimum! An off-centre track can modulate the sound, resulting in some distortion.
Both machines now reproduce sound that`sparkles on all applied types of track!
I also discovered that a very small amount of dust, within the optical sound lens on one machine, had reduced the sound level by about 20%. A cotton bud dampened with isopropol lifted the dust and left the lens clean.
I have to admit that in the past, and the absence of proper alignment equipment, my track setting was far from perfect!
My local film presentation society members, now have the test films to ensure all their 16mm projectors are at their best!
| IP: Logged
|
|
|
|
|
|
|
|
|
|
David Fouracre
Expert Film Handler
Posts: 123
From: Staffordshire, United Kingdom
Registered: Aug 2013
|
posted September 09, 2016 09:54 AM
Simon,
My suggestions for optical sound lens alignment check.
I am assuming you have the standard optics for B&H units
and the lens is set within a cast alignment fixing.
This would have a brass hex adjustment screw for the lateral
track centering, and a slotted screw to lock the focussing of the lens.
First. check you have the correct exciter lamp, and it has not
blackened or shows any finger marking.
Carefully place marks both along and around the lens outer tube, to allow return to existing position.
Find suitable tool to fit the brass hex lateral adjustment screw. Lace-up the buzz track test film and run, preferably
listening through headphones (with the treble control at max)
You should hear NO tone at this point. The buzz track has two
tones on it, one low about 300Hz and the other about 1000Hz.
These are set either side of the edge of your optical track.
If you hear any tone, this means the optics are off-centre and
adjustment of the lateral (in or out) should be made until the
tones disappear.
If you hear an intermittent tone that comes and goes, that suggests the film is weaving as it travels, and this may require
attention to film guides/rollers (possible lubrication).
The frequency test film should be run now, firstly to identify
the highest frequency recorded (this may be listed with data supplied with the film, or have narration within the film itself). You are listening for the highest frequency available.
Most important find or "make" a tool to rotate the optical lens
within it`s casting. I modified a plastic clothes peg (narrowed the thickness and placed thin rubber in jaws to help with grip)
this "tool" will have to be thinned to about 4mm in order to get between the exciter and the lens end.
Important! the adjustment of the focussing is very critical and requires only VERY small movement during alignment!
We are looking to obtain the maximum output at the highest frequency available from your test film, and adding a test meter across the amplifier output, would provide a visual indication in addition to the perceived audio,(10vAC range).
Rotation of the lens sets azimuth, and left to right affects the focus. Both are important and I found that focus 1st then azimuth,alternating until you obtain the optimum works.
I found that running a repeat azimuth test, allowed that "tiptop" result I was after.
When that point is reached, secure the locking screw!
As far as flutter testing (high frequency speed variation) is concerned, this is usually caused by incorrect bottom loop size
and/or lubrication of the stabilisation rollers adjacent to the sound drum. Incorrect gate pressure can also cause flutter.
I wish you well!
David
[ September 09, 2016, 11:05 AM: Message edited by: David Fouracre ]
| IP: Logged
|
|
|
|
|
|
|
UBBFriend: Email this page to someone!
Printer-friendly view of this topic
