Individuals, Clubs and Federations are invited to contribute to research questions about on-screen brightness using projectors, and what is considered satisfactory.
Follow this process to obtain a measurement of brightness, and your subjective opinion. [Amended 19/7/6 to require all meters used in readings to be set to 100 ISO (ASA)]
1. Set up your projector system in blackout as usual. The projector may be slide or digital, or you can repeat for two or more.
2a. For a slide projector. Project a blank white image using an empty slide mount in the gate.
2b. For a digital projector. Project a blank white image. You can make a white image eg, in Photohop, and maximise it to full screen.
3. Measure the width of your projected image.
4. Measure the brightness of your image using some form of light meter. For standardisation, readings should be taken by reflection from the screen, and be recorded at 100 ISO in ‘Exposure Value’ (EV), to the nearest 0.5.
4a. Meter set to 100 ISO. Pointing a light meter at the screen, make sure the meter is close enough to make the white screen the only relevant object. Read EV directly, or use the table below for conversion. Check by reversing the light meter to look at the projector from the screen. The EV should be about 2 higher.
4b. Camera set to 100 ISO. Using through the lens metering, view so that the white screen is the only object. Read the exposure and convert to EV using the Table.
At ISO 100, and aperture f 8.0
|
Shutter(sec) |
EV |
|
4 |
4 |
|
2 |
5 |
|
1 |
6 |
|
1/2 |
7 |
|
1/4 |
8 |
|
1/8 |
9 |
|
1/15 |
10 |
5. Now project some typical slides/images, and consider whether the images are
· too dim (you would prefer not to use this setup)
· a bit dim (but acceptable)
· about right
· a bit bright (but acceptable)
· too bright (you would prefer not to use this setup)
E-mail your results to mark.buckley-sharp@tiscali.co.uk to include
1a. For a slide projector.
· The bulb power (150W or 250W)
· Whether run at full power or reduced power (economy mode) for the measurements
· The f-stop of the lens
1b. For a digital projector.
· The lumen specification at full power
· Whether run at full power or reduced power (economy mode) for the measurements
2. The WIDTH of your projected image.
3. Your EV reading reflected from the screen for a white image
4. Your opinion on brightness
You can download a WORD document here to use to fill in and then e-mail your results.
You can see a summary here of results so far.
The PAGB Honorary Secretary has written to Federations asking for a brief summary of current policies or strategies for the introduction of projected digital images at Federation level.
Responses should be sent by e-mail to mark.buckley-sharp@tiscali.co.uk
You can see a log here of submissions so far.