4 added room lighting
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What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing only a few refresh cycles including a partial one- which may give you inconsistent results.

In the case of DLP projectors, the projector uses a rotating filter wheel with different coloured wedges, and the tiny mirrors on the DLP chip adjust the light intensity at each pixel as the different colours go past as the filter wheel spins. Persistance of vision gives you a full colour result. If your exposure time isn't an exact multiple of the filter wheel rotation time, one or more of the colours will be overexposed relative to the others. This will show up more where the exposure time only covers a few rotations of the filter wheel.

With a CRT based projector, you get similar problems - but this time relative to how many time the projector paints the raster during the exposure. Problems here (with a 3 CRT projector) will usually show up as a different exposure between bands, where parts of the screen are painted n times and others n+1. I'd expect the 3 colour channels are likely to be painted in sync with each other, so this would probably show up as mostly a brightness variation.

Also, if you're not in a blacked out room, the room lighting may affect results. 60Hz electric lights will usually give you a 120Hz flicker, (50Hz/100Hz in the UK) which can give you different base lighting intensity depending on where your exposure falls in the mains voltage cycle. Daylight will also give you a base lighting intensiry, but tends to change fairly slower (barring clouds across the sun).

And one thing I forgot - your projector bulb may have brightness variations for the same reason as the room lighting. With an incandescent filament rather than a fluourescent tube, the flickering's likely to be less pronounced since the filament is going to stay hot, but there may still be a small variation as the voltage/current changes during the AC mains cycle. (from a quick check on the web, opinion seems to be divided on this - some people seem to think the thermal inertia of the filament is enough to prevent flickering, others think there still may be some present - see https://physics.stackexchange.com/questions/13400/what-invisible-flicker-do-different-types-of-light-bulbs-have)

What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing only a few refresh cycles including a partial one- which may give you inconsistent results.

In the case of DLP projectors, the projector uses a rotating filter wheel with different coloured wedges, and the tiny mirrors on the DLP chip adjust the light intensity at each pixel as the different colours go past as the filter wheel spins. Persistance of vision gives you a full colour result. If your exposure time isn't an exact multiple of the filter wheel rotation time, one or more of the colours will be overexposed relative to the others. This will show up more where the exposure time only covers a few rotations of the filter wheel.

With a CRT based projector, you get similar problems - but this time relative to how many time the projector paints the raster during the exposure. Problems here (with a 3 CRT projector) will usually show up as a different exposure between bands, where parts of the screen are painted n times and others n+1. I'd expect the 3 colour channels are likely to be painted in sync with each other, so this would probably show up as mostly a brightness variation.

Also, if you're not in a blacked out room, the room lighting may affect results. 60Hz electric lights will usually give you a 120Hz flicker, (50Hz/100Hz in the UK) which can give you different base lighting intensity depending on where your exposure falls in the mains voltage cycle. Daylight will also give you a base lighting intensiry, but tends to change fairly slower (barring clouds across the sun).

What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing only a few refresh cycles including a partial one- which may give you inconsistent results.

In the case of DLP projectors, the projector uses a rotating filter wheel with different coloured wedges, and the tiny mirrors on the DLP chip adjust the light intensity at each pixel as the different colours go past as the filter wheel spins. Persistance of vision gives you a full colour result. If your exposure time isn't an exact multiple of the filter wheel rotation time, one or more of the colours will be overexposed relative to the others. This will show up more where the exposure time only covers a few rotations of the filter wheel.

With a CRT based projector, you get similar problems - but this time relative to how many time the projector paints the raster during the exposure. Problems here (with a 3 CRT projector) will usually show up as a different exposure between bands, where parts of the screen are painted n times and others n+1. I'd expect the 3 colour channels are likely to be painted in sync with each other, so this would probably show up as mostly a brightness variation.

Also, if you're not in a blacked out room, the room lighting may affect results. 60Hz electric lights will usually give you a 120Hz flicker, (50Hz/100Hz in the UK) which can give you different base lighting intensity depending on where your exposure falls in the mains voltage cycle. Daylight will also give you a base lighting intensiry, but tends to change fairly slower (barring clouds across the sun).

And one thing I forgot - your projector bulb may have brightness variations for the same reason as the room lighting. With an incandescent filament rather than a fluourescent tube, the flickering's likely to be less pronounced since the filament is going to stay hot, but there may still be a small variation as the voltage/current changes during the AC mains cycle. (from a quick check on the web, opinion seems to be divided on this - some people seem to think the thermal inertia of the filament is enough to prevent flickering, others think there still may be some present - see https://physics.stackexchange.com/questions/13400/what-invisible-flicker-do-different-types-of-light-bulbs-have)

3 added room lighting
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What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing only a few refresh cycles including a partial one- which may give you inconsistent results.

In the case of DLP projectors, the projector uses a rotating filter wheel with different coloured wedges, and the tiny mirrors on the DLP chip adjust the light intensity at each pixel as the different colours go past as the filter wheel spins. Persistance of vision gives you a full colour result. If your exposure time isn't an exact multiple of the filter wheel rotation time, one or more of the colours will be overexposed relative to the others. This will show up more where the exposure time only covers a few rotations of the filter wheel.

With a CRT based projector, you get similar problems - but this time relative to how many time the projector paints the raster during the exposure. Problems here (with a 3 CRT projector) will usually show up as a different exposure between bands, where parts of the screen are painted n times and others n+1. I'd expect the 3 colour channels are likely to be painted in sync with each other, so this would probably show up as mostly a brightness variation.

Also, if you're not in a blacked out room, the room lighting may affect results. 60Hz electric lights will usually give you a 120Hz flicker, (50Hz/100Hz in the UK) which can give you different base lighting intensity depending on where your exposure falls in the mains voltage cycle. Daylight will also give you a base lighting intensiry, but tends to change fairly slower (barring clouds across the sun).

What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing a few refresh cycles - which may give you inconsistent results.

In the case of DLP projectors, the projector uses a rotating filter wheel with different coloured wedges, and the tiny mirrors on the DLP chip adjust the light intensity at each pixel as the different colours go past as the filter wheel spins. Persistance of vision gives you a full colour result. If your exposure time isn't an exact multiple of the filter wheel rotation time, one or more of the colours will be overexposed relative to the others. This will show up more where the exposure time only covers a few rotations of the filter wheel.

With a CRT based projector, you get similar problems - but this time relative to how many time the projector paints the raster during the exposure. Problems here (with a 3 CRT projector) will usually show up as a different exposure between bands, where parts of the screen are painted n times and others n+1. I'd expect the 3 colour channels are likely to be painted in sync with each other, so this would probably show up as mostly a brightness variation.

What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing only a few refresh cycles including a partial one- which may give you inconsistent results.

In the case of DLP projectors, the projector uses a rotating filter wheel with different coloured wedges, and the tiny mirrors on the DLP chip adjust the light intensity at each pixel as the different colours go past as the filter wheel spins. Persistance of vision gives you a full colour result. If your exposure time isn't an exact multiple of the filter wheel rotation time, one or more of the colours will be overexposed relative to the others. This will show up more where the exposure time only covers a few rotations of the filter wheel.

With a CRT based projector, you get similar problems - but this time relative to how many time the projector paints the raster during the exposure. Problems here (with a 3 CRT projector) will usually show up as a different exposure between bands, where parts of the screen are painted n times and others n+1. I'd expect the 3 colour channels are likely to be painted in sync with each other, so this would probably show up as mostly a brightness variation.

Also, if you're not in a blacked out room, the room lighting may affect results. 60Hz electric lights will usually give you a 120Hz flicker, (50Hz/100Hz in the UK) which can give you different base lighting intensity depending on where your exposure falls in the mains voltage cycle. Daylight will also give you a base lighting intensiry, but tends to change fairly slower (barring clouds across the sun).

2 expanded explanation
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What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing a few refresh cycles - which may give you inconsistent results.

In the case of DLP projectors, the projector uses a rotating filter wheel with different coloured wedges, and the tiny mirrors on the DLP chip adjust the light intensity at each pixel as the different colours go past as the filter wheel spins. Persistance of vision gives you a full colour result. If your exposure time isn't an exact multiple of the filter wheel rotation time, one or more of the colours will be overexposed relative to the others. This will show up more where the exposure time only covers a few rotations of the filter wheel.

With a CRT based projector, you get similar problems - but this time relative to how many time the projector paints the raster during the exposure. Problems here (with a 3 CRT projector) will usually show up as a different exposure between bands, where parts of the screen are painted n times and others n+1. I'd expect the 3 colour channels are likely to be painted in sync with each other, so this would probably show up as mostly a brightness variation.

What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing a few refresh cycles - which may give you inconsistent results.

What type of projector are you using? It may be worth trying a much longer exposure time, especially if you're using a DLP projector that uses a rotating filter wheel, or a CRT based projector. Either will have a relatively slow refresh rate, so your 1/40th second exposure may be capturing a few refresh cycles - which may give you inconsistent results.

In the case of DLP projectors, the projector uses a rotating filter wheel with different coloured wedges, and the tiny mirrors on the DLP chip adjust the light intensity at each pixel as the different colours go past as the filter wheel spins. Persistance of vision gives you a full colour result. If your exposure time isn't an exact multiple of the filter wheel rotation time, one or more of the colours will be overexposed relative to the others. This will show up more where the exposure time only covers a few rotations of the filter wheel.

With a CRT based projector, you get similar problems - but this time relative to how many time the projector paints the raster during the exposure. Problems here (with a 3 CRT projector) will usually show up as a different exposure between bands, where parts of the screen are painted n times and others n+1. I'd expect the 3 colour channels are likely to be painted in sync with each other, so this would probably show up as mostly a brightness variation.

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