Using DSLR as 'tint' meter...

I'm having the windows on my car stripped of aftermarket tint and retinted, a bit lighter for better night vision.

Can one use the light meter in a DSLR camera to get a reasonably accurate reading of visual light transmission (VLT) of glass (with our without tint applied)? I.E., for example put camera meter in spot mode, apeture priority - observe shutter speed shift on bare glass compared to the tinted glass....ratio of two readings I think would yield VLT percentage.

My car has 'privacy glass' on the rear windows, which cuts the VLT, so I'm interested to know how much light transmission is reduced by the glass.

Yes, I am aware many tint shops have meters, but some don't...I'm wanting to sort of do a double check on their tint matching recommendations.

Thanks/Bill

wgosma wrote:

I'm having the windows on my car stripped of aftermarket tint and retinted, a bit lighter for better night vision.

Can one use the light meter in a DSLR camera to get a reasonably accurate reading of visual light transmission (VLT) of glass (with our without tint applied)? I.E., for example put camera meter in spot mode, apeture priority - observe shutter speed shift on bare glass compared to the tinted glass....ratio of two readings I think would yield VLT percentage.

My car has 'privacy glass' on the rear windows, which cuts the VLT, so I'm interested to know how much light transmission is reduced by the glass.

Yes, I am aware many tint shops have meters, but some don't...I'm wanting to sort of do a double check on their tint matching recommendations.

Thanks/Bill

You should have a series of glas windows with known VLT. If you would have this series you could plot something like a does-effect curve: plot VLT of glas window versus the exposure time your camera would give for each of your screens with known VLT with a constant light source and lens and aperture as well as ISO setting of your camera.

If you get a useful plot you could use your camera under same setup, get the exposure time and see on your plot which VLT the window will have.

This is the way you calibrate each technical gear that is used to do some measurements.

Of course, a darker window will cause more extinction of light compared to a plain glas screen. But I don't think that it is that easy to get useful values from your camera exposure time if you just have one measurement  - maybe compared to glas without protection. An exposure time measured twiche as long as with plain glas will give a hint on the extinction of light by a tinted screen. It looks like you have the half amount of light. But I don not know, if there are other parameters you have to take into consideration to compare your value with an offical measurement with calibrated gear. Quality of light in terms of light colour, direction and kind of light source may be a factor as well as if there is reflection on th screen etc.

Best regards

Holger

Privacy tints should be dark enough that simply comparing exposure of the same scene through the window & with the window open will give a fair idea. For best results you want a scene of even brightness & the sky will often do especially if you meter from the same point

You should be able to see how many stops darker it is through the window. Av (on fixed ISO) is the simplest mode to use as it only changes one variable and you don't even have to remember the aperture scale & he times are much easier for fractional stops.

For the front windows the tint will not be dark enough for this approach - IIRC it shouldn't be less than 18% to be legal in the UK. My brother found to his cost after buying a second hand car with tinted windows that police cars here carry tint meters.

I'm sure you can work this last bit out, but I'll include it anyway. Each stop of extended exposure is a drop in light of 50% so %Transmission is 100- (100/stops)