Quick question on lightmeters
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An incident reading doesn't take the subject, it measures the light falling on it. A reflected reading is taken off the subject, and all the light is scrambled and averaged.
Either way, the meter then places that tone where (it thinks) 18% grey tone should be.
Either way, the meter then places that tone where (it thinks) 18% grey tone should be.
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I like simple light meters. I've been using the Sekonic L-308s this weekend and it did everything I needed of it - simple, accurate, fast to use. And it's about £130.
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Apart from flash metering, there is nothing you can do with a hand meter that you can't do with a built-in meter (including incident readings) and a great deal that you cannot.
I have a Sekonic 308 which I use for studio flash metering, but I haven't used a hand meter for anything else in 30 years.
Metering for film can be a complicated business, depending on the type of film, the result you're after and how difficult the subject is. But generally, what you're suggesting, no not really - unless you have a good idea of what that tone is and how much compensation to apply.
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As always thank you for your informative replies Richard.
I was working on a similar assumption to Digital. So if I was taking a picture of my son who is wearing a white shirt, I can take a reflective reading from the white shirt and place that roughly +2 stops above the reading?
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because I am using a film camera that doesn't have a very reliable spot metering system but moreso to find out exactly how a light meter works and how the exposure readings from a lightmeter fall in with a zone metering system.
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You're welcome Hassan
Digital is different to film, and both slide film and negative film are different.
Slide film is most critical because there is no secondary process (ie printing or post processing) that can adjust the final result. That is decided at the moment of exposure.
Leaving aside digital and things like ETTR technique (expose to the right, of the histogram) an incident reading works for slides because it makes a basic assumption that the film will blow to white at three stops down from 18% grey. In practise, that's about right and rarely would you want to change it even with predominently light or dark subjects. Furthermore, there's not much latitude either side.
That works for negative film too, but since you can rearrange the tone scale in printing there are beneifts to making sure you centre the exposure around the most important tones in the subject, rather than 18% grey. If you have a dark subject, giving more exposure will put a lot more tone detail in the shadows. And since negative film is very tolerant to over exposure, you don't have to worry much about the highlights blowing. They don't 'blow' as such, they just clog up and detail is reduced, but it's still pretty much there - this is the major difference to digital where you quite quickly reach a point where the highlights blow to pure white whith no prospect of recovery.
Basically, with negative film there is the opportunity to both optimise key tones exposure and extend the dynamic range. Check out Ansel Adams' famous work (he of the Zone System) and there's a distinct HDR look to many of his pictures. You can also abuse negative film heavily - which is how fixed exposure disposable cameras work.
With your son's white shirt, on slide film an incident reading is favourite - which is the same as taking a reflected reading off an 18% grey card. If you take a reflected reading off his shirt, it would put that tone at the mid 18% grey point, meaning you'd be wasting at lot of the film's dynamic range available above that and with the main downside of underexposed shadows. So you would modify it as you suggest and two stops sounds about right, but that ultimately depends on how white the white shirt is, and the result you want bearing in mind all the other tones in the scene. White is not a tone as such, call it bright grey if you like because it varies a lot - a shirt may look white, but so do specular reflections which are much brighter (and you generally don't worry about much, but they can influence the exposure if you're not careful) and so is the sun white, but about a million times brighter.