Sekonic L508 dome vs spot inconsistency

[Andrew Ito]

I've got a Sekonic L508 that is exhibiting some strange behaviour. When I take an incident reading with the dome the exposure is typically 1-1.5 stops brighter than when I use the spot meter to read something approximately 18% grey. Is this something others have experienced? I made sure to cover the spot metering viewfinder when taking the incident reading. I guess I could be off in what I judged as 18% grey but my exposures taken using the spot readings are right on.

On a side note, when shooting in the studio with strobes, the readings were right on with my digital exposures.

Any ideas? Should I take the meter in for calibration?

[Henry Ambrose]

Andrew, if you spot meter a gray card from different angles you'll get different readings. There may be nothing wrong with your meter at all. Its not uncommon to experience varying readings especially in the field with a subject that is "something approximately 18% grey" and at who knows what angle to the meter. The subject may look 18% gray but the light it reflects to you may well be something different than what you expect. I usually use multiple spot meterings to determine if the scene will fit in my film's range and figure exposure from there.

Anyway, unless your readings used to agree and now don't, I would not worry about the meter.

[Robert Oliver]

are you sure you are switching the meter from incident to spot meter mode?

I made that mistake once. cost me some images.

[Andrew Ito]

are you sure you are switching the meter from incident to spot meter mode?

I made that mistake once. cost me some images.

I'm fairly certain that I'm switching modes properly.

As far as what I'm metering being "approximately 18% grey", that is probably the problem. I have heard that spotmetering an 18% grey card will not always be the proper technique when you have to consider light reflecting off of it. Perhaps what I think is 18% grey is actually off of that.

[Aender Brepsom]

I often get the same thing with my Sekonic L-608. I always attributed these variations to my misjudging of what is an area of 18% grey. That is why I always take multiple spot meter readings and use an average shutter speeed/f-stop combination from all of my meterings.

regrads

[Bob Gentile]

I don't use an incident meter, but I've always wondered about this. Maybe those more knowledgeable can clear it up for me.

It seems to me that this is to be expected. An incident meter will read all the light that's falling on a subject. The subject will absorb some of that light and reflect the rest. A reflected meter (eg, a spot meter) will read the reflected light minus the absorbed light. So it should show a lower light reading.

No?

[Ralph Barker]

. . . So it should show a lower light reading.

No?

Yes, maybe, but not so much for that reason. The reflective meter is giving you an exposure that will, in theory, render the metered area as a middle gray. Thus, the reading depends on both the tone of the metered area and its surface characteristics - i.e. whether the reflected light being metered also includes spectral reflections. So, the reflective reading needs to be interpreted in order to arrive at the appropriate actual exposure.

[Helen Bach]

I don't use an incident meter, but I've always wondered about this. Maybe those more knowledgeable can clear it up for me.

It seems to me that this is to be expected. An incident meter will read all the light that's falling on a subject. The subject will absorb some of that light and reflect the rest. A reflected meter (eg, a spot meter) will read the reflected light minus the absorbed light. So it should show a lower light reading.

No?

Another slant on Ralph's answer: the incident dome absorbs light so that the amount of light reaching the cell is the same as would be reflected from an 18% grey card, if the incident meter is designed to give an 18% grey reading.

I have an L-508C and find that the incident meter agrees very well with the spot meter used with an 18% grey card.

Best,
Helen

[Colin Robertson]

Hi Andrew. I suppose the first question is, 'what do we think the meter is doing?' As I understand it, when I take an incident reading the meter should be calibrated to give a setting which will record an 18% grey card as zove V. That is, based on the strength of the illumination not the reflectivity of the subject. With a reflected light meter I should get a setting which records the subject as zone V, regardless of the actual brightness of that subject. That is, a reflected meter will try to make a black subject zone V. And a white subject, and a grey subject . . SO, perhaps the next step is to meter something which is not 'nearly' 18% grey, but actualy 18% grey. As I understand it, an incident reading (which is what I tend to use) and a reflected reading of a Kodak grey card should be almost exactly the same, barring angle of reflection on the card. There was a thread about this once before, I think, which got a bit heated. Sorry I can't recall who posted it. I'll try and find it for you.

[Bob Gentile]

Yes, maybe, but not so much for that reason. The reflective meter is giving you an exposure that will, in theory, render the metered area as a middle gray. Thus, the reading depends on both the tone of the metered area and its surface characteristics - i.e. whether the reflected light being metered also includes spectral reflections. So, the reflective reading needs to be interpreted in order to arrive at the appropriate actual exposure.

Sure. I think that's what I was trying to say. Thanks.

An incident meter would tell me how to expose for the light that's falling on the entire scene. But when I point my reflective meter at the breast pocket on Uncle Louie's navy blue suit, it tells me, "Whoa! Open up, Bobby. I don't see much light comin' back at me. You gotta open up a few stops if you wanna make this suit come out middle grey!" Heh. Heh. Sure. Uncle Louie would like that, eh?

So, with that in mind, a reflected meter can't show more light than an incident meter reports, can it? (I mean... under most normal circumstances.) A subject can't reflect more light than what's falling on it -- it can only reflect less. (And it's up to the shooter to understand the difference in the measurements and adjust accordingly.)

Are we saying the same thing, Ralph?