Sekonic L-358 underexposure bias?

[Dante_Stella]

Having fought with thin b/w negatives for a while, and having eliminated developing as the cause, I checked my L-358, which seemed to want to underexpose by 2/3 of a stop. Getting into the exposure comp (press both ISO buttons and turn) and turning it to -0.7 (minus means increasing the exposure) brought the exposures to alignment with my GA645's onboard meter.

Has anyone else had this experience? I get the impression that the meter is by default set to expose conservatively for slide film - which is something of a non-issue now.

Thanks
Dante

 

[thegman]

Not had this experience, but you could try comparing it to a digital camera meter, that wil be modern and should go for accuracy over favouring negative film.

 

[shimokita]

If you are talking about the theory behind luminance and illuminance light measurements then I could suggest the following link:

"Average Scene Reflectance in Photographic Exposure Metering" - Douglas A. Kerr (30-Jan-2005)
http://dougkerr.net/Pumpkin/ > Optics, photography, and imaging

Specifically the difference between measuring reflected light using a gray card vs. incident measurements.

If you are referring to the measureable results from your Sekonic L-358, I can't help you... I use a Sekonic L-758D, mostly in spot mode where I get desired results by compensating from the shadow area where I want detail.

Having read different articles at "the Pumpkin", I will be testing the L-758D incident readings suggestions.

Casey

 

[Dante_Stella]

Casey - it's not an incident vs. reflected vs. grey-card reference issue - they all underexposed with this one. The L-758D may be calibrated with no margin of error; the L-358 seems more oriented more toward the casual user, so it's probably set to avoid mishaps.

Thegman - meters in digital cameras are actually less useful than older meters for the simple reason that they take color into account. So I found it easier to use a mostly colorblind meter in the GA. Now it seems to be coming in within 1/3 of a stop, which is close enough for T-Max 400.

Dante

 

[shimokita]

Dante - just a quick clarification question. How does the L-358 do with flash exposure measurements... also "underexpose by 2/3 of a stop"?

Casey

 

[Gumby]

The 358 and 758 are calibrated the same - identical calibration constants, K. And the repeatability specs are identical too. If you don't have some exposure compensation programed in that is causing your underexposure, then I suspect your meter needs to be serviced. Both are professional meters and neither is "oriented more toward the casual user". Casual users haven't needed a meter for almost 2 generations.

 

[shimokita]

Gumby - my understanding is that the K constant is used relative to reflective meters and the C constant is used for incident meters. As such the L-358 would not use a K constant. The question of course would be, has the L-758D and L-358 implemented the same C constant, which I "guess" they would but thus far this has not been considered in this thread and it's the reason (for me) that I will test (in the future) in more detail the incident measurements of the L-758D.

... indeed casual users most likely would not use an incident only meter at present... at the same time I would assume that pros might use a version up from the L-358... don't know ;-).

Casey

 

[Dante_Stella]

Dante - just a quick clarification question. How does the L-358 do with flash exposure measurements... also "underexpose by 2/3 of a stop"? Casey

Good question - I've never used it for that - but since the book says compensation affects all modes, I would expect it to act the same.

The C vs K constant is actually an interesting thing to consider - the 358 is an incident meter with a reflective attachment (Lumigrid) as an afterthought. I use it primarily for reflected, which makes me wonder whether a meter can only really be calibrated for one at a time (that would also explain two layers of compensation / calibration).

I've also found tons of references on the net to underexposed, so in starting to wonder whether it is normal.

Dante

 

[shimokita]

Edit: I stand corrected:

Calibration Constant : the following is from the L-358 user manual
Incident light metering : Lumisphere C = 340
Incident light metering : Flat diffuser C = 250
Reflected light metering : K = 12.5
_______________________

Calibration Constant : the following is from the L-758D user manual
Incident light metering : Lumisphere C = 340
Incident light metering : Flat diffuser C = 250
Reflected light metering : K = 12.5
_______________________

Casey

 

[Gumby]

I've also found tons of references on the net to underexposed, so in starting to wonder whether it is normal.

I did that search also, but didn't find "tons"... just a couple. In at least one discussion it was discovered that an exposure compensation offset had been programmed. Have you checked that?

 

[Dante_Stella]

I just got it back from factory recalibration. Same behavior. I asked the techs about this - they are all computer calibrated; MAC does not do special adjustments; if you find it underexposes, use the calibration function.

So my surmise is, yes, underexposure bias to favor slides and digital.

Dante