Handheld Spot Meters vs Camera spot meter

[Adrian]

I have a Soligor spot meter, a Canon DSLR and a Canon EOS3 film camera. You'd think they'd agree with their metering, but they don't. I notice the following, all set for ISO 100, f/8, cameras using 50mm lenses focussed at infinity.

Dusk sky:
Soligor: 1/8 (EV9)
DSLR: 1/15
EOS3: 1/20

Brick wall (same light as above)
Soligor: 1s (EV6)
DSLR: 0.8s
EOS3: 0.6s

Wood finish desk under incandescent light (about mid-grey)Soligor: 1/8s (EV9)
DLSR: 1/8s
EOS3: 1/10s
Jonan Elite HH meter (reflected): 1/8s
As above, incident: 1/8s

I use my Soligor spot meter all the time and get reasonable exposures on B&W film so why the fuss? Well, I shoot slide film too and often choose to meter the sky as a highlight. I used my DSLR to meter the sky yesterday (because it was to hand) and made a test exposure. I was horrified to see a 1 stop difference compared to the Soligor spot (so did I just over-expose by 1 stop on film?, don't know yet!) So I metered some green grass - almost exact agreement with the Soligor spot meter.

I'd be tempted to think the old Soligor meter was out of cal, but it agrees with my general handheld meter and the other cameras for mid-grey.

Is it something to do with DSLR sensors being more sensitive to blue light, or the spot meter in the DSLR being too clever for its own good (e.g. just using green or blue light to meter, not the overall spectrum)? I don't know.

Any ideas what's going on? Anyone else find this? I just 'fessed up to also shooting digital! )

[Mike O'Pray]

A statistician might say that the data is too limited to draw definite conclusions but it would seem to me that of the three examples of light conditions and "zones " it is only the sky where a slide exposure might be far enough out to make a real difference to how well it turns out.

I wonder if it is dusk sky only? I wonder if "normal" daylight sky reveals as great a difference?

I take it that the dusk sky was uniform. Can you rule out aiming the Soligor at say a particularly dark part of the sky but not the two camera spots without realising this had happened?

If there was a darker area then a spot meter might pick this up better than your naked eye which had assumed that the sky was more uniform than it was

What is true is that unless the zone you are measuring is quite large or quite near then the camera spot meter will cover a much larger area than the 1 degree Soligor spot meter and tend to cover more than the spot it is aimed at.

It might be worth another dusk sky measure making sure that the sky is very uniform or making sure the area of the sky being measured is the same and seeing if you get different and more consistent results.

As we are talking potential error in slide film only and not digital then a check with all three instruments on a grey card in the same light should establish consistency. If it does to within a third stop ideally but a half stop might be OK then the Soligor should do a good job when measuring for slide work.

Mike

[DaveP]

All my meters on digital cameras, mamiya 7, pentax spotmeter and other cameras I've owned recently (gs645, mamiya 645, nikon fe) have all agreed to an extent which is close enoughnfor slide film. I might be lucky in that respect.

I have a mate who owns a soligor meter and its about 2/3-1 stop out compared with my pentax.

[AlanJones]

Originally Posted by DaveP

I have a mate who owns a soligor meter and its about 2/3-1 stop out compared with my pentax.

All very interesting, but have you seen any results where a comparison can be drawn? It will be interesting to hear and see more.

[marty]

I see the in-camera meters are pretty close. The first thing that comes to my mind is that the spotmeter optics focal is way longer than 50mm, thus you're framing a narrower field. My point is that given the small angle of measure you might not be metering the very same spot.
It might be worth to check out what the reading will be with a lens of similar focal length to the spotmeter's one mounted on the cameras.

Cheers, M.

[alexmuir]

I have a Capital digital spot meter which I think is a re- badged Soligor. It has a 1degree spot and a 100mm focal length lens. It seems to be my most accurate meter, and I use it quite often, even with cameras that have a spot facility. I have found that it gives good readings for transparencies, but that probably depends on what you aim it at. Alex

[Adrian]

Thanks for the ideas. When I did the sky-comparison I was careful to meter the same spot (i.e. not clouds or closer to the horizon).
I'll try the idea of putting a 100mm equivalent focal length on the DSLR or 35mm camera. I think 1/3 stop error might be acceptable but 1 stop is a huge difference, so there's something strange happening. I see the same 1 stop difference for sky readings between the Soligor and the camera spot meters over a range of light levels - not just dusk.

[Adrian Twiss]

Can you be sure that the angle of acceptance of your in camera meters is 1 degree. I believe the spot meter on my canon T90 is actually about 3 degrees but is a sport meter compared to the centre weighted option.

[EdBray]

Quite often different meters will read the same spot and give a different readings, some are also more/less accurate in various types of light. My Sekonic 758D has an adjustment control for matching with other meters/cameras.

This is another reason for finding your personal EI for film using the lens, camera and meter you normally use, change any one of them and your personal EI may also change.

[DaveP]

Originally Posted by AlanJones

All very interesting, but have you seen any results where a comparison can be drawn? It will be interesting to hear and see more.

Don't have any results, just comparing the readings when out shooting.

The other thing to consider of course is that a meter might have a nonlinear response. I had a Kenko meter which was great but would routinely underexpose by about 2/3rds of a stop for light values below 6EV.