I'm shopping for a spotmeter (a real 1 degree meter, useable down to EV1 - so please, no suggestions for Sekonics * or Gossen Starlite).
So far, I have tested the Gossen Ultraspot 2 and the Minolta Spotmeter F, but am not satisfied: Both are rather sensitive for infrared light (hot stove element +3EV, IR diodes like in TV remote controls or IRDA computer interfaces +5-6EV!); the Ultraspot is non-linear below EV 2.5 (checked with ND filters), while the Minolta (though being linear within 0.3EV over the complete sensivity range down to EV1) has internal flare problems (i.e. is sensitive to light sources quite a bit outside the marked 1 degree circle in the viewfinder).
Now it's clear to me that it's probably not a beginners exercise in opto-electronics to construct and produce a precise spotmeter for photographic purposes, but given the amount of money these devices cost and the experience that the manufacturers have, I had expected them to perform far better!
Is it really necessary to buy a Zone IV modified meter in order to get something that delivers reproducible measurements instead of approximations and reason for guesswork (what amount of IR radiation might this subject contain, am I measuring far enough from distinct bright spots, can I rely on the meters results if the light level is this low)?
What are the downsides of the Zone IV modified meters? I suppose you have to pay for better filtering and baffling by decreased sensivity... down to which EV value are they working reliably, and are they useable for slide film? Or is the spectral sensivity matched to BW film in a way that makes them less useful than an unmodified Pentax meter for shooting slides?
Has anybody checked the Seconics 778 regarding IR sensivity, baffling, linearity and spectral sensivity?