Spherical diffusers . . .

[j.lukow]

As I mentioned in a past post my Minolta Auto-meter pro is missing the spherical diffuser . . .

Does this mean that I can't do accurate incident light readings, only reflected or do I need to adjust my reading some how?

Thanks in advance,
Jim

[Jieffe]

Yes.

As a stopgap, you could take a reflected reading of your palm and adjust your exposure 1 stop down (e.g. you measure f5.6 on your hand, expose for f8 ).

[j.lukow]

, okay . . .

If I understand this . . .

Don't take incident readings, until I have a difusser.

I assume that since this meter has a switch for going between incident and reflected mode - the palm and adjust one stop isn't required.

Thanks,
Jim

[j.lukow]

I forgot, if people haven't guessed yet, I'm a meter newbie.


Jim

[estudleon]

The spherical diffuser is used to meter the light that incide (incident light) over the subject to photo.

And that incidence is measured considered all the light sources that fall into the scene.

But if you use a plane diffuser and put the meter form the subject direct to the light source (unique, like the sun) and looking to it, you will have the same measurement than with the spherical if in the scene exist only one light source. (system used in hollywood's films).

[Seele]

Jim,

To start with, you really need to get a replacement diffuser to get your meter working properly.

estudleon,

This also brings up the different diffuser design philosophies, as proposed by Phillip Smethurst and Dan Norwood, the AVO-Smethurst and Norwood Director exposure meters were made to these two theories respectively.

Smethurst proposed the use of a flat diffuser, which conforms to the cos4 (that is cosine to the power four) principle. This means that the more to the side the light source is, the less it would be read by the meter; in other words, it gives the photographer the option to give more control.

On the other hand, Norwood suggested a semi-spherical diffuser, which takes into account of side - and to a small degree, back-lighting, which is easier to understand if you just take a single, straight-foreward reading, and it tends to give slightly less exposure when compared to the Smethurst type receptor.

The most advanced Norwood-type diffuser ever made was the Weston Invercone for Weston Master IV and later models (the smaller one for the Master III, although not flat, still conforms to the cos 4 principle). Using plastics materials of different light transmission densities in carefully shaped assemblies it keys each light incident angle to its effectiveness to the metering cell.