Smaller-Than-One-Degree Spotmeters

[Vlad Soare]

Hi guys,

Am I the only one who finds one-degree spots to be too "fat"?
Are there finer spotmeters, like, say, half a degree, or even smaller?

Thanks.

[Darin Boville]

They used to make a 1/2 degree once upon a time--may still be made for all I know.

But why buy some $$$$ specialized thing? Just take your current spotmeter--I assume the front is threaded for filters?--and attached a Raynox telephoto adapter. It comes with various adapter rings (plastic) so you might not need anything else. The Raynox's are normally used for video cameras and point and shoot.

--Darin

[Jeff Conrad]

I completely agree. Unfortunately, I don't know of many alternatives other than the long-defunct SEI photometer. There is the Minolta LS-110 (http://www.konicaminolta.com/sensingusa/products/Light-Measurement/luminance-meter/ls100-ls110/index.html) luminance meter, which measures 1/3 degree, but it's calibrated in luminance units rather than camera settings, and the last time I checked, the price was just over $3k.

[Vlad Soare]

Yes, it's threaded, though I don't know the diameter; I'll have to measure it. It's a Pentax V.
I didn't know about that adapter. I'll look into it.

The luminance units thing wouldn't be a problem. I'm sure I could get used to it. On the other hand, its $3k price would be a big problem. :D

Thanks.

[Darin Boville]

Here's the adapter lens that I have:

http://www.raynox.co.jp/english/video/hd2205pro/index.html

It's thread is slightly smaller than my Pentax Digital. But I held it up to the lens and it worked fine--spot indicator behaved correctly (falling off quickly from light sources, etc), very light weight, not expensive. Used ones on E-bay, I bet--these are popular items.

Your meter has a 46mm thread...might be another Raynox lens that is closer in size or maybe it won't matter....

--Darin

[BetterSense]

My homemade spotmeter has about a .4 degree spot in daylight. Mine is built to be compact; it would be easy to make one perhaps .1 degree just by using a larger lens.

[Marek Warunkiewicz]

But would you not have to recalibrate due to the loss of light in passing through more glass?

[BetterSense]

No; if you keep the F/stop ratio the same, differences in light transmission among single-element lenses can be ignored for photographic purposes.

The people proposing to use supplementary magnification lenses on factory-calibrated spotmeters do have me wondering if the resulting readings will be valid. It seems to me that if you could increase the effective focal length of the lens you would indeed get a smaller spot size, but the reading will only be accurate if the resulting system has the same aperture as the original spotmeter. Otherwise you will have to apply a correction factor, or else your film will be over exposed.

[Darin Boville]

Just checked my Pentax Digital + Raynox combo. Correction is one stop (fine tuning you can do with your regular film testing, of course).

But then again, as I said, I used a telephoto adapter that may be too small in terms of diameter. Plus there are weaker ones (mine is something lime 2.2x).

--Darin

[RichardRitter]

One of the last projects I was working on with Fred Picker was a 1/2 degree spot meter with a new different type of photo cell that did not see IR light. The meter was a dream to work with. Problem was the marking genius said the meter would not sell and put an end to the project.

[rdenney]

But would you not have to recalibrate due to the loss of light in passing through more glass?

It's easy enough to check--just read a gray card with and without the screw-in supplemental lens, and apply the change to your ISO setting.

Rick "digging for his cheapie Raynox video-cam telephoto" Denney