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This does lead into a project I want to do, basically a light meter to determine photographic exposure at very low light levels. I have a few transconductance amplifier boxes (well two) that do a gain a 10^9. One is an EG&G PARC 181. The other is ... uh buried someplace.

My intent was to do I to V, using a dark current for nulling the result. I have a few UDT PIN-10D, so I suppose I could do a V measurement with a dark diode. I'm building a "one of", so cost isn't an issue. In fact, measuring open circuit voltage would get around the issue of having to buy a hard to find high value resistor.

All I really need is a repeatable measurement. I would use empirical data to make my own calibration table.

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Batesville Casket Company.

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manual focus is not much use with a 320 pixel LCD display, unless you intend to produce images at that resolution or worse.

On a sunny day (12 Apr 2009 09:46:44 GMT) it happened Jasen Betts wrote in :

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That is actually not completely true. You can do good interpolation on focus, very good even. And my Canon A470 has incredible through the lens auto focus, it works 100% reliable, has several modes, and will take over where you cannot see it on the viewfinder. Decent [video] cameras can also have an on screen waveform display, you just go for max frequency, or max amplitude of the area of interest while adjusting focus, when the area of interest has enough vertical detail. It all does not depends on the viewfinder size really. For example the Canon HV20 video camera has an option to enlarge the area of interest in the viewfinder, and uses 'peaking', the same high frequency enhancement, that can help you focus, page 50 of the manual:

Hobbs

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Ah-ha. Something useful (TTL focus) that can be achieved only with flipping mirrors, a rather notable drawback. Moving parts cost money and cause vibrations. .

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Canon did it with a partially silvered prism in the light path, though the insertion loss was an F-stop, IIRC. The body was impressively expensive, too.

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That was the Canon EOS RT, which used a pellicle mirror to shorten the shutter lag to only 0.008 seconds. As you say, it had the drawback of reducing the available light for both the film & the viewfinder:

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That's the idea, though the EOS was later. The one I'm thinking about was on an FTb chassis (could have been an F1 but it wasn't an interchangeable viewfinder). I don't see it in the Canon museum so perhaps it was a special purpose camera and not generally sold.