[photo-3d] Re: Halogen viewer bulbs

["John Goodman" <jgood@xxxxxxxx>]

DrT wrote:  

> It is quite possible that the bulbs have nearly identical
> [voltage vs current] curves, with 2.5V/0.83A and 2.8V/0.85A
> being two points of this curve.

Unfortunately, the only test equipment I have is a cheap VOM. 
This may be accurate enough for DC voltage, but it only 
measures currents up to 300 mA. And I can't vary the voltage 
continuously to get a V/A curve. I simply checked voltage 
across the terminals in a red-button, off and on.

	with fresh alkalines:
open circuit voltage:	3.0 (or slightly higher)
2.8V 0.85A on:		2.8
2.5V 0.83A on:		2.9

	with partially used alkalines:
open circuit voltage:	2.9 (or lower)
2.8V 0.85A on:		2.5 
2.5V 0.83A on:		2.6

It seems that using 2.8V bulbs with alkalines means they'll be at 
or below their rated voltage. 2.5V bulbs will be well above their 
rated voltage, until the batteries have been used for some time. 
When using NiCd or other rechargeable batteries, 2.8V bulbs 
might be underpowered, since such offer less voltage to start 
with (~1.35 volts?).

2.8V 0.85A bulbs, however, are significantly brighter than 2.5V 
0.83A bulbs, when A/B tested with the same batteries. The 
published ratings are 35 and 23 lumens, respectively (at their 
rated voltages, of course). A 50% increase in brightness is, 
what, about a third of a stop?

Previous posts have noted that tweaked Realist viewers with 
extra-bright lighting may not offer the most pleasing or 
"natural" degree of verisimilitude. However, imho, brighter can 
be better than not bright enough, since dense areas of 
transparencies may contain information that can only be seen 
by light passing through.

It might be interesting if sellers of the various viewer lightbulbs 
told us the approximate sales ratios among the ones they offer. 
Similarly, it would be nice to hear from people who use battery 
viewers a lot, if blown bulbs are a fairly common occurrence 
(once a month, say) or quite rare (once a year), and which 
bulbs were in use.

John Goodman

 

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