Richard Schaetzl wrote:
>Silicon cells need a strong filtering to conter there strong
>red-infrared sensibility, hence the name silicon-blue-cell SBC. It´s
>clear, that this filtering can not give them the same frequencial
>response as the human eye.
The name "Silicon Blue" refers to the blue-enhanced response over standard
silicon cells. Such cells have IR filtering to remove their sensitivity to
infra-red. I didn't say they had the *same* response as the eye, only
*similar*. They are certainly closer than CdS cells which have very little
sensitivity at the blue end. The blue-enhanced response of the SBC makes it
a closer approximation to human eyesight than a CdS cell.
>BTW CCDs are also made from silicon and they are sensitive to IR too,
>astrophotographer like them because of this characteristic.
CCTV surveillance cameras also exploit this; by using IR illumination the
camera can see, but human eyes still think it's dark.
>> CdS cells tend to be more sensitive at
>> the red end,
>
>CdS are more sensitive to yellow (like the human eye) than to other
>colors.
*Peak* response is usually in the yellow region, yes, but there is a lot
more sensitivity at the red end of the spectrum than the blue end. I
should have been more specific.
>> which is why TTL meters based on CdS cells tend to underexpose
>> b/w film through red and orange filters -
>
>This happens also with SBC
As I said - my SBC-celled OM-2SP and OM-4 exhibit this.
>>They're also too slow to work
>> usefully in a spotmeter.
>
>Minoltas first spotmeter worked with CdS
What was its low-light capability like? For that is when CdS cells are
slowest to respond. My Minolta Spotmeter F has a little lamp in the
display so you can see it in low light levels. Unfortunately, when it's
dark enough to need the lamp, the meter only reads "E" because the light
level's too low for it to measure! The OM2 and OM4 series are much more
sensitive.
Regards
Richard
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|