Fuji SLR Camera loses 2 stop (or more) sensitivity with prolonged "on-time"

[Graphic]

Has anyone else experienced this phenomenon:

I am a convention photographer and often do on-site portraits with
studio-type lighting.

The last 2 times that I used my Fuji S620-Z camera (with sensor chip
very
similar to the S-1 from what I understand) I had the camera turned on
for
most of 6-hours then most of 10 hours on 2 separate days.

The first time, the exposures took a sudden nose-dive towards 2-stops
under-exposed and I blamed my lights since I did not carry my
falshmeter
(ok,ok...this is only case where digital has caused me to get lazy
and want to lighten my camera bag to the max.)

On the second occassion I brought my light meter plus my back-up
lights
that I *always* carry.

The same thing happened: sudden 2 stop decrease in sensitivity over
the
initial flash meter reading of F5.6.

ONLY this time I pulled out the flash meter--- Still reading F5.6...ok
shoot some more photos and the histogram shows that the f2.8 photos
are on
the button... repeat procedure over the balance of the 200+
portraits...EXCEPT, now F2.8 is underexposing the last 3 subjects, so
rather than re-rig the lights I move the stand in closer for perfect
exposures at F2.8 ...finish up the session and the flash is reading
1/2
stop over F5.6 (remember I moved the lights in closer).

NOTE on the lights: I am using el-cheapo screw in type e.f. that are
ganged-up 4-lights to a fixture aimed into an umbrella. Not elegant
but it
always works as well as the expensive alternative *and* always
consistently
with film exposures.

What this means is that to get a 2-stop loss in speed, the equivalent
of 3
out of 4 independent flash units need to fail consistently with the
Fuji
digital camera and work perfectly with the flashmeter even when the
pops
are intermixed between the two. I think this rules out the e.f. as the
culprit.

Any ideas about the true cause and solution?

TIA
Wayne Catalano
[email]graphic99@mindspring.com[/email]

[CSM1]

"Graphic" <graphic99@mindspring.com> wrote in message
news:bep5bj$n2r$1@slb6.atl.mindspring.net...

> Has anyone else experienced this phenomenon:
>
> I am a convention photographer and often do on-site portraits with
> studio-type lighting.
>
> The last 2 times that I used my Fuji S620-Z camera (with sensor chip
> very
> similar to the S-1 from what I understand) I had the camera turned

on

> for
> most of 6-hours then most of 10 hours on 2 separate days.
>
> The first time, the exposures took a sudden nose-dive towards

2-stops

> under-exposed and I blamed my lights since I did not carry my
> falshmeter
> (ok,ok...this is only case where digital has caused me to get lazy
> and want to lighten my camera bag to the max.)
>
> On the second occassion I brought my light meter plus my back-up
> lights
> that I *always* carry.
>
> The same thing happened: sudden 2 stop decrease in sensitivity over
> the
> initial flash meter reading of F5.6.
>
> ONLY this time I pulled out the flash meter--- Still reading

F5.6...ok

> shoot some more photos and the histogram shows that the f2.8 photos
> are on
> the button... repeat procedure over the balance of the 200+
> portraits...EXCEPT, now F2.8 is underexposing the last 3 subjects,

so

> rather than re-rig the lights I move the stand in closer for perfect
> exposures at F2.8 ...finish up the session and the flash is reading
> 1/2
> stop over F5.6 (remember I moved the lights in closer).
>
> NOTE on the lights: I am using el-cheapo screw in type e.f. that are
> ganged-up 4-lights to a fixture aimed into an umbrella. Not elegant
> but it
> always works as well as the expensive alternative *and* always
> consistently
> with film exposures.
>
> What this means is that to get a 2-stop loss in speed, the

equivalent

> of 3
> out of 4 independent flash units need to fail consistently with the
> Fuji
> digital camera and work perfectly with the flashmeter even when the
> pops
> are intermixed between the two. I think this rules out the e.f. as

the

> culprit.
>
> Any ideas about the true cause and solution?
>
> TIA
> Wayne Catalano
> [email]graphic99@mindspring.com[/email]
>

If I took a guess, I would say the electronics are heating up in the camera,
making the sensor less sensitive to light (the ISO is drifting). Is your
work area air conditioned?

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