Prasad:

Mabuhay! My email program is giving me errors so I don't know
if this post made it to the list. I am forwarding it directly
to you. Sorry if you get it twice!

Gene Horr

-----------------------------------------------

Prasad:

I can understand your concern. I thought SE Texas and S. Florida
held the the temp/humidity extremes. Manila just about knocked
me to my knees when I got off of the plane!

This subject came up a couple of weeks ago. I have worked with
SBIG cameras in ambient temperatures from -5 C. to 30 C.

The pictures taken with in the cooler temperatures are better. But
it is not a dramatic difference. You can still take good images
with a hot ambient temperature. The biggest effect is that the
dark current is higher. The purpose of the dark frame procedure
is to remove this "noise". The dark frame subtraction does do
a very good job in removing the noise. Unfortunately, since the
noise level is higher with the hotter temps., more of the noise
leaks through. You can fight this with a higher signal/noise
ratio (more on this later).

The second problem you will run into is that since the dark
current is filling up your CCD "well" faster, you have less
"room" for the signal. In short, you are more limited in your
exposure times.

Fortunately, there is a procedure that fights both of these
problems at the same time. The procedure is stacking images.
Since you are taking multiple short exposures you don't have
to worry about "filling up" the CCD "well". And the main
reason for stacking images is that it improves the signal/
noise ratio. Voila! Both problems solved at the same time!

Take care,

Gene Horr


>
> Hi
> I am new to this list. I don't own any CCD. I want to know more about
> CCDs. Here is a question:
>
> I know that all CCD chips have a Peltier device to cool and the
> temperature is taken down to -10 deg C or lower. This may work fine in
> places where the ambient temperature is low. Will it still give
> "sufficiently" low temperature where I live (Manila, Philippines) - the
> night temperature never goes below +20 deg C. Would it mean that I would
> not be able to get sufficiently low dark current - giving me poor/noisy
> images?
>
> Prasad

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