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LAPTOP REMOTE CAPTURE & CONTROL vs LCD VIEW SCREEN (cont.)
The disadvantage is the USB upload time which can be well over a minute. The twin BIONZ processors in the Sony
a900 can transfer the raw 26Mb image file to the LCD view-screen in one or two seconds. By reducing the image size
to <S> 2x2 binning, the upload time can be reduced to less than a minute, which is still too long compared to the
upoad time to the view screen. The Sony "Image Data Suite" also only allows you to view the uploaded image @ x4.
Where a laptop does have a decided advantage is when photographing the Sun in H-alpha. Providing the laptop can be
placed either in the shade or within a nearby shed, it will be much easier to check the uploaded image is precisely
focussed. But because the upload times are so much longer for the raw files, than checking them on the LCD view-
screen, it is better to try to obtain a close focus on the view-screen first.
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EXPOSURE
Set the lens lever to <M> and the PASM mode dial to <M>. The telescope adaptor does not have a confirm feature, so
the camera does not receive any information, either focal ratio or the presence of a lens. It is possible to set the PASM
mode dial to <A> aperture priority and set the focal ratio, but for all the sophistication of the metering system, it is
better to calculate exposure times and bracket ±2 stops if necessary. When photographing the Moon pay particular
attention to the terminator. The dark areas near the terminator, if underexposed will be exhibit Chroma noise.
Increase the exposure time if necessary until the dark areas are correctly exposed, even if it causes the limb to be
burnt out. Frames may be stacked during the processing phase to increase dynamic range.
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EXPOSURE
The exposure time is calculated using the following formula:
2
f /#
where
t =
S * B
B values are published in "Astrophotography" by Barry Gordon 1985 Willmann Bell Inc.
An exposure time calculator is available from Glen LeDrew at "The Starry Room" <
For example: Moon @ First / Last Quarter, TEC140APO @ prime focus + x2 Barlow ef/# = 14; B = 40; ISO100
2
14
196
1
sec. Bracket the exposures ± 2 stops
t =
=
≅
100* 40
4000
20
-
MANUAL MODE OPTION
-
CALCULATING EXPOSURE TIMES
f/# is the objective focal ratio or the effective focal ratio
S is the ISO rating of the sensor
B is the Brightness Value
>
g_ledrew@hotmail.com
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