Sony A900 - Alpha 24.6MP DSLR Camera Manuale - Pagina 21
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UN-DAMPED VIBRATION -
It is important that the telescope is properly balanced, both about the polar axis and the Declination axis. Any
imbalance, especially about the Dec. axis, will result in un-damped shutter vibration. The electromagnetic shutter
release produces a sharp recoil. Because the shutter blind is raised vertically, it maybe effective to rotate the DSLR
body so the direction of shutter travel is perpendicular to the Dec. axis.
Image vibration due to shutter release recoil manifests itself as duplicated or elongated image details, aligned in the
same direction (typically in the plane of the dec. axis). Un-damped vibration will prevent the critical focus being found.
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CHECKING FOCUS
ELECTROMAGNETIC SHUTTER RELEASE
The Sony a900 LCD view-screen can be used to
check focus at x19 (raw file). It has sufficient
resolution to make a precise check on focus at night.
The only difficulty in using the view-screen to check
focus is when photographing the Sun in H-alpha.
The H-alpha image is low contrast and it is difficult
judging the precise focus owing to reflections off the
view-screen. Reflections maybe reduced by using a
screen cover PCK-LH4AM which is plane polarised.
Additionally a Hoodman LCD screen Loupe will enable
the view-screen to be seen @ x1 without any
reflections marring the image. The screen Loupe
does not magnify the view-screen pixels, it fits over
the 3" screen to remove glare.