Sony A900 - Alpha 24.6MP DSLR Camera Manual - Página 7
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TELESCOPE ADAPTORS
Eyepiece projection enables a far larger image scale at the expense of a slower effective focal ratio.
The adaptor needs to have three parts: the focusing mount nosepiece that fits into the 2-inch eyepiece collet; the
eyepiece section, preferably adjustable so the amplification may be varied; the DSLR bayonet adaptor.
I have examined numerous commercial eyepiece projection adaptors & not one of them was a well thought out design,
or well made, so I designed & had the late Ron Irving machine it for me. The camera bayonet section is identical to the
prime focus sleeve adaptor.
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EYEPIECE PROJECTION
The amplification factor of
an eyepiece projection
adaptor is calculated from:
L
A =
−1
Fe
where
L is the projection
distance (field stop to image
plane)
€
Fe is eyepiece
focal length
The effective focal ratio is
prime focal ratio times the
amplification.
The best type of projection
eyepieces are either Plössl
or Orthoscopic. I use a
25mm Plössl.