For Finding and Centering Astronomical Objects for Astrophotography with Parfocal Eyepiece |
Finding and centering astronomical objects in the view finder of
consumer grade Digital Rebel or 20D cameras or older film cameras (e.g.,
EOS 650) can be challenging. A sturdy (flexure free) eyepiece holder that
can hold a parfocal eyepiece is a useful aid to astrophotography and can
be constructed from a Canon EF lens rear cap and threaded 1.25 inch
eyepiece holder.
The example I photograph below uses a Televue 25mm
Plossl eyepiece shown in position that is parfocal with the sensor/film
plane of EOS cameras (A 19mm panoptic worked fine too). The eyepiece
holder will not work with guiding eyepieces (e.g., 12.5mm Orion) or ST-4
as the working distance is too large.
Items needed to make a parfocal 1.25 eyepiece holder: 1) Canon
rear lens cap E (Canon
# 2723A002- $7); 2) Eyepiece holder unscrewed from cheap 1.25 inch
star diagonal (If you don't have one, you can purchase a threaded eyepiece
holder [e.g.,
Borg
part 7317 for less than $25]). The cheap Celestron 1.25 star
diagonal I took the part from came with the OTA I purchased and costs
$33
new at the time of writing. I have two other cheap diagonals that
came with used telescopes or guidescope in my junk part box that are
similarly constructed.
Tools I used to make the eyepiece
holder: 1) 3/8 inch drill and 5/16 inch drill bit; 2) Grinding tool (I
used a Dremel power tool with grinder attachment).
©
2004, William L. Castleman
Initially
posted 19 December, 2004