Folks,
I've been shooting 35mm with a Takahashi Sky-90 for awhile.
I've been wanting to make larger prints and so recently
picked up an AP Traveler and Pentax 67 body. First results
are at
http://www.cse.ogi.edu/~tleen/astro/GammaCygni67.html .
Compare with the 35mm shot at
http://www.cse.ogi.edu/~tleen/astro/GammaCygni.html .
The change from f/4.5 to f/6, and the larger format poses a
bit of a challenge. Though not visible at the scale posted,
there is some field rotation in this shot; and I need to go
deeper than this 1hr exposure. Unless I get better alignment,
I'm not going to be able to go to the longer exposures required.
Does E-200 push ok -- I'd like to make 16x20 prints.
Focus is also a bit ambiguous. I use a knife edge on 35mm,
but a cheap 50x Edumund pocket microscope on the 67 ground
glass screen.
My mount is an AP-400 on their aluminum tripod. According to
Astro-Physics, it should be sufficient to hold the Traveler,
reducer, and Pentax 67.
My usual alignment procedure is to use the polar scope and
then drift align at 200-300x through the scope; making adjustments
until there is no declination drift over a five menute period. This
can take me a LONG time -- up to two hours on a bad night. Then I
interchange the diagonal for the flattener with camera, and
rebalance the mount. I believe this step -- taking off the diagonal
and adding the substantial weight of the medium format flattener
and the 67 camera -- is throwing off my alignment.
Any thoughts or suggestions?
I guide with an STV and E-finder (100mm FL). I've tried to polar
align using the STV/E-finder, but a high-power eyepiece picks up
the drift quicker than the E-finder. I'd rather not go to a longer
lens (added weight and expense) for the STV just to facilitate
polar alignment.
Should I force myself to do the drift alignment with the STV to
avoid adding extra weight after I do the alignment? Should I
just add some dead weight to the mount while I'm drift aligning?
Do I need a pier instead of the tripod? Should I be looking into
a beefier mount?
(Incidently, the STV with 100mm FL E-Finder gives me
guiding errors at or below an arc second. So the
guiding is working very well.)
Thanks for suggestions.
Todd
I've been shooting 35mm with a Takahashi Sky-90 for awhile.
I've been wanting to make larger prints and so recently
picked up an AP Traveler and Pentax 67 body. First results
are at
http://www.cse.ogi.edu/~tleen/astro/GammaCygni67.html .
Compare with the 35mm shot at
http://www.cse.ogi.edu/~tleen/astro/GammaCygni.html .
The change from f/4.5 to f/6, and the larger format poses a
bit of a challenge. Though not visible at the scale posted,
there is some field rotation in this shot; and I need to go
deeper than this 1hr exposure. Unless I get better alignment,
I'm not going to be able to go to the longer exposures required.
Does E-200 push ok -- I'd like to make 16x20 prints.
Focus is also a bit ambiguous. I use a knife edge on 35mm,
but a cheap 50x Edumund pocket microscope on the 67 ground
glass screen.
My mount is an AP-400 on their aluminum tripod. According to
Astro-Physics, it should be sufficient to hold the Traveler,
reducer, and Pentax 67.
My usual alignment procedure is to use the polar scope and
then drift align at 200-300x through the scope; making adjustments
until there is no declination drift over a five menute period. This
can take me a LONG time -- up to two hours on a bad night. Then I
interchange the diagonal for the flattener with camera, and
rebalance the mount. I believe this step -- taking off the diagonal
and adding the substantial weight of the medium format flattener
and the 67 camera -- is throwing off my alignment.
Any thoughts or suggestions?
I guide with an STV and E-finder (100mm FL). I've tried to polar
align using the STV/E-finder, but a high-power eyepiece picks up
the drift quicker than the E-finder. I'd rather not go to a longer
lens (added weight and expense) for the STV just to facilitate
polar alignment.
Should I force myself to do the drift alignment with the STV to
avoid adding extra weight after I do the alignment? Should I
just add some dead weight to the mount while I'm drift aligning?
Do I need a pier instead of the tripod? Should I be looking into
a beefier mount?
(Incidently, the STV with 100mm FL E-Finder gives me
guiding errors at or below an arc second. So the
guiding is working very well.)
Thanks for suggestions.
Todd
