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low-end scope/mount for digicam?



 
 
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  #1  
Old August 4th 03, 10:05 PM
Larry Stedman
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Default low-end scope/mount for digicam?

Is it possible to take decent short exposure pictures (15 seconds) of
double stars and bright star clusters with a scope on an EQ-1 mount and
clock drive? Say an 80mm f/5?

How about on an EQ-2?

Or using a Nexstar 80?

Or an ETX of some flavor?

Larry Stedman
Vestal
  #2  
Old August 5th 03, 03:56 AM
Frank Bov
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Default low-end scope/mount for digicam?

Larry,
Good to hear you're still around!

The rule of thumb for exposure time is 700/f.l. With an ST80 - 400mm -
you've got 2 seconds from a stationary mount before star start to trail. As
your mount begins to track, your exposure times increase. Pretty quickly,
it's the steadiness of the mount that matters more than the accuracy of the
drives.

So, how about stacking ten 1.5 second images from a sturdy tripod?

HAve fun,
Frank

"Larry Stedman" wrote in message
...
Is it possible to take decent short exposure pictures (15 seconds) of
double stars and bright star clusters with a scope on an EQ-1 mount and
clock drive? Say an 80mm f/5?

How about on an EQ-2?

Or using a Nexstar 80?

Or an ETX of some flavor?

Larry Stedman
Vestal



  #3  
Old August 5th 03, 08:53 AM
Per Erik Jorde
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Default low-end scope/mount for digicam?

Larry Stedman writes:

Is it possible to take decent short exposure pictures (15 seconds) of
double stars and bright star clusters with a scope on an EQ-1 mount and
clock drive? Say an 80mm f/5?


It should work. I have managed up to 30s with such a mount and lens (a
F=90mm) with a Cookbook CCD camera. These easily reach mag 12 stars,
or below, so you are not limited to just bright stars and clusters
with this setup. Some exposures may show excessive trailing due to
large periodic errors, however. At best I have managed a few
half-decent 30s exposures through the telescope (4.5" F=1000mm) on
this mount, but this exercise is a study in futility. I bought a Vixen
GP-DX mount a few days ago for that purpose.

Good luck!

Per Erik
  #4  
Old August 8th 03, 04:42 PM
Larry
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Default low-end scope/mount for digicam?

"Frank Bov" wrote in message . ..
Larry,
Good to hear you're still around!

The rule of thumb for exposure time is 700/f.l. With an ST80 - 400mm -
you've got 2 seconds from a stationary mount before star start to trail. As
your mount begins to track, your exposure times increase. Pretty quickly,
it's the steadiness of the mount that matters more than the accuracy of the
drives.

So, how about stacking ten 1.5 second images from a sturdy tripod?

HAve fun,
Frank


Frank,

Always good hearing from you, too! Interesting formula. I like your
idea of stacking multiple short exposures. Now, let's see, my
reflector with the steadiest mount is my Starmaster. With a 7" dob of
965mm, that means less than a second before stars trail!

Have a question, though, for you and the group… wouldn't the
magnification make a difference? Not just the focal length?

I mean at 200x, the stars move through the field a lot faster (I
understand that the Earth still moves the same speed, but the % of the
fov that is covered by the stars/second changes greatly). So, I'd
assume better pics with shorter, less obvious trails at lower
magnfication.

Or, am I missing something? Obviously I must be!

Larry
 




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