Help me choose a telescope

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  • Member since
    February, 2014
Help me choose a telescope
Posted by Praveen on Monday, February 10, 2014 1:08 PM

Hi, I'm new to astronomy and searching for a good telescope for viewing and astrophotography(DSO). I've shortlisted some telescopes, not sure which one is better. I have a Canon 550D.

Refractor scopes:

1) http://www.tejraj.com/refractors-sk909eq2.html

SK 909 EQ-2
D=90 / F=900mm F/10 Refractor  / EQ2  Mount  

2) http://www.tejraj.com/astroview90mm.html

Orion AstroView 90 EQ Refractor

D=90 / F=910mm F/10.1 Refractor /Orion EQ-2 mount

3) http://www.tejraj.com/messier-ar-90x900.html

BRESSER Messier AR-90 90/900 EXOS 1

D=90 / F=900mm F/10 Refractor / Mechanical EXOS 1 mount

-------------------------------

Reflector scopes:

4) http://www.tejraj.com/reflectors-sk1149.html

BKP1149 EQ1 Reflector

D=114 / F=900mm F/7.8   EQ1 

5) http://www.tejraj.com/spaceprobe-130eq.html

Orion SpaceProbe 130 EQ

D=130 / F=900mm F/6.9  Orion EQ-2

6) http://www.tejraj.com/spica.html

BRESSER SPICA   German-type Equatorial Mount EQ2

D=130 / F=650mm F/5

 

 

 

Please suggest a good telescope. 

 

 

 

 

 

Moderator
  • Member since
    July, 2001
  • From: PA, USA, Earth Moderator
Posted by DaveMitsky on Monday, February 10, 2014 3:01 PM

Unfortunately, none of those telescopes is a good choice for prime focus astrophotography.  A small, fast ED refractor (80mm f/6 or f/7) on a solid equatorial mount with a dual-axis drive would be a far better, albeit more expensive, option.

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

  • Member since
    March, 2008
Posted by Antitax on Monday, February 10, 2014 3:35 PM

Praveen

Hi, I'm new to astronomy and searching for a good telescope for viewing and astrophotography(DSO).

   Hi, Praveen.

   It's difficult to find a beginner telescope that's good for visual and photo. Visual requires larger diameters, but photo can be done with very small diameters (starting at 80mm) and short focal lengths. They need heavy and accurate motorized mounts, plus they cost a lost compared to bigger, purely visual scopes.

   It's better to have a small motorized scope for imaging, and another large manual scope for picking up lots of light from the faint deep sky. Imaging scopes also need lots of light but instead of grabbing it at once with a large objective, they do long exposures so the small amount of light they collect piles up on the sensor for a long time, minutes or even hours.

   Planetary photography doesn't take long exposures, which might make it look easier than deep-sky photo, but it requires very, very, long focal lentghs, which are difficult to master. Many newcomers assume they want to do astrophotography because they don't know how difficult and costly it gets compared to common daytime imaging.

   Maybe it's better to put photography on hold until you know more about its challenges, and get a large, simple scope to start your exploration. It's impossible to go wrong with a dobsonian scope, it avoids the complication and cost of the equatorial mount.

  

TS 8x40 Wildlife, 10x50 Marine/Fujinon 16x70/TS 80mm triplet, 6x30 finder, EQ-3 mount, TS 2" 99% diagonal/Celestron C5+ and 6x30 finder, DIY tripod/5" Bahtinov/12" GSO dob, 8x50 finder/Meade 2" 24mm 82°/Hyperion 24,13,10mm 68°/TS Expanse 17mm 70°/SW 7mm Panorama 82°/Ultima 2x barlow/Astronomik UHC-E filter/Baader O-III/Astro Solar 5" & 80mm filters/Sky Atlas 2000/Rükl's Moon Atlas/Canon 400D/5mW green laser

  • Member since
    February, 2014
Posted by Praveen on Wednesday, February 12, 2014 9:55 AM

Tried reading some more and heres what i understood, the ones listed above require barlow lens to connect with dslr to be able to focus. Adding barlow lens increases the focal length requiring sturdier mount and tripod, to avoid shake and for tracking. Increases f ratio requiring more longer exposure time, so to avoid star trailing we need a good motor drive, or a goto mount. correct? 

 

http://www.tejraj.com/shorttube80a.html

Orion Short tube 80A Astro Version

http://www.tejraj.com/cg3-eq-mount.html

http://www.tejraj.com/eq_mount-eq2.html

http://www.tejraj.com/eq2-mount.html

 

Will this work?

Moderator
  • Member since
    July, 2001
  • From: PA, USA, Earth Moderator
Posted by DaveMitsky on Wednesday, February 12, 2014 12:40 PM

That's right but even the best driven mounts require guiding or autoguiding for long exposures due to periodic error.

http://www.themcdonalds.net/richard/index.php?title=Astrophotography_Mounts:_Periodic_Error_Correction

http://www.themcdonalds.net/richard/index.php?title=Astrophotography_Equipment:_Autoguiding

An 80mm f/5 "shorttube" achromatic refractor is going to produce a lot of chromatic aberration (false color).  That's why I suggested a higher focal ratio 80mm ED refractor.  (Apochromats are ideal but will cost even more than ED refractors.)

Another option is an 8" f/10 SCT, which won't be capable of widefield shots but will be better for planetary (and smaller DSO) imaging.

You may find these sites useful regarding telescopes suitable for astrophotograpy:

http://www.astropix.com/HTML/I_ASTROP/SCOPES.HTM

http://www.themcdonalds.net/richard/index.php?title=Astrophotography_Equipment:_Telescopes

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

  • Member since
    March, 2008
Posted by Antitax on Wednesday, February 12, 2014 1:16 PM

   I never tried this 80mm tube but it's only an achromat, really fast but not corrected like an apochromat, and it's not only about chromatic error, other aberrations exist.

    Last summer some friends and I did a long run of photos with my little 80mm f/6 apo, however the mount was a heavy Losmandy that also carries our club's Celestron 11-inch and its counterweights. We attached either my Celestron 5 reduced to 800mm or my 80/480mm apo on top of the large Celestron.

   Guiding was excellent but even with this heavy rig it's tough to image well with focals longer than 1 meter. Look at what can be done with two small mass-market scopes, a good heavy mount, and simple cameras, plus the right processing:

http://www.youtube.com/watch?v=zRloL2K1r5Q

   But see how his mount (he's a taiwanese guy) is beefy and nothing like those you're thinking of.

TS 8x40 Wildlife, 10x50 Marine/Fujinon 16x70/TS 80mm triplet, 6x30 finder, EQ-3 mount, TS 2" 99% diagonal/Celestron C5+ and 6x30 finder, DIY tripod/5" Bahtinov/12" GSO dob, 8x50 finder/Meade 2" 24mm 82°/Hyperion 24,13,10mm 68°/TS Expanse 17mm 70°/SW 7mm Panorama 82°/Ultima 2x barlow/Astronomik UHC-E filter/Baader O-III/Astro Solar 5" & 80mm filters/Sky Atlas 2000/Rükl's Moon Atlas/Canon 400D/5mW green laser

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