What are criteria to compare and evaluate different 12 inch truss Dobsonian telescopes? I'm primarily interested in comparing mirror quality and weight (price I can do myself of course). Two examples of the category I'm asking about are the Sky-watcher 300P Flextube and Meade Lightbridge.

One of them appears to have a fan to cool the mirror, how can I evaluate that in terms of a positive or negative towards performance?

  • $\begingroup$ Questions about specific brands of telescopes are off topic. $\endgroup$
    – Mike G
    Oct 25, 2019 at 3:38
  • 1
    $\begingroup$ @MikeG I've edited the question accordingly. Very often new users are unfamiliar with the site and SE doesn't require any reading of the help section before asking, so for a new user's first question, a helpful edit s probably more instructive than the insta-close. $\endgroup$
    – uhoh
    Oct 25, 2019 at 4:48
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    $\begingroup$ There are many different aspects to compare for 12" truss Dobs and I think you should start with finding some reviews of the ones you are interested in. If then you have specific questions, or points you want clarified, then edit your question, $\endgroup$
    – Dr Chuck
    Oct 25, 2019 at 7:40
  • $\begingroup$ Dobson would be appalled :-), as his whole point was to build a quick, cheap, powerful telescope. He used to tell his students to stop over-figuring &polishing their primary. $\endgroup$ Oct 25, 2019 at 14:21
  • $\begingroup$ @DrChuck is right. You can also look for amateur astronomy clubs in your area. They may have both observing parties where you can go and look through telescopes, and meetings indoors where you can meet other amateur astronomers and discuss telescopes. Before buying one it's a really good idea to spend a lot of time reading and discussing with others. You might decide that your interests are best severed with a different kind of telescope than you originally anticipated! You might also find a used telescope that is either cheaper, or better for your needs than a new one. $\endgroup$
    – uhoh
    Oct 26, 2019 at 2:01

1 Answer 1


The cooldown fan is purely to speed getting the primary mirror to the local ambient temperature. It is not used - and should not be left on during observation, as it'll undoubtedly be a vibration source.

That shouldn't be a significant factor in your final decision. I would go with total weight, and perhaps adaptability to an equatorial mount for star-tracking.

  • $\begingroup$ There's some optimum for weight which likely varies from person to person. Too light, and you'll get more jiggle. Too heavy and you won't be able to carry it. Quality of X and Y axis bearings matters a lot too. $\endgroup$ Nov 1, 2019 at 15:47

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