Advice re telescope choice

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    Posted by Americo Watkins at 16:13 on 2011 Jul 10

    Hello,I’m about to embark on setting up the best observatory I can before I get married. It will be the only chance I will ever get I expect.My line of research will primarily be photometry/astrometry of asteroids, and obtaining light curves of exo-planets. Also S/N and GRB’s DSO if time allows. I’m aware this may seem ambitious, but I have already started (as a novice) with the asteroids using robotic telescopes and I’ll just see how things progress.I plan to obtain a Paramount ME mount.Re- telescopes I’m considering either a 14" -16" Meade LX200 ACF or the Celestron 14" edge OTA only.The celstron being more expensive than the 16" Meade. But the Meade has the greater light gathering power and the new ACF may well perform well enough.I have obtained limited advice so far which tends towards the Celestron sharp edge to edge images.Does any body have experience of either or both telescopes. I would appreciate any advice re optical performance and/or performance of the tube. i.e flexture, mirror shift. Comments for or against either would be welcome.many thanks for your time,Eric


    Posted by Richard Miles at 19:32 on 2011 Jul 11

    Evening Eric,I saw Brian Warner’s response to your query and would support his comments, viz. that the 14" Celestron EdgeHD OTA would be a good choice. There is supposed to be a special telecompressor lens for this OTA soon. As to mount – here you would be better off with a fork mount to avoid the meridian telescope flip which causes a discontinuity in flatfielding of the CCD camera before and after the meridian flip. It is a great regret that Celestron have never made a fork mount and that their standard OTAs do not have support attachments on both sides of the tube. Presumably the bolt holes exist – maybe someone who has such an OTA will comment about putting one on a fork mount.Richard


    Posted by Nick James at 21:31 on 2011 Jul 12

    Eric,Despite Richard’s advice I wouldn’t spoil a good Celestron by putting it on a fork. Meridian flips are not a big deal with modern GEMs such as the ME and, in my humble opinion, the advantages of a GEM for imaging in terms of balance, flexibility and sky access far outweigh the minor inconvenience of a meridian flip. There is certainly no reason why flat fields should be different one side of the meridian than the other since the instrumental flat doesn’t change and any sky gradient over a narrow field wouldn’t be handled by a library flat anyway.I’m biased since I have a C11 on a CGE but I would go for the Edge-HD Celestron and the ME. Celestron have a reputation for better optics than Meade and the ME will outperform any other mount you might reasonably buy.Nick.


    Posted by Andrea Tasselli at 08:27 on 2011 Jul 13

    For what you want to do I’ll go for the largest aperture you can afford. Contrary to others’ hints the Meade optics are not bad at all and as far as the field covered is reasonable the image is acceptably flat. More importantly, the Meade ACF optics are liable to be reduced (i.e. made faster) far more effectively than the EdgeHD and are more robust in collimation. If I may add a suggestion is to limit yourself to a 14" in both cases as the 16" is really a behemoth and I wouldn’t want to think how to deal with it alone. Another good thing about the Meade is that they’re cheaper than the EdgeHD.Andrea T.


    Posted by Americo Watkins at 22:45 on 2011 Jul 13

    Evening Richard Thanks for your comments and advice. I believe I may have replied to you individually rather than as a post on the forum.I’m just wondering about the flat fielding discontinuity as a result of the meridian flip as mentioned by Richard, the results of which might expain Bruce Gary’s remarks in his book "Exoplanet observing for amatuers p.14 2nd Ed. "but the meridian flips invariably produce shifts in the exoplanet light curve and this can be annoying" or maybe not.Would I be right is saying that due to the shift that each of the pixels would not cover exactly the same field therefore the flat fielding would not be identical to the earlier images and hence affect the photometry results.BTW have results for Emma (NB/2) ready just need to work out some mid-point times for stacked images.Eric


    Posted by Americo Watkins at 22:51 on 2011 Jul 13

    James, thanks for your comments.Do you find collimation stability and any mirror shift a problem? Particularly after any slewing or median flips.I know these can be problems with sct’s but have the newer versions improved on this. I know Meade have a mirror lock. How about the celestron’s. I plan to use an automated draw tube focus.Cheers eric

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