Telescope Reviews: Re: 80 or 90 for imaging?

Hi there Craig!

Welcome to Cloudy Nights and the ETX forum in particular.

Well, my first response would be to say "aperture is king" so go for the '90 if your budget can stretch (or even a 125 if you look at the second-hand market).

However, you ask about an ETX for imaging.

The mount that the ETX has (an Altitude / Azimuth or Alt-Az) is NOT really suitable for imaging - unless you are looking to image the Moon and the brighter planets.

The Alt-Az mount is only really suitable for SHORT exposures. Anything longer than about 30 seconds will introduce "field rotation", and the only way around this is to polar align the telescope and drive the telescope in only one direction (Right Ascension). The Meade field tripod has a built-in wedge to facilitate this.

If you plan on taking images of Deep Sky Objects (or DSO's for short), then an Alt-Az mount is not really suitable for this purpose. The gearing inside the ETX mount is also really not up to the job.

To get great astroimages, then a stable equitorial mount (known as a GEM) IS A MUST. These are polar aligned and have more expensive (and precise) metal worm gearing.

Cheap scopes with a stable mount will out-perform more expensive scopes on poor mounts.

You also need to think about WHAT is doing the imaging. Most folks think that a DSLR is the way to go, but many people use webcams (often suitably modified for long exposures) and then stack many, many images using suitable software to improve the S/N ratio.

You can, of course, get decent images of the Moon and brighter planets using a digital compact camera but again, several frames that have been stacked, along with suitable "flats" (that is all over white frames) and "darks" (that is all over black frames) will improve matters dramatically

Art

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If I like it, the wife says that we can't afford it!
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Meade ETX105 (a nice "Grab & Go" scope) & Celestron NexStar 6SE with Bob's Knobs.

Various EP's from 6mm to 26mm, Baader Hyperion 8-24mm Zoom, a 2x Barlow, 2" diagonal and 7Ah PowerTank.
MRF and Antares 8x50 RACI finder scope - both for the 6SE's OTA, whilst the ETX gets a plain RDF.

Canon EOS 400D DSLR (un-modded) and SPC900 webcam. Finally climbing the AP Learning Curve!

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