Telescope Reviews: Questions about ETX-90PE UHTC

I'll leave the photo and autoguiding to the more seasoned AP'ers here.

First off, the batteries. Generally you'll get about 16-20 hours cumulative usage off a single set of high-performance (alkaline or similar) cells. The rechargeables could present tracking, slewing and motor error issues. I say "could", which is all dependent on a case-by-case situation. Generally, the rechargeable cells have a 0.2-.03 volt drop compared to their non-recharge counterparts. With 8 AA cells, this can equate to a cumulative loss of 1.6-2.4 volts peak power right at the start. Depending on how "fussy" your motors are, they may work fine, and they may start balking at not having enough juice to run properly. This is why many folks run these scopes either off AC or carry an external battery or power supply like a PowerTank.

With regard to observing DSO's... depends on the DSO, largely. Globular and open clusters look pretty good, although because of the long focal length and relatively high magnitude, some of the larger ones will be harder to compose in the eye piece without dropping the power and/or getting wide field EP's. On objects like nebulae and galaxies... objects with low or diffuse surface luminosity... this may not be the best instrument for those objects, at least for observation purposes. At f/13.8, while the contrast would be good it would tend to dim the object to pretty close to the background. This is the same for the ETX-125, which is the "big brother" to the 90. I have heard some folks have overcome this somewhat by creative use of focal reducers and speciality filters, but haven't verified this myself.

In summary, these are excellent scopes for solar system objects and brighter DSO's. For fainter targets, you may need to consider something with somewhat faster optics (a short-tube refractor, for instance.)

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Tim

Champion of small aperture scopes everywhere!

Meade ETX-125PE
Meade ETX-80
Celestron FirstScope 76mm Mini-dob

Updated: 09/16/2009