Telescope Reviews: Explore Scientific 9mm 120°

I had 1.3 nights to use this EP. The first night had pretty good skies for Ft. Davis Texas, not as good as I have seen (like last year) but pretty good. The second night was a short session the was ruined by clouds early in the night. The other 2 nights it remained cloudy, so this observation report will remain sketchy.

The Ep is very sharp, both on axis and as far off axis as I can actually see.

The width of the FoV has a strange effect. Observers in the desert with nearly 180 degrees of sky and little obscuration of the horizon have a distortion effect. This effect is caused by both extinction and by refraction (through the curved atmosphere). The effects cause the stars on the very horizon not to look as if the sky were a semicircle but that of a bowl with a flattened edge. The sky "looks" flatter at the horizon than at zenith (or basically anything over 30 degrees.)

The 9ES120 has this same effect. Stars remain sharp with nary pin cushion nor barrel distortion easily visible. However, as one looks towards the ege fo the field, it looks to be farther away (like the horizon above) than it should be. Note carefully: this is not an effect associated with aberations in the EP (distortion being one of these).

It is a very comfortable 9mm EP to pan around the sky searching for stuff--although lower powers are more forgiving due to their wider FoVs. Comfortable in that the exit pupil is high enough off the eye lens that you don't feel constrained (like many EPs in this focal length). The flat undistorted FoV is nice to watch as one pans around--and I am generally one who does get sea sick when using EPs with significant pincushion or barrel distortions.

This report remains sketchy due to the atmospheric conditions and the short amount of observing time had with this EP in the focuser. The telsecope used was a 20" homemade DOB used with a Paracorr-1.

I did spend some time on NGC7331 and Stephan's Quintet nearby with the 9ES120. The visible FoV is about as wide as my 13E, the stars are sharp (as the sky permitted seeing.) I also compared this to my original T1 9mm Nagler. The coatings and light throughput of the 9ES120 was at least on par with the 9NT1 the scatter from the coatings less (20 years less cleaning, more modern coatings,...) and usefully more eye relief.

Anyway, that is my story and I'm sticking to it. Sorry for the brevity, but the skies just did not deliver an ability to test it more strenuously.

I did notice that the 9ES120 wants the Paracorr tunable top to be set at 5 whereas the 31NT5 and the 21E use position 1 and I have parfocalized my 13E to use position 1 also. The 9ES120 will get parfocalized similarly.

Picture included to scope out the monsters.