Discovery Telescopes 17.5" f/5 TD

4.0 Discovery 17.5" Truss Dob

Very nice optics and a functional structure at a reasonable price.

Construction quality not the greatest.

I purchased my Discovery 17.5" truss dob used via Astromart, and I'm pretty sure this particular one was made about 2004 or so. The scope is fairly well constructed although the use of staples for much of the assembly reminds me of cheap furniture. I've had to beef up part of the rocker box with wood screws because the staples were coming loose.

As with many commercial dobsonian scopes, this one is front heavy when used with a heavy eyepiece (and that is with just a Telrad mounted on the OTA). I replaced the stock JMI DX-3 focuser with a dual speed Moonlite unit - much nicer to use. The scope is just narrow enough to fit through most doorways with the wheelbarrow handles attached which makes moving the heavy structure much easier. The scope holds collimation pretty well, better than most truss dobs I've used. The optics appear to be very good although I've not had good enough seeing to push them to the limit. A cooling fan or better yet, fans are required to get the nearly 40lb mirror cooled near ambient temperature and to minimize heat current turbulence from the mirror. My particular example has a plywood and kydex upper tube assembly which much nicer looking and I would guess lighter than the current version which uses a piece of sonotube for the OTA. One thing is for sure with this scope - a ladder is required since the eyepiece height at zenith is 87".