Posts Made By: Ron Oehlert

Recently discovered an 8" f/7 in town w/o filtration provided what a 6" f/8 reveals in the country per dso's, so now have a 12" f/5 town project and a 10" f/4.5 easily-portable instrument to play with whenever the snow melts (at my age my feet are too unstable to risk an icy fall). Despite some town light pollution, the Milky Way is still naked-eye visible from my backyard altho not so prominent as in the country; do you think nebula filters would be of worthwhile benefit under such circumstances (I've not tried them)? Out of town is still the typical jaw-dropping rural Kansas skies of which *Scotty* Houston wrote about in his former S&T column.

Like most such suppliers, Optica b/c was an importer, not a manufacturer. Typically this may have been mfg by Circle-Tee or other Japanese mfg; look for a possible stamping on the side to indicate mfg. Any given Barlows' magnification is determined by it's negative focal length & distance lens is placed in front of an eyepiece (vary that length & vary the magnification factor). Fixed-power Barlows typicaly require an eyepieces' focal plane be placed at or very near the top of the Barlow housing in order to achieve the stated magnification (other placement results in other magnification, a spacer tube will result in greater magnification same as placing a Barlow in front of a Star diagonal vs after).

A fixed dovetail mounting on a GEM Newt reflector will result in some precarious (if observer is on a ladder) or at least uncomfortable eyepiece positions (typically with fixed mounting the eyepiece axis is parallel to the Declination axis and opposite the Declination counterweight for all-sky usage). Far better are clamping rings around the tube or mirror cage which allow repositioning (by rotating around the optical axis) the eyepiece orientation with respect to where the scope is pointing. If an open-truss tube is used with a dovetail-mounted mirror cage, then a fully-rotating upper cage is required for varying eyepiece orientation (this method requires great precision in upper cage to tube construction to retain collimation per object to object). My own 6" f/8, 8" f/7, 10" f/4.5 & 12" f/5 reflectors are all GEM mounted with rotating clamp rings which provide for comfortably prolonged observations and can readily accomodate all ages (heights) of viewers. The one exception I can think of & pertains to your larger aperture, is that a fixed focuser mounting which aligned downwards in the same direction as a GEM's declination shaft counter weight shouldn't be too high off the ground for most observing from the Northern hemisphere; except at the Zenith or near the horizon, you'd always be tilting your head backwards & looking slightly upwards into the eyepiece with such an arangement.

From a simple web search per US-Canada border crossing regulations: U.S. citizens do not need a passport for travel to Canada; all that is required is a photo I.D. and proof of citizenship such as a birth certificate. The telescope can be considered personnal baggage regardless of whom transports it.

I also have 10" f/4.5 Starfinder and it too has an excellent mirror, besting my 8" f/7 Cave Astrola on Jupiter the other night. The Cave mirror dated Aug 1971 displays identically perfect star-patterns on each side of focus while the Meade is not quite so perfect but sufficient that it's greater aperture wins the resolution contest along with greater light grasp as a bonus. I've mounted my 10" Starfinder on a Starfinder-16 GEM with Parallax rings and exchanged the original 6X30mm finder with a 10X60mm and upgraded the stock focusser.

That seems to be a long focal length negative lens or a weak Barlow. Any Barlow will move the focal point back, but typical commercial Barlows provide too much image amplification for anything but lunar & solar system photography.

Multi-coated lenses often have a green color while single-coated lenses typically appear blue. Differing focal length objectives accounts for longer or shorter tube. IOW these two examples were either made at different times or in different factories or even out-sourced. Makes no diff unless you were wanting to binocular mount them, however the longer focal length one may provide sharper views especially near the edge of the FOV (trial them on the Moon tonight).

They used to be marketed as high-resolution eyepieces for Lunar & planetary examination. They are true dis-similar Plossls with good back focus and narrow AFOV compared to today's norm. I have an earlier 1.25" set preceeding the rubber eyecups with a 2X friction-fit Dakin (available in 2X & 3X before the 2.4X mounting became their std). Questar contracted with Venonscope for eyepiece production, thus the treaded version. The eyepieces preceeded the scopes (Chester Brandons' eyepieces originally before Vernonscope took over production), so likely they were originally aimed at long-focus achromats & reflectors but due to their design also worked well at shorter focal ratios. At the time of the Vernonscope 94 refractor, Vernonscope also marketed a 20mm *Brandon* wide angle which was a very nice imported Japanese Spottingscope-threaded Erfle fitted with a 1.25" adapter that also accepted Vernonscope filters; this eyepiece was short-lived in their lineup I suspect due to being Not *made in usa* despite it's excellent quality. Vernonscope also marketed their own mfg 1/2" fl Erfle with an 85 degree AFOV.

Clear, cold (below freezing) and no wind in central Kansas allowed great viewing all night. Limiting naked-eye visual magnitude was 3 during totality here in town. Seeing was poor, about 4 or 5 on the 10-point Harvard Observatory scale so I left Mars & Saturn for another night. With the unaided eye & telescopic views the Moon appeared pale orange just like Mars. Scopes used were a 10" @ 35X and a 5" @ 16X plus a 10X60mm finder. Took a moment to also view M-13 during totality and it showed well @ 80X despite the poor Seeing.

My 20mm & 15mm QX are arranged thus (but only three spacers): from the eye end, a thin-edged plano-convex singlet with plane(flat) side towards eye, followed by a thick doublet (look for a line around the edge that indicates two lenses glued together) with it's flat or flattest side towards the eye lens, followed by another plano-convex singlet (which has a somewhat thicker edge than the eye lens) & arranged with it's curved side towards the eye end, finally a plano-concave(inward curve) singlet with it's flat side towards the field stop or telescope side. Yours should be similar, and select spacer arangment that prevent each pairing from actually touching each other (although they may be quite close on axis). IOW, try the thinnest lens placed flat side towards eye end, followed by the thickest lens with it's flat side also towards the eye end, followed by the other positive (outward-curved surface) lens placed flat side towards telescope end and lastly the negative lens (the one with an inward-curved surface on one side) placed flat side towards telescope end. The spacers prevent adjacent glass surfaces from actually touching each other (although they may be quite close on-axis) so examine closely to deduce which goes between which lenses; the correct arrangement might be a medium one between 1st pair of lenses, thickest spacer (or perhaps two spacers?) between next pairing followed by the thinnest spacer last (in front of the concave lens element). When assembled correctly, the field stop should be in sharp focus & a fingertip or other object placed within the field stop should appear sharp when properly placed. If any lens has two curved surfaces, the least-curved side should correspond to *flat* in the above directions. I can't help with the 4th spacer, unless it were needed with another for proper width (as I indicated above) or required at one end; you may need to experiment with spacer placement.