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Posts Made By: Ron Oehlert

February 21, 2003 03:37 PM Forum: Equipment Talk

RFT telescopes

Posted By Ron Oehlert

The age-old definition is a telescope that has an exit pupil of ~7mm, or a magnification of about 1.43x per centimeter of aperture or 3.62x per inch. A wide AFOV eyepiece is mandatory. So at 36x, 3mm exit pupil, your xt4.5 does not qualify. Ron Oehlert

February 22, 2003 03:21 PM Forum: Equipment Talk

UO Super-Erfles

Posted By Ron Oehlert

Essentially true about the 20 swapped for the 25, but I don't know about the UO's. I have an old Celestron *Erfle* 20mm that is really a 25mm common ortho (Vixen) with the addition of a plano-convex extra field lens giving it a 20mm fl with the same true field as the 25 but with the corresponding wider AFOV. I also have a 6" f/8 newt and use this eyepiece alone or barlowed for most of my viewing, except for the occasional 32mm Konig type I (1.25" format) and a circle T 12.5mm ortho barlowed at the other extreme. I find this eyepiece has nearly the identical ortho performance as the 25mm mode (extra field lens removed) but with some very minor softening and distortion at the extreme edges. The UO's originally were advertized as a new 5-element format, and could very well be this ortho plus extra field lens configuration. BTW, this design was originated in the 1920's by Goerz using a meniscus field lens rather than a PCX with the usual abbe triplet and eye lens. Ron

February 26, 2003 06:52 AM Forum: Equipment Talk

eyepiece clean/repair question

Posted By Ron Oehlert

I've done this to all my eyepieces, more than once. You should know just by looking at it if you feel confidant in disassembly. I've used jeweler's screwdrivers and pocket knives to unscrew the retaining rings and was careful enough not to mar the finish. You have to be careful and remember or make notes of the order and way they face of each element. If you couldn't fix a faucet or a toaster or grind your own mirror, then nah, don't try this at home. But then I also repair old vacumm tube radios and stereos so I'm a bit of a tinkerer. Ron

March 19, 2003 08:52 PM Forum: Telescope Making

Folded / Flexed Reflector designs

Posted By Ron Oehlert

The 3rd reflection will turn things around from the normal orientation of east-west & north-south as seen in a newtonian reflector. Something to consider; it may even present a correct orientation as seen with the un-aided eye, or perhaps right side up but reversed left to right- the exact orientation I'm not sure of, but so informed of the change you can search out the new orientation. One advantage of flexed mirrors is that they can be tweaked to perfection in response to temperature changes during the observing period. Ron

March 23, 2003 09:10 AM Forum: Eyepieces

Uncemented eyepieces for solar projection

Posted By Ron Oehlert

Prolonged solar projection will indeed melt or burn the cement in doublet eyepiece lenses, and will also crack glass in uncemented designs. I no longer use projection in a 6" aperture due to ruined eyepieces, even cheap ones. DIY with film aperture filters is too inexpensive to do otherwise, advise him in this direction. Ron

March 23, 2003 06:06 PM Forum: Equipment Talk

Help with my focuser!!!

Posted By Ron Oehlert

What you want to do is measure the distance from the tube to your eyepieces (where they fit into the focuser) and choose a new focuser that allows that same freedom to focus. The height of the new focuser body, plus about half of it's focus travel, should be about equal to your present measurement. Ron

April 18, 2003 10:51 PM Forum: Telescope Making

fuzzy spider

Posted By Ron Oehlert

You are right. To repeat; A. Danjon believed that as the vanes cooled off they became surrounded by a layer of warm air that creates the spikes by refraction (rather than diffraction) and his colleague A. Couder eliminated them by covering the vanes with polished aluminum (S&T April 1978, page 354 in Gleanings for ATM's article Star Images in the Presence of Aberrations). My curved vanes are of aluminum and not painted. John Westfall, then director of the ALPO, praised this scopes' quality. Ron

July 19, 2003 04:35 PM Forum: Telescope Making

Mirror Aluminum Finishes

Posted By Ron Oehlert

Back in the '50's & '60's, it was well known that aluminum as a mirror coating oxidized in the presence of air to form an extremly thin, clear, protective AlO coating that didn't alter over time. The use of a hard SiO overcoat merely added further protection against sleaks, but was/is not neccesary to preserve the reflective surface. Dudley Leroy Clausing added berillium to aluminum to give it resistance to sleaks and his Beral mirror coatings were not overcoated (mine has survived decades). All the parts on my 6" reflector, including tube, are of either aluminum or brass, left *natural* with no clear overcoat. I removed the paint on focusers, etc. and buffed. Ocasionally I use Brasso on the brass focuser tubing, but for the most part leave alone. This scope has survived decades of outdoor extremes with no corrosion, and looks as good as the day I made it. Granted, except for the brass, my finish is satin but still you may wish to give your option #4 a try, and can always do further treatment later if not satisfactory.

July 19, 2003 07:45 PM Forum: Equipment Talk

Vignetting with nebula filter

Posted By Ron Oehlert

Since the inside thread diameter is about 28.5mm, anything you screw into it will of necessity obscure the edge of that 27mm field stop. But why does the filter have to be screwed in? It will also work held in front of the eyepiece between it and your eye, and now you have no vigneting.

September 7, 2003 10:28 AM Forum: Eyepieces

Meade Research Grade Eyepieces

Posted By Ron Oehlert

In 1978, there were 4mm, 7mm, 10.5mm, 16.8mm & 28mm ortho fl and 20mm fl erfle in the Meade Research-Grade line. By January, 1982, 7mm, 12.4mm & 15.5mm fl were added to the Research-Grade erfle line. From ads in S&T.