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Posts Made By: Ron Oehlert

July 18, 2010 05:40 PM Forum: ASTRONOMY

Package lost between Canada and South Carolina

Posted By Ron Oehlert

Rather than Lost & based on my own Canada-to-USA as well as ordinary Parcel shipments within the CONUS, my opinion is that you simply have not allowed sufficient time for delivery. Be patient a bit longer; I've also ordered from world-wide many times.

July 30, 2010 08:27 AM Forum: Telescope Making

Wax bearings?

Posted By Ron Oehlert

Applying a coat of wax to bearing Surfaces affects Friction of those surfaces but the wax itself does not provide Support.
Wax is relatively soft & if were the sole supporting material should deform under the weight of the scope.

August 1, 2010 10:48 AM Forum: Equipment Talk

Alignment of my hybrid Ultima 2000

Posted By Ron Oehlert

Prior to GoTo computers, mounts were manually aligned. How-To instructions can be found in older Amatuer Astronomy or Telescope Making books available from your local Public Libary.

August 7, 2010 07:30 PM Forum: ASTRONOMY

Good Seeing?

Posted By Ron Oehlert

Hi, given your apparent penchant for accuracy from the lunar eclipse discussion below, what was the actual observed seeing per the venerable Scientific 1-10 Seeing scale at the time of observation? The CSC 1-5 scale is just a prediction for advance planing purposes & should not be applied to recording actual observation conditions, eh?

August 13, 2010 10:45 AM Forum: Refractors

collimating a refractor via diag. (non coll. lens

Posted By Ron Oehlert

Of course it is wrong (but it may be tedious to improve on the present setting). If rotating the diagonal shifts the center, then the diagonal is not fully collimated with respect to 90-degrees (the tubes may be mechanically offset). If the circles are not centered, then again the diagonal is not accurately collimated. BTW, I've found an old Edmund Prism diagonal to be far more accurate with respect to center AND more importantly, high-magnification planetary resolution than a modern expensive dialectric mirror diagonal (despite RCs' claim that diagonal mirror surface accuracy matters not). If you cannot align the diagonal any better, THEN do your critical observing with the diagonal in its' best orientation AND place the object of interest in the off-center spot where the alignment is best. In addition to diagonal alignment, objective alignment & focuser alignment are also factors.

August 18, 2010 11:30 AM Forum: Beginning Astronomy?

Light Polluted Skies - TMB 92 SS or 130 SS?

Posted By Ron Oehlert

Reality is that travel itself is never as convenient as ones' backyard. I'd opt for the larger scope which has more resolution & light grasp regardless of location, and just put up with the greater bother when travel is possible. BTW, if you have any yard available, locating over grass is better than on concrete patio per local Seeing conditions.

September 6, 2010 08:59 PM Forum: Home Observatories

Something Missing?

Posted By Ron Oehlert

Not with the furnace/water heater venting where they do = very poor viewing from or over roof top.

February 18, 2011 10:30 PM Forum: Eyepieces

Plossl vs. Ortho

Posted By Ron Oehlert

No apologies neccessary, we all started at the beginning. Be aware that true Plossls are not common; most such named are simply symetrical types (both lenses are identical). And some so-called orthos are in reality symetricals, too, if examined via disassembly. But well-made examples of either should provide virtually same detail in the view. And many of either type are made in the same overseas plant but with various *Brands* applied to order. True ortho examples are the no-longer produced vintage Telescopics & UO Pro series (same eyepiece with different top caps) or the old Meade professional series. The present UO orthos are same as the common orthos offered by most suppliers in days past & poccess same-curve elements (very good, but not as good as the dis-similar curves true orthos 1st mentioned above). Excellent True Plossls are the former Claves & the still-made Vernonscope Brandons. Per your questions intent, purchase well known Brands of either labeled design if buying new & realize fine results. In that context, labeled design is of little matter to viewing results (merely ad hype instead) but quality mfg is (avoid budget examples). A longer focal length eyepiece will offer greater ease of viewing & when combined with a Barlow amplification lens retains that ease at higher magnifications, surpassing the result of equivalent shorter focal length eyepieces alone. Example: a 25mm or 20mm focal length eyepiece will provide 20X~36X or 25X~45X with your 500~900mm objectives & a 2X or 3X Barlow doubles or triples those magnifications. Equivalent high powers from a single 6mm eyepiece requires the eye to be placed uncomfortably touching the eyepiece.

February 20, 2011 11:17 AM Forum: Beginning Astronomy?

10" DOB Why can't I see the obstruction?

Posted By Ron Oehlert

If you used a long-enough focal-length eyepiece you Would see a shadow of the secondary mirror superemposed on the focused image, but such a long focal length eyepiece would also be impractical due to its' having an exit pupil much larger than your eye can manage, so much of the scopes' 10" aperture would be wasted (the maximum human eye pupil dilation in a dark-adapted situation is about 5 to 7 mm depending on the individual & as previously mentioned a 32mm focal length eyepiece provides 7 mm diameter exit pupil in your scope so is the lowest power eyepiece you can use most effectively). An easy way to actually see the effect is to place a finger directly in front of one of your eyes with Both eyes open; notice it appears as if you are looking thru that finger when looking at something across the room. In such a way the larger primary mirror seems to look thru the smaller secondary mirror even tho the secondary is directly in the primarys' incoming light path. This Secondary obstruction is the inherant defect of a Newtonian reflector, a refractors' inherant defect is defocusing of the various colors of light since from the center to the edge all magnifiying lenses (even eyepieces) resemble Prisms in cross-section (prisms turn *white* light into a rainbow of individual colors). Unobsructed reflectors have Coma (a flaring of star images away from the central axis) as their inherent defect. Each such defect affects the image similarly so given equally well-made & same-size optics, each telescope type performs equally per image resolution. Newtonian optical design reflectors such as yours (Dobsonian refers to the mounting arrangement) are easier & lower cost to implement than equal aperture refractors or tilted-component off-axis reflectors due to fewer optical surfaces to make well and glass quality (reflectors do not look thru their glass). Hope this helps.

February 20, 2011 11:48 AM Forum: Beginning Astronomy?

10" DOB Why can't I see the obstruction?

Posted By Ron Oehlert

Joe, in your scope a 12mm eyepiece magnifies 95X, an 8mm provides ~140X & a 4mm gives 285X. I would think the 4mm could be used effectively only rarely (image becomes dimmer & less sharp at high magnifications) when the Earths atmosphere that you are looking thru is very steady. And even 95X is rather high for much Deep-Sky (nebulae & galaxies & star clusters) viewing. When you acquire a 20mm wide field (or even a 16mm wide field) type eyepiece & either a 28mm, 30mm or 32mm lowest power eyepiece you will be thrilled even more! So you still have something to look forward to beyond your 1st view. 32mm will give you 35X (28mm = 40X), 20mm = 57X & 16mm = ~70X in your scope; 32mm will give the widest True Field of view possible in a 1.25" barrel size & would provide great viewing pleasure while casually sweeping the Milky Way. True field is the actual area of sky seen & Apparent field is the angular width encompassed by the eyepiece itself (Wide Field types have greater angular area); a wider Apparent field does provide a wider True field vs same focal length eyepieces of lessor apparent field.