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Posts Made By: Ron Oehlert

September 10, 2003 08:57 PM Forum: Telescope Making

Replacing or augmenting a focuser

Posted By Ron Oehlert

Sounds like you don't have an original focuser. 4" distance from tube would have been about right for *tall* focusers of the day, especially with the Parks or Telescopics' sky-micro focusers (both were original equipment depending on model/year of mfg). You could place a spacer block between focuser and tube, replace the focuser, or move mirror/cell further back in tube to compensate; this last will require re-collimation of primary, but that's not difficult. I wouldn't replace the tube; it's a Parks fiberglass and much better than anything else. Some long-focus Cave Astrola 10" scopes had an add-on Parks shorty tube at the mirror end to extend the length (as seen in S&T ads), both aluminum end-rings mated. You might contact Parks for such as another alternative if you require the additional tube length. If the mirror is original (will be engraved in script with Thomas Caves' own hand on rear) then you have a fine scope indeed. Ron

September 11, 2003 09:44 PM Forum: Eyepieces

Scopestuff eyepieces

Posted By Ron Oehlert

Just search forum for UltraWide, these are the same as the ones sold by Orion (Expanse) and others (Skywatcher) and have been discussed here previously. Ron

September 20, 2003 07:35 PM Forum: Telescope Making

Front Aperature Calculations

Posted By Ron Oehlert

See the disscusion between myself and Vladimir on 9/9/03, subject Diagonal for Photography, 5 pages back. Your present aperture will act as a baffle, and may be a good thing. Our discussion was not limited to photo-only scopes. Ron

September 20, 2003 07:59 PM Forum: Equipment Talk

Orange C8 Info

Posted By Ron Oehlert

How much dust is too much? Actually dust scatters less light than you would suppose and in moderate amounts affects performance not at all. So 1st do no harm, because a scratched optic is scratched forever. In over 30 years I've cleaned my 6" newt mirror (open tube at both ends) only a few times (a few times too many). If sending to Celestron or losing observing time on Mars for instance is not in your budget now, then do so later and don't worry about it. Ron

September 22, 2003 07:00 PM Forum: Telescope Making

scratch on primary mirror

Posted By Ron Oehlert

Possibly (probably) it will scatter some light; but the amount of scatter should be negligble, I.E. you won't notice it (your eyepieces probably scatter more light than would be introduced by a scratch). Also, examine the scratch with a magnifying lens ( a low-power eyepiece with barrel removed would do, as long as lens set remains in housing), it may just be a sleek in the coating rather than a scratch in the glass itself; in this case more sleeks may occur due to frequent/inappropriate cleaning method(s) and when you eventually re-aluminize the mirror the *scratch* will be gone. Also, if this scratch is primarily in the central area *hidden* by the secondary shadow (as is your index mark) then it is of no consequence. Ron

September 27, 2003 08:07 PM Forum: Equipment Talk

Diffraction rings

Posted By Ron Oehlert

If all you want to do is check collimation, then even a big blur will do. Center the out-of focus bloated image of a star or planet and see that the central obstruction shadow is also centered within the image. I always do this 1st when I bring the scope out for the night. Temperature stabilized optics & lack of turbulance (local and atmospheric) together with high power is needed to define the rings within this bloated image, and their similarity between the outside-of-focus and inside-of-focus images indicates optical quality. If you need to adjust collimation, place a finger in front of the scope and use it's shadow to help identify the proper screw. Ron

October 4, 2003 06:23 PM Forum: Equipment Talk

Edmund and UO orthos

Posted By Ron Oehlert

That's an interesting question. I assume they are from the same Japanese factory, i.e. circle T branded. However, Edmund has offered these same ortho's for decades ($17 in the early '70's) and judging by past/present Edmund Technical Optics catalogs showing various astro eyepieces, barlows & focusers their stock/offerings of some previous items has become depleted over the years. If the Edmund orthos offered today are from past, much older stock I'd be inclined to pay the premium. I have a Parks supplied 12.5mm circle T ortho purchased decades ago and it's (my example) optical quality was condsidered exceptional by a former director of the ALPO. Whereas the design should be same, opticians pass on and perhaps the prior generation were more keen. If an inquiry to Edmund on the status of the original stock purchase indicated older production, I'd pay the premium with no qualms myself. Otherwise they should be identical. Ron

October 5, 2003 10:45 AM Forum: Equipment Talk

UO Orthos Overated?

Posted By Ron Oehlert

That S&T review did state within the text that those Orion orthos were not up to the performance of ortho's in general. They also had a different body/barrel than the current UO offerings. At the time of the article, those Orions's were basically the only common ortho's in the US marketplace, except for Edmund's (who were pushing their RKE's instead). Ortho lens sets can be mfg with identical radii for economic reasons, but those are not up to the true Abbe in performance. Ron

October 5, 2003 06:32 PM Forum: Equipment Talk

Lunar viewing

Posted By Ron Oehlert

Besides a designated moon filter, an orange or yellow filter will reduce glare/improve contrast on the moon and serves double duty as a planetary filter. I've used inexpensive gelatin filters from photography stores cut to fit in a plastic slide holder held between eye and eyepiece. Ron

October 12, 2003 10:30 AM Forum: Equipment Talk

Question about different Solar filter styles.

Posted By Ron Oehlert

The main difference between full-aperture and off-axis solar filters is initial cost. Ron