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Posts Made By: Mike Hosea

August 27, 2003 04:33 PM Forum: Telescope Making

lightweight focuser.

Posted By Mike Hosea
My recommendation:

http://www.kineoptics.com/HC-2.html

Your existing focuser looks a little tall, so you might want some kind of interface plate between the HC-2 and the cage to put the focal plane at the right place. Not sure, but it should be easy to adapt in any case. Getting farther back is always easier than getting closer in.
--
Mike

August 29, 2003 03:23 AM Forum: Telescope Making

1.25" or 2" Kineoptics focuser for 7" f5.7 Dob

Posted By Mike Hosea
What size is your secondary, and how far is it from the secondary to the focal plane? My basic thinking is that you don't want to rule out 2" eyepieces if you have enough illumination to take advantage if the desire should arise, but if not, then 1.25" is a good way to go.
--
Mike

September 1, 2003 03:25 AM Forum: Eyepieces

Using a 2" barlow with 1.25" eyepieces

Posted By Mike Hosea
2" Barlows usually have longer focal lengths as compared to their nominal magnification factor. This is a GOOD thing. It leads to less vignetting and pupil throwout. Problems would be things like balance or perhaps protrusion into the light path of Newtonians with low-profile focusers--that sort of thing. I have no opinion on the current UO model. The one I tried was nothing special, but it was an earlier model. The Tele Vue Big Barlow is a safe bet, as is the Astro-Physics Barcon. And of course there is the Tele Vue 2" 2x PowerMate, which may work better with your longest focal length 2" eyepieces than the Big Barlow.
--
Mike

September 3, 2003 03:14 AM Forum: Equipment Talk

Barlow vs Powermate

Posted By Mike Hosea
There's a huge difference when used with long focal length eyepieces since vignetting and pupil throw-out are eliminated. Also, you get approximate parfocality in 1.25" star diagonals. Frankly, I prefer the Barlow with shorter focal lengths. As to why 2.5x? No clue. Maybe it had something to do with the fact that the 5x 1.25" Powermate came first. Also the old 1.25" Tele Vue Barlows were 2.5x and 1.8x. I don't think Tele Vue has any special appreciation for building a set of eyepieces around specifically a 2x Barlow.
--
Mike

September 3, 2003 08:07 PM Forum: Equipment Talk

Maximum Useful Magnification

Posted By Mike Hosea
The atmosphere is a variable filter. Sometimes it ruins the image at relatively low powers, and sometimes it doesn't. There's also the matter of getting enough retina involved to easily make out fine detail. I routinely use about 362x in my 10" Dob on targets like the moon and Saturn. These targets tend to have plenty of contrast to spare for most detail. Jupiter and Mars tend to look better in the 200x-275x range. Going higher seems to drop the contrast too much. As for maximum, I sometimes use 50x per inch with the moon and with globular clusters. I have gone higher, but have rarely (never?) had a better image than at about 500x. For one thing, I have problems with floaters.
--
Mike

September 8, 2003 01:37 PM Forum: Equipment Talk

need help with a meade 14mm uwa

Posted By Mike Hosea
Roman,

The lens layout can be found on the Meade site. However there is only one retaining ring for the upper part of the eyepiece, so IF everything is in its proper place, you should be able to stop the rattling by hand-tightening the retaining ring.
--
Mike

September 9, 2003 05:17 AM Forum: Eyepieces

Nagler type 4 and 6?

Posted By Mike Hosea
The 12mm Type 4 (the oldest Type 4) is a 6-element eyepiece with plenty of eye relief. The 11mm and 13mm Type 6's are newer in design, have 7 elements, and sport 12mm of eye relief. The eye relief difference is one reason why the sizes are so different. Another seems to have something to do with the Type 6's employing more high-index "exotic" glass types. The price difference reflects the different costs in making these eyepieces, and the type 6 and type 4 designs are apparently very different--no reason to expect their costs to be similar just because their focal lengths are.
--
Mike

September 9, 2003 05:00 PM Forum: Equipment Talk

UO Prism for MK-67?

Posted By Mike Hosea
If the UO prism diagonals are still made in Japan, I'd say yes, they are significantly better than the stock cheapos. A 'correct-image' prism is still just one hunk of glass, but it has more facets than the standard right-angle.

I think the standard prism should work fine. There are things to worry about with cheap mirror diagonals, too, e.g. collimation is frequently a problem with any mirror diagonal that is plastic or cast metal. If you bother to deal with such problems in an inexpensive diagonal, those high-end diagonals made of machined aluminum can start looking more and more like bargains.
--
Mike

September 9, 2003 09:24 PM Forum: Equipment Talk

Derlin tip screws

Posted By Mike Hosea
Maybe McMaster-Carr? (www.mcmaster.com). Scopestuff (www.scopestuff.com) is also a good place to find hard-to-find things of that nature, but it will cost you.
--
Mike

September 11, 2003 04:59 AM Forum: TeleVue

Powermate vs. eyepiece only

Posted By Mike Hosea
Yes, the Powermate will retain the Nagler's 82 degree apparent field of view, but of course it will be an 82 degree field on what is effectively a 9/2.5=3.6mm eyepiece, kinda like a 3.5mm Nagler.

The main downside is that you're talking about a 3.6mm eyepiece comprised of 11 optical elements in 6 groups, whereas a 3.5mm Nagler Type 6 would have 7 elements in 4 groups. An experience planetary observer should be able to see the extra scatter from the additional 4 air-to-glass surfaces in the combination with the Powermate, but the image should compare well in terms of sharpness, and probably most observers would not feel disadvantaged. The 4mm Radian will give a little bit less magnification and so might be preferable in some scopes for that reason at least.
--
Mike

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