Posts Made By: Jim Richberg

I have *two* of the "20-45X" Nikons (which APM translates as 9-21mm) for use with my binoviewers. They are definitely brighter than any other zooms I've used (N.B.--I haven't had the fortune to try a Leica).

They are advertised as parfocal throughout their zoom range-- they're not, although the focus adjustment is minor. They're not quite as crisp in image quality as a good ortho, but overall I'm quite satisfied with their views.

My biggest complaint is on the zooming mechanism-- while the knurled/rubberized area in the middle of the eyepiece would seem to be the zoom and can be rotated, I believe it is actually part of the APM adapter. The zoom mechanism is a ring at the top of the eyepiece and has the rubber eyecup attachee to it. This will not be intuitive to anyone you let use the eyepiece-- even if you tell them about it first. I've also found it fairly stiff to turn (it requires enough force that I tend to use my free hand to prevent the eyepiece from slipping in the diagonal or binoviewer holder).

I had something similar happen last winter. Well, actually there was no dog or truck involved, but on a not-too-chilly winter night (barely below freezing) my Astrozap shield also split next to the velcro when I loosely rolled it at the end of my observing session prior to returning it to its mailing box for storage. I emailed Joe on repair options, and he instead replaced it for no charge.

This is the kind of customer service that gets my repeat business.
Jim

Actually Jeff, older laptops have the advantage over the new Pentium 4/Athalon-class machines for telescope control, since the new laptops seem to have abandoned including an RS232C serial port in favor of USB ports exclusively. Your scope interface will probably be through a serial port. There are USB to serial adapters, but that's an extra piece of hardware, and I've heard that some of them have timing issues when used with planetarium programs and don't accurate track the scope's position or send it data at the appropriate rate. At the same time, you'll possibly/probably want at least one USB port to keep you CCD options open. Most "middle aged" laptops (Pentium II's or III's) had both a serial and a USB port, so you ought to be fine with an Ebay or other second-hand machine.

"How much" processing power is adequate depends largely on the software you will use. I've used some planetarium programs like Earth Centered Universe that run quickly will on an old Pentium II/266 mhz machine, and others like "Cartes du Ciel" that want something faster than a gigahertz of horsepower if you aren't going to wait 10 seconds for each screen update. I've heard that The Sky is another computationally quick one.
Jim

Ryan,
I went in search of the same thing, in my case because I wanted to display every star I could see in the field of a 16" scope when I was playing "what's that object" or "what's the faintest thing in the field". There doesn't seem to be a perfect solution, but the following three Catalogs will take you deeper than the Tycho catalog in Cartes du Ciel, which has "hooks" to allow youto display them. "The Sky" level 4 can use them as well. Other programs may use them, but these are the only two I've tried first-hand.

1. Hubble Space Telescope (HST) guide stars-- 19 million stars down to Mag 15. The GSC-ACT is a more compact storage of this data, with the coordinates adjusted to correspond to those of the Tycho catalog. Fits on one or two CD's.

2. USNO SA 2.0-- 55 million stars, mostly mag 16-19 Fits on a CD, I believe

3. USNO A 2.0: 525+ million stars down to mag 20. Takes 10 CD's.

The problems with the HST and USNO SA catologues in my experience are: 1. they are intended for guiding purposes rather than as a comprehensive sky survey, hence in densely populated areas of the sky they omit a fair number of stars; 2. because they are compiled by computer, they contain some spurious data (spikes from bright stars etc.) and can have coordinates-- or more typically, magnitudes-- that are somewhat off. The GSC and USNO SA datasets would seem to be complimentary in their coverage by magnitude, but in fact they overlap a fair bit and if you have both toggled on in your planetarium software, some brighter objects may be displayed at least three times (once by each catalog plus whatever stellar baseline data your software uses). This is visually confusing, although you can de-conflict things by looking at the data for each object displayed.

The USNO A 2.0 dataset I believe is comprehensive (with half a billion stars, you'd certainly think so!) but is too large to be distributed in toto over the internet, and the Naval Observatory has run out of copies to give out. Bill Gray of Project Pluto has started a number of sets circulating on a "loaner" basis for folks to copy and pass on. (I've got one, in fact.)

Hope this helps!
Jim

Doug,
I replaced the hex bolts on my 2.14 with "Serv-A-Lite Clamping Knobs" that have black plastic heads with a nicely milled ringe aroudd the top for easy hand-turning. I found that #10 size, 32 thread per inch in 1/2" length worked fine for my holder. I got mine at a Sears Hardware store for $1.99 each. They work great!
Jim

It's a standard 1/4" coarse threaded bolt-- I don't recall the length off-hand. You can probably find this dimension on-line via a search (especially since many have used the bolt hole for a mirror lock-up), at the MAPUG archives, or the Meade web site.

Alternatively, since the bolts cost a nickel or less at the hardware store, you can buy a couple of different lengths and try until you get the right one. (I think it is between 1.5-2").
Jim

David,

You don't say how good the surface accuracy of your current mirror is-- going from a run of the mill 1/10 wave secondary-- possibly with a turned down edge-- to the typical "quartz quality" uniformity of flatness will make a huge difference. IMO this is probably even more significant than the backscatter reduction from the smoother polish. I recently upgraded an indifferent quality (and poorly mounted) Meade 4" secondary to a high quality (1/15th wave, 1/100 RMS, Zygo certified) Pyrex 3.1" one, and the difference was like night and day! Together with a 0.25" masking of my primary to cover the mirror clips and a TDE, I was able to *double* my useful magnification ceiling from 360X to 700X on a 16" scope. I'm beeh toying around with the idea of having a custom-made 1/20 wave 3.1" quartz diagonal made to see if it yields any further performance increase over the Pyrex one. I probably wouldn't see the difference in performance more than a couple of times per year, at best.

Jim

John,
I've had good luck with Astrosystems, Protostar, and Novak secondary holders and spiders. I especially like the Astrosystems four-point "tool-less" approach (thumbscrews) for collimation on 3.1" and larger holders, and like the Protostar clutch system. (I ended up making my own holder that combined features of both!).

Astrosystems also makes highly-regarded primary cells; I'd stay away from the UO one because their "nine point" suspension is actually nine rubber pads on three radial arms, vice floating triangles.

I've got a JMI DX1 on my 16" Dob, but if I were doing it over again I'd look seriously at a Starlight Feather Touch focuser. Get a two-speed model if you are planning to do much planetary observing.

Re secondary mirrors, the best deal I've found has been Antares Optics. (They're a sponsor here.) They test each of their pieces and send the Zygo interferometer print with each, and their prices are good to excellent, depending on size and availability from stock. I have a Pyrex 3.1" (1/15 wave, 1/100 RMS) and a fused quartz 2.14 (1/18 wave, 1/100 RMS), and both have performed up to their specs.

Jim

Vladimir,
As with every thing else, "it depends". Some of the factors are:
1. How comfortable are you with ATM'ing and tweaking/improving on a manufactured scope?
2. How much weight are you comfortable hauling around?

I was in your shoes a couple of years ago -- I had a 10" LX200 and when I saw a two month old Starfinder 16" within driving distance for sale here for under a thousand bucks, decided to get it for the 3-4 times per year I was likely to go to dark mountain skies. It was virtually unusable in its stock configuration (Meade cut more corners than I could count), but when I got done customizing it I had a scope that is so much superior to the LX200 for visual work that the old SCT only gets used once or twice a year when I decide to go imaging! Aperture really matters-- I can see color in M42 and consistently pick out 6 stars in the Trapezium, neither of which I could do with my 10" SCT.

Some say the Meade-- much less any f/4.5 scope-- cannot be a decent planetary performer. I strongly disagree. I've been able to use mine above 700X, and recently saw the Maxwell Division in Saturn's rings, plus did the tough double split of Gamma Virginis/Porrima (nearing 0.5 arc-sec separation). On my last clear night out, my scope was at one of our club sites in the company of an Obssession 18 (Zambuto mirror) and a JMI NGT-18 (Galaxy mirror) and fully kept up with them in terms of optical performance. (I think my collimation was better, which certainly helped.)

The Meade mirrors of late have been pretty consistently "OK". Odds are you'll get one with a turned down edge and a raised center (masked by the oversized secondary), but the surface will be smooth and the Strehl and RMS will be "diffraction limited" even if the Peak-to-Valley rating is mediocre. I found that masking my primary by 1/4" both covered the mirror clips (major diffraction producers) and boosted the Strehl and RMS significantly. You'll also want to either downsize the secondary or at least remount it, since Meade's tape mount generated enough internal pressure to create horrible astigmatism in my secondary.

A Starfinder is a good way to "start modestly" and then customize/upgrade component by component. I've more than doubled my initial investment in the scope... but now its fully customized for my body, observing style, and mode of transportation (everything is "quick release" to fit in my car), has DSC's, Dob-Driver motorization, a JMI DX1 two speed focuser, a Short tube 80 and Telrad finders, and an upgraded secondary and associated hardware. Buying all of that on a ready to use scope would have been considerably pricier.

OTOH, if you're looking for immediate gratification and a good experience out of the box, I'd steer towards a smaller but higher quality scope at a similar or slightly higher price point. Jim

Gary,
If you've got access to a group-- be it A) a Special Interest Group, B) workshop (like some of the Clubs run periodically), or at least C) a glass-pushing friend, it will be far easier. I went with option B-- a weekend workshop run by a club (Delmarva Stargazers) for my initial foray this past February. In about 14 hours of hard work I ended up with decent 10" Pyrex mirror (1/10 P-V, 1/45 RMS, super smooth polish). It isn't rocket science (but it is an art!), and mistakes (other than breakage) aren't critical since 'anything you grind in, you can grind out.' Try it, you'll like it! Doing it solo out of a book would be a lot more daunting, though. Jim