Posts Made By: Tony Leung

34mm axiom is decent on my 8" f/6 dob. Edge 20% does get a little unsharp - but not enough to bug me... However, the 34mm magnification is not one that I use too often on my moderately polluted suburb backyard...
Too bad, if you were in the bay area, i could lend you one to try

I currently have a XT8 dob. Looking to upgrading the scope (vs replacing all the major pieces - focuser, mirror, etc - which would cost just as much and I'll still have a ugly shell).

New scope (dob) requirements:
(1) 8" to 10" mirror with better coatings (96%+ vs 88%)
(2) Better mechanics - fit and finish, bearings, focuser, etc.
(3) f/6 or slower preferred
(4) small enough to move out from garage to backyard easily and observe and move around yard (to get different viewing angles to avoid lights) and tear down within 2 hrs (excluding cooldown)...
(5) Under $1.5K unless extra cost REALLY justifies what you get...

So what should it be? A Discovery 8" or 10" PDHQ? Or what?

How portable is a 10" PDHQ?

I've decided to upgrade (fix up) my Orion XT8 first, instead of blowing money into a new scope. Hopefully, I will appreciate my equipment more this way... The items I'll be attempting to change, in order of importance (one item at a time), are:
(1) Alzimuth bearing and/or surface.
(2) Secondary and Primary Mirrors
(3) Focuser

Let's start with item one: What is the best way to improving the alzimuth bearing surface and or bearings.

(a) Can I buy a circular base plate (with ebony star surface?) that I can use to replace that bottom circular piece which presses against the current teflon bearings (drilling and screwing ok, preferrable no cutting - especially circular cuts - and sanding).

(b) Or is there a thin circular bearing surface I can just add - screw in - to the bottom of my base, between the current laminate surface and the teflon bearings?

(c) Should I replace the teflon bearings also?

(d) Maybe someone sells the complete rotating base pieces complete with bearing and bearing surfaces that I can just screw into my current XT8 craddle???

My estimate for Item 1 fix should cost between $10 and $100. Any and all ideas (including any ideas where fixing up my xt8 is a mistake or good idea) are welcome.

Thanks

Now that I've got my azimuth bearing and future focuser upgrades pretty much figured out, its time to think about upgrading my XT8's primary and secodary mirrors - for that extra transmission (92% total vs 77% total transmission - equiv to an extra 3/4 inch in aperature right?) and quality difference - better smoother surfaces and pyrex low expansion...
Thinking about Discovery 8"f/6 enhanced mirrors and diagonals...

Now questions/opinions:

(1) First off. Is it worth it? Or are my chinese optics good enough? Will I notice a difference (Transmission wise and image quality wise)?

(2) How easy is this? Sounds easy enough. Take off mirror cell and swap out primary. Take off secondary vanes, floss off old secondary, and silicone in new mirror. But, if I use say like discovery's f/6 pyrex mirror will that extra 20mm of focal length and thicker mirror also give me grave pains without moving the primary mounting backwards in the tube? I guess I better take that mirror cell off and check if it can accomodate a thicker mirror (will I need a new mirror cell?). Is Discovery's mirror thicker? Better call Discovery too...

(3) Are there better value mirror choices for enhanced coatings (95-97%), pyrex, hand figured optics?

O.K., I changed my Orion XT dob's alzimuth bearings by swapping out the teflon pads and added the ebony star surface. Seems to work good... Smart old me, decided to change the altitude bearings also. Since it seemed so easy. Now my bearing surfaces are too smooth on the altitude and with my scope so out of balance, it'll swing easy to one side or the other...

So what should I do (short of adding ebony star surface to the altitude surface):
(1) Sand the teflon surface with very fine sandpaper.
(2) cut down the teflon surface
(3) Try like hell to rebalance the scope - i don' think this will work by itself...
(4) Go to Orion and beg for some cheap pads

Your suggestion is greatly appreciated.

I have a Megrez 80II with Illuminated finder and have the following issue with the finder's battery holder which could easily shorten the battery's life and was wondering if anyone else has noticed this. Here Is an exerpt of an email I sent to WO:

"The problem is this type of issue will probably go unnoticed. Symptoms will show up as shortened battery life and/or batteries going dead between uses. My batteries lasted less than 3 months of light usage before dying. This seems kind of short for me. Compare this with my EZ Finder on my Orion Dob which has been running since January with heavy usage and still going strong (and on that unit, i've even left the LED on by accident for a few days once!)."

"As i've indicated on the previous email. When I took out the batteries to change/inspect. One measured (with 1K ohm load) 2.9V which is good, whereas the other measured only 2.1V, which is more or less dead! Obviously one battery fared better than the other. With the lower battery's "+" terminal hitting (shorting to) the side wall of the battery compartment (which is NOT insulated - PROBLEM), the upper battery which is also connected to the lower battery's "+" and to the battery compartment's case and side wall is effectively shorted and will therefore drain (and finder illumination is effectively running on ONE battery). The lower battery touching the battery compartment's side wall seem very easy too.... "

"If you're still not convinced that the lower battery can short to the battery compartment's inside side wall, do the following experiment. With the battery cover off, and with only ONE battery in the compartment, turn on the finder. Look thru the finder, and use your finger to lightly push the single battery to one side: the finder's illumination will light up... "

I kinda of like them undercuts. Gives me confidence my heavy eyepieces won't fall out. Works great with setscrews. Even on compression rings its ok, even though they do catch a little once in a while...

Maybe they should make undercut edges with a smooth angle gradient versus the hard right angle cuts which are not so compression friendly...

Rigel's new starlite mini is pretty cool. Lot smaller and lighter than the original, and still has nice brigtness control. The original Starlite was just way too BIG and HEAVY for hanging around the neck... And the smaller button flashlights like the Pelican L1 I used was just too bright (even with modifications to run with less voltage and added filters) and without brightness control.

Only minor things about the Starlite mini are that its a little less rugged than the original, but still not bad, and the brightness control is not very linear (it would slower increase in brightness from very dim to dim, and then fairly quickly jump to fairly bright). Anyways, its still pretty good, and it still beats anything i know of by a wide margin.

Anyways, go get one if you're still using the bulkly original... Or let me know if you guys know of something better.

After observing all the messier and a lot of brighter NGC objects later last year with my 8" dob, I decided to try to do more with less. Using only a Megrez 80mm and mostly one eyepiece - 13mm @ 38x, I tried to find and observe the messier objects again (under my moderately polluted mag 5.0 skies). Well, after last nite, i can say i'm done!!!

I think it was actually EASIER this second time around, even with a lot smaller scope. Initially, M101 and M74 gave me a little trouble. But after waiting for them to be ideally situated higher in the sky and using my latest secret weapon - Orion's dark cloth observing canopy to cover my head and eyepiece from stray light - even those became apparent and not hard. In the end, only M98 gave me a bit of grief - being intermittently visible (at <50% of time) even with averted vision. Also, I had saved M61 for last, remembering that i had read a comment that it was hardest, but that ended up easy too...

... anyways, I'm off to my next project - maybe using my 8" and observing all the Caldwell objects (at least the ones above -40 degs dec). I'm kind of happy and sad at the same time. Happy to be able to finish the Messier Objects with just an 80mm and only half decent mag 5.0 skies. But I'm kind of sad to be not a "beginner" anymore. There's definitely a strong sense of anticipation, excitement, and adventure of discovery with being a "begineer" that I'll miss! So, any beginners out there reading this, I encourage you to take your time and enjoy every step of your learning curve in this hobby.

I have an Orion 8" f/6 dob with the following eyepieces (with prices I paid new, and comments):
(1) Celestron Axiom 34mm ($180, very good, flat very wide 70deg field, but 20% edges not sharp)
(2) Orion ED-2 25mm ($55, alright - thinking of tossing or replacing this one)
(3) Orion Lantanum SuperWide 17mm ($215, excellent)
(4) Orion ED-2 9.5mm ($55, good - thinking of replacing with a SuperWide 8mm)
(5) Celestron Ultima 7.5mm ($74, very good for planets/double stars, but tight on eye relief)

Let me know how your 10" f/6 Discovery goes. I was thinking of upgrading to that exact same scope...