Posts Made By: Tom Mengel

February 17, 2005 07:05 PM Forum: Telescope Making

Messing with lens element spacing for over-correct

Posted By Tom Mengel

Hi all,

I have a old 4 element (in two groups of two) 96mm F5 (480mm) lens mage in Germany under the brand of Rollenstok that I’ve made into a cheap “copy-scope”. It actually works very well (particularly for the color correction and field flatness – those 4 elements do make a difference!) but it’s noticeably over correct at infinity due to it’s primary role as a copy type lens. Even with that said it gives pretty good images up to about 10X/inch but then the in/out focus reveals the correction problem. I can make out Cassini’s division on Saturn and 4/5 bands on Jupiter but there is a “focus haze” that is real annoying at higher powers and if I could zero that out it would actually be a pretty good scope.

My question for the lens gurus: Can re-spacing the front and rear groups in a lens of this type help the correction when focused at infinity? Is it as simple as taking off the front retaining ring and putting in a spacer? Or am I going to just mess the whole thing up, in which case I’ll just keep it as a RFT.

Thanks!

June 10, 2005 04:35 PM Forum: Equipment Talk

Possible scope cover idea

Posted By Tom Mengel

I would like to leave my 8 inch SCT up for up to a few weeks at a time in my backyard. So like many other backyard observers I have been trying to brainstorm ideas for a cheap-easy semi-permanent cover for my SCT. I know there are many available “systems” out there (Desert Storm covers, industrial strength 55 gallon poly bags liners, etc.) some of which I’ve actually tried, But short of a roll-off shed of some kind they just don’t provide enough long term unattended protection.

My requirements are as follow:

Non-permanent (no covenant boards or permits or complains from my wife)
Good weathering resistance (Sun/UV resistance, waterproof sealing, not affected by high winds).
Some kind of hard material (it hails here in Colorado in the Denver area on very short notice).
A good thermal “R” value to keep the OTA temperature equalized during the day/night cycle.
Has the potential to put some kind of active cooling (Pettier (sp?) junction) in place later.
System can be adapted for either a tripod or more permanent mounting system.

One idea I’ve come up with is to buy two relatively cheap camping coolers to join together. This would be done in a top-to-top manner discarding the original hinged top doors and having the top cooler upside down to make a larger two-piece shell.

These coolers are rugged (covered inside and out with tough plastic with dense foam in between), can be made both weather and thermally air tight, and are cheap. The only major issue is joining the two coolers together with some kind of sealing lip/gasket and latching arrangements so that it is water-proof and figuring out how to adapt the bottom cooler to sit on the peer/tripod and fit/clamp tightly in place but still come off easily when it was time to observe. If at a later time this idea works well I can figure out how to install an active cooler system to bring the OTA to night temperatures 3 or 4 hours before the sun actually sets and have it thermally “equalized” (cooled down) and ready to go that much sooner.

BTW – I got this idea from watching a nature program with two professional photographers going out in the wild for 6 months. No fancy-dancy pocket-laden signature photo bags or expensive aluminum gear boxes in sight. All of their (very expensive) equipment was well wrapped in thick foam sheeting and stored in garden variety picnic coolers with some straps and locks installed for the top doors. I figured they may know something I don’t . . . or maybe they were just being cheap wink . But with equipment costing into 6 figures and their livelihood on the line in remote places the system must have some merits.

Any comments?? If there is interest I can try to put any results I get here on AM.

June 24, 2005 10:42 PM Forum: Equipment Talk

Re: most knowledgeable

Posted By Tom Mengel

This kind of “Beauty Pageant” is not a good thing in the long run. I think each person would bring his/her own area of knowledge to the table as a piece of the composite, and no one is better than the rest. All persons mentioned in your post are great in their own fields and one of the biggest thrills for me personally here on AM is to see what they have to say on any giver subject (even if the knowledge is "at odds" at times). I can truthfully say I’ve learned a tremendose amount from these folks over the time I’ve been reading their posts. I also firmly believe there is no "best" of the group for the above reason: the subject of equipment is just too broad.

And since everyone's mileage will always vary trying to pin one down one person as "king of the hill" will only result in more heat than light with no clear winner emerging. And the resulting flame wars might just drive a few aforementioned folks off the boards to all our collective loss.

August 26, 2005 06:49 PM Forum: Equipment Talk

Li-ion batteries

Posted By Tom Mengel


After running out of juice on my Magellan I and quite inaccessible clock drive on my LX-10 in the mists of observing I'm looking to mount some Li-ion batteries into my Meade tripod body. There are several spaces in the top casting that could hold some AA-size cells quite nicely and the power density on the Li-ion cells could be around 1500 to 2000 mA/hr, so that I could power a Mag. I and the scope clock drive both for several days to a week (or more) without needing to recharge.

My question - I want to gang these cells in series to procedure 14.4 volts (12 total 1.2V cells). I could use 3 4X AA-size cell holders and recharge the "standard" AA cells in a charger like what you can get at any photo or discount store for digital camera batteries, but that would mean taking them out of tripod head and the holders to put them into the charger each time they needed recharging. What I would prefer is to hard-wire them into the tripod head with a small 3 LED charge monitor from Radio Shack and then have an external charger I could even leave in place while running the computer box and clock drive and be able to know when I needed to recharge (and still have lots of juice left so things don’t start to die on me).

Since Li-ion’s need special chargers I can’t just use a 14 volt source to do this. Does any one know of such charger sources or plans to build one? I found one place that sells both the cells (as a small 2000 mA/hr pack at 14.4 volts) and a charger but it's over 50 dollars with tax. If I can get 1.2 volt 1800 mA/hr cells from American Sci. and Surplus for about $1.50 each and either build or get a cheap charger for far less this would then be doable.

Any ideas??

Thanks for any info! Dark skies.

TM

March 3, 2006 08:40 PM Forum: Deep Sky Observing

Now for another concern . . .

Posted By Tom Mengel

(NOTE - See home page NEWS - TM)
...

From the BBC . . . Jet Contrails will render ground-based telescopes a thing of the past in 40 years:

http://news.bbc.co.uk/1/hi/sci/tech/4755996.stm

...

Tom Mengel
(Moderator Equipment forum)

April 10, 2007 12:18 AM Forum: Equipment Talk

TREO 700p bluetook link - anyone done it?

Posted By Tom Mengel

Hello to all.

I have a TREO 700p running Palm Planetarium SW and have installed the Bluetooth driver for the PDA"s built in link. I need to attach a serial Bluetooth adaptor to a Meade Magellan I DSC so it will drive the planetarium maps.

Any one lurking out there that have done this or have words of wisdom in the matter?

Thanks!

Tom Mengel
Moderatore EQUIPMENT Forum

November 4, 2009 09:40 PM Forum: Equipment Talk

Scope downsize

Posted By Tom Mengel

Hi all,

I’m finding myself in a (unfortunately) common situation of a “early forced retirement” while my wife is preparing for grad school. The bottom line is my well loved (and used) LX-10 is way to large for my projected future life style (and in truth it was getting to be a pain to set up anyway). So now I’m in the process of “trading down” to a smaller scope that must be able to hibernate in a closet corner in what may end up as compact student housing for the next few years.

I don’t want to rekindle the seeming never ending “Cats vs. Refractors” or “DOBs vs. Cats” threads but would like some feedback on small footprint scopes that involve minimal setup efforts. What I want is at least a 5 inch aperture and easy to carry (possible down stirs) to transport to a dark site. Area contenders range from USC in LA (not renown for dark skies) to Cornell in Ithaca NY (small town in the mountains – probably OK skies).

Right now I’m leaning towards trading “even” for something down the lines of a Celestron G5 on a EQ 3 mount. GOTO is nice but not requirement, just want a utilitarian setup that works well. Figure an older LX-10 with a adjustable field tripod and Magellan I DSC would be a fair dinkum trade for a newer, smaller setup.

Your thoughts?


April 27, 2010 04:03 PM Forum: Equipment Talk

A collection of real "Star Treks"

Posted By Tom Mengel

I just ran across a really neat site I thought I would share with you all Astromart. This is from the ESO large telescope PR site (check out the E-ELT section if you have incurable aperture fever . . . primary is 42 meters (half the size of a football pitch) in diameter and will out-resolve Hubble!! YOWSA!!!). 8O

The URL below is for a video library that tacks together images all the way from amateur telescopes to the most advanced earth-based sites in a Star Trek kind of video. This will really give you an idea of what we have in amateur compared with the big boys and how this really is the golden age of astro research.

http://www.eso.org/public/videos/archive/category/starclusters/

Enjoy!

September 10, 2010 05:42 AM Forum: Equipment Talk

Re: laser pointer eye damage

Posted By Tom Mengel

I just bought a cheap 5 mW green pointer for experimenting with aiming my scope. Works very well but I did notice many 20 to 100 mW pointers and one even claiming to be a 300 mW unit (my understanding is that focused a 300 mW beam can even be used to etch/cut aluminum).

Even with the 5 mW low power unit I would never aim it so that I or any one around me would get the beam in their eye. It's indeed scary that some manufacturers are so irresponsible.


May 19, 2011 01:28 AM Forum: Equipment Talk

Re: Black Touch-Up Paint for C-11 Ultima

Posted By Tom Mengel

If Celestron give you no joy I'd put it in your car and go to a GOOD auto body shop (maybe one that does old car restoration) for a suggestion for a paint retailer. Then have the paint place match it (plain enamel, Emeron, or whatever and exact color) and give you a touch up bottle.

With old cars they have to re-paint parts and match the color all the time as paint actually changes color as it ages, so you do NOT necessarily want to use new paint as it may not match the old anyway.

Then again you can just go buy some Krylon black glossy/matte/flat down at the local big box if your not too choosey wink