Posts Made By: Keith Lawson

In the realm of mountings, is there such a thing as "overkill"?

Keith

See here:
http://www.telescope.com/jump.jsp?itemID=251476&itemType=PRODUCT&path=1%2C2%2C4%2C10

All,

Well... I decided not to sell my lens and went ahead and completed the construction of the refractor. This was my original intent but this old telescope maker doesn't have the drive of youth anymore. I'm glad I completed it. Views are awesome as one would expect from a refractor this large. The final paint and detailing will be completed when it gets a little warmer in the high desert.

The OTA sets up in 3 pieces so this is actually a portable 8 inch refractor. The end tubes attach to the center straight truss with hand knobs.

The Mount sets up in about 10 minutes. The ota takes about 5 minutes. No tools needed.

Keith

In this corner the beloved Celestron C-9.25 mounted on a Meade LXD 750 and in the other corner a standard 8.5" achromat mounted on a Meade DS-16 mount. Who will win

Tonights high res targets: Saturn, the moon and a few choice double stars. Both scopes cooling at present. Results later tonight.

Please excuse the soft photo.

All,

Even though this is not quite telescope making, it will be a heavy modification.

The C-9 mods have begun! The optics in this scope have impressed me enough to begin some serious mods to make it a better instrument. A cheap APO killer for the lack of a better term. Since I can't afford a TAK, AP, or TMB in the 150 to 180mm size, I guess this will have to do.

The photo shows the newly finished ventilated dew shield (yes, it will be painted). I purchased the tube for the dew shield from Hastings Pipe. The ring was from a scrap piece of aluminum. A reduced secondary size (currently 36%) and closed loop cooling system is next.

According to my calculations the finished OTA should be at least as good as a 6" APO for contrast, equal to a 8" F/15 mak for pure high performance, light grasp equal to a 8.5" achromatic refractor and of course the resolution will still be what you would expect from a 9.25". Time will tell

Keith

I just received an Intes M715 yesterday. Just finished with my "second light" session. As usual the seeing sucked but this scope pushed through it giving me some nice high contrast views. Anyone into lunar/planetary/multiple star observing and thinking of dropping some long green on a APO refractor should give this scope some serious consideration. The performance is that good

Keith

All,

I had the sawdust flying this weekend. This OTA was designed around a 6.3" F/10 Ukraine lens from Surplus Shed. The cell is different in that it would be somewhat difficult to make it "push-pull". I decided to go with shims behind the mounting plate for alignment. Very easy to align if the OTA is square. I was originally going to use the cell for alignment (that's the reason for the "fancy" arms that keep the cell in place) but opted for the lens mount plate instead. I will make a retaining ring in the future to replace the "arms". The focuser is collimatable.

A dew shield is forthcoming and I will do the filler/sand/paint thing soon.

Keith

Hi All,

This is updated version of a scope calculator I posted sometime ago. I know there have been many shareware/freeware programs for calculating the performance parameters for telescopes and eyepieces but I never found one that gave me all the info I wanted and many did not have the ability to print. This is a simple spreadsheet but with it you can get general information on what to expect in telescope/eyepiece performance. Many of us own more than one scope and many eyepieces. We can sometimes scratch our heads trying to remember what magnification we are running on the scope we are using (ever been asked that question at a star party?). You can print the spreadsheet for use as reference at the scope or use it in your laptop while observing. I find that I use it quite often when doing scope comparos.

It was made using Excel. Since we can only post images here, if you want the spreadsheet just drop me a line at [email protected] and I will be happy to send it to you. If you like it and think someone else can use it please feel free to "spread" it around (Pun intended).

As you can see in the screen shot there is some useful info. All the white areas are for data entry. Put in your own telescopes, eyepieces and obstructions. Those of you who are comfortable with spreadsheets, you can edit anything in it to suit your needs including the simple formulas, colors, fonts, etc. I have added a performance area that deals with secondary obstructions. Beginners please note that the contrast factor (aperture equivalent) is not the same as light grasp. As an example the spread sheet shows that a 180mm F/15 Maksutov with a 25% obstruction is equal to a 140mm APO in contrast (both scopes are optically excellent) but the Maksutov will have higher resolution as well as higher magnification potential and greater light grasp. You can also "run the numbers" to see if upgrading your old scope to a new one is worth it (like going from a 8" telescope to a 9" telescope).

Also, please do not flame me about the calculation concerning optimum planetary magnification. I know that we can run more under good seeing conditions with a given instrument. The number represents the best "general visual acuity limit" (.75mm exit pupil). I'm posting this for anyone who could use this kind of info other than me

Keith

Maybe someone with ties to the "industry" can answer a question for me. Why are there no SCT's designed for high resolution/high contrast observing? The cost of a 10 inch MAK or Refractor is well beyond the financial abilities of the people I associate with yet I find this size of telescope to be excellent when you balance the size of the scope against high power image brightness, detail, and average seeing conditions. A 10" cooled high definition SCT produced by Celestron or Meade should be affordable to all who desire a medium cost, large, high power instrument.

Forget the computerized bells and whistles which can break or fail. Just an affordable pure high performance instrument on a nice GEM. Yeah, I know I'm old school and probably out in the twilight zone but, for me, there is something special about observational simplicity.

The image is a "paper" SCT telescope that I have been playing around with off and on for a few years. It has a 26% secondary obstruction, 100% illumination to 1/4 of a degree field of view. Image contrast should be equal to a 185mm APO and the small relative obstruction would make the instrument less sensitive to seeing compared to "standard" SCT's. At F/14 multi-element eyepieces are not needed and longer focal length eyepieces would render high powers with good eye relief. Hey GSO, care to make a lunar/planetary Schmidt? I would buy one 8)

Keith

Hi All,

This info is for anyone in need of a source for large diameter pier tubing. I received my new aluminum pier today and had it marked and drilled in about 20min. I picked aluminum tubing for a portable setup. I will purchase a steel one for a permanent pier in the future. If you have some old pier legs lying around or an older Cave, Meade, etc mount you can make a nice replacement pier to your length instead of living with the factory "standard". The cost was very easy on the bank account and made this old telescope maker smile The mount in the picture is one of the older Meade Starfinder mounts that has been modified for better performance. It's supporting a Meade 127 ED.

You can choose from steel, aluminum, and stainless steel (expensive). You can order on line. The pier in the picture is 6" 11 gauge aluminum. Here is the source: http://www.globaltecheng.com/products.htm

Keith