Posts Made By: Keith Lawson

Anyone know of a source for lens refiguring :S

Hi All,

I don't know if this is the right place for this but it is for all telescope users. 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. Most of us own more than one scope and we 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 at the scope or use it in your laptop. 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

As you can see in the screen shot there is some useful info. All the purple areas are for data entry. Put in your own scopes and eyepieces. Those of you who are comfortable with spreadsheets, you can edit anything in it to suit your needs including the simple formulas. Two scopes may not be enough for you or you may want everything in inches, etc. I'm posting this for anyone who could use this kind of info other than me

Keith

I just got a Meade 178 ED a couple of days ago. I have had many refractors over the years but this was my first APO! What a beautiful beast Put everything together on the evening of the 21st. First light revealed the dreaded comatic star image in the center of the field of view in a medium power eyepiece (160x). I had made sure the lens and focuser were aligned earlier so this was not the problem. I had seen this in other refractors before. Looks like the lens elements had shifted during rough shipment. Crap :C Well..... I dreaded a trip to Meade (wait, wait, wait) and did not want to return the instrument after finally finding one in excellent shape. After getting over my initial dissapointment I found a way to fix it and I'm now having a ball. Second light was a blast. Textbook star images 8) Mars was "off the hook" at 320x The tiny polar cap was easily visable during moments of steady seeing. This 50 year old man was laughing like a little kid on a new bike!

I found that the collimatable lens cell has a collimation setup for the second element. It's tricky to use but it works. It's a lot like trying to collimate a Chromacor which can be a pain but this took me about 20 minutes using my daytime artificial star. Last nights tests confirmed about a 1/6th to 1/7th wave overall correction (ronchi[250 line grating] & star test). I pushed the instrument to 426x (Antares 7.5 & barlow)and the image remained crisp and well detailed. Not bad at all I'm glad I was able to fix it "in house". My question is: Has anyone else had the same expererience?

Keith

Hi All,

Does anyone who owns a Meade Apo and mount know if there is a way to do a 2 star alignment without using polaris as one of the stars? I can do a single star alignment, a HP alignment, and a two star polar alignment but can find no information in the manual concerning how to perform a simple 2 star alignment. This is what the manual says concerning the "critical" alignment of the LXD750 mount:

*A "critical" alignment will improve the pointing accuracy of the telescope to 2 arc-minutes or better. This type of alignment requires accurate SITE information, time, date, proper selection of the two alignment stars, and a reticle eyepiece to exactly center the alignment stars. These steps generally require only a few extra seconds to accomplish, and improve the telescope's positioning by a substantial amount. Using the "critical" alignment will provide telescope positioning suitable for all but the most demanding pointing applications—including CCD imaging with larger chip cameras, like the Meade Pictor 416XT and Pictor 1616XT CCD cameras.*

This info tells you what you need but not how to select the two alignment stars for the alignment. All Meade computerized mounts can do this so I'm guessing there is a way to do it for the LXD 750. This would be great for star party use since the polar alignment could be a rough alignment but the computer would compensate for any polar alignment error.

Keith

New Meade Max Robotic Mount 8O Sure is pretty! Just wish it was more in my price range

Would anyone be interested in a machined aluminum HD parallelogram bino mount with a 20lb bino capacity? (20lbs for the bino and 20lb counterweight for a total of 40lbs capacity) It would be in kit form to save on the cost. (you choose your own finish and put it together) At my last check a mount of this capacity was in the 700.00 range. What good is it to have 100mm binos that can cost as little as 200.00 and have to spend up to 700.00 to mount it well :S The prototype is complete. (waiting for the tripod to arrive) I'm just looking for some feedback.

I know that in designing a standard achromat cell there can be a little slop in the tolerances between the OD of the lens and the ID of the cell. Say .002" to .004". So what about a APO doublet?

The steep inner curves cause the lenses to be very intolerant of lens shifting. I performed some experiments some time back on a couple of optical design programs and was surprised to see how little shifting it took to destroy the high power imaging of 2 element ED APO lens (.0015"/.038mm.).

I have a Meade 178 ED that has the best overall lens correction of any refractor I have owned to date (I've had a few in 30yrs). I love what I see through it. It gives stunning images but I find that from time to time I have to do a "little" minor tweaking of the lens to realign it (on axis colimation is spot on). It has the new lens cell that Meade designed some time ago to "fix" the shifting problem and I have reworked some of the issues concerning it but as a refractor user I could care less to have to do a realignment every month or so.

I can machine a new cell to a tolerance of +/-.0001" if I have to. So my question to you is this: What are some of the "points" to remember in fabricating a cell for a APO doublet? Please forgive my ignorance. If I'm asking too much (trade secrets) I will understand if you don't answer this question.

Seeking to fix a problem,
Keith

This was a beat-up scope I bought a few years ago that I rebuilt and then sold in 04. When it came up on Astromart I jumped at the chance to get it back. It's one of those Celestron "nulled" scopes that are rare finds in commercial SCT's. At high power on a night of good seeing the double-double shows 4 white airy disks (very tiny) surrounded by a single diffraction ring each. I have resolved stars to the diffraction limit with this scope. This is not your "average" SCT.

As is usual of me I can't leave well enough alone and machined openings in the OTA to aid the cooling off of the optics. With this scope I didn't want to go through the process of machining another closed loop cooling system but I find that it works well enough to have been worth the trouble of machining the cutouts and covers. Cooling is not as fast/good as closed loop cooling but you can sure see the difference when the covers are removed during observing. I'm a lunar/planetary/multiple star observer BTW.

I love to tinker with telescopes and optics. For me that's half the fun

Keith

Ok, before you start telling me I'm in the wrong forum, let me explain There are some glass pushers out there that have made a lot of mirrors but have made lenses also. I'm in need of a custom made barlow for a planetary Newtonian project. The final instrument will be 10" F/15. This is a purely visual lunar/planetary instrument. The primary will be F/6. The barlow will be ahead of the diagonal and the secondary obstruction will be only 18% including the housing for the lens/diagonal combination.

The barlow is a flint forward design. At final focus the 100% illuminated field will be 1/2 degree and the star images will be diffraction limited to a 1/4 degree field of view. The glass components for the barlow are BK7/N-SF5.

Any mirror makers out there that are small lens makers too?

Keith

Star testing an 8.5 inch F/12 refractor. Yes, it's one of those Hong Kong lenses. Just got it last week. The Meade LXD750 just barely holds it. Good enough for star testing though. The seeing has been bad but I'm having fun anyway. I can tell right off that it easily beats my C-11 for high-res work. I wouldn't have the C-11 out on a night like this. Initial impressions are very good. The lens tests good enough to go ahead and build a nice OTA. Any other ugly scopes out there?