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Posts Made By: Thomas Bennett

September 27, 2011 02:14 PM Forum: Beginning Astronomy?

1.25" vs 2" eyepieces

Posted By Thomas Bennett

Hi Jack,

I also have an 11” Celestron (Nexstar 11 GPS) and agree with all the posts recommending a low power eyepiece since you will likely use this more than any other eyepiece.

One way to do this is to purchase a long focal length 2” eyepiece like my 30mm Widescan III that gives about 93X with a 0.9 degree field of view in my NS11.

Another option is to purchase an F6.3 reducer/corrector and use a longer focal length 1-1/4” eyepiece like my 20mm Widescan III that gives about 88X with a 0.95 degree field of view with the R/C in place. The R/C will also improve the off-axis image by reducing the field curvature that is inherent in older SCT designs – stars at the edge will appear sharper.

Gook luck, Tom

January 11, 2012 10:08 AM Forum: Eyepieces

eyepieces for C-14

Posted By Thomas Bennett

For deep sky viewing on my Nexstar 11 GPS, I really like using a Celestron F6.3 reducer/corrector combined with a 20mm Explore Scientific 100 degree EP. Trying to go wider with a 30mm 84 degree EP resulted in severe vignetting so the 20mm ES100 is about the limit. An R/C would reduce a C14's focal length from about 150 to 100 inches and improve its off-axis performance.

April 10, 2012 03:02 PM Forum: Celestron


Posted By Thomas Bennett

Sorry to hear about your corrector plate mishap Tony.

I had my 90’s era Celestar 8 SCT side-by-side with a smaller premium Mak-Cass last night looking at Saturn and noticing how the C8’s image was showing more detail and brightness. A good C8 can perform well if its optics have not been tampered with as yours may have been. Since you already have a lot of C8 accessories, replacing your defective C8 with a well-performing one would be one good approach.

If you want to get into mirror testing, the primary mirror may be usable as a Hindle Sphere to test convex optics.

- Tom

April 23, 2012 02:14 PM Forum: Telescope Making

Mirror Figuring Question

Posted By Thomas Bennett

Hi Chuck,

Sharp images are always a good sign.

You don't mention the focal length of your mirror. The Ronchi test is less precise with faster mirror - less than about F6.

The Foucault will show surface roughness, turned-edge, and zonal errors by direct inspection. To test for spherical aberration, test results depend a lot on how skilled you are at matching the brightness of opposing zones on the mirror face while moving the knife-edge back-and-forth. I tested a bunch of completed mirrors (commercial and homemade) to increase my skill-level before trying to use it to figure my own mirrors.

Good luck with figuring, Tom

May 10, 2012 02:08 AM Forum: Home Observatories

trying to post my dome for sale- How do you uploa

Posted By Thomas Bennett

[QUOTE]Jeff Jarnot said:

I'm trying to post an add here (for my $12 plus $10) and cannot for the life of me figure out how to post images w/ my classifieds. Anyone up to a solution on this one? I've searched the archives too.

Hi Jeff,

The following has always worked for me but I've never done a pay-per-ad.

After filling in the Item Details screen, hit the continue button to reach the Photos screen, and use the Browse or Upload buttons to input the path to the JPEG image you want to upload. See attaced image.

September 12, 2012 10:46 AM Forum: Equipment Talk

Need some help ASAP

Posted By Thomas Bennett

Hi Mike,

This is a "German Equatorial Mount" or GEM. You only need a single drive motor on the polar axis (PA) to track objects. The PA needs to be parallel with the earth's axis-of-rotation in order to track properly. The drive will move the telescope in the same direction that the sky is rotating (due to earth's rotation) which makes the object you're viewing appear to stand still. A rough alignment of the PA is adequate for visual observing by pointing it towards the star Polaris AKA the "North Star". Your picture shows the PA pointed straight up (90-degrees). Once you install a drive motor, you will need to lower the angle of your PA to equal your latitude which is about 43-degrees for Massachusetts and point the PA towards Polaris.

- Tom

March 14, 2013 05:42 PM Forum: Mounts

clock-drive eq mount with 30 pound payload?

Posted By Thomas Bennett

Hi Anthony,

The Comet Hunter OTA weight is listed at 15.4 pounds. I don't think my old tank-like Russian MN61 Mak-Newt weighed as much as 25 pounds but it might have been close!.

- Tom

April 9, 2013 10:20 AM Forum: Equipment Talk

Nextstar 6SE Diagonal

Posted By Thomas Bennett

Hi Tom,

I mounted a C8 HD OTA on my SE mount and had to use a direct-attach 2" SCT diagonal to clear the base when pointed near zenith. Even with this diagonal, the OTA had to be pushed forward far enough on its dovetail so that the diagonal wouldn't strike the base. The heavy diagonal and eyepiece helped maintain balance well enough for the mount to work although it was struggling a little with all the weight. You should have less of a problem with a 6" SCT OTA and might be able to use your conventional diagonals.

- Tom

May 24, 2013 09:32 AM Forum: After Dark

Celestron Edge HD 1400 Focusing issues

Posted By Thomas Bennett

Hi Siddharth,

You could try adding a long extension to see if the scope is coming to focus behind the current eyepiece location or remove the diagonal and see if the scope is coming to focus in front of the current eyepiece location. There are 2 mirror lock knobs on the back of the OTA but since you’ve already verified the primary mirror is moving, they must be disengaged. Is there an astronomy club in your area where other Edge HD owners might be able to help you?

- Tom

November 4, 2013 01:59 PM Forum: Eyepieces

8mm Ethos

Posted By Thomas Bennett

Hi John,

Short focal length Ethos eyepieces tend to get used mostly on my TV85 APO (600mm FL) and Comet Hunter Mak-Newt (730mm FL). On my Celestron NS 11 GPS (1760mm FL with F/6.3 reducer/corrector in place), the 21mm and 13mm are the most used. IMHO, the 8mm would be too much power on a C9.25 to act as a general purpose eyepiece.