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Posts Made By: Thomas Bennett

February 11, 2014 03:39 PM Forum: Mounts

Need to find a dovetail base for this Maksutov (?)

Posted By Thomas Bennett

Hi Daniel,

I’ve seen these referred to as a "shoe" where the foot of the finder bracket fits into the shoe mounted on the telescope. The shoe for my Orion finder is a fairly common size but about half the size of the one in your picture. If yours is a non-standard size, your only shoe source may be from the manufacturer of the finder bracket. Other options might include buying a set of standard rings with shoe included that fits the finder, or drilling holes in the foot that corresponds to mount points on you telescope.

The finder looks kind of heavy so taping the foot to the scope ala Telrad/Quickfinder securely may not be possible.

Good Luck - Tom

April 3, 2014 01:30 PM Forum: Equipment Talk

TV Genesis SDF vs Astro-Tech 111EDT or Meade 6000 115mm Apo

Posted By Thomas Bennett


This appears to be more of a trade-off than an upgrade. You'd be giving up the flat-field of the Petzval-design Genesis for a slight increase in aperture. Field curvature is quite evident in my TV-85 at low power while it wasn't apparent in a previously owned non-SDF Genesis. This is not an issue with planetary viewing but wide fields look better when everything is in focus.

- Tom

December 22, 2014 03:24 PM Forum: Celestron

Mating scope and mount

Posted By Thomas Bennett

My SE mount works great with a 60mm Lunt solar scope and was usable with a 15-lb 6" Russian Mak-Cass + accessories which is about the max I'd want to put on the SE. There's also limited clearance when the mount is pointed near zenith so I had to push the Mak-Cass OTA forward beyond its balance point to clear the base. The SE seemed to handle the weight but the off-balance configuration was awkward. I tried a C8 OTA on the SE once and found it a bit oversized for the mount and preferred using an ASGT GEM instead.

Celestron's Starsense (haven't tried one yet) is suppose to automate the alignment process in twilight and/or light-polluted conditions and might be an option with your existing GEM.

Good luck - Tom

January 14, 2015 03:30 PM Forum: CCD Imaging and Processing/Deep Sky

Hyperstar Alternative?

Posted By Thomas Bennett

Celestron made their own Fastar lens systems prior to Hyperstar but discontinued these about 10 years ago. One came up for sale on A-Mart recently (ad 875809) for $250. You might be able to find another one with a "wanted" ad.

Good Luck, Tom

March 20, 2015 10:54 AM Forum: Telescope Making

Re-machining a 16" Mirror

Posted By Thomas Bennett

Hi Mark,

A thick mirror deforms less than a thin mirror so its mount can be less complicated. Thinner mirrors have the advantage of reaching thermal equilibrium faster and weighing less but they require a more complicated mount to maintain their optical figure. A 16" F/8 scope with 3" thick mirror sounds more like an observatory-based instrument where portability (less weight and size) is not a concern.


April 6, 2015 06:38 PM Forum: Off Topic Discussions

Curvature Of The Earth Failure, Geez....

Posted By Thomas Bennett

The author of this article appears to have collected a bunch of dots but connected them together all wrong.

SBX is a high-resolution/narrow-field X-band radar designed to discriminate between warheads and decoy warheads (not 'actual missiles' and 'decoy rockets' as the article states) and provide targeting data to interceptor missiles based at Fort Greely Alaska and Vandenberg AFB in California. This is done after missile launches have been detected by IR surveillance satellites and tracked by lower-resolution/wider-field S-band radars that cannot discriminate between decoys and real warheads.

In an attack by a rogue nation (you can probably guess who) which is the scenario our missile defenses are designed for; all incoming warheads would be well within the 25-degree field of the SBX radar. The whole purpose of making SBX sea-mobile is to allow moving it to locations to optimize line-of-site coverage on an ellipsoidal earth.

December 22, 2015 03:33 PM Forum: Maksutovs

Casual Mak for moon

Posted By Thomas Bennett

Hi Paul,

It's not a Mak but I've got an old white-tube Celestron 5+ OTA with excellent optics and is very portable. The C5+ OTA only weighs about 6 pounds compared to 8.6 pounds for a 127mm Mak and is also smaller in size.

January 9, 2018 01:15 PM Forum: ASTRONOMY

Properties of Light Question

Posted By Thomas Bennett

Hi Carter,

As a first year astrophysics student, you’re probably studying classical electromagnetism as summarized by Maxwell’s equations while the behavior of photons is more accurately described by Quantum Electrodynamics (QED) as devised by Feynman, Schwinger, and Tomonaga for which they won the Nobel Prize in 1965. Feynman’s book QED: The Strange Theory of Light and Matter is a good introduction to this topic.

Photons travel like a wave but interact like a particle. This behavior can be observed in Young’s double-slit experiment and in interferometers.

In Young’s experiment, photons are emitted (by a single emitter) on one side of a screen that contains 2 slits and detected (by one of multiple detectors) on the other side of the screen. Photons are emitted and detected one-at-a-time like particles. Photons take every possible path between the emitter and detector but the screen (with 2 slits) reduces the possible paths to just 2.

Even though the photons are emitted and detected one-at-a-time like a particle; an interference pattern is produced as the detections build-up at the detectors that indicate each photon travels through both slits and interferes with itself like a wave. If a detector is placed at either slit to determine which slit the photon went through, the interference pattern will not be produced.

October 23, 2018 04:50 AM Forum: Eyepieces

Eyepiece Thread Consistancy

Posted By Thomas Bennett


I just purchased a new 17.3mm TV Delos and am unable to thread standard filters (one color and one IR from different manufacturers) more than 1/2 turn into the EP barrel. The same issue occurs while trying to attach the filters onto a couple other TV eyepieces (24mm Panoptic and 3-6 Nagler Zoom). The filters fit all my older TV Plossls and Celestron Ultimas and some of my newer TV eyepieces.

Any ideas on what's causing this?

Thanks, Tom

February 25, 2019 07:06 PM Forum: Equipment Talk

Build a C8 binocular telescope?

Posted By Thomas Bennett

Hi John - I think most binoscopes use refractors or reflectors to achieve wider fields-of-view. A  C8 binoscope would be a fun project but it might not be much different than using a binoviewer on a C11. I use a binoviewer on my C14 (great for lunar and planetary) but its field-of-view is quite limited.