Steve's Asteroid Occultation Equipment Configurations
Orion ShortTube 80
A relatively small, fast 80mm refractor. But with the newer PC-164C-EX camera I can record stars down to about mag 10.
Orion 120mm f/5.0 refractor
A larger version of the ST-80. This records stars down to mag 11 or possibly 12 in very good conditions.
I picked up a used C8 a couple of years ago. This scope is much lighter than the C14 so I use it for remote sites whenever possible. With an f/3.3 focal reducer and a PC-164c camera many observers have recorded occultations of mag 11 stars. Great option - cheaper, lighter, and much smaller than the C14 but still works for most occultation targets.
C14 - aka the "light bucket".
Depending on the color of the star I should be able to record occultations for stars down to mag 12 with a PC-164c camera and a Meade f/3.3 focal reducer. I always use a Meade f/3.3 focal reducer with the C14 as this gives me another magnitude of sensitivity. This scope uses a lot of room in the car and it is heavy (my back problem has resurfaced recently so I need someone else along to use this scope now). It is expensive but not bad considering the 14" aperture. Overall - an excellent choice for occultations if you have the car space, the budget, and a strong back (or an assistant).
Losmandy G-11 with Gemini
I bought this mount with the C14. The G-11 has a dovetail plate for attaching scopes so I can easily use it with any of my scopes. The G-11 breaks down into pieces that are small enough and light enough for me to easily fit into the car. I have a strong preference for equatorial mounts over Alt/Az for occultation expeditions. Just point the mount close to the pole star and you are ready to go. The one problem with GEMs (German Equatorial Mounts) - for objects that transit the meridian you have to be careful when the scope must end up on the west side of the mount for the event.
I also bought the Gemini GOTO system with my G-11 and I can recommend it highly. I can "align" the goto system in about five minutes but the mount defaults to standard tracking so I don't even have to align it if I don't need the GOTO capability.
The G-11 + Gemini combination is expensive but a bargain considering the functionality when compared to the more expensive models from AstroPhysics. The new CGE mounts from Celestron could become good competition. The mount can easily handle the C14 for occultation work and short duration photography but I have heard that people would not recommend the combination for long exposure photography (the c14 is a little beyond the design specs for the G-11).
This is great little German equatorial mount but no GOTO or Digital Setting Circles. It does have dual drive slewing and I consider this a hugely beneficial feature for a "manual" mount. It can easily hold my C8 but not the C14.
Other comments on scopes/mounts:
For brighter star occultations many observers now use 80mm or smaller scopes with lightweight tripods. Since these setups do not have tracking, you must pre-point the scopes. But these small scopes have a wide field of view and that makes pre-pointing more viable. Scotty Degenhardt pioneered this approach with his "mighty mini" systems. You have find more info on this approach by reviewing the posts to the IOTA Yahoo group and exploring the links at the IOTA websites.
I use the PC-164C from Supercircuits or the newer version the PC-164C-EX. The camera is "auto-gain" so it is a little tricky to use for lunar occultations. If you want a manual gain version, you have two options: find someone to modify your PC-164c (ask on the IOTA Yahoo Group ), modify it yourself, or spend more money for a camera with the same ultra-sensitive CCD detector and manual controls. Note: This is not the same camera as the PC-164C EX. The EX version has more resolution but it is not as light sensitive.
The PC-164C has a standard "C" mount for mounting to a lens. To mount the camera to a telescope I use a "C" to 1 1/4" adapter from Adirondack Video Astronomy . I screw the "C" end into the camera and insert the combination in my 1 1/4" eyepiece holder. There are several other options using combinations of "T" adapters and "C" to "T" adapters, etc. But I prefer the AVA adapter because it is simple and it works. If you use another option, make sure that the distance from the focal point of the telescope (in the eyepiece holder) to the CCD in the camera can be adjusted down to around 1 1/2" or less.
Watec also makes a good series of cameras including some more expensive cameras which can integrate frames for longer exposures and reach very dim stars.
Note: when switching between eyepieces and cameras it is a good idea to use a bright source (e.g. moon) to determine the number of turns (and direction of turns) to focus the camera after removing a focused eyepiece. It can be very difficult to acquire focus on a dim star when switching from an eyepiece to the camera. I usually never use an eyepiece. I start with the camera in the scope and use a bright star or moon to focus. Then I leave the camera in the scope when searching for the target star.
I have a few older DV camcorders which can record from an A/V input. This is a good option for recording an event. It is very portable and has its own battery based power. The only downside is the relatively small screen. It can be difficult to spot dimmer stars on the small screen. And it is getting harder to find inexpensive versions of these products now. Most manufacturers are moving to non-tape MPEG based products for there low-end camcorders. Because these use very lossy compression I avoid these products for occultation work.
AC/DC TV/VCR Combo
This is a backup that I have used in years. I picked up this small "portable" unit on sale and it has worked very well for occultation work. I can power it with either AC or DC. It has front inputs for video/audio input.
I always use two options for timing. My primary timing source is a GPS based video overlay device - it overlays the time of each field on the video. For every event I also record WWV (shortwave) on the audio track as a backup time source.
GPS Time Overlay System
Recommended Video Overlay Device: IOTA-VTI KIWI-OSD (approx $250 US)
The IOTA-VTI labels each video field with the time of the VSYNC pulse and this time is accurate to less than a millisecond (more accurate than we need).
Radio Shack sells a Shortwave receiver with digital tuning for about $70. Just make sure it can tune 5Mhz, 10Mhz, and 15Mhz. To improve reception, several people have found good results by constructing a "long wire" antenna from a couple hundred feet of insulated wire (for more info see the posting on the IOTA Yahoo Group ).
To feed the audio signal into the video recorder I use I miniature microphone with a built-in preamp - $12.95 from Supercircuits, the PA3 . I use an extra long audio cable to connect the PA3 to the video recorder so I can place the WWV receiver well away from the telescope and other equipment (avoids RF interference).
Yes, you need to power all this equipment. If I can get AC power I use a bunch of Radio Shack "wall wart" DC power supplies or a Radio Shack 3Amp regulated 12VDC power supply.. When I have to use DC power I use a couple of auto "jump-start" 12V batteries that I picked up at a local marine electronics retailer. Basically, these are just rechargeable batteries (around 19Amp hours) with built in jumper cables, a light, and a most importantly - a cigarette lighter socket. I have a couple of cigarette light DC power cables that I picked up at radio shack.
All of the above equipment uses the same 12V DC power connector and polarity. The equipment all uses a center positive, 5.5mm/2.1mm power connector. I found all the necessary connectors and cables at Radio Shack.
I have "organized" my "occultation recording equipment" into a single hard plastic Rubbermaid container with bubble pack for padding. This box contains the VTI device, the camera + 1 1/4" adapter, the Shortwave receiver, the PA3; plus, all the video, audio, and power cables are connected. All I do now is pull out the GPS receiver and lay it where it has an open view the sky, pull out the WWV receiver and turn it on, pull out the camera and plug it into the scope, pull out the A/V cables for the VCR and plug them into the VCR, then plug in the 12VDC power for the whole thing. For power distribution, I built up a small box to acts as "DC power strip" and plug in 12VDC via either an AC "wall wart" or one of the 12V battery packs. Recently I started using Y-adapter cables instead of the small box. You can get Y-adapter power cables from Supercircuits. This setup keeps my stuff organized together, reduces errors due to mistakes in connecting all the pieces (they are already connected) and speeds up the whole process of setup for an event (often important when chasing around looking for clear sky).
2012 - Nov - 2