just Tony
Senior Member
A couple of years ago I shifted my hobby investments more towards photography and somewhat away from astronomy to better match where I was spending my time. One of the items I stepped away from was an extremely capable German equatorial mount which wasn't being fully utilized in part because of its 110 pound weight and the long-ish setup time. However I still wanted a tracking mount for wide field photos. "Wide Field" meaning what I get from any of my camera lenses that range from 16 to 300mm. The question was, what to choose?
a. New German equatorials seemed to end up running about $1000 once I selected a satisfactory one.
b. Air-travel portability wasn't a consideration. Being transportable via car was good enough. I'd consider the pricey AstroTrac if I was headed to Australia for a weekend.
c. I could easily get by without a Declination axis.
I ended up purchasing a used Celestron CG-5 over at AstroMart for $200, complete with polar alignment scope and steel tripod. The aluminum tripod has a poor reputation but the wood version seems to be about as well liked as the steel one. The tripod setup is a bit clumsy but it can be transported without folding the legs in hatchbacks, wagons, SUVs and minivans.
I wasn't going to use the Declination axis so I unbolted it (2 screws). That saves a fair amount of weight due to both the axis assembly itself and the counterweight.
The bare aluminum "hockey puck" you see above is a custom bit I had locally machined for $35 that serves as a mounting point for the Really Right Stuff lever clamp.
Dovetail clamps are my standard mounting technique for terrestrial shooting and they are doubly useful when working in the dark; triply useful when your fingers are cold. This enhancement is worth considering no matter what one uses for a tracking mount, but this one happens to be irrevocably commited to the job because I drilled out the center hole in order to free up the optical path of the polar alignment scope which lives inside the hollow Right Ascension axis. There is a happy coincidence with the clamp: an old polar scope reticle illuminator I have is a good fit in it.
Here is the mount supporting my biggest payload, a 300mm f/2.8:
Going from the bottom up starting at the RRS clamp there is:
A generic dovetail plate from Kirk Photo, with 3/8-16 thread.
RRS BH-55 ball head (or I could use any 2-axis head).
Wimberley Sidekick which strictly speaking is just a luxury. The added lever arm probably lengthens the damping time but that's still well within one second. When everything is locked down it all feels extremely solid.
The box connected to the camera is my own interval timer design which is based on a microcontroller. It's not unique other than being much easier to set than any of the commercial units I've seen and it uses a rechargeable lithium battery. The CG-5's C-cell battery box has been replaced with a lead-acid battery. A full night of operation will use less than 1/2 of the charges.
If you start a thread about equipment in this forum at this time of year it's probably traditional to show an example image of M42 that was made with it. I won't make any claims of accuracy on the colors because I did my shooting under a heavily light polluted suburban sky and had to work to coax the detail out while killing the sky glow. This image is heavily down-sampled from a substantial crop (30% of the area) out of the D800 frame. 6 layers aligned and averaged in CS6, 25 seconds each. In the original frames the four brightest members of the Trapezium are just barely resolved, but they merged in the downsampling, Curves, and Level treatment.
Summarizing this customized mount for use as a tracker:
a. The cost was relatively modest (vs a purchase of new commercial equipment), about $400 total when I lump in the modified RRS clamp. That's more than one would spend on a barn door mount but with superior operational qualities IMO.
b. The payload capability is much more than the heavy 300/2.8 pictured above.
c. Mechanical setup time is about a minute including basic polar alignment. The mount head includes geared adjustments for the azimuth and elevation axes.
d. Basic alignment has been adequate for lenses up to 105mm with exposure times up to 4 minutes.
e. With the 300mm and basic alignment I can go for a minute. For longer exposures I'd want to tweak the alignment via the drift method.
f. Dovetail mounting is a tremendous luxury and insurance, vs. fiddling with screws in the dark.
g. It's "portable enough" for my use model but it's not what I would consider to be a candidate for international air travel.
h. The steel tripod is no lightweight but it could support a truck. The wooden leg option is probably lighter and just about as good. I have never heard anything good about the aluminum leg option so be wary about them.
i. It's easily converted back into a full 2-axis mount for a telescope via just a few screws.
a. New German equatorials seemed to end up running about $1000 once I selected a satisfactory one.
b. Air-travel portability wasn't a consideration. Being transportable via car was good enough. I'd consider the pricey AstroTrac if I was headed to Australia for a weekend.
c. I could easily get by without a Declination axis.
I ended up purchasing a used Celestron CG-5 over at AstroMart for $200, complete with polar alignment scope and steel tripod. The aluminum tripod has a poor reputation but the wood version seems to be about as well liked as the steel one. The tripod setup is a bit clumsy but it can be transported without folding the legs in hatchbacks, wagons, SUVs and minivans.
I wasn't going to use the Declination axis so I unbolted it (2 screws). That saves a fair amount of weight due to both the axis assembly itself and the counterweight.
The bare aluminum "hockey puck" you see above is a custom bit I had locally machined for $35 that serves as a mounting point for the Really Right Stuff lever clamp.
Dovetail clamps are my standard mounting technique for terrestrial shooting and they are doubly useful when working in the dark; triply useful when your fingers are cold. This enhancement is worth considering no matter what one uses for a tracking mount, but this one happens to be irrevocably commited to the job because I drilled out the center hole in order to free up the optical path of the polar alignment scope which lives inside the hollow Right Ascension axis. There is a happy coincidence with the clamp: an old polar scope reticle illuminator I have is a good fit in it.
Here is the mount supporting my biggest payload, a 300mm f/2.8:
Going from the bottom up starting at the RRS clamp there is:
A generic dovetail plate from Kirk Photo, with 3/8-16 thread.
RRS BH-55 ball head (or I could use any 2-axis head).
Wimberley Sidekick which strictly speaking is just a luxury. The added lever arm probably lengthens the damping time but that's still well within one second. When everything is locked down it all feels extremely solid.
The box connected to the camera is my own interval timer design which is based on a microcontroller. It's not unique other than being much easier to set than any of the commercial units I've seen and it uses a rechargeable lithium battery. The CG-5's C-cell battery box has been replaced with a lead-acid battery. A full night of operation will use less than 1/2 of the charges.
If you start a thread about equipment in this forum at this time of year it's probably traditional to show an example image of M42 that was made with it. I won't make any claims of accuracy on the colors because I did my shooting under a heavily light polluted suburban sky and had to work to coax the detail out while killing the sky glow. This image is heavily down-sampled from a substantial crop (30% of the area) out of the D800 frame. 6 layers aligned and averaged in CS6, 25 seconds each. In the original frames the four brightest members of the Trapezium are just barely resolved, but they merged in the downsampling, Curves, and Level treatment.
Summarizing this customized mount for use as a tracker:
a. The cost was relatively modest (vs a purchase of new commercial equipment), about $400 total when I lump in the modified RRS clamp. That's more than one would spend on a barn door mount but with superior operational qualities IMO.
b. The payload capability is much more than the heavy 300/2.8 pictured above.
c. Mechanical setup time is about a minute including basic polar alignment. The mount head includes geared adjustments for the azimuth and elevation axes.
d. Basic alignment has been adequate for lenses up to 105mm with exposure times up to 4 minutes.
e. With the 300mm and basic alignment I can go for a minute. For longer exposures I'd want to tweak the alignment via the drift method.
f. Dovetail mounting is a tremendous luxury and insurance, vs. fiddling with screws in the dark.
g. It's "portable enough" for my use model but it's not what I would consider to be a candidate for international air travel.
h. The steel tripod is no lightweight but it could support a truck. The wooden leg option is probably lighter and just about as good. I have never heard anything good about the aluminum leg option so be wary about them.
i. It's easily converted back into a full 2-axis mount for a telescope via just a few screws.
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