ETX and piggybacks

[ksodbartman]

So I'm looking into getting a piggyback for my ETX-125. The one available from Scopetronix (http://www.scopetronix.com/piggyback.htm) looks pretty good, but I have a nagging feeling about it. They talk about felt padding on the inside of the ring so the tube doesn't get scratched up, but I'm just leery about the idea of a compression ring going around my tube. My worry is that by tightening the ring to hold the camera I might distort the tube, either temporarily or (worse) even permanently.

Has anyone around here used this type of piggyback, or heard of any problems (like this or otherwise) associated with them?

[aurora]

I have not.

But you could do a star test before and after attaching the ring, and see if you could detect any astigmatism. If the tightened ring was modifying the light path, it should show up in a star test.

My thought though, was whether the ETX had a beefy enough motor to support anything on a piggyback? Maybe if the camera was really light?

[SarahMc]

The ETX-125 tube is pretty hefty - at least mine is. I don't know if they've changed them in the last five years or so, but mine's pretty thick aluminum. I wouldn't worry about it much, unless you're prone to over-tightening things to the point of failure. I'd be more concerned about the mount's rigidity and tracking accuracy, as well as those plastic gears on the dec/ra motors.

[Fr. Wayne]

http://www.weasner.com/etx/guests/guest_125ec_newold.html

and some pictures
http://www.weasner.com/etx/photo.html toward the bottom

[Tog_]

Edited... I just looked at it and it's different than I originally described

I built a piggy back for my ETX-90. It's ugly. Other mounts call it names, but I made it for about 5 bucks and it places no stress on the tube.

You will need:
One large flatwashers, diameter 1.5 inches with a 1/4 inch hole. 1.25 is better if you can find one.
Two 1/4 inch nuts to fit the next item
1 bolt, 1/4x20 and it needs to be long enough for the camera body to clear the tube.
Copper pipe connector. I found these at a hardware store. They are 1.25 inner diameter on one end and 1.25 outer diameter on the other. This means they will fit in the EP hole in the ETX and an EP can be set in the end of the tube. The ones I found are about 2.5 inches long.
Grinder or a file and some time.
Electical tape (or duct tape, for a truly MacGuyver look)

Place one nut on the bolt. Place the washer on the bolt and secure the other nut to the end.
Lock it down as tight as possible with the two nuts.
set the washer/bolt thing on the wide end of the copper tube.
Wrap it in electrical tape Thread this into the tripod mount of your camera and set it in the upper EP hole in the ETX.
Tighten down the EP locking screw and you're done.

You can still use the rear EP hole for viewing with the camera in place. Be careful when setting this up, as the flip mirror may hit the loer bolt if it sits too low. I used this on my ETX-90 to take a few exposures of 90 seconds or so using only the supplied tripod legs. Mine is one of the first, and doesn't have an Astrostar. It tracked well enough with a 200mm lens. Of course, you will want to be careful to make sure that the EP holder can supprt the weight of the camera, but since it presses toward the tube, rather than rocks back, I don't think it would be a problem. If you like I can try to post some pics tomorrow night.

[ksodbartman]

Oooh, please do post images of this contraption!

[Tog_]

Okay, I still can't fugure out thumbnails so here are links.

Here is the finished product (http://img.photobucket.com/albums/v205/Epim/HPIM0228.jpg) with an unused copper tube and a C cell battery (for scale purposes only.)*

Inside is a 1/4x20 bolt (http://img.photobucket.com/albums/v205/Epim/HPIM0232.jpg). (same size used for tripod mounting screws) and a nut. The top (http://img.photobucket.com/albums/v205/Epim/HPIM0229.jpg) is a washer, held on with another nut. The washer is held to the tape with electrical tape.

The device screws into the bottom of the camera body (http://img.photobucket.com/albums/v205/Epim/HPIM0231.jpg).

Slip into the upper EP holder (http://img.photobucket.com/albums/v205/Epim/HPIM0230.jpg). (After rotating the mirror into the the straight through viewing position.) Front View (http://img.photobucket.com/albums/v205/Epim/HPIM0233.jpg).

If you knew someone with a metal lathe you could make something similar out of metal and have it look like it was built on purpose.

I'm not sure if this would be tall enough to clear the 125 or not. You could always extend the bolt a bit, but I would recommend adding more nuts to the bolt to prevent screwing it too far into the camera body.

*pet peeve in pictures of anything ment to show size is a lack of common item for scale. This is most common with pictures of spiders. You se a pictur of a spider hanging in a web with a caption that says, Look at the size of this monster!!! Would it have killed them to put a quarter in the frame. It might be a tiny spoder with a macro lens... End rant :)

[ksodbartman]

That's pretty crafty of you. Thanks!

[Torsten]

Nice idea Tog. I have the ETX-90 classic too, and had dismissed the idea of piggybacking because I thought the drive was too poor. Now I think I'll try that.

[Tog_]

Thanks

I dont have the pics anymore (I had all my best ones in an envelope that I can't seem to find:cry:) but I took some shots from northern Montana with this set up, using that same camera and a 55mm lens. Both shots were about 90 to 120 seconds of the big dipper area. It was one of these pictures that pointed out the little triangle I now use to find M51. I didn't notice any problem with the motor.

If balance is an issue, the two holes on the underside of the tube could be used to attach a counterweight, possibly using a pair of eye bolts to mount a rod to hold the wieght out in front of the balance point. Never tried it though.