Tag: celestron

Nexstar SE Wedge

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The final part of my Nexstar project was getting it on a wedge which would make auto-guided long exposure shots possible. Unfortunately, the Nexstar wedge has long since been discontinued and even if it hadn’t — $160 for a weenie little wedge for this scope was a bit much for me. So I decided to buy a cheap used wedge from an older Celestron system and make whatever modifications were needed to get it to work with the Nexstar.

What I didn’t expect was how little modification was needed to get an old 1980’s era Celestron C8 wedge to work with the Nexstar SE. All the holes, both on the tripod and drive base lined up perfectly and the only modification I really had to make to the wedge was to hammer out the center guide peg.

Mounting the Nexstar

In the first photo on the right, the wedge with the center peg removed has been mounted on the Nexstar SE tripod. The center peg on the tripod fits well as it is much smaller than the space left by the removed wedge peg. The tripod bolts hold everything in alignment and there is little to no lateral movement of the wedge in relation to the tripod. The bolts are 5/16" x 24 x 1.5" cap screw bolts from the local hardware store. The azimuth adjusters work perfectly with this setup as long as you don’t tighten down the cap screw bolts too much.

One rather major item of caution is the length of the bolts that attach the Nexstar drive base to the wedge. Inside the drive base is a gear (right under the fork arm) that rides very close to the opening for the mounting bolts and is completely unprotected. (Seen in the 2nd photo.) If a bolt is too long and protrudes very far inside the telescope, this gear will bind against the mounting bolt probably causing damage to the drive base. These bolts are 3/8 x 16 — I got lucky and had an extra set from my old Losmandy GM-8 that were the right size but much too long. I cut and sanded them with a Dremel and then added some thick washers just to be extra careful. The final image on the right shows underside of the wedge with the Nexstar mounted.

Another modification I made was to remove two of the rubber feet from the Nexstar base to allow for more latitude range before the Nexstar base impacts with the side of the wedge as the drive base is slightly wider than the wedge. With the rubber feet removed I can get the latitude all the way to the 14 degree mark before the base connects with the wedge — with the rubber feet on, this was more like 30 degrees. The rubber feet peel off without too much difficulty and if I ever what them back on, they’re easy to reattach with some rubber cement glue. (I left one of the rubber feet on to designate the ‘top’ of the mount.)

Adding a Latitude Adjuster

My very first telescope back in 1999 was a Meade LX50 on which one of the first modifications I made to it was upgrading the rather flimsy wedge latitude adjuster that came with that scope. Since then I’ve had the old adjuster kicking around from box to box mainly because I’m a pack-rat but now I’m glad I never threw it away! The length of the bar turned out to be too long for the Celestron wedge by only about 3mm. I cut and sanded the bar down to size with Dremel cutting and grinding disks (at one point I had to wear work gloves because of how hot the bar was getting!) until it was a snug fit and then ‘painted’ any visible scuffs with a black Sharpie. The end result almost looks like it was meant to be there. 😉

Once down to size, I fixed the bar in place to the lowest point on the latitude guide groove on the wedge with a couple of bolts and washers to hold it in place. The long latitude adjustment screw fits well to the underside of the wedge and since this setup is not going to take a bunch of weight (certainly much less than the LX50 it was originally designed for!) it works very nicely. This modification also added a great deal of stability to this wedge. I was lucky to have saved the LX50 latitude adjuster and I think that even if I didn’t have it, I would have eventually wound up trying to make something similar out of wood.

One thing I’d eventually like to add is a pair of knobbed bolts in place of the current cap-screw bolts I have for the latitude adjustment on each side of the wedge so I can loose the allen wrench I currently have to use to loosen them.

Nexstar SE Camera Platform

If you’ve enjoyed these tips and are in the market for electronics or photo gear, using these links to buy from TigerDirect or Amazon.com or alternatively using the PayPal Donate button to make a small contribution helps me keep this site going. Thanks!

I recently picked up a used Nexstar 6/8 SE mount and tripod with the idea of using it not only as a grab-and-go for my 72mm f/6 Orion EON (and hopefully a 5 or 6" SCT OTA down the line) but also in the hopes of using it for some lightweight wide-field long-exposure and time-lapse astrophotography.

I wanted to side-by-side mount a DSLR camera and wide-angle lens combo alongside my unused Celestron 9×50 finderscope from my CPC800 and use an Orion Starshoot autoguider attached to the finder to guide the whole contraption for long exposure photos. That this setup can run on batteries and is lightweight enough to chuck in the back of the car for camping trips made this a really interesting camera platform despite the Nexstar’s well known astrophotography limitations.

Celestron 9×50 Finderscope Autoguider

I found a few pages and forum posts (http://bit.ly/N5GJ7D, http://bit.ly/QoZl9f and http://bit.ly/MUgGDD) with instructions on making an adapter for Orion’s autoguider using PVC pipe fittings but unfortunately all of them required drilling a hole in the finder which I didn’t want to do. I wanted a solution which would require no modifications to the finder and would be easy to undo.

Luckily, while fooling around with the finderscope one afternoon I realized that the threads on the back of Celestron’s 9×50 Model # 51611 finderscope that the cross hair eyepiece attaches to are common 2" SCT threads! Given that the 1.25" adapter on the Starshoot autoguider attaches to a standard T-thread on the autoguider body all I needed to find was a male SCT to male T-thread adapter to fit everything together.

I had no clue if such a beast existed and after a little bit of googling I found what I needed at http://agenaastro.com — their Blue Fireball T / T2 Male Thread to SCT Male & M48 was exactly what was needed to make this work. (Seen in the first photo on the right.) This adapter is very low profile and easily allows the finderscope to achieve infinity focus with the Starshoot autoguider.

As shown in the middle and bottom photos on the right, the whole thing comes together in a nice, compact and sturdy assembly and it fits perfectly on the standard Celestron finderscope mount with no modifications needed.

Side-by-Side Camera/Autoguider Mount

Next up was finding a sturdy way to mount the finderscope and camera on the Nexstar.

From a previous project I had a mounting bar with a center hole tapped for a standard 1/4-20 tripod stud with 4 untapped holes on each side. A couple of bolts and washers from the local hardware store worked to mount the Celestron 9×50 finder mount securely to the bar.

To attach the whole thing to the Nexstar, I used the mounting block from the Orion EON 72mm f/6. (Which normally rides piggyback on my CPC800.)

The second photo shows the system all set up with the finderscope, Starshoot autoguider and an IR modified Canon 300D. One of the lenses I plan to use with this setup is a Zenitar 16mm fisheye but unfortunately, the finderscope is mounted so far forward that it projects into the Zenitar’s 180 degree field of view. So I’ll either need to crop the resulting images or figure out some way of mounting the camera further forward or the finderscope further back.

The last image shows everything attached to the Nexstar SE mount and ready to go. Note that I did have to remove the plastic altitude gear covering for the side-by-side mounting to fit which detracts a bit from the looks but everything still works fine.

I love how compact and multi-functional this setup is and can’t wait to get some time out in the field with it. Running with rechargeable batteries for the mount and with spare batteries for the camera and my netbook I think I can get a solid evening of imaging with this setup without ever needing a power plug.

The next step was to adapt a cheap, old wedge for the Nexstar

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