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DSLR Won't Focus on Celestron Reflector - Fixed!


Greensheep2k8
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Hi,

First post. Not really a discussion topic, really just an overview of a mod I did in hopes of possibly benefitting one or two other readers.

Anyway will try to keep this brief. Recently bought a Celestron 130 EQ as my first scope and had great intentions of using it with my long standing Sony a200 DSLR to capture at the least some good moon shots and then who knows what.

Got everything setup and was dissapointed to find that I couldn't move the focuser far enough in to get focus on anything more than 20m away. It didn't take long on Google to find that this is a relatively common problem with a lot of modern reflectors.

Found a few threads with suggested solutions, mainly fitting low profile focusers. But having already stretched my meager budget to buy the scope, I couldnt really stretch to the £70+ for a new focuser that would have certainly needed me to drill into the tube to fit it. So I found a slightly more 'homebrew' solution.

Now I'm not suggesting for a moment that anyone else try this, this is just an account fo what I did and it worked. It's up to you whether to try something similar yourself if you're in the same situation.

1.

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I knew I had to mount my standard T adaptor and sony mount as close to the focus tube as possible.

2.

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Although the standard clamp was functional enough, It has some wasted length so i removed the clamp to see what was actually on the focus tube.

3.

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No surprises it was threaded. So without a method of making a similarly theaded part for my T adaptor I instead used a hole saw (from a cheap DIY shop kit) to cut a hole in a piece of 5mm acrylic (ebay) and then sanded the hole larger bit by bit until it just fit over the threads on the focus tube. Tight enough to prevent the camera dropping off or light getting in but not so tight as to risk damaging the tube itself.

4.

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So theres the piece of acrylic after being slipped over the threads of the focus tube. You can see in the picture that there's one or two threads exposed past the acrylic, so I sanded them down so they were flush. This still left 3/4 of the original thread intact so the standard eye piece clamp fits just as it did originally.

5.

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With the focus tube now flush to the acrylic, I glued (super glue of course) my Sony T adaptor onto the acrylic taking care to get it as central as I could onto the focus tube,

6.

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This would have been fine on its own, but I wanted to still be able to hold 1.25inch filters in line with my camera. The original T adaptor wouldnt screw fully onto my sony T adaptor due to the acrylic, so after screwing it on as far as i could and making sure it was all straight an level, I glued it onto the T adaptor with some epoxy along the threads.

7.

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I had originally tried grinding down the original T adapotor to get it to sit into the Sony mount but eventually found that this was unnecessary when using the epoxy.

8.

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So after sanding down the excess acrylic and giving everything a good clean, this was the end result. Everything light tight and snug enough to hold my camera securely without affecting the scopes operation with its standard eyepieces.

9.

However, this was in the middle of the daytime and being that I couldnt test the results for another few hours, I began to wonder whether I'd given myself enough extra travel. So after taking a look at the focus mount itself, I figured that I would cut off about 3/4 of an inch from the end of it, again without affecting the original operation of the scope at all, so thats what I did!

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No real explanation necessary, I just cut off the excess focus mount up to the point of the rack clamp underneath, then sealed the resulting gaps in the moulding with some epoxy and painted the rear to keep it light tight.

10.

So that's it. Gave myself about an extra 1 1/2 inch of focus travel without affecting the scopes original operation. Granted I've comepletly ruined the warranty but that was always going to be the case.

Not the best weather conditions here tonight, but did manage to capture a few pics, here's one:

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Also got a few pics of Alcor, Alioth and Vega. They're not worth posting but they were in perfect focus with a good 1/3inch of focus travel to spare, and there were no signs of the focus tube encroaching on the field just incase anyone's wondering.

Well looks like this thread has ended up longer than I'd anticipated.

Anyway, like I said earlier, I'm not suggesting that anyone try this themsleves. I did this off my own back and it's worked out really well. There are other less drastic solutions such as low profile focusers and barlows, however I wanted to get my scope working as it was and thats what I've done, my next investment will be a barlow and a few filters and I'll see where that takes me.

Hope it can be of use to a few other people who've bought similar scopes with the intention of using their DSLR for astrophotography.

Jay.

Edited by Greensheep2k8
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