Orion XT8 Fine focus knob by drcameron

Last crawled date: 3 years, 1 month ago

My grip wore out on the right focus knob of my Orion XT8 telescope (https://www.amazon.com/Orion-8945-SkyQuest-Dobsonian-Telescope/dp/B001DDW9V6?dchild=1&keywords=orion+xt8&qid=1614538756&sr=8-2&linkCode=sl1&tag=drcameron-20&linkId=cf4f3d185e43447e5f3454d7e385e45f&language=en_US&ref_=as_li_ss_tl) . I was going to add a TPU pad. Instead I designed a fine focus knob. It's not as good as a 10:1 reduction with a commercial fine focus knob, but the ~ 2:1 reduction has been nice to have for a minimal investment. I used the inner rod connectors from CoffeeRoast's excellent design and rebuilt everything else. This focus knob is simply press fit over the stock knob - right side only. The left knob has a screw that makes adding a much larger knob complicated. I've included a smaller diameter knob, if you want one for the left too.
The increased radius (1.5x larger) results in an arc length increase of a similar 1.5x. This alone reduces the focus movement 1.5x for the same motion compared to the stock focus knob. The ability to also control the speed more effectively also gains an incremental control over focus adjustments, hence the ~2:1 reduction.
The smaller model is about 1.36x larger, so also gives some improvement in focus control.
I included a couple of photos to show the images I took with my cell phone using this focus knob to bring the moon and Orion nebula into focus using the SVBONY cell phone adapter (https://www.amazon.com/Orion-8945-SkyQuest-Dobsonian-Telescope/dp/B001DDW9V6?dchild=1&keywords=orion+xt8&qid=1614538756&sr=8-2&linkCode=sl1&tag=drcameron-20&linkId=cf4f3d185e43447e5f3454d7e385e45f&language=en_US&ref_=as_li_ss_tl).
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