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Orion's 100ED Crayford focuser upgrade

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After a slight mishap last fall with my mount being blown over, I've been needing to replace my focuser assembly due to a slightly bent pinion shaft.

As always money being tight I opted for the inexpensive? ($129.95 US) Crayford focuser upgrade for my 100ED refractor.

One thing I was kind've anxious about, is on the Orion site for this focuser, it did not specify the amount of focus travel this unit had. My old focuser had a whopping 133.89mm of back-focus from being fully seated.

Since a lot of my imaging is at a higher F ratio than most folks, and I use all but the last 4mm of the focus travel imaging at F/18. Even my 6mm illuninated reticle requires a lot of back-focus. I wondered if I would be having to buy an extension tube as well. But, I had to have a focuser, and I wanted a crayford, so I ordered the upgrade.

Sure enough upon arrival after inspecting the new focuser, it only has a mere 75.78mm of back-focus. A difference of 58mm. Also, my old focuser tube actually a has 3 baffles inside to help deter any reflection anomalies. The new focuser tube has none?

After staring at the two units for a minute or two, slightly disgusted, I did what anyone would do...I took them apart.

The two focuser tube casings looked identical. After unscrewing the crayford assemblies apart I discovered the pinion shaft on the new crayford was larger in diameter than the one on the old focuser. Also there were four rubber washers used to space the assembly away from the focuser tube. This I figured out, was due to a slight difference in the focuser tube support roller bearings located inside the tube casing.

I removed the new short focuser tube, inserted my old long one in it's place, and reinstalled the crayford assembly to the casing. This only required removing those little rubber washers from the process to work perfectly.


And VIOLA! A Crayford focuser with 133mm of back-focus.

Fine focusing for planetary and deep sky is MUCH easier using a the Crayford as opposed to the old focuser. The action is just a tad stiff, definitely not a "feather touch," but it get's the job done.

The bottom line:

For $129.95 plus shipping, it is what it is. Shame one can't buy just the Crayford assembly by itself and just bolt it on one's original focuser for about half the cost.

Would I recommend it? If you don?t have the money for a more expensive model yes, it has definitely made the task of focusing much easier.

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