Drop $5 at a pawn shop then spend a little time on a lathe and you can have
a nice little helical focuser for your short-focus telescope project.
Here is an of example of one of these adaptations.
With the advent and widespread use of digital cameras, finding inexpensive lenses for old 35mm SLR cameras is a snap. Each of these old lens assemblies contains its own helical focusing assembly ready for adaptation to use on a telescope or other optical project.
Step 1: Remove the glass.
Step 2: Take it from there.
In this example, the brass tube in the center accepts the OD of an old T-adapter for 35mm photography. This then accepts a couple of draw tubes that extend to reach any focus over a 3-4 inch range for use with 1.25 inch eyepieces. Make longer tubes to give you more range.
To use, just pull out an extension tube to rough focus, then use the lens focusing mechanism for fine adjustment. This particular lens's internals provide about 3/8 inch of fine focus travel.
A photo of the focuser closed to it's shortest height:
And a photo of the focuser's tubes extended:
The base of the focuser is a female T-thread to fit the end of a particular refractor's male T-threads. Of course, you can make it into anything you want. I have used this item to make many astrophotos.
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