New Guidescope Build

Stub Mandrel · June 5, 2018

While my homebrew 50mm x 182.8mm guidescopes have proven perfectly good with the 130P-DS, I have found the need to swap in a 0.925" every time a bit of a pain. Also with the HEQ5 I thought a longer f/l would be a good idea, particularly combined with the 150PL.

At f3.5 I have had no trouble finding plenty of guidestars so I thought a larger, longer focal length lens of similar focal ratio would work well.

The small guidescopes were made by shortening cheap toy 50x300 scopes, fitting inexpensive coated achromat objectives from AstroMedia and 3D printing new, better fitting, drawtube holders.

The new guidescope uses a plastic Synta focuser bought cheaply from Astroboot, one of the better ones it has an adjustable and lockable gib. Although nothing to write home about, it's possible to set the drawtube action stiff but smooth and lock it easily - ideal for a guidescope.

I got a 60mm x 228.1mm fully coated achromat objective from AstroMedia.

For the scope body I used a section of aluminium tube. I shortened the focuser and bored out the end on my lathe (a bit of a challenge to hold it!) I shortened the drawtube and blackened the end. I 3D printed an double ended plug to fit it to the scope tube.

I 3D printed a combined lens cell and dewshield, using the 'fuzzy surface' option in Cura. I sprayed the inside of it with matt black heat resistant paint.

Tested with 32mm and 25mm EPs on distant trees, it give surprisingly clear, sharp views without noticeable CA which is a surprise at f3.8 but no doubt shorter EPs would show up its weak points. My impression is that the lens is superior to the 50/163mm. With a crosshair eyepiece I think this would make a very nice finderscope. ?

It's tempting to fit Astromedia's 70 x 280.1mm objective to my (currently 700mm) Lidl/Bresser scope just to see what happens ?