Dial Indicator for Accurate Focus

[avandonk]

Some time ago I installed a dial indicator on my 150mm Achro so I can focus very accurately after changing filters without losing the framing of the object no matter how dim. They come in two flavors analogue or digital. Either will do but the analogue are only about $40 from Bunnings.

It is simply a matter of taking test exposures say 0.2mm apart and then checking which position is closest by inspecting the images on your computer screen. The animated gif is three images (100% crop)using a Halpha filter on the achro and they are 0.2mm apart. It is then just simply a matter of resetting to the best focus position with the dial indicator.

If you note the temperature of your optic on different time/nights and focus position, you can also get an accurate idea how focus changes with temperature.


Bert

[leon]

Nifty idea Bert, I can see how this can get pretty much spot focus each time without to much effort, I like it, and might just look into that idea.

Leon

[GeoffW1 (Geoff)]

Very nice engineering solution to this problem.

What about expanding this to an illustrated article?

Cheers

[seeker372011 (Narayan)]

clever idea

I purchased a digital vernier from Aldi to accomplish a similar outcome but that is hand held...this is much more elegant.

[avandonk]

You can use a digital caliper in the same way. I use one on my 100ED it is not connected to the drawtube in this image as it is set up as a guidescope.

It is not as easy to fix a digital caliper tothe 150mm achro due to the big jump in diameters.

Bert