3D-Printed Finder Guider

This is a 3D-printed finder guider that I built from a 60mm achromatic objective in a metal cell from Sheldon Faworski, a length of 2" cardboard mailing tube, and some parts 3D-printed from ABS.

The 3D-printed parts include:

  • an adapter to marry the lens in cell with the cardboard tube (with suitable tapering down that does not vignette the lens aperture)
  • an adapter with two tapped grub screws to allow a standard 1.25" nosepiece to be attached to the finder guider (an ASI120MM is attached)
  • two guide scope rings
The 2" mailing tube was cut to the exact length so that the ASI120MM only just reaches focus. The ABS parts were then epoxied to the cardboard tube.



Viltrox EF-NEX IV AF Adapter on Sony A7 II Brief Impressions

I have written about the Viltrox EF-FX1 before.

TL; DR - the EF-NEX IV performs pretty much the same way as the EF-FX1, is marginally better in some cases, and worse in other cases.

AF performance is by and large acceptable to mediocre, with two notable exceptions: the Canon 16-35mm f/4 L IS and 10-18mm f/4.5-5.6 IS STM will not AF. On the plus side, the A7 II actually manages to AF the Canon 180mm f/3.5L Macro, which the EF-FX1 was unable to. AF is quite slow and not very reliable however.

The EF-NEX IV also manages to report the focal length properly (which the EF-FX1 could not), and it can detect APS-C lenses and automatically crop (I was unable to get the "tunnel view" with the 10-18mm IS STM).

Quick Test: Canon 300mm f/4 L (non-IS) for astrophotography

The Canon 300mm f/4 L (non-IS) from the 1990's is one of Canon's discontinued, older and slower telephoto lenses. It does have UD glass. Because I already had the artificial star set up, I decided to see what star shapes look like off-axis on a Canon EOS 6D full-frame body.

Note that this is a contrived test using a 50 micron artificial star, 8m away (because it's cloudy).

And here it is:

It is not bad at all.

Compare to the APM Lomo 80mm f/6 Super-Apo triplet ("the best 80mm APO in the world," according to some), with the Televue TRF2008, which got the best results in my artificial star test:

Not too bad a showing for the Canon, I must say, given that the Canon is a 300mm f/4 (75mm aperture). The Lomo is the equivalent of a 384mm f/4.8 so not too far off.

Conclusion: the Canon superficially looks capable of challenging the "best 80mm APO in the world" on full frame.