17.5 inch f4.6 Newton

2004                               2006                                2008                               2010

“Be honest. You want to observe through the biggest telescope you can get your hands on. A statement by David Kriege, the author of the book “The Dobsonian telescope”, which decribes the phenomenon of” aperture fever “aptly. After I finished building four versions of a 17.5 inch f4.6 Newton I could look back on ten years of trail and error, of designing and constructing. A ten-year obsession to create a large, yet practical, telescope. In the end I build four versions over the course of 10 years.

After several attempts at constructing a 6 inch f8 Newton (in split ring, fork and Dobson configuration) in the 90s building a big telescope seemed a daunting affair. Around the year 2000 I had plenty of ideas on what I wanted to build, but buying an affordable mirror also seemed to be a tricky hurdle. Most of the large mirrors for amateurs were being made in the US at that time and importing one was costly.

In June 2001 I was fortunate to spot an advert in which a 17.5 inch f4.5 Newton on a heavy metal splitring mount was offered. Since I was only interested in the optics, I had to convince the owner to sell the mirrors separately. If he hadn’t I would probably have spend my money on a 8 inch Celestron. In the end I got my 17.5 inch mirror and a 3.5 inch secondary.

Although the Netherlands has some reasonably dark areas, I don’t live there. So my telescope needed to be portable. Around the year 2000 ATMers in the US started building ultralight portable telescopes. Like a lot of amateurs I was fascinated by the 16 inch stringtelescope that Dan Gray build in 1999. In a radical attempt to reduce the weight of traditional aluminum tubes, this telescope has three pairs of strings which are tensioned by two carbon tubes. The advantages of this design are: a lighter secondary ring, fast setup and breakdown of the telescope and no complicated truss connections. This was the type of telescope I was going to build.

The first try