Lukehurst ‘Classic” Dobsonian Sizes

[dobbyisbest]

Friends, I was wondering if any of the proud owners of Lukehurst dobsonians (the "classical" ones, not the ultra lights) would be so kind as to share photos and measurements of the primary mirror boxes or rocker bases (Width, Length) for the particular aperture size they have. I’m in the process of readying myself, for when one of them come up in the used market again, to be able to make the decision to embark on any long trip with confidence… and just knowing those dimensions is enough for me to make and informed guess for the rest of it. I’m basically trying to ascertain how they compare in size (footprint) against commercially available options of the same aperture (the measures of which I am very familiar with) and other "yardsticks” like the measures that Obsession provide here in the Lower Assembly row: https://www.obsessiontelescopes.com/telescopes/Obsession_Specs.pdf

By example, the Obsession 18" Classic’s rocker base width is 25"/63cm long (and the shape looks fairly square), and I would compare that to the Skywatcher 400p/16" that has a base diameter of 840mm! What I’m trying to determine is whether the Lukehurst dobs yield similar reductions in size.

I’ve been drooling over an attractive Obsession 18" Classic that has been listed for sale in the UK for some time now, but I just cannot make the price work against my budget, and more so because when I’m actually looking to move to something smaller than what I currently have - a 14" dob that measures about 45cm on each side (excl. alt bearings). I’m also avoiding ultra lights/compacts because of a typical lack of sturdiness. I really don’t like the faf that come with those (from own experience and from I can read on SGL and CN), and I still want be able to dodge trees without sacrificing too much aperture. Therefore I think a 12" or 10" in the classical models would be more suitable for me, but probably not with the base sizes that the commercial dobs come with. The Lukehurst dobs are also typically well priced according to the ABS archives.

Your efforts and input would be appreciated, and any other comments would of course also be very welcome 🙂

 

 

 

 

 

[Piero]

FWIW, the measurements you ask for my classic 12" F6 dob made by Lukehurst and redesigned by me are as follow:

- rocker box front/back: 487mm, side: 523mm.

- mirror box side: 433mm

 

Note that the trunnions stick out a bit laterally on each side due to his choices in rocker box side panel thickness (quite likely 18mm in these small telescopes - although it looks like the same thickness in much larger apertures), trunnion design, and exaggerated clearance between mirror and rocker box.

 

Regarding your sentence "The Lukehurst dobs are also typically well priced according to the ABS archives.", well, that's very subjective. They are more affordable than obsession telescopes because they are made in the UK (including the mirror) AND they are built more cheaply. Some examples about my latter point are: 

- choice of plywood thickness, grade, provenience

- little stainless steel and often use of undersized metal (e.g. lower truss attachments)

- mirror cell made out of wood with "ad hoc" triangles and mirror edge support...

- undersized truss poles with plastic inserts to make lower truss connectors

- plastic in the secondary mirror holder

- paint over varnish in general. I didn't want mine to be painted so he applied 1 coat of sprayed lacquer where he felt necessary leaving parts uncoated (e.g. UTA, wheelbarrow handles, trunnions)

- ...

 

Both Obsession and Lukehurst dobsons are designed for speed production, just not in the sense of commercial telescopes. There are a few engineering aspects which can be improved in Obsession telescopes and these improvements have been applied by the telescope makers who started off from Kriege's design. Said this, a lot of thinking and sensible choices are in Kriege's design...

If you have time I would encourage you to get a copy of the dobsonian telescope book by Kriege in order to understand concepts and reasons behind the obsession telescope design. Following that you might realise that many aspects in Lukehurst design make little to no sense. How about the views? Well I saw how these were affected by direct experience sadly. On a positive note, this pushed me to understand dobsonian telescope making as well as build my 16" F4 dob (aka Nunki) and then redesign this 12" F6 to make good use of it.

Edited May 10 by Piero

[dobbyisbest]

Thanks Piero.  Just to clarify, are those measurements of the sides the same as the original scope that you got before the redesign, or only after?

 

I saw your build project and your redesign looks fantastic, btw!

 

 

[Piero]

1 minute ago, dobbyisbest said:

Thanks Piero.  Just to clarify, are those measurements of the sides the same as the original scope that you got before the redesign, or only after?

I saw your build project and your redesign looks fantastic, btw!

Thank you.

That's correct. I didn't redo the mirror box and rocker box, but only modified their depth and improved air flow. The original mirror cell was ditched though.

---

FYI, I expanded my answer above as you were posting.

[dobbyisbest]

Thank you for the expanded and comprehensive answer, Piero. 

I have a copy of the book and have consulted it before to help me better understand and tweak my current dobsonian. Where you’ve had to deal with astigmatism, maintaining collimation was my big issue, and whilst I’ve managed to deal with it over time I certainly don’t want to have to deal with that again. If I buy a Lukehurst, that and the size/weight will be the main things I look out for. The impression that I get is that they are more sturdy than than lightweight design of my current one, and  believe your initial reports were positive about the the collimation

Unfortunately, your report is perhaps one of three or four reviews out there (rather, I’d call yours a philosophical journey 😉), and there are many others out there who don’t seem to have any problems and only have praise for the Lukehursts. So I’ll give it the benefit of the doubt and will always inspect first, but for the moment I’m really just looking for motivation to drive potentially hundreds of kilometers should one come up, and all I need for that really are dimensions. But I did invite other comments and yours are much appreciated, thanks!