Yes we need a `Starry night with camp-fire and bottle of Port' section of the forum for this sort of stuff. It would be good if moderaters had a simple `eject to the camp-fire ' button.
Yes we need a `Starry night with camp-fire and bottle of Port' section of the forum for this sort of stuff. It would be good if moderaters had a simple `eject to the camp-fire ' button.
Yep
Quite miss the "Port and Cheese" sessions we used to have at WA astrocamps. Was a good break between observing sessions and helped everyone calm down, relax a bit and remember that the voices in the dark were real people.
Here is my 90mm achromat. It is basically a smaller version of the 6", similar construction. The focuser is a GSO 2 speed with dielectric diagonal. The focuser adapter is homemade from brass. The mount shown is the same one for the 6" refractor just with less counter-weights and a different dovetail clamp and plate. The lens is an Antares 'Vixen spec' traditional style achromat made in Japan, magnesium fluoride coatings on all surfaces, 1500mm focal length. I am in the process of making a portable mount for this scope but young children and study commitments have been taking priority.
Last edited by anj026; 13-03-2008 at 09:58 PM.
Reason: add pictures
The construction is the same principal used for the 6" refractor that is shown in my review of the D&G 6" f15 lens. It uses 4mm marine ply with baffles acting as ring frames. Check out that review and if you have any other questions I will try my best to answer.
I bought the lens online from Hands On Optics in the US. It is listed under accessories; parts; Antares. I paid about $160-170US and feel it is worth it for a quality hand made lens (made in Japan). It is shown as 93/1500 but actually works out to 90mm clear aperture once mounted in a cell. It comes without a cell but Hands On will probably be able to supply one if you ask them. The Antares 4" lens' come with a cell but are $350US. I used one that I purchased from Meridian Telescopes in the US for about $30 and then modified it to suit the wooden tube. If you are handy with a metal lathe the cell should be easy enough to make yourself.
16" F.45 String Truss Dob - just operational and first light 8 hrs before leaving for the 2007 SPSP.
Entire instrument designed to fit into the boot of a Holden Astra sedan - and it does too
Few changes since then. More photos to follow.
Cheers,
Ian, I'm very impressed and as I am interested in the possibility of building a lightweight and compact 18" reflector, I wonder what weights you ended up with and where you got you mirror and plans
No formal plans I am afraid, lots of inspiration off the web though. Mirror second hand through IIS (20yo Meade), repolished and refigured by Mark Suchting.
The objective lens system is actually the optics from an ex NASA satellite tracking camera. "MOTS". There appear to be 6 or more elements contained within the 500mm long lens cell. In the centre of the cell is an adjustable iris diaphram just like a normal camera lens - just that this one is on steroids. The objective cell is 220mm diameter, 500mm long and weighs 26kg if I recall correctly. Mounting it was a significant exercise. I have attached some additional images that hopefully show how it works. The whole scope weighs more than my 407mm F4.5 Dob!!
While it was designed to deliver a 200mm diameter flat and orthoscopic photographic image, it is not much as a visual instrument and I don't use it. Great fun to build though .
In order the images are:
Objective cell prior to mounting after I had fitted some mounting rings to firtinside a 250mm diameter tube.
Next 2 from the front showing iris partly closed and fully open.
F/Ratio Change Knob below focuser F5 - F16.
F/Ratio change drive gear.
Internal collimatable diaginal mirror.
Cheers,
Hi s/scope - I'm rather intrigued by your 8" refractor: you comment that "it is not much as a visual insrutrument and I don't use it" -
could you elaborate a bit on that please, and let me know whether you've used it for any sort of imaging?
I ask, because for nigh on 40 years now, I have possessed a somewhat similar lens assembly that I allways harboured the idea of transforming into a scope of sorts.
Mine is a compound lens assembly, not having disassembled it I don't know the number of lens, but several at least; it has an objective diameter of 6&1/4" with a focal length of 50". (f8) This can be varied, like yours, by an iris diaphragm that is operated via a rotating ring on the lens body.
I had it on excellent authority to have been formerly utilized as a type of telephoto lens by Adelaide's "Advertiser" daily paper by the sports photographer: it originally came mounted onto a long rectangular box that was tripod mounted, the rear end of the box holding a large photographic plate/film. Evidently it had some fame as the camera responsible for some classic football and Test cricket photographs.
It's provenance prior to this was (reputedly) that of being a sophisticated camera lens; part of a speciallized aircraft reconnaissance job. I think, given the era when I bought it (circa 1970) it was more likely to be such than something akin to your lens prior life - satellites only being 14-15 years before it came into my possession. The lens are optically coated, it is quite a heavy assemblage and that is about it.
Have entertained ideas about employing it for some use for many years, and how I've managed to drag it around with me all these years is a minor miracle in itself! Would be interested to hear your thoughts, and if you would elaborate a bit on the question I put to you above.
Compared to a Newtonian of similar aperture, this refractor exhibits significant CA, dimmer image and lower contrast. My primay interest is visual DSO observing and therefore not much use to me.
On the plus side a very flat field and in monochrome light, very sharp indeed.
I had to build a mount for it to find this out. I guess you will have to go through the same process with your lens.
Let's see... When I was 11 I made the 6" f/8 the optics of which I still have. Then the 10" f/9.2 which we used at school. It had three eyepiece ports and the secondary mirror moved around to three detents to make observing easier. Following that there were a few more reflectors of various apertures from 10" to 18". Then I was asked to do a 16" f/4.5 for a guy with low COG. Then I made a couple of front ends for a few dobs and a 20". Then I did the 27" for the ASV along with a couple of other guys (that's a 27" upper cage assembly on my garage wall). Hmm, think that's enough.
Wow! There are some amazing scopes here that I'm sure will affect my next project's direction. This is the 2nd version of this scope that I'm continuing to tidy up. Everything but the trusses packs into the ball. Thanks for looking! - j
should rename the car Tardis.
, I reckon there is something really nice about a wood scope tube 
.
