11 inch Refractor

[JA]

Yes 11 inch is a big refractor and something I'd like to undertake as a project using an 11 inch Plano-Convex lens I acquired a couple of years ago. The lens forms part of a Perkin Elmer 916mm focal length f/4 Type 1 Aerial Camera lens and was used as a surveillance / spy camera in the Lockheed U2 and SR-71 aircraft and imaged on to 9 x 18 inch film. Image of the lens / camera below.

The Plano-Convex lens is just over 270mm in diameter and has a focal length, as best I can currently measure it, of 840mm and is a precision piece of glass and hardware.

Possible uses could be as...

1. An 840mm focal length ~f/3 singlet refractor, possibly used for narrowband or solar imaging.

2. An ~1020mm (Need to recheck) focal length ~f/3.8 Classical Dialyte refractor using the the 270mm diameter, 840mm focal length Plano-Convex lens with a long focal length negative / diverging lens. One I have access to is a 76mm diameter, -1250mm focal length Negative meniscus lens. The lenses would be spaced apart so that all of the converging rays from the plano-convex lens intercept as large a diameter as possible of the 76mm diameter negative meniscus lens, and hey presto a long focal length refractor.

I have a large bore Moonlight refractor focuser which I could implement with the optics. To facilitate mounting and testing the refractor would probably need to be in some sort of large timber construction with built in optical rails to move the negative meniscus lens fore and aft and also support the 11 inch front element and focuser. Then there's collimation, etc... I could even go further and find some one to aspherize the plano convex element for improved performance as a singlet refractor.

At the moment it's a bit of a thought experiment as I have a bit too much on to devote time to it, but I'm always thinking of it and whenever I see large diameter tubes I take a good look. I need something in ~300mm. I have a short length of 200mm diameter aluminium tube (thanks MattT:thumbsup:) and some Parallax brand tube rings to suit, but then joining the 300 to the 200 needs to be solved.

One day.

Best
JA

[mura_gadi]

Just had a little history brief...


“These lenses were also used in the Samos satellite program and a modified version of these optics were later used in the lunar mapping programs. Designed by Dr. James Gilbert Baker, very few were made and they are one of the best optical systems ever manufactured. This one is #8. The lens overall dimensions: :21″ x 21″ x 35″ the weight over 200 pounds.”

Read more: https://photorumors.com/2012/01/23/now-this-is-a-lens/#ixzz7RPdNrqNJ

If you think about the requirements of the camera/lens, operate at 60,000ft or more, at 800kph or more and take photos that allow for vehicle recognition/identification at ground level... Pretty sure the SR-71 pilots were the first of the armed forces to use medically prescribed stimulants for military deployment... next to the satellites dropping camera roles out its in a league of its own.

[Stefan Buda]

So you acquired only the front element of the lens?

[JA]

Yes Stefan, unfortunately only the front element which weighs in as ~11kg from memory, with its mounting ring. I think I will still be able to make some sort of concoction with it:D

Best
JA

[JA]

Thanks for the info Steve. It's a real beast for sure at 200 pounds !! The part of it that I have, the front element, is a respectable chunk of that at ~24 pounds.
,
Best
JA

[AstroViking]

What a monster of a lens. I'd love to see the finished product.

[mura_gadi]

You could make a nice 23mm+ thick plywood donut(OD 300mm/ID 200mm) from structural ply, that would be an easy option to bolt the two tubes together. Then you could use a thin plate cover of the same dimensions for a welded seam between the two and it could be coated later...

[JA]

Thx Steve. As it happens I was thinking about something along those lines made of stacked layers of mdf or ply glued and screwed with one side fitting inside the 300mm side (not too thick and not interferring with the light beam) and the other side going on the outside of the 200mm tube. For development and testing though I'd make a long ply box with an internal rail (think optics bench) to fit any internal optics and then if it shows promise go crazy on something more elaborate.

Thx and

Best
JA

[Meow]

(Following, with interest. Wow!)

[leon]

JA seems you have a few options at hand, however have you considered the industrial Sewerage Pipe Reducers, they are very heavy duty and reduce from 300mm to specific diameters.
It might be a thought.

Talk to a Plumber or someone who works with this stuff.

If you go to Bunnings for instance they have heaps of Poly Piping and reducers of all sizes, although they don't carry this Industrial Stuff it might give you an idea in what I am on about.

Leon

[JA]

Hi Leon,

Thanks for the suggestion. I had considered large diameter 300 to 350mm storm water and SWV pipe, but had not considered the reducers which I could potentially use with the 200mm aluminium tube I have. Good point. I will have to take a look.

Best
JA

[mura_gadi]

We have a supplier of marine flexiply here, that will go down to 200mm+ circumferences. 5mm and 8mm thickness, you might go close at 8mm for strength and flex.

The other one is sonotubes, bunnings stock them but I can't think of the Australian name. Concrete form work tubes...

[JA]

Hi Steve,

I hadn't thought of flexy ply, but I don't really want to make the tube from scratch as I have a wonderful 900mm long 200mm diameter thickish Aluminium tube (thanks again MattT !!!) that I have the correct Parallax tube rings for- it's more a matter of dealing with and joining on a 300mm section.

I have thought on the sonotubes and I have a short length of something similar that I was considering using to help as a prototype if i went for an afocal type arrangement which would only need to be about 550mm long . It would comprise the 270mm plano convex front element and ~100mm plano concave rear element to make a ~2.7x afocal lens which could be coupled to the front of an existing ~100mm telescope - I should have mentioned it as option 3 in my first post. It could turn my 300mm f/2.8 lens in to an 800mm f/2.8 - It would be great to try to see what's possible or not.

My first job is to make up an optical bench of sorts to test/confirm exact focal lengths and adjust lens element positions. I have a simple idea for that and will soon share a picture here.

Many thanks

Best
JA

[JA]

Thanks guys... now the pressure's on:D

Best
JA

[xthestreams]

Could you get Diego to make you a carbon fibre tube? Seems to my complete n00b brain that the self-weight of wood would result in pretty significant sag?

[JA]

Hello XT,

I wouldn't make a final device from wood, but perhaps a prototype to mockup lens spacings, etc... or simply dispense with a prototype if I get what I need testing wise from an optical bench setup of the lens elements, etc. More than likely the final device would be made from Aluminium tube, but you never know perhaps in CF instead. Thx for the suggestion.

Best
JA

[mura_gadi]

The material is less import than the type of beam/support and distance of loading.

You get a board/beam and it will sag at a calculated distance by weight, for the strength, put it in a tube and your dynamics change completely.

Take a A4 sheet, a 5 cents piece placed on the opposite side width wise and the paper/span will fail. Roll that paper into a tube(single thickness) and you can place a couple of dollar coins in the end and the span will hold.

Tubes are great, better than squares, diameter is a big factor and your starting at around 12". Hence guessing 5mm and 8mm options being fine.

Sub's are tubes for a reason...

*Things like stress to strain numbers can be found in the full product pdfs occasionally, US sites seems to be very good for full pdfs on wood ... (Modules of Elasticity is it???)

[Meow]

He doesn’t make them. A company in Qld does…

[JA]

Here are all the pieces so far....
11 inch Optic
200mm Aluminium Tube
200mm Tube Rings
Moonlite large refractor focuser (balanced on a shot glass:D)

image below

Best
JA

[ChrisV]

That looks mega awesome. This will be interesting to follow!!
Good luck

[MattT]

Wow JA….go big or go home!

How far from the 200mm tube does the objective sit?

I have an idea for mounting as I have thought on and off, mostly off, about a 9” Istar f9 achro or 10” f11r30, on the same 200mm tube which I have another piece just waiting to be used. Never could get the funds together to buy as Im waiting for the US$ to drop like it did years ago when 90oz cents bought the mighty us$…I digress.

Other question is how long in f ratio, does the 76mm lens make the scope?

I got the mount for such a monster as you know.

Would like to see the beast in real life if possible too?

Interesting project.

Matt

[JA]

Hi Matt,

OPTION 1...
The objective is a 270mm ish singlet with an approximately 840mm focal length if I use it as a singlet. So in this case I would need to trim the 200mm tube and add support for the 270mm lens perhaps with a 300mm tube or open truss type addition.

OPTION 2...
If instead I use it in what I understand to be a classical dialyte configuration (A converging objective lens with a diverging lens spaced some distance away in the "light cone" of the converging lens) I calculate I could achieve a 1020mm focal length, using an available 78mm negative lens with approx neagtive1250mm focal length that I have on order. All the focal lengths need to be verified with more precision when I set it up on an optical bench of sorts.

The 200mm tube you so kindly gave me fits the 200mm parallax rings I already had so I am hoping to use that together with a (yet to be acquired) ~300mm aluminium tube grafted or welded on to the 200mm tube to support the 270mm lens in its nude /unmounted state. So that would be ~ 150mm infront of the existing 900mm tube. An of course then mount the large Moonlite refractor focuser on a yet to be machined aluminium disc / donut that could possibly fit inside the 200mm tube (~194mm ID).

OPTION 3...
There is another potentially more interesting way to use the large objective lens and that is for me to make a giant afocal (telecentric) lens. Like the type used to screw on to the front of camera lenses or video cameras to get a typical 1.4 to 2x magnification. With the focal lengths and optics that I have I could make an approximately 2.7 x afocal lens. Using the 270mm Plano Convex 840mm focal length lens and a 125mm Plano-Concave Negative305mm focal length lens that I have and spacing them at approximately 535mm apart so that both lenses have a sort of "common focus" I could generate an output beam 100mm in diameter, which if fed in to another 100mm refractor would increasse its aperture by 2.7 times whilst maintaining its f ratio. So a 100mm f/11 refractor I have would become a 270mm f/11 refractor. Resulting in an equivalent FOV to an ~3000mm focal length - kind of cool. Just don't ask me about chromatic abberation. It would be a trial and error alignment / collimation process. Given the focal lengths and spacings of the lens elements, this option would be ~500mm long and approx 300mm in diameter and sit in front (somehow) of an ~100mm or smaller telescope. The scope and the afocal lens would need to be mounted on a common rail/s to maintain good alignment/ collimation.


It makes it an approx 1020mm focal length (from memory - recheck calcs?) in what I understsand to be known as a classical dialyte configuration so approximately f/3.8



Your mount is a Beautifully crafted BEAST for sure



You're more than welcome to see it before / during/ after. Thx again for the 200mm tube. It certainly makes the job easier.

Best
JA

[JA]

Thanks Chris _ I'm looking forward to some progress soon, even if it's only acquiring another bit to use or optical bench testing.

Best
JA