TheSkySearchers

I was wondering if anyone here could chime in on what type of lens elements this could be? A friend of mine gave this to me the other day for free. I looked up on the web and it is a Bell Howell 36" F/8 Type I (914mm FL) Objective. It was used in U2 Spy Planes back in the day. Now this is just the Objective part. The full version as seen in the photos has a shutter fixed to it and some type of rear element Lens. Well I don't have them and thinking why can't I make a refractor of it. Since those two parts were for making Very Large Photos I think.

Also, the rear glass of the objective is somewhat curved as shown in the photos. I can take more photos if needed.

Now for my questions.

- Does anyone know what type of Lens Elelement it could be? Acro, APO, Doublet etc... Ad if so, could it be Airspaced or Oil used in it?
- Can I use this to make a refractor or do I need that Rear Element which could be a corrector of some sort or to aid in the Camera that was used, I think they were Ultra Wide Format?
- If I can make it a refractor, would the focal length be (914mm) or different since I don't have the Rear Element?




The Blue Part is the Glass Objective





Rear Hole

Thanks in Advanced

ahh it must be 36'' focal length ,''camera lense specs'' .

Is the glass itself about 5.5 inches in diameter? so the second element must be some sort of barlow lense . f8 at 36" (914mm) fl = 114 mm front objective lense diameter which isn't correct shown in your measurement . so it looks like you will definitely need another element to get the lense to a usable focal length

edit: so let say ahh the lense is 5.5'' that's 139x8 = 1112mm , so the second lense is a focal reducer ?

yobbo89 wrote: ↑Tue Aug 29, 2023 1:13 pm ahh it must be 36'' focal length ,''camera lense specs'' .

Is the glass itself about 5.5 inches in diameter? so the second element must be some sort of barlow lense . f8 at 36" (914mm) fl = 114 mm front objective lense diameter which isn't correct shown in your measurement. so it looks like you will definitely need another element to get the lense to a usable focal length

edit: so let say ahh the lense is 5.5'' that's 139x8 = 1112mm , so the second lens is a focal reducer ?

Thanks Rob, I was thinking the rear lens was a corrector/reducer of some sort lol. I think the objective is around 6.5"-7" When I get back home I will check it out more.

Now the X factor in the rear lens, could that be a corrector/reducer that is specifically made for Ultra Large Format Camera? If so , then could I get someone to make a corrector of some sort? It is kind of gona be a work in progress over the next few years. I want to machine the tube ect... Even if it is not the sharpest, I think it is kind of cool to say this was taken from a U2 Bommber spyplane Lens lol. I read that the same lens was shownin the movie" The Courier" which was made in 2020 and about the Cold War with hte Russians.

Thanks Again Rob and soon enough I should be back up imaging,
Brian

i had a look on ebay, there's a few complete ones, they go for about $500+ , big image circle

yobbo89 wrote: ↑Tue Aug 29, 2023 5:16 pm i had a look on ebay, there's a few complete ones, they go for about $500+ , big image circle

Yeah, I kind of wish I had it complete, but Free is better lol So correct me if I am wrong. If that rear element was used for an Ultra Large Format Cameras, Could I find another corrector or have one made and put it in the imaging train specific for today's Astro cams like the ZWO6200mm or 2600mm? I know I would probably have to have the rear element custom-made.

Also what kind of a guess do you think the Len elements are in the Objective? I know I won't find out until it is taken apart and cleaned. And by the way the objective weighs 10lbs lol

Hi @TheButcher
These aerial survey lenses were designed for 4x5in 5x7in or 8x10in. The rear element is a corrector/flattener for the large image circle. If you are going to put a smaller digital sensor behind it, you might get away with nothing (try it) or a modern field flattener.

My astronomy mentor, Arthur Page, had a Wray astrograph, a 9" diameter f4 lens that could shoot onto 4x5 in or 5x7 in glass plates. He also had two Ross lenses, perhaps 4" diam @ f10. The picture shows the mount. The main instrument was a Coulter 12" f15 classical cassegrain with a large photoelectric photometer hanging off the back. Arthur is looking through a 4"f15 Unitron Refractor finder/guidescope. The Wray is sitting between the forks. The Wray weighed about 40kg. The mount is a custom made fork mount. The Fork base plate was a 1 metre diameter circular 1 inch steel plate with massive forks and a worm drive that from memory was 24-30 inch diameter.

You can't see the two Ross 4" astrographs, they are hidden behind the instrument from this angle. Having two, he could image two plates with R & B filters simultaneously.
.



Your lens will be an achromat on anastigmat definitely not an APO. These are probably at least 50 -80 years old lens designs and predate ED and APO glasses that only began to be used in the 1980's/90's.

Remember that the principle was that the focal length was long and the large format was only contact printed or very slightly enlarged. A 2 X enlargement of an 8x10in plate produces a 16x20in print. The lenses are not really good enough for high enlargement used with modern small sensors.

I would suggest that the results will be less than optimal unless you get the original corrector and shoot large format film. The project will cost a fair bit. The point of all the talk of my mentors scopes is to show that you will end up with a very heavy OTA that will require a very expensive solid mount to support it.
In my opinion, you are probably wasting money and you'd get better results with an small Chinese APO refractor (ED80?) and a flattener.

Cheers
Joe

Thanks for all that info Joe, very interesting Now, I think I may end up making it some kind of showpiece or something or selling it rather than spending the money to try to make it a scope and take your advice and just go for a modern APO again. Hopefully, I will be back up and running again this year imaging.

And Thanks Again for giving such detailed info about the lens and your explaining your Mentor's setup.
Brian

Thanks for the interesting post .