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7th & 8th Order Fresnel Lenses

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Postby epona » Mon Mar 28, 2005 6:29 pm


The Point Areana Lighthouse in CA has the history of illumination which was written by Thomas A. Tag on its web site.

The web site is www.pointareanlighthouse.com

No picture are shown of 7th and 8th order fresnel lenses, however the site does show the other orders of lenses.
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Postby Zachary » Mon Mar 28, 2005 8:24 pm


That's the page I linked in the first post
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Postby Terry_Pepper » Mon Mar 28, 2005 8:44 pm


And thus the circle is complete :D
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Postby island » Mon Mar 28, 2005 9:26 pm


So now where do we go? Maybe contact Tom Tag.
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Postby Keeper » Mon Mar 28, 2005 9:37 pm


I've read that 7th and 8th order lenses were used exclusively in the British Empire. They were definitely used at some minor lights in Canada, but I can't name any examples offhand. I've never seen anything smaller than a 6th order lens.

By the way, there's a myth that's often repeated that the 1898 bivalve lens installed at the south tower at the Navesink Twin Lights in New Jersey, and now on display there, is a hyper-radial (or hyper-radiant). I became personally acquainted with that lens when it was on display at the Boston Museum of Science when I worked there in the 1970s. It was quite huge and beautiful. Despite the fact that many sources say it's a hyper-radial, the folks at the Twin Lights Historic Site and lens expert Jim Woodward say it's actually a 2nd order lens.
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Postby island » Mon Mar 28, 2005 10:25 pm


At least one source says the Cape May 1st Order was a hyper-radial. A hyper would have been a very tight fit in either the Nav. or CM lanterns.

I am wondering if these elusive 7th and 8th order lenses were "classical" Fresnels with a cartadioptric and dioptric sections or just dioptric lenses such as used for post lights and buoys. The 5-days Lens Lantern and the AGA Acetylene lanterns are examples of dioptric lenses.
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Postby Maria » Tue Mar 29, 2005 8:49 am


In an effort to settle this question once and for all, I e-mailed the Scottish Lighthouse Museum (http://www.lighthousemuseum.co.uk/) to see if they had any pictures. I'll let everyone know if I get a reply.

In the meantime, check out their amazing display of lenses (click on the Inside Museum photos). They also re-installed the hyper-radial in the Kinnaird Head tower. =P~

I can't wait to visit!

8)

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Postby island » Tue Mar 29, 2005 8:52 am


Email this morning from Chris Mills---
Hi Dave-

Nice to hear from you. Interesting that you should ask about 7th and 8th order lenses...although I am not aware of any eighths being used in Canada, the sevenths were very common in the Maritimes, and to the best of my knowledge in Ontario and BC, for many years. The 7th order lens was manufactured by Chance Brothers, and I am told that it was a standard ships light (possibly an anchor light) that was turned into a lighthouse lens, by placing it on legs and providing it with a base and a ring into which a double-burner keosene lamp was set.

There are two 7th order lenses still in situ in NS lights, but neither is in use. The lenses were once very common -- now they are as scarce as hen's teeth in these parts.

The NSLPS had a lights and horns night at the Maritime Museum in Halifax last week, and it was a great sight to see a little 7th order lens with an operating kerosene light inside!

All the best,

Chris

and, yes, they are dioptric only.

More--

The 1940s CG Aids to Navigation Manual includes first through six order lenses and there is no specific mention of seventh or eighth order lenses. Smaller lenses were described as triangular lanterns, post lanterns (150 and 200mm) and lens lanterns (300mm). These small lenses were dioptric only. Never-the-less they are based on the original 1822 Fresnel design.

edit: I think the lens sizes in the CG manual must have been diameter, not radius. A 300mm radius lens would make for a mighty big steamer lens lantern.
Last edited by island on Tue Mar 29, 2005 12:35 pm, edited 2 times in total.
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Postby Hersh » Tue Mar 29, 2005 9:51 am


Thanks for digging up all this info for us, you guys are really getting into this one!!!!
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Postby ron » Tue Mar 29, 2005 9:53 am


i think we have some of these lens laying around at work
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Postby Terry_Pepper » Tue Mar 29, 2005 11:55 am


I emailed Tom Tag this morning. I will let you know if he can shed any additional insight on the matter.
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Postby island » Tue Mar 29, 2005 12:07 pm


More from Chris Mills--
Steamer lenses -- that's it. There's a lovely restored 7th order in the lantern of the Gilberts Cove light on Saint Mary's Bay in NS. It's a 270 degree configuration. I have a 360 at home, as well as the brass frame for another and enough prisms to make up one section -- a little restoration project for me when I have some more time.
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Postby Zachary » Wed Mar 30, 2005 6:33 am


This seems to be like Island described
Zachary wrote:Image
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Postby island » Wed Mar 30, 2005 6:42 am


The question is -- Were 7th and 8th order lenses used in the U.S.? The answer is --Yes, many. These small "drum lenses" were designated by inside diameter, not by radial order.

This is the lens that appears in the photo of the triangular oil lantern posted above in this topic. It is a 150mm (inside diameter) lens which is equivalent to a 75mm (radius) 8th Order Fresnel. The lantern appears to be Series B lantern produced between 1936 and 1940.

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Postby ron » Wed Mar 30, 2005 6:57 am


there are a lot of 150 and 200mm lens used on light buoys
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