7th & 8th Order Fresnel Lenses

[Optics]

I have sent information and photos about the 7th and 8th order lenses to Terry Pepper and will let him respond since I am joining the discussion when it has been going for quite some time.

Tom Tag

[plebetkin]

joining an on-going discussion is what it is all about. Don't be shy and dive right in. What you have to say will enlighten many of us, and we do pride ourselves here as being friendly.

[Terry_Pepper]

Tom, Welcome to Lighthousing.net.

For those of you who may be unaware of Tom’s work, please allow me to introduce him to the group.

Tom is without a doubt the foremost authority on the technological history of lighthouse illumination in the US, an active member of the Optical Working Group of the World Lighthouse Society, and serves as Technical Advisor to the United States Lighthouse Society. He has written three insigtful books on the histories of Little Sable Point, Big Sable Point, and the White River lighthouses, along with numerous technical papers. Tom and his wife Phyllis have also researched and colated the premier database of Great Lakes lighthouse keepers, which they have graced me with their permission to incude on my website Seeing The Light.

As he indicated in his posting, we corresponded on this subject of these small lenses over the past 24 hours, and here are Tom's comments from that email:

The 7th and 8th order lenses were used mostly in Scotland and Canada. They were also known as Steamer lenses.

They were used in buoys and in small harbor beacons. They were cut glass - not pressed and were made by Chance
Brothers and others. There were 2 sizes for the 7th order 140 mm focal and 100 mm focal. The 8th order was 75 mm focal.

Below, you will find three of Tom’s photos of such lenses. The first two are 7th order examples, and the third is of the 8th order.

[Hersh]

Thanks for the info Tom, and thanks to Terry for passing it on to us.

Tom, feel free to jump in any time, that's when these threads get interesting.

Regarding the 7th & 8th order lenses, here are a couple snapshots I took just because they looked like some sort of Fresnel. The first was on display at the Grand Traverse lighthouse museum, the rest were inside the Museum Ship Valley Camp at Sault Ste. Marie.
















What do you think????

[Optics]

Hi All,

Thank you to Terry Pepper for the great introduction.

Mike - the photos you show are interesting. The top photo is probably a 6th order lens lantern lens. They were made by removing the upper and lower catadioptric prisms from a 6th order lens. The item on the right is the base of a Funck-Heap 4th or 5th order lamp.

The second photo is a temporary Fresnel lens light. They were mounted on tri-pod legs and used to provide a temporary light. They were also used by the military for temporary runway lighting and by surveyors.

The third photo down shows 2 cut glass lenses, it is hard to tell their exact size from the photo. They could be cut glass buoy lenses and could be 7th order in size or if larger they could be the same lenses as in the first photo. Lens lantern lenses.

The 4th and 5th photos are both of buoy lanterns mounted inside external lantern housings. These were probably used as small beacon lights on pierheads or breakwaters. Photo 4 appears to be a cut glass lens and photo 5 appears to be pressed glass.

[Hersh]

Thanks for the insight Tom, I'm glad to have the info on these.

For those who haven't been there, the museum ship Valley Camp is a great experience. It's a maritime museum inside a retired great lakes bulk freighter. They have at least one 4th order Fresnel on display in addition to the small ones I posted here, and tons of shipping displays including one of the lifeboats from the Edmund Fitzgerald. (And my little secret, I think it's the best boatwatching spot in all of Sault Ste. Marie.)

[Grover1]

Tom,

What a pleasure to have another authority represented here on LH.net. For sure you are going add much ... for sure we are going to learn much ... thanks for signing on ...

What are the chances I would pick up an old issue of LH Digest last night and find this article ... Maybe it enhances the discussion somewhat

http://www.lhdigest.com/Digest/StoryPag ... ryKey=1802

And, "what are the chances II,"

... that there is also an article in there about how the "battle for Currituck Lighthouse" has finally been won ...

Barry

[Grover1]

Mike,

Almost forgot ... thought those pictures were great ...

Thanks for posting them ...

[Leah Loar-Mays]

Welcome, Tom!! It's great to have you here.

[Optics]

I made an error in my description of the 7th order lenses that was quoted by Terry Pepper. There are 2 sizes 125 mm and 100 mm - (NOT 140 mm and 100 mm). I wrote the information from memory and should have looked it up first.

PLEASE NOTE: This has been corrected see message dated April 22 to see why.

[ron]

Back to work this morning, and looking at a 1910 List of Lights it appears that the 7th order was quite common in the fixed range lights sites, replaced by the W&T FA240. Explains why there are so many laying around

[Larry]

By having Tom, Terry & Ron on here (among others), it really does prove that youlearn something new every day. Thanks for starting this thread Zachary. It has been very en lightening.

[island]

I thought it might be appropriate to mention that there are other small lenses out there somewhere. These are the drum lenses of various sizes used for the small AGA acetylene lights: 150, 200, 300, 350 and 375mm.

[Optics]

This topic has bothered me since I wrote to Terry Pepper back at the end of March. I found that I had 140mm, 125mm and 100mm as the focal length for a 7th order lens in various charts I had developed. I decided that I better find all the original input and make sure that I had not confused diameter lengths with focal lengths.

I contacted the Maritime Exchange Museum which has the best collection of lenses of this style and found they had the following cut glass buoy style - drum lens sizes:

4th Order 250mm focal length
5th Order 187.5mm focal length
6th Order 150mm focal length
7th Order 100mm focal length
8th Order 70mm focal length
they also had a smaller lens of 50mm focal length

I then contacted Chris Mills in Canada who has a Canadian 7th Order lens, which is a cut glass dioptric belt fixed lens used widely in Canada, and had him measure it. He found that it is:

7th Order 125mm focal length

So now I had 2 sizes for 7th Order -- 125mm focal length and 100mm focal length and one known size for 8th Order of 70mm focal length.

In the "Meeting Minutes of the Institution of Civil Engineers" for November 17, 1868 there is a report by David Marr Henderson, who worked for Chance Brothers, which says:

"Various Sizes of Catadioptric Lights.... In addition to these there have been made, (1) the annular lens, shown in section Fig. 15, Plate 2, for improving the old reflectors, and called the Seventh Order; and (2) an apparatus with an internal diameter of 0.15 meter = 5.906 inches, called the Eighth Order (fig. 16), which has been used for small fishing stations, ships' lights, and for floating light vessels."

I looked up the figures mentioned and found that the 7th Order had a 100mm focal length and the 8th Order had a 75mm focal length.

Next I went to "A History of the Firm of Chance Brothers & Co. Glass and Alkali Manufacturers" and on page 163 find:

"At the other end of the scale were several varities of lights of smaller radius than the 150 millimeters of the sixth order. A special application of these small apparatus was for ships' signal lights. .......... We have accordingly designed a set of Shiplights on the general principles applied to the great Coast Lights of our construction. They are truly dioptric, formed not of moulded or pressed glass but of pure optical glass accurately curved, ground and polished, having a focal distance of 125 millimeters, or 4.92 inches,and comprising a cylindric belt with five lens-rings -- six pieces in all -- the height being about 6.5 inches."

Well we finally see that there appear to be 2 sizes of 7th Order with focal lengths of 125mm and 100mm and also 2 sizes of 8th Order with focal lengths of 75mm and 70mm.

[island]

So we have a 7 and and a 7-1/2 and an 8 and 8-1/2. With all the sizes of smaller lenses I can see why the lighthouse authorities in this country began designating lenses by inside diameter instead of order.

I note that the original Fresnel Orders were 1 through 3 but with a 3 large and small and a 4 large and small. This was changed to 1 through 6. With the proliferation of lens sizes the system of Orders became rather disorderly.

David