It's quite a big lens, isn't it ?

[John]

I'm sure some will have seen this photo before but it's new to me.

The gentleman in the waistcoat is cleaning the 40 inch objective lens of the Yerkes Refractor. The gentleman with the beard is Alvan Clark. I assume that Baader Wonder Fluid is being used

[Ptarmigan]

I'm sure some will have seen this photo before but it's new to me.

Link ?

Is this the one where they are drilling a hole through the lens to stop a crack progressing further ?

EDIT

sorry, ignore that, hiatus on my internet !

and not the hole deal either wikiying says that was not found/done till after Clark was dead

[John]

I vaguely recall the hole drilling thing being done to a big lens at some time in the past but I'm not sure it was the Yerkes.

[Ptarmigan]

Not sure if you caught my edit as a result of my internet interruption !

Yes deffo the 40" Yerkes in my memory on its crown element.

But it does not get any mention on the Yerkes official sites ! ?

This is the closest I can get to what I remember :-

" A few years after the telescope went into operation a crack started to develop in the front lens. At this time Alvan Clark had passed away and there was real concern about having to replace the front element and who at that time had the skill to do the job. To prevent the crack from propagating across the lens a small hole was drilled (red arrow) just in front of where the crack was heading. When the crack reached the hole the stresses were relieved and it stopped propagating. There are small pieces of black tape covering the hole. "

from this site http://www.rickalbrechtphoto.com/Astronomy/Large-Observatories/Yerkes/22240822_K2Qg4B/1776553667_Lm8wqTR#!i=1776553667&k=Lm8wqTR

There are a few other refs via google to the crack, but nothing especially authoritative.

As far as I know the hole stopped the crack developing further and it still remains so.

Dont know where I saw the pic of them working on it, pre internet ! Prob. Burnham or Norton or the like !

[ronin]

I like the idea of drilling a hole to stop a crack progressing. :eek:

Ask about cleaning a lens/mirror now and it is generally don't even look at the objective they are so delicate. Back then it was "Get a drill out and drill a hole in the objective". :rolleyes:

Times have changed a bit. :grin:

I would love the replies to a post asking "Slight crack forming in my mirror, what size hole do I need drill in it? :laugh2:

[Moonshane]

Autoglass repair Autoglass replace?

I love historic photos like this of guys doing things we would never dream of. This applies to all my lifetime's hobbies. There's nothing like experience to give you the courage that comes with knowing exactly what you are doing.

[Dave Lloyd]

I don't suppose the light gathering power of a lens that size would be affected by a bit of black tape. No Autoglass technicians in those days.

[Moonshane]

Really Dave? I had no idea. ;-)

[spaceboy]

I'm well on my way to getting one of these. Only another 34"s to go

[Beulah]

It's a fascinating image for many reasons.

One of which is the workmanship in turning the aluminum (?) objective holder...assuming this was taken in the late 1800s...

[Jim Steele]

Those images give me apperture feaver!! I bet it would be awesome on tight doubles

[ollypenrice]

Wonderful picture and not one I'd seen. The story of the crack and the hole is also new to me. Great thread, John. I love astronomy history.

Olly

[Thom]

Was this the scope that had a gun regularly fired in front of it to 'improve seeing'?