Threading 77mm threads on the inside of the lens

[George A.]

Hi!

I have two lenses that don't have the 77mm threads on the inside of their front elements (all the other lenses in the set do).

I'd like to have a matching set - plus I like the ability to screw in 77mm filters when I need do.

Anybody knows a good place or has any suggestions as to whom to approach in order to thread these front elements?

In or around New York would be ideal, but I'm open to suggestions.

Thanks! 'd appreciate it very much.
George


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[Jeffrey T. Morgan]

You know, there may be a MUTCH better way than what I am about to suggest, but what about carefully glueing in something like this:


http://www.bhphotovideo.com/c/product/11688-REG/B_W_65041214_72mm_to_77mm_Step_Up.html

 

[Vance Colvig]

Might consider looking for an 86mm -77mm stepdown ring and have the outer diameter turned down to .001- .002 inch larger than the inside diameter of the lens, then warm lens to 120 degrees F while at the same time cooling the ring as could as you can get in a freezer. Remove ring from freezer and drop in the lens. When temperatures normalize this should provide a firm resistance fit. Should work well as long as the recess you are mounting into is also aluminum and not plastic. Both should materials have the same expansion coefficient. By using the above mentioned procedure, you will be able to remove the ring in the future without damage to the lens by screwing on a metal cap by tapping the overhang from behind while securely holding the forward lens barrel. Glueing is easier and quicker but may not be reversible without damage to the lens should you choose to do that in the future. .

 

[Peter Moretti]

Don't you also have to be careful about contact with disimilar metals? E.g., I believe that contact between aluminum and ferrous metals causes a very slight electrical flow that is corrosive.

 

[Vance Colvig]

Couldn't agree more Peter. Lens barrels since the 60's are typically made of aluminum unless plastic. Don't know of any or have ever heard of any made with ferris materials such as steel. Earlier lenses were often made of brass or had brass components. Steel, brass and bronze have different thermal expansion rates, and thus would probably not be advisable for that reason also. Never seen any magnesium in lenses, but have on camera bodies, and this would be a very bad mix in my opinion for both reasons.

 

[George A.]

The two lenses are Canon K35s. Not plastic front elements.

I am attaching a picture showing one lens that has the inner 77mm threads.
Only two of the lenses in the set don't.

I am trying to attach the 77mm to 80mm front ring by Cordvision (which makes life much, much simpler).

I'm curious if the cold/hot method will work with the Cordvision ring. I'd still prefer a normal inner thread on the front element.
George

 

[Nick Gardner]

I have a set of k-35s, and they all have threads. Can you post pictures of your lenses? I think the only practical way to do this is to disassemble the lens, put the lens front on a lathe and cut the threads. I imagine it would be prohibitively expensive. Every k-35 I have ever seen has an 80mm front (except the 18mm of course). I'd be interested to see whats up with your lenses.

Nick

 

[George A.]

Hi Nick,

We have two sets.

In one set, all the lenses have inside threads. On our second set, the 24mm and the 55mm miss the inner 77mm threads (the rest have them).
Just a minor difference in housing.
No big deal, really, but it would be nice to have all lenses identical.

Take care!
George