Ever wondered why lenses cost so much?

[gummi]

I've been tossing up buying a coupla new lenses and was complaining about the cost of getting new lenses, wondering if we were being ripped off or is it justified? Did a quick search and found this on another site:

http://www.youtube.com/watch?v=X7_wL0ZZi6k

After watching that I feel better about spending lots of $$$ on a lens! Hope it helps all of you out there who wonder if its all worth it or at least justify to the powers that be (i.e the other half) that it is!

[latch]

Absolutely fascinating!

When I was an undergraduate physics student I had a friend who ground his own 8-inch telescope mirror (like a lens, but only one side matters). It took him weeks of work, and watching him do that gave me a lot of respect for the cost of good photographic lenses.

[DanW]

There's also a 3-part series on the production of a Canon 500mm F4:

http://www.youtube.com/watch?v=OkWsk9rXpcU

Pretty interesting stuff.

[gummi]

I can't believe your friend actually ground out his own lens Latch! How did it turn out?

Thanks for the link Dan, it's even closer to what I wanted to find out!

[tntman]

OMG! That is an awesome clip!

Now I know my L lens are worth their money! hahaha...

Actually at the older prices from last year, they are worth it, but some are on a rise! DAMN you Canon!

[Mr Darcy]

I can't believe your friend actually ground out his own lens Latch! How did it turn out?

It was a mirror not a lens. I've done this, though only with a 6" mirror. It is painstaking, but the results will blow your socks off. Far better than the commercial offerings. It has something to do with the randomness of the human machine. Artificial machines introduce a repetetive motion which leads to distortions amplifying rather than cancelling out. (This was true when I made mine about 25 years ago. It may not be true anymore)

[gummi]

I can't believe your friend actually ground out his own lens Latch! How did it turn out?

It was a mirror not a lens. I've done this, though only with a 6" mirror. It is painstaking, but the results will blow your socks off. Far better than the commercial offerings. It has something to do with the randomness of the human machine. Artificial machines introduce a repetetive motion which leads to distortions amplifying rather than cancelling out. (This was true when I made mine about 25 years ago. It may not be true anymore)

Mr Darcy, know of any resources I could look up to do this? (google right?) sounds like a VERY interesting thing to do! Its strange the first time I do something it turns out fairly good, the next time pretty bad, then worse and then i steadily get better at it. things seem to follow the same pattern no matter what im doin!

[Potoroo]

Artificial machines introduce a repetetive motion which leads to distortions amplifying rather than cancelling out. (This was true when I made mine about 25 years ago. It may not be true anymore)

I'm not sure I follow you. I would have thought that since grinding lenses is fundamentally mathematical that computer control should give more consistent results.

[Mr Darcy]

Artificial machines introduce a repetetive motion which leads to distortions amplifying rather than cancelling out. (This was true when I made mine about 25 years ago. It may not be true anymore)

I'm not sure I follow you. I would have thought that since grinding lenses is fundamentally mathematical that computer control should give more consistent results.

When I did this was in the days before computer control was readily available. So I was talking about mechanical controls rather than CNC machines.

What it boils down to is that any mechanical system will introduce a repetetive element. OTH human drive will always be, to a certain extent, random. We simply do not make EXACTLY the same motion every time. That is why no one can consistently split their first arrow, even on an indoor archery range, where environmental effects are controlled. They might get close every time but...

In this case (mirror grinding) the lack of repetition (same stroke, same spot, same direction, same pressure) means that errors tend to be cancelled out rather than reinforced. It is about the only case I know where O'Reilly* does not hold sway. But then you have to do the hard grind (no pun intended) yourself, so maybe he has the last laugh after all.

A CNC system may do better, but it would need to be very carefully programmed.




*O'Reilly's Law: Murphy was an optimist

[Mr Darcy]

Mr Darcy, know of any resources I could look up to do this? (google right?)

Sorry I missed this before.
Google is probably your best bet. There used to be a store, Astro Optical, in Crows Nest (Sydney) that could supply information and blanks (you need two). I'm not sure if it is still there. Big V can probably tell you.
I worked from a book:
"Building a low cost Telescope" by Eric Whitcombe Revised 1979. No ISBN that I can find in my copy.

Hmm. You live in Pyrmont according to your profile. I would try the Museum in Harris St as your first port of call.