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Flektogon Bubbles
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PostPosted: Tue Feb 28, 2012 10:14 pm    Post subject: Flektogon Bubbles Reply with quote
I've got the chance to pick up another MC Flektogon 35mm f/2.4, but it has an air bubble at the edge of the front element.

I know this isn't really a problem but would it affect the price?


PostPosted: Tue Feb 28, 2012 10:17 pm    Post subject: Re: Flektogon Bubbles Reply with quote
Alternate Internet ID wrote:
I've got the chance to pick up another MC Flektogon 35mm f/2.4, but it has an air bubble at the edge of the front element.

I know this isn't really a problem but would it affect the price?


Depend from glass , well known Biotar lenses has bubbles in glass, if I find similar ones from any glass from that years I think huge plus due made from same glass than Biotar.

On a latest MC lens this is a faulty , but I don't think so effect price more than 10%.


PostPosted: Thu Mar 01, 2012 9:05 am    Post subject: Reply with quote
It seems logical to me that the price should be reduced.

The thing is that on eBay everyone is kind of crazy, and sometimes they pay way more than I would.

It surprised me the price that one of the Flektogons I sold fetched:

http://www.ebay.co.uk/itm/300636395049

So nowadays big discounts are becoming way less common. When I have an item with some flaws, even minor, I use eBay because on other channels even offering a low price they get ignored.

Even being minor it had front element scratches, a non perfect barrel, and an abused filter ring. It was an excellent performing copy though, and I tried to remark that.

The bubble, being on the extreme it can be placed in a position of the image circle that remains outside of the cropped 3:2 rectangle, basically at 12 or 6 o'clock. What it's not that sure is that if in a backlight situation the rays that are crossing the bubble will change its trajectory and end up on the image. What it is clear is that in one part there is a one more air surface.

If possible I would try it first, and of course, if the price is just 10% less than a copy without issues, I would buy one without bubbles.

Does someone having with a lens with a bubble confirm or deny its effects on IQ?

Was jenna that crappy to sell lenses with bubbles on the front element? Did the bubble appear after manufacturing? I'm curious about bubbles.


PostPosted: Thu Mar 01, 2012 10:04 am    Post subject: Reply with quote
rafa1981 wrote:
It seems logical to me that the price should be reduced. .....

Was jenna that crappy to sell lenses with bubbles on the front element? Did the bubble appear after manufacturing? I'm curious about bubbles.


On the contrary, the bubbles are a sign of highest Zeiss quality, given the manufacturing limitations years ago.

Quote from http://www.zeisscamera.com/services_overhaul-cIIa-lenses.shtml

Why the Bubbles in the Lens Glass?

Modern glass making has changed a lot in modern times. It wasn't so long ago that the bubbles in the glass were a sign the lens was of the highest possible quality. How quickly we have gotten used to photographic lenses that do not have bubbles in them. When optical glass is made all of the ingredients are mixed in a container that can take high temperatures called a crucible. The ingredients are melted at very high temperature. Even when it is melted, glass is very viscous and thick. When the melted ingredients are stirred to mix them together, the mix tends to pick up air which forms bubbles and the ingredients used in the older optical glasses tended to generate gasses as they melted. The bubbles are removed from the glass by allowing the crucible to sit in the high temperature furnace while the bubbles rise to the surface of the melted glass. Up until about 25 years ago the materials of which crucibles for optical glass making were made could not withstand the effects of the extremely high temperature at which glass is made for very long. There was a time limit on how long the crucible could stay in the furnace. In order that the crucible not fall apart it was necessary to remove the crucible from the furnace before all of the bubbles had time to rise through the melted glass and escape from it. Another problem is that the melted glass was corrosive to the inner surface of the crucible. It was necessary to remove the crucible from the furnace before corrosion of the inner surface of the crucible caused impurities to ruin the batch of glass. Another problem is that making the highest quality optical glass required higher temperatures than did lower quality optical glass. So it was possible to make lenses without bubbles, but only if the glass was of a lower quality. Back then, no bubbles in the glass meant it was cheap.

The overall effect of these factors was that for a very long time small bubbles in the glass of a lens were an indicator of the highest quality. It is still such an indicator today for lenses which were made prior to around 1975. Sometime around 1975 crucibles for optical glass making were developed which could withstand the high temperatures required for making the highest quality optical glass long enough so that the molten glass could be left in the furnace until all of the bubbles had risen out. These crucibles were also resistant to the corrosive effects of molten glass on the inner surface of the crucible. Since then high quality optical glass has been virtually bubble free.

So when you are looking deep into a Zeiss lens for your Contax camera, and you see some little bubbles deep inside, rejoice because you have found a rare and special jewel that will take most excellent photographs. The bubbles are photographically insignificant and do not affect the quality of the pictures the lens will take. They are merely an indicator of great quality.

Also keep in mind that when a lens blank contains bubbles it is only natural that during the grinding and polishing process where glass is removed that some of these bubbles will become partially exposed. These exposed bubbles will appear to be small tiny pits on the surface of the glass on both the front and rear elements. These are natural, to be expected and cannot be avoided. They are an artifact of the lens glass being superior.


PostPosted: Thu Mar 01, 2012 3:32 pm    Post subject: Reply with quote
I let the one with the bubble go as it was way too expensive for my taste.

I double checked my own copy and guess what - a bubble! I managed to buy it at a bargain basement price so I'm not too concerned.

The bubble smaller than in the one I was looking at, but I've never noticed it affect any pictures.

I'm curious about Zeiss serial numbers having looked at rafa1981's ebay listing - it has 8 digits - mine only has 5. Does that mean it's a lot earlier - can they be dated by the serial number?


PostPosted: Thu Mar 01, 2012 3:42 pm    Post subject: Reply with quote
Alternate Internet ID wrote:
I let the one with the bubble go as it was way too expensive for my taste.

I double checked my own copy and guess what - a bubble! I managed to buy it at a bargain basement price so I'm not too concerned.

The bubble smaller than in the one I was looking at, but I've never noticed it affect any pictures.

I'm curious about Zeiss serial numbers having looked at rafa1981's ebay listing - it has 8 digits - mine only has 5. Does that mean it's a lot earlier - can they be dated by the serial number?


one of the best lens ever biotar 75mm f1.5 with many bubble in glass


PostPosted: Thu Mar 01, 2012 3:49 pm    Post subject: Reply with quote
Awesome Peter!


PostPosted: Wed Apr 18, 2012 12:22 am    Post subject: Reply with quote
peterqd wrote:


for a very long time small bubbles in the glass of a lens were an indicator of the highest quality. It is still such an indicator today for lenses which were made prior to around 1975. Sometime around 1975 crucibles for optical glass making were developed which could withstand the high temperatures required for making the highest quality optical glass long enough so that the molten glass could be left in the furnace until all of the bubbles had risen out. These crucibles were also resistant to the corrosive effects of molten glass on the inner surface of the crucible. Since then high quality optical glass has been virtually bubble free. [/i]


Interesting. The largest bubble I have seen was in a Pentax 40mm Pancake (a good mm and not that far from the center!) and this lens was first produced in 1976.


PostPosted: Wed Apr 18, 2012 12:24 am    Post subject: Reply with quote
+1 what Peter wrote.
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