American lenses and bubbles

Hello, all. I just picked up an inexpensive older wide angle, the

Ilex Calumet wide field 90 f/8. The rear cell has a small scratch

on the outside surface nearest the shutter, and the front cell has a

small bubble on an inside element. When I stop down to f/16 (where

I'll be using the thing most of the time) I can't SEE either, when

holding the lens up to a window, but I know that some bent rays are

probably passing through the defects and making it to the image

formed on the film plane. My question, for you lens experts, is

this: If the aperture at f/16 obscures the defects from sight

(looking from both sides), does that mean that any effects they

might have would be only at the extreme edge of the film? As an

aside, the Seiko shutter opens past f/8, so I�m hoping I�ll have a

little more light for focusing. I don�t remember my old Super

Angulon 90/8 doing this�

I should add that the title refers to the fact that I've seen several old Ektars with bubbles, but only one German lens. What was the deal with American optical glass?

It's not just American lenses. I had a Zeiss 50mm Tessar lens for a 35mm camera that had a small bubble in it. The lense was very sharp and did not exhibit any unusual flare. I wouldn't worry to much about it. The fact that your lense is probably uncoated will probably be more of a concern than the bubble.

It's not the nationality of the lens but the age that is associated with bubbles. Bubbles were an artifact of the manufacturing process associated with better optical glass. Metals were added to the glass to clarify it and improve the refractive index, and they had to be added at a low temperature, hence the bubbles. While not desirable in themselves, they were taken as a sign of high quality glass. Many of the best Ektar lenses were of that era, but you can also find bubbles in, say, Voigtlander or Zeiss lenses of the 1950s. Your Super Angulon was probably just newer.

In physics optics classes I taught, one of the eyeopening concepts students appreciated was that: "Every part of the lens contributes to every part of the image". You can cover half of a lens and still see all of the image, although the intensity is cut in half. A scratch or other imperfection anywhere on the lens will scatter some light over ALL of the image, decreasing contrast. However stopping down restricts some of the marginal rays, so a defect away from the optical center has a smaller effect than one near the center. Aberrations due to marginal rays which are (harder to correct) are also reduced at smaller apertures. Hence one reason for stopping down. To answer more directly to your question: a scratch at the edge of the lens will not produce a defect at the edge of the film, rather, it may reduce contrast over the entire image plane.

Thanks for the fast responses. I should have added that I previously looked at a bunch of Photo.net posts on lens bubbles, and have had a couple of lenses w/bubbles (a 127 Ektar, for one), so I'm not worried too much about performance,I was just never sure exactly where the effect of the abberations would appear. I'll shoot a couple of transparencies and see what they look like. The lens looks nice, and is single coated throughout (and the coatings are in good shape).

Bubbles are universal. I have a Dallmeyer 6"/1.9 Super Six with a more-or-less 0.2 mm diameter bubble dead center in its huge front element. Coated post-war lens, too.

 

On the other hand, my 65/8 Ilex is bubble free. Apropos of /8 Ilex wideangles, if yours is wasp-waisted like a Super Angulon it should be a very very good lens. Mine is outstanding, I'm delighted with it. Also, FWIW, mine came in a useless #00 electric shutter, I got an old #00 Compur Rapid for it. The shutter's diaphragm opens much wider than f/8, but the lens has a field stop. Does yours?

 

Cheers,

 

Dan

I'm amazed at how you determine all american glass to be like this based on "several lenses"?

I have that lens, and it also has a few "tiny bubbles." They don't

effect my image quality; however, your mileage may vary. The

lens is a good performer for the price, and the Seikosha shutter

has done a pretty good job so far. The lens is not uncoated -- it

was made in the 1960s and is single-coated. Check out the

Jan/Feb 1996 issue of View Camera for more info on these

lenses, and also this thread:

 

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_i

d=003z80

Thanks for the responses. Howard hit the nail on the head. About seven years ago, when I got my 4x5, I was believing the hype about how the proverbial "few cleaning marks won't effect image quality," until I tried a handful of Ektar 127s (the camera's stock lens-I tried several because I wanted to be able to use the rangefinder). There were noticeable differences in contrast between lenses made over the same period ('46-'50, all coated) resulting from the effects of cleaning marks and the lens cement beginning to turn a bit opaque (turned out the one that came with the camera was the best). Over the period of a couple of years I handled many Ektars, Wollensacks and a few Ilex lens, along with Schneiders, Goertz, Fujica, etc. I should have written that I noticed several from the American group had bubbles in the glass. My sample size was easily more than 100 old lenses (seen at the Buena Park monthly camera show, Pro Photo Connection in Irvine, Many's in LA, etc.). Since I made the original post I have remembered that there was more than one German lens with bubbles, but looking at lenses made after WWII, I definitely saw more bubbles in the American glass. This could, of course, just be my experience from those couple of years of looking at a lot of lenses. As an aside, the instruction book for my GW670II notes that �scratches on the lens surface can reduce its sharpness far more than you would think," plus effect contrast. If Fuji says it, it must be true! ;-)

 

Dan: It looks like I can get about 1/2 stop more than f/8 for focusing, maybe not quite that much. It's been a couple of years, but I think my mid '60s Super Angulon 90 was wide open with the shutter at f/8, with no more room. I wonder if this Ilex has the original shutter? (Seiko LS22, f/8-64). The lens design looks identical to the SA90f/8, except for the clever omission of filter threads.

 

Daniel: I would like to see the thread you posted a link for, but it didn't lead me anywhere. What forum was that in, on greenspun?

The Ektar 127's one prewar uncoated; one 1946 coated; but NOT marked with the Kodak -L marking; and one that is a coated with -L marking circa 1947. The latest 1947 version with coating and a few bubbles was tested at 1:10; VERSUS a Schneider Componon and a Rodenstock process lens. The Ektar resolved the highest at the center; and tis the oldest lens. The Componon was better at the edges; and best overall; at 1:10; for copying artwork. The 80 lines/mm at the center for the bubbled Ektar 127mm F4.5 @F22 is not too shabby of a lens design. I doubt that one could measure any difference between a bubbled and non bubbled lens; in any practical test. It is like worrying if a stockcar will be slower; if a small dent is in the bumper; the size of a BB.

Paul: Sorry about that. This forum used to be on greenspun, and that was an old address. Try this one:

 

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0033l6

"80 lines/mm at the center for the bubbled Ektar 127mm F4.5 @F22 "

 

I didn't think this was possible. What's the highest possible resolution from normal light at F/22?

Hi,

 

Some scratches and bubbles nearly not affect the image quality. Dont bother. But haze and cleaning mark (many thinly scratches) will do harm to contrast. In this occasion, buy another one.

Try enlarge an good photo (30"or more) to make sure the quality and style of your lens.

 

 

 

Dennis

Some years back, I heard the story that Nikon invented the technology to make bubble-free optical glass, and that the industry has since adopted it. As I have seen bubbles in many older lenses, I can't believe that only American-made lenses show them. For example, of the many Kodak Ektars I've seen and used, I've never seen one with a bubble in the glass; so perhaps everyone's sample size is too small to be accurate.