How to test lens transmission

[Tin Can]

Randy Moe posted the words "too rare" ...this guy collects and uses the rarest of rare equipment like a madman...

Ha, you found my old nickname from my early motorbike years.

'Madman Moe' LOL AKA '10 Grand' as I always shifted at 10K revs. New Hondas were something.

I dislike old electronics. They alway fail. I collected tube radios since the 50's when I was a kid. I have plenty of non-working old electric gear. I made my own pirate radio station in 1966.

I'll trade a you Wire Recorder, which precedes Tape recorder.

As for collecting. I have less than 5% of my former collections.

Now will you answer my question?

Do you see significant, more than 20% variation, in lens transmission from lens to lens? As measured by the old Horse?

[desertrat]

Several years ago I saw a post at another photographic forum, I think the poster was Richard Knoppow, stating that the optical glass made before world war two was "filthy" by modern standards.

Later on I downloaded and read a book on lenses in the early 20th century, I think it was by Hans Harting, translated into English. He stated that thick lenses like cemented quadruplets and quintuplets absorbed an appreciable amount of light and slowed the whole lens system down somewhat.

I rigged up a test fixture using an old American Optical research style microscope illumination lamp with condenser and iris, and a Weston Master exposure meter for the sensor. The light pencil was made small enough so all of it would reach the sensor.

My test subjects were a Wolly RR, an old uncoated Dagor, and a Turner-Reich triple. All of these lenses have 4 air-glass interfaces. The meter readings were taken before and after the lens was inserted in the light path.

The RR absorbed a small amount of light, a small fraction of a stop. The Dagor absorbed a little more. The T-R triple absorbed a whopping stop and a half, roughly.

Unfortunately I can't find the piece of note pad paper I scribbled the readings on.

[Tin Can]

Several years ago I saw a post at another photographic forum, I think the poster was Richard Knoppow, stating that the optical glass made before world war two was "filthy" by modern standards.

Later on I downloaded and read a book on lenses in the early 20th century, I think it was by Hans Harting, translated into English. He stated that thick lenses like cemented quadruplets and quintuplets absorbed an appreciable amount of light and slowed the whole lens system down somewhat.

I rigged up a test fixture using an old American Optical research style microscope illumination lamp with condenser and iris, and a Weston Master exposure meter for the sensor. The light pencil was made small enough so all of it would reach the sensor.

My test subjects were a Wolly RR, an old uncoated Dagor, and a Turner-Reich triple. All of these lenses have 4 air-glass interfaces. The meter readings were taken before and after the lens was inserted in the light path.

The RR absorbed a small amount of light, a small fraction of a stop. The Dagor absorbed a little more. The T-R triple absorbed a whopping stop and a half, roughly.

Unfortunately I can't find the piece of note pad paper I scribbled the readings on.

Yes, paper disappears, but your memory is good.

I like empirical science.

[Willie]

Manual or automatic shutter? Need to know before recommending ATF or MTL, dinosaur or synthetic. ;-)

[EdWorkman]

So back in the 1930s or so movie days, how did those folks determine T stops ?
I understand that T-stops were used to get consistent exposure account/despite the problems discussed above
I'll bet that the web would give up a technical article or book on the subject, maybe

[Dan Fromm]

Ed, I expect that they measured transmission photometrically.

I had some cine cameras with zoom lenses that seemed a lot slower than marked (Beaulieu 4008ZM with Angenieux 8x8B, marked f/1.9; Nikon R-10 with 7-70/1.4 Cine-Nikkor). The cameras auto exposure systems worked well, gave me properly exposed Kodachrome. To find out what the lenses t-stopped at I aimed them at an evenly exposed blank wall, saw what aperture the cameras selected and then metered the wall reflected with a Lunasix 3. I made sure than only the wall was visible in the cameras' finders and metered with the Lunasix from close enough that the meter's cell saw only the all. The f/1.9 Angenieux t-stopped ~ t/3.3, the f/1.4 Cine-Nikkor ~ t/2.8. And then I understood why both cameras were useful at highish framing rates only around mid-day.

Similar tests with other Beaulieus and 6-66/1.8 and 6-70/1.4 Schneider Cinegons found that they t/stopped at t/1.8 and t/1.4 respectively. These surprised me considerably.

To answer the obvious question, yes I knew the cameras' shutter speeds at 18 fps and I'd tested to make sure they ran on speed.

[EdWorkman]

thanks Dan
I found a reference, a 1949 conference of The Society of Motion Picture Engineers, but no details whatever

[Jac@stafford.net]

Several years ago I saw a post at another photographic forum, I think the poster was Richard Knoppow,

I traded some literature with Richard long ago. With trepidation I ask: what became of him?
.

[Jim Andrada]

Video lenses are usually marked in T-stops instead of F-stops Maybe that's what makes them so expensive.

http://www.bhphotovideo.com/c/produc..._95_3_7_L.html

I'd have this one on my video cam if it weren't for 44,650 little reasons.

[swmcl]

I once used a Sekonic meter on incident mode with the lumisphere retracted and placed it flat onto the centre of the ground glass under the darkcloth. I then compared the light hitting the ground glass with one old petzval lens to the other known lens - a Sironar S 180mm. Shoot the camera towards a nice bright even light source or take a photo of the sun through a white plastic sheet or something.

When the lightmeter reads the same for both lenses the amount of light is the same. ie the aperture is the same.

(I think I'm right ...)

:-)