Exposure time for step wedge?

[Photo Engineer]

I found this while searching:

http://www.worthyshorts.com/docs/book_details/book_detail-zwick1/WS-detail-zwick1.html

This is a short summary and part of a huge analysis. In one part, I was a "subject" and in another part I assisted Daan on and off in working with subjects and gathering data on the prints.

It may be of interest.

PE

 

[Mr Bill]

PE, I'm smiling as I read this, sorry to misdirect the thread. Did Daan Zwick possibly have an autographed photo of Marilyn Monroe, thanking him for his emulsions? (I'm not sure where this idea comes from)

 

[Mr Bill]

Stephen, thanks for the response. I made some estimates of lens fall off, with a roughly normal lens (using the cosine^4 rule), estimating that a diagonal sensi wedge on film, exposed in camera, would have a fall-off of roughly 2/3 f-stop near the corner.

I wanted to play a bit further, but don't have time right now.

 

[Stephen Benskin]

Stephen, thanks for the response. I made some estimates of lens fall off, with a roughly normal lens (using the cosine^4 rule), estimating that a diagonal sensi wedge on film, exposed in camera, would have a fall-off of roughly 2/3 f-stop near the corner.

I wanted to play a bit further, but don't have time right now.

The worst part is all the unknowns.

As we know,
There are known knowns.
There are things we know we know.
We also know
There are known unknowns.
That is to say
We know there are some things
We do not know.
But there are also unknown unknowns,
The ones we don't know
We don't know.
- Donald Rumsfeld

Are you getting fall off or not. How off-axis is step tablet density X. What about the size of the image circle for each lens. My 58mm barely covers the 4x5 frame and there is noticeable vignetting. My 300mm can cover 11x14. Too many variables and known unknowns for me.

 

[Photo Engineer]

Daan probably knew her, knowing Daan.

As for exposing a step wedge in a camera, or using a step wedge to determine the characteristics of a film....

It is like using a point to define a line. It takes 2 points to define a line, otherwise the possible interpretations are infinite. With a step wedge, you are using macro densities, but the micro densities (or those proportionate to your film size) are what are important.

I think I made that point.

PE

 

[Kirk Keyes]

+1

I’m very interested in learning about this method.

I was at his home in 2005, but here's what I remember. I wish I had taken a photo of it, but all I got were shots of him and his darkroom.

Alan Ross has a large box that has an array of Wratten ND filters mounted on one side of the box, and then he places the camera in the opposite side of the box. The walls of the box are opaque so no light comes through. I think it was made of foam-core - I forgot to take a photo of it, but I think it was black foamcore. The end with the ND filters is say 2x3 feet, and the opposing side is perhaps 1 ft sq. It looks similar to a home-made softbox.

There's 9 or 12 square holes in the large end in which he mounts the ND filters, with one hole that has no filter and then ND filters in the other holes, each one a stop denser than the next to give a good range of exposure values.

He focuses the camera at infinity, places the lens in the small end of the box, and seals it to keep light from getting in (with a darkcloth perhaps, I forget). The box is aimed at his window and he shoots the sky with it. I think he meters through the box at one of the tagets to get his exposure value. And then he shoots the ND filters. The box is big enough and the filters (I think he used 3 in. sq. Wrattens NDs) are big enough that even though they are out of focus and unsharp, they are large enough on the film that one can easily take readings with the densitometer and not have to worry about measuring the blurry edges of the filters on the neg.

This approach helps take the camera system into account - the lens flare, the camera bellows flare, the reflection of light off the surface of the film back into the camera, the shutter speed and aperature. Of course flare varies with every lighting situation, but this seemed like a good allround way to do it.

Alan also pointed out that one can use theatrical lighting filters instead of the Wratten filters and save yourself a LOT of money...

 

[Chuck_P]

There's 9 or 12 square holes in the large end in which he mounts the ND filters, with one hole that has no filter and then ND filters in the other holes, each one a stop denser than the next to give a good range of exposure values.

Interesting stuff. Alan Ross was a significant contributor, I believe, to the book by John P. Schaefer that I referenced earlier in this thread. Just to clarify, your saying he used 0.3 (one stop) ND filters with this technique and was able to expose a sheet of film to record all the filter densities on one sheet. Neat. Essentially, I believe, that is what a 21 step wedge acts like when exposed to the sheet, a series of 0.15 ND filters, every two steps equivalient to one stop of exposure difference.

 

[Kirk Keyes]

your [sic] saying he used 0.3 (one stop) ND filters with this technique and was able to expose a sheet of film to record all the filter densities on one sheet. Neat.

Yes - and yes, it is neat. I've been meaning to make one myself, to augment my use of a Stouffer 4x5 step-tablet under my enlarger to add flare to my testing.

Also, I always kind of wondered why Ross didn't end up doing the updates to the Ansel Adams books by John P. Schaefer you mentioned...

 

[Stephen Benskin]

There's an ANSI standard on testing for flare. The one I have is:

ANSI PH3.615-1988

Lens and lens systems - method for testing veiling glare

 

[Uhner]

This approach helps take the camera system into account - the lens flare, the camera bellows flare, the reflection of light off the surface of the film back into the camera, the shutter speed and aperature. Of course flare varies with every lighting situation, but this seemed like a good allround way to do it.

That is an interesting set up.

Many thanks.

 

[Photo Engineer]

PE, I'm smiling as I read this, sorry to misdirect the thread. Did Daan Zwick possibly have an autographed photo of Marilyn Monroe, thanking him for his emulsions? (I'm not sure where this idea comes from)

In the interest of clearing this up for mystified APUGgers, Daan did indeed know Marilyn Monroe and have a personally autographed picture from her.

Here is a scan of it from a Kodak publicaiton for your edification and amusement.

PE

 

[Mr Bill]

Yes, that is what was gnawing at my memory! I'm sure I must have seen it in a book somewhere.

As I recall, Daan and one of his cohorts spent time in Hollywood straightening things out. When they finally had to return to Rochester, I imagine that Marilyn was heartbroken, thus her plea to be remembered in his emulsions.

Very cool! When I mentioned this, I thought perhaps you might have seen it on his desk; I can't imagine how you were able to dredge up an actual image!

 

[Photo Engineer]

Daan and I spent many hours together in his office and lab. His office, later in his career, was next to Jim Bartleson's office and so when I went to see one of them, I usually ran into the other. I remember Daan and I having a lively discussion about the special effects in Star Wars I and also on the practicality of building a real light sabre.

Daan is getting on in years now, but I see him off and on at Retiree lunches. I was at his home a few years back to help him with a computer problem, to make his fonts and icons larger as his eyesight is failing, but in spite of that he keeps up a lively presence in teaching and being active.

When I was at his home, his wall was decorated with memorabilia from the campaign to elect Mayor Johnson in Rochester who is a personal friend of Daan's. At work, he had pictures of his family on his desk, but this photo was framed on the wall at one time.

He went to Hollywood to spend time working with 20th Century Fox and was accompanied by George Higgins. George also has a picture but with a different comment. His says "All I am, I owe to you and to Kodak".

PE