New article, setting expsure by Ev

[Doug Kerr]

We sometimes encounter cameras shutters that allow us to set the camera exposure in terms of exposure value (Ev), a quantity that reflects the joint effect on exposure of shutter speed and aperture. An example is the Prontor SVS shutter often found on Graflex Century Graphic cameras with the Graflar 101 mm lens.

I have just posted to my technical information site, the Pumpkin, a new tutorial article, "Setting Camera Exposure in Terms of Ev", available here:

http://doug.kerr.home.att.net/pumpki....htm#SettingEv

This brief (!) article explains what Ev means (and doesn't) and the significance and use of the Ev scale on camera shutters.

Ev is a part of an overall system called APEX, The Additive System of Photographic Exposure. An extensive discussion of this entire system is given in my companion article, "APEX - The Additive System of Photographic Exposure", available here:

http://doug.kerr.home.att.net/pumpkin/index.htm#APEX

[Diane Maher]

Thanks for letting us know about the articles.

[RDKirk]

Doug, old man, glad you're still writing.

[Dave_B]

Doug:
As always, good work. I learned a lot. As a fellow nerd, your web site is a joy to read. On another subject, you wrote in an earlier article about Graflok backs. You talk about them being a standard. However, I have two versions of Graflok backs that are different. One is from new Toyo 45CF. The distance between the arms that catch the pins on the body of the camera is ~146mm. The distance between the same arms on a Graflok back from a Crown Graphic camera from the early fifties is ~129mm. Are there various versions of Graflok backs or have I missed something? Thank you in advance for your help.
Dave B.

[RDKirk]

Dave,

There is a lot of presumed commonality between back accessories for Toyo and Horseman. Can you tell if that difference would affect how film plane devices and outer accessories attach to the Toyo versus conventional devices?

[al olson]

Doug, some additional history on the EVS.

Initially EVS was called LVS (Light Value System) when Kodak introduced it on the Retina IIIc 35mm cameras. It was later called EVS, but the exposure settings are identical.

My Retina was purchased in 1955, but I believe the camera was introduced perhaps a year earlier. The camera was made in Germany. The lens is a Schneider Xenon and the shutter is a Syncnro Compur. Kodak later improved on the light meter and called it the Retina IIIC (big 'C').

My camera has a built-in light meter with a needle-match that results in a reading of the LVS value. The LVS values were engraved on the shutter speed ring (opposite the engraved shutter speeds) where the coupling lever is set into the knurled notch. The notches allow the setting the coupler to be set to the nearest half LV.

As in your example, this couples the shutter speed dial with the aperture dial so the desired combination can be obtained by setting them opposite an index mark.

I loved the convenience of this design. The camera is compact -- The lens retracts into the camera, but very heavy for carrying in the pocket. The Schneider Xenon is an excellent lens, the between-the-lens shutter is quiet, and the meter is accurate. I still use this camera today.

I agree with your observation that it was innovative for its time but technology eventually made it obsolete. However, my Sekonic light meter still provides exposures in EVS. Certainly, the 'EV' term is more precise when discussing exposure compensation, rather than using 'stop' which refers to aperture rather than shutter speed.

[Doug Kerr]

Hi, Dave,

Doug:
As always, good work. I learned a lot. As a fellow nerd, your web site is a joy to read. On another subject, you wrote in an earlier article about Graflok backs. You talk about them being a standard. However, I have two versions of Graflok backs that are different.

I think I didn't make this sufficiently clear, but what is standard among the "international standard" backs is (a) the interface between the focusing plate and the "back foundation" (my term) for a standard film holder and (b) the interface by which an "accessory" (such as a roll film holder) goes onto the back foundation once the focusing plate has been removed.

The way the focusing plate is held on varies considerably between manufacturers, and that is considered a proprietary interface. (Thus, focusing plates are not necessarily interchangeable.)

My apology for lack of clarity in that regard (a matter that I only came to understand recently myself!).

Best regards,

Doug

[Doug Kerr]

Hi, Al,

Thanks so much for the additional info. Finding out just how this all came about has been very difficult.

I already have a second edition in the works whose current draft introduces Light Value as practiced in the early Polaroid Land cameras (95, 95A, 80). I'll incorporate the scoop you just sent me as well.

I also include a picture of my new Prontor SVS with EV coupling.

It should be released within a couple of days.

Thanks again so much for helping with this project.

Best regards,

Doug

[Doug Kerr]

Hi, Al,

In the Polaroid system of setting exposure in terms of Light Value, LV=Ev-9. That is, LV 2 corresponds to Ev 11.

Is that consistent with what Kodak used on your cammie?

(Recall than 1 sec and f/1.0 gives Ev 0, and the Ev goes up by one unit for each "stop" of decrease in exposure.)

Thanks.

Best regards,

Doug

[Dave_B]

Doug:
Thank you for the information. It now makes perfect sense (thanks to your explanation).
Best wishes,
Dave B.