I recently purchased an old, but useable, Zeiss Ikon Nettar so that I might dabble in the medium format. I'm about half way though the first roll of T-MAX 100 on the camera when the following came to mind:

When using my Canon and the "Sunny 16" rule, a shutter speed of 1/125 would be the order; but with the Nettar the max shutter speed is 1/100. So I guess the heart of the question is "Is ISO 100 film actually made with the 1/125 shutter in mind?" Thus, should I open up half a stop or so on the Nettar for best results?

Many thanks in advance.

-- Wes Sechler (wes_sechler@muccmail.missouri.edu), December 23, 1997

Answers

I would think that the difference between 100 and 125 asa is going to be negligable, in fact I am sure of it. Your best bet is to keep records of your exposures so that when you process the film and make a contact sheet you will know what exposures were the most accurate. I am quite certain that the shutter is not going to be very accurate as far as actual speeds are concerned, but if it "sounds" the same at a given speed each time that it is released, then it will be consistent. After a while you begin to recognize the sound that shutter speeds make, especially at 1/30 and below. You might even compare it to a camera you are used to and see if the sound of the shutters at relative speed ie 1/10 to 1/15 are comparable. Keeping records and comparing them to your end proof will tell you a great deal.

-- MTHOMPSON (MTHOMPSON@CLINTON.NET), December 23, 1997.

100 vs 125

Let me make another suggestin. !00 to 125 iso is a cifference of 1/4 stop. Does not sound like much, but its a full quarter of a stop and depending upon what type of image you are making ,it could be a great deal. I would suggest that you do open up that 1/4 top . But first ,as suggested , have the shutter speed checked at a repair shop.

-- j megargee (mvjim@interport.net), January 01, 1998.

The difference between ISO 100 and 125 (1/3 stop) on black and white film would only be noticible for deep shadow details if you were underexposing (and using a spot meter, had done all of the zone- system testing, and were holding your development to +/- 1 degree, ....). Since you are over-exposing (and from the sounds of it, guesstimating exposure), it will disappear into the noise.

From experience with several old Zeiss folders, your shutter speed is likely to be a bit slow (altho I bought a beater 1934 Super Ikonta C which was within 1/3 stop at all speeds).

-- John Lehman (ffjal@aurora.alaska.edu), January 08, 1998.