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JimBob · Joined: 03 Oct 2008 Posts: 12 Location: Wichita, KS

I'm finally set up for some LF photography and I'm starting to calibrate my TMax/XTOL development times. Unfortunately, the shutter speeds on my Graphex shutter are different than the speeds on my Sekonic meter. The Graphex speeds are 1/5, 1/10, 1/25, 1/50, 1/100, etc. versus the 1/4, 1/8, 1/15, 1/30, etc. on more modern cameras.

When metering with the Sekonic, should I just use the closest shutter speed on the Graphex, or is there some handy shutter speed conversion from the older scale to the newer one? I'd like to eliminate this variable before burning through a stack of film.

I'm off to Yellowstone for the first time next week so any help would be appreciated.

mopar_guy · Posted: Tue Jun 30, 2009 1:50 am Post subject:

I thought that T-Max was supposed to have more exposure latitude nowadays as compared to when it was first introduced. Some exposure tests using roll film is the easiest way to determine if the results will suit your purposes.

Dave

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

They run about 1/3 of a stop, but in reality, the Graphex shutter is probably closer to the sekonic numbers than its own.

I"m sure there's an easier way, but if you subtract the log of the larger fraction from the log of the shorter fraction then divide that by .3031 you'll get the decimal equivalent of fraction of a stop.

ex:

log of 1/4 = -.60206
log of 1/5 = -.69897

The difference is .09691 / 0.3=.32303 which is 1/3 of a stop

But before I get out the quill and slide rule, I'd find a way to see what the shutter is REALLY doing.

I think you'll find out that the speeds are about a 1/2 stop off and vary by as much as a 1/3 stop, particularly on the low end.
_________________
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tsgrimm · Joined: 04 Apr 2004 Posts: 158 Location: SE Michigan

Don't forget to take a camera loaded with "Kodachrome" that can be tossed in a backpack for short hikes. There are many things to see and do in and around Yellowstone and all the western National Parks besides the major tourist attractions.

Have a nice trip, and I hope that you have a chance to go back a second time.

Henry · Posted: Wed Jul 01, 2009 1:37 am Post subject:

JimBob, you can do what I did and get ahold of a GE DW-68 meter; it's calibrated in Graphex shutter speeds. I also use a Gossens LunaPro F, which is calibrated "the other way." The GE is usable only in daylight situations, not low-light, but otherwise I prefer it as it uses no batteries and it perfectly matches the vintage of my Century (1954). The b/w film I use (Ilford XP2 Super) has enough exposure latitude to accommodate any inaccuracies in the metering, and besides which I "overexpose" it at EI100 (vs. its rated speed of EI400) to yield a negative that scans well. You can pick up a DW-68 cheap on the 'bay. I got mine at a camera show for $15, in original box with instructions.

Now for transparency film it's safer to go with the modern meter, since exposure latitude is zilch and you need to be "right on."

JimBob · Joined: 03 Oct 2008 Posts: 12 Location: Wichita, KS

I took Les's advice and built a shutter speed tester that plugs into my sound card. I ran through all the speeds on the Super Graphic and the results were better than I expected. The speeds are within 10%-12% for 1/25-sec and longer, but the errors really stack up at speeds faster than 1/50. 1/200 measures closer to 1/100 and 1/400 measures around 1/150.

I printed up a tiny chart to keep with the camera that shows the measured vs. indicated speeds for future reference. When metering with the Sekonic, I'll pick the closest measured speed, and err on the side of overexposure.

For anyone who is interested, here are the selected vs. measured speeds:

1 sec : .98 sec
1/2 sec: .49 sec
1/5 sec: 1/6 sec
1/10 sec: 1/11 sec
1/25 sec: 1/22 sec
1/50 sec: 1/40 sec
1/100 sec: 1/67 sec
1/200 sec: 1/111 sec
1/400 sec: 1/143 sec

Just for fun, I ran the same exercise with my RB67 and the results were similar.

glennfromwy · Joined: 29 Nov 2001 Posts: 903 Location: S.W. Wyoming

Your shutter speeds should be fine. Better than most, actually. You will find that in order to get good depth of field with large format, you need to stop down further than with smaller formats. For landscapes that means f/22 or smaller, and slow shutter speeds. Your slow speeds look good enough for transparencies. You're good to go. Be prepared for road construction delays in the park and have fun.
_________________
Glenn

"Wyoming - Where everybody is somebody else's weirdo"