I was also yearning to run old flash holders, and last year found a place in Los Vegas that sold me a couple of new manufacture zinc carbon 22.5v batteries for a very reasonable price.
For my flash holders that take 15V batteries I pry the old guts out of the carbon zinc battery can, and re-use that can and end contents. I pack in a modern tiny 12V alkaline battery , and fill the empty negative terminal space with a short piece of 1/4" copper tubing or wadded up aluminum foil to link it to the old 15V battery contact.
12V alkalines are used in most NA car makers key fobs to power the remote door unlocking transmitter.
The down side to getting all the old flash holders to work is that it gives you a reason to buy up flash bulbs. I am presently holding between 400-500, mostly in ag2, ag3, and ag-1, both B and uncoated sorts. The 48 M25's I had I traded to someone with a functional Graphic holder.
It is interesting that they list a GN for '1000, as this speed was only found on FP shutters. I don't think any of my boxes for class M bulbs list a GN for that speed. Are you sure you don't have class F bulbs?
Notice how different it is from '30, in which the film records the entire blast of light, though. You lose over two stops by clipping the duration of the flash.
You also lose a fair amount of light by using the B bulbs instead of the clear ones. I try to only use the B ones for color film, but I am all out of clear #25/G.E. #5 bulbs, and only have #40/G.E. #11 bulbs left in the clear variety.
Excellent point on whether or not the chart I was looking at was for M or F bulbs, I didnt think of that. However, now Im completely confused. The box that had the chart was a Sylvania 25b box with a woman holding a camera on the front, looks like probably from the late 60's or possibly 70's and it doesn't say M or F anywhere on the box. I pulled out my other boxes which are all the older Sylvania yellow and black boxes, they are Class M and are Press 25 and Press 25b bulbs. The yellow and back boxes provide guide numbers on the sides but the blue bulb guide numbers are different from the clear bulb numbers (as would be expected). Also, the boxes don't use ASA but use "Daylight Exposure Index" instead. Can someone please explain the difference? The Press 25b boxes list Daylight Exposure Index from 8-32 and shutter speeds up to 1/200 where the Press 25 boxes (clear bulbs) list Daylight Exposure Index from 8-160 and shutter speeds up to 1/400.
I plan on running several sheets of Tmax 100 4x5 through a Speed Graphic and 1 or two rolls of Tmax 100 35mm through the Argus C3 to test the exposures. Can anyone shed any light (no pun intended) on the best guide numbers to use when using Press 25 and Press 25b bulbs with modern Tmax 100 film? This would be extremely helpful! Also, how do the Cress Photo charts compare to the charts on the original Sylvania boxes and which would be preferable to use?
My Speed Graphic is shooting through a Carl Zeiss Jena 135mm Tessar that has a maximum shutter speed of 1/200. Any help finding the best guide numbers using both 25 and 25b bulbs running Tmax 100 4x5 through this would be a big help. Also, Im running out of 25b but there seems to be no shortage of 25 so I'm probably more inclined to run several tests using the 25's.
Thanks for all of your help everyone! I anxiously awaiting your input!
Ok, I just placed a call to a friend who has more experience going back decades then anyone else that I know and he provided me with the following solution that you can apply to any bulbs that you come across:
Guide numbers are figured by measuring light at a specific distance relative to the ISO (ASA previously) using a light meter and then multiplying the f-stop reading by ten.
Process (for ISO 100):
Have an assistant hold a tested and trusted light meter with hemispherical (domed) attachment (I use a Sekonic) 10 feet away from you. Use a tape measure to be as accurate as possible. Make sure that you are in a room that allows you to control your ambient light. Don't do this outside or in a room with bright open windows or anything that will cause any excess ambient light to throw off the reading. Have your assistant, at a 10 feet distance from the flash bulb, point the meter at the center of the bulb. Have the meter set to flash (not ambient or flash w/ cord). Have the assistant trigger the meter and immediately after you know they've triggered the meter ignite the flash bulb. Keep in mind that the longer you wait to ignite the flash the more skewed the reading will be because the meter will be recording ambient light from the moment it is triggered so ignite the flash bulb immediately. Now take the f-stop reading from the meter and multiply it by 10. This is your guide number for that particular flash bulb type. Use this guide number to figure the f-stops for any distance that you may be shooting just as you have before i.e. Guide Number divided by distance in feet (lamp-to-subject) equals f-stop.
Back to the Sylvania bulbs. Can anyone confirm that all Sylvania 25 and 25b bulbs are class M? I have some of the later white boxes with the woman holding a camera but I cant find any class makings on the box. The yellow and black boxes say Class M right on them.
Sylvania Press 25 and Press 25B ARE Class M (Medium peak bulb).
Press 25 (ISO100):
up to 1/30 sec = guide number 280
1/60 sec = guide number 260
1/125 sec = guide number 220
1/250 sec = guide number 180
1/500 sec = guide number 130
Press 25B (ISO 100)
up to 1/30 sec = guide number 190
1/60 sec = guide number 180
1/125 sec = guide number 150
1/250 sec = guide number 120
1/500 sec = guide number 90
I always try to err on the side of over exposure. All of these guide numbers assume a scene of average brightness. If the scene has a lot of dark colors, open up the aperture. If the scene has a lot of white, close the aperture more.