To be sure the bulbs flashes properly, clean the fitting. Remove dust and corrosion with a Scotch Brite before using them.
The slash gun needs to be cleaned especially the contacts need some extra attention. No corrosion should be left to guarantee reliable working.

Bulbs may look the same, but they're real different.

Flashbulbs may be grouped in 4 classes according to the time of peak of illumination and some other characteristics.

 Class F(ast) Bulbs: peak of illumination within 5 milliseconds.  GE SM and Wabash SF 

Class M(edium) Bulbs: peak in 20 milliseconds.   Photoflash # 22 and Super-flash Press 40 and Westinghouse #11


Class S Bulbs: peak in 30 milliseconds. Photoflash # 50.

Bulbs for 4x5 Focal Plane Shutter!

The duration of a flash should take plenty time to cover the whole 4x5 inch film negative.
Time needed to illuminate the whole surface while the slit of the focal plane shutter travels along the film from top to bottom.
If the flash goes out before the slit finished its travel along the film, the negative would be exposed for just a small portion.
Therefore it is essential that you use the right bulb for the appropriate shutter and film size.
The bigger the film size the longer the flash duration should be. However that rule applies only for the focal plane shutter camera. The in between central shutters such as the Grafex or Rapex shutter will do with a SM or SF flashbulb according to the shutter speed you prefer.
In summary you can say that shooting with a Graflex camera equipped with a focal plane shutter the following flashbulbs can be used.

Sylvania 2A FP (Focal Plane) E27 screw.
Comparable to GE No.31 or Philips PF45

Class FP: long peak focal plane shutter bulbs such as the # 31 and Sylvania super-flash No. 2A

The Sylvania 2 A -formerly Wabash- made for use with up to 4 x 5" Focal Plane shutter.

This Long peak bulb is specially made for stopping the action at 1/1000 sec. up to 160 Ft or 60 meter producing 80.000 lumen.

Focal Plane Shutter 4x5      
Film speed ASA/DIN 100/21 125/22 400/27
Shutter speed 1/200 - 1/250 130 180 260
Shutter Speed 1/400 - 1/500 90 130 180
Shutter Speed          1/1000 65 90 130

To find the "f-stop" divide flash number by distance in feet between flashbulb and subject.

Focal Plane 4x5 inch film 100 ASA  - 

Shutter Speed 1/200 - 1/250

FLASHNUMBER = 130 - distance = 24 feet

130/24 = f stop 5,6





For use with the

Supermatic Shutter

 for the normal in between the lens shutters like the Kodak Supermatic, Graphex or Graphic shutter or any other shutter equipped with a flash bi-post or other synchronise contact.
For use with Bulbs, set control lever to M. This enables to ignite the bulb milliseconds before the diaphragm is completely in open position to reach its peak.



Speed Midget flashbulbs have a single contact bayonet base for quick insertion. Overall length 2 1/2 inches. 

Speed Flash flashbulbs. The effective flash duration last about 1/100 second with the SF and 1/200 for the SM at 1/2 peak

These bulbs are recognizable as they do not have wire or foil inside the bulb. The flash of about 5000 lumen seconds is produced by the primer mixture on the tips of the two lead in wires, igniting in an atmosphere of oxygen.



The GE # 5 Synchro press

Efficient Bulb for use in midget reflectors. Very popular with the press. Not suitable for the Focal plane shutter for speeds faster than 1/30 sec.


The G.E. # 6 Focal Plane 

A midget bulb with longer flash duration designed for use with the miniature focal plane. Camera size 35 mm to 2 1/4 x 3 1/4.

As you can see these bulbs are unsuitable for the larger 4x5 inch camera. Duration is too short


The upper side of the picture is dark, due to the fact that the GE#6 peaks too short to cover the 4x5 inch sheet film, during the time the focal plane shutter slit, travels along the film surface. We'll need Special Bulbs

Focal Plane No. 31 and Superflash no. 2A

These bulbs are designed for use with the larger focal-plane shutters up to 4 x 5 inches in film size. They have an extend peak of illumination, which is required for the focal-plane synchronization. Not to be used with front-shutter synchronization. The effective light output of these flashbulbs is around 80.000 lumen seconds.

Instantaneous Flash with 4 x 5