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  1. #1

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    Flash Bulb Question P25 and #5 vs M25 and M5 or later M3

    The Sylvania Press 25 (P25) and the GE #5 were out it the 1950s, maybe earlier.They were similar flashbulbs in both size and light output but with different names. Both were filled with Aluminum and were roughly the size of eggs.

    In the later 1950s they came out with the grape sized M25 by Sylvania and M5 by GE flashbulbs. The M denoted that both the bulb and metal base was mini or midget. These bulbs were filled with Zirconium and produce about the same amount of light as the much larger P25 and #5 flashbulbs. Both were advertized to reach peak brightness fast and hold that output for a long time. That is a long time by flash bulb standards. By the 1970s or earlier it seems that all the M25 and M5 bulbs were gone and replaced by M3 bulbs by Sylvania and GE.

    My question is was there really a difference between the older M25 and M5 bulbs and the newer M3 bulbs or was this just a name change to help novice photographers figure out what bulb to use. The published guide numbers for the M25 and M5 are very similar to the M3 guide numbers.

    Was there perhaps a difference in the time to peak. I have an M5 package that lists 20 milliseconds to peak and a later M3 that lists 17.5 milliseconds. Perhaps the older time was just rounded off to 20 ms.

  2. #2

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    I thought that M5 bulbs were replacements for GE #6 or Sylvania FP26 (used for 35mm focal plane synchronization). M3's were class M like Press 25 or GE #5.
    Dave

    "She's always out making pictures, She's always out making scenes.
    She's always out the window, When it comes to making Dreams.

    It's all mixed up, It's all mixed up, It's all mixed up."

    From It's All Mixed Up by The Cars

  3. #3

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    Actually the P25 and P26 from Sylvania and the GE #5 and #6 were made together for many years. The P26 and # 6 did have a much flatter peak. This allowed their use with focal plane shutters. Times were published for speeds up to 1/750 of a second on the packages I have. I believe that the M3 bulbs also has a flatter and longer peak similar to the P26 and #6 bulbs. In addition the GE #6 and FP26 were larger bulbs with larger bases just like the GE#5 and Press25.

    You may be correct in that the M in M3 and M5 may indicate medium peak and not mini or midget bubs as I had thought.

  4. #4
    Jim Jones's Avatar
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    It was the 2A, FP-26, and FP-26B that had fairly flat output from 15 to 30ms for use with focal plane shutters. The Press 25, M25, M5, and 25 peaked at about 20ms, with half-power points at about 15 and 30ms. The M2 peaked at about 13 ms, and the SF at about 7ms.

  5. #5

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    Thanks Jim,
    Kodak used to provide inserts with their films like Kodacolor-X. They included guide numbers for common flash bulbs. All bulbs had Guide numbers for both X and M sync listed for various shutter speeds. However the M2B was only recommended at X sync at 1/30th sec. (M sync was listed at Not Recommended on the table). I always wondered about this. If the M2B peaks at only 13ms that explains it.

    For those who don’t know.
    With a M Sync the camera sends power to the bulb and starts the burn then typically waits 20ms until the bulb is at full power before opening the shutter. That is because most Medium peak bulbs took 20ms to reach peak light output and 20ms later (40ms after pushing the button) the light is almost gone. If an M2B that peaked at 13ms were used at M sync then the shutter would not open until 7ms AFTER peak and over 80% of the light output would be gone before the shutter opened.

  6. #6

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    From my Sylvania Dealer catalog.
    Sylvania M-3 Flashbulb
    Synchronization: Ideal for both class M shutters and simple box cameras.
    Rapid initial rise and relatively flat output characteristics meet
    requirements of most late model focal plane cameras.
    Light output: clear 16,000 lumen seconds, Blue 10,000 lumen seconds.
    Peaks at 17 milliseconds. A medium range lamp.
    Base: Miniature pinless: Miniature adapter fits it to midget base reflectors.
    Reflector: For maximum light output, use a 3" polished reflector

    Francis in VT

  7. #7

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    The M5 and M3 are very similar. Although the M5 is slightly brighter, it doesn't make that much of a difference (less than 1/3 stop). The reason for the number change was due to a change in the composition that changed the bulbs from class M (medium peak) to class MF (medium peak, long duration).

    One thing to note: although the #5/P25 and M3/M5 have similar guide numbers, they do not have similar light output. The larger bulbs are about a stop brighter, but they are designed for 5" reflectors. The M-base bulbs are designed for 3" reflectors, which focuses the light more, giving an equivalent (or similar) guide number.
    "Panic not my child, the Great Yellow Father has your hand"--Larry Dressler

  8. #8

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    So:
    M5 is class M (medium peak)
    M3 is class MF (medium peak, long duration)
    Is that correct?

    Also how long is a long peak?

  9. #9

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    Three months ago, I was using some Sylvania FP-26 bulbs from the 1960's and in the box there was a paper from Sylvania that suggested M5 bulbs as a replacement for the FP26 (FP26 are Focal Plane, not class M).
    Dave

    "She's always out making pictures, She's always out making scenes.
    She's always out the window, When it comes to making Dreams.

    It's all mixed up, It's all mixed up, It's all mixed up."

    From It's All Mixed Up by The Cars

  10. #10
    Sirius Glass's Avatar
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    FP-6 is also a Focal Plane bulb and not an M class. [GE IIRC]
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

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