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

brianmquinn · Mar 15, 2011

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.

mopar_guy · Mar 16, 2011

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.

brianmquinn · Mar 16, 2011

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.

Jim Jones · Mar 18, 2011

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.

brianmquinn · Mar 18, 2011

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 dont 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.

Francis in VT · Mar 18, 2011

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

nickrapak · Mar 21, 2011

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.

brianmquinn · Mar 21, 2011

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?

mopar_guy · Mar 21, 2011

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).

Sirius Glass · Mar 22, 2011

FP-6 is also a Focal Plane bulb and not an M class. [GE IIRC]

brianmquinn · Mar 23, 2011

As per the information posted here I went looking for a dealer information and found this on eBay. I bought it and just got in the mail today. Take a look.

brianmquinn · Mar 23, 2011

The seller sheet I posted pre-dates the M-25B and M3.
I have a box of:
Sylvania NEW! Zirconium-Filled M-25B flash bulbs.
These must have come out in the late 1950s after this publication.
The M-25B has the small S.C Min. base that the M-2 has.
The box states that the total light output is 8,500 Lumen Seconds for the M-25B.
It also states "Set Synchronizer for 15 milliseconds"
This is fairly close to the Press 25B with a total output of 9,000 Lumen Seconds.

I assume that the M-25B is similar to the GE M5B.

brianmquinn · Mar 24, 2011

Dug further into my collection and found a similar age box of clear M-25 bulbs.
They are rated at 16,000 Lumen Seconds.
Fairly Similar to the Press 25 rated at 20,000 Lumen Seconds.

nickrapak · Mar 24, 2011

Looking further into it, GE must have changed the classification of the M5s at some point. I have a box of M5s that mention that they are class M and will only work with M-sync (or a slow shutter). I also found a newer box of 6Bs that recommend AG-1B, M3B, or M5B to replace the bayonet-base bulbs, meaning at some point the M5 must have become a brighter version of the M3.

brianmquinn · Mar 24, 2011

It looks like the M3 bulb came out in 1963

This information in an April 1963 Article in Popular Science.

Westinghouse is introducing ...The M3 will take the place of the No. 6, M5 and M25 bulbs...Zirconium filling in the new bulb comes to a high intensity level (twice the output of aluminum) quickly and maintains it for a long time.... It can be used for most focal-plane shutters, all leaf-type shutters

Now if anyone had a graph of the light output of the M3 that they could post that would be great. We could compare it to the 1957 Sylvania dealer sheets I posted we would have a good idea of how it stacked up to the FP-26 bulb (quite similar to the the GE No. 6).

Sirius Glass · Mar 24, 2011

brianmquinn said:
I I posted we would have a good idea of how it stacked up to the FP-26 bulb (quite similar to the the GE No. 6).

No, actually the Sylvania FP-26 bulb is the same as the GE No. 6. Just different manufacturer.

Steve

brianmquinn · Mar 24, 2011

The GE 6B (LEFT) and the Sylvania FP 26B (RIGHT) were similar in terms of light output. They were not identical however. See Photo. In day to day use you could most likely interchange them and never see the difference in the prints. So in that respect you could say there were the same.

Note in the Sylvania Data Sheet posted above there is a table with a column heading titled : Nearist Comparable Bulb (Other Mft.) There the 6 B is listed as being roughly equal to the FP 26B

windly9 · Mar 31, 2011

Help please!!

Hi, does anyone know if the midget size bulb(like M25) will be fit ok into a flash unit that usually uses bulb like P25 or GE 5 or another way round. Are they having same size in base and can they interchange with each other?

Thanks!

mopar_guy · Mar 31, 2011

windly9 said:
Hi, does anyone know if the midget size bulb(like M25) will be fit ok into a flash unit that usually uses bulb like P25 or GE 5 or another way round. Are they having same size in base and can they interchange with each other?

Thanks!

No. The base of the M-25 is smaller and different. There are adapters to use M series bulbs in flash units designed for #5 type bulbs. Also the #5 or Press 25 bulbs will not work in the M series flash guns. Press 25 or GE #5 bulbs were designed to work with five inch reflectors and the M series bulbs were for a three inch reflector. Changing reflector size can make a difference in guide number.

brianmquinn · Mar 31, 2011

Moplar_guy is almost 100% correct. I do know of one exception however. Kodak used to make a flash gun with the name of Kodalight IV Flasholder. It has a 4 inch reflector and will take a bulb of the #5 or Press 25 size just as easily as an M2, M3, M5 or M25 bulb. However it was a pin connector for Kodak cameras, not a near universal hot shoe mount. Perhaps Kodak (or someone else) made a version that would connect to a PC socket or hot shoe. I just have never seen one like that.

As Moplar_guy pointed out smaller bulbs worked best with a smaller reflector and larger ones with a larger reflector. That is likely why Kodak picked a mid point 4 inch reflector for this dual use flash gun.

brianmquinn · Mar 31, 2011

Here is a photo of the guide number info. on an old* box of GE M2 bulbs. See the note about the reduced guide number when using an adapter for this small bulb when used in a flash made for the larger No. 5 or Press 25 bulbs. For those not skilled at guide number calculations; you loose about one stop of light with an adapter.

*Back before they changed the film speed rating system and Tri-X was only rated at 200. If anyone knows when they revised the system by how they set film speed and any details please let me know. If nothing else it will help me date this box of flashbulbs.

windly9 · Apr 2, 2011

continue...

What about these:

1. Does it mean that if the flash unit can take GE No. 5 , then it surely can take Sylvania Press 25 or other bulbs that has boyanet base?

2. What is the different between M2, M3 or M25?

3. Why don't we just use Blue bulb since it can be used when taking both B&W and color photo. Why is clear bulb needed since it is only used on taking B&W?

Thanks guys!

windly9 · Apr 2, 2011

Questions...

brianmquinn said:
Here is a photo of the guide number info. on an old* box of GE M2 bulbs. See the note about the reduced guide number when using an adapter for this small bulb when used in a flash made for the larger No. 5 or Press 25 bulbs. For those not skilled at guide number calculations; you loose about one stop of light with an adapter.

*Back before they changed the film speed rating system and Tri-X was only rated at 200. If anyone knows when they revised the system by how they set film speed and any details please let me know. If nothing else it will help me date this box of flashbulbs.

Hi, what will happen when adapter is used to install smaller bulb like M2 on Flash unit originally for larger bulb like No.5? Any effects or differences when taking photo? BTW, what is guide number and what are they used for and how to use them?

You said: "For those not skilled at guide number calculations; you loose about one stop of light with an adapter." >> Do you mind explain it?

brianmquinn · Apr 2, 2011

Answers:
1. Does it mean that if the flash unit can take GE No. 5 , then it surely can take Sylvania Press 25 or other bulbs that has boyanet base?
Any flash that takes a No. 5 will also fit a No. 6 or Press 25 or 26B

2. What is the different between M2, M3 or M25?
The M2 is the same size but has less power, and a slightly lower color temp. My first question that started this thread was how do the M3 and M5 or for that matter the M25 differ. So I cant say exactly.

3. Why don't we just use Blue bulb since it can be used when taking both B&W and color photo. Why is clear bulb needed since it is only used on taking B&W?
The blue reduces the light output. You get more power if you use B&W and clear flash. Also when flash bulbs came out it was all for B&W as that was the film at the time. You can use clear flash with a blue filter and color film or skip the filter and use blue flash.

brianmquinn · Apr 2, 2011

For Guide Number see....

http://www.flashbulbs.com/flashbulb_basics.htm

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

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