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Guide Number help
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Numinous



Joined: 25 Mar 2008
Posts: 8
Location: North west of Atlanta

PostPosted: Sat Apr 05, 2008 9:12 pm    Post subject: Guide Number help Reply with quote

Would anyone have a clue as to the guide number for an 11B bulb at ISO 400? The table on the Cress website didn't help me at all.
I've acquired a bunch of 11Bs and 22Bs, Cress helped with the 22s.

Also, which M sync, red or black?

Thanks in advance,

Numinous
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45PSS



Joined: 28 Sep 2001
Posts: 3229
Location: Mid Peninsula, Ca.

PostPosted: Sun Apr 06, 2008 1:06 am    Post subject: Reply with quote

Use Red sync with shutter speeds marked in red, black sync with shutter speeds in black on the shutter speed dial of the shutter.
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Les



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

PostPosted: Sun Apr 06, 2008 2:47 am    Post subject: Reply with quote

One rule of thumb is that guide numbers increase by a factor of 1.414 when the speed of the film is increased one stop.

Bill Cress's website says 11Bs in a 6-7" reflector with 200 speed film has a rating of 240.

240x1.414=..and the slide rule says...339 I'd use 320. F32 @ 10ft is a whole lot easier to find than f33.9
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Numinous



Joined: 25 Mar 2008
Posts: 8
Location: North west of Atlanta

PostPosted: Sun Apr 06, 2008 3:03 am    Post subject: Reply with quote

Les,
was Cress referring to ISO numbers or Exposure Index numbers, and, are they the same?
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Les



Joined: 09 May 2001
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Location: Detroit, MI

PostPosted: Sun Apr 06, 2008 3:39 am    Post subject: Reply with quote

Interestingly all the other tables say ASA, this one says Exposure index.

I pulled up my 8th ed. Photo Lab Index, and alas, all of the flash data was written for Weston film speeds.

Which makes me wonder if he didn't create that table by converting Weston to ASA, which isn't perfect, thus he used the Exposure Index.

There are some very technical differences between ASA, and EI, but for the man behind the camera, use them as though they were the same. If your exposures are coming out over exposed, increase the Guide Number.
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Numinous



Joined: 25 Mar 2008
Posts: 8
Location: North west of Atlanta

PostPosted: Sun Apr 06, 2008 2:33 pm    Post subject: Reply with quote

Thanks, Les, I appreciate it. I guess I'll have to calculate a factor to figure out a GN for 400 ASA . . . oops ISO.

And, BTW, 45PSS, duh, silly me, I should have looked closer.

Any comments on the use of 11B and 22B bulbs?

Thanks,
Numi
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C. Henry



Joined: 13 Dec 2005
Posts: 358
Location: North East Georgia, USA

PostPosted: Sun Apr 06, 2008 6:11 pm    Post subject: Reply with quote

(comment)
Save the blue bulbs for daylight balanced color film!

C. Henry
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Numinous



Joined: 25 Mar 2008
Posts: 8
Location: North west of Atlanta

PostPosted: Mon Apr 07, 2008 12:20 am    Post subject: Reply with quote

I was planning on using the bulbs with TXP and maybe Polaroid 52. Ummmm,
am I going to blind my subjects? Guess I'll have to tell them to look camera left.

Salut
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C. Henry



Joined: 13 Dec 2005
Posts: 358
Location: North East Georgia, USA

PostPosted: Mon Apr 07, 2008 5:35 pm    Post subject: Reply with quote

Blue bulbs (11B, 22B & 25B) give light with almost the same color balance as daylight. Clear flash bulbs have a color balance close to tungsten photo flood lights.
If I recall correctly the guide numbers for 25B(blue) bulbs was almost the same as clear 25 bulbs. I assumed that the same also applied to 11 & 22 bulbs as well.
There is no reason why blue bulbs can't be used with black & white film.
On the other hand with daylight balanced color film it is preferable to use blue bulbs because using a filter on the lens to correct the color with clear bulbs required an increase in the exposure by a filter factor to compensate for the loss of light in the filter.

C. Henry
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mopar_guy



Joined: 07 Aug 2008
Posts: 126
Location: Washington, the State

PostPosted: Sat Dec 06, 2008 5:30 pm    Post subject: 22B vs 2B Reply with quote

Hi,
I have also turned up a few GE 22B bulbs and would like to try them with some Portra 160. ISO 160 should be closer to guide number 300 at 1/100 sec.
I also have a handfull of Sylvania #2B bulbs. Are these roughly equivalent to the GE #22B?
Regards,
Dave
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Les



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

PostPosted: Sat Dec 06, 2008 6:27 pm    Post subject: Reply with quote

22B (or #5) are about the size of a walnut, Unless there was a change that I don't know about, a #2 is a full sized light bulb with a light bulb thread (aka edison base) and put's out a whole lot more light than a 25
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C. Henry



Joined: 13 Dec 2005
Posts: 358
Location: North East Georgia, USA

PostPosted: Sat Dec 06, 2008 7:28 pm    Post subject: Reply with quote

From the Photo Lab Index page 10-08:

No. 5B (BLUE FILTER)
B-11 Bulb, S.C. bayonet base
Total light: 9,400 lumen seconds
Approximate peak lumens: 680,000

No. 22B (BLUE FILTER)
A-19 Bulb, Medium screw base
Total light: 32,000 lumen seconds
Approximate peak lumens: 1,900,000

From the Photo Lab Index page 10-13
Guide number tables
No. 22B with 6-7 inch Polished Reflector
for ASA film speeds 125, 160, 200
M sync shutter speed: 1/30 and slower 340; 1/50 & 1/60 300; 1/100 & 1/125 250; 1/200 & 1/250 190; 1/400 & 1/500 135

Hope that helps.

BTW I think that Les is thinking of a #25B bulb which was Sylvania's # for a bulb almost the same as a GE #5B.

C. Henry
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Les



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

PostPosted: Sat Dec 06, 2008 9:10 pm    Post subject: Reply with quote

C. Henry is correct on all counts!!
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mopar_guy



Joined: 07 Aug 2008
Posts: 126
Location: Washington, the State

PostPosted: Sun Dec 07, 2008 3:34 am    Post subject: Reply with quote

Thank you C. Henry.

Now I can do some tests. As for the Sylvania 2B bulbs I can do a test to compare with the GE 22B. In physical size the 2B is slightly larger than the 22B. If the light output is only slightly different, the print film ought to get a usable image.
Kind regards,
Dave
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C. Henry



Joined: 13 Dec 2005
Posts: 358
Location: North East Georgia, USA

PostPosted: Sun Dec 07, 2008 6:11 pm    Post subject: Reply with quote

From the Photo Lab Index page 10-17
Table of properties of Sylvania Superflash Lamps

2B; Class M; Approx. Total Light Output 33,500 lumen sec.; Approx. Peak Lumens 2,000,000; Bulb Shape A-19 Medium Base.

As this is only about 5% over the light output of the 22B bulb I would suggest tweaking the guide numbers up only about a tenth of a stop or so, if at all.

C. Henry
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