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| b800 problem http://www.paulcbuff-techforum.com/viewtopic.php?f=8&t=1725 |
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| Author: | nshadows1 [ Sat Aug 27, 2011 10:09 pm ] |
| Post subject: | b800 problem |
Is it possible that the flash bulb will "wear out" I use the b800 for product photography I used to get correct exposure @f22 (22.7 light meter reading , .7 to account for my polarizing filter) iso100 250ss with the light about 3 feet away from the subject with the flash power set between 1/2 and 2/3 of the way depending on how far the light was from the subject. While using tonite I had to turn the power all the way up and it still wasnt quite enough so I had to go to iso 200. I also noticed that the whole second 1/2 of the power range from 1/2 power to full power only changed my light meter 1 stop, even though I know the light varied more than that from the actual picture exposures. I also notice my light meter will vary from 22.1-22.8 when I trip it even with out varying the light power. Im not sure whats going on. The equipment is about 4 years old. Is my light meter broken or acting up? My sekonic s308 has been dropped, and not sure the condition of the wires. Can the flash bulb be giving sporadic output? can it be wearing out. I have a lot of sessions to do on a deadline not sure what I should do Thanks in advance for any advice |
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| Author: | Photodan [ Sun Aug 28, 2011 1:07 pm ] |
| Post subject: | Re: b800 problem |
If you ever heard of the inverse square law, you will know that if you double the distance from light to subject, you will reduce light by a factor of 2 or 1/4th the power. you say you used to get more power but if your doing close lighting shoots than a few inches can change your exposure quiet a bit. Also remember that a polarizer can change an exposure by 1.5 stops depending on how it's turned. The difference between 1/2 to full power is one stop. 1/4 to 1/2 is one stop. 1/8 to 1/4 is one stop. One stop is doubling or halving the light depending on which way you go. You sound confused about why 1/2 to full only changed one stop, that's what is supposed to happen. If your reading 2/3 stop changes from pop to pop, with all things being equal, than that's a problem. Could be your meter, or your light. Since you do product work, I'm sure you have some white board and some black board. I would overlap one of each so you can fill half of your viewfinder with white and half black. Than set up a perfect exposure by your meter and shoot of 6 or 8 shots and look at the histogram, you should see a spike just before it climbs on the left side and another spike on the right side. That should tell you if the flash is consistent. |
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| Author: | Photodan [ Sun Aug 28, 2011 1:15 pm ] |
| Post subject: | Re: b800 problem |
I forgot to share my experience with the flash bulbs. Yes they can wear out but usually they just stop working or become unreliable. I may be wrong but I think they keep roughly the same light output throughout it's life. I've never seen one get weaker with age. TC would be a better person to answer that. |
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| Author: | nshadows1 [ Sun Aug 28, 2011 1:24 pm ] |
| Post subject: | Re: b800 problem |
hey thanks for the reply. I phrased the power metric wrong. by 1/2 power i actually meant the dial 1/2 way which corresponds to 1/4 power and by 2/3 i meant the dial 2/3 of the way which corresponds to 1/2 power. http://www.paulcbuff.com/popups/ab/ab_y ... k_0710.php Im so used to adjusting it by hand with out looking and just metering. I somehow worry its a combination of the wires and light. I can tell the flash power has declined. Not sure if stepped on or rolled over and tangled wires is generating the variable light meter readings . I will replace the wires today and see if that helps the metering. Do you know if flashes slowly lose their power? I imagined them just burning out like a light bulb in the bathroom. But Im a newbie self taught and the only light ive ever owned |
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| Author: | Technical Support [ Mon Aug 29, 2011 9:53 am ] |
| Post subject: | Re: b800 problem |
Flash tubes won't get dimmer and dimmer (perhaps over the course of a handfull of shots), they will either work or not work. It sounds as though there is something more going on in the light which would need to come in. Before that, I would do a controlled test with the meter and light. Set the light up 10' or more away and meter using only the 7" reflector. At 10' you should expect just shy of f/11 at full power ISO 100. |
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