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Old Nov 6, 2006, 2:59 PM   #1
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Hello,

I am thinking about buying thethe Vivitar 285 HV Flash, over the P20 because it throws light over 140 feet. I was just wondering what the maximum shutter speed would be if i was going to use the flash with the P850.... A guy at a camera shop said that 1/500th or 1/250th of a second, with the flash, some of the photo would be dark because of the camera not sync.... corectly... I would be using it to take hockey photos....

Going to a game tonight...

Help ASAP..

shooting_rubber.
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Old Nov 7, 2006, 11:24 AM   #2
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When you get to the Arena...set up where your going to be shooting the photos....then take some practice shots. You'll be surprised at the high speeds you can use because of the bright ice! Don't expect perfection on the first outing...you'll get better as you attend more games!

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Old Nov 9, 2006, 11:11 AM   #3
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Ok, The shutter speed has to do with flash sync., for these cameras stay at 1/250 or less.

The flash:

The Vivitar has a Guide number of 140 in feet for ISO 100 @ the maximum Flash zoom setting of 105mm.

the guide number of 140' does not mean it can reach 140 feet it means the calculation is in feet.

The following formula is true for any flash, and camers.

the formula f(stop) = GN/distance also can be illustrated as Distance = GN/F(stop)

therefore if your best fstop (lowest) , whatever is f3.5 the max distance is 40 feet at iso of 100, shutter speed is inconsequential, as long as it is at or below 1/250.

if you had a f2.8 lens, which the P850/712/880 has but only at 28mm then the max distance would be 50 feet at an iso of 100. when the camera is at a higher zoom the lowest f/stop is greater then f2.8 ie 3.5.

So., get behind the boards. Actually the ambient light from the rinks lights should get you enough light, the strobe will only help if the subject is close, if that is the case, the P20 would still be your best bet, because it will adjust the light ouput of the flash automatically.

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Old Dec 6, 2006, 3:31 AM   #4
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Hi,

I have a P880. Accidentially I have just tested the flash sync with my 3rd party flash (Soligor 280AZ): the maximum shutter speed is 1/125 that I can use with my flash. 1/160 resulted in almost totally black pictures. I guess that P850 is similar from this point of view. I have never used a P20, but it may allow faster shutter speeds, since when I use the internal flash of my P880 the 1/160 works well.

Actually if your really need flash (the actual light is much lower than needed) then the shutter speed does not really count, since the main part of the light is coming from the flash. Usually flashes provide the light for a very short period of time (less than 1/500), so I do not think that bluring can be a problem.

However as the calculation from Thegreygeek shows, most probably you will not able to provide enough light from a flash in a hockey arena. Note also that a high ISO value increases the disctance. (E.g., ISO 400 doubles the distance.)

Be careful with any 3rd party flash. The trigger voltage can be quite high, which may break your camera if you use it in the hot shoe.

Gyuri
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Old Dec 6, 2006, 11:36 AM   #5
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wgyuri wrote:
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However as the calculation from Thegreygeek shows, most probably you will not able to provide enough light from a flash in a hockey arena. Note also that a high ISO value increases the disctance. (E.g., ISO 400 doubles the distance.)
Just to make sure there's no misunderstanding on how this works.

ISO 400 would roughly double the distance compared to ISO 100 at the same aperture (which is what I think you mean. but I want to make sure the Poster doesn't think that doubling the ISO doubles the range).

Each time you double the ISO speed, flash range increases by approximately 1.4x.

So, a strobe with a GN of 140 feet at ISO 100, when used at ISO 400 and f/3.5, would give you a maximum flash range of approximately 78.4 feet (compared to a max range of around 40 feet using at it ISO 100 and f/3.5).

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Old Dec 8, 2006, 5:34 AM   #6
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JimC wrote:
Just to make sure there's no misunderstanding on how this works.**
ISO 400 would roughly double the distance compared to ISO 100 at the same aperture (which is what I think you mean. but I want to make sure the Poster doesn't think that doubling the ISO doubles the range).
Each time you double the ISO speed, flash range increases by approximately 1.4x.
So, a strobe with a GN of 140 feet at ISO 100, when used at ISO 400 and f/3.5, would give you a maximum flash range of approximately 78.4 feet (compared to a max range of around 40 feet using at it ISO 100 and f/3.5).
[/quote]

Your understanding is correct. When you double the ISO speed flash range increase by the square root of 2, which is approximately 1.4. It means if you double the ISO speed twice then in theory the maximum flash coverage is doubled.
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