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strength of flash head for studio

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TarMoo is off-line
25 January 2014 06:49
tarmoo
Photographer
tarmoo
Location
United Kingdom
Kent
Chatham

Some of the cheaper Bowens flash units only have 1/500 second duration, which is not much use if you are trying to freeze movement. I have the Elinchrom BRXi 500 heads and they have a duration of 1/1558 sec, but the lower powered (and lower priced) 250ws BRXi units one have durations of 1/2700 sec.

In terms of power, I think a 250ws unit is more than enough for most amateurs unless they have a massive studio. The problem is usually turning it down enough rather than needing full power. If buying again I would opt for the 250/500 kits as you can get a larger range of power.

The other issue is if the lights have build in wireless triggers or if you have to buy these separately.
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HowardJ is off-line
25 January 2014 14:47
HowardJ
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HowardJ
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Surrey
West Midlands

I use Elinchrom 400W and 500W lights usually on less than half power so they recycle quickly. I have 8 heads and use them in different combinations depending on the shoot. I think having a number of lower power heads gives you more flexibility, but that's just me.


OldMaster is off-line
27 January 2014 15:02
OldMaster
Photographer
OldMaster
Location
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Hertfordshire
Harpenden

..."Charts!...High level mathematics!...Flashmeters!.......I'm surprised you guys buy anything.....Just use common sense!.....jeeeez." !!

Try telling that to my graduation company where we work to 1/10th of an f-Stop!! Its how I got to my calculation stated earlier in this post. Two 500 watt/s heads (old style both at 45degrees), 40" soft white brollies (bounce) at around 12ft and "half power" gives F8 at the subject position. We meter of course because you might have a black ceiling or a white ceiling or anything in between.

In truth this effects the white balance more than in it seems to effect the power settings which will have something to do with the efficiency/losses through the brollies. As a rule of thumb if you wanted GN equivalents, very roughly you multiply the watt/sec spec square route by 4..so a 500 watt/s head would result in a GN in excess of 80 which works out about right and is based on a "standard" parabolic reflector..a brollie tends to halve this figure..


OldMaster is off-line
27 January 2014 15:06
OldMaster
Photographer
OldMaster
Location
United Kingdom
Hertfordshire
Harpenden

Tarmoo makes a very relevant point, some of the larger heads have quite a long "burn time", usually around 1/500th-1/700th sec. If you want to freeze movement, dancers, etc you will need "high speed" flash head. Check the specifications. Bowens do them but they are much more expensive than their standard models. You should be looking at 1/1500 upwards for it to be a true "high speed" flash head...!


Steven Jardine is off-linePlatinum Member
27 January 2014 15:32
RedChecker
Photographer
RedChecker
Location
United Kingdom
Buckinghamshire
Stoke Mandeville

For dance photography it is considered that you need a 1/2000th of a second flash duration for completely freezing motion. Bear in mind most flash manufacturers quote flash speeds in t/0.5 figures which are around 3x shorter than the full flash value that you actually need (t/0.1 value). So for example, if you see a head quoted at giving 1/1500th (t/0.5) then its actual duration for freezing movement will be approximately 1/500th.

Some Bowens heads are notoriously slow. My Gemini 500 heads are quoted at 1/700th which equates to ~1/230th in real terms.

Bear in mind that spare flash tubes for 'fast' heads are also significantly more expensive than standard tubes (~£250 as opposed to ~ £70 for Bowens ones)
When you are dead, you do not know that you are dead. All of your pain is felt by others. The same thing happens when you are stupid.


w4pictures is off-line
27 January 2014 16:33
w4pictures
Photographer
w4pictures
Location
United Kingdom
London
Chiswick

Quote from RedChecker
For dance photography it is considered that you need a 1/2000th of a second flash duration for completely freezing motion. Bear in mind most flash manufacturers quote flash speeds in t/0.5 figures which are around 3x shorter than the full flash value that you actually need (t/0.1 value). So for example, if you see a head quoted at giving 1/1500th (t/0.5) then its actual duration for freezing movement will be approximately 1/500th. Some Bowens heads are notoriously slow. My Gemini 500 heads are quoted at 1/700th which equates to ~1/230th in real terms. Bear in mind that spare flash tubes for 'fast' heads are also significantly more expensive than standard tubes (~£250 as opposed to ~ £70 for Bowens ones)




Interesting. I've always assumed that, for briefest flash duration, Profoto heads are the things people crave. However, I have also assumed that any flash head, or speedlight for that matter, has a shorter flash duration as the power output is reduced. Is that so? i.e. if you take your Bowens head at say !/230th at full power, will that duration drop to say 1/10,000th at minimum power?

I do agree that I'm usually struggling to turn the things down enough. I've ND'd flash heads before, bunged chocolate gel, full CTO and a bunch of frosts on them to drop the output, especially when working with mixed lighting.


Steven Jardine is off-linePlatinum Member
27 January 2014 17:33
RedChecker
Photographer
RedChecker
Location
United Kingdom
Buckinghamshire
Stoke Mandeville

Quote from w4pictures
Interesting. I've always assumed that, for briefest flash duration, Profoto heads are the things people crave. However, I have also assumed that any flash head, or speedlight for that matter, has a shorter flash duration as the power output is reduced. Is that so? i.e. if you take your Bowens head at say !/230th at full power, will that duration drop to say 1/10,000th at minimum power?




Both Profoto and Broncolor are very much on-par with one another in terms of flash duration and are about the fastest on the market (they now go up to ~1/25,000th IIRC).

The increases/decreases in speed depend upon the design of the flash units. Speedlights and generator packs tend to be faster at lower power settings (as you'd expect). Mono blocks on the other hand I've heard are slower at lower power, I believe this is due to their design dropping the voltage sent to the flash tube. Lower voltage ultimately equals a slower burn. Some manufacturers are decent enough to quote speeds across the power range and some quote the speed for each stop of power adjustment.
When you are dead, you do not know that you are dead. All of your pain is felt by others. The same thing happens when you are stupid.



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