Below is a chart of a sky taken outside at about 2pm in october (today) it was shot first straight all at 100iso, all at 250th of a second which is the typical sync of many of todays dslr's you may have to adjust to suit a faster or slower sync speed. The first set to the left was straight from the camera facing the direction but not at the sun, it was to the right top corner, shot at f- 4.0, 5.6, 8.0, 11.0, 16.0, 22.0 the last shot you see the sun in the shot, the second set (middle) was straight from the camera with a .3Neutral density and a Circular Polarizer on the camera and was shot at f- 4.0, 5.6, 8.0, 11.0, 16.0, 22.0 the last shot you see the sun in the shot. the last set was facing away from the sun (sun at your back, overhead) shot with the same .3ND and CP on the camera. here is a link to larger shots with all shooting data http://stepheneastwood.com/tutorials/skychart/skychart.jpg you pick the sky color you want and see what setting you are at, remeber it is better to have more power than less, and you can always adjust your shutter from 1/250th down to brighten up a bit while maintaining the same flash power on the subject.
How is this useful? well now you know what exposure for the sky to look how you want it, the flash will need to be tested with the modifier you want to use at the distance you want to be at. Set up your flash/modifier and meter for the maximum power setting at the given distance. You will need to have as much power as indicted by the f stop in the first row, or to shoot wider open to reduce depth of field look at the options in row two and three and remember that you now need to account for a .3ND and CP which means your flash needs you need 1 stop more light to account for the .3ND and the CP is variable but has a filter factor Between 2.3 and 2.8 (approx. +1.3 stops) so best to account for 2 stops. What does that mean? it means if you have a strobe that can shoot at f 22 with all modifiers at the distance you choose, you will shoot at f16 but if you put a ND and CP on your camera it will reduce the flash effectively by 2.5-3.5 stops so your flash can really only effective compete in this scenario at f5.6-8.0 So to have enough power to block out the sun you may need a flash powerful enough to shoot at f45 to f64.
All light modifiers (softboxes, Beauty Dishes, Octobanks, Diffusers) eat up some light, some are more efficient than others, so you need to test with the modifier at the distance you want to work out to figure the real light. here is a chart from alienbees about how much light they put out at a given distance with certain modifiers, as to its accuracy I am not aware but I trust them to be fairly accurate. I have nothing for or against alienbee but I am happy to show that they have numbers and I believe they will back them up, so if these numbers work for you than all is great of not you would need more power from alternatives, Hensel, Elinchrom, Speedotron, Profoto, Broncolor, and white lighting all offer more powerful battery powered options you can explore. Edit, whitelightning has since added th zeus line of pack and head strobes in 1250 and 2500 ws power units, they can be found here http://www.alienbees.com/zeus.html . They are more powerful than the monolights and well priced and as such will be more powerful than the below monolights.
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" output measurements _______________B400 _________B800 ___________B1600 Standard 7-inch Reflector____________ f11 2/10 ______f16 2/10_________ f22 2/10 11-inch Reflector ____________________f22__________ f32_____________ f45 48" Silver Bounce Umbrella ___________f8-f11 ________f11-f16_________ f16-f22 48" Shoot-Thru Umbrella ____________f5.6-f8 _________f8-f11 _________f11-f16 Medium Softbox ___________________f11-f16 _______f16-f22_________f22-f32 |
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The output readings have been measured with a Gossen Ultra Pro flashmeter (ISO 100) placed 10-feet from the flashtube for direct reflector specs, 10 feet from the center of the radiating fabric for umbrella specs, and 4 to 6 feet from the center of the radiating fabric for softbox specs. Measurements were taken in the center of 20' x 27' white room with 20' ceilings. Readings may vary when taken in other environments and with other meters, as different brands of flashmeters can vary by as much as 1 whole f-stop in their interpretation of "correct" exposure values. The following accessories were used for these measurements: 7AB/R: The Standard 7” Reflector on the AlienBees Flash Units (silver field reflector, 80º beam spread); 11R: The 11” Reflector (silver long throw reflector, 50º beam spread); U48SW: 48” Silver and White Reversible Umbrella (silver side used for silver bounce reading), U48TWB: 48” Shoot-Thru Umbrella (black cover removed for diffused reading); and SB2436: 24” x 36” Medium Softbox (silver lined rectangular softbox, double-diffused with the second internal diffusion panel in place). " ___ Quoted from the alienbees website http://www.alienbees.com |
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Vivitar 285HV Straight head full zoom, full maual, full power 1/250th 100iso 10' f 8.0___ ______ _7' f 11 9/10 ____ __ __ 5' f 16 5/10 normal zoom, full maual, full power 1/250th 100iso 10' f 5.6 8/10_______7' f 8.0 5/10_ _ ___ ___ 5' f 11 4/10 wide zoom, full maual, full power 1/250th 100iso 10' f 5.6 4/10 ______ 7' f 8.0 2/10__________5' f 11
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Lumedyne 1/250th 100iso repeated results 5 times with ac unit connected. Bare reflector 400 ws _________10' f 16 1/10________7' f 22 1/10 _________5' f 32 1/10 200ws__________10' f 11 4/10________7' f 16 5/10__________5' f 22 3/10 100ws__________10' f 8 3/10 ________7' f 11 4/10 __________5' f 16 5/10 50ws___________10' f 5.6 3/10_______7' f 8 2/10 ___________5' f11 3/10 19inch octobox (norman) front diffuser on. 400 ws _________10' f 5.6 8/10 ______ 7' f 8 5/10 ___________ 5' f 11 4/10 200ws__________10' f 5.6 _ _ _ _ _ ___7' f 8 ___ ____ _ __ __ 5' f 11 100ws__________10' f 4.0 2/10 __ _ _ _7' f 5.6 1/10_____ ____5' f 8 2/10 50ws___________10' f 2.8 1/10 ____ __7' f 4. 4/10_______ ___5' f 5.6 19 inch octobox (norman) no front diffuser 400 ws _________10' f 11 2/10_______7' f 16 _ __ _ _ _ __ _ _ 5' f 16 9/10 200ws__________10' f 8 2/10 ________7' f 11 3/10 _________ 5' f 16 100ws__________10' f 5.6 6/10_______7' f 8 5/10 __________ 5' f 11 50ws___________10' f 5.6 9/10_______7' f 5.6 ___ _ __ ___ _ 5' f 4.0 |
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Using a Photogenics StudioMax III 320b full power ISO 100 1/250th: Standard 7" Reflector 10' - f 11 9/10 __________7' - f16 9/10________5' - f 22 7/10___ 45" Eclipse umbrella-distance from center lightstand 10' - f 4.0 5/10 __________7' - f 5.6 2/10_______5' - f 5.6 9/10 5' Octodome-Silver inserts and front diffuser attatched measured from front diffuser 10' -f 5.6_______________ 7' -f 8 __ ___ __ ___ 5' -f 8 7/10 24x32" Multidome w/silver inserts 10' -f 5.6_______________ 7' -f 8 __ ___ __ ___ 5' -f 8 7/10
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JTL 300 mobilite full power 1/250th 100iso 7 inch reflector 10' f 5.6 9/10___ ______ _7' f 8.0 8/10 ___ __ __ 5' f 11 6/10
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some shots where some of this was evident you can check the link I posted on the first page of this post, everything was shot with both a ND and CP on the lens at all times. It was shot for a Tutorial dvd on lighting and this topic was just one section of it. http://www.plasticmagonline.com/misc/mva_beach1
Stephen Eastwood
http://www.StephenEastwood.com
Below is a copy of a response I gave from another post about overpowering daylight as well.
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OK, lets say the correct exposure for a typical sunny day is f16 at 1/100th at 100iso. You want the background dark, lets say three stops under exposed, so you need to start by upping your speed, but many current digital SLRs are limited as are some medium formats, so lets say you max at 1/200th flash sync speed. that gives you a correct exposure for the background at f11 at 1/200th at 100iso. Now you can make the background dark by setting your f stop to f22 and the background is two stops under, but maybe you dont want to shoot at f 22 or more. So now you place a Circular Polarizer on the lens, that can adjust you from 1.5 to 3 stops bringing your proper exposure to 1/200th at f4-f8 depending on how much you cut the light. But in order to get the background dark three stops you would still have to shoot at f11-f16 again you may not want to be there but rather shoot at f 8 or even f5.6 so you add a ND 1 stop 2 stop or 3 stop to the lens, lets say you start with a 2 stop ND filter, that can give you the following proper exposure 100iso 1/200th f5.6 for a three stop under you shoot at f16 now add a Circular Polarizer and dial it down to a proper exposure or 100iso 1/200th f2.8 for three stop under shoot at f8 Since you are actually adding a lot of ND and CP to the lens, you still need enough power from the flash to shoot as iff they were never there. So you still need to meter a flash at f 22 or more to over power the sky and subsequently overpower the fact that you have 3-4 stops of ND/CP on your lens. It is always better to have some more ND than you will need and more flashpower than you need since you cannot create more ND or Power, you can of course shoot at a great depth of field, numerically higher f stop or slightly underexpose a raw in processing if you shoot digital and shoot raw, but that is not a great way to start off, its better to do it the correct way to start. Could always go out and set an f stop of lets say f 8 shutter of 1/200th put on the ND/Polarizer you need to get the background dark enough for you and then and turn the flash up till it looks good, thats how I learned, and still do it. 1200 ws from a profoto, elinchrom and/or hensel in a large silver lined SB with internal diffuser may be pushed and get about f 16-f22, without internal diffuser maybe 1/2 - 1 stop more. This all depends on what you want to shoot at f stop wise. A beauty dish without grid will spread enough for a full body at 6 feet, a beauty dish will overpower daylight at 10 feet at about f 22 or slightly higher for a white silver gains about 1 to 1/12 stops over that. Now if you want to have a little more fun, bring some gels for the lights, I most often use 1/4 to 3/4 blue for the lights which if white balanced for that on the model the background goes warm, or reverse and use warm on the model to get a blue cold look to the background, and if dark enough you can start to have a moonlit color begin. Of course you may need even more power for this as you are now cutting down the lights power with gels. Also works great on ringflashes Stephen Eastwood |
©Stephen Eastwood 2008 www.StephenEastwood.com www.StephenEastwood.com/bio www.StephenEastwood.com/Tutorials