Studio flash questions...
Seymore
Banned Posts: 1,539 Major grins
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Seymore
Banned Posts: 1,539 Major grins
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You want to put the strobe just far enough from the umbrella to get even illumination but no further. I dial the power way down on the strobe and take a picture of the umbrella to see how even my illumination is.
Shoot through umbrellas are more efficient and let you place the diffusuing surface much closer to your subject giving you effectively softer light. The downside is the scatter light everywhere (including into your lens which can cause flare). Reflecting umbrellas provide better control of the light.
Normally as close as I can while keeping all the hardware out of the frame. It is very rare that I want the light any further from my subject than it has to be. However, if you have limited control over the power ratio you may want to adjust the relative distances of your strobes to adjust the contrast between them
If you put the umby too far from the strobe head, you may suffer the effects of light spill around the edges of the umby. This is uncontrolled light and may impact on the quality of your photographs. It will, at the very least, prove to be frustrating.
For the third response - the distance between the diffused light source and the subject will impact on the quality of the light hitting your subject. Specifically, the further the light source is from your subject, the more the light will approximate a point light source. This will have the effect of diminishing the effect of your light modifier and increasing the sharpness of your shadows on your subject. This is one technique you can use to mitigate the effect of using a modifier that is too large for your subject - just move it further from the subject. Also worthy of note, but quite a bit less significant, is the fact that you strobe light will fall off in accordance with the "inverse square law" - basically you loose 2 stops for every doubling of the distance between your subject and your light (see here for one reference).
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A couple of other unsolicited pointers.
1. The shoot-through type umbrella could impact the color balance of your subject because it will bounce back light all over the area. With most white shoot through umbrellas, an equal proportion of the light (50%) is bounced back and passed through. If you are shooting in a small room - especially one with colored ceiling and walls; the color of that room may impact the total color balance of your image. It is pretty easy however, to use custom white balance and to place a translucent white disk over your lens - this may or may not correct the light to the color you are happy with. At one time, AMVONA on eBay, sold shoot through umbrellas which had a black opaque covering over the open side of the umbrella and a hole through which to poke the flash head. This should have been a great compromise between the lighting you can obtain with a softbox and the ease of setting up umbrellas. I wanted to get a couple of them but, waited too long and they are, for some reason, no longer available. Who knows? Maybe they didn't work as well as I expected that they would work.
2. The distance from the strobe to the umbrella is not always the same. It has a lot to do with the size and shape of the reflector of the strobe. I have not tried liquidair's solution of shooting the umbrella, but it seems logical. I used to do this by trial and error. The image is of an umbrella set up I use for dog portraiture.
3. I think that this item was covered but, I don't remember. The distance from the light modifier (be it a shoot through or reflected umbrella or a soft box) is critical. The farther away from your subject, the smaller the light source appears and the harsher the light, conversely, the closer to the subject, the larger the source appears to be and the softer the lighting. That is why strobes with several power settings (rather than just high and low) are best. You can reduce the power and place the modifier closer to your subject.
4. White reflected or shoot through umbrellas tend to have softer lighting than silver bounce umbrellas which are more specular. In my dog portraits, I use a white umbrella from overhead as the main light and a silver umbrella from camera side to provide a somewhat specular fill. This accentuates the texture of the dogs coat.
5. In regards to softboxes; there are good softboxes and better softboxes. The best softbox will incorporate a light baffle which will soften the light more efficiently. Additionally, if you have the ability to remove the reflector from your strobe and use the softbox over a bare bulb; the light will be much softer.
Small items can be most efficiently shot using a light tent. Just use two reflector strobes on either side of the tent. This will give soft, somewhat shadowless lighting. You don't need modifiers on the strobes because the tent is one big modifier. These tents can be fabricated by the photographer but, are available so inexpensively from eBay that IMO they are not worth fabricating. The eBay tents also fold up kind of like the car windshield shades. Of course like windshield shades; they can sometimes drive you bonkers trying to fold them.
You can shoot larger items with light boxes, umbrellas or by simply bouncing your light off reflective sheets of some type of material such as white foam board.
For those larger items, you can also fabricate very large diffusers from PVC pipe and use a translucent plastic shower curtain as the diffusing material.
This is my umbrella setup for dog portraiture.
White bounce umbrella from overhead and silver bounce umbrella from camera side.