How do I chose the right size/power of flash for still life photography?

Question

I'm planning to change my lighting setup from fluorescent lamps to flash, after the guidance given in this question.

At the moment, my two fluorescent lamps are in a softbox which point away from the subject (still life). The light therefore bounces around my office come studio (approx 4m x 3m), which is conveniently painted white to avoid colour cast, and provides a gentle even light onto the subject. I have fitted roller blinds to the window so that most of the natural light is blocked out and doesn't affect the shoot.

There are two of these lamps both rated at 35W, which according to the manufacturer is equivalent to 150W incandescent lamps. With these, I'm shooting at about 1/8 sec at f/5.6 and ISO 200.

My plan is to buy two flash/strobes to replace both lamps.

What size flash/strobe do I need to purchase to be able to light my subject with an aperture of f5.6? I still plan to fit them in a softbox and fire them away from my subject to keep that soft illumination.

Do I purchase a couple of speedlight equivalents with a GN of 50 to 60 or do I buy some studio flash kits? That causes more confusion as they are rated in Watts. Does Watts translate to GN somehow, for comparison purposes?

My concern is that if I buy the incorrect power, I'll either end up with too much and have to shoot at ISO 100 at F/22 or not enough power even at F/5.6 and ISO 12000.

The flashes I've looked at so far all have variable power, but the range doesn't seem that wide. Should that be a worry?

Of course, if my plan is all wrong, please feel free to correct my before I waste my hard earned cash on the wrong kit.

Answer 1

I still plan to fit them in a softbox and fire them away from my subject to keep that soft illumination.

A softbox faraway gives more harsh light than closer. Keep that in mind.

Yeap the Yongnuo or similar flashes can be regulated fom full power to 1/128, so you have a lot of options to regulate them. But some cheap (but double price) studio lights goes only from 1 to 1/4 - 1/8. Of course you can put a pice of cloth on them or a gel to lower the intensity.

I made a quick test. I'm too lazy to mount the softbox, but I bounced it on a white wall.

A YN 560iii reflected on a white wall at 3 feet (to emulate a softbox), at 1/4 power gives you the f5.6 at ISO 100 you wan't. I took the reading with an incident lightmeter at also 3 feet from the same wall. I am not saying that you should buy them or not. It is the one I have at hand.

So you have plenty of room to play.

If you buy some of thoose, I really recomend using rechargable batteries above 2300 mAh, and a radio trigger.

Answer 2

General wisdom is that you use studio strobes if you need more power/light. You use speedlights if you want portability and your lighting needs are modest.

Most of us start with speedlights because of the Strobist website. It's where a lot of us learned to light. And the reason speedlights are central to this style of lighting is because most folks already had one, and they're very small, portable (battery-powered), and cheap. And unlike a studio strobe, you can use one both on and off the camera. So that same light you're setting up for a studio product shoot can also be used on the camera for a run'n'gun event or social shoot, and are easier to take on location.

In addition, if you're shooting small still lives, with relatively small subjects, then you can actually work in much closer, and you'll need less light. So, speedlights are probably going to be more than sufficient for what you want to do in your other post. The question is what else are you going to need the flashes for?

It's when you need to shoot, say, a family of five, outdoors in bright sunlight, that a speedlight might not cut it, power-wise.

OTOH, getting two $70 manual speedlight and finding out they're not powerful enough at the highest setting is not nearly as much of a mistake as getting two $300 studio strobes and finding out they're too powerful on the lowest setting. :)

Answer 3

As far as your concern with having too much power that requires shooting at f/22; that is covered here: How can I shoot in a studio at the widest apertures?

I highly doubt any set of entry level Yongnuo flashes(as an example) will have trouble providing enough power to shoot as you describe unless you are having trouble overpowering an ambient. Since it sounds like you have the ambient under control, I don't think you have anything to worry about.

For details on guide numbers, we have a tag where you will find lots more information: guide-number and also see: What features should one look for when selecting a flash?