Correct output for studio lights?

[Markvetnz]

I am slowly putting my feet into the murky waters of studio lighting. I recently bought a Bowens Gemini 500R 3 light kit. I have had no problem setting it all up and syncing (sic?) it with my camera or 580EX. In a studio situation, once I have metered for a specific shutterspeed at a specific ISO, I set the measured aperture. My question is about setting the output power of the strobes. Is this purely a creative issue, depending on the type of shot I want to create? I know the output is influenced by the setting itself, the position of the light relative to the subject and and the type of diffusion used.

I have seen videos of pros metering each light (background, focal points etc). Surely they must end up with a combination of aperture settings.

Another question. As far as TTL metering goes, can this be used with the strobes using a PW TT1 and TT5 setup or can these only be used with TTL capable speedlites?

[Colin Southern]

Hi Mark,

I recently bought a Bowens Gemini 500R 3 light kit.

Congratulations on the new purchase

I have had no problem setting it all up and syncing (sic?) it with my camera or 580EX. In a studio situation, once I have metered for a specific shutterspeed at a specific ISO, I set the measured aperture. My question is about setting the output power of the strobes. Is this purely a creative issue, depending on the type of shot I want to create? I know the output is influenced by the setting itself, the position of the light relative to the subject and and the type of diffusion used.

Shutterspeed has only an incidental effect on strobes because they "do their thing" in around 1/1000th of a second regardless of what shutterspeed you have set. Assuming you have no ambient light then you could leave theoretically leave the shutter open for a month without exposing the sensor until the strobes flashed, so in reality you want a shutterspeed that's high enough to minimise ambient light, but low enough to remain under X-Sync speed (keeping in mind that x-sync speed for a strobe will be under what it is for a speedlite). So in reality, studio photography is all done in manual exposure mode @ 1/125th or 1/100th, and usually @ ISO 100 or ISO 50 unless your lights are under-powered. You could use a higher ISO, but you're just letting in more ambient, which is rarely a good thing.

So in summary, 1/125th, ISO 100, and adjust the lights to give you the aperture you want for the DoF you want (I typically shoot @ F11 because I've governed by the minimum power output of my lighting setup, unless I want to use ND filters, but these degrade AF performance, so I tend to avoid them) (other option is to use ND gels on the strobes, but that's difficult when modeling lights are being used).

Another question. As far as TTL metering goes, can this be used with the strobes using a PW TT1 and TT5 setup or can these only be used with TTL capable speedlites?

I see that PocketWizard have released receivers for common studio strobes (Elinchrom, Bowens etc), but I can't see them working ETTL, as studio strobes work differently (Speedlights always charge up to the same voltage, but they don't full dump (the output is cut off at a certain point). A studio strobe on the other hand (usually) charges up to a preset level and then full dumps, so they wouldn't be able to change the level of charge quick enough for ETTL. Keep in mind also that if you increase the output of a studio strobe it adjusts to the new settings in a second or two, but if you DECREASE the output you either have to wait and wait ando wait for the voltage to bleed off, or you need to full dump them.

I have seen videos of pros metering each light (background, focal points etc). Surely they must end up with a combination of aperture settings.

The short answer is, "we use a light meter". The long answer is, "we use a light meter".

Whether or not you end up with a bunch of apertures depends on how you're using the meter; in normal mode, yes (so you learn that F5.6 is two stops less that F11), but in reality you adjust your key light first, and then set that reading as a reference in the lightmeter and use the meter's contrast function for the rest of the measurements (and in the above example it would have showed you "-2.0".

You need to have key / fill / hair / background lights on different channels so that you can build up the lighting one by one (if you try to do it all at once you'll make it 10 times as hard). When you have the ratios right you then take a final reading (not forgetting to take your lightmeter out of contrast mode first!), and set that in the camera, and you're "good to go".

For lightmeters I use (and recommend) a Sekonic L758DR (or a L758D and add the radio module seperately later), or if that's too pricey, the Sekonic L-358 is the next best thing (which also takes the RT-32 module). The other thing you'll find to be an enormous benefit is some form of large screen to shoot tethered too (you just CAN'T make accurate lighting decision on a 3 inch camera screen).

Hope this helps!

[AlanP]

Using an external light meter to determine the f stop does not give a completely accurate exposure. The f stop is based on the geometry of the lens. There are two sources of error not accounted for. Real lenses do not transmit 100% of the light, and light striking the sensor element at an angle is not 100% captured (especially wide aperatures). The movie industry has adopted a t stop (transmissive) that compensates for the losses. The camera manufacturers are aware of the losses and compensate in camera when you use the camera's light meter. Here is an interesting read on the subject.

http://www.luminous-landscape.com/es...acturers.shtml

Alan

[bambleweeney]

Using an external light meter to determine the f stop does not give a completely accurate exposure...
Alan

Actually that was a pretty interesting article. Not exactly sure how it's going to affect me personally ... but yeah, interesting.

[Colin Southern]

Using an external light meter to determine the f stop does not give a completely accurate exposure. The f stop is based on the geometry of the lens. There are two sources of error not accounted for. Real lenses do not transmit 100% of the light, and light striking the sensor element at an angle is not 100% captured (especially wide aperatures).

Hi Alan,

The Sekonic L-758DR can be profiled to the individual camera & lens, so it's capable of over-coming the above 2 potential issues that you mention, but in reality it's somewhat of a moot point though because a highlight is only going to be 2 stops higher than a middle gray, and even a light meter and/or in-camera metering isn't going to put a medium gray 2 stops down from the camera's maximum (in reality it's usually close to 3), so the levels still need to be adjusted in post processing (and even then they depend on if you're post-processing for print or online display). Additionally, as the article you referenced points out, manufacturers are tweaking ISO gain to compensate to a degree anyway.

Add to that the fact that there's more than enough lattitude in a RAW capture, and the reality is that even an unprofiled light meter is close enough.

On a side note - interesting as the article was - my personal opinion is that it's somewhat of "an answer in search of a problem"; there are many things that have the potential to throw off a "perfect exposure" (if anyone can even agree on what that actually is!), so in reality - again personally - I just accept the fact that in most everyday situations (including all studio work) what's captured by way of basic metering techniques is well within the safety margins, and will need to be tweaked in PP anyway.

[Colin Southern]

Actually that was a pretty interesting article. Not exactly sure how it's going to affect me personally ... but yeah, interesting.

I think the fact that not a single manufacturer has responded to the open letter is an indication that it's not something they're going to be spending a lot of time on.

[Markvetnz]

Thanks for the advice guys. It's confirmed that I'm basically on the right track. I had a play around with the strobes this afternoon had the ISO at 100 and the shutterspeed at 100 and then messed around with the power output on the lights.

I typically shoot @ F11 because I've governed by the minimum power output of my lighting setup

I understand what you're saying. Using a single umbrella and a softbox about 4 feet from the subject, the lowest setting I could use was 5.0. More typically I was shooting at around 7.1 and 8.0. Kind of puts to bed the theory that portrait work has to be done with the lens wide open! Just creats lots of unwanted DOF issues.

the Sekonic L-358 is the next best thing

I picked up one of these with the Bowens kit . After having it for a few days I wonder how I ever got by without one. I suppose if you have done 100000 studio images you get to know how your lights, lens and subject interact.

The learning curve has just got a little steeper.

[Colin Southern]

I understand what you're saying. Using a single umbrella and a softbox about 4 feet from the subject, the lowest setting I could use was 5.0. More typically I was shooting at around 7.1 and 8.0. Kind of puts to bed the theory that portrait work has to be done with the lens wide open! Just creats lots of unwanted DOF issues.

It really depends on the effect people are after; I have a vari-ND filter that I can use to knock back the light so I can shoot at wider apertures, but the irony is it reduces AF performance - even on a 1D series - right at the time you need superior AF accuracy. The minimum power I can get from my 1200RXes is 2.5 - so I have to use around 5.5 on the key light for a 3:1 contrast ratio (which is pretty typical), and that inturn usually means F11. My light table is even worse; with minimim output on the table alone I'm usually at F11 / F16 - and by the time I add other lights I'm often at F22!

I picked up one of these with the Bowens kit . After having it for a few days I wonder how I ever got by without one. I suppose if you have done 100000 studio images you get to know how your lights, lens and subject interact.

The learning curve has just got a little steeper.

Yeah - you definately get a feel for it. If you're always having to adjust the exposure upwards in PP just add a bit of compensation directly into the lightmeter (say 1/2 stop); so long as your highlights are OK it'll save you having to add so much fill light control in PP. Make sure you always shoot a grey card too.

[rob marshall]

My question is about setting the output power of the strobes. Is this purely a creative issue, depending on the type of shot I want to create? I know the output is influenced by the setting itself, the position of the light relative to the subject and and the type of diffusion used.

Where you place the lights relative to the subject affects the power that reaches the subject. A light placed at 3ft from the subject will give more light on the subject than the same light (at the same power setting) placed 6ft away. It will also give a softer light the closer it is to the subject. So, if you can't set the light low enough for say f/2.8, you can move the light further away, but the problem there is it will give harsher shadows and a harder look.

I always use ISO100 and 1/125s. If using more than one light I'd just get a reading for each light on it's own (with the other switched off) then take a final reading for both. It's never entirely accurate, because if you want a more creative look you will have to move away from what the meter says. The camera/lights don't know what you want to create, they only give a reading for what they sense.

[Colin Southern]

So, if you can't set the light low enough for say f/2.8, you can move the light further away, but the problem there is it will give harsher shadows and a harder look.

Sometimes it's all you can do, but it also comes with it's own set of "challenges" in that the light then bounces around the room more which can, for example, throw light onto black backdrops.