Beginner Hilite and flash help

[Jim_Tod]

I’ve recently bought a lencarta studio kit and a used lastolite hilite and i’m experimenting with the lighting. First thing i found was that i might not have enough space between the hilite and the subject to stop there being a bit of the hilite light affecting the hair. I dont have a lot of space left to pull it forward.

Would appreciate some advice on iso and flash power as i might be getting a bit confused, if i double iso on camera and adjust main flash and hilite flash- will this help reduce blowout - thinking that inverse sq for light from backround would have bigger impact than the stop of a difference in the main light.

Also prepared to be completely wrong on this and i just need to find a bigger space

 

[admirable]

Increasing the ISO affects the ambient light and the flash light.

 

[Garry Edwards]

If you can't increase the distance, then you just have to accept that both the destruction of fine edge detail and wrap are inevitable by products of using the Hi-Lite as a background. Many people dress this up as a benefit, to create a "unique look" that only a few million other people are producing....

You can control wrap to some extent, simply by masking off the areas of the background that won't appear in the finished shot, or by masking it even tighter and painting in the masked area in PP

 

[Phil V]

As above, the simple fact is that to do a white bg effectively requires space, theoretically the hilite lessens the space required, you just have to turn it down as much as you can.

We do keep saying; the clean white background look is simple to achieve, you just need loads of space. But everyone wants to do it in a shoebox and then complain about the results.

Sell the hilite, buy a pop up grey and unleash your creativity, rather than trying to solve a self created problem.

 

[Jim_Tod]

Thanks all. Not got a problem with the hi-lite per se but was trying to understand whether iso/ inverse sq was my friend but clearly not.

Have a couple of backgrounds for the hilite incl grey and green chroma so will try these.

I like the hi-lite style and i’m very much at learning what works and what doesnt’ here. Usually a landscape or nature tog so flash new to me

 

[Phil V]

The inverse square law is the enemy of the white BG, making it a uniform white means it gives off enough light to interfere with nearby subjects, so your subject needs to be a good distance away to avoid that.

 

[sk66]

Thanks all. Not got a problem with the hi-lite per se but was trying to understand whether iso/ inverse sq was my friend but clearly not.

The answer is yes and no... If you have the ability to drop the BG light power then do that, it will reduce the wrap/bloom (ISL). But you do not want to restore it's effectiveness(affect) by increasing the ISO to compensate. If it means the BG comes out less than pure blown to hell white, it's nothing that a bit of post work can't fix easily enough (usually).

 

[HoppyUK]

Thanks all. Not got a problem with the hi-lite per se but was trying to understand whether iso/ inverse sq was my friend but clearly not.

Have a couple of backgrounds for the hilite incl grey and green chroma so will try these.

I like the hi-lite style and i’m very much at learning what works and what doesnt’ here. Usually a landscape or nature tog so flash new to me

ISL can be friend or foe, and quite often both at the same time. Know it, work with it and never against it. Resistance is futile

FWIW I still like the pure white background look (like millions of paying customers ) and a fair amount of wrap reflected off the background and 'wrapping around' the subject is integral to that. If you get rid of it completely (by moving the subject well forward and screening off the background) it looks wrong and unnatural and destroys the effect.

I also like HiLites, because they make a difficult technique a lot easier and pretty decent results can be achieved in relatively small spaces. TBH I wouldn't worry too much about wrap just yet, as the usual problem (that seems to be driving your question) is about exposure levels on the background and subject. The way I set up is using blinkies, shooting just the background. The light must be as even as possible all over (two lights in the HiLite) then adjust flash power until the blinkies are just flashing. Then set the key light (subject light) so that it's about 1/2 a stop less bright than the background - NOT the two stops that is often quoted, as that bleaches away fine detail like hair and induces a ton of flare that washes out colour and contrast. You'll almost always need to do a bit of cleaning up in post-processing, too.

There's more to it than that - fine tuning exposure levels, moderating wrap and controlling flare with distance, screens and flags etc - but that's the basics of it. Get some practise, google around, practise some more, try a few things. If you're new to studio work, doing the pure white look well is jumping in at the deep end

 

[Jim_Tod]

Thanks guys.

Only home at weekends so will practice when I can. Appreciate the advice- sure I'll be back for more.

If you're new to studio work, doing the pure white look well is jumping in at the deep end

I hadn't appreciated this bu then again that's why I'm a beginner at flash.

 

[Jim_Tod]

The inverse square law is the enemy of the white BG, making it a uniform white means it gives off enough light to interfere with nearby subjects, so your subject needs to be a good distance away to avoid that.

Think I've got it- Inverse square law relies only on distance so reducing flash by a stop and increasing ISO by a stop gives the same exposure but without any change in distance all I've done is reduced the absolute level of light falling on the subject from the hilite by half which is then bumped back up by the ISO stop to be the same relative exposure. However if I can double the distance from the background to the subject then I'll only have a quarter of the power falling on the subject- so a bit like stops, every increase in multiples of 1.4x distance for separation will halve the background light on the subject. Is that about right?

 

[mike weeks]

so a bit like stops, every increase in multiples of 1.4x distance for separation will halve the background light on the subject. Is that about right?

Yep, good old square root of 2

Mike

 

[Phil V]

... Is that about right?

Yes

 

[Garry Edwards]

Think I've got it- Inverse square law relies only on distance so reducing flash by a stop and increasing ISO by a stop gives the same exposure but without any change in distance all I've done is reduced the absolute level of light falling on the subject from the hilite by half which is then bumped back up by the ISO stop to be the same relative exposure. However if I can double the distance from the background to the subject then I'll only have a quarter of the power falling on the subject- so a bit like stops, every increase in multiples of 1.4x distance for separation will halve the background light on the subject. Is that about right?

Theoretically yes, you've got it.

In practical terms though it doesn't work quite like that, because the ISL strictly applies only to a point source of light operating in a vacuum, which doesn't apply in strict terms because although each individual point source of light will follow that immutable law of physics, there are untold millions of separate point sources of light coming from the background, all from different positons and all travelling different distances from each other at different angles so, at fairly close distances, if you double the distance you won't get a quarter of the light, it might be closer to half the light.

But, that's what we have to work with so the rule of thumb here is to ignore the marketing hype and get as much distance as you can between Hi-Lite and background (but if you run out of space it's generally a bad idea to switch to a wideangle lens to increase the distance, because the effect of the perspective distortion that results will usually be even worse than the effect of the background light).

Also, as Richard pointed out, use the camera blinkies to determine the minimum amount of overexposure needed and use post processing to make the background as white as you want it to be - ignore the ignorant mis-information all over the web about overexposing the white background by two stops - 0.7 of a stop is fine.

FWIW, I have a friend who flatly refuses to do white background shots unless he has 7m of space between subject and white background - but that's a counsel of perfection that most can't afford, and most of us have to compromise a bit, he's a top fashion photographer who simply won't compromise and who can afford to turn down work

 

[HoppyUK]

Think I've got it- Inverse square law relies only on distance so reducing flash by a stop and increasing ISO by a stop gives the same exposure but without any change in distance all I've done is reduced the absolute level of light falling on the subject from the hilite by half which is then bumped back up by the ISO stop to be the same relative exposure. However if I can double the distance from the background to the subject then I'll only have a quarter of the power falling on the subject- so a bit like stops, every increase in multiples of 1.4x distance for separation will halve the background light on the subject. Is that about right?

Well, yes and no. You've got the ISL right, but strictly speaking that only exactly applies to a point light source - which a HiLite is not. For example, a speedlight is small enough to behave quite like a point source, so if you move that from 1m to 2m, you'll lose close to 2 stops, if you do the same with a softbox you'll lose around 1.5 stops, with a HiLite I'd guess at around a 1.0 stops drop. Another factor is the environment and a small light walled room with an average height white ceiling reduces ISL effects.

But using the ISL is a crude tool for moderating brightness, as it also affects a lot of other things, when a simple adjustment to power output does the trick. I would use distance more to moderate wrap from the background than exposure.

Edit: crossed post with Garry, and I would respectfully suggest that the fashion photographer he refers to is not looking to achieve the same kind of result. He wants to eliminate wrap, whereas for the effect I think you're after a lot of wrap is integral to it.
And for clarity, moving the HiLite back won't affect exposure seen by the camera - it will stay exactly the same, but smaller in the frame. That's ISL for you But it will reduce the amount of light striking the back of the subject, both in terms of exposure and wrap.

 

[sk66]

so a bit like stops

It's exactly like aperture... that's how I remember it. I.e. if the light is right on the subject and at 4ft, and the background is at 8ft the BG will be 2 stops under (f/4-f/8).

 

[Jim_Tod]

In practical terms though it doesn't work quite like that, because the ISL strictly applies only to a point source of light operating in a vacuum,

You've got the ISL right, but strictly speaking that only exactly applies to a point light source - which a HiLite is not.

OK- It's good enough for me to use to start planning shots with as I practice and then see where to tweak but we wouldn't want to be using it to plan a set up for the only shot of the day.

I would use distance more to moderate wrap from the background than exposure.

It's this that I have a problem with I think- slight highlights around the neck/ hait sort of stuff.

I have a friend who flatly refuses to do white background shots unless he has 7m of space between subject and white background

I wouldnt have been asking the question if I had that- hoping for a dry no wind day and I might pop it outside and see what I can do with a bit more space

 

[HoppyUK]

<snip>

It's this that I have a problem with I think- slight highlights around the neck/ hait sort of stuff.

<snip>

Did you see the edit to my post above? Maybe I've misunderstood, but what you've just described is 'wrap' - the background reflecting off the subject, neck, cheeks etc. That is defined by the width of the background relative to the subject, so the way to reduce it is either to make the background smaller, by blanking it off, or better and often easier is to move it back. Distance is your friend here, as it also creates space where you can position screens, either between subject and background, or between subject and camera - both have different effects. Moving the camera back and shooting with a longer lens is also beneficial as it reduces the size of the background needed and makes flare easier to control.

Edit: there's a lot to take in here You might be better off putting the pure white look to one side for a bit and start with just one light and a white/silver reflector. There's so much you can do with that (in any event, it's the main key light that does the lion's share of the lighting, regardless) and learn a great deal in the process. Then add extra lights one at a time, each one with a clear and specific purpose. I'd also say that with lighting, IMHO less is more

 

[sk66]

An interesting affect of the ISL with white BG's like the hilite... as you move it farther away you do not have to increase it's brightness, because it is also smaller. Less light concentrated into a smaller area gives the same exposure.