high contrast scene, manual flash, spot meter, film!

[stewart_thorp]

<p>Hi there, are there any rules of thumb about adding flash to a delicate scene - I am already exposing for shadows and underdeveloping film to reduce range, and I want to add a subject and flash to highlight the face.<br>

I have just bought a minolta spot meter, and this measures flash well, but it will have no regard for ambient exposure, and anyway I have it just right, if I keep aperture same for ambient but decrease shutter speed I will loose detail in shadows, so I guess I will meter how I have been, BUT how do I ascertain flash output?<br>

Have been shooting this particular scene a few times, from inside a sawmill looking out into the outside area in indirect sun, but have got nice detail inside as well. <br>

I will do some test shots with digital, but was wondering if there were any good methods to get accurate flash levels, I have not got back yet, but was thinking of metering for ambient and just adding flash to suit, but am shooting kids so have very limited time for useful shots/bracketing.<br>

Using; MF film camera, B&W, 300W/S softbox strobe, and it is manual only, 1/1 to 1/64th </p>

<p> </p>

[paco_rosso]

<p>Rules of thumb to sum lights:</p>

<p>You have two lights.<br>

See the difference in stops.<br>

1 If difference is 0 stop, both are equal, then the sum is 1 stop higher: f:8 + f:8 = f:11<br>

2 If difference is 1 stop, then sum is 2/3 stops greater than the higest of them: f:8 + f:11 = f:11 + 2/3.<br>

3 If difference is 2 stops, the sum is 1/3 greater than the hisget. f:8 + f:16 = f:16+1/3<br>

4 If difference is 3 or greater, then the lowest of them has no effect: f:8 + f:22 = f:22<br>

(Actually, when the difference is 3 stops the sum is only 1/6 greater than the highest).</p>

<p>So:<br>

If the difference beetween ambiente light and flash light is 1 stops, this is the flash is at the same power than ambient light.<br>

If the difference is 1,5 (1+2/3) stops, then the flash is 1 stop greater than the ambient.<br>

If the difference is 1 stops (1+1/3) the power of the flash is twice the ambient.<br>

If the difference is 3 or greater then the exposure of the figure is due only to the flash.</p>

<p>ONE WAY TO CALCULATE THE ADJUST OF POWER.<br>

So ¿How can you deal with this?<br>

<br />Mesaure the light in the face without flash. This is Eb (b from base)<br>

Measure the light in the face with flash, this is Et (t from total). This is the sum of base light (ambient) and your flash.<br /> It is: Et = Eb + Ef.<br>

You know Eb and wants to know how to adjust your flash to get than unknown Ef.<br>

Let's talk in illuminance, Lets write illuminances over the base (all light wrote in ratios over Eb):<br>

Eb / Eb = mb = 1.<br>

Et/Eb = mt = 2^nt<br>

Ef/Eb = mf<br>

Now:<br>

Et = Eb + Ef<br>

Divide all by Eb and then:<br>

Et/Eb = Eb/Eb + Ef/Eb<br>

So:<br>

mt = 1 + mf<br>

Then the light your flash must produce is:<br>

mf = mt-1<br>

And this is the adjusto in power (ratio of lights is the same as ratio of power).<br>

mf is how many times the flash is greater than the ambient light (in the face).<br>

mt is the how many time the light measured by your photometer (with flash) is greater than the ambient light.<br>

For example:<br>

You have a face read (without flash) f:4.<br>

You wants the face will be 1 stop over ambient, then:<br>

The total light is 2:1 (mt = 2)<br>

So the flash must be adjusted to give a mf = 2-1 it is a mf:1.<br>

Shoot your flash and read the ligth. It is mt. ¿How many is mf? (the light aported by the flash)<br>

First write the photometer read in ratio over the ambient light.<br>

For example, you read a f:4 in ambient and a f:11 with flash.<br>

The amount of light submited by the flash is:<br>

f:11 is 3 stops greater than f:4, so the ratio is 2*2*2 = 8:1<br>

mt=8<br>

Then: mf = mt-1 = 8 - 1 = 7.<br>

You want mf =1 so you need to reduce the power to 7:1, this is 2+8/10 stops.<br>

(Remember: from 100 asa to 200 there is 1 stop, from 200 to 400 there is 1 stops -this sums 2 now- and one third over 400 is 500 and 2/3 is 640, 1 stop is 800 and you wants 700 (this is 700:100,, 7/1) so from 100 asa to 700 there is more than 2+2/3 but less than 3 stops, you can suppose 8/10). ASA sensitivity numbers are the same relation than lights.<br>

So, set the power of your flash to maximum and then reduce 2 + 8/10 its power to achieve a face with 1 stop over ambient.</p>

<p>ANOTHER WAY:<br>

The to reduce the contras in a figure from a value mi (initial contrast in ratio) to another me contraste (final, end, contrast, in ratio) the flash must give a light ma with is:<br>

ma = (mi-me) /(me - 1)<br>

(ma stands for light added).<br>

And procedure is the same: read the flash at max power, read the ambient light. writedown the numbers in ratio over the ambient light. Rest 1 to the read of the flash.<br>

Divide the ma calculated over the mf and this is the amount of power reduction you must adjust in your studio light.<br>

This second procedure is what I use to control the contrast in a chiaroscuro composition with a lateral light to the figura (the bride at the window).</p>

 

[craig_shearman1]

<p>The basic idea here is the you want to balance the exposure for the scene inside the barn to match the exposure for what is seen outside. You need to meter the outside, then bring up the lighting levels inside the barn to match. For sake of example, let's say you're using 400 speed film and it's bright sun outside and your camera has a leaf shutter (so you can use any sync speed you like). Exposure for bright sun outside at ISO 400 is 1/500 at f/16. Set your camera at that. Adjust your flash (either with its power control or just by moving the distance between it and the subject) until it is also metering f/16. That gives you a one-to-one ratio between the indoor scene and the outdoor scene. If you want the outdoor to be a little darker that the subject inside, go to f/22 and move your flash closer to compensate (or turn up the power). Balancing things this way should eliminate the need to adjust development.<br /><br />One question,of course, is if the scene inside the barn is more than you can light with just one flash. If so, you can use additoinal flashes to bring up areas beyond the main subject. Depends on how much gear you have and how complicated you want to get with the setup. Obviously there are a lot of nuances and details to be worked out so it all looks like natural rather than looking lit.<br /><br />If kids are involved, you need to get everything set up, metered and ready to go before you bring them in.</p>

[rodeo_joe1]

<p>I always thought that Minolta's flash meters measured flash and ambient together - what model do you have Stewart? In any case the usual metering method for flash is incident, but you could use a grey or white card to effectively turn a reflected reading into an incident one. I'm not convinced of the value of using a spotmeter for the purpose you want, because it still won't allow you to visualise the balance of flash and ambient, especially the effect of crossed shadows and the like.</p>

<p>So my advice would be to measure a grey or white card at the subject position, and then place that tone wherever you want it to fall. Most likely this will be toward the shadow end (zone iii-iv?) since you probably don't want the interior lit up as bright as the outside. A simple sheet of white copier paper makes a good substitute for a bought grey card. You just open up 2.5 stops from the indicated reading to get the equivalent of 18% grey reflectance (approx zone v), or what an incident reading would have given. You then need to subtract stops or zones again to place that interior mid-tone where you want it. This may even bring you right back to the original white-card reading!</p>

<p>Sorry if the above sounds complicated, but I'm sure it takes longer to explain than to do. BTW it sounds like you're into the zone method, in which case you'll have Ansel Adams' book trilogy (I would hope). Pp 172 - 174 of "The Negative" explain about using fill-flash with some illustrations, although Adams confusingly uses 'light units' to describe the flash power. In terms of a lighting ratio, my personal preference for fill flash is somewhere between 8:1 (3 stops) and 4:1 (2 stops). Any higher than this and IMHO the fill starts to dominate and look unnatural, as seen in the last example in Adams' book.</p>

[bebu_lamar]

<p>Minolta only made 2 models of meters that can measure flash and in spot mode. The Spotmeter F and Flashmeter VI. I have the flashmeter VI and it does measure both flash and ambient together in both incident and spot mode. I just check the manual for the spotmeter F and it does the same.</p>

[stewart_thorp]

<p>Thanks for the replies, Paco that is the most mathematically awesome reply! It makes sense, but I am going to re-read it a few times and let it sink in! <br>

Craig yes I agree, ready to roll with kids - these two are under 3, very limited timeframe !! In this case I have the exposure perfect for the scene, and want to introduce subjects at a certain plane within the image, so my thoughts were that I will test fire the flash with the meter, and adjust flash output until I get an 18% reading on the face, but at the predetermined scene exposure?<br>

Rodeo and BeBu, I have the Minolta F, so yes it does both, I have just got it, and had a play last night with the sync cord, very cool. but as you know it is either ambient OR flash at one time. If I measure using grey card, then the exposure I have for the scene will change, as the flash will effect such a small part of it, and I already have an exposure in mind that gets all the nice shadow detail etc zone wise. I am currently digesting the Zone books, which is a real bender, and I have been consulting different sources, but also the reason I have bought this spot meter! I am loving 'Placing' zones. Also this meter is cool as I can use the EV setting to super quickly determine the contrast range in seconds. <br>

So I think based on your replies, and an idea I have kicking around, (given that I have found a great exposure that gives me the scene that I have visualized) is that I will get a grey card or patient adult subject, and meter their face for an 18% value that matches the scene exposure as I adjust flash output. I don't think I will have too much shadow as I have a decent size softbox and the area is not against any adjacent planes in the image.<br>

Great replies! Wow my eyes have really been opened - I have just got back into B&W and photography in general after a 15-20 year break, and am learning all of this super amazing stuff, and buying all of this super amazing film gear for not much (and top darkroom stuff) that I just didn't grasp before or not possible financially (12-16 years old) like deviating from development times and medium format.<br>

Have to say I am very excited and thoroughly stoked at how varied and large photography really is. Its huge, and every single photographer has a different and valid take on it. Good times.</p>

[bebu_lamar]

<p>I am sorry for not being clear. When in flash mode the Minolta spotmeter F measure both flash and ambient at the same time. It's the same for all Minolta flashmeters. That is why you have to set the shutter speed in the meter when you measure flash. If you change the shutter speed setting you will have different readings although small until you set it to quite a slow speed to have significant exposure from ambient light. So all the math isn't necessary when you use a flashmeter. </p>

[rodeo_joe1]

<p>Stewart, a skin tone isn't necessarily (or even frequently) 18% reflectance. It very much depends on the ethnicity of the person, their exposure to sun etc., etc. So don't just point the meter at someone's face! Also, if you're overexposing and pulling development, you need to set the meter for your own EI rating of the film, not it's box-marked ISO value.</p>

<p>Personally I wouldn't use spotmetering for this purpose. If the meter has an incident dome, then just use that; it'll give an almost identical reading to a grey card, but without the expense of buying one, or the inconvenience of carrying one. All you need to do, by the sound of it, is to establish the correct exposure for the flash. An incident reading is the most direct and reliable way to do that. There's no point in making things more complicated than they need to be by trying to spot meter what doesn't need to be spot metered. Just (1) set the meter to your personal EI for the film; (2) fit the incident dome into place; (3) walk over to the subject position; (4) point the meter back at the camera position and (5) take a reading. The incident dome will automatically set the skin tones where they should be.</p>

<p>If you want to retain the interior shadows the way that they were without flash, then you need to flag off or snoot down the flash onto the people only. A softbox isn't ideal for this, as you'd have to fit a large skirt around it or a narrow angle egg-crate grid. It's doable, but IME it'll take some experimentation to get the coverage just the way you want it. That's why most professionals use digital these days - instant feedback!</p>

[bebu_lamar]

<p>But Stewart meter is a spot only meter. It's the Minolta spotmeter F.</p>

[stewart_thorp]

 

<p>BeBu, I'll look into this, that would be helpful if it did both, although since it is only a 1deg spot it won't take the whole composition into account if I am aiming it at the face? A lot of experimentation is in order I think.<br>

Rodeo Joe, I guess the 18% face value I mentioned was just an example referring to the fact that I wanted to increase exposure on the face using flash, but without affecting ambient exposure. The position of the subject in the composition is in a darkish spot and is lost in the overall image. Without knowing too much about it, as I am shooting B&W only in film, and average Caucasian skin I was guessing that 18% would yield a good tone in grey. I will still bracket flash and ambient. I was not interested in other types of meters at this stage, as I specifically got this spotmeter to learn more about using a camera manually for exactly how I want tones to sit in the overall exposure zone-wise, and if necessary adjust development for high contrast scenes. I have always relied on auto metering, but now my 2 favorite cameras RZ67 and GX680 don't have meters, and I want to control and understand how the frame is exposed based on my visualization of the scene. I do have a digital body for instant feedback and matrix metering for a 'second opinion' and yes I can see why pro's would find that useful! I am definitely not a pro, and the whole point of this entire exercise for me revolves around the darkroom and bringing my negatives and prints to a level I am happy with. So I guess for most it would be stepping back 20 years or more or just plain going back to the dark ages, but for me its like Christmas, and I am enjoying shooting more than ever. There is simply nothing more magical to me than a set of freshly developed well exposed negatives hanging in my drying cabinet after a good day out behind the lens. I would have been disappointed if I was a sailor and someone gave me a treasure map as a PDF haha! <br /> Also with regards to the softbox in this instance I think it will be OK, as where the subjects will be is actually outside, and I can hide the flash behind some pillars to the side. Also I wanted a big light source for a softer light. I have so much to learn, and am trying to be economic, as each frame costs. This is where digital is great, but I figure I can learn some rules of thumb, and apply them with success learning with the spot meter and get consistent exposures based on the image I had in mind. Huge process, but I'm up for it.</p>

 

[rodeo_joe1]

<p>Sorry for going on about incident metering. I'm not familiar with the Spotmeter F and I assumed it was an all-purpose meter with a spot facility. Anyway, you can still use it for an average reflective reading by using the grey or white card method I described earlier.</p>

<p>Placing skin tones is quite difficult. Caucasian (or any other) skin can vary widely in its reflectance, and depending where on the face you meter. The human head is a complex shape and it's the direction and hardness of light that reveals its shape and texture. You can spotmeter from the forehead and get one reading, then meter from the cheek and get a completely different reading, depending on lighting. Only face-on bland lighting will give a uniform meter reading, but it'll also give a bland picture. So I really think that this is one situation where forgetting the zone system would pay off. Even if it doesn't seem quite as much fun to take a plain old reflected grey card reading.</p>

<p>BTW, the point about skirting, gridding or flagging off the softbox wasn't about hiding the light source, but about directing the light exactly where you want it and preventing it from spilling into areas where you don't want it. The light on the subject will still be as soft, but the light is contained in a tighter pool.</p>

[ellis_vener_photography]

The Minolta Spotmeter F has two very useful functions that haven't been discussed: the highlighlight and shadow value

calculators.

 

They are easy to use. Take a reading of the brightest point with detail in your scene take the reading and then push the

"H" button. The meter will then calculate an aperture setting base don your chosen ISO and shutter-speed. Hit the M

(Memory) button and the read other areas.

 

The highlight with detail calculation gives you a mid tone reading about 2.5 stops darker than the highlight reading. Why

2.5 stops instead of four stops (zone IX)? Because 2.5 stops over exposed was about the limit of almost of all normally

processed transparency films.

 

The shadow value calculator works pretty much the same way except that as I recall it places the shadow with detail

value about 2 stops under the calculated midtone value.

[stewart_thorp]

<p>Thanks Ellis, it sure seems to be a fantastic meter, and even though B&W seems to have slightly more latitude than transparencies, it works out very similarly for the zones with slightly altered processing depending on the film! I am learning all of its ins and outs at the moment - of course with film it will take longer - have to process, translate my notes etc. </p>