mood_lover Posted February 11, 2015 Share Posted February 11, 2015 <p>I am trying to take shallow depth-of-field studio portraits with flash, with required settings 1/200 and f/2.8 for example. Both of these settings have to stay this way, so I am wondering if theres a way I can have my light meter tell me what the ISO should be or even what the flash power should be? <br /><br />Im sure this is a complicated question, thanks for help.</p> Link to comment Share on other sites More sharing options...
dhbebb Posted February 11, 2015 Share Posted February 11, 2015 <p>Not directly, you will need to work by trial and error, selecting a power setting and placing the flash at a certain distance from the subject to see what aperture your flash meter says. If this is smaller than 2.8, just switch down the power and/or move the flash further away until you get a working aperture of f2.8.</p> Link to comment Share on other sites More sharing options...
jeff_b2 Posted February 11, 2015 Share Posted February 11, 2015 <p>You do not need a light meter to answer those questions. You need a tape measure. Indoors with a 1/200 shutter speed the ambient lighting won't have much effect so you only worry about the strobe. Most strobes have either a printed chart on it or in the manual or even on electronic display that shows the relation of ISO to distance to aperture at a given power. Measure physical distance from flash to subject and choose flash power based on the ISO and f-stop you want.<br> If you want to use your meter you may have to do some math. If the meter only allows you to set static ISO and then displays measurements in f-stops you just convert one to the other. ISO 100 to 200 is one stop just like f/2.8 to f/4. So if you set the meter to ISO 200 and measure flash at f/4 at the subject you have 2 choices. Shoot ISO 100 and f/2.8 in camera at that flash power. Or reduce flash power by 1/2 and shoot at ISO 200 f/2.8.</p> Link to comment Share on other sites More sharing options...
jordan2240 Posted February 12, 2015 Share Posted February 12, 2015 <p>Not really answering the question, but I'm guessing your shutter speed does not have to stay at 200. Unless you have a ton of ambient light coming in, you can probably drop it down quite low without affecting the exposure, though there's likely no reason you'd want to.</p> Link to comment Share on other sites More sharing options...
paul_k1664875007 Posted February 12, 2015 Share Posted February 12, 2015 <p>Generally speaking, unless you shoot with a studioflash that allows changing the settings via your Sekonic meter ( I believe the Paul Buff's and some Bowens do) the solution for your problem is simple if somewhat labor intensive.<br> For the sake of discussion let's assume you're using a studioflash with an open reflector (so without any kind of diffussor like a softbox or umbrella), or a speedlight, both pointed directly on the subject. To keep things simple let's also assume you can change the output on the studioflash, if only by hand, (or are able to put the speedlight in Manual mode).</p> <p>Select the power level on your flash which you think will get the desired amount of light for the exposure of f2.8 at ISO 100 you're after, let's say 1/2 power.(in the case of a speed light, reduce the output in a similar way).<br> Position the light at the distance and angle where you (depending on the kind of lighting, and shadows created) you think you want it be.<br> Dial in the ISO 100 you stated you want to work with on your flash meter, and take an exposure reading (incident reading, from the position of the subject in the direction of the camera).</p> <p>Let's say you get a reading of f11 at ISO 100.<br> This means the exposure is several f numbers/stops above the desired f2.8.<br> You can easily see on the LCD of your lightmeter how much. It shows in big numbers the aperture number found, and in the small bar underneath the range of varying values, the position where the number found is relative to the f number you're after (in the enclosed picture it's f6.3, and as you can see the 2.8 is two and a half f numbers/stops to the left).<br> In this example the aperture found is f11, giving a difference of 4 stops (i.e. from f2.8 to f4 to f5.6 to f8 to f11) so that's the effective amount of light you'll have to make your flash produce less/less to reach you subject.</p> <p>You can do that by e.g. changing the power output of the flash units, changing the distance between the flash units and the subjects, putting an ND filter on the flash units of on the lens, or changing the light modifier.<br> Of course the result can't be calculated exactly beforehand, so you'll have to probably make several changes and take several readings till after some trial and error you get the desired result.</p> <p> </p><div></div> Link to comment Share on other sites More sharing options...
craig_shearman1 Posted February 12, 2015 Share Posted February 12, 2015 <p>Set the shutter speed on the meter to 1/200, although it doesn't really matter since the shutter speed doesn't affect the exposure from the flash. Then pop a test shot and see what f-stop the meter says. Adjust the ISO setting on the meter up or down and pop again until it tells you 2.8.</p> Link to comment Share on other sites More sharing options...
bob_bill Posted February 12, 2015 Share Posted February 12, 2015 <p>ISO should probably be the lowest possible, usually the camera's optimized ISO. Raise only if need more sensitivity for higher shutter speed, smaller aperture. Here, you know the desired aperture. Set the meter for the ISO, and shutter speed. On prior post, I mentioned how shutter speed controls the non flashed area so that is your choice if there is ambient. If I recall, your camera's sync speed was 1/250. If there is minimal ambient, you could drop the shutter speed to say 1/160 as insurance against bumping the shutter wheel past the max sync speed that can cause a black band on part of the image. </p> Link to comment Share on other sites More sharing options...
ellis_vener_photography Posted February 12, 2015 Share Posted February 12, 2015 Set your meter and camera to your lowest ISO and 1/200. Set your manual flash to its lowest power setting. Now take a reading. If you are below f/2.8 , increase flash output. If above there are a couple of things to try 1) move flash away from subject. 2) add diffusion to the flash or change light modifier. It's really that simple. Link to comment Share on other sites More sharing options...
bob_bill Posted February 13, 2015 Share Posted February 13, 2015 <p>When Ellis speaks about metering, I listen: Link to comment Share on other sites More sharing options...
mood_lover Posted February 13, 2015 Author Share Posted February 13, 2015 <p>Thank you all for the helpful responses, I realize my question was totally wrong. Solving for ISO is not the issue since strobes are so powerful I would actually need LOWER than 100 ISO to be able to use f/2.8. If I'm using the lowest flash powers possible, and my meter is still reading as too much light, and if I cant move my lights, is my only option to add diffusion inside my softboxes somehow? Why wouldn't an ND filter on my lens work? I have no idea how you ND a flash unit!</p> <p>I'm thinking about buying a pair of AlienBee B800s (10ws-320ws) and I'm wondering if I would be able to do a 2:1 ratio while still having such a wide aperture of f/2.8. Or perhaps I'm better off using less-powerful continuous light if I want to use shallow dof?</p> Link to comment Share on other sites More sharing options...
AJG Posted February 13, 2015 Share Posted February 13, 2015 <p>You can get ND gels for your lights if you need them--Rosco makes them. An ND filter over your lens will make your viewfinder a lot darker and much more difficult to focus and compose with. You may change your mind later about shooting at f/2.8, and you would then be grateful for the increased power of the Alien Bee.</p> Link to comment Share on other sites More sharing options...
mood_lover Posted February 13, 2015 Author Share Posted February 13, 2015 <p>Yes you're right. Maybe I can buy a good strobe and just use it's modeling light (I mean, if the B800s one is powerful enough). This way I'll have options!</p> Link to comment Share on other sites More sharing options...
AJG Posted February 13, 2015 Share Posted February 13, 2015 <p>If you go that route, be aware that the Buff X series have 250 watt modeling lights and metal construction while the Alien Bees modeling lights max out at 150 watts and are plastic bodied. I haven't heard anything bad about the Alien Bees in terms of durability, but if you're supporting a large soft box the construction might be a concern. One other thing: the modeling lights are on rheostats so that they can visually approximate flash power, but if you dim them they will also drop in color temperature. Lower flash power shouldn't change the color temperature by anywhere near as much as dimming the modeling lights will.</p> Link to comment Share on other sites More sharing options...
mood_lover Posted February 13, 2015 Author Share Posted February 13, 2015 <p>Hmm great points. If I wanted to use a 4x6' or a 5' octa what would you recommend? Others have told me that a B800 can support large softboxes</p> Link to comment Share on other sites More sharing options...
mood_lover Posted February 13, 2015 Author Share Posted February 13, 2015 <p>@Andrew: I'm looking at Rosco's ND gels, how do they work? Do I just tape them over the bulb of the light inside my softbox? If they don't cause strange color casts that might be the answer to my issues!</p> Link to comment Share on other sites More sharing options...
AJG Posted February 13, 2015 Share Posted February 13, 2015 <p>I would keep them away from the bulb--they are heat resistant, but probably not that much. Many years ago I burned holes in some expensive polarizing gels with the 1000 watt quartz bulbs I was using at the time. Someone at Rosco could probably tell you what temperature they can withstand. Good quality ND gels should have reasonably accurate color--these have long been used in the film industry where people tend to be very critical about such things.<br> As for your other question, I have used 30" x 60" Buff soft boxes (and a 36 x 48 Photoflex Whitedome ) on X series without problems. I don't own any Alien Bees, so I can't speak from direct experience about them.</p> Link to comment Share on other sites More sharing options...
mood_lover Posted February 13, 2015 Author Share Posted February 13, 2015 <p>If I cant tape them on the bulb itself how would you recommend I install them? Tape it to the inner baffle?</p> Link to comment Share on other sites More sharing options...
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