Scot wrote: > > I'm going to attempt a family portrait with 9 folks. I have a Porta Master > 400 with three heads. I have a flash meter only which reads the flash quite > accurately. > My question: If I set up in shade or open skylight how should I adjust my > exposure? Simply! If you meter the scene with your camera or meter (reads ambient too?), then you simply compare the exposures required and make the appropriate (simple) adjustment. > I can take an ambient reading with my camera. Is there a formula to combine > the two? Ah, so what's the simple adjustment... OK, let's say you're flash meter tells you that you need f/8 and you're shooting at 1/60 Your meter tells you that at f/8 your requaired shutter speed (for ambient light) is 1/15 sec. In this case the ambient light is 2 stops less intense than the flash, so use f/8 @ 1/60. The film will be technically overexposed by 1/4 of a stop (but that's hardly noticable). Shadows and distant objects will have (at best) 2 stops less exposure than your subject. It may be obvious you used a flash :-) Now, perhaps the ambient meter reading is f/8 @ 1/60. In this case the exposure from flash and ambient will be the same. The simplest solution here is to expose at f/11 @ 1/60. Shadows will be filled very well (perhaps too well) but that's another topic :-) At the other extreme, the ambient metering may indicate f/16 @ 1/60. In this case, the flash will be overpowered by the ambient light. It will provide exposure 2 stops less than ambient (which will fill in shadows and place highlights in eyes -- but not add too much to overall exposure). In this case expose at f/16 @ 1/60 and notice the subtle efect of the flash. So the simple rule is: Shoot at the reading (flash or ambient) that gives the least exposure (highest f/no) as long as the readings are at least 1 stop apart. If the readings are less than a stop different, do the saem, but close down half a stop. If they're exactly the same, stop down 1 stop. Now that's simple, but there are times that you will want to alter shutter speed and aperture to (almost) independently adjust the exposure from ambient and flash. Note that this works best with cameras having leaf shutters as they don't suffer from having a max sync speed. now, if you _really_ want a formula, you've come to the right place ;-) assuming both meter readings are for the same shutter speed, the aperture you should use is: a = sqrt(a1^2 + a2^2) so if meter readings (at same shutter speed) are f/5.6 and f/8, you should use something around f/9.7 (which is half a stop less than f/8 -- and these crazy numbers are the reason for the rule of thumb above) or for shutter speeds s = 1/(1/s1 + 1/s2) so if meter readings (at the same aperture) are 1/1000 and 1/250, then you should use 1/200. The rule of thumb above also applies. In general, since half a stop either way is often insignificant, rules of thumb work very nicely. If in doubt bracket an extra 1/2 a stop for neg and -1/2 a stop for tranny. I have a nice flash meter that does all of this for me, but often it's easier to do it in your head :-) (I've left my flash meter behind, but , regardless of what my wife says, I've never left my head behind). > Also flipping through a portrait book at Border's today the photog > overexposed by one to two stops for neg film on all of his portraits. Is > this common? It is if you open up the shutter 2 stops. > Also what is the difference between Portra 160 nps and npc? dunno. Google for it :-) Google tells me to look here http://phototechmag.com/buying_colorflm.htm And from that article "Fuji NPS: better grain in the saturated primaries than NPC or Portra, but worse on pastels, midtones, and skin tones" and it continues... "Contrast Kodak Portra 160 NC and Fuji NPS: this was a draw; both films ranked only slightly behind Portrait 160. Portra had greater midtone contrast, giving it a slightly higher overall contrast, while NPS had a bit more highlight contrast combined with a bit less shadow contrast. Saturation Fuji NPC: a close second to Reala, but fell behind in the reds and oranges, primarily due to a relatively desaturated magenta. Fuji NPS: close to NPC. NPS had better saturation in the reds and oranges, but was weaker in greens, blues, and most pastels. Rendition of the primary colors Fuji NPC: produced the best overall rendition, with an excellent magenta. The yellow was too red; the green was too weak and blue Fuji NPS: overall a very similar rendition to Reala, but the colors were somewhat duller. Neutrality of gray scale Fuji NPC: again tops the list with a near perfect neutral gray from highlight to shadow. Fuji Reala and NPS: both had neutral midtones and shadows, but noticeably pink-warm highlights. Flesh-gray balance There was surprisingly little difference in how these films rendered light skin tones, but marked differences in the rendering of dark skin tones were notable. Each produced a very good or excellent light skin tone, but none did very well with dark skin tones; in fact, some did quite badly. The poor rendition of dark skin tones dominated the following rankings; the first five films were similar in skin tone quality, while the last three were markedly worse. Kodak Portra 160 NC and Fuji NPS: tie for first place. Portra produced the best dark skin tones (although still too ruddy) and excellent light skin tones. NPS produced slightly better light skin tones, but slightly poorer dark skin tones. Fuji NPC: still worse dark skin tones; the light skin tones were a bit pink. Overall color rendition Fuji NPS: had this film just a touch more saturation, it would have taken first place. Overall, the hues were more accurate than in Reala; it’s the chroma that was lacking. NPS produced the best blues of the bunch. Its greens on the whole were second to none, although the yellow-green patch came out more avocado in color. Fuji NPC: the saturation is right up where it should be, but the higher contrast distorts many of the colors. Darker colors became too dark and, in the case of blues, too saturated and too cyan. The hard-to-reproduce purple patches, both light and dark, were way off. Pastels were otherwise good. Magenta was desaturated compared to other colors." And his conclusion (paraphrased).... Use the one you like the best :-) Steve
