Quote:
Originally Posted by missinglink786
Okay here we go....im wondering how you choose exactly what f stop you set your lights to....i've been setting my key light 6.7 and shooting at 6.7 as per the instruction i recieved at dave blecman's wonderful workshop.... i just never really questioned that i guess. however, after reading a few articles here and there i came across a maxim shoot where the photographer shot at f18...even though the key light was f16 and the background lights were f22....i understand the background lights were brighter to obtain pure white on the background but why did he purposely underexpose the model? In the image she seemed perfectly exposed. I guess what I'm getting at is does it matter what you choose as your starting f stop as long as the ratios are right? for example setting your key light at f 8 as long as the other lights are ajusted accordingly? or seeing your key light at f 22 as long as everyting follows accordingly.... i know the f18 shot would have had greater depth of field but would that necessarialy make the image sharper? is that why it was shot at f18? Also if working f stops in the studio are generally higher....i.e. f 5.6 and up....how come all the "pro" lenses are the ultra fast f 2.8 lenses? it seems that 2.8 would be pretty out of place in the studio....im sorry if these questions appear stupid but im new to this and this has just been bothering me it probably has a very simple and obvious answer. also if someone has any info about how to best calibrate a light meter to your camera id love the info! thanks!
|
I think you're doing a bit of over analysing. Essentially you set up your lights and then you meter them main light by standing at the subject position and pointing the incident bulb at the camera. This reading will tell you what fstop to use. Will you change that fstop? You might. It depends on the reflectivity of the subject. Obviously dark subjects absorb more light and light subjects reflect more. So most photographers will adjust the fstop up or down to compensate for this.
If you want considerable DOF, then you use the fstops in the f8 to f22 range, but if you want a very limited DOF, then you will opt for the F2.8 to f5.6 range. So that's why the F2.8 lens can be useful. But more often than not the F1.2 to f3.5 range is desired for low light situations rather than strobe lighting.
Shooting at f18 or in that range does not make the image sharper unless that happens to be the sweet spot of the lens and usually that won't be the sweetspot. F8 is often the sweetspot for lots of lens. But if you focus on the most critical part of the subject (usually eyes for models) then that area will be sharp no matter what fstop.
Calibrating meters can be done in a number of ways. One easy way, is with a gray card and the camera's histogram. Put a gray card at subject position and take a meter reading with your meter. Now shoot a shot of the gray card at full frame (the card fills the view finder). Now look at the histogram. If the exposure is right on, then there should be one spike in the middle. If not, adjust the fstop up or down, and shoot again. Keep doing this till the spike is in the middle. You now know what the correct fstop was for that shot. If the meter did not give you that reading, then you need to adjust it to do so, or mentally compensate when using the meter. Then you should compare the histogram results of the camera to the histogram of the same image in Photoshop to see if they agree. If not, then adjust again so that the meter will give you a spike that's in the middle for Photoshop.
Cheers,
rfs