Question about lighting...

[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!

[R_Fredrick_Smith]

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

[missinglink786]

Thanks for the reply RFS. but from what you said couldnt I just set up my lights (using one light for example) and just not even adjust it just shoot it at whatever the meter gives me? I just thought there was more of a reason for choosing a given starting fstop.

In the same respect, it seems that most properly exposed are relatively bright. What are the ideal settings to shoot a dimmer more romantic if you will glamour image... for example, a lot of JimmyD's images have a darker more romantic quality to them i think.

[R_Fredrick_Smith]

Originally Posted by missinglink786

Thanks for the reply RFS. but from what you said couldnt I just set up my lights (using one light for example) and just not even adjust it just shoot it at whatever the meter gives me? I just thought there was more of a reason for choosing a given starting fstop.

In the same respect, it seems that most properly exposed are relatively bright. What are the ideal settings to shoot a dimmer more romantic if you will glamour image... for example, a lot of JimmyD's images have a darker more romantic quality to them i think.

As already stated, the choice of fstop is to control the DOF. If you have a choice of fstop, then you choose the one that will give you the DOF you want for the shot. But that means you have to be able to control how powerful the lights are. Suppose you want to shoot at f22 but all you have is one 120ws strobe. Then, unless you put the light very close to the subject, you won't be able to use f22, because there won't be enough light.

Suppose I want to shoot at f11 for DOF reasons. I set the power of my strobes and the distance from the subject and meter the lights. I then adjust them up or down and/or back and forth (distance) until I get the meter reading I want.

Normally, all images should be properly exposed, no matter what the intent. But you can control the effect of the light and the "mood" of the shot by how you use and/or modify the lights you have. The primary reason for adjusting the fstop from the one the meter gives, is as already mentioned, to compensate for the lightness or darkness of the subject.





Consider the two images above. One is fairly bright, the other much darker. What's the difference in the lighting? Well in one case more of the light is hitting the subject and the other less light is hitting her. The fstop chosen for each was based on how much light was hitting the subject.

Suppose, on the first image, I wanted it even darker. I could have added a black reflector to the setup (for example). Or I could have closed the binds some more.

Cheers,
rfs