Beginner question on exposure variations

[celeborn]

Hi, I am giving some demonstrations on photography to a 4th grade class (and learning much myself) and last week we took pictures to demonstrate depth of field. Using an F-5 with and 85mm 1.4 lense and 400 iso color film we took exposures using the aperture priority setting at 1.4 and 16. We used natural light coming through the window. The pictures taken at f.4 were very contrasty and the pictures taken at f16 had an even not so contrasty exposure. The pictures demonstrated depth of field very well, but I was surprised at the difference in exposure. Is this a characteristic of the film? I am assuming the very short exposure time had a lot to do with it. But I have never seen this show up so dramatically before. Thanks for taking the time to read this. And many thanks to whoever takes the time to explain it.

 

[Konical]

Good Evening, Celeborn,

If your film was color negative and you had it printed at a one-hour facility, remember that the automated printing process has a huge effect on the appearance of your results. Given the latitude of CN film and the tendency of the machinery to make every print look "normal," results can be a little strange sometimes. Using transparency film is usually better for the kind of comparative results you're after because it eliminates the printing variables. Also, are you absolutely sure that you remembered to make the appropriate shutter speed change each time you changed the aperture?

Konical

 

[celeborn]

You nailed it on the one hour facility. I was using auto exposure on aperture priority so no adjustment was necessary, I trust the meter in the f-5. I know there is a reciprocity effect on very long exposure times but even at f16 the exposure was about 1/15th of a sec. and that would not cause that. The exposure at f1.4 was about 1/1000 of a second. I was shooting color negative film, so you were right about that. Any other comments? Thanks. Richard

 

[Konical]

Good Evening Again, Richard,

Better for your purpose to use the camera on Manual. You shouldn't be running into any significant reciprocity problem at 1/15 with most films.

Konical

 

[celeborn]

Thanks again. I get another hour with the class this Friday. I am going to spin the wheel. We'll shoot all apertures and bracket some shutter speeds and see what happens. Maybe even take it down to a photolab. We'll still shoot the same film. Richard

 

[Ed Sukach]

I had to check this out: f/1.4 @ 1/1000 "reciprocitizes" to f/11 @ 1/15 - one stop different than f/16. Not a great deal, really, but this might be some indication of a variation in lighting and or metering. At times, slight shifts in camera position, or field coverage, lighting angles, sundry other factors - can affect metering significantly.
Reflective metering, as is used in all "automatic" in-camera meters, is more sensitive to variations like this than incident metering.

 

[celeborn]

Thanks for your imput Ed. We were shooting on a tripod with a prime lens. We probably shifted the angle slightly for each shot, but the difference was only noted between f1.4 and f16.

 

[Ed Sukach]

Thanks for your imput Ed. We were shooting on a tripod with a prime lens. We probably shifted the angle slightly for each shot, but the difference was only noted between f1.4 and f16.

"Only" between f/1.4 and f/16? Were there exposures made at other apertures?
What kind of ISO 400 Color film was used? Color negative films and even reversal - generally have more latitiude than -1 stop ... but there may be some high contrast types that are unusually sensitive to exposure variations... Although I doubt it here.
It begins to sound like an error in the shutter or aperture controlling circuits/ mechanicals.

Wait .. a thought ... was the sole source of light "daylight through a window"? Ordinary florescents actually "pulsate" at the AC current frequency, turning off and on at 1/60 second.
Could that have been a factor?