Help me fool my film camera

June 29, 2012 8:08 AM

How can I trick the auto-exposure setting on my film camera?

I recently acquired a Canon AE-1 and I just got back my first roll of slide film. I'm pretty happy, but I feel like it slightly over-exposes, set on auto, by my tastes, anyway. I want to fool the auto-exposure into taking shots maybe 1 full stop less exposed. My first thought is to set the ASA dial to a faster speed than the actual film. So say I'm shooting Fuji Velvia 100 -- if I set the ASA dial to 200 will that trick the camera enough? Is there a known source of math for this?

I can't do this in post, as I'm shooting slides, and intend to project the originals as part of an anachro-AV program.

posted by Devils Rancher to Media & Arts (15 answers total)

Best answer: Setting the ASA dial should work. Each doubling of the number is 1 stop (i.e. 100, 200, 400, 800, 1600...).
posted by 0xFCAF at 8:12 AM on June 29, 2012

Response by poster: Excellent! I'm very happy overall with what I'm getting -- just need this final tweak. Off to buy more Velvia!
posted by Devils Rancher at 8:13 AM on June 29, 2012

Response by poster: Follow-on question -- it seems obvious, but I could bracket ostensibly by changing the ASA dial between shots?
posted by Devils Rancher at 8:14 AM on June 29, 2012

0xFCAF has the correct and most obvious answer for changing exposure in full stop increments. If you need to change exposure in increments less than that, you can have whoever develops your film "push" or "pull" the developing time to correct for over/underexposure ("pushing" is extending development time to account for underexposure, "pulling" is reducing development time to account for overexposure). Both techniques change the saturation and contract characteristics of the film slightly, but most film is very tolerant out to 1/2 stop either way.
posted by saeculorum at 8:28 AM on June 29, 2012

Each tick between the marked 100, 200, etc., is 1/3 stop. You could bracket by changing the ASA dial each shot, but it could be faster to bracket by shooting in manual mode. Frame your picture, note the aperture reading in the finder, manually set your aperture to that, then as you shoot each click on the aperture ring is 1/2 stop. You can do this bracketing without taking the camera from your eye much (or at all if you have the winder).
posted by caclwmr4 at 8:43 AM on June 29, 2012

Best answer: The rule of thumb for slide film is to meter for the highlights, so slight overexposure is a common problem with auto mode. Slide film exposure latitude is much lower than color print film, so I wouldn't underexpose by more than half a stop. I've had decent luck shooting Velvia at 125, and caclwmr4's suggestion to bracket manually is good as well, but the ideal is reading the highlights with a handheld meter if time isn't a factor.
posted by Lorin at 9:18 AM on June 29, 2012

Response by poster: I don't have a handheld meter, so I'm going to continue to rely on the internal one, but that's a good point about the latitude. I sure saw that with Kodachrome back in the olden days of yore. Adjusting the camera in manual mode seems fraught because the HUD only reads the F stop in auto-exposure mode, so I'd be guessing at the shutter speed. Or does this camera even adjust the shutter speed? I need to read the manual again.

Anyway, it seems like by far the easiest thing to do, since it's quite close really, is to stop it down 1/3 to 2/3's using the ASA dial. I'm gonna try another whole roll of the Velvia 10 set at 125 & see how that goes. I'm really looking to keep this simple enough to just grab random things as they strike my fancy - color washes, & abstract stuff.

Thanks, all! I'll have results of the first batch up on my Flickr stream here soon, and hope to project a tray-full on top of my band while we play at our next outing.
posted by Devils Rancher at 11:00 AM on June 29, 2012

The shutter speed and the aperture numbers are engineered to either double or half the amount of light reaching the film, and the ASA/ISO will either double or half the film's sensitivity. So once you determine a perfect light reading for a particular situation (using any camera or meter), you can play with these in order to get greater depth of field (smaller aperture) or stop the action (faster shutter speed). If you move two stops with one, just move two stops the other direction with the other, and your exposure will be identical. Just remember that the greater the aperture number, the smaller the aperture.
posted by weapons-grade pandemonium at 12:08 PM on June 29, 2012

Obviously with film the ASA is predetermined, but you can lie to the camera to get the exposure you want. You can tweak the ASA of the sensor with a digital camera.
posted by weapons-grade pandemonium at 12:10 PM on June 29, 2012

I'm really looking to keep this simple enough to just grab random things as they strike my fancy - color washes, & abstract stuff.

Based on this, you might want to look into crossprocessing. Get your hands on some expired slide film at a discount and have it processed as color print film. Overexposure can actually be beneficial in this case, and you'll definitely see some interesting colors.
posted by Lorin at 2:46 PM on June 29, 2012

I don't know this camera, but can you just use the camera's meter in manual or semi-manual mode? That is, take the camera's auto settings and apply them manually (with appropriate adjustments), or override them to make the exposure what you want.
posted by GeeEmm at 4:06 PM on June 29, 2012

Response by poster: I could do that, but the point of the question was to double-check my thinking about how to do what I wanted via auto-exposure. I spent 20 years as a Pentax K-1000 owner, and I got an awful lot of shots wrong with it, & the AE mode on this Canon is very good.

All the pictures on the first roll I took look to be just a tad more exposed than I would have wanted them -- (it's just a personal taste thing, really they're fine)-- so a global solution will fit nicely, I think.
posted by Devils Rancher at 7:18 PM on June 29, 2012

An alternative solution would be to shoot your Velvia 100 at 100 (also referred to as shooting it at box speed). But since you consider this a half stop overexposed (which, in all honesty, could just be your camera), ask your lab to pull half a stop when developing. They might charge you a dollar for this, but you'll also find that pulling slide film reduces contrast which you might find helpful if you're out in midday sun.

Lorin is correct about exposing for highlights (shooting to the left as opposed to digital's shoot to the right) and I find that using an incident meter results in so few wrong exposures that I consider it cheating. I never leave home without my Sekonic. I couldn't disagree more about crossprocessing perfectly good slide film, but to each their own. ;)

(Me? I shoot Provia 100F at 50 most of the time, Velvia is a sometimes film much like cookies now are apparently a sometimes food. Films not dead, not even on MeFi.)
posted by Brian Puccio at 10:19 AM on June 30, 2012

Also, if you like Velvia 100, try Velvia 50, it's more punchy. Avoid Velvia 100F, it's less punchy. If you don't want the punchy look, might as well go with Provia.
posted by Brian Puccio at 10:22 AM on June 30, 2012

Response by poster: So, thought I'd update. Even 1/3 of a stop on the ISO (Shooting Velvia 100 with the ISO setting at about 125) resulted in inferior pictures. The midtones of the roll were indeed a little richer, but the highlights were dull & the shadows went really dark. My slide scanner is choking on this roll, so I guess I'm going to go back to trusting the folks who made the Program mode.
posted by Devils Rancher at 2:20 PM on November 8, 2012