Background should be taken into consideration too. My first impression would be to under expose by 2/3 or one stop ( or whatever works) for the same reason mentioned above.

Take some test shots and see which one works better for you.
Try to avoid bright background or you would end up with a horse silhouette which might not be what you are looking for


A hint: "When photographing the bears you will usually be photographing a white bear in the snow. This means that your camera will tend to underexpose, resulting in a gray bear. You will need to compensate for this by overexposing by 1 to 1 1/3 stops depending on the whiteness of the bear (some are a light cream)"

Good luck.

Let me get this straight: 1. Shoot in the pre-dawn morning, morning, afternoon, golden hour, dead of night, or any time you can find the horse, but always with the lens cap off; 2. Meter from a gray card, the palm of your hand (+ 1-9 stops depending on lens cap position), or Sharpshooter's left buttock (+ negative 3); 3. Use a flash or roadside flare, but be sure to feed a massive dose of bute to the horse before approaching closer than 200 yards.

Yep, that will all work.

There are three other things I would suggest, in all seriousness: 1. If you use a flash, check with the owner and pre-flash the horse from within 3-4 feet so the horse knows what's going on (Keep in mind that horses are split-brained, so you want to work both sides, lest the left brain be saying, "Uh-yup, this is sure fun," while the right screams, "It's the flaming son of Beelzebub, kick the crap out of him!"). 2. Horses look best with their ears forward, listening in your direction, so bring a "clicker" (one of those little, metal things we used to get in Cracker Jacks but now pay $4 for at the Dollar Store), or grab a handful of grass and toss it up (better yet, have someone else stand next to you and toss bits up) as you're taking your shots; 3. If the field size permits, get the horse running at you as you shoot. Don't worry about getting run over, the horse hates collisions more than you do, and sticking your non-shooting hand and arm out to the side of your body will convince him that you're really, really too big to overrun. I've worked with as many as six horses being run at me and have never come close to being hit. (WARNING: Do not try this technique with horned animals, wolves, or alligators.)

Enjoy.

You don't need a gray card if you understand what you are doing. Meter the horse and adjust accordingly. The zone system is remarkably accurate and extremely convenient, and not hard to learn. Gray cards and incident meters are ok when you can get to the position of the subject and measure the light falling on the subject and the contrast range is within the camera's capability. I exclusively use an incident meter with a flash attachment in studio because it is the most convenient and accurate way to balance lighting. Outside, I use my "horse-sense" (yes, an intended pun), along with the in-camera spot meter to measure the actual light being reflected - I don't have to stop, walk over to the subject measure the light with a gray card, expodisk incident meter, etc and hope it doesn't move before I can get back to where I want to take the picture. The in-camera spot meter just makes more sense in terms of convenience and accuracy. I have had this discussion with several people, and can point out situations were it is just not practical to always use a gray card or an incident meter. Think of how you would do this at a late afternoon baseball game where you are in the stands, in the shade, and the ball players are on the field, some in shade (this could work), but the others are on the field in bright afternoon sunlight. Or how you would evaluate the exposure for a stage performance - a rock concert, a show, or even a speaker at a lectern who has a floodlight illuminating them. There is no way you will be able to use a gray card/incident meter to measure.

Learning and using the zone system is a fundamental skill - measuring what the camera "sees" is just as valid and accurate an approach as assuming that you can measure the light falling on the subject, and hope that the brightness range being reflected by the subject will be within the camera's dynamic range. Most of the time it is, but when it isn't the method fails.

Read and learn:

http://photography.tutsplus.com/tutorials/understanding-using-ansel-adams-zone-system--photo-5607
http://www.normankoren.com/zonesystem.html
http://www.alanrossphotography.com/category/tech/zonesystemandmetering/
http://dpanswers.com/content/tech_zonesystem.php

As far as professionals using fill flash with horses - that is generally forbidden, due to the unpredictability of the horse's reaction to the flash. I spend a few years shooting equestrian competitions in Westchester, Putnam and Fairfield counties in the NY metro area. No flash period.

Technically, you're right, Gene. But if the OP is asking a question the way he did, I'd guess he probably needs to crawl and walk before he runs. Innocently, he probably just wanted an answer like, "f/8 and be there."

When I trained school photographers, we always started with simple, rote formulas. Once our troops mastered those, we explained the principles behind the formulas... which wasn't often, because 95% were not interested in knowing why. They just wanted reliable results, fast.

But for the five percent who cared, the zone system, spot metering, etc. made lots of sense. They had to have a grasp on what meters do, how incident, reflective, and spot meters work, the zone theory, and all the stuff in those linked tutorials (good stuff, BTW!). Once they understood that, they handled the tougher assignments.

The situations you described where incident readings, gray cards, and ExpoDiscs don't satisfy are very real, and I've encountered all of them and more. Pre-planning and site visits for pre-metering eliminate some issues. Knowing how to place tones in their zones handles more of it. Knowing a lot about the nature of light and light sources helps, too. Experience and testing fill in the gaps, and still, we always want better tools and knowledge.