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How do I get "perfect" exposure with off-camera flash?


TPF Noob!
Oct 26, 2009
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New York
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I've been learning to use off-camera flash for my eBay photos. The setup is a Canon SX170IS point-and-shoot on manual, with an old garage-sale Vivitar speedlight (one power setting, non-adjustable), triggered from the on-camera flash by a ten-buck optical slave, shot through a cheapo shoot-thru umbrella.

The results aren't great by any means, but they're a lot better than what I used to get.

Unfortunately, I just can't seem to figure out how to get consistently correct exposures. I understand the theory behind flash exposure - ISO, aperture and flash-to-subject distance. I've read a hundred tutorials on the Strobist and watched a hundred more on YouTube, all of which have been helpful in their own way. I check my histogram and do plenty of "chimping."

Yet whenever I bring the photos into my computer and look at them in Lightroom, I see what you see here: images that look decent (for a setup that cost less than $250 total, anyway) but the exposure is inconsistent. Slightly over, slightly under. Once in a while I get lucky, but I can't rely on luck.

Sure, I could correct in Lightroom, and I do if I have to, but that's not really the point here.

So how do I get consistently correct exposures? Do I need to shoot tethered? Buy a handheld meter? Resign myself to post-processing?

I know the answer is out there somewhere, because the internet is full of perfectly-exposed photos, but this is baffling me.

Here are a few sample shots. I feel like the first one is pretty close to being right, the second and third are underexposed, and the fourth is overexposed. These were all shot on the same settings (ISO 100, 1/200, f4.5, same flash distance, full flash power since it only has one setting, camera on a tripod) and no post-processing other than resizing and "sharpening for the web."

(These photos are the least embarrassing set I could find; I've shot plenty more where despite my best efforts, the exposure is too out of whack for me to even want to look at. )

Thanks for any help!




For your setup, you're doing pretty darn good! To be honest, with the gear you have, I don't know that you can get too much better. If you can't vary the power level of the flash, then you're limited. Your only options are to either move the flash closer or further (which adds it's own issues), or to start adding neutral density gels to the flash.

The next thing is realize that probably 99.9% of those "perfect exposures" you see all over the 'net didn't come out of the camera that way. Almost every image needs some tweaking, and that's been the case since photography came into being. In the darkroom we dodged, burned, over & under developed, etc, etc. The only difference now is our hands don't smell like vinegar! Your thinking correctly, in that you want to get it as close as possible in-camera, but don't think you can always get it perfect. I just finished a series of headshots on Friday evening shot with top of the range Nikon speedlights, Pocket Wizard triggers, and Lastolite modifiers and a Nikon D800 with an 85mm 1.4 and metered with a high end Minolta flash meter. When I looked at the images in LR, I still bumped the exposure by about 1/3 stop.

What you may (should?) consider if you want to do more of this and make it easier is to get a flash with variable power output. A used Yongnuo, Sunpak, or similar third-party speedlight can be had for as little as $30 at my favorite store, Craig's List (or similar, local 'site). I would also use a diffuser of some sort, something as simple as a translucent plastic bottle draped over the flash head, or some white, ripstop nylon on a dowel or PVC pipe frame will make a world of difference as well.
I am no expert but it could be that your subject is moving. Even the slightest movement will effect exposure. The reflection of the flash of the object at different angles will effect the outcome.

If you leave the subject. In the same position and take multiple photos without touching the subject, do the results stay the same or are they different?

Picture 1 looks good
Picture 2 you are creating a lot of shadow making it look darker
Picture 3 you are only lighting the base of the lock
Picture 4 looks good to me.
Tie a string to the center of the umbrella, right in the center, where the shaft's cap exits the top of the umbrella. You can use the string to ensure a center-of-beam aim of the flash, as well as precise distance between shots. It's possible that the flash is not outputting a consistent pop of flash. And keep on mind, at close flash to subject distances, even a very small difference in distance between frames can and will create a significant distance in the exposure: at CLOSE distances, due to the inverse square law, light from a source falls off at a VERY high rate! As the light is moved farther away, the rate of falloff in intensity moderates.
Thanks for the responses. I've always felt like I don't want to upgrade my equipment until I'm at least cracking the glass ceiling of what it can do (plus, I can't afford new stuff anyway). But it sounds like I'm headed in the right direction at least. Thanks!
You can't get 'perfect' exposure in the entire scene using of camera hot shoe flash units.

A good hand held light meter that can read flash (strobe), incident, and reflected light is a valuable aid to setting up off camera lighting.
You've gotten some good responses by some good people. Let me add my 2 cents.

1. "Perfect Exposure"....what does that mean? For an intriguing still life? For a product sale? For an appealing wall photo? For a crisp, tack-sharp photo? The right white balance? So be clearer in your head about what it is you're looking for. It's obvious that you're "meh" about your photos (though I actually think they're not bad for your level of experience and setup).

2. Just looking at the examples you submitted, all of them would produce different exposure even if your ISO, aperture, shutter speed were identical. Let me explain: you're shooting at different angles. The more light you get bouncing off of that pale wood service, the brighter your picture is going to be. If you're shooting automatic, your camera's computer is going to see all of that light wood and up your shutter speed b/c the camera's brain says that you've got a much lighter background (than if you were shooting against the wall). If you wear a white shirt for one picture (and a dark shirt for another), the white shirt serves as a reflector and will affect the light for a shot that is closer to the subject.

3. For product photography, I would argue it's almost impossible to shoot without having some level of post-production work required. That's b/c you're trying for minimalist photos (the product and...,nothing else!) so small flaws (the dimple on the hamburger bun, the small scratch on the side of lock, the split thread on the leather watch band) that stand out when the item is the only thing in the shot and it's close up. So if your standard is: how can I shoot brilliant product photography that almost never requires post-production, than that may be an impossible standard even for a pro. Good product photography yes--it can be an assembly line where you set up, shoot, and move on. But expect to do some post-production work with almost all product photography work. And yes, it's always best to get as much right in-camera. That said...

4. Set up a production line and standardize stuff as much as possible. A tripod is good for this. Get your setting, get your angle, set up your lights, shoot...then pull out the SD card and take a look. Continue tweaking until you've got a result where you're happy with your exposure. Then mark the location of the tripod and the product. Note your camera settings. Then begin the assembly line. Even if post-production tweaking is required, you should be able to do batch processing.

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