Why do shots with flash seem sharper to me than non-flash shots?

[CuriousMike]

I was playing with my off-camera flash some more ( i've not gotten serious with it, but have fun pulling it out once in a blue moon.)

As I'm looking at some of the photos, it just appears to me that almost every shot I took with flash, the subject has a much sharper appearance than those shots I take in natural light.

In my mind, it's a vast difference.

Maybe I'm confusing "sharpness" with better (?) light?

I don't have (a) and (b) examples, but I'm tempted to try.

I go thru my catalog of people photos and the eyes just never seem to pop like they do when I'm flashing.
Self-portrait

1:1 crop of me and the puppers

My son attemping "the squint" ( a technique I read in a photo magazine a couple months back)

 

[destrekor]

Well, it could be one of two things.

The enhanced brightness could increase relative contrast, and if there is great separation between the subject and background, that boost in contrast creates an even greater appearance of separation which helps create a pop, if you will.

It could also perhaps be that your shutter speeds have been a bit too slow without flash, and the flash helps capture and freeze motion, thus you can get away with slower shutter speeds.

Even if subjects aren't moving, perhaps there is just a slight bit of camera shake, just enough to make what would be "pin sharp", and turn it into just sharp. Thus, flash is helping bring it closer to pin sharp.

 

[estarkey7]

My vote is for shutter speed differences. It's easy to check, just look at the soft natural light shots shutter speed and the flash shots.

But there is another phenomena that could be at work. If you expose a shot properly with flash, and that same shutter speed and aperture leave the subject so underexposed they are almost black, now the flash is controlling exposure and not the shutter speed.

The duration of a flash light pulse is around 1/2000th of a second. So it's so fast that it can freeze the action of your subject if it would be severely underexposed without flash.

Here is another secret. You cannot control flash subject exposure with the shutter speed, only the aperture. Now you can control ambient exposure with shutter speed. A quick way to demonstrate this is by setting your camera in manual mode, to let's say f/5.6 ISO 100 and shutter speed at 1/60th and flash in manual mode half power, with a subject and a light source in the frame (like a lamp or flashlight). Now take the same picture but only adjust the shutter speed to max x-sync, which is around 1/200 for most cameras. You will see your subject had the exact same exposure, but now the light source is dimmer! This proves that shutter speed will not effect exposure. But if you kept the flash at the same power, ISO, flash power and shutter speed, and changed only the aperture, you see the subject and the light source is dimmer.



I know I threw a lot at you and I hope I explained myself in a way you can grasp.

Hope this helps!

 

[estarkey7]

I'm going to add a photo when I get to my pc....

 

[estarkey7]

Well, I can't add a photo to this thread for whatever reason, so I'll have to do it in another post I guess.

 

[CuriousMike]

When I'm using off-camera flash, I consider the camera settings to be the exposure for the background, and the flash-power the exposure for the subject.

I've actually noticed that 1/100 to 1/200 of a second doesn't seem to impact the subject ( but it can the background. )

Since I'm limited to 1/200 (250th?), if I want to have the background go away, I do that by setting a smaller aperture ... and boosting the flash power to bring the subject back into exposure.

I think that's sorta what you're saying.

 

[CuriousMike]

I'm fairly aggressive with my shutter speeds - I will often use auto-ISO to something far greater than 1/shutter speed.

I think I have it where if i'm shooting my 85, the camera is boosting ISO to ensure I have a minimum of 1/400 ( roughly ).

 

[Syborg1211]

At equivalent settings, camera shake and possible under-exposure on natural light photos are the culprits in my mind. Generally speaking though, I'm usually at a smaller aperture when using flash so that can be the reason for the sharpness difference.

Edit: I do feel your pain though. I also think when doing natural light and having a big aperture that autofocus becomes much more critical. Most of my natural light photos that turn out soft I attribute to missed focus. My damn camera's been shifting backfocus more and more over time.

 

[Amargorojo]

I agree with akmc. There are times when you just cant get your eye to the viewfinder and being able to use the LCD is huge. Much better than spray and pray.

 

[JohnAlmighty]

Light! that's it!

 

[turtile]

The flash is only fired for a fraction of the time the shutter is open. Due to this fact, most of the light collected is completed is a very short time.

You can even lower the flash duration so you can get away with low shutter speeds.

 

[estarkey7]

The flash is only fired for a fraction of the time the shutter is open. Due to this fact, most of the light collected is completed is a very short time.

You can even lower the flash duration so you can get away with low shutter speeds.

Uh, not if the ambient exposure is significant, which is dependent on available light and ISO. Yeah, you could shoot 1/15, but you would have to be in a nearly pitch black room at ISO 100 to do so. If ambient conditions attribute to the exposure, you will still end up with a blurry shot.

 

[Syborg1211]

As others have said, flashes put out all their light in a very short duration. It's also very even light. I think the lower sharpness can be attributed to shot noise in natural light. While being in daylight may allow you to have short shutter speeds, the randomness of natural light can lead to some noise in your image. Better explanation:

http://www.dpreview.com/articles/81...e-shedding-some-light-on-the-sources-of-noise

 

[Paladin3]

Uh, not if the ambient exposure is significant, which is dependent on available light and ISO. Yeah, you could shoot 1/15, but you would have to be in a nearly pitch black room at ISO 100 to do so. If ambient conditions attribute to the exposure, you will still end up with a blurry shot.

I like to mix ambient with my flash when doing environmental portraits or event photos inside, so a slow shutter speed can really help me brighten the otherwise dark background. I used to shoot 1/30th and even 1/15th @ f/2.8 back when 400iso film was considered fast, especially with a wide angle lens. My goal is a well lit subject in a well lit room with a single flash, often bounced.

Mixing ambient and flash is a great way to go. Using a gel over your flash head to match the ambient light is another neat trick. There is no one set way to do it, because conditions, subjects and equipment vary.

I took this photo last year of neighbors cleaning up after a storm knocked down trees and blocked the highway. It was minutes after the storm passed at around 7:30 pm and pretty dark out. It's wide open, f/4.2 @ 1/30 and 800 iso. The flash stopped the action, and the combo of a slow shutter speed, high iso and shooting wide open gave me some background detail. It would have been even better, or I could have used a slightly faster shutter speed, with either a faster lens or a camera that handles higher ISOs better than my D80. Also, notice how much warmer my flash was than the ambient light. A gel to cool the color of my flash would have helped a bit.

 

[Brian Stirling]

When using flash the shutter speed is usually limited to about 1/250 of a second, BUT the duration of the flash itself could be as little as 1/5000 second or even faster with a full power flash being longer at about 1/1000 second.

So, when using flash the image is frozen in time by the short duration of the primary light source -- the flash!

Very high speed photography, like the kind that freezes the motion of a bullet, is the result of very high power and extremely short duration flash units -- like 1/250,000 second or even faster. The typical consumer flash unit isn't going to be much faster than about 1/10,000 second.


Brian