Sharpness EF500mm with flash

[snakeroot]

Question about sharpness.

 

This photo has two 100% crops of a photo taken with a 500mm f4 lens

and two 580 flashes using the ST-E2 remote.

 

The sharper foreground crop was taken at 1/30th sec f4, the

background 1 sec at f9 (there was some incandescent lighting in the

room).

 

I don't understand the difference in sharpness, (both exposures have

the same unsharp masking in CS2).

 

Any explanation?<div></div>

[bennyboy]

Is this just a once off? I'd repeat the lens quite a few times and average out the results.

[bobatkins]

There's something wrong with your technique or you're not telling us everything or you're incorrect that the only difference was shutter speed and exposure.

 

Why does the "sharp" image show so much more noise (or compression/sharpening artifacts)? Sharpness might differ due to subject movement I suppose, but the noise/artifact level should be the same.

[John Crowe]

Perhaps movement of the subject or the camera during the 1 second long exposure has created the softness.

[snakeroot]

Actually this is one example in a series, as I went from 1/30th up to a 2 second exposure, the sharpness further degraded. A sharper image was obtained at 1/60th but I didn't include that because the 580's were positioned differently and the exposure was a little different, but the sharpness was clearly superior.

 

Is it noise with the longer exposures, perhaps more pronounced because of flash?

[snakeroot]

No movement, timer exposure on a tripod.

[John Crowe]

To get those eV values looks like the sharp image was done at high ISO while the smooth image was done at low ISO, hence the longer exposure with smaller aperture. These two eV ratings are not equal yet exposures are pretty close.

[snakeroot]

Guess I don't understand ISO's and eV's. All I did was vary the shutter speed on my Mark II using Tv mode. Used the 2 sec timer feature, and unmasked in CS2 to exactly the same settings.

[John Crowe]

Seems like it is moving anyway, particularly consistent with your 1/60 being even sharper. How about focus, manual or auto? Is it possible the autofocus is changing at time of exposure?

[snakeroot]

AF was used, single point right in the middle of that flower. Same position of the tripod and subject each time. I depressed the shutter halfway before engaging the 2 second timer, and heard the confirmation beep for AF each time, then depressed the shutter completely to start the timer.

 

Again, there are a series of photos showing more softness with longer exposure times.

 

I can't rule movement out entirely, but I don't thing that's the case.

[John Crowe]

Do you have mirror lock-up on that camera that you can try using? Even on a tripod mirror flap can cause havoc, usually in the 1/15 to 1/8 range but with a 500mm lens the effect may be more pronounced.

[snakeroot]

Excellent suggestion John, will attempt the same series with mirror lockup, I bet you hit the nail on the head.

 

I went back and looked at the 2 second exposure and it really isn't all that much fuzzier than the 1 second exposure.

 

Didn't realize that flash would need mirror lockup too, but it makes sense with the 500mm lens.

[bobatkins]

Flash doesn't need mirror lockup. Flash duration is maybe 1/1000s, for closeup work maybe 1/10,000s.

 

Ambient light exposure is what's slow.

 

MLU won't affect the noise/artifacts. It's not the result of exposure differences.

[mark_chappell]

<I>Flash doesn't need mirror lockup. Flash duration is maybe 1/1000s, for closeup work

maybe 1/10,000s.</i><P>

 

Yes, but it sounds like he was using the flash as fill-in, not the main light source, so much of

the exposure was from ambient light at whatever shutter speed was in effect. Thus, MLU

might have helped. How stable was the tripod? Was stabilization on or off? IS should be

able to handle 1/30 sec on a reasonable tripod, but I'm not sure about a 1 sec exposure.

[snakeroot]

I locked the shutter up and took several more exposures, there is much less softening of longer exposures now.

 

Seems to be a lot of noise in the faster flash pictures though.

 

IS was off, shutter was locked up in both. Both from a Mark II 1Ds with a 500mm F4 IS, Gitzo 1348 with a Wimberly Sidekick, remote shutter activation.

 

Single AF point in the center flower.

 

The grainy image to the right was taken at 1/30th f4, the one to the left 1 sec at f11. Both unmasked in CS2 to 100%, pixels 2, Threshold 0.

 

See my next post for similar exposures with IS on.

[snakeroot]

Two 100% crops again in this image, shutter lockup on each, all other parameters the same except IS is turned on here.

 

Left crop 2 sec at f16, right crop at 1/60 f4. Both with two 580EX flashes.

[snakeroot]

Moral to my story, MLU with longer exposures and IS on the tripod using flash fills, I just hope it's reproduceable.

[John Crowe]

These seem to be getting underexposed, and are you using some sort of camera program that allows it to change the ISO setting because your exposures as stated vary widely. I'll try to explain. Assuming that 1s and f11 is correct exposure then the following possible exposures would also be correct:

 

 

1s - f11

 

 

1/2s - f8

 

 

1/4s - f5.6

 

 

1/8s - f4

 

 

1/15s - f2.8

 

 

1/30s - f2

 

 

So your exposures which you say are 1/30s - f4 are underexposed by 2 stops which would explain the grain or perhaps your camera has a safety shift mechanism which is setting a higher ISO by 2 stops which also could account for the grain.

 

 

I would now forget Av or Tv and all program modes and try manual setting of both aperture and shutter speed so you have absolute control over the exposure. The first thing you need to find is the correct exposure value. Once you have that then start closing the aperture and increasing the shutter time, 1 stop increments. Good luck.

[snakeroot]

Thanks for your help John, I think I've got it figured out. You are exactly right, the images were badly underexposed, and Photoshop automatically adjusted the output to the best setting.

 

I exposed this image correctly in manual mode, after a ton of practice settings. I also learned a good bit about MLU's importance, and IS on a tripod.

 

This 500mm lens is very nice to learn on, thanks again.<div></div>

[John Crowe]

Wow! Much better! Is this the same technique, indoors with fill flash? Glad to help out.

[snakeroot]

Yes, same technique indoors with fill flash. I used the TCN-80 to time bulb exposures at an aperture setting of 18 for 45 seconds for that particular photo. I used the ST-E2 with two 580EX flashes, and used the 1.4x and two 25 mm extension tubes. As you know, MLU and IS on a tripod was necessary.

 

Photoshop's auto dialogue box barely changed that exposure at all.

 

Interesting how your focusing really drops down to about a 6 foot range with those 25 mm extensions. Can't focus anything closer that 10 feet or further than 16. Fun stuff this Canon equipment.