/p/ - Photography » Thread #297809

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Anonymous Fri 21 Nov 2008 04:36:00 No.297809 View View Reply Original Report

Quoted By:

I've been Googling and reading up on flash sync and I 'sorta' understand some of the principles about first and second curtain etc. My trouble comes in the form of understanding how having flash sync locked to 1/200 in aperture mode helps when the flash fires at up to 1/4000. Sounds like I am trolling but I'm just plain dumb :)

ac !!VPzQAxYPAMA

ac !!VPzQAxYPAMA Fri 21 Nov 2008 04:51:00 No.297813 Report

Quoted By:

Basically, think of a flash photo as two exposures in one. First you have the big bright flash that lasts like 1/4000th of a second, but after that, you still have the shutter open for however long it is.

Since the exposure time of the flash part of the photo is fixed by the flash itself, your shutter speed doesn't actually affect that, so that's controlled entirely by the aperture and ISO.

Since the light from the flash falls off extremely rapidly with distance (I wanna say inverse square, but I'm too lazy to check my facts), what ends up happening is that the flash lights up a specific part of the photo and the rest of the exposure mostly just exposes your background.

Anonymous

Anonymous Fri 21 Nov 2008 04:54:00 No.297815 Report

Quoted By:

Rather than explain, I'll give you an experiment you can try yourself.

In manual mode (just so you can tell it to do things it shouldn't be doing), use 1/500th or faster shutter speed and turn the flash on. Take a picture.

First and second curtain are very different, and are really just there for controlling shots that have motion blur. You generally want first curtain for everything because the motion will be frozen at the moment you release the shutter rather than trying to count down before the shutter closes.

Anonymous

Anonymous Fri 21 Nov 2008 04:56:00 No.297817 Report

Quoted By:

The max x-sync speed is the fastest that the camera can shoot while the entire shutter curtain is open.

Anything faster than the x-sync isn't actually a fully open shutter curtain, but a slit that is sliding across the sensor. The shutter speed is faster, but not all of the sensor is revealed all at one time, so the flash only partially exposes the sensor when you exceed the x-sync.

ac !!VPzQAxYPAMA

ac !!VPzQAxYPAMA Fri 21 Nov 2008 04:57:00 No.297818 Report

Quoted By:

Of course, if the shutter is open longer than the flash exposure, the foreground that you flashed on is still going to get exposed while the shutter's open, so if it's a moving subject, it'll still get blurry around the edges.

Therefore, the reason you'd want to lock the exposure to 1/200th is when you don't give a damn about getting your background exposed properly and just want to make sure your main subject is sharp and clear.

The reason for 1/200th specifically and not 1/4000th is that the way focal-plane shutters like those found in most SLRs works is that there's a maximum physical speed for the shutter and anything faster is achieved by not opening it all the way.

So at 1/200th, the shutter opens all the way and so the whole sensor gets exposed when the flash goes off, but at 1/400th the shutter only opens halfway and moves across the frame half-open like that, so each part of the sensor is getting hit with light for 1/400th of a second but there's no time during that where the entire sensor is exposed. If you have a camera like this and fire an external flash above the sync speed, you'll only get a bright stripe across the frame where the flash went off and the rest will be underexposed.

Clear?

Anonymous

Anonymous Fri 21 Nov 2008 05:00:00 No.297819 Report

Quoted By: >>297835

Easier yet. When shooting w/ flash, the shutter speed determines the ambient exposure, ie. how bright the background is in relation to the subject.

The aperture determines how much power you need. http://letmegooglethatforyou.com/?q=guide+numbers

Learn and make a chart for yourself about the relationship b/w distance, aperture, and power.

Anonymous

Anonymous Fri 21 Nov 2008 06:02:00 No.297835 Report

Quoted By:

>>297819
Boy that's tough to get my head around. I fail at math miserably lol. I am gonna have to do some flash tests with moving objects to see how much blur I get at various settings both with and without flash sync on. I think it might help me see just what is going on. A desk fan would possibly work for this?

Anonymous

Anonymous Fri 21 Nov 2008 06:23:00 No.297843 Report

Quoted By:

Hmm. Strange. I'm not seeing it. Does the external flash need to be in manual mode?

Anonymous

Anonymous Fri 21 Nov 2008 06:31:00 No.297847 Report

Quoted By: >>297857

I must be doing it wrong. Perhaps I need to go out and shoot fill flash in daylight to test it. Using a Canon 450D with 430EX Speedlite flash here. The only thing I have found is increasing the F stop to a larger number slows the shutter too much in low light and by forcing flash sync to 1/200 results in being able to shoot at higher F numbers gets past this problem. Manual mode requires FEC to be applied. Not seeing any bands on the images at any settings I have tried thus far.

Anonymous

Anonymous Fri 21 Nov 2008 06:34:00 No.297848 Report

Quoted By:

I wonder if the Auto Lighting Optimizer is processing any differences out.

ac !!VPzQAxYPAMA

ac !!VPzQAxYPAMA Fri 21 Nov 2008 07:08:00 No.297857 Report

Quoted By: >>297884

>>297847
Put it in manual, set the shutter speed to 1/2000th, take picture.

It's possible the 430ex is too smart to let you do this and will just lock you to a max of 1/200th...

Anonymous

Anonymous Fri 21 Nov 2008 08:45:00 No.297884 Report

Quoted By:

>>297857
You have hit the nail on the head. The 430EX is not letting me go any faster than 1/200 regardless of what I set the shutter to. As soon as I hit the shutter button it goes back to 1/200. Is there any way to overide it?

Anonymous

Anonymous Fri 21 Nov 2008 09:03:00 No.297900 Report

Quoted By:

Looks like FP mode is only available with the 580EX on this camera. That's REALLY annoying if you want to do fast flash sync photography.

Anonymous

Anonymous Fri 21 Nov 2008 09:09:00 No.297903 Report

Quoted By: >>297905

Take it off ETTL, fire both the shutter and flash on manual. Soblem fucking prolved.

Anonymous

Anonymous Fri 21 Nov 2008 09:13:00 No.297905 Report

Quoted By:

>>297903
I have. Makes no difference.

Anonymous

Anonymous Fri 21 Nov 2008 09:42:00 No.297915 Report

Quoted By: >>297916

Found it at last. There is a high speed function on the flash itself. I did not have it enabled. Works in E-TTL mode or manual. Had to dig into the flash manual to find out.

Einta !!MWv3ICYobCM

Einta !!MWv3ICYobCM Fri 21 Nov 2008 09:48:00 No.297916 Report

Quoted By: >>297919

>>297915
Yeah, you just set it to HS>> and it works.

Anonymous

Anonymous Fri 21 Nov 2008 09:55:00 No.297919 Report

Quoted By: >>297928

>>297916
Well I don't know what all the fuss about first curtain/second curtain light/dark banding is but even at a high shutter speed I don't see any. Unless of course I misunderstand how high speed flash works. Perhaps the limiting to 1/200 in Non-HS mode is in order to prevent you from seeing that happen? In other words the flash and camera takes care of it all for you?

Anonymous

Anonymous Fri 21 Nov 2008 10:18:00 No.297928 Report

Quoted By: >>297937 >>297945

>>297919
The curtain setting has nothing to do with the banding. The simplified answer for the curtains is that 1st curtain freeze the motion when you release the shutter and 1nd curtain freezes it at the end of the exposure.

With such a high shutter speed, the flash is firing right away anyway. More than likely, any flash designed specifically for your camera is too smart to let you fuck it up. You might have to find an old flash, or one made for another brand of camera. It should still sync up, but probably won't be able to communicate any extra info with the camera.

Anonymous

Anonymous Fri 21 Nov 2008 10:55:00 No.297937 Report

Quoted By:

>>297928
It's OK I watched the Strobist vid all about it. Yeah I have an old flash I could try but why bother? It looks like they make it pretty much idiot proof (Well if you know what the fuck you are doing in the first place that is).

Anonymous

Anonymous Fri 21 Nov 2008 11:29:00 No.297944 Report

Quoted By:

You'd have to tape the pins except the middle one to go past sync speed without going in high speed sync. Only then will you see the semi exposed frame thing.

Einta !!MWv3ICYobCM

Einta !!MWv3ICYobCM Fri 21 Nov 2008 11:34:00 No.297945 Report

Quoted By:

>>297928
Yep. Think 1/20 or 1-second exposures. If the flash fires at the beginning of a 1/20-second exposure of a person running to the right, you get this:

|==== where | is the person frozen and = is blur. The blur is in front of them, and it looks weird - blur *shouldn't* predict motion, it should trail (as in, that's what seems more natural).

If it fires at the end, you get this:
====| so the blur is behind them.

Anonymous

Anonymous Fri 21 Nov 2008 11:50:00 No.297953 Report

Quoted By: >>298087

So what do you do with these dolls? Do you play with them or what?

And do you hide in a closet when you have people over?

Anonymous

Anonymous Fri 21 Nov 2008 21:15:00 No.298087 Report

Quoted By:

>>297953
People?

Anonymous

Anonymous Fri 21 Nov 2008 21:30:00 No.298092 Report

Quoted By:

First time I fired my camera too fast for the flash I thought I broked my camera

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