Overexposure Problem - DPChallenge Forums

Canon EF-S 18-55mm f/3.5-5.6

04/15/2004 11:46:43 AM · #1

THIS PHOTO is overexposed and I can't figure out why... Here is the exif data:

File: CRW_4336.CRW
File size: 6,676KB
Image Serial Number: 143-4336
Camera Model: Canon EOS 10D
Camera serial number: 1020300016
Firmware: Firmware Version 2.0.0
Date/Time: 2004:04:14 13:10:00
Shutter speed: 1/200 sec
Aperture: 1.8
Exposure mode: Av
Flash: External E-TTL
Flash EF guide number: 2047.97
Flash exposure compensation: -1
Metering mode: Evaluative
Drive mode: Continuous
ISO: 100
Lens: 50.0 mm
Focal length: 50.0mm
AF mode: One-shot AF
Image size: 3072 x 2048
Image quality: Raw
White balance: Auto
Color space: sRGB
Saturation: Normal
Sharpness: Normal
Contrast: Normal
Tone: Normal
Custom Functions:
CFn 15: Shutter curtain sync: 2nd-curtain sync

I shot this with my 50mm f/1.8 lens at f/1.8. I was using the 420ex flash with the omnibounce and FEC set to -1. I tried several of these with the flash and overexposed all of them. I was shooting in aperture priority. I'm looking for ideas about why my camera's metering and e-TTL flash metering would not have handled this shot properly...

General

Kodak Z7590

04/15/2004 11:53:00 AM · #2

Not sure but it due to 2nd-curtain sync

Message edited by author 2004-04-15 11:57:09.

Olyuzi

Panasonic Lumix DMC-GX7

Panasonic Lumix G 14mm F2.5 ASPH

04/15/2004 11:55:45 AM · #3

Hard to tell what the ambient lighting was but I'll take a guess and say that the cameras evaluative metering was confused by dappled lighting of the forest of the background and the difference with your subject in the foreground. Did you try partial metering off of your model's skin?

Message edited by author 2004-04-15 11:56:26.

RHoldenSr

Canon EOS-5D

Canon EF 70-200mm f/4.0L USM

04/15/2004 11:56:40 AM · #4

Judging by the bright sunlight condition I would say the shutter speed was to slow for the F1.8. Seems to me that F1.8 is going to suck up a lot of light at 1/200s.

Shutter speed: 1/200 sec
Aperture: 1.8

I don't see the line that actually says the flash was fired?
Did you fire the flash also?

Flash: External E-TTL
Flash EF guide number: 2047.97
Flash exposure compensation: -1

Canon EF 17-40mm f/4.0L USM

04/15/2004 11:57:20 AM · #5

I'm thinking that my flash could not adjust downward enough for the available light to provide proper fill flash... I can't think of any other reason it's overexposed.

jimmythefish

Canon EOS-10D

04/15/2004 12:16:23 PM · #6

Nothing more than overexposing as a result of 1/200th at f/1.8. It has nothing to do with the flash. You're overexposing your ambient shot, adn the flash is just kicking you when you're down. Try high-speed sync with a manual exposure or, better yet, stop down a bit as well.

sn4psh07

Canon EOS-10D

04/15/2004 12:34:17 PM · #7

I can only think of two possibilities, the less likely first: --

1) Canons E-TTL metering has a lot of problems if you do not use the centre AF square, this has been corrected with version two. Version two of e-TTL is only available in the 1D mark 2 however.

2) there was too much ambient light, I know others have already pointed this out. I am not sure if the 420 EX supports super focal plane mode, but if it does then use that as it supports higher shutter speeds. The 10D has a maximum flash sync speed of a 200th of a second unless you are in super focal plane mode. The flipside of this situation is that you may have set a custom function (I can't remember which one) which automatically sets your shutter speed to a 200th of a second when using the flash.
Either way this would be the most likely problem.

I hope this in some way helps you.

Edit -- corrected typo.

Message edited by author 2004-04-15 12:35:22.

dwoolridge

04/15/2004 12:39:54 PM · #8

You have to put the flash in high-speed sync mode for (bright) daylight fill flash.

You may also have to change a custom function so that the shutter isn't restricted to 1/200th in aperture priority mode.

willem

Sony Alpha a6700

Sony E 18-135mm f/3.5-5.6 OSS

04/15/2004 12:44:57 PM · #9

Sunny F16 rules says you should use 1/100 F16 at ISO 100.

Cloudy ? Open up 2 stops.
In shadow or heavy overcast adjust approx 3 stops.

In your case : ISO 100, 1/200 S requires therefore F5.6 or F4, not F1.8

But I guess you knew that ? Your question is probably more why your camera did not make that right choice, is it ?

04/15/2004 12:47:28 PM · #10

You need high speed sync mode enabled. Otherwise your camera won't go faster than 1/200s.

Sunny, outdoors, but under trees, ISO 100 at f1.8 - probably about 1/2000 sec or so.

Av mode only sets exposure for the ambient light -the flash output is ignored for exposure calculation. But without high speed sync, your camera will not go beyond 1/200sec (though it should have flashed the X-sync speed in the displays)

lmeidt4495

04/15/2004 01:06:56 PM · #11

I have a 10D and I have to shoot at -1/2 to keep from overexposing most of the time. But I see from your imges that you either don't have the same problem or you work around it.

Message edited by author 2004-04-15 13:16:45.

04/15/2004 04:13:28 PM · #12

Originally posted by willem:

Yes.. I have some investigation to do. I'm conflicted now about how my camera operates. Normally, when I have my flash on and the required shutter speed is faster than 1/200, I get a flashing icon warning in the viewfinder. I didn't get this for these shots. The only thing out of the ordinary that I need to test for is the fact that I had a custom function set for 2nd curtain sync that I forgot to change back before i started shooting.

I'm being told that my camera is limited to 1/200" in A priority mode which is news to me. I don't use the flash much outdoors, but having it on the camera could be limiting me to 1/200". I shoot a LOT in aperture priority mode and I am used to seeing my flashing icon warning when the shutter speed is faster than the sync speed.

I need to do these tests:

1. find a bright scene
2. set up for f/1.8 with the 50mm lens
3. shoot the scene
4. put on the flash
5. try it again

Results in a while...

dwoolridge

04/15/2004 04:20:56 PM · #13

Originally posted by jmsetzler:

I shoot a LOT in aperture priority mode and I am used to seeing my flashing icon warning when the shutter speed is faster than the sync speed.

I'm not sure if the 2nd curtain sync setting affects that, but if Cf.6 (on the D60) is set to fixed, you won't get the flashing icon warning. You'll only get it if it's set to auto.

Edit: It's Cf.3 on the 10D.

Message edited by author 2004-04-15 16:22:19.

Canon EF 24-70mm f/2.8L USM

04/15/2004 04:31:13 PM · #14

Test 1
A Priority
ISO 100
f/1.8
1/1000"
No Flash

Test 2
A Priority
ISO 100
f/1.8
1/200
With Flash

(The flash did indeed limit me to 1/200" which I was unaware of until now)

Test 3
A Priority
ISO 100
f/1.8
1/1500
With Flash (Hsync)

In the original shot in this thread, my camera probably did warn me because it did in this example. I just probably didn't notice it.

kiwiness

Canon Canon 1d x Mark II

04/15/2004 05:14:04 PM · #15

Originally posted by Gordon:

I've only found out about this recently and have been experimenting a little with the X-sync speed mode! I am quite surprised at the quality of portrait shots I can get with 1/2000sec even 1/4000 sec in sunny conditions.

jimmythefish

Canon EOS-10D

Canon EF 17-40mm f/4.0L USM

04/15/2004 05:44:22 PM · #16

no self-respecting portrait photographer would dream of a daytime portrait without fill flash!

Originally posted by kiwiness:

Originally posted by Gordon:
You need high speed sync mode enabled. Otherwise your camera won't go faster than 1/200s.

Sunny, outdoors, but under trees, ISO 100 at f1.8 - probably about 1/2000 sec or so.

Av mode only sets exposure for the ambient light -the flash output is ignored for exposure calculation. But without high speed sync, your camera will not go beyond 1/200sec (though it should have flashed the X-sync speed in the displays)

I've only found out about this recently and have been experimenting a little with the X-sync speed mode! I am quite surprised at the quality of portrait shots I can get with 1/2000sec even 1/4000 sec in sunny conditions.

Message edited by author 2004-04-15 17:44:42.

kiwiness

Canon Canon 1d x Mark II

Canon EF 24-70mm f/2.8L USM

04/15/2004 05:50:45 PM · #17

Originally posted by jimmythefish:

no self-respecting portrait photographer would dream of a daytime portrait without fill flash!

I have always used fill flash, but never in X-sync mode.... always learning something new :)

jimmyn4

Canon EOS-7D

Sigma 24-70mm f/2.8 EX Aspherical DF for Canon

04/15/2004 05:58:09 PM · #18

Just out of curiosity the exif data notes that you were using the evaluative meter setting. Couldn't that effect overexposure as well?

04/15/2004 06:43:05 PM · #19

Originally posted by jimmyn4:

Just out of curiosity the exif data notes that you were using the evaluative meter setting. Couldn't that effect overexposure as well?

In Av mode, it is going to do evaluative metering, for the ambient light - so basically sunny 16, outdoors, with an average scene - that gives the 1/1000ish results John saw in his later tests.

With the flash on, in non-high speed mode, the camera is fixed to the X-sync speed or slower, so it'll pick 1/200 to 30 seconds. It needs to do 1/1000th.

So with the f-stop fixed at 1.8, and the shutter speed fixed at at most 1/200, the camera did the best it could - 1.8 at 1/200s blowing everything out.

It begs the obvious question - why not always use high speed sync mode.
Reason is the flash is used quite differently in HS mode - continually firing at a lower power, throughout the entire shutter travel time. In normal mode, you get one, very short (1/10,000s or so) high power pulse of light, which shuts off when the exposure is 'done' based on the required flash output. This then lets you stop motion, use first or second curtain sync creatively etc.

If you use HS mode, you don't get the same motion stopping effect (though its still a relatively short 'light period' 1/200s to 1/4000s, depending on ambient light, but also the power control has to modulate across the entire time the shutter is open (to avoid shadowing) but can't so easily predict when to 'shut off' (i.e., you need x amount of power in y time - but you don't know x in advance, but you do need to provide it continually for y - basically impossible to 'solve', unless you FEL, which can help) This often means that in HS mode, the power output is a lot lower.

I think I have a reasonable understanding of this, but feel free to better explain the power output calcuations for HS mode, as I'm a bit sketchy on it (as is probably obvious)

Sigma 24-70mm f/2.8 EX Aspherical DF for Canon

04/15/2004 06:45:20 PM · #20

Incidentally - this is about the one situation where the higher lowest ISO on the Nikon D70 might be an issue, though it is has a higher X-Sync speed (1/500s I believe) and obviously a higher max shutter speed (1/8000) compared to the canon bodies. The higher x-sync basically puts you back in the same situation as with the canon bodies, I believe ISO 100, 1/250s at any fstop is the same as ISO 200, 1/500s, for the same fstop.

jimmyn4

Canon EOS-7D

04/15/2004 07:19:25 PM · #21

Originally posted by Gordon:

Originally posted by jimmyn4:
Just out of curiosity the exif data notes that you were using the evaluative meter setting. Couldn't that effect overexposure as well?

In Av mode, it is going to do evaluative metering, for the ambient light - so basically sunny 16, outdoors, with an average scene - that gives the 1/1000ish results John saw in his later tests.

With the flash on, in non-high speed mode, the camera is fixed to the X-sync speed or slower, so it'll pick 1/200 to 30 seconds. It needs to do 1/1000th.

So with the f-stop fixed at 1.8, and the shutter speed fixed at at most 1/200, the camera did the best it could - 1.8 at 1/200s blowing everything out.

It begs the obvious question - why not always use high speed sync mode.
Reason is the flash is used quite differently in HS mode - continually firing at a lower power, throughout the entire shutter travel time. In normal mode, you get one, very short (1/10,000s or so) high power pulse of light, which shuts off when the exposure is 'done' based on the required flash output. This then lets you stop motion, use first or second curtain sync creatively etc.

If you use HS mode, you don't get the same motion stopping effect (though its still a relatively short 'light period' 1/200s to 1/4000s, depending on ambient light, but also the power control has to modulate across the entire time the shutter is open (to avoid shadowing) but can't so easily predict when to 'shut off' (i.e., you need x amount of power in y time - but you don't know x in advance, but you do need to provide it continually for y - basically impossible to 'solve', unless you FEL, which can help) This often means that in HS mode, the power output is a lot lower.

I think I have a reasonable understanding of this, but feel free to better explain the power output calcuations for HS mode, as I'm a bit sketchy on it (as is probably obvious)

I'm confused now, I just checked my camera out and I was able to change metering modes in Av. Sorry, I just don't understand. I always thought most people used the center weighted mode? I don't really understand the other stuff you guys are talking about so excuse my inexperience.

EddyG

Canon EOS-1D Mark II

Canon EF 70-200mm f/2.8L IS USM

04/15/2004 07:57:00 PM · #22

Do you have C.Fn 03 set to 1? This locks 1/200th shutter speed in Av mode which is great for exposing in low-light situations (since normally Av meter meters for ambient, and uses the flash for fill.)

Quoting from here:

Side note: Option 1 shuts off the camera's exposure meter, and can cause massive overexposure if used in bright daylight. Be Careful!

BTW, I always have my flash set to "high speed sync"; tests have shown that at speeds below 1/200th, the flash functions "normally", so there is no reason not to leave it set that way as far as I can tell...

Message edited by author 2004-04-15 20:03:41.