How does this happen?

[Laurie]

Why is the 2nd image darker, even though it has a higher ISO and exactly the same aperture, and shutter speed.
My only guess is that even though it says the flash fired, it didnt recycle fast enough and never went off


<a href="http://www.flickr.com/photos/thefonz/384479321/" title="Photo Sharing"><img src="http://farm1.static.flickr.com/70/384479321_640ba2167b.jpg" width="500" height="332" alt="DSC_9672" /></a>
EXIF:
Exposure: 0.002 sec (1/500)
Aperture: f/5
Focal Length: 50 mm
ISO Speed: 1600
Exposure Bias: 0/6 EV
Flash: Flash fired, auto mode


<a href="http://www.flickr.com/photos/thefonz/384479322/" title="Photo Sharing"><img src="http://farm1.static.flickr.com/153/384479322_a0874b82ec.jpg" width="500" height="332" alt="DSC_9673" /></a>
EXIF:
Exposure: 0.002 sec (1/500)
Aperture: f/5
Focal Length: 50 mm
ISO Speed: 200
Exposure Bias: 0/6 EV
Flash: Flash fired, auto mode

I also realise these photos arent v-good. I didnt get very many good ones
anywho

[gstark]

Laurie,

I'm confused.

You're asking why the second of these is darker, but it's the first one here, as presented, that's the problematic one.

So ... I'm going to try a couple of edjakated gesses here ...

The first image as presented was, in fact, the second of the two images that you made, and that these were shot over a very short space of time, and with the camera's ISO setting on auto-ISO.

If I'm correct in those assumptions, then the camera, at ISO 200, has used a fair bit of flash power to make the first image. It's fine.

Taking the second image very quickly after making the first, though, didn't provide enough time for the flash to recycle, so the camera bumped the ISO to the maximum (1600) but there still wasn't enough light to do the job. Hence it's underexposed.

Because both of these images have the same EV settings (1/500 and f/5) I'm also going to say that you shot them with the camera in manual mode, which in this case, for your settings, probably worked against you to: with a shutter speed of 1/60 you may have been able to rescue something in the first image (as presented)

[Laurie]

Sorry Gary,
I edited the post and put the 2nd image (which is now the first one) first and forgot to change my original post

i am asking why the first image (the darker one, DSC_9673) is dark with the same settings.
These were shot in Manual Mode (not sure why lol)
sorry for the confusion

[gstark]

No problems, Laurie.

How are the rest of my assumptions then?

[Laurie]

No problems, Laurie.

How are the rest of my assumptions then?

I would have no idea. but they sound possible.
however the first photo listed, was the first photo taken!
so the sb800's must of fired.

[beetleboy]

I'd say Gary is spot on here - at ISO 1600 you would see something if the flash fired (at f5) so I'm thinking it didn't actually fire but the camera thinks it did?

Bottom line is; the flash definitely didn't fire in the darker shot.

[Steffen]

Taking the second image very quickly after making the first, though, didn't provide enough time for the flash to recycle, so the camera bumped the ISO to the maximum (1600) but there still wasn't enough light to do the job. Hence it's underexposed.

The flash not having recharged in time would be my guess, too. However, you raise an interesting issue: does auto-ISO take into account the fact that the flash wasn't ready at the time of exposure? That would be a cool (if unexpected) feature.

Also, at 1/500s the flash would have operated in FP-sync mode during the first shot, which would have sucked the capacitor totally dry. The second shot, again in FP-sync mode, wouldn't have had a chance without a fully recharged flash.

I found FP-sync mode quite treacherous recently. If you don't watch it the camera cranks the shutter speed up above flash-sync speed and you end up with hugely reduced flash power. I reckon I'll change that on my camera and will enable FP-sync only when required.

Cheers
Steffen.

[beetleboy]

Doesn't the D70s sync up to 1/500th? I thought it did?

[Steffen]

Wow, does it? I didn't know. That would be cool! How do they do that, a combination of mechanical and electronic shutter?

Cheers
Steffen.

[beetleboy]

Yup..electronic shutter.

http://www.dpreview.com/reviews/nikond80/

Shows the D80 is 1/200th compared to 1/500th of the D70s..D80 only has a mechanical shutter.

[Yi-P]

I think D70 is one of the cameras nowadays that can sync up to 1/500 without using FP sync.

[gstark]

Taking the second image very quickly after making the first, though, didn't provide enough time for the flash to recycle, so the camera bumped the ISO to the maximum (1600) but there still wasn't enough light to do the job. Hence it's underexposed.

The flash not having recharged in time would be my guess, too. However, you raise an interesting issue: does auto-ISO take into account the fact that the flash wasn't ready at the time of exposure? That would be a cool (if unexpected) feature.

Laurie has clarified the situation regarding these images, ans stated that the darker image was in fact the first one taken.

In that instance, I'm wondering if the flash had actually had a chance to fully charge before making the exposure?

Steffen, to answer your question regarding ISO, to some extent, I think the answer will be yes, but probably not for the immediately obvious reasons.

Consider the purpose of the pre-flash - to help determine exposure. If the pre-flash doesn't sense enough light, it could probably adjust ISO as required, trying to make the best of things. The problem here is that the ISO is the only part of the EV equation that the camera can change, because the aperture and shutter were manually set to their respective values, and from what we're seeing, there was very little power available for the exposure in the flash.

[gstark]

Doesn't the D70s sync up to 1/500th? I thought it did?

It syncs at all shutter speeds.

Up to 1/500 it's mechanical, using the tradtional two curtain shutter in front of the sensor. At speeds faster than 1/500, there's an electronic shutter built in to the sensor, and that is used.

But there's a few hoops you need to jump through to use those features. For instance, the default sync speed in the various auto exposure modes is 1/60. IIRC, to use the SB800 and D70 and have it sync at one of the faster speeds requirees you to use a manual shutter speed setting (as Laurie has done) and then blank off one of the extra connections in the hotshoe.

[beetleboy]

Doesn't the D70s sync up to 1/500th? I thought it did?

But there's a few hoops you need to jump through to use those features. For instance, the default sync speed in the various auto exposure modes is 1/60. IIRC, to use the SB800 and D70 and have it sync at one of the faster speeds requirees you to use a manual shutter speed setting (as Laurie has done) and then blank off one of the extra connections in the hotshoe.

RE your last statement Gary; to clarify for some people - you can sync up to 1/500 (with the camera in M mode) without covering any extra connections but if you want to go above that (and not use FP-Sync) then you need to do the connection trick!

[gstark]

Liam,

Yes, exactly. Thank you.