Exposing correctly with a strobe at night

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dixontoby

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Hi there.

I did a shoot the other night of a rugby player diving for the line, freezing in mid air using two strobes on one side of him. It was shot on a d90 with a nissin di8666 flash and a cheap jessops flash (which wasn't important really needed).

Anyway, since it was shot at night, and only part of the player was lit up, the histogram gave little indication to how well exposed the photo was. So i used the LCD on the camera. To me the images were correctly exposed and resolved the required detail.

However, when i got back i found the images on the computer to be under exposed. They required the exposure dial in aperture to be shifted quite far to the right. So basically i am wondering how you expose correctly in such situations? I'm shooting in RAW for the record.

Any advice would be great.

Thanks
 
Did you magnify the view finder 1 to 1? If you do you get a view.
 
Press the play button on your camera to view the image then look down the buttons at the left of your screen for the magnifying glass. This will allow you to get a better view.
 
oh right, yes i've been doing that. as i said, the images appear well exposed. When zoomed in on the viewfinder, highlights seemed correct but everything was very dark back at Aperture.
 
cowasaki said:
How is the histogram?
Click to expand...

In the images with mostly black (of the night) and the person lit (taking up a 1/8 of the frame), the histogram has just a small blip to the left. However when the exposure slider is adjusted in aperture so he is correctly exposed, the histogram only changes fractionally.

On second looking, in the photos where the person takes up more of the frame i blame bad technique since the histogram is more usable than i thought at the time. Do you think its a case of requiring experience about what makes a good histogram given such lighting conditions?

Still not sure how i would expose with a small subject a black everywhere else though.
 
The histogram doesn't lie. If you've got loads of black then it will obviously show a lot of that, but the lighter areas, although small in area and therefore small on the histogram, should still be over to the right.

The LCD image will reflect this (they are generated off the same JPEG created from the Raw) but I'm thinking that maybe if you were viewing at night the LCD looked artificially bright. What does it look like when viewed in normal daylight, or even by good room light?

Have a look here for info on reading histograms http://www.sekonic.com/images/files/HistogramsLightmetersWorkTogether.pdf TBH they can be tricky little blighters sometimes - I posted this link a little while ago and asked who could do the quiz on there and match the images to the histograms, and nobody got them all right!

For that reason, I always have blinkies enabled - the flashing highlight over-exposure warning. Unless you have at least some part of the image flashing, nothing is going to be pure white. In other words, another way of doing it is to crank up the exposure until the blinkies flash, and then back it off a fraction - basically 'expose to the right' technique which means you are optimising exposure and maximising the amount of information recorded on the sensor.

It is very possible to get over-exposed looking images on the LCD in this way, even though they actually are not. But you need to post process them to pull them back down again. The big advantage, and it really does work very well, is that you get maximum separation of highlight detail, plus you pull the shadows out of the mirk so that, even when you have darkened them back down again in post, there is a lot more separation and detail there.

Expose-to-the-right is a great technique for optimising image quality. The danger, and it's a real one, is that you accidentally blow the highlights and they can't be recovered. If you want to practise this, then play with the Picture Styles pre-sets and get to know the limits - adjusting the contrast level particularly makes a difference of at least a whole stop to how far to the right you can go.
 
The picture is what you should be looking at, not the histogram.

How does the histogram know what you want? People place too much emphasis on histogram spread - all it is tellling you is the percentage of pixels at a certain tone...lots of black in the image means lots of left hand side pixels. Big white screen (polar bear on a snow field) and the histogram will tell you everything is white - yes, that's right, with a polar bear on a snow field, it is! Do you know what, there won't be many black pixels either!

If there is a lot of black background the histogram will try to convince you that your image is rubbish and too dark by showing a big bunch to the left.

If the player is correct, then your exposure is fine, provided there are no horrible black holes in his face or anything where the lighting missed or an arm cast a shadow.
 
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