Long exposures

[Fox Paw]

Last week, I attended a class on photographing scenes by moonlight. It lasted three hours. I didn't learn much.

This past weekend, I bought a copy of Popular Phoptography that had an article on the same subject. With regard to determining the exposure, the author recommended testing the exposure at ISO 1600, then adjusting, bearing in mind that exposure time and ISO are reciprocal. Not being very technical, it took me a while to slog through that. I concluded that it should take sixteen times as long at ISO 100. I don't know if I was right, but I took the following test shot in my backyard this evening and it seemed to work. At 1600 (f8) it told me 13 seconds. I did some mental math and exposed for 3'30". It's not a great photo but the exposure seems about right.

http://cornflakeaz.smugmug.com/Other/Very-odds-and-ends/St-Francis-2/920546219_cLxCT-900x900.jpg (http://cornflakeaz.smugmug.com/Other/Very-odds-and-ends/9861833_XicoE#920546219_cLxCT-A-LB)

Anybody know anything more about this?

[KMann]

The photo is entirely fine. I love the molding of light on St Francis. I wonder if there isn't an overall red cast. I'm not sure because I just calibrated this new computer in win 7 and I'm not sure about the driver. Please tell me if St Francis is reddish?

I used to be able to do those sorts of calculations on the fly back in the bad old days but I have lost the knack. I think you're right. The nice thing about digital photography is the fact that there is no film reciprocity to worry over. Isn't that great?????

[Fox Paw]

Yes, it had a color cast. I'm not good at noticing them or identifying what color they are--as you may have noticed :)--but the eyedropper on St Francis made quite a change.

http://cornflakeaz.smugmug.com/Other/Very-odds-and-ends/St-Francis-4/920765953_wNzeT-900x900.jpg (http://cornflakeaz.smugmug.com/Other/Very-odds-and-ends/9861833_XicoE#920765953_wNzeT-A-LB)

One thing I noticed with the shots I took last week at the class was that there were white balance problems with all of them. Maybe a gray card and a test shot with it at 1600 is a good idea.

[KMann]

I really like this photo, Fox. But then, I'm partial to crazy people who like animals best. :)

I wonder what's up with the colour casts. Are you shooting in RGB in your camera? Is it set to something like landscape (which tends to red it seems). Once I had pointed it out you saw the red, so it isn't your eyes. I see it because I trained myself to see it. Worked as a pressman all those years ago, and in book production. Had to see it or get fired.

[Terri]

Interesting. I agree with K that the exposure in the first image is perfectly fine, but the color cast is what throws the image off. I don't shoot digital, but can't imagine that your exposure settings would contribute to the magenta cast. You easily corrected it in the second image, too - removing the magenta but the exposure remains intact throughout the frame.

[KMann]

Terri, Fox's camera has a number of colour correction settings available. Off the top of my head they are: standard, faithful, landscape, portrait, something something. The landscape setting provides a colour boost in greens and reds - a little like Fujichrome. The faithful setting is a lot like Agfa slide film. These settings are carried forward in the metadata and might have contributed to the overall cast of the first iteration of this shot.

Colour cast is often ignored while we're thinking about something else.

[Fox Paw]

"Colour cast is often ignored while we're thinking about something else."

That's what happened here. The camera was set to standard (as always) with automatic white balance, which I use when I don't know what else to set. I was concentrating on figuring out the exposure time for such a long shot.

As I said, the long exposures my class took last week all had white balance oddities. I'm guessing the combination of moonlight and ambient light produces strange colors. It's not hard to fix if you want to fix it. I might or might not, depending on the shot. We usually think of color casts as bad because we're trying to replicate what the eye saw. Here, my eyes couldn't see anything. It was too dark. I wasn't trying to replicate that.

[Matt Needham]

I concluded that it should take sixteen times as long at ISO 100. I don't know if I was right...

You are. 1600, 800, 400, 200, 100 = 4 stops = 2x2x2x2=16

Strange color casts are common with long exposure night photography in my experience. Even though digital doesn't suffer from reciprocity failure like film there are plenty of other things that could affect it. If the moon is at a low angle more of the red end of the spectrum gets through the atmosphere. An artificial light a block away, which you would never notice with your eyes, could be affecting it. Light reflecting off all sorts of urban surfaces can change the color. Also I assume AWB is probably optimized for shorter exposures.

[Matt Needham]

I go to Cambridge In Colour mostly for the technical info, but check out the galleries for sweet moonlight photography.

http://www.cambridgeincolour.com/cambridge-gallery.htm

[ann]

that is the magic of long night exposures, the colors, as our vision just can't see this way.

i would second cambridge site for lots of terrific technical info as well as photos. with so many in cyber land throwing out mis information this is a place i trust.

[Fox Paw]

Matt, thanks for confirmation of the theory and for the link. What kept me away from this kind of photography in the past was that I had no idea how to calculate the exposure time. Now I have an idea!

Some of those photos at the Cambridge site are stunning.

[KMann]

Matt, thank you for the reference. I have enjoyed the photos of Cambridge in the past but failed to notice the excellent information that is included in the site. Wonderful!

[christopher walrath]

You are. 1600, 800, 400, 200, 100 = 4 stops = 2x2x2x2=16

Not to hound this but . . .

ISO100= normal exposure (1)
200 = 2X EXPOSURE
400 = 4X EXPOSURE
800 = 8X EXPOSURE
1600 = 16X EXPOSURE

Look familiar?

[Matt Needham]

This article on long exposures shows an example of a light leak from through the viewfinder. It's always been my understanding that the issue with the viewfinder cover was that light could enter the viewfinder and mess with the metering if in an auto exposure mode. Not that it could actually cause a light leak. I'm going to have to do some testing with my cameras.

http://www.ephotozine.com/article/Shoot-very-long-exposures-14015

[ann]

i have an ir photo i took at 10 secs. the camera was on a tripod using a cable release. i stood at the side of the camera and forgot to close the viewfinder eye piece, and low and behold, there was the sun in the photo. of course it was at my back at the time of the shot :) it did have the grace to place itself in a terrific place. just a gift from the photo "gods"

[KMann]

I'd love to see that ann! what a hoot!

[ann]

if i can figure out how to get it small enough to post i will do so. i seem to have "issues" with posting here, but then perhaps everywhere as i seldom do so. Even my website was handled by another.

Computers have given me grey hair :) of course it has nothing to do with my age !

[KMann]

Oh well, I am partial to grey hair. I have a nice patch myself.