A Question About Light

[canonloader]

In the last few years, I have noticed some differences in how well my lenses work here, in relation to summer or winter. I live on or close to Latitude 45 North. It's my thought that at the summer solstice, you not only get more hours of sunlight, but because it is at a higher angle, the light is stronger. Now fast forward to Winter solstice, not only do you get less hours of sunlight per day, but it is weaker, because the angle is far lower.

In short, because winter sunlight may look just as bright, it really isn't. So, for sake of arguement at Summer solstice, a shot that is perfectly exposed at ISO 200, f/8 and 1/200th of a second, would be way under exposed at Winter Solstice?

So, in point of fact, the further North or South you live from the equator, the faster the lenses you need to buy for good shooting? :mrgreen:

[Cyth0n]

I know that the sunny 16 rule is more like the sunny 8 rule in Britain.

[canonloader]

If I had a ligth meter, I would test the light and keep a record of it, but as it is, it's just a guess. But it sounds logical. :)

[tzalman]

I know that the sunny 16 rule is more like the sunny 8 rule in Britain.
Oxymoron?

[[Hyuni]]

^
haha that's exactly what I was going to say!

To the OP, sounds logical, but in reality it probably wouldn't be much of a drastic change.
There's just too many variables to say that it would be the case. I know that air pollution is worse in the summer than in the winter.

[20droger]

A Liverpudlian friend assured me that they have several nice days a year.

[number six]

A Liverpudlian friend assured me that they have several nice days a year.

A friend from Newcastle was ecstatic one year because summer came on a Saturday.

:p

[20droger]

Actually, the sunlight in winter is virtually identical in strength to the sunlight in summer, when measured at right angles to the angle of incidence. The difference comes over large areas, such as the ground, where the average angle of incidence is at a greater angle from the perpendicular in winter than it is in summer.

However, since subjects are rarely lying flat on the ground, the exposure is a function of the subject relative to the angle of incidence.

And it's not the equator that matters, but the zenith relative to the sun at the moment in question. The sun may be at zenith anywhere between the Tropics of Cancer and Capricorn, approximately latitudes 23½° North and South.

[canonloader]

The difference comes over large areas, such as the ground, where the average angle of incidence is at a greater angle from the perpendicular in winter than it is in summer.
When the angle is lower, each photon has to go through more air. But I have also read that when the angle is lower, the light is spread out more, as the light from a flashlight with a wide angle diffuser would be, compared to a spot beam. It all comes from the same bulb, but is diffused or concentrated. On the earth, the winter angle acts as the duffuser.

[Cyth0n]

I've found that here in the UK, winter sun photos look much less harsh and flat than summer sun photos. I can't find any photos that prove the point though.

[John_B]

canonloader,
Well in winters on this side, the air is usually much dryer then warmer months. Humidity does affect sunlight so it may help equal it a bit?

Warmer months are usually a bit warmer in colors because of pollution/humidity (even in the wooded mountain areas) and heat waves not to mention a lot more colors from growth ;)

[canonloader]

I'm going to keep my eye out for a light meter. I want to test this myself. :)

[20droger]

Actually, more air does absorb more light. So in theory, winter air should be a tad less bright. This is offset almost exactly in the northern hemisphere, however, because the Earth is slightly closer to the sun. The solar constant remain pretty much the same in both summer and winter.

The southern hemisphere gets a double whammy, however, and does have a lower solar constant in winter. Whether it's enough to be noticeable, I dunno, but I suspect not.

Seasonal pollution is another matter entirely. Here in southern Arizona, we get haboobs in the months leading up to the monsoon. One haboob can have a severe impact upon the quality of light for weeks thereafter. Once the monsoon hits, the air is washed and everything becomes visibly brighter and cooler (no relationship to actual temperature, which can still be well over 100°F).

I would suspect that the dimmer winter in the U.K. is more due to very high thin cirrostratus clouds than to the amount or angle of the sunlight.

[tzalman]

Actually, more air does absorb more light. So in theory, winter air should be a tad less bright. This is offset almost exactly in the northern hemisphere, however, because the Earth is slightly closer to the sun. The solar constant remain pretty much the same in both summer and winter.

The southern hemisphere gets a double whammy, however, and does have a lower solar constant in winter. Whether it's enough to be noticeable, I dunno, but I suspect not.

Seasonal pollution is another matter entirely. Here in southern Arizona, we get haboobs in the months leading up to the monsoon. One haboob can have a severe impact upon the quality of light for weeks thereafter. Once the monsoon hits, the air is washed and everything becomes visibly brighter and cooler (no relationship to actual temperature, which can still be well over 100°F).

I would suspect that the dimmer winter in the U.K. is more due to very high thin cirrostratus clouds than to the amount or angle of the sunlight.

Haboob? You ain't seen nothin' 'til you try one of ours:
http://photos.imageevent.com/elied/coast/huge/1_1384_filtered.png

[nwa2]

I tested my 40D last summer in Scotland when I first got it against the sunny 16 rule. Exposure was spot on compared to the matrix meter recommendation.

[20droger]

Haboob? You ain't seen nothin' 'til you try one of ours:
Oh, I dunno about that. We had a little haboob last year that dropped visibility to about 4 feet. And we had the multi-car pile up to prove it.

We often get mini-haboobs when some jokers are tearing through the underbrush in their ATVs too close to a major road, 200 yards of zero visibility is such fun at freeway speeds.

And what I really love is when a haboob comes just before a cloudburst, and it rains mud.