Lighting and simply physics

Garry Edwards

Garry Edwards

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Garry Edwards
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Do you groan when you hear 'physics'...?
I was having a conversation today with someone who simply didn't realise that the reason I'm able to work so quickly in the studio and hardly ever need to adjust my lighting (much) is because my whole approach is physics-based.
to be more specific, it's all about the practical application of Newton's Inverse Square Law, which affects not just how much light reaches the subject but also how much light reaches the various parts of the subject, how it affects the background, how it affects the softness or otherwise of the lighting and so on.

And the fact that when we understand the technical aspects (of anything) to the point where we don't need to think about them, we have the capacity to be creative, because no energy is being expended on technical aspects - just as an experienced driver can watch the road without thinking about changing gear.

So, the question is this.
If I can make a good job of explaining simple principles in a simple way in a video, will people watch it and learn from it?
Or will the subject matter kill the view numbers?

Edit: I'm better at physics than typing: The title sould say simple, not simply:)
 
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Will depend how you pitch it, if you mention physics, some people will run for the hills :)

Better to "lure" them in and then mention the dreaded P word!
 
I would agree with @johnnypanic, mention physics and I would certainly run for the hills, the mere idea leaves me cold. I don't do much studio work but can usually get my lighting where I want and need it [simple] very quickly just based on experience of the kit I use but always happy to learn more. I can hand on heart say I only once tried learning the inverse square law, and rather like physics O-Level at school [which I failed dismally] it left me looking cross eyed and non the wiser. Since then I have always worked by eye and rarely need more than a couple of test shots to be where I want to be [I am sure the tech heads will be drawing sharp breaths at such confessions :LOL: ] but like I say, teach me an alternative way of working in a way I can understand and I will be there.
 
Garry Edwards said:
If I can make a good job of explaining simple principles in a simple way in a video, will people watch it and learn from it?
Or will the subject matter kill the view numbers?
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Anyone who is vaguely interested in learning will watch the video if its pitched right in the title and within 30 secs or so of the intro. Whether they learn from it assuming as noted you've done a good job is down to the viewer, are they a muppet or not ;)
 
I don't know...
For me, knowing about the inverse square law and "how it works" as a physics principal didn't help much. It wasn't until I realized that it works exactly like the aperture numbers that it became "functional." Once I learned that all I need is one light source w/ "correct exposure" and I can add/move/set lights with relative ease.
 
I would find it useful but i hate reading and prefer to learn by watching or listening to someone then giving it a go. I have read up on the ISL and think i understanding it but would be good for me to hear an explaination of it and practicle demonstartion of it. (Gary if you run a workshop on it to video it put my name down to attend;))
 
Will look forward to it Gary, i would like to understand it.
 
ding76uk said:
Don't call it photo physics or something like. It will bring up images ou programmes that ran in the night on BBC2.

Karl Taylor has already done something similar

http://petapixel.com/2014/07/01/inverse-square-law-light-explained-simple-terms-photographers/

If it got much more complicated than that then it would turn a lot of people off.
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Thanks for that, I've now watched it. Basically that video is about the quantity of light, but the ISL also dramatically affects the quality of light, so if I do this I want to concentrate on that angle.
James83 said:
I would find it useful but i hate reading and prefer to learn by watching or listening to someone then giving it a go. I have read up on the ISL and think i understanding it but would be good for me to hear an explaination of it and practicle demonstartion of it. (Gary if you run a workshop on it to video it put my name down to attend;))
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Well, if we do run with this I will probably invite people along.
 
Garry Edwards said:
Thanks for that, I've now watched it. Basically that video is about the quantity of light, but the ISL also dramatically affects the quality of light, so if I do this I want to concentrate on that angle.

Well, if we do run with this I will probably invite people along.
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I think a "general discussion" on the topic could be helpful but I think it has to be kept "less technical;" because technically, most of the information out there is "wrong."
Photographer's lighting is not a point light source, it's a "collection" of point light sources so the inverse square law doesn't work exactly... especially at the short distances modifiers are ideally suited for (it becomes more of an "inverse double law").
And modifiers do not make your light source "larger," they break the light into "a larger collection" of point light sources; which further contradicts the inverse square law...
These things dictate what light source is chosen, what modifiers are used, and how they are placed... but I don't really know how to explain it in a way that won't cause the internet to irrupt in a furor (I've tried).
 
sk66 said:
I think a "general discussion" on the topic could be helpful but I think it has to be kept "less technical;" because technically, most of the information out there is "wrong."
Photographer's lighting is not a point light source, it's a "collection" of point light sources so the inverse square law doesn't work exactly... especially at the short distances modifiers are ideally suited for (it becomes more of an "inverse double law").
And modifiers do not make your light source "larger," they break the light into "a larger collection" of point light sources; which further contradicts the inverse square law...
These things dictate what light source is chosen, what modifiers are used, and how they are placed... but I don't really know how to explain it in a way that won't cause the internet to irrupt in a furor (I've tried).
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Well, you're right about that and there seem to be some people who don't seem to realise that Newton wasn't actually talking about photographic lighting back in 1687:)
I think that explaining it in technical terms is unnecessary and will only lead to 'experts' disagreeing.
I once tried to explain it to a student who was one of these 'creative' photographers who didn't see the point of understanding the basics, but although she didn't see the point, she did think that I had got it all wrong. When I tried to explain it more, she suggested that there were no right or wrong answers and that it was all a question of degree - I ended that conversation by agreeing with her about that, and pointing out that I had a degree and she didn't:).
What needs to be done is to explain the enormous benefits of applying its broad principles to studio photography, and I think I can do that easily enough.
 
sk66 said:
I think a "general discussion" on the topic could be helpful but I think it has to be kept "less technical;" because technically, most of the information out there is "wrong."
Photographer's lighting is not a point light source, it's a "collection" of point light sources so the inverse square law doesn't work exactly... especially at the short distances modifiers are ideally suited for (it becomes more of an "inverse double law").
And modifiers do not make your light source "larger," they break the light into "a larger collection" of point light sources; which further contradicts the inverse square law...
These things dictate what light source is chosen, what modifiers are used, and how they are placed... but I don't really know how to explain it in a way that won't cause the internet to irrupt in a furor (I've tried).
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We've had this debate on here before, and strictly speaking the inverse square law only applies to a point light source suspended in a vacuum or something. But as a working rule of thumb it works pretty well with studio lighting.

For example, if you take a typical softbox and measure the brightness at 1.0m, at 2.0m it will have dropped by around 1.5-1.8 stops (depending on the environment/room etc) and in practical terms that's pretty close to the 2.0 stops you'd get with the ISL strictly applied.

If you test it with a smaller light source, it will follow the ISL very closely. Bear in mind that when calculating exposure using guide numbers with a speedlite, GNs use the ISL.

The other thing is the ISL changes the effective size of the light source according to distance, eg move a softbox back and the light gets harder. That effect follows the ISL exactly.

TBH, I think that's pretty much all you need to know about the ISL, and while it's essential knowledge and the ISL is always at work, it's really not hard to understand and use. In practice it can be made even more simple: eg "studio flash exposure is very sensitive to distance, and small changes have a much greater effect than you might expect."
 
I broadly agree, and if I go ahead with this then my angle will be very much that small changes of distance create big changes in effect, I think that relatively few people appreciate that fact, most people already know that the light loses intensity over distance but they don't necessarily appreciate how much difference a change of distance makes to the lighting of a 3 dimensional subject (at close distances).
 
Garry Edwards said:
Thanks for that, I've now watched it. Basically that video is about the quantity of light, but the ISL also dramatically affects the quality of light, so if I do this I want to concentrate on that angle.
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Bin the word physics and call it 'The Science and Art of Lighting'
 
It is my understanding that the ISL effects the quantity of light and the ratio of light source size to subject size effects the quality of light. Works for me.
 
Broric said:
I'd find it very useful

Disclaimer: I have a PhD in Physics
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I take that as a massive compliment, your qualifications are way ahead of mine
 
DemiLion said:
Bin the word physics and call it 'The Science and Art of Lighting'
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I had this thought too. I had to study some physics as part of my job and although I didn't overly enjoy it, understanding rather than recall/knowing is better.

I thought about calling it "the science behind the magic" but probably because of the great book I'd previously read!
 
HoppyUK said:
We've had this debate on here before, and strictly speaking the inverse square law only applies to a point light source suspended in a vacuum or something. But as a working rule of thumb it works pretty well with studio lighting.

For example, if you take a typical softbox and measure the brightness at 1.0m, at 2.0m it will have dropped by around 1.5-1.8 stops (depending on the environment/room etc) and in practical terms that's pretty close to the 2.0 stops you'd get with the ISL strictly applied.
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Yes, at distances greater than ~2x the size of the modifier it's reasonably accurate and it works exactly like f/stops. If @ 2 you have a "correct" exposure 2.8 is one stop less.. and 4 is two stops, 5.6 is three, etc, etc.
But, a modifier is "best" when used at a distance roughly equal to it's size. And that's because a modifier doesn't "really" make the light source larger (you're just filling it w/ the existing light spread) but rather a modifier breaks the light into many more point light sources, each with it's own spread. This is what allows it to "see around edges" in order to create "wrap" and "soft light." And it's why, if you want to "straighten out" the light, you need to use grids and not snoots/doors/flags. At these distances the inverse square law becomes less "usable" while placement becomes much more significant.

It's in the "transition zone" where you see the most significant changes in light character/quality with changes in distance (where a modifier transitions from acting more like a point light source and following the ISL to acting like "a collection of point light sources" and not following the ISL).

I don't have a good "rule" for falloff at short distances (I just figure ~1/2 ISL), but at short distances you're not making (relatively) large changes to placement so it's usually more of "a refinement" than "a change."

The other thing is the ISL changes the effective size of the light source according to distance, eg move a softbox back and the light gets harder. That effect follows the ISL exactly.
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The ISL has nothing to do with "hardness," it's just intensity. "Hardness" is affected by how "parallel" the light is when it hits the subject. I.e. acting more like a point light source with more parallel rays, or "a collection of point light sources" each with their own spread. (The further away you move "a collection of point light sources" the more they intermix before they reach the subject, which more closely resembles a point light source; which is why it more closely follows the ISL and becomes "harder.") A point light source will be just as "hard" regardless of it's distance (i.e. it will never be able to "see around edges" and "wrap"). And when you make changes to the distance of a source being used at relatively large distances it will have little/no affect on the "quality" of the light... in fact, using a modifier and the type of modifier becomes relatively insignificant (other than focus/spread).

I'm guessing it's these things (transition/short distance) that Gary wants to show (?) but the tie to the ISL is hard for me... in fact, the whole "modifiers make lights larger" and "distance makes the light smaller" things are hard for me because they are "wrong." But the ISL, size, and distance things are "close enough" that they generally work and it's what everyone knows/says. But, IMO, they are just "wrong enough" to be misleading and cause "confusion." It's "why" few people understand how significant distance is, and it's why people think a 24" softbox 6ft away is "good lighting."

It took me a long time to understand this... I don't have a PHD in anything...
Gary, if you could find a way to explain/demonstrate this in a way that is technically accurate and clears up the confusions I think it could be a big benefit to most... I've tried explaining how distance and the transition between "point light source" behavior and "collection of light sources" behavior are what really affects the quality of light with little success... Maybe you can do better.
Once I understood that it's not "larger size" but rather it's "a larger collection of light sources" everything made obvious sense... what the different modifiers do and how/why (shoot thru/bounce/softbox/grid/doors/etc, etc) and why distance matters so much (or doesn't).
 
I agree with your first sentence Steven, but I'm sorry to say, not much else. And you're making this way, way too complicated.
 
Garry Edwards said:
I take that as a massive compliment, your qualifications are way ahead of mine
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I understand the physics, the inverse square law, etc but the practical application and how it actually changes a photo is still very useful to see.
 
Just call it lighting Tricks That work.

The inverse square law is certainly helpful. However it has its limitations when considering focussed or modified light.
it is not something I bothered much about with studio lights. ratios become very much automatic the more you move lights around, till you reach the point when you can just place them.

I loved the old 3K and 5K spot lights... you just put them where they cast the right shaped shadow texture and form, flooded them as necessary, then used a giant rheostat to get the right light level. .. colour spoiled all that. and you could make toast at the same time.
 
HoppyUK said:
I agree with your first sentence Steven, but I'm sorry to say, not much else.
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I'm not surprised...
And you're making this way, way too complicated.
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Probably... at least in trying to explain it. Application is easy enough though (same stuff, just slightly different reasoning).
 
HoppyUK said:
I agree with your first sentence Steven, but I'm sorry to say, not much else.
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Let me see if I can make it easy to understand visually. If you cover half of a softbox does the result look like a large softbox flagged off (hard delineation) or does it just look like a smaller softbox? It looks like a smaller softbox; and that's because that's what it is. And the same is true for every point/area along the surface.

To keep it simple I'll divide a softbox into only three sections and consider it to be perfectly diffused.
In this first example the softbox is placed close to the subject. And each of the three sections has it's own fan of light hitting the subject.
8464-1412439818-197b9c8f82616d7e0ad432087c3baf5d.jpg

Due to the varying distances we create a difference in illumination and contrast. This follows the inverse square law, but it's for every point on the surface, not the modifier as a whole. The middle section will be one stop less, and the furthest section will be 2 stops less (oversimplified). The furthest section also has the greatest angle which allows it to "see around" the side creating more wrap. If I don't want the wrap I need to flag off the spill...and that's what a grid does. A grid is basically dividing the surface into many smaller softboxes and flagging them individually (w/ a tighter grid being more effective).

In this next image I have moved the subject further away.
8465-1412439827-6b26444ec71aa31fd405513b27367554.jpg

Now the differences in distance are much less significant and the angles are much smaller. The softbox is now acting more like a single uniform source, and the inverse square law can be applied to it as a whole (because the differences in illumination from the sections is negligible). And because the angles are shallower/more parallel (as seen by the subject) the edges will be harder with less wrap. It is also a lower contrast result. And because there is less angle/wrap a grid would be less effective. In fact, the further away we move it, the more it acts as a single source and the less relevant it becomes to even use a softbox in the first place.

The distance at which it changes from acting as a group of light sources to acting as a single light source is controlled by the size of the modifier in relation to the size of the subject being lit. For it to be "effective" the tree have to be approximately the same (i.e 20" softbox lighting a 20" subject from 20" away). And it will be "much more effective" when the size of the softbox is greater than the other two.
 
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It's not that I don't understand what you're saying Steven, it's more that I disagree with the relevance to a practical understanding of the ISL for newcomers, and to what I imagine Garry intends to be quite a simple video explaining the key aspects.
 
HoppyUK said:
It's not that I don't understand what you're saying Steven, it's more that I disagree with the relevance to a practical understanding of the ISL for newcomers, and to what I imagine Garry intends to be quite a simple video explaining the key aspects.
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Ah, I see. I can't really disagree... as I see it, the application of the ISL and "distance makes the light larger" is oversimplification and "misleading." Might as well leave it as you said:
In practice it can be made even more simple: eg "studio flash exposure is very sensitive to distance, and small changes have a much greater effect than you might expect."
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But for me, understanding the how and why is "better." And if I could have learned all of this in the beginning I think I would have been better off. I made all of the same mistakes as many of buying too small of modifiers, and using them from too far away in a white room, thinking I was accomplishing something.
 
sk66 said:
Ah, I see. I can't really disagree... as I see it, the application of the ISL and "distance makes the light larger" is oversimplification and "misleading." Might as well leave it as you said:

But for me, understanding the how and why is "better." And if I could have learned all of this in the beginning I think I would have been better off. I made all of the same mistakes as many of buying too small of modifiers, and using them from too far away in a white room, thinking I was accomplishing something.
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In principle and in general, I would also opt for some of the why as well as the how, but in this case I would just draw the line at a much lower level than perhaps you would.

And going further into it raises other questions that IMHO just confuse the issue. For example, in your diagram you have a three-dimensional subject positioned to one side of the light. So not only are you are going to get ISL effects going on there, also angle of incidence and cosine law effects too. Then you have a theoretical softbox with perfectly even brightness when they're not like that in practise, so to some extent there will be an off-axis reduction in brightness simply because there's less light coming out of the softbox towards the edges, something of a slight feathering effect.

All that stuff is always happening too of course, but here I think it just confuses what I see as a pretty simple message :)
 
Thanks to everyone for the comments.
Yes, the title will be all-important, certainly we can't mention physics, maths etc. Maybe "The magic of 3D studio lighting" or something along those lines
I think my approach will be to demonstrate the magic of creating depth by varying exposure from front to back of a simple subject (probably a head) with a single light. The effect will be self evident, especially if shot against an unlit white backgroud several feet behind.
And then overlay distances and f/ onto the screen.
The ISL can sort of be referred to in passing at this point, but without labouring it.

I think that complex technical explanations, maths and equasions would just kill interest - people who get what I'm doing can do their own research later if they want to.
 
The effect on the background Garry, as you mention above, I would say is import to illustrate. For example, one of the most common ISL effects is when newcomers have a subject a few feet in front of a white background, and it comes out grey. Then they move the light closer to make it brighter and it gets darker!
 
HoppyUK said:
The effect on the background Garry, as you mention above, I would say is import to illustrate. For example, one of the most common ISL effects is when newcomers have a subject a few feet in front of a white background, and it comes out grey. Then they move the light closer to make it brighter and it gets darker!
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lol

That reminded me of my wee studio days where I had a white paper roll and would confuse the Hell out of people by shooting White to Grey to Black background images on it :D

Dave
 
I would call it "Studio Lighting Demystified".
 
Garry Edwards said:
Thanks to everyone for the comments.
Yes, the title will be all-important, certainly we can't mention physics, maths etc. Maybe "The magic of 3D studio lighting" or something along those lines
I think my approach will be to demonstrate the magic of creating depth by varying exposure from front to back of a simple subject (probably a head) with a single light. The effect will be self evident, especially if shot against an unlit white backgroud several feet behind.
And then overlay distances and f/ onto the screen.
The ISL can sort of be referred to in passing at this point, but without labouring it.

I think that complex technical explanations, maths and equasions would just kill interest - people who get what I'm doing can do their own research later if they want to.
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Sounds good to me...
If there is one thing I think get's underestimated/underemphasized/misapplied a lot is modifier size -vs- subject size -vs- working distance (not even considering reflective convex objects). That and ambient light/spill control.
 
Replying to the original post....

Some will, some won't. I've encountered people on photography forums who don't understand what "inverse" means, and will go out of their way to avoid learning anything. Especially if there's the slightest hint of maths (even an equals sign frightens them).

I personally believe that, as stated above, knowledge is power, and knowing why something happens makes it easier to be in full control. BUT - many people don't want this level of understanding, as they can just shoot, shoot and shoot again with digital until they get it right.

What you need is an audience who actually want to learn; and that might just be the hardest thing to find.

My own disclaimer probably should be a degree in theoretical chemistry, which did involve a certain amount of maths (particularly in quantum mechanics).
 
StephenM said:
Replying to the original post....

Some will, some won't. I've encountered people on photography forums who don't understand what "inverse" means, and will go out of their way to avoid learning anything. Especially if there's the slightest hint of maths (even an equals sign frightens them).

I personally believe that, as stated above, knowledge is power, and knowing why something happens makes it easier to be in full control. BUT - many people don't want this level of understanding, as they can just shoot, shoot and shoot again with digital until they get it right.

What you need is an audience who actually want to learn; and that might just be the hardest thing to find.

My own disclaimer probably should be a degree in theoretical chemistry, which did involve a certain amount of maths (particularly in quantum mechanics).
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I agree. I always try to encourage people to learn, but there's nothing I can do about the people who either don't want to learn or who think that they don't need to, that's their problem, not mine.

Very largely, digital photography HAS contributed to the attitude that knowledge is irrelevant and that all that's needed is a large memory card and PP skills.
My own history is probably very similar to that of most people of my generation, except that I was lucky enough to be sponsored by my employer for a degree course.
As an amateur, starting at age 11 with a folding 620 camera, I had to understand the basics, I couldn't afford to waste film, and didn't want to wait days for the film to be delivered and then find out that I'd messed it up. And later, as a trainee pro, I would have been sacked if I'd wasted materials through ignorance or lack of care - large glass plates were very expensive.
Exposure meters did exist at that time, but they were so insensitive that they couldn't be trusted to give accurate results with artificial light, so we had to rely on a benchmark exposure (e.g. f/11 at distance of 2 feet) and then simply apply the ISL to calculate all other exposures at all other distances, which could get a bit complicated with multiple lights. Then of course we had different surfaces to photograph, different angles too which meant an understanding of cos. The only workaround to that was to shoot a 'polaroid' - except that polaroids didn't exist at that time, except in an amateur format, so we used bromide paper instead. That had an ISO of 0.5 and of course produced a negative, but it helped reinforce the decisions we had calculated using simple maths.

After a while, an understanding of basic physics and maths meant that these calculations became instant, at which point they weren't any kind of a nuisance and having that knowledge enabled us to use it creatively. My view of creative photography is that it has to stem from a technical base because if the technical understanding is there then absolutely no brain power is used on anything other than creativity.. I don't have a lot of time for people who think that all that matters is being creative, because if they turn out good work it's always by accident:)
 
Garry Edwards said:
I agree. I always try to encourage people to learn, but there's nothing I can do about the people who either don't want to learn or who think that they don't need to, that's their problem, not mine.

Very largely, digital photography HAS contributed to the attitude that knowledge is irrelevant and that all that's needed is a large memory card and PP skills.
My own history is probably very similar to that of most people of my generation, except that I was lucky enough to be sponsored by my employer for a degree course.
As an amateur, starting at age 11 with a folding 620 camera, I had to understand the basics, I couldn't afford to waste film, and didn't want to wait days for the film to be delivered and then find out that I'd messed it up. And later, as a trainee pro, I would have been sacked if I'd wasted materials through ignorance or lack of care - large glass plates were very expensive.
Exposure meters did exist at that time, but they were so insensitive that they couldn't be trusted to give accurate results with artificial light, so we had to rely on a benchmark exposure (e.g. f/11 at distance of 2 feet) and then simply apply the ISL to calculate all other exposures at all other distances, which could get a bit complicated with multiple lights. Then of course we had different surfaces to photograph, different angles too which meant an understanding of cos. The only workaround to that was to shoot a 'polaroid' - except that polaroids didn't exist at that time, except in an amateur format, so we used bromide paper instead. That had an ISO of 0.5 and of course produced a negative, but it helped reinforce the decisions we had calculated using simple maths.

After a while, an understanding of basic physics and maths meant that these calculations became instant, at which point they weren't any kind of a nuisance and having that knowledge enabled us to use it creatively. My view of creative photography is that it has to stem from a technical base because if the technical understanding is there then absolutely no brain power is used on anything other than creativity.. I don't have a lot of time for people who think that all that matters is being creative, because if they turn out good work it's always by accident:)
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You started with film Garry ???

I thought few of those cave paintings were yours :D

Dave
 
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