Iso/F-Stop/Shutter Speed Relationships

tl;dr below - better to read the whole thing.

All of these factors do exactly the same thing - control how much light hits the sensor of the camera. In a perfect world, there would be only one setting: "Light level."

Some of them, though, have a subtle bearing on a shot which the others don't necessarily provide.

Aperture controls light. The larger the aperture (smaller number), the more light hits the sensor. It also controls depth of field. A larger aperture gives a shallower depth of field. If that depth of field is important to your shot - as it is for the purposes of coin photography - you have to use the other two factors to get enough light onto the coin. So, for coin photography, you need to find the largest aperture that will give you acceptable depth of field (you use the largest-possible so as to minimize the effect on how much light hits the lens). For dSLR photography, that "magic number" is about f/8. For point-and-shoot photography, more like f/4-f/5./6.

ISO controls light. The faster the ISO speed (higher number), the more light hits the lens. This is usually a factor in sports photography or other times when you want to "freeze" fast action - using a faster ISO lets you use a much faster exposure to get enough light, and those really fast exposures are what you need to freeze action. The tradeoff of faster ISO is greater noise, which we do_not_want in coin photography. So, we want to use the slowest-possible ISO (lowest number) we can in order to minimize noise. In the real world, the average dSLR will let you use ISO 400 all day, and most are fine at ISO 800. That ability gives you much greater latitude for lighting - you don't need as much light, nor does it need to be as direct. Very few point-and-shoots can use ISO400 without showing visible noise; indeed, only the best of them will allow ISO200.

Exposure controls light. The slower the exposure, the more light. Plain and simple. In regular photography as well as coin photography, you tend to want the fastest exposure possible, to minimize the chance of shake affecting your picture. This is the simplest setting - all it does is change how much light you see - but it's the most important for coin photography.

In coin photography, aperture is dictated by how much depth of field you want. ISO is dictated by the abilities of your camera to control noise. For both, you want the single "best" number that gives you what you want while minimizing the tradeoffs. Your only way of making up for the limitations imposed by that is exposure.

Your "best practice" as a coin photographer is to settle on a single aperture and ISO setting for a given camera/lens combo, and vary exposure and/or lighting to get the shot you want. Now, for some of us mounting and vibration control are limitations and those limitations force you to use more light so you need a faster exposure to avoid vibration. Heck, when I'm doing magnifying shots, even with equipment designed to shoot coins at magnification, a truck passing by on the road 100ft away can affect the shot.

There's a reason I spend so much time harping on solid camera mounts.

The more light you can bring to bear without blowing out features of the coin, the more leeway you have to play with the three settings discussed here. That could be a lot of light - some of my best shots were done with 150 watts of halogen light, enough to give me a tan while I was shooting. As long as you're not turning your coin into some sort of Archimedes-esque reflector weapon, more light is always better. It's easier to subtract light than it is to add some, especially if it requires interrupting a photo session for a trip to the store.

There's a reason why I always harp about quality lighting, and why Ray has spent as much time experimenting with lighting covers as he has lenses.

Tl;dr: Your camera decides ISO and Aperture. Exposure is your friend.

Thanks John for your post, But My Post is far deeper in reasoning than simply adjusting any of these three PRIMARY attributes of the camera....IT is why I wrote this post
TO CLARIFY to many readers on this forum,
One can see clearly if the ISO goes up so does the light with no changes to the other two, Also of the ISO remains the same by changing the shutter speed, the light is brighter or darker....The F /Stop does essentially the same in some regards........As it seems to influence what the ISO and shutter speed RESULTS are.....
For most applications....it very simple,
But for coins its new world for most, and I feel, the link of understandings has not quite been fully spoken..
the theory yes,,,And I'm not demeaning anyone as it has been
implyed for many months/years....ISO/F/stop and shutter speed are the key ingredients TO WHAT END...?
If you simply change any of these YES the combinati0on results in the light changes in the out come of the picture......
THE REAL ISSUE is the DEPT of FIELD, Which Ray and Dave
have been talking about, in the out come of the lenses capabilities... AS Dave NOTED ABOVE, the out come of the variailes are not simply the lessening or brightening
of the object, but the sharpness of detail.....in the final picture...some must stack pictures to combine the fact that the field of focus of the center and the rim of coins are not fully in focus, so to produce the full in focus effect they stack the photo's to produce the coins true picture...
This post is about the total concept in which, coin photography is based, in general this forum answers the questions of what you are working with, and how to get the most of it,,, My post is simply trying to condense all I have learned , for coin photography, to the bare elements of importance...not the lens, which is significant, but to the why of "old glass or new", and the specific reason of depth field in the macro world or old glass under and used with the bellows....Think about it....

Without RESURECTING old threads....Which are truely great if you have had someone let you know what threads to link you all to, to the Meat and Potatoes of coin photography,,,Which are spread about even in this forum, usually generally answered due to the specific nature of the camera and make...
My question or resolve is to take the make of the camera out of the equation, so as to understand the fundamentals,

And its not like this or other forums do not address something like this.. but yet a barage of the same questions of basic photography always imply's itself on these pages...
we need to explore on the higher level....
of what the LENS ratings imply...Mostly the F/stop...
The reason any lighting can be manipulated is due to the three basic attributes of the camera functions...
ISO, F/stop, ans shutter speed...
These are the basics which all lenses function, and they may be LESS the quality of GLASS or better, still have
the same attributes of performance....
It seams in general one can simply higher the ISO to improve the light, or brightness....or to simply adjust the shutter speed to do the same...
yet in reallity...the purpose of coin shooting is:
to capture the correct appearance of the coin in hand....
Thats why we are here......
REMEMBER, I have said......these are principles
NOT INCLUDING lenses or there premium SPECIALTY values /MACRO's or such...For a reason.....you do not need to spend the money to go brezerk on any lens as long as you know what kind of lens you need to do what you what to do...Most advertize all in wonder lenses to fulfill your need....
Most of of us "here know" with the above info the basics are crucial to be able understand the fine points...Much "old glass" can be purchased by any one not even knowing what the are needing to know...
and its a steal in quality for the price!!
More later.....

Thanks for your reply...I had to reread as are the fundamental points of getting a GREAT picture...everything
else is about normal....The true purpose of this thread was to find out for "coin photography"..what these 3 points..
main influences are and why.....
Rereading, SD has explained the what and why.....
"primary point" is the depth of
field..where the quality of definition is equal across the
entire coin..strong center strong edges..
While point and shoot camera's do
not address the depth of field issue, your combinations of the 3 points above WILL help you get a fine picture...I still have a 2004 canon power shot pro I was going to throw away until I found this foreum....I used there knowledge to
get amazing results....G