Mike...fstops?

Elizabeth Schott · 01-30-2006, 11:32 PM

MIke I just wanted to ask you a quick question about shoot artwork.

Is the AV setting the same as the f Stop?

Is it better to come it a large opening like 5.6 vs a smaller one - 11?

I am never sure if it can affect the information recorded or add/take away from glare etc.

Thanks, Beth

Mike McCarty · 01-31-2006, 08:51 PM

Beth:

Aperture and f stop are the same thing.

Because of basic optical principles, the absolute aperture sizes and diameters depend on the focal length. For instance, a 25mm aperture diameter on a 100mm lens has the same effect as a 50mm aperture diameter on a 200mm lens. If you divide the aperture diameter by the focal length, you will arrive at 1/4 in both cases, independent of the focal length. Expressing apertures as fractions of the focal length is more practical for photographers than using absolute aperture sizes. These "relative apertures" are called f-numbers or f-stops. Whew.

If you place the camera in "Aperture priority" you are telling the camera what aperture you want (not to vary), and allowing the camera to select the most accommodating shutter speed in which to properly expose the scene.

Likewise, if you place the camera in "Shutter speed priority" you are telling the camera what shutter speed you desire (and not to vary) and allowing the camera to select the best aperture to properly expose the scene.

Keeping in mind that proper exposure is not the result of two absolute factors: aperture and shutter speed. These two items are dynamic. So, if one moves, the other must make some corresponding move in order to bring the exposure back into sync. More light given with a wider aperture = less time needed to expose the sensor (film). And visa versa.

Basically, aperture controls depth of field, or, how much of the scene is brought into focus. A small number, such as f2.8 (very wide aperture), would result in a very shallow depth of field. For example: only those couple of inches from the tip of the nose to the back of the ear would be in focus. Those items from the tip of the nose back to the camera would be out of focus, as well as anything from the back of the ear and beyond. If you choose a larger aperture number, such as f11 or f22, you could bring your subject into focus as well as the mountains in the distance.

As this relates to photographing your art work ... It would seem to hold true that if you are in focus with the face of the canvas it shouldn't matter what aperture setting you have selected. Given that the canvas is a flat plane without depth. It would also seem prudent to give yourself some depth of field, although I'm not sure why.

Per usual, these are the musings of a "photog generalist" who tries his best to avoid real technical knowledge. Anyone should feel free to set me straight.

Elizabeth Schott · 02-01-2006, 11:23 PM

Quote:

Per usual, these are the musings of a "photog generalist" who tries his best to avoid real technical knowledge. Anyone should feel free to set me straight.

Mike thank you SO much! I hope to be a generalist like you in anything. This information is so helpful and knowledgeable!

Richard Monro · 02-02-2006, 09:57 AM

Beth,
Adding a polarizing filter to your camera lens can be a great way to eliminate glare when shooting your paintings.

Elizabeth Schott · 02-02-2006, 10:10 AM

Richard I feel like a real "igniroad" when it comes too this, it might be my old Pentax K1000 training that messed me up, but I remember you have to step down or something and it didn't register on my meter or... I didn't have depth of field preview. So I have stayed away from them out of fear even though my Canon does have one!

Thanks for the reminder, I'll just need to be a big girl and learn to make it work!

Richard Monro · 02-02-2006, 11:23 AM

Beth, let us try to make the process a little easier. When you want a lot of depth of field, use a high f stop like f16. Then let the camera set the shutter speed. If the shutter speed is too slow and you get less than crisp pictures, you need to go to a lower f stop such as f11, f8 or even lower. (it will depend on how much light you have on the subject) Your canon should have auto focus so let it do the hard work there. Just remember, as a rule of thumb the higher the f stop number the slower the shutter speed and vice versa... and there is lots of room to play any number of combinations of f stop and shutter speed.