Camera Purchase

There are two problems being so close:

- Lighting. It's hard to get anything other than side-lighting between camera and coin. The camera and lens will shadow any lights from above. All is not lost, as you can rig up individual bright white LEDs to shine on the coin, but that's a project. Note that one inch is a lot different from two inches. At one inch lighting is very difficult. At two inches you are almost at a point where the Jansjos will sort of work.

- Perspective. When you are really close to the coin, you are looking straight-on toward the middle of the coin but angled toward the edges. This is an unnatural perspective and is a big reason many of the pros use very long lenses. Personally I am happy with the perspective on a Cent at around 4" away, and Dollar around 7" away, which is what I get from a 75mm lens. At 4", for a 19mm coin (Cent), the perspective angle is about 5 degrees. At 2" it is about 10 degrees, and at 1" away it is 20 degrees.

Sorry to confuse...the 75mm lens I mentioned goes on a DSLR or bellows. Won't work on a point and shoot, as P&S lenses are fixed. My point was to give example of the working distance you should shoot for to get enough room for lighting and natural perspective.

I will take this opportunity to describe some thoughts I've been having on Downsizing and Cropping. Most of my work goes into getting good full-screen images of coins, ie the coin fills the sensor completely top to bottom, or nearly so. For reference, My camera sensor is 3264 tall, nearly the same as the 3000 tall SX300 you are contemplating.

I took pictures of my reference Toned 1957-D Lincoln in two ways:
- Filling the whole frame as I usually do. Magnification is about 0.8
- Filling half the height of the frame. Magnification is about 0.4

Lighting was exactly the same between shots.

I post-processed the half-frame image by first converting it from 4928x3264 to 2464x1732. I then cropped the coin out of the image in an 800x800 crop as above. That is the first shot you will see below.

I post-processed the full-frame image by first converting it from 4928x3264 to 1232x816, a 4x reduction. I then cropped the coin out of the image in an 800x800 crop. That is the second shot you will see below.

I did this to show that although apparent quality is reduced by less downsizing, the quality can still be OK for Web viewing. Note that I had to use a 90mm lens to get as low as 0.4 magnification on bellows, so there is not much difference in perspective between the shots. You can see the lighting shift a little bit due to the perspective change since the angle between the light and the lens changes between shots, but it is not dramatic.

One thing that is dramatic is the improved depth of field of the 2x reduced image vs 4x. DOF, for a given aperture, is lower as magnification increases. I suppose I should have made the two images at the same "effective" aperture but was not that careful.

Now to my recommendation for using the SX300, and possibly for all point and shoots that require you to get extremely close to the coin for full frame shots. Try staying farther away, and arrange your final image size of the coin to be slightly smaller than 1600 pixels tall. This will allow you to downsize by a factor of 2, thereby improving final image quality, and still crop to the standard 800x800 pixel image. It also keeps the edges of the coin away from the edges of the image circle, so any aberrations or field flatness issues are minimized. The smaller image will allow you to get the camera farther from the coin for more lighting flexibility, and perspective will be improved.

PLEASE NOTE that the important thing here is to get some image quality improvement by INTEGER downsizing of the image. In my example I tried a 2x and 4x downsize. NEVER do non-integer downsizing, as this forces the algorithm to invent data by interpolation and sharpness suffers. I am sure a 3X reduction will be as effective as 2X or 4X, perhaps more so since the center pixel lands on the downsized pixel. I'll need to explore that concept, but I am sure there is no disadvantage. This means depending on your camera sensor, you can shoot the coin at 1600 and downsize 2x, or 2400 and downsize 3X.

Half-Frame Composition, 2x Downsizing, 800x800 Crop:


Full-Frame Composition, 4x Downsizing, 800x800 Crop