Of course given that I don’t even have a fully functional dark room right now, this means that I don’t get to post anything unless I get the images scanned in at the 1 hour photo place when they are developed (which wont work with my B&W stuff since I am developing that myself). This costs money, and the results aren’t exactly something to write home about. So I thought, why not use my DSLR, I have flashes and I have close up filters. A proper macro lens would be nice, but with the close up filters I could get the lens close enough to fill most of the image with a single 35mm frame. Here is a brief run-down of the experiment.

I took a Tupperware container that I placed upside down over some white cardboard, placing my flash to the right pointing directly to the side of the container. This would provide a relatively diffuse light source.

I took a few shots at various apertures until I had some options to work with in Photoshop. These were shot in RAW as I would need the added bit depth.

It took a bit of playing around in PS to get things right. Just converting the negative image and then inverting it results in terrible results, the colours were off, the contrast almost non existent. So how do we get a better image?

The first thing to do is make sure that the white balance is set correctly. The problem with colour negatives, is that they have a very strong orange colour cast. So the first thing you do is take the white point selection tool in RAW converter, and select the blank film around the picture. This is the white of the negative image.

Now select the highlights option (this will show the blown highlights as red) and increase the exposure until you have as much of the film around the picture red without any of the picture itself over exposed. Reduce brightness to 0, and increase the shadow slider until the negative image looks about right. This will take practice, but after a few tries you will get a feeling for it. Now you can open the converted RAW file in PS.

The image I used for this test was from a batch that I had gotten processed and scanned in at one of our local 1 hour labs. The resulting scan from that lab was horribly saturated and sharpened so much that there was no chance of getting any decent enlargements out of it. Given that it doubled the cost of processing the film, I just don’t feel it was worth it. The canon shot that I did with this quick setup had much more faithful colours, and due to less sharpening had way fewer artefacts in the image. With a proper macro lens I would have been able to achieve close to the camera’s full 8 megapixels, and even with just my close up filters, I was able to achieve an increase in size over the 2.2 megapixel scans. The thumbnails below link to web sized versions of the photo, as well a 100% crop comparison.

Fuji Scan

Canon Photo

100% Crops

The Basics

So you want to know what aperture and f-stop are in a couple of lines? Well aperture governs the amount of light that a lens lets through to the film/digital sensor, and aperture is indicated by the f-stop. f-stop numbers available vary by lens, but most will have a series of f-stops somewhere in the following range: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45.

The smaller the f-stop, the larger the aperture; so f/1 is a very large aperture, letting in a lot of light, while f/45 is extremely small letting in almost no light. Each increase in f-stop (i.e. from 1 to 1.4, or 4 to 5.6) halves the amount of light going through the lens, and thus to maintain the same exposure you must also slow the shutter speed down by half (i.e. 1/250th sec will need to be 1/125th sec). So when a photographer says to “stop down”, you need to increase the f-stop number; and using a lens “wide open” means using the lens with the smallest f-number available to it.

So why was this strange and seemingly random set of numbers chosen? Well first we need to look at how light works…

Distance & Light Intensity

There is a law in science called the Inverse Square Law: Any point source which spreads its influence equally in all directions without a limit to its range will obey the inverse square law. The law describes, to put it simply, the effect that when distance is doubled from such a point source (like a flash) the intensity of the light is reduced by four.

To determine the distance change when doubling or halving the intensity of light, we multiply or divide the distance by √2, which is 1.41 (rounded off for ease). As you may have figured out already, when doing flash photography, one can easily change the distance of the flash to achieve the same effect as stopping up or down.

f-stops

So now you can see, the f-stops on a lens follow the sequence of the powers of the square root of 2 (rounded off for ease). Each stop down (large f-number) halves the light, each stop up (smaller f-number) doubles it. Now these numbers are not the only f-stops you can have, and most modern cameras allow increments of 1/2 or 1/3.

But what do these numbers actually represent in the lens?

Aperture size and Focal length

Well the “f” in f/1.4 stands for focal length. So a 50mm lens with a f-stop of 1.4 would be 50/1.4 which equals 35.7. This is the diameter of the aperture, and as you can see the diameter for a lens with a longer focal length would have to be even larger to gain the same f/1.4 (an f/1.4 85mm lens for examples would have an aperture of 60.7). This explains why you don’t get 600mm f/1.4 lenses that fit onto a 35mm body.

Just as an experiment, calculate the aperture diameter for a 50mm lens at f/1.4 and f/2. Then calculate the area of each aperture circle (πr²). Assuming you did the calculations correctly, you’ll find that the are of the aperture at 1.4 is twice that at 2 (with some errors due to rounding).

What aperture affects

Well now that you know what aperture does, many may be asking why don’t you just always use the lens wide open? Well aperture affects many more things than just the amount of light entering the lens. I’ll briefly list them here, though they will be covered in more detail at a later date.

• Aperture effects DOF (depth of field: the area that appears to be in focus), with large apertures having very shallow DOF and the DOF increasing as the lens is stopped down.
• Using a lens wide open will often result in vignetting and aberrations.
• Stopping the lens right down will result in diffraction, thus effecting sharpness.

So what f-stop should you use? Well in the end it’s all about what you want from your shot; if you need as much of the photo to be in focus as possible, stopping down is the answer; to narrow down the DOF to help emphasise the subject of the photo, you’ll want to use the lens wide open. However, the sharpest pictures will generally come from the mid ranges, f/8 – f/11.

Don’t worry about it too much though, it’s better to get the photo at a less than perfect f-stop than to not get it at all!