From: Allan Goodall <agoodall@a...>
Date: 5 Apr 2001 13:03:17 -0700
Subject: [OT] Lens and Filter Considerations (was RE: [OT] Digital Cameras)
> On Thu, 05 April 2001, "Bell, Brian K (Contractor)" wrote: > OPTICAL Zoom. One of the important things is OPTICAL zoom. Yes, this is very important. Another thing to watch out for, which I don't see mentioned here, is the "focal length" of the lens. I won't go into any optical physics here, but the focal length indicates how wide a field of view you can take. This is a number given in millimetres. A focal length of 50mm is roughly that of the human eye. (Some prefer to say 35mm, but lets not quibble.) Anything above 50mm is "telephoto". Things far away are brought closer to you. Anything below 50mm is wide angle. You see a wider picture than your eyes can see. The wider the angle, the more distortion you'll see. 35mm lenses typically have very little distortion. You'll see a fair bit of distortion (but you can usually live with it) at 24mm. I believe fish-eye lenses (which you aren't going to find on an affordable digital camera) start at 16mm. For miniatures, a telephoto zoom (70mm and up) is more useful than wide angle. You can back up the camera, and "zoom in" to the model to make it look much bigger. For almost every other type of picture I take on a regular basis (landscapes, battlefields, group shots, conventions) wide angle is more useful. Why is this important? Isn't knowing the zoom amount good enough? The amount of zoom in a digital camera is usually rated as "#x" where "#" is a number. Typical numbers are 2x, 2.5x, 3x, 10x. This is the number of times of magnification that you can get out of the lens. The resulting image, though, depends a lot on the focal length of the lens. Some examples: I saw one digital (an expensive one) rated as 2.5x zoom, but this was less meaningful than hearing that it's the equivalent of 28mm to 70mm. That means that you can take wide angle pictures up to slightly "zoomed in" pictures. I saw another that was 10x zoom. Ah, much better, you may think. 10x versus only 2.5x. But this came out to 37mm to 370mm. It offered a bigger zoom, pulling in images from MUCH further away, but it didn't have anywhere near the same wide angle capability. If you wanted a camera that could take a nice, wide battlefield shot, this 10x zoom camera isn't it. I saw another, much cheaper, camera with a 3x zoom. Reading the specs, I found this was equivalent to 35mm to 108mm. For miniature picture taking, this is a more useful lens than the first expensive camera and is probably, practically speaking, just as useful as the second expensive camera. Again, though, it doesn't have that nice wide angle ability of that 2.5x zoom. So, just hearing that it zooms better doesn't mean much. In fact, for average folk, that 2.5x zoom camera is more versatile than either the 3x or 10x. You want to know what the lens' focal length is along with the "optical zoom" amount. Oh, and one piece of advice. The rule of thumb for holding a camera in your hand is 1 over the focal length of the lens. So, if you have a lens with a focal length of 50mm, you shouldn't shoot any slower than 1/50 of a second before you put the camera on a tripod. Likewise, if you have a 370mm lens, you should have it on a tripod if you are shooting at less than 1/400 of a second speed. For miniatures, you should be putting it on a tripod anyway. Remember this when you look at cameras and when you set the camera's speed and f-stop. Ah, f-stops. Pay attention to the f-stop. This is a number following an "f". The standard f-stops are f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, and f32. This number represents how wide the lens can open to let more light in. It's a fraction, so the smaller the number, the larger the opening (think of 1/2 being BIGGER than 1/32). Okay, so why is THIS important? The bigger the opening, the more light that gets in. The more light that gets in, the shorter the exposure time. This is usually only useful in "real life" with people moving around, and stuff. (And when to mount the camera on a tripod, see above). Not a big deal miniatures wise, you might think. Except, the wider the opening, the more light gets in from the "sides" of the front of the lens. The effect is what's known as "depth of field". Only a small band of area from in front of your subject to behind your subject will be in focus. If you open the lens wide, the band is narrow. If you make the opening very small, the band of what's in focus gets bigger. This is why, those of us with glasses, can sometimes see better when we squint through our eyelashes. Zooming (optical zooming, that is, not digital zooming) has a big effect here. A wide angle picture will have more of the subject in focus than if you zoom in. A long focal length will result in a much narrower "depth of field". How does this affect miniatures? Say you are taking a picture of a Stargrunt figure aiming a gun. You have a long zoom lens on your camera. You have the camera on a tripod and have backed it off a couple of yards away from the miniature. The You have the camera set at f2. You look through the viewfinder. The figure fills up the viewfinder (which is what you wanted) but you suddenly realize only the figure's face and hand are in focus. The back of his helmet and almost all of the gun are blurry. You open it up to f32, and now all of the figure -- and the piece of sky blue cloth you put behind it -- are in sharp focus. You want something in between, maybe f5.6, or f11, to make the background blurry but all of the figure crisp and sharp. I like to have a lens that can go up to f11 at least for miniature work. The more f-stops, the more options you'll have. Remember that the bigger the focal length, the narrower this depth of field, so the longer the focal length of the lens the higher the f-stop number you want. Test out the camera at various f-stop settings in the store, if you can. > LCD Viewer. An LCD viewer is a big help for situations like taking One thing about an LCD viewer: some viewers aren't very powerful and it's all you can do to see them in bright sunshine! This is a problem on a number of low end cameras. > Lense size. (Higher End Models only) Is the lens in a standard size First, make sure the lens has a thread that can take filters! Second, it probably IS a standard size, as there are a number of standard diameters. The most common is 52mm (often shown on lenses with the number 52 beside a circle with a slash through it). I personally have lenses with diameters of 49mm, 52mm, 58mm and 64mm. You can't go wrong with 52mm. A UV filter is very worthwhile. So is a circular polarizing filter. This is probably the most useful, but least understood by amateurs, filter you can get. Again, without any physics, a polarizing filter cuts out "polarized light". In other words, it cuts out reflections off of non-metalic surfaces. It won't stop you from taking pictures of someone in a mirror, but it will cut down on glare on, say, a gloss-coated miniature (or light bouncing off a piece of glass). At GenCon last year, I let Mike Miserendino use my polarizer on his digital camera. He took a picture of a B5 Minbari model, painted in gloss paint. Without the filter, there was a lot of reflected glare on the model from all the lights in the dealer's room. With my filter, he was able to cut down all the glare except for some very extreme reflections on the leading surfaces of the ship (which, in actuality, gave the ship a 3D look). Polarizing filters also saturate the colours: blues look more blues, reds look more reds, etc. Note that if you're a perfectionist on colours, some polarizers will make people look pale and perhaps add a slight blue tint to extreme whites (additional filters can correct this, or get a better polarizing filter). For outdoor shots, the cut down the haze on a humid day, and they can cut through light fog. If you can't get a digital with a removable lens, or one with a macro setting (which essentially takes a telephoto setting and lets you focus on something VERY close up), you can consider "close up filters". These usually come in a set of three, set for 1x, 2x, and 4x. Each filter magnifies the image. Add the 1 and the 2 to get three. Add all three filters and you get a 7x magnification. These aren't as good, optically, as an expensive lens, but they are an economical alternative. There are lots of other filters you can get, some for special effects and some for colour correction. Most digitals have built in colour correction for florescent and indoor lighting, so that's usually not a problem (and one area that digitals shine over traditional film cameras). If you get fancy, you may want to use colour filters, gradient filters, fog filters, star filters (makes a point of light burst into a many pointed star; and if you are thinking of shooting FT ships and don't see how THIS can be neat, shame on you!), etc. A good system for use special effects filters is the Cokin system. It's a plastic holder that mounts on a ring that screws onto the lens. You slip a cokin filter (sometimes these are round, but most often square, plastic or glass) into the holder. They are cheaper than equivalent stand alone filters, and come in a wide variety. I have a polarizing filter I hardly use with it, having given it up for a standard polarizer. But I use it a fair bit with special effects filters.