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Old Jul 16, 2009, 9:02 PM   #1
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Default Effective focal length on DSLR

Wanted to upgrade to DSLR but I have a few questions which I hope someone can answer.

1) How much does a typical 400mm lens cost?

2) From what I read, Canon DSLR has a focal multiplier of 1.6, thus does it mean that the effective focal length of the camera is 560mm (400*1.6)? If we add a 2X telephoto and the camera will turn into 1120mm monster?

3) I had a Canon SX10 and when I used the lens at night for indoor sport, I get really dark and unusable image. I heard it is because of the f/5.6 slow aperture. My concern is will DSLR do better as I realized the cheaper kind of 400mm has f/5.6 aperture. I seem to read about some author saying that the aperture measure in DSLR and camera different.

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Old Jul 16, 2009, 9:57 PM   #2
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1. That depends on the lens. For example, in the Canon lineup, you've got several different 400mm lenses. They run from around $1199 for the least expensive one (400mm f/5.6L) to around $6999 for the 400mm f/2.8L IS. You've also got a number of lenses with 400mm available from third party manufacturers like Sigma and Tamron

2. If you buy a Canon dSLR using an APS-C size sensor (and Canon makes dSLR models with larger sensors, too), then you need to multiply the focal lens by 1.6x to see what focal length lens would give you the same angle of view on a 35mm camera. So, yes, if you buy a Canon dSLR model with an APS-C size sensor, then a 400mm lens would give you the same angle of view you'd have using a 560mm lens on a 35mm camera. As for using a 2x TC with a 400mm lens, you'd end up with the same angle of view you'd have using a 1280mm lens on a 35mm camera. You'd have an effective focal length of 800mm (400mm x 2), which would give you the same angle of view you'd have using a 1280mm lens (800mm x 1.6) on a 35mm camera.

But, keep in mind that you lose 2 stops of light with a 2x TC. So, you'd really want to stick with an f/2.8 zoom going that route (i.e., the $7000 model in a 400mm lens in the Canon lineup), since the effective aperture would be down to f/5.6 (and most entry level models are not going to Autofocus at anything dimmer than f/5.6). In addition to light loss, you'll also have some amount of optical degradation using a TC. In a pro level body, you can probably get away with using one on a slightly dimmer lens. But, it's not a good idea to use a 2x TC on a dimmer lens, and your shutter speeds would probably be slower than desired for low light sports trying to go that route.

3. If it's too dark, chances are, you had the camera set so that your shutter speed was too fast for the lighting, ISO speed and aperture being used, resulting in an underexposed image.

Your best bet would be to start a new thread in our "What Camera Should I Buy" forum and let members know more about the use for the camera, along with budget. For example, what kind of "indoor sport" at night? You'll need a dSLR capable of higher ISO speeds, *and* a very bright lens for indoor sports or sports under the lights at night if you don't want a lot of motion blur. You're not going to have a bright lens trying to use a Teleconverter (because of light loss through one).

Some of our Sports Shooters like the Sigma 120-300mm f/2.8 for low light sports when they need a longer zoom. But, I think you'll find that they are shooting from the sidelines, not the stands.

Low light sports is very demanding. It's not something you want to try with a dimmer lens (unless you want a lot of motion blur). Again, I'd start a new thread in our What Camera Should I Buy forum and give as much information as possible for better responses (budget, type of sports, venue/conditions you'll be shooting in).
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Old Jul 17, 2009, 1:45 AM   #3
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The good news is that any DSLR with a decent zoom lens will give you much better low-light results than you are getting now with the P&S. The pictures will be cleaner at high-ISO and the AF system will be much better.

The bad news is that indoor sports demands all 3 of the following things:
1. Good access (shooting from the stands is poor access).
2. Good equipment (read VERY expensive, and it's the camera too not just the lenses because the AF system is put under huge strain in low-light fast action photography.)
3. A lot of skill and technique.

An entry level DSLR will only take you from terrible to poor. If you want to move up to reasonable then you need a mid-level DSLR and lenses. If you want to go to good or excellent you need very expensive kit and years of practice. It's important to have realistic expectations here.
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Old Jul 17, 2009, 4:53 AM   #4
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Thanks both of you for your answers. As I have just started working, I think I better stay away from this type of photography because of the cost involved
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Old Jul 17, 2009, 5:46 AM   #5
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As mentioned, the low light performance of the larger APS-C will make a lot of difference.
For example, if you look at the comparative performance, the SX10 at ISO 200 has around the amount of noise as the Canon EOS T1i / 300D DSLR has at ISO 3200.

So if you were shooting the SX10 at 1/30 sec at ISO 200(560mm equiv), then for the same amount of noise(at ISO 3200), the DSLR would shooting at 1/500th sec with a 400mm (560mm equiv @ F5.6).

Last edited by dnas; Jul 17, 2009 at 5:50 AM.
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Old Jul 28, 2009, 11:43 PM   #6
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Default Effective focal length on DSLR

Digital photographers commonly talk about effective focal lengths,where the actual lens focal length is multiplied by the DSLR’s crop value. So a standard DSLR kit zoom lens with a focal length of 18-55mm on, say, a Nikon cropped body, would actually give an equivalent coverage of 27-82mm.
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Old Aug 5, 2009, 11:23 PM   #7
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To calculate the effective focal length of a lens, the focal length multiplier of the camera must be used. The three most common multipliers are 1.5, 1.6 and 2.0.
Canonís entry level cameraís multiplier is usually 1.6. Nikon, Sony, and Pentax usually have a multiplier of 1.5. Olympus and Panasonic have a multiplier of 2.
A 50mm interchangeable lens on a DSLR with a 1.5 multiplier would have an effective focal length of 75mm. On a DSLR with a 1.6 multiplier the effective focal length is 80mm; itís 100mm on a camera with a multiplier of two.
Full frame DSLRs do not have multipliers or, more correctly, they have a multiplier of one. This is because their sensor format has the same area as 35mm film.
Wide angle shots and focal length multiplier

If you take a lot of wide angle shots, lenses like the popular 28mm wide angle lens will no longer give a wide angle of view. When attached to a DSLR with a crop fact, it becomes effectively equal to a normal lens . For wide angle shots, youíll need a super-wide angle lens (eg. 12mm, 10mm).
Conversely, a long telephoto lens effectively has a longer telephoto length on a DSLR with a crop factor than when used on a full frame camera. A 25omm on DSLR with a 1.6 crop factor becomes 400mm. A nice plus for wildlife photographers.
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