Originally posted by: Chaotic42
As far as lighting goes, is there any kind of formula for shutter speed vs f-stop? For example, if a shot would come out well with a 1/60s speed at 1.8, would it come out well with 1/100s for 1.4?
This site seems to explain stops pretty well (I felt lucky when I searched). I'm horrible with nomenclature but I'll attempt a quick explanation. Basically, one "stop" refers to a halving or doubling of the amount of light that hits your sensor/film.
With ISO, to get a one stop difference in light, you either double or halve the ISO (sensitivity). ie, the difference between ISO200 and ISO 400 is one stop. The difference between ISO 200 and ISO 800 is two stops.
With shutter speed, to let in twice as much light, you use a shutter speed that's twice as slow. ie, the difference between a 1/30 exposure and a 1/60 exposure is one stop (assuming you keep aperture and ISO constant).
Aperture controls the size of the hole that lets in light and is measured in terms of diameter, and f-stop is the ratio of that diameter and the focal length. But, to get half or twice as much light, you need to double or halve the area of the hole. Since we're now talking about areas but aperture is measured with distances, there's a square root of 2 term in there. A one stop difference in aperture corresponds to a 1.4x factor between f-stops. ie, an f/1.4 aperture is one stop bigger than an f/2.0 aperture. An f/4.0 aperture is one stop smaller than an f/2.8 aperture.
That website shows how you can adjust the 3 settings and still get the same exposure. You can give and take stops between the 3 settings.
Also, people also use the word "stops" when referring to dynamic range. ie, people say things like "Film has 7 stops of dynamic range, while my d-slr only has 6." (I made those numbers up). That should make sense, right?
Hopefully that was not too convoluted and factually correct.
The 50mm f/1.4 gives you an extra 2/3 of a stop over the 50mm f/1.8. I think people say it's also of higher quality. I have a 50mm f/1.8 and it works for me just fine. However, if you're looking for a general purpose lens, 50mm might be a bit too long on a DX camera. It gets closer into the portrait range. Perhaps you should look at a
35mm f/2 or a
28mm f/2.8 if you want something general purpose. You could also look into a constant f/2.8 lens walkaround zoom lens. The
Tamron 17-50mm f/2.8 is an excellent lens (optics perhaps in the league of the Nikkor 17-55mm f/2.8) and is at a reasonable price point. It's quite a popular lens.
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