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07/26/2006 02:46:06 PM · #1 |
how much more light would a 1.8 lens get than a 2.8? Is there a huge difference?
At 1.8, if I was was 25-30 feet away shooting kids ballet am I likely to have issues with too short DoF?
The widest I've ever been able to shoot is f3.5 and it's just not good enough for those dark ballet performances ;) |
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07/26/2006 02:48:47 PM · #2 |
Are you speaking of the 50/1.8? Focal length makes a difference in DoF.
For a 50mm lens at f/1.8 focused at 25 feet, you have between 4 and 5.5 feet DoF, depending on what assumptions you make in the calculation. Looking on-screen at 100% magnification, you'll probably agree with the 4-foot figure.
Edit:
for 85mm, f/1.8, 25 feet, you're looking at 1.4 feet DoF and at 100mm, same conditions, 1.0 feet. Compared to 4 feet at 50mm.
Message edited by author 2006-07-26 15:00:35. |
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07/26/2006 02:51:40 PM · #3 |
| probably either an 85 or 100 actually. |
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07/26/2006 02:55:57 PM · #4 |
f/1.8 is 1 and 1/3 stops faster than f/2.8. Since 1 stop lets in twice as much light and 2 stops lets in 4 times as much light, f/1.8 would let in about 2.5 times more light than f/2.8.
In terms of shutter speed, it means that if you are metering, say, 1/30 with 2.8, you will be able to shoot at 1/80 at f/1.8, assuming your ISO stays constant.
Message edited by author 2006-07-26 14:57:53. |
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07/26/2006 09:24:51 PM · #5 |
Thanks Zal and Kirbic
Just out of curiosity - how do you calculate the DoF? (hopefully it's not TOO complicated...) |
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07/26/2006 09:52:06 PM · #6 |
Originally posted by Megatherian:
Just out of curiosity - how do you calculate the DoF? (hopefully it's not TOO complicated...) |
It's not really something you can do in your head, but luckily, someone invented DOFMaster |
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07/26/2006 09:58:17 PM · #7 |
FWIW, if you have been shooting at f3.5, f 1.8 will give you 2 stops more light.
Message edited by author 2006-07-26 21:59:13. |
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