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Old Mar 4, 2005, 6:38 AM   #1
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Will I be able to get lower aperture number if I use a teleconverter? Will I get a very shallow DOF with it?
Lets say my camera has 3.0 aperture number. If I attach a teleconverter, will I get less aperture number like 1.0 or 2.0 etc?

Thank you.
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Old Mar 4, 2005, 8:02 AM   #2
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Glass wrote:
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Will I be able to get lower aperture number if I use a teleconverter? Will I get a very shallow DOF with it?
Lets say my camera has 3.0 aperture number. If I attach a teleconverter, will I get less aperture number like 1.0 or 2.0 etc?
No. The aperture number is the focal length of the lens divided by the aperture opening (size of the hole in your camera's lens) . So if you fit a 2x teleconverter, the hole is the same size but the focal length is twice as much. Therefore the f-number is twice as big, and you'll get a *bigger* depth of field, e.g., f/16 instead of f/8. But note that the teleconverter is unlikely to give as sharp as a result as your prime lens, and the exposure time will be twice as long, meaning that camera shake is more likely.

To get a smaller depth of field at any given f-number you'll have to fit a wide-angle converter, or buy a new camera with a bigger zoom range.

Good luck,

Alan T
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Old Mar 4, 2005, 8:34 AM   #3
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A teleconverter has the OPPOSITE affect. If your lense is f2.8, a 1.4 teleconverter will cost you one stop and make the lense f4.0

If you put a 2x teleconverter on a 2.8 lense you lose 2 stops - the lense now functions like a f5.6.

So your DOF will get wider not more shallow
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Old Mar 4, 2005, 8:44 AM   #4
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Alan T wrote:
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Glass wrote:
No. The aperture number is the focal length of the lens divided by the aperture opening (size of the hole in your camera's lens) . So if you fit a 2x teleconverter, the hole is the same size but the focal length is twice as much. Therefore the f-number is twice as big, and you'll get a *bigger* depth of field, e.g., f/16 instead of f/8. But note that the teleconverter is unlikely to give as sharp as a result as your prime lens, and the exposure time will be twice as long, meaning that camera shake is more likely.

To get a smaller depth of field at any given f-number you'll have to fit a wide-angle converter, or buy a new camera with a bigger zoom range.

Good luck,

Alan T
So if I use Macro and Wide angle converter, I get a smaller DOF?
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Old Mar 4, 2005, 10:38 AM   #5
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Glass wrote:
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So if I use Macro and Wide angle converter, I get a smaller DOF?
A wide angle converter will usually not get the whole picture - without distortion/vignetting

Here's some help with diopters - http://www.photoblink.com/info.asp?A...es/bugPics.xml
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Old Mar 4, 2005, 11:07 AM   #6
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WOW, that professor's macros are amazing; well written and totally understandable article. Thanks for sharing NFL

TG
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Old Mar 4, 2005, 5:16 PM   #7
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Just to give you an idea of the size difference with the teleconverter.This was shot witha sigma 70-300 APO Super Macro II f4-f/5.6 with a 2x Kenko Teleconverter Super 300.

http://www.gaida.co.uk/main.php/view...t/FullMoon.jpg

This was shot with the same lens a few months back without it.

http://www.gaida.co.uk/main.php/view...night/Moon.jpg
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