EF 75-300mm f/4-5.6 III USM

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EF 75-300mm f/4-5.6 III USM

FAQ ID: 51427
Last modified: 10-Jun-10

FAQ: Why do I get blurred photos when I use closed diaphragm?

Helpful Information:

This problem is known as diffraction. Diffraction flare is produced when using a small aperture of diaphragm (F22 - F32).
This phenomenon is caused by the wave-like nature of light. Light rays are diverted in several directions when they graze one thin sheet.
This phenomenon is more frequent in macro photography.

Solution:

The aperture value must be at least F16.
The lens works better using medium diaphragm values.

The formula for the optimum aperture is the following:

Kf = optimum aperture
u = circle of confusion
= wavelength
m = magnification power

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EOS 10D	EOS 20D	EOS 20Da
EOS 300D	EOS 30D	EOS 350D
EOS 5D	EOS D30	EOS D60
EOS 1D	EOS-1D Mark II	EOS-1D Mark II N
EOS 1Ds	EOS-1Ds Mark II	EOS 400D
EF 100mm f/2 USM	EF 135mm f/2 USM	EF 135mm f/2.8 Softfocus
EF 14mm f/2.8L USM	EF 15mm f/2.8 Fisheye	EF 200mm f/2.8L II USM
EF 20mm f/2.8 USM	EF 24mm f/1.4L USM	EF 24mm f/2.8
EF 28mm f/1.8 USM	EF 28mm f/2.8	EF 35mm f/1.4L USM
EF 35mm f/2	EF 400mm f/5.6L USM	EF 50mm f/1.4 USM
EF 50mm f/1.8 II	EF 85mm f/1.2L II USM	EF 85mm f/1.2L USM
EF 85mm f/1.8 USM	EF 50mm f/1.2L USM	EF 100-400mm f/4.5-5.6L IS USM
EF 24-105mm f/4L IS USM	EF 28-135mm f/3.5-5.6 IS USM	EF 28-300mm f/3.5-5.6L IS USM
EF 300mm f/2.8L IS USM	EF 300mm f/4L IS USM	EF 400mm f/2.8L IS USM
EF 400mm f/4 DO IS USM	EF 500mm f/4L IS USM	EF 600mm f/4L IS USM
EF 70-200mm f/2.8L IS USM	EF 70-300mm f/4.5-5.6 DO IS USM	EF 70-300mm f/4-5.6 IS USM
EF-S 17-55mm f/2.8 IS USM	EF-S 17-85mm f/4-5.6 IS USM	EF 70-200mm f/4L IS USM
EF 100mm f/2.8 Macro USM	EF 180mm f/3.5L Macro USM	EF 50mm f/2.5 Compact Macro
EF-S 60mm f/2.8 Macro USM	MP-E 65mm f/2.8 1-5x Macro Photo	Extender EF 1.4x II
Extender EF 2x II	Life-Size Converter EF	TS-E 24mm f/3.5L
TS-E 45mm f/2.8	TS-E 90mm f/2.8	EF 100-300mm f/4.5-5.6 USM
EF 16-35mm f/2.8L USM	EF 17-40mm f/4L USM	EF 20-35mm f/3.5-4.5 USM
EF 24-70mm f/2.8L USM	EF 24-85mm f/3.5-4.5 USM	EF 28-105mm f/3.5-4.5 II USM
EF 28-105mm f/4-5.6	EF 28-105mm f/4-5.6 USM	EF 28-200mm f/3.5-5.6 USM
EF 28-80mm f/3.5-5.6 II	EF 28-80mm f/3.5-5.6 V USM	EF 28-90mm f/4-5.6 II USM
EF 28-90mm f/4-5.6 III	EF 35-80mm f/4-5.6 III	EF 55-200mm f/4.5-5.6 II USM
EF 70-200mm f/2.8L USM	EF 70-200mm f/4L USM	EF 75-300mm f/4-5.6 III
EF 75-300mm f/4-5.6 III USM	EF 90-300mm f/4.5-5.6	EF 90-300mm f/4.5-5.6 USM
EF-S 10-22mm f/3.5-4.5 USM	EF-S 18-55mm f/3.5-5.6	EF-S 18-55mm f/3.5-5.6 II
EOS 450D

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EF 75-300mm f/4-5.6 III USM

EF 75-300mm f/4-5.6 III USM

FAQ: Why do I get blurred photos when I use closed diaphragm?

Click here to view all applicable modelsClick here to close the applicable models list

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