canon 35mm f2 is usm

[kevin2]

can anyone tell me what the fixed marks 22 11 and the red dot on the focus ring indicator signify

[Waddizzle · Accepted solution]

The numbers are an aperture settings.  They are showing the approximate depth of field at those aperture settings.  As you vary the focus, you can read off of the focus ring how deep the DoF would be.

The lens in the image is focused at the hyperfocal distance.  I am not sure about the red dot.  

[Waddizzle · Accepted solution]

The numbers are an aperture settings.  They are showing the approximate depth of field at those aperture settings.  As you vary the focus, you can read off of the focus ring how deep the DoF would be.

The lens in the image is focused at the hyperfocal distance.  I am not sure about the red dot.  

[RobertTheFat]

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@Waddizzle wrote:

The numbers are an aperture settings.  They are showing the approximate depth of field at those aperture settings.  As you vary the focus, you can read off of the focus ring how deep the DoF would be.

The lens in the image is focused at the hyperfocal distance.  I am not sure about the red dot.  

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It appears to me that the lens is focused at infinity, not at the hyperfocal distance. I think that the two numbers to the left of the vertical bar point to the hyperfocal distances at f/22 and f/11 when the lens is focused at infinity.

[ebiggs1]

Now for the correct answer.

The white lines are the DOF, or hyper focus, you use the hyper focal distance scale to know which parts of your image will be in focus at different aperture settings.  The red dot is used to adjust the focus if you're shooting using an infrared filter. When set to infinity the focus ring is turned slightly to the left so that the infinity marking appears in line with the red dot. For 99% of us it is useless. The side ways "L" is a variable infinity because infinity can come at slightly different places depending on several factors.

[RobertTheFat]

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@ebiggs1 wrote:

Now for the correct answer.

The white lines are the DOF, or hyper focus, you use the hyper focal distance scale to know which parts of your image will be in focus at different aperture settings.  The red dot is used to adjust the focus if you're shooting using an infrared filter. When set to infinity the focus ring is turned slightly to the left so that the infinity marking appears in line with the red dot. For 99% of us it is useless. The side ways "L" is a variable infinity because infinity can come at slightly different places depending on several factors.

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I don't think you're right about the sideways "L", Ernie. I think it's just a pointer that shows where they would have put the "infinity" symbol if it wouldn't have encroached on the space for the "2".

I think your explanation alludes to the fact that AF lenses can often be adjusted beyond infinity to keep them from banging against the stop during auto-focusing. But I don't think that's relevant to the meaning of the marker.

[kvbarkley]

Ernie is correct, while the EF35 f/2 dos not mention it, my 70-300 II does:

BTW, the manual for the EF35 f/2 explains answers all the OP in detail.

[RobertTheFat]

Obviously I was wrong and Ernie was right. Live a lot, learn a little. 

[ebiggs1]

Ok then we will move on. 

I really don't know the answer to this since I don't like and don't use filters often (PS works so much better) so I can't say if the red dot is useful with a DSLR.

Digital cameras usually have infrared filters on the sensor which work to block out almost all of the infrared information coming in. I have a friend that had a 1D Mk II modified (removed that filter) to see infrared but I don't know if he now has to use the red dot. It makes for some interesting photos.

You can buy screw on infrared filters but I have not used one.

[kvbarkley]

In the EF35 f/2 manual it states that it is for a particular wavelength of IR. I don't know if that is the wavelength that silicon senses when you convert a DSLR to IR.

I do know that IR can screw up your autofocus:

http://www.bobatkins.com/photography/technical/focus_vs_light_source.html

[Waddizzle]

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@RobertTheFat wrote:

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@Waddizzle wrote:

The numbers are an aperture settings.  They are showing the approximate depth of field at those aperture settings.  As you vary the focus, you can read off of the focus ring how deep the DoF would be.

The lens in the image is focused at the hyperfocal distance.  I am not sure about the red dot.  

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It appears to me that the lens is focused at infinity, not at the hyperfocal distance. I think that the two numbers to the left of the vertical bar point to the hyperfocal distances at f/22 and f/11 when the lens is focused at infinity.

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The hyperfocal distance is infinity focus.  The distance changes with aperture.  The image of the lens shows the hyperfocal distance for f/11 to be a little more than 6.5 feet, and a little less than 6.5 feet at f/22.  This matches up with the very bottom of this chart.

Those distances are almost exactly what this chart is showing at f/11 and f/22 on the bottom row.