topic Re: canon 35mm f2 is usm in EF & RF Lenses

canon 35mm f2 is usm

kevin2 — Wed, 23 Oct 2019 10:41:36 GMT

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

Re: canon 35mm f2 is usm

Waddizzle — Wed, 23 Oct 2019 11:57:47 GMT

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.

Re: canon 35mm f2 is usm

kevin2 — Wed, 23 Oct 2019 13:00:48 GMT

Thanks

Re: canon 35mm f2 is usm

RobertTheFat — Wed, 23 Oct 2019 13:34:05 GMT

@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.

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.

Re: canon 35mm f2 is usm

kvbarkley — Wed, 23 Oct 2019 14:01:48 GMT

The red dot is for infrared focus, because the wavelength is different, you need to focus at a slightly different point. It does not mean much for a DSLR. 8^)

Re: canon 35mm f2 is usm

ebiggs1 — Wed, 23 Oct 2019 14:01:43 GMT

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.

Re: canon 35mm f2 is usm

shadowsports — Wed, 23 Oct 2019 14:09:42 GMT

Red dot on hyper focal distance scale.

Good questions.

Its the infrared focusing mark. Believe its a carry over from days gone by. With infrared film you actually had to focus at a different place than normal because the infrared spectrum of light is different than what we see with our eyes. No idea how to replicate digitally, but I guess it can still be done.

*****All 3 of us posted over one another LoL

Re: canon 35mm f2 is usm

ebiggs1 — Wed, 23 Oct 2019 14:17:52 GMT

"*****All 3 of us posted over one another"

It would seem so.

In fact most lenses don't have many marks on them at all anymore.

Re: canon 35mm f2 is usm

kevin2 — Wed, 23 Oct 2019 14:24:10 GMT

Thanks everyone. Appreciate your help and knowledge

Re: canon 35mm f2 is usm

kvbarkley — Wed, 23 Oct 2019 14:41:20 GMT

The cool adaptive LCD display on my 70-300 II does not have an infrared mark. 8^)

I am hoping for a firmware update so that it will show the hyperfocal distance.

Re: canon 35mm f2 is usm

RobertTheFat — Wed, 23 Oct 2019 15:44:45 GMT

@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.

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.

Re: canon 35mm f2 is usm

kvbarkley — Wed, 23 Oct 2019 16:23:21 GMT

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.

Re: canon 35mm f2 is usm

RobertTheFat — Wed, 23 Oct 2019 18:36:14 GMT

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

Re: canon 35mm f2 is usm

ebiggs1 — Wed, 23 Oct 2019 19:47:53 GMT

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.

Re: canon 35mm f2 is usm

kvbarkley — Wed, 23 Oct 2019 20:40:52 GMT

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

Re: canon 35mm f2 is usm

Waddizzle — Wed, 23 Oct 2019 22:50:25 GMT

@RobertTheFat wrote:
@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.
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.

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.