Faking Infinity

[Dmitri]

Hi, the canon kit lens doesn't have the much talked about Infinity setting. How would one fake it to do the near / far focus thing?

Thanks.

 

[reg]

Focusing to infinity is just focusing really really far away for the focal length you're at (i.e. a 200mm focuses to 150ft before hitting infinity, a 28mm focuses to 30ft before hitting infinity but those numbers are just pulled out of thin air) unless you're talking about something else?

 

[Dmitri]

Supposedly it's a way to get near objects and far objects properly in focus.

Edit: I should mention that it's technique usually associated with landscapes (or what I have read of it).

 

[reg]

That would be hyperfocusing, not infinity and that's just by going to a small aperture and focusing.

 

[Moglex]

The idea is that you focus your lens in such a way that objects at 'infinity' are at the minimum acceptable sharpness.

This gives you the maximum range of distances at which objects are of acceptable sharpness.

The distance upon which you focus is called the 'hyperfocal distance' and the range of acceptable sharpness goes from half that distance to infinity.


See Here for a more detailed explanation.

 

[Dmitri]

Thanks a lot, Moglex. I'll check that out.

 

[ksmattfish]

Hi, the canon kit lens doesn't have the much talked about Infinity setting. How would one fake it to do the near / far focus thing?

Google "DOF calculator", and you can find out what the approximate hyperfocal distances are for commonly used apertures and focal lengths. For instance 18mm @ f/8 are common settings when I'm shooting landscapes. I know the hyperfocus distance is about 7.5', and when I focus on something about 7' or 8' from me everything from 4' to infinity will be in the DOF.

 

[usayit]

Google "DOF calculator",

www.dofmaster.com

 

[ksmattfish]

www.dofmaster.com

Yeah that's really cool. There are also probably DOF programs that can be uploaded to cell phones, etc...

 

[manaheim]

That would be hyperfocusing, not infinity and that's just by going to a small aperture and focusing.

Well... that's not quite it. (no offense!)

Hyperfocal focusing is focusing to infinity, and then pulling back a bit from there to get the objects closer to you in focus as well. It generally requires a range finder on the lens, but you can figure it out with some work and/or a rangefinder chart. (I've not done the chart thing, I just know it's possible)

You can do hyperfocal focusing even with a very large aperature. It's also uber-sexy if you do, because the image will not suffer from as many light refraction issues.

Info on hyperfocal focusing: http://www.great-landscape-photography.com/hyperfocal.html

Focusing range chart: http://www.dofmaster.com/hyperfocal.html

 

[Alpha]

Addendum to the above:

The hyperfocal point is a sort of "false infinity." It's a focal point where everything beyond it is automatically in focus, per optical laws.

 

[manaheim]

Addendum to the above:

The hyperfocal point is a sort of "false infinity." It's a focal point where everything beyond it is automatically in focus, per optical laws.

Good point, and nice catch. Thanks, Alpha.

 

[Moglex]

Addendum to the above:

The hyperfocal point is a sort of "false infinity." It's a focal point where everything beyond it is automatically in focus, per optical laws.

I presume that our eyes always focus on the hyperfocal distance when we focus on 'infinity' but I've never seen that confirmed.

I'm pretty sure that way, way, back a lot of little creatures who actually focused on true infinity were naturally selected out by nearby out of focus predators. :mrgreen:

 

[Alpha]

I presume that our eyes always focus on the hyperfocal distance when we focus on 'infinity' but I've never seen that confirmed.

I'm pretty sure that way, way, back a lot of little creatures who actually focused on true infinity were naturally selected out by nearby out of focus predators. :mrgreen:

Perhaps someone with more physics or opthamology knowledge than I can weight in on this, but I think that may be only partly true. I say that because I don't think the converse of hyperfocusing is true.

That is, at the hyperfocal point, everything beyond it is automatically in focus. But at infinity, things in front of it (up to the hyperfocal point) aren't necessarily in focus.

At the hyperfocal distance, everything beyond that point is far enough away that incoming light is effectively parallel and therefore in focus. But with the lens itself focused at infinity, only things at infinity are truly in focus.

But I stand to be corrected.

 

[Helen B]

At the hyperfocal distance, everything beyond that point is far enough away that incoming light is effectively parallel and therefore in focus. But with the lens itself focused at infinity, only things at infinity are truly in focus.

But I stand to be corrected.

The same criteria for apparent focus apply in front and behind the plane of true focus. There is only one plane of true focus, though when the lens is focused at infinity that concept gets a bit out of hand.

If you focus at the hyperfocal distance the image of an object at 'infinity' will not be in true focus - it will be defocused, but not noticeably so (by definition).

If you focus on 'infinity', then a point that is at the hyperfocal distance will appear to be in focus - it will have the same degree of blur as a point at infinity would have when the lens is focused on the hyperfocal distance.

This property is shown by the DoF markings on a lens - it it weren't true it would be a lot harder to put DoF markings on a lens - the relative location of the DoF marks would have to change as the lens was focused.

Best,
Helen