Infinity Focus - what is it about?


Apr 20, 2010
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#1
Hi all cs-er,

i've a question which i still yet to have a conclusion or a clear answer to it ...



i notice there is a infinity symbol on the 15-85mm lens ... i've google it and it seems like it is 'infinity focus' ..

but under what kind of situation will it be useful for?

quoted from wiki
'In optics and photography, infinity focus is the state where a lens or other optical device forms an image of an object an infinite distance away. This corresponds to the point of focus for parallel rays. The image is formed at the focal point of the lens.
In practice, not all photographic lenses are capable of achieving infinity focus. A lens used with an adaptor for close-up focusing, for example, may not be able to focus to infinity.'


some forum say

'Scenery at night where the autofocus might work poorly (e.g., expanses of
city lights, where the autofocus zone happens to be empty)...

Astronomical photography...

Photography through scientific instruments where you want to aim the camera
into the eyepiece, with the camera's focus locked...

And if you are going to have manual focus at all, infinity has to be the end
of its range.'


some say

'just means the focus is onto infinity ( most often for landscape style stuff )'

so what is the accurate way for explaning it?

really appreciate your time to explain for me ...
 

dingaroo

New Member
Dec 6, 2009
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#2
My own explanation:

Infinity focus ... imagine you are shooting a landscape view, and in that you have 3 rows of mountain ranges. There is the front one that is closer to you, the range in the middle some distance farther away, and the last one that is furthest away from you.

Obviously, when you want to shoot, you want to capture all the mountain ranges sharp. But where do you focus? The one in front, middle or back mountain range? For me, I would set my lens to infinite focus.

This way, all three mountain ranges are sharp. Of course, set your aperture to a high number, like 8, or 11 or higher. Else you will get a bokeh effect in your picture, which you may not want in a landscape photo.

Other senior members can correct me if I'm wrong.

Cheers!
 

wootsk

Deregistered
Aug 12, 2007
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Small Island
#4
When you are shooting something that is further than your lens max focus distance.

Example will be fireworks.
I seems newbies who set AF mode while trying to shoot fireworks -_-", set lens to MF mode, turn to infinite focus and shoot. Unless you telling me your lens got so long focus distance to the sky.
 

wootsk

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Aug 12, 2007
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#5
My own explanation:

Infinity focus ... imagine you are shooting a landscape view, and in that you have 3 rows of mountain ranges. There is the front one that is closer to you, the range in the middle some distance farther away, and the last one that is furthest away from you.

Obviously, when you want to shoot, you want to capture all the mountain ranges sharp. But where do you focus? The one in front, middle or back mountain range? For me, I would set my lens to infinite focus.

This way, all three mountain ranges are sharp. Of course, set your aperture to a high number, like 8, or 11 or higher. Else you will get a bokeh effect in your picture, which you may not want in a landscape photo.

Other senior members can correct me if I'm wrong.

Cheers!
If you are shooting mountain, there is no way that your lens can focus that far. so in short, no matter which mountain you aim, it will all be focus to infinite. Once in infinite mode, it doesn't matter which F-stop you are using as everything beyond your max focus distance is the same. Bokeh only works when the subject you are focusing on is within your lens focus distance. But bear in mind when in infinite mode, all within your focus ditance will be blur and even more blur as it is close to you depending on the F-stop.
 

night86mare

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Aug 25, 2006
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#6
My own explanation:

Infinity focus ... imagine you are shooting a landscape view, and in that you have 3 rows of mountain ranges. There is the front one that is closer to you, the range in the middle some distance farther away, and the last one that is furthest away from you.

Obviously, when you want to shoot, you want to capture all the mountain ranges sharp. But where do you focus? The one in front, middle or back mountain range? For me, I would set my lens to infinite focus.

This way, all three mountain ranges are sharp. Of course, set your aperture to a high number, like 8, or 11 or higher. Else you will get a bokeh effect in your picture, which you may not want in a landscape photo.

Other senior members can correct me if I'm wrong.

Cheers!
it is unlikely that you will get non-infinity focus on ANY of the three mountain ranges, if you think about it. so this is a moot example... :)

infinity focus is just there on the scale. beyond a certain point, everything further will be in focus at that point.. check out your secondary school physics if you've forgotten.. lens diagrams and all.

a much more relevant situation (which actually has nothing to do with infinity focus) involves hyperfocal distances. this happens when you need extreme depth of field. for example, you are using a 10mm to capture a starfish very close to the lens together with the entire wide expense of beach background. focusing on the starfish would render bg OOF. focusing on the background would render the starfish OOF too. switching to manual focus and reading off the hyperfocal distance charts you have, together with stopping down (balance between depth of field + diffraction).. you will get the best picture with maximum depth of field from front to back.

where infinity focus will probably come into play is as they say, at night. if what you are shooting is likely to be at infinity focus, then as there is insufficient light for your lens to lock in autofocus, you will have to switch to manual focus.

other cases include having a very dark filter over the lens, like the nd110 (10 stop nd filter) or hoya r72.
 

Octarine

Moderator
Staff member
Jan 3, 2008
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Pasir Ris
#7
In auto focus mode it's irrelevant. Camera and lens will do the job, the scale is just for information purposes. For manual focus .. well, you got most of the answers related to taking images. Which topic do you feel is not covered? Not sure whether an answer abut the positioning of the focusing group within the lens will be of any help. Read a bit more about manual focusing (when to use it) and hyperfocal distance.
Apart from that focus on shooting.
 

night86mare

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#8
btw, all the explanations you have quoted are accurate what. i don't see why you feel confused. it isn't as if they are conflicting.
 

Apr 20, 2010
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#9
thx everyone for the heads up ...

yeah im still new to photography and this is my first time to come across infinity focus:D ... i'm still learning through googling and asking (to confirm and understand better)... :D

really appreciate everyone's help ..
 

wootsk

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Aug 12, 2007
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#10
Ya, TS it will also help to read up on how AF works apart from hyperfocal distance. Please note that it is still possible to AF in night by aiming at certain point and increasing the ISO.

BTW goat, what is a moot example? Use simplier english please, I got a C6 for english for O-Level. (Barely made it)
 

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