Focusing to infinity

ziggy©

ziggy©

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There's still a depth of field when you focus to infinity. I'm not sure how it works with that photo though - at infinity I would have thought the background would have been in focus, with perhaps the players not in focus.
 
Infinity is as far as you can see, probably a few thousand light years at night :) It means that in effect you have focused as far as the camera can see, think horizon. The area in focus in front of that point will vary depending on the aperture f16 quite a lot, f2.8 not so much. To maximise the amount in focus you need to focus on the hyperfocal point which isn't infinity. A bit like 10 ft in front of the focus point and 20 ft behind will be acceptable.

Look up Hyperfocal distances on Google. It's a case of maximising the area that you want to be in focus.
 
Ok i see what you mean. I must have been confused with "Focusing at the hyperfocal distance" and "Focusing at infinity". I thought that they meant the same thing. I guess what you are saying is that the camera has a limit as to how far away it can focus. What i still dont understand is how it then decided that the two players were at infinity? I would have thought that infinity would be miles away.

If you look at the other examples from the link, the focus distance for the majority of the other pictures is 42 meters. Im guessing that since the pictures were taken in a football stadium the camera should have no problem focusing anywhere on the stadium. I have also focused on objects miles away when taking landscapes. Why has the camera suggested that the distance was infinity in this case?

Thanks in advance :)
 
Don't know the technical reasons, but my sigma 12-24 focuses at infinity when focusing on something at the other end of the room that's about 4foot away.
 
Infinity is the distance beyond which everything is sharp, as you say. So clearly that image was not focused at infinity.

It was also shot with a long lens, and the effective distance where infinity begins varies a lot with focal length. As mentioned above, on an ultra-wide it's hardly more than a few yards away, but on a long telephoto it can be a hundred yards or more, due to the magnification effect.
 
ziggy©;3494727 said:
Ok now i am confused again. I thought to get everything to be sharp you have to focus at the hyperfocal distance not at infinity?
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Hyperfocal distance is the focus setting for maximum range of depth of field, which always has infinity at one end, and a closest distance that varies with focal length and f/number.

hollis_f said:
I'm not surprised. If I didn't know that statement was garbage I'd be confused.
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You've lost me Frank. It reads okay to me.

What's garbage? What's your definition of infinity?
 
A camera can only focus on one specific point, now there will be a range in front and behind that focus point that will still be acceptably sharp, that range increases as the aperture gets smaller, ignoring diffraction issues for the moment. As you focus closer and closer the range covered gets smaller as it also does if you use a wider aperture. The secret is to decide how to utilise this range that is acceptably sharp.
 
Hi,

So how does the DOF preview work? This is something I've never 'got' I have just bought the canon 100mm IS macro lens and at f2.8 the area in focus is VERY small, so when I was experimenting and took a photo of a plant at the weekend barely anything was in focus! I understand aperture so tried again at f11, which improved the area of focus. But how do you keep a small area sharp and get the lovely bokeh?
 
Thank you all for responding. All comments are very helpfull and very much appreciated :)

I do understand how DOF works. I know that the wider the aperture (smaller number) the less depth of field you get and the narrower the aperture (i.e. the larger the number) the more depth of field you get.

Getting back to the original question, i was not really asking about how DOF works as i think i understand it already. I was more interested in how DOF is affected when hyperfocal distance focusing and infinity is added to the equation.

Originally i was not aware of the difference in focusing on Hyperfocal distances and infinity. Ken did clarify that quite well. Here is what i have understood so far - Please do correct me if i am wrong

1 - The camera has a limit as to how far it can focus. Once you focus beyond this limit you are focusing on infinity. This has nothing to do with hyperfocal distances. The DOF rules will still work as they always do even when focusing at or beyond infinity. i.e. the range in front and back behind that focus point which is sharp will depend on the aperture used.

2 - When focusing at the hyperfocal distance (Usually a third into the scene), the range in focus should be from the hyperfocal distance focus point all the way up to infinity. Basically this means that the majority of the scene behind the focus point should be acceptably sharp.

And here is what i dont understand

- If you focus on the hyperfocal distance, would the aperture used matter? i.e. if you use a wide aperture (small number) will the range that will be sharp still be to all the way upto infinity?

- On the picture i used as an example, i have understood why the background was not in focus. This is because the photographer did not focus on the hyperfocal distance but he focused at a point at infinity. The bit that i find confusing is why did the camera treat a subject that is at 42 meters to be at infinity - Is there an exact range as to what the point of infinity is for a specific camera or does this depend on the lens/focal lengths etc?

- Is there a big difference between something being in focus and being sharp? Or do they mean the same thing?

Thanks in advance
 
ziggy©;3496597 said:
- On the picture i used as an example, i have understood why the background was not in focus. This is because the photographer did not focus on the hyperfocal distance but he focused at a point at infinity. The bit that i find confusing is why did the camera treat a subject that is at 42 meters to be at infinity - Is there an exact range as to what the point of infinity is for a specific camera or does this depend on the lens/focal lengths etc?
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There's something wrong with the exif on that image. There's no way that the players would be in focus and the background not in focus if the lens was focused to infinity - vice versa would be more likely.
 
There's something wrong with the exif on that image. There's no way that the players would be in focus and the background not in focus if the lens was focused to infinity - vice versa would be more likely.
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I think what is confusing people (or me for that matter) is that the photographer did not focus to infity. He/She focused at a point at infinity.

If i understood the comments posted above correctly, focusing at a point at infinity does not necessarily mean that everything from the focus point upto infinity will be in focus. (You have to focus at the hyperfocal distance to get everything upto infinity to be in focus).

Could it be that the exif is showing that the focus distance is infinity meaning that the point at which the focus point was set was beyond the range at which the camera can measure the focus distance?
 
HoppyUK said:
Infinity is the distance beyond which everything is sharp
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hollis_f said:
I'm not surprised. If I didn't know that statement was garbage I'd be confused.
Click to expand...

HoppyUK said:
You've lost me Frank. It reads okay to me.

What's garbage? What's your definition of infinity?
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Does it really read OK? So when I use my 10-22 lens at f/11 and focus on something 2m away, then infinity is just 38cm way? Because everything beyond 38cm is in focus (or within acceptable focus for the real pedants). Saying that infinity is 38cm with this lens is just wrong.

What's my definition of infinity? Well, photographically speaking, it's the distance at which light rays from an object are parallel when they strike the detector. Or (because that distance is truly infinite) it's the distance at which an object needs to be for the light rays from it to be effectively parallel, such that the detector can't tell if they are or not.
 
hollis_f said:
Does it really read OK? So when I use my 10-22 lens at f/11 and focus on something 2m away, then infinity is just 38cm way? Because everything beyond 38cm is in focus (or within acceptable focus for the real pedants). Saying that infinity is 38cm with this lens is just wrong.

What's my definition of infinity? Well, photographically speaking, it's the distance at which light rays from an object are parallel when they strike the detector. Or (because that distance is truly infinite) it's the distance at which an object needs to be for the light rays from it to be effectively parallel, such that the detector can't tell if they are or not.
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But I didn't say that Frank. Or anything like it. I said "hardly more than a few yards" not 38cm. Here:

HoppyUK said:
Infinity is the distance beyond which everything is sharp, as you say. So clearly that image was not focused at infinity.

It was also shot with a long lens, and the effective distance where infinity begins varies a lot with focal length. As mentioned above, on an ultra-wide it's hardly more than a few yards away, but on a long telephoto it can be a hundred yards or more, due to the magnification effect.
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In practise, if with my 17-40L on full frame (similar to your 10-22) at anything over about 8-10m it focuses exactly on infinity and doesn't move even when I point it at the horizon. However, and this is the point I wanted to make, if I then fit a 70-200L 4 it doesn't reach the infinity position until well over 100m or even further.

The picture linked by the OP was taken on a 300 2.8 and with lenses like that you hardly ever reach the true infinity position, and no way was that image focused at infinity, despite what the Exif says.

BTW, I like your definition of infinity. What I tried to say, obviously not very clearly, was supposed to mean the same thing ;)
 
For whatever reason the EXIF in your sample picture is just wrong! There is no way the photographer focussed at or to infinity. Infinity has nothing to do with that picture at all!

In photographic terms, infinity refers to a distance great enough to be unaffected by finite variations. In practice this means most subjects beyond 1,000 meters or, in landscape terms, the horizon.

The hyperfocal distance is the point where from half that distance to infinity are recorded acceptably sharp.
 
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ziggy©;3496597 said:
Thank you all for responding. All comments are very helpfull and very much appreciated :)

I do understand how DOF works. I know that the wider the aperture (smaller number) the less depth of field you get and the narrower the aperture (i.e. the larger the number) the more depth of field you get.

Getting back to the original question, i was not really asking about how DOF works as i think i understand it already. I was more interested in how DOF is affected when hyperfocal distance focusing and infinity is added to the equation.

Originally i was not aware of the difference in focusing on Hyperfocal distances and infinity. Ken did clarify that quite well. Here is what i have understood so far - Please do correct me if i am wrong

1 - The camera has a limit as to how far it can focus. Once you focus beyond this limit you are focusing on infinity. This has nothing to do with hyperfocal distances. The DOF rules will still work as they always do even when focusing at or beyond infinity. i.e. the range in front and back behind that focus point which is sharp will depend on the aperture used.

2 - When focusing at the hyperfocal distance (Usually a third into the scene), the range in focus should be from the hyperfocal distance focus point all the way up to infinity. Basically this means that the majority of the scene behind the focus point should be acceptably sharp.

And here is what i dont understand

- If you focus on the hyperfocal distance, would the aperture used matter? i.e. if you use a wide aperture (small number) will the range that will be sharp still be to all the way upto infinity?

- On the picture i used as an example, i have understood why the background was not in focus. This is because the photographer did not focus on the hyperfocal distance but he focused at a point at infinity. The bit that i find confusing is why did the camera treat a subject that is at 42 meters to be at infinity - Is there an exact range as to what the point of infinity is for a specific camera or does this depend on the lens/focal lengths etc?

- Is there a big difference between something being in focus and being sharp? Or do they mean the same thing?

Thanks in advance
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You're getting confused here, so a few comments.

Infinity and hyperfocal distance are quite different. Use Frank's definition of infinity above, and note that the effective distance where infinity starts varies with both focal length and f/number.

The reason for that is that true infinity doesn't exist, as the light rays from a distant subject are never absolutely, truly and perfectly parallel. However, there comes a point when they are so close as makes no difference. The reason why this distance varies with focal length etc is because longer lenses magnify any slight discrepencies and they become visible. It is conceptually related to depth of field in that sense.

Hyperfocal distance setting and the 'focus one third in' rule are compeletely different. One-third-in only works for subjects at normal walkabout sort of range, where you know both the near and far points needed to be sharp - say a small group of people for example. The amount of DoF you get in front and behind the subject varies with distance - close up it can be 49/51%, and at distance there is much more behind - like miles behind, sometimes literally.

HFD is a technique for obtaining maximum distance of sharpness, and as such must always include infinity and one end, to the foreground. It is also subject the the rules of depth of field, which disregard absolute sharpness and swap it for 'effective' sharpness - ie, details that appear absolutely sharp according to DoF viewing parameters, even if strictly speaking they are not as sharp as they could be in theory.

If you try to use one-third-in for distant landscapes, first of all one third of infinity is impossible to calculate ;) and what usually happens when people have a go is that they lose out on a lot of potential foregound sharpness. Check it out on the calculator here www.dofmaster.com

HFD setting only really works with wide-angles as the closest point of acceptable sharpness gets too far away very rapidly as focal length increases. To use HFD technique with the linked image, the photographer would have to have used about f/7,000 - way beyond practical range anyway :eek:

Good thread on all this stuff here http://www.talkphotography.co.uk/forums/showthread.php?t=255258
 
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