Faking Infinity

[Hertz van Rental]

But I stand to be corrected.

I'm afraid you need to be. You have made a few basic errors there.
I blame your teacher

Firstly, only the exact point a lens is focussed on is actually in focus.
The region either side of this point, known as the depth of field, is merely a region of acceptable sharpness. That is to say, anything in there is not actually in focus, it's just not out of focus enough to be noticeable.
Or to put it another way, as object move further away from the point of focus they become more and more out of focus until you can see it.
What is 'acceptably sharp' is subjective and is determined by the resolving power of the eye. The textbook definition is 'the least separation of two points at which the eye can still distinguish that they are separate'.
Under normal conditions with normal sight this is a separation of 0.25 mm viewed at a distance of about 430 mm. This limiting separation is often called the 'circle of confusion'.
It can be seen from this that the overall sharpness of any photograph is determined by how big you enlarge it and the distance you view it from.
You can see this effect at work on digital images.
Enlarge one and you will see that it is made up of small squares, but make the image smaller and - when the squares are smaller than the circle of confusion - they disappear and the image looks sharp.
On the camera side of things, the depth of field is a function of the focal length of the lens, the aperture and the circle of confusion.
If a lens is focussed on 'infinity' then the depth of field means that there will be objects nearer to the camera that are in acceptably sharp focus. The depth of field will also allow objects beyond infinity to be in acceptably sharp focus.
As you may imagine, this is a waste of depth of field.
A point very roughly half way between the nearest acceptably sharp object and infinity is designated as the hyperfocal distance.
The hyperfocal distance therefore is merely the distance which, when the lens is focussed on it, gives the greatest depth of field.

If you want me to explain more - or make it clearer - then I will have to start drawing diagrams.
Alternatively, you could try reading a book on the subject.

 

[Helen B]

What is 'acceptably sharp' is subjective and is determined by the resolving power of the eye. The textbook definition is 'the least separation of two points at which the eye can still distinguish that they are separate'.
Under normal conditions with normal sight this is a separation of 0.25 mm viewed at a distance of about 430 mm. This limiting separation is often called the 'circle of confusion'.
...
Enlarge one and you will see that it is made up of small squares, but make the image smaller and - when the squares are smaller than the circle of confusion - they disappear and the image looks sharp.
On the camera side of things, the depth of field is a function of the focal length of the lens, the aperture and the circle of confusion.

Just to clarify: 'circle of confusion' can be used to describe any image of an object point that is not itself a point - it doesn't matter whether it is inside a size limit, on the limit or outside it. It may be clearer, therefore, to call the limiting value the 'maximum acceptable circle of confusion'.

Best,
Helen

 

[Moglex]

Just to clarify: 'circle of confusion' can be used to describe any image of an object point that is not itself a point - it doesn't matter whether it is inside a size limit, on the limit or outside it. It may be clearer, therefore, to call the limiting value the 'maximum acceptable circle of confusion'.

Best,
Helen

Once again, Helen, you seem to be overcomplicating things just for the sake of it.

Anyone who has studied the subject knows that but, quite honestly, you are not clarifying anything with posts such as the above - merely introducing pointless and potentially confusing detail that has no actual value for photographers.

Anyone who wants or needs to go to that sort of level can read an optics text just as you have. It's really nothing more than noise here.

 

[Helen B]

Once again, Helen, you seem to be overcomplicating things just for the sake of it.

Anyone who has studied the subject knows that but, quite honestly, you are not clarifying anything with posts such as the above - merely introducing pointless and potentially confusing detail that has no actual value for photographers.

Anyone who wants or needs to go to that sort of level can read an optics text just as you have. It's really nothing more than noise here.

Thanks for your opinion. I have little respect for you or your opinions, so I'll ignore it.

I have more faith in the members of TPF - I don't think my clarifiation would be considered a complication by many of those interested in this subject.

Best,
Helen

 

[Moglex]

I have more faith in the members of TPF - I don't think my clarifiation would be considered a complication by many of those interested in this subject.

That might make sense if it was actually a clarification.

It isn't.

Photographically speaking it's simply an entirely pointless obfuscation.

When photographers use the term 'circle of confusion' they always mean 'maximum acceptable circle of confusion' so telling them that it actually means something else is not helpful, it's just sophistry.

 

[Helen B]

That might make sense if it was actually a clarification.

It isn't.

Photographically speaking it's simply an entirely pointless obfuscation.

When photographers use the term 'circle of confusion' they always mean 'maximum acceptable circle of confusion' so telling them that it actually means something else is not helpful, it's just sophistry.

That's just your opinion. I don't share it. I'm truly grateful to you for expressing it, though I hope that you do not intend to tell me what I should or shouldn't post. I know that the term is often shortened, and have often shortened it myself, but I also think that it is worth remembering that it can be applied to any blur circle of any size or even shape. That you find that confusing is not a worry to me. Just ignore it.

Best,
Helen

 

[Moglex]

That's just your opinion. I don't share it. I'm truly grateful to you for expressing it, though

You're very welcome.

I hope that you do not intend to tell me what I should or shouldn't post.

Heaven forfend!

That you find that confusing is not a worry to me. Just ignore it.

I don't find it confusing as I have known it for a very long time.

I was just pointing out that as photographers always use it to mean the same thing, your post cannot add anything useful to their knowledge and may serve to confuse anyone who is already struggling with the concept.

Should you wish to post such information it is, of course, entirely up to you.

 

[monkeykoder]

I'd have to say I would find Helen's post rather useful if I didn't already have the information in hand. In studying optical phenomenon in photography it is useful to know when the wording being used is technical or slang. If one wanted to go further in their studies than mere competence one would be confused as to why the term "circle of confusion" was used in other instances than the one previously mentioned. Foreknowledge might help and reduce said confusion.

 

[JerryPH]

A lot of you people are just *so* above me, but I'm pretty sure that you can simply apply a little formula and get about any hyperfocal distance you need as long as you know a few details of your equipment.

H = (I X I) / (F X D) where:

H is the hypeforcal distance
I is the focal length your lens is set at
F is is the aperture your lens is set at
D is the circle of confusion diameter (D = 0.02501 for 35mm film as mentioned above)

Example:

Using my 105mm lens set at F/8.0 with my dad's Nikon F2A camera, using the above info means that the hyperfocal distance in feet would be 55 feet. Everything from 55 feet to infinity would have an acceptable focused look to it.

I do not think that sensor crop factor would have very much to do with it as all the tests that I did showed that using the above info gave me better focused objects than when I applied the crop factor to the "I" (focal length) numbers (no great scientific tests, maybe about 50-60 shots).

 

[manaheim]

That might make sense if it was actually a clarification.

It isn't.

Photographically speaking it's simply an entirely pointless obfuscation.

When photographers use the term 'circle of confusion' they always mean 'maximum acceptable circle of confusion' so telling them that it actually means something else is not helpful, it's just sophistry.

Not for nothing, but Helen is an incredible and helpful resource on this forum. A great many of us wait for her to weigh in on topics like this and really appreciate the depth of her understanding.

I'm not sure how she's going to feel about my speaking up here, but really what I'm mainly trying to say is "Hey Helen, even if Mog doesn't value you, I sure as hell do."

'course, not like my opinion carries any more weight than anyone elses.

NO BASHY HELEN!

 

[Hawaii Five-O]

Helen and a lot of other people on here have been a big help to me with my film questions:thumbup: She always has good information in her posts.

 

[Dubious Drewski]

Yeah, we've got a good group of people here. This is why after trying many other forums, I've decided to make this place my home.

Anyway, I'd like to know - is the hyperfocal distance really such a precise thing? Whenever I tell people I'm focusing on the hyperfocal, I'm just turning the ring to infinity then moving back a millimeter or so. Isn't that where it would be on every single lens?

I'm missing something huge, aren't I.

No matter, I've never been big into landscape photography.

 

[Moglex]

Yeah, we've got a good group of people here. This is why after trying many other forums, I've decided to make this place my home.

Anyway, I'd like to know - is the hyperfocal distance really such a precise thing? Whenever I tell people I'm focusing on the hyperfocal, I'm just turning the ring to infinity then moving back a millimeter or so. Isn't that where it would be on every single lens?

I'm missing something huge, aren't I.

Yes, particularly at the higher f numbers.

At, say, f22, on a wide angle lens the DOF towards infinity is enormous.

Have a look at the DOF table Here to get some concrete examples of where the hyperfocal distance is for a 50mm lens.