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Hyperfocal/zone focusing confusion
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PostPosted: Thu May 21, 2015 12:13 pm    Post subject: Reply with quote

Rudolf,

As I've proved some postings above, the difference of quality of presented pictures mainly depends on the size of presentation.
The larger the intended size for presentation will be, the less the "average" method is recommended.
In the analog film times we have all been less demanding, unless a real big slide presentation was intended. For normal paper pictures any difference of super sharp compared to "within limits" was barely visible.
The more people intend to crop their pictures for larger view of the more important parts of their pictures, the more the problem will increase. That was hardly done in film times, that's also a reason for the different perception of the same issue.
That's more or less the whole story about it.


PostPosted: Thu May 21, 2015 2:10 pm    Post subject: Reply with quote

tb_a wrote:
Rudolf,

As I've proved some postings above, the difference of quality of presented pictures mainly depends on the size of presentation.
The larger the intended size for presentation will be, the less the "average" method is recommended.
In the analog film times we have all been less demanding, unless a real big slide presentation was intended. For normal paper pictures any difference of super sharp compared to "within limits" was barely visible.
The more people intend to crop their pictures for larger view of the more important parts of their pictures, the more the problem will increase. That was hardly done in film times, that's also a reason for the different perception of the same issue.
That's more or less the whole story about it.


Yes I get that now Smile

My take away is as follows:
My original understanding was flawed, as I assumed the in focus area would be equally in focus across the dof.
I can still use this technique, especially on film, but be somewhat conservative in expectations and expect some sharpness fall off away from the focal plane.

Very helpful thread!

Thanks all!


PostPosted: Thu May 21, 2015 6:29 pm    Post subject: Reply with quote

TAo2 wrote:
Hi Rudolf,

Hyperfocal distance is not "an area". As said above, it is a calculated point, dependent on focal length and aperture setting. The definition is "the distance between the camera and the nearest point that is still acceptably sharp when the lens is focused on infinity". It should not be confused with DoF (although that is part of it).

Taking your example, a 50mm lens, set at f8 would give a hyperfocal distance of 12.5 metres. So, if ye set the lens at 12.5 metres, then everything from half that distance(6.25 metres) to infinity will have an acceptably sharp DoF. Re. FF and APS-C, a 50mm lens is still a 50mm lens, the equivalent angle of view changes (narrows by the "crop factor" for each lens) not the focal length.

There are formulae tae use where ye can calculate DoF for all yer lenses individually. Or download Hyperfocal distance tables.

Formula for Hyperfocal distance - H = F²/cf

H=Hyperfocal distance
F=focal length
C=Circle of confusion
F=f number

Formula for DoF - Dn = HD/H+D - Df = HD/H-D

Dn+Df are near and far limits of DoF
H=Hyperfocal distance
D=Focused distance

So, DoF for a 50mm lens @f8, focused at 5 metres is...

12.5 x 5 divided by 12.5+5 = 3.57 metres
12.5 x 5 divided by 12.5-5 = 8.33 metres

DoF extends from 3.57 metres tae 8.33 metres. Cool


Your formulas are confusing as written. It took me a while to figure out that your "Formula for DoF" is actually two formulae and you used a minus sign as a separator. So, it would be clearer to write them as:

Dn = HD / (H + D)
Df = HD / (H - D)

Also, you have F written twice, for two different variable values. Although it appears that you used it only once, F = Focal length, in this case. Let's let N = f number. If you would like to calculate DoF by itself, this formula can be used:

DoF = (2NC[F^2][D^2])/([F^4]-[N^2][C^2][D^2)]

Here it is, lifted from Wikipedia's page on the subject,, using their variable values. It's more legible to read this way:


Note that Wikipedia also shows a wavy equals sign in their formula. It means the value derived from the formula is an approximate one. I believe this is because the Circle of Confusion can be subject to some interpretation.

This entire subject is quite interesting and can get quite involved. Wikipedia goes into considerable depth on the topics of Hyperfocal Distance and Depth of Field. See:


http://en.wikipedia.org/wiki/Hyperfocal_distance
http://en.wikipedia.org/wiki/Depth_of_field


PostPosted: Thu May 21, 2015 7:29 pm    Post subject: Reply with quote

Hi CT,

Where do ah begin? Ye really think that.....

DoF = (2NC[F^2][D^2])/([F^4]-[N^2][C^2][D^2)] is easier tae understand than...


Formula for DoF - Dn = HD/H+D - Df = HD/H-D

Dn+Df are near and far limits of DoF
H=Hyperfocal distance
D=Focused distance
??


and that ...



is more legible? More legible for a mathematician, perhaps...

The minus signs are not minus signs - they are dashes - punctuation marks.

The DoF formula is one formula, consisting of 2 logical parts - near and far limits of a particular DoF, not 2 formulae

The second capital F should have been lower case, it was an unnoticed typo and for that - I deeply apologise... Cool


PostPosted: Fri May 22, 2015 2:13 am    Post subject: Reply with quote

As a matter of fact, I do think what I wrote out is easier to follow. You just need to parse the brackets, which I put in there for clarity, after all. It would have been much clearer if my keyboard would respond the way I write -- which is why I cut and pasted the formula from Wikipedia -- to make it clearer.

When you write out a formula, I would suggest you think about using different punctuation marks than dashes -- because of their double meaning. Commas, semicolons, elipses -- any of these would have been better than minus signs -- ahem, dashes. I spent a good 15 or 20 minutes trying to figure out what was going on with your formula until I realized they were punctuation! More legible indeed!

If you want to call it one formula, fine, but it's two equations, then, because it's two separate calculations.


PostPosted: Sun May 24, 2015 10:04 am    Post subject: Reply with quote

I have found this site which may be very helpful for further understanding of the topic:

http://www.dofmaster.com/dofjs.html

Unfortunately my Ricoh GXR-M isn't listed there... Sad
However, it's a nice feature anyway.

Have fun.