Towards a better method of calculating hyperfocal distances?

[wiltw]

Ordinarily, both Depth of Field calculations and Hyperfocal Distance calculations are based upon the FALSE assumption that they human eye is FOOLED into seeing a certain diameter Blur Circle (vs. a perfectly focused 'Point') and thinking 'In focus'...what is commonly referred to a 'Manufacturer Standard' CoC assumption. Our optical practitioners actually strive to correct our vision to even better standards than 'manufacturer standard', So when we look at a print we actually see 'blurry' rather than 'in focus' (as the charts and DOF scale marks on lenses would fool us into thinking.) That is a key reason that so many photographers decades ago would use the DOF scale marks on lens that was 1-2 EV larger aperture than shooting aperture...if f/16 was shooting aperture, they consulted the DOF scale marks on the lens for f/8.
IOW the standard CoC diameter assumption is too large, in the computation of most calculators and tables and DOF scale marks on lenses! A standard DOFcalculator says 100mm f/8 lens focused at 10m has DOF zone of 5.4m, but what our optician corrects our eyes to has DOF zone of only 1.7m !

And if your calculations for DOF or Hyperfocal Distances are applied to an even bigger print (than 8" x 10") the calculations are INVALIDATED because the Blur Circles are magnified in the enlargement process and the eye CAN more easily see 'blur' rather than 'point' even more dramatically!

One problem in using Hyperfocal Distance calculators is that modern AF lenses (even the ones first available in the 90's for film cameras) have such spatially compressed distance marking that if you needed to set 18' on the distance, where in the gap between 10' and Infinity does one FIND 18' vs. any other distance?! For the 100mm f/8 lens, the Hyperfocal Distance is at 117m...just WHERE is that found on the distance scale, even a manually focused fixed FL lens?!

 

[sk66]

And if your calculations for DOF or Hyperfocal Distances are applied to an even bigger print (than 8" x 10") the calculations are INVALIDATED because the Blur Circles are magnified in the enlargement process and the eye CAN more easily see 'blur' rather than 'point' even more dramatically!

I'm not sure what you mean by "fooled," but this is the only part I would particularly disagree with; because the CoC standard does not assume an 8x10 print. It assumes a print/display viewed from a distance equal to its' diagonal (e.g. 8x10 viewed from 12"). I.e. when it is viewed as a whole image and occupies the humans ~ 45˚ horizontal/55˚ circular primary/central FOV (which is also the field of view of a "standard lens" BTW).

A larger print is assumed to be viewed from a greater distance; keeping the relative blur point size/visibility constant.

 

[wiltw]

I'm not sure what you mean by "fooled," but this is the only part I would particularly disagree with; because the CoC standard does not assume an 8x10 print. It assumes a print/display viewed from a distance equal to its' diagonal (e.g. 8x10 viewed from 12"). I.e. when it is viewed as a whole image and occupies the humans ~ 45˚ horizontal/55˚ circular primary/central FOV (which is also the field of view of a "standard lens" BTW).

A larger print is assumed to be viewed from a greater distance; keeping the relative blur point size/visibility constant.

The usual DOF calculation assumes that an 8" x 10" print is viewed at about 25cm...the number you see as a published Circle of Confusion diameter is that almost-visible Blur Circle diameter scaled back to film format size...for 135 it is about 1/8 of the acceptable Blur Circle on the 8" x 10" print.

For larger priints (>8x10), unfortunately most folks do not use the 'correct viewing distance' ...I doubt most increase viewing distance much for 11" x 14" pint, they continue to stick their noses up as close, rendering invalid the assumed size of the acceptable Blur Circle on the print.

From Wikipedia:

Circle of confusion diameter limit in photography[edit]​

In photography, the circle of confusion diameter limit (CoC limit or CoC criterion) is often defined as the largest blur spot that will still be perceived by the human eye as a point, when viewed on a final image from a standard viewing distance. The CoC limit can be specified on a final image (e.g. a print) or on the original image (on film or image sensor).​

​

With this definition, the CoC limit in the original image (the image on the film or electronic sensor) can be set based on several factors:​

​

1. Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision,[7] is approximately 25 cm. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.
2. Viewing conditions. If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate. A comfortable viewing distance is also one at which the angle of view is approximately 60°;[7] at a distance of 25 cm, this corresponds to about 30 cm, approximately the diagonal of an 8-inch × 10-inch image (for comparison, A4 paper is 8.3 in × 11.7 in, 210 mm × 297 mm; US Letter paper is 8.5 in × 11 in, 216 mm × 279 mm). It often may be reasonable to assume that, for whole-image viewing, a final image larger than 8 in × 10 in will be viewed at a distance correspondingly greater than 25 cm, and for which a larger CoC may be acceptable; the original-image CoC is then the same as that determined from the standard final-image size and viewing distance. But if the larger final image will be viewed at the normal distance of 25 cm, a smaller original-image CoC will be needed to provide acceptable sharpness.
3. Enlargement from the original image to the final image. If there is no enlargement (e.g., a contact print of an 8×10 original image), the CoC for the original image is the same as that in the final image. But if, for example, the long dimension of a 35 mm original image is enlarged to 25 cm (10 inches), the enlargement factor is approximately 7, and the CoC for the original image is 0.2 mm / 7, or 0.029 mm.

 

[sk66]

The usual DOF calculation assumes that an 8" x 10" print is viewed at about 25cm..

Wow, that wikipedia entry is pretty poorly written...

The accepted CoC standard is d/1500 (where d is sensor diagonal) which is .03mm (.0288) on 35mm sensor, and results in 0.168mm in an 8x10 print. Which corresponds/rounds to the ".2mm in the final image" as noted in the first line you quoted.

1. Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision,[7] is approximately 25 cm. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.

I edited the part regarding viewing conditions so it makes more sense and reads appropriately.

"2. If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate.
A comfortable viewing distance is also one at which the angle of view is approximately 60°.
This corresponds to about 30 cm (for 8x10), approximately the diagonal of an 8-inch × 10-inch image."

The first line is just a restatement of the previous note. The second line is also true; at any distance. The third line as edited is also true, but 60˚ at 25cm corresponds to an A5 image (14 x 21cm; 5.5" x 8.3" ) or a 5x7 postcard... both are referenced in CIPA documents (Japanese standards).

You can define the CoC limit in almost any manner you would like as appropriate for the intended use... the wikipedia says "often defined as." But there is an accepted/reference standard, I used to have a PDF from Zeiss on it regarding lens markings, but I can't find it now.

I'm not sure that one can say "most don't use correct viewing distance." You can say there is no real way of controlling the viewing distance used in most situations. And some are quite likely to use a shorter distance to critically evaluate an image. But in order to actually see an image as a whole, and recognize all of the elements at once, it must fit w/in the 55-60˚ field of view due to the way the human eye works.

I do agree that "the standard" is a low bar and very likely inadequate... heck, it requires less than 2MP resolution in any size image. d/3000 corresponds to corrected vision and a high contrast image (e.g. vision test chart).

 

[Deleted member 97794]

Never used hyper focal distance in my life. It’s a good way to sell apps though.

No, me neither. I wouldn't describe myself as a technical photographer but I think I would have learned about Hyperfocal distance had I ever had issues focussing using conventional methods.

 

[AndrewFlannigan]

... I think I would have learned about Hyperfocal distance had I ever had issues focussing using conventional methods.

Hyperfocal distance was very important to users of medium and large format cameras, before 35mm became the most common format.

When your standard focal length is 50mm, it's usually acceptable to check the scale on the lens mount, to see if your depth of field will do for the scene you wish to record. With 28mm or shorter, it's pretty much irrelevant, while with 100mm or more, most people need to use their rangefinder or screen, to figure out which aperture will be needed to cover the distances required.

 

[Deleted member 97794]

Hyperfocal distance was very important to users of medium and large format cameras, before 35mm became the most common format.

When your standard focal length is 50mm, it's usually acceptable to check the scale on the lens mount, to see if your depth of field will do for the scene you wish to record. With 28mm or shorter, it's pretty much irrelevant, while with 100mm or more, most people need to use their rangefinder or screen, to figure out which aperture will be needed to cover the distances required.

Ah, perhaps why I've never needed it then, I've never shot medium format.