Quick question on DOF calculator

[Space Face]

I've just read this thread, found it very interesting and learned a couple of things too.

 

[JBPhotog]

Huh? A Nikon D850’s image dimensions are 27.52 inches on the long side, not 68 inches.

I know you are passionate on this issue but as I stated earlier, 40+ years of commercial product work contradicts your assumptions that the LCD is sufficient. When the client requires their product to be sharp, knowing just how many mm of DoF is a huge advantage.

 

[fmw]

Additionally to what @WayneF summed up nicely. If one is seeking the actual DoF then using a calculator that specifically identifies the sensor size, CoC, focal length and f-stop is the only accurate method. My experience shooting product over the past 40+ years in all formats tells me that knowing the physical width in inches or millimetres of the DoF is an asset.

Back when cameras actually had DoF preview buttons that functioned well with the focussing screen, a visual was possible but for critical work measurements are required. This is supported by the ever present whinging from many people of the lack of DoF indicators on modern lenses.

Depth of field is a measure of acceptable sharpness, not true sharpness. It is up to the photographer to determine what is acceptable. I'll take the monitor screen and a monitor magnifier every time over a table. Cameras do have DOF preview. It is that little screen on the back of the camera.

 

[JBPhotog]

Additionally to what @WayneF summed up nicely. If one is seeking the actual DoF then using a calculator that specifically identifies the sensor size, CoC, focal length and f-stop is the only accurate method. My experience shooting product over the past 40+ years in all formats tells me that knowing the physical width in inches or millimetres of the DoF is an asset.

Back when cameras actually had DoF preview buttons that functioned well with the focussing screen, a visual was possible but for critical work measurements are required. This is supported by the ever present whinging from many people of the lack of DoF indicators on modern lenses.

Depth of field is a measure of acceptable sharpness, not true sharpness. It is up to the photographer to determine what is acceptable. I'll take the monitor screen and a monitor magnifier every time over a table. Cameras do have DOF preview. It is that little screen on the back of the camera.

Just to clarify, DoF calculators are based on the Circle of Confusion measurement for that size of sensor and the actual sharpness from the deviated focus point.

Any bias introduced by the photographer can be challenged by the viewers perception of sharpness so by that standard DoF is is irrelevant. This contradicts the science behind actual DoF and how it is calculated for the sensor, CoC, lens, aperture and focused distance.

I wouldn’t call reviewing a captured image on the LCD a preview by definition. One can use Live View to preview the DoF but many people find the pixel resolution lacking and LV has issues with studio flash work to determine DoF.

 

[fmw]

Additionally to what @WayneF summed up nicely. If one is seeking the actual DoF then using a calculator that specifically identifies the sensor size, CoC, focal length and f-stop is the only accurate method. My experience shooting product over the past 40+ years in all formats tells me that knowing the physical width in inches or millimetres of the DoF is an asset.

Back when cameras actually had DoF preview buttons that functioned well with the focussing screen, a visual was possible but for critical work measurements are required. This is supported by the ever present whinging from many people of the lack of DoF indicators on modern lenses.

Depth of field is a measure of acceptable sharpness, not true sharpness. It is up to the photographer to determine what is acceptable. I'll take the monitor screen and a monitor magnifier every time over a table. Cameras do have DOF preview. It is that little screen on the back of the camera.

Just to clarify, DoF calculators are based on the Circle of Confusion measurement for that size of sensor and the actual sharpness from the deviated focus point.

Any bias introduced by the photographer can be challenged by the viewers perception of sharpness so by that standard DoF is is irrelevant. This contradicts the science behind actual DoF and how it is calculated for the sensor, CoC, lens, aperture and focused distance.

I wouldn’t call reviewing a captured image on the LCD a preview by definition. One can use Live View to preview the DoF but many people find the pixel resolution lacking and LV has issues with studio flash work to determine DoF.

It is the photographer who is making the image. The photographer's perception of acceptable sharpness is the only one that matters. If a client is involved then it is acceptable to create multiple images and allow the client to communicate a preference. Otherwise, it is up to the photographer.

 

[JBPhotog]

Additionally to what @WayneF summed up nicely. If one is seeking the actual DoF then using a calculator that specifically identifies the sensor size, CoC, focal length and f-stop is the only accurate method. My experience shooting product over the past 40+ years in all formats tells me that knowing the physical width in inches or millimetres of the DoF is an asset.

Back when cameras actually had DoF preview buttons that functioned well with the focussing screen, a visual was possible but for critical work measurements are required. This is supported by the ever present whinging from many people of the lack of DoF indicators on modern lenses.

Depth of field is a measure of acceptable sharpness, not true sharpness. It is up to the photographer to determine what is acceptable. I'll take the monitor screen and a monitor magnifier every time over a table. Cameras do have DOF preview. It is that little screen on the back of the camera.

Just to clarify, DoF calculators are based on the Circle of Confusion measurement for that size of sensor and the actual sharpness from the deviated focus point.

Any bias introduced by the photographer can be challenged by the viewers perception of sharpness so by that standard DoF is is irrelevant. This contradicts the science behind actual DoF and how it is calculated for the sensor, CoC, lens, aperture and focused distance.

I wouldn’t call reviewing a captured image on the LCD a preview by definition. One can use Live View to preview the DoF but many people find the pixel resolution lacking and LV has issues with studio flash work to determine DoF.

It is the photographer who is making the image. The photographer's perception of acceptable sharpness is the only one that matters. If a client is involved then it is acceptable to create multiple images and allow the client to communicate a preference. Otherwise, it is up to the photographer.

Where did I state it isn't the photographer who makes the image or that it wasn't up to them to decide which part of the image is sharp or not? I think we both agree this is up to the shooter. Shooting commercial assignments requires clear understanding off the clients expectations and meeting them from a technical point of view.

I was simply pointing out that "real" DoF is determined by a host of device specifications that one can not ignore it they expect to get a three dimensional object in focus. You can't cheat those physical characteristics. If the decision is made to shoot wide open and only capture a few millimetres in focus, then go ahead. Additionally, if the subject dimensions exceed the DoF required, then decisions need to be made which part of the subject is important. But simply stating that the photographer can dictate what is technically sharp by arbitrary parameters that they impose onto the viewer is ridiculous. Sharp is sharp, blurred is blurred, those are the actual parameters of DoF.

 

[Original katomi]

This may sound really daft
When I am doing table top macro work, I first photo a 150 mm rule at mid point and see what the DOF is

 

[WayneF]

Most users have no clue what the concept of DOF calculation is. That included me for many years, until I looked into it, and then it becomes obvious. The focal length and distance and f/stop can compute what the lens does (f/stop has less effect on DOF than distance or focal length), but then CoC is the judge of the acceptable limit that is computed. CoC is overwhelmingly size related. Because when we enlarge images, we can see more detail, which includes recognizing the blurry spots.

For example consider a full frame sensor, or 35 mm film size. Its size has usual CoC limit of 0.03 mm diameter. Which has the meaning that when enlarged to the DOF standard viewing size of 8x10 inches (203x254 mm), it is enlarged 7.518x so that the CoC now becomes 7.518x larger, to about 0.22 mm enlarged size (it has a precise size, but which depends on CoC divisor chosen. If 0.03 mm, it is 0.22558 mm. If 0.0288 mm, it is 0.21685 mm.). But the idea is that it is the 7.5x larger than 0.03 mm, to be a test of if the eye can perceive it.

The meaning of that enlarged CoC size is that is carefully considered to be just barely NOT perceived by the human eye in the final print (very much like the Snellen charts the optomitrist uses on his 20/20 or 6/6 eye charts, the sizes of the letters are carefully computed). You will see a large chart on the wall at 20 feet or 6 meters, and a tiny handheld chart for up close reading. Size Matters. Snellen charts use 20/20 letters 5 minutes of angle size to see a letter, but DOF is more critical, more like 2 minutes of angle to be a just imperceptible spot. The DOF calculator is computing for a standard 8x10 inch image viewed at 10 inches (25 cm).

Viewing an image 10 times smaller must compute DOF with a CoC 10 times smaller so that when enlarged 10 times more to viewing size, it will be this same barely NOT perceptible size. And they do. That is why CoC is computed from the sensor diagonal, so all of this is true. It allows different size sensors to compute the same DOF, with blur size to be limited to be under human vision limits. Again, this is why smaller sensors have smaller CoC.

Trying to judge this from a postage stamp size 36x24 mm image what the eye might see in a 203x254 mm enlargement is not wise planning. It has no concept of the concept. Today in digital, some cameras do allow digital zooming, which is handy, but AFAIK, not with known numbers to measure how it will look later when finished.

 

[WayneF]

This may sound really daft
When I am doing table top macro work, I first photo a 150 mm rule at mid point and see what the DOF is

That is wise, and it can compare the typical horrible macro DOF with the "hey, that might even be acceptable", but critical work should be examined at the final viewing size. Macro distances (at magnifications typically greater than 0.1x) cannot compute DOF, because the marked focal length is for infinity, and the focal length changes when up close, and we also should measure the distance to an unknown node point probably inside the lens somewhere (which matters when up so close). We don't actually know any numbers.

So instead of computing DOF, macro work typically uses the magnification or reproduction ratio (of the field of the perpendicular ruler instead of the distance direction).

 

[Derrel]

Huh? A Nikon D850’s image dimensions are 27.52 inches on the long side, not 68 inches.

Really?

 

[JBPhotog]

Huh? A Nikon D850’s image dimensions are 27.52 inches on the long side, not 68 inches.

Really?

Yep.
D850’s max resolution is 8256 x 5504. 8256/300 is 27:52” 300 ppi is the native resolution of NEF files for post production.

 

[Derrel]

40x60 inch Print shot at ISO 6400 and lighted by one, single LED lamp.... With detail down to the pores in the face. And yes a 40 by 60 inch print ,made by a man who has been printing images for 30 years. Watch the video, look at the prints, your 27.5 inch figure is flat-out real world incorrect.

or check out the Imaging Resource website which lists outstanding quality from the D850 in making 30 by 40 in prints. Something they have been testing for literally years and years.

Or check out Tom Hogan's website which reveals that 288 PPI is actually virtually indistinguishable from 300ppi, and in fact might be a better PPI level than 300, due to the way inkjet printers do their dithering.

360 PPI might be required if you are going to lay a magnifying glass on an image... But billboard-sized images can be made from files with extremely low pixels per inch, since viewing distance is so great.

 

[JBPhotog]

*Serious thread derailment warning*

Don't mistake native resolution with enlargement possibilities, they are two distinctly different issues.

Back in 1984 I worked with a photographer who shot for a a billboard ad on 35mm Kodak Plus-X outputted to a 16x20 fibre based print produced on a point source enlarger. The resultant print was reproduced on CYMK film plates which produced the billboard panels. It looked fantastic at the usual viewing distance however it was reproduced at @85 dpi for output printing.

Similarly, all the ad agency work I do requires native resolution files and no surprise, the native resolution is 300 ppi. Open a Tiff file in PhotoShop that has been converted from Nikon Capture NX-D, Option-Command-I and the resolution is 300 ppi.

Viewing distance and dpi of a print are not the same as the native resolution of the original file which is captured in ppi.

 

[WayneF]

Similarly, all the ad agency work I do requires native resolution files and no surprise, the native resolution is 300 ppi. Open a Tiff file in PhotoShop that has been converted from Nikon Capture NX-D, Option-Command-I and the resolution is 300 ppi.

Viewing distance and dpi of a print are not the same as the native resolution of the original file which is captured in ppi.

But you read way too much meaning into PPI, which you mistakenly call native resolution. I may misread your words, but you said "captured", and the image is "captured" in pixels, independent of any PPI notions.

PPI is pixels per inch. The camera knows how many pixels it will create, but the camera has NO CLUE what size the image will be printed, or even if it will be printed, or how many different print sizes it might be printed (the camera has absolutely no concept of inches yet). Neither does any image processor know inches you might print, at least not until the print menu (or Resize menu) might specify the inches to it.

300 ppi is a "handy" number cameras just routinely stick in there, but they don't know your print goal. They have to put some PPI number there, because if left blank, Photoshop will assume 72 dpi which will show a print size of a few feet, which is a serious confusion. GIF files for example, have no field to specify PPI, so Photoshop will always assume and show 72 dpi for them. PPI has no meaning until meaningfully defined from inches.

The "native resolution" of an image has come to simply be the pixel dimensions, such as 6000x4000 pixels. That is not the actual lens resolution, it is merely the digital sampling reproduction of the lens image (a count of pixels). PPI is only just a bare number written into the output file, arbitrarily guessed by the camera, not meaningful, at least not until the Print menu or Resize menu specifies our goal for inches.

(Speaking of Adobe ACR) Raw processors have a menu to specify the PPI that the output JPG or TIF file will specify. They have a default, or it can be whatever PPI that you have specified for it to specify (which is as "native" as it gets). Regardless how you may crop it, it will say that same PPI for any image size you output. And of course, print menus will later specify a PPI for your specified inches.

In the Print menu, if the image width is 6000 pixels, and if you specify 20 inches for it, then ppi becomes 6000/20 = 300 ppi. If you specify 240 inches (20 feet), then ppi becomes 6000/240 = 25 ppi. But again, until your inch goal is specified, PPI is a totally meaningless (undefined) number UNTIL the print size in inches is specified, which then specifying inches should recompute PPI = pixels/inches. But until OUR GOAL IN INCHES is specified, pixel dimensions are the only thing known.