DOF Master clearly wrong

Pistnbroke

In the programme DOF Master it I put in D810/600mm F8 100ft it says depth of field is 4 ft ...clearly wrong ...more like 0.4 of an inch.....so why? Are they using a wrong circle of confusion figure ?

Coastalconn

@100 feet that sounds about right. If you really want to get confused, do the same thing with a DX camera...

Ironheart

According to the standard DoF calcs, 600mm @ f/8, 100ft away gives 3' 11.8" DoF.
The only "assumption" is a CoC of 0.030 mm which is the standard for a FF (FX) camera.

You could argue a smaller CoC for a 36mp sensor, but even if it is half (ridiculous IMO) e.g. 0.015 the DoF would be 2' at 100ft. The only way to get smaller DoF is to get closer. E.g. at 20ft, the DoF is about 2".

My version of DoF master doesn't even have the D800 in it... What version are you using?

EDIT:

In playing with the on-line version (my iPhone one is broken) it looks like they are using 0.030mm for a CoC for the D800 which is correct for a FX.

2nd EDIT:

If you are looking at the image at 100%, you will perceive a much smaller DoF. Print it out 8x10 and look at it from a foot or so away. You will see the larger DoF.

Pistnbroke

I am looking at it from a bird photography point of view ...4ft of DOF ...no way... maybe 1 inch

Paperman

DOF may be a few percent off but expecting 1" in 100 ft / 2.5cm in 30 meters is simply unreal Pistnbroke.

Looking at it from a different ( and very simple ) perspective, 1 inch is 1/1200th of 100 ft. Let's say you are taking a portrait from 5 ft with a 50mm ( similar coverage in frame ?? ) . Will you expect the DOF be something like 1/1200th of 5ft - that is 1/12th of an inch ( 2 mm ) like the size of a rice grain ? ... That means the whole face will be a blur other than the iris you focus on .( The actual DOF is 3-4 inches at f1.4 )

And don't forget, you are at f8 !

Pistnbroke

Well if I get me 600 mm tamron at F8 and take a picture of a bird at 100ft away about 1 inch of depth of field is what I get ...my test target is a statue about 6 inches in front of a fence ....face in focus but not the fence and not the end of her nose when I focus on her forehead !!

Correlli

The point is, that the DOF calculation is based on the assumption that you print your image and look at the print from a "normal viewing distance" - the larger the print the further you are away from it. If you look at the image on your monitor and zoom in all the way this assumption is not true anymore.

The circle of confusion for 35 mm sensors is 0,03 mm (as others have said above) but the pixel size of the D810 is 0,005 mm. So with the normal calculation a point that is spread over an area with 6 pixles in diameter is still considered in focus.

If you print your file (without cropping) a CoC of 0,03 mm is fine. If you look at the image at 100% on your monitor you might want to decrease the CoC to 2x the pixel size.

Paperman

Still the difference will not compare to the difference between 4 ft and 1 inch. ( 50x )

Correlli

True. What I wanted to say is that there is not right or wrong definition of depth of field. It depends on the circumstances and personal taste (ask 10 people about the fence in the image the Pistnbroke mentioned and you will get 11 different opinions about its sharpness).

Ironheart

At that far away, you should have a couple of feet of DoF to work with. If you are seeing that shallow of a field, you may be front focused, i.e. All of the DoF is in front of your subject, and you are just nipping it with the edge of the DoF? Remember the further away the subject, the greater the DoF.

Also as both I and @Correlli have pointed out, viewing size and distance matter. The standard DoF calcs, the CoC values, are set by a person with normal vision (20/30-20/40) viewing an 8"x10" enlargement of the whole frame at ~1 foot. A 36mp image, viewing a section at 100% zoom on a 27" monitor, would be like looking at a 4'x8' enlargement from 1 foot away. Of course what is "acceptably sharp" will be different. Make an 8x10" print of your test shot and tell me what you see, I won't ask you to print a 4'x8' print

Pistnbroke

Well front focus etc is not an issue that's spot on but I think I have worked out whats going on. If I view the whole frame with the bird in the middle then the "focus" is acceptable for say 2ft in front and 2 ft behind. If I go in to 100% ( that's a sensor 3.6mm x 2.4mm ) then at this "magnification" equivalent to using a 6000mm lens much less is in acceptable focus.

Am sure most of you have been saying the same thing in your own way so thanks everyone ...my brain is now aligned.

WestEndFoto

This raises a good point. I have often found myself dissatisfied with focus when I zoom in (except for the focus point which is fine). However, when I look at it normally, it looks fine.

manhattanboy

WestEndFoto said:

This raises a good point. I have often found myself dissatisfied with focus when I zoom in (except for the focus point which is fine). However, when I look at it normally, it looks fine.

This issue is why companies like Lyrtro tried to make a run at Light Field Photography.
This is also why more megapixels is a dual edge sword...the focus needs to be spot on or 100% is going to look like it's soft. Remember that when you buy the D850/D900.

Paperman

At the pixel level, I am guessing motion blur will be more of a concern than the focus issue. The frame is likely to move/shake more than a pixel ( what was that - around 1/200 th of a milimeter ? ) in any direction at any speed with/without VR at such focal lenghths.

WestEndFoto

That is always an issue. But if 1/50th of a second works for a D810 then 1/40th of a second will work for the next generation.

TriShooter

I understand what Pistnbroke is saying. Bird photographers frequently crop images so will usually pass on a shot that is less than tack sharp at 100 percent on the original image. Also what appears to be in focus on a full-screen monitor is often just not good enough unless it is for something like FB where the image is being downsized which sometimes helps to make a marginal shot look better than it really is to the viewer.

spraynpray

Yup. I'm the same with my Macro. Unsharp at 100% = delete.

Pistnbroke

Isn't it nice to be on a site where members can have a sensible discussion without going into "I don't like him he said XXX so I will ignore him"

WestEndFoto

OK Pistnbroke, I will undelete and unblock you....