Author Topic: DOF settings. Simple or Diffraction Aware?  (Read 1011 times)

russellsnr

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DOF settings. Simple or Diffraction Aware?
« on: July 26, 2017, 09:28:38 AM »
Hi, Can someone please explain the differance in simple terms between the Simple and the Diffraction aware options? Have looked at the Userguide and all that I can see is  DOF near and DOF far and that I understand, there is also a link 
'See also Focus distance' that sends you to 'This topic does not exist yet

You've followed a link to a topic that doesn't exist yet.'
Thankyou.
Russ


Walter Schulz

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #1 on: July 26, 2017, 09:36:31 AM »
Do you know what diffraction is?
Same question for "Circle of Confusion" ...

In very simple terms:
You know DOF is dependend on focus distance and aperture (narrow opening = higher aperture number) and focal length.
You might not know resolution for higher aperture numbers may be reduced. It's called diffraction and it's a law for optical physics.
"Simple"  = Don't care about diffraction. Use distance, aperture, focal length for calculations.
"Diffraction Aware" = Compute and don't let diffraction reduce resolution.



We're not talking about macro photo conditions here, I hope ...

russellsnr

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #2 on: July 26, 2017, 10:18:22 AM »
Hi, Diffraction concerns the amount of light in photography terms hitting the lens/sensor. "As
you stop down the aperture on a lens the light passing through tends to diffract,
reducing sharpness, though DOF is increased. The reason for this is that the
edges of the diaphragm blades in the lens tend to disperse the light. At larger
apertures this diffracted light is only a small percentage of the total amount
of light hitting the sensor, but as the aperture is stopped down the
amount of diffracted light becomes a larger percentage of the total amount of
light being recorded."
And yes I have a good idea about the COC but like most photographers do not understand the maths of it as COC but do as DOF.

Walter Schulz

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #3 on: July 26, 2017, 10:25:40 AM »
Hi, Diffraction concerns the amount of light in photography terms hitting the lens/sensor.
The way you put it down in your own words sounds wrong. You may mean the right thing but I cannot tell from this sentence if you got the concept.

russellsnr

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #4 on: July 26, 2017, 10:41:26 AM »
OK, So should you use   the Simple or the Diffraction aware options?

Walter Schulz

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #5 on: July 26, 2017, 10:43:45 AM »
Yes.

russellsnr

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #6 on: July 26, 2017, 10:47:34 AM »
Anyone here that explain these options in plain ENGLISH please as I asked in the OP. Many Thanks. Russ

Walter Schulz

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #7 on: July 26, 2017, 10:55:45 AM »
In very simple terms:
If you haven't been bothered by diffraction effects yet, you're doing just fine with "Simple".

russellsnr

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #8 on: July 26, 2017, 11:07:05 AM »
Thankyou.

JohanJ

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #9 on: July 26, 2017, 11:25:02 AM »
Anyone here that explain these options in plain ENGLISH please as I asked in the OP. Many Thanks. Russ
for better understanding of diffraction effects please have a look at
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

In general DOF calculation tries to approximate inifinite problems by using finite formulas. There are simpler formulas which deliver good results in most cases. Option "defraction aware" takes into consideration difraction effects and it leads to a more complex formula. However whether you benefit from the result is depending on your shooting scenario.

Sent from my SM-T719 using Tapatalk

60D.111 / 100D.101 / M2.103

russellsnr

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #10 on: July 26, 2017, 11:44:30 AM »
Thankyou JohanJ.

garry23

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #11 on: July 26, 2017, 06:19:12 PM »
@russelsnr

To further help and demystify diffraction, 'all' you need to do is remember that things are only in total focus at one distance, the focus duistance. As you move away from that point things defocus, based on your lens optics, kicks in. Because your eyes and brain are not perfect, you are not aware of this defocusing until you are :-). In other words, from the point of focus, out to a near and far point, you see things in sharp focus.

Also, this defocusing does not occur symmetrically, unless you are at a true macro arrangement, i.e. magnification of 1 or more.  For macro, the depth of field is very small.

The point where things become visibly blurred can be calculated, making a few simplifying and practical assumptions about the lens.  You only need to know the point of focus, the aperture value, the focal length and your 'quality factor' called the circle of confusion, i.e. the blur spot that is projected on the sensor.

ML provides this focusing info to you, eg focus distance and near and far depth of fields. However, the current ML builds do not calculate the DoFs correctly, because of the way ML does its sums, i.e. it uses integer math. A fix is in hand.

Until the fix, consider using my focus bar, which does all the correct math.

As for the diffraction, this is a blur that is there through the scene and essentially the same at all distances, other than extreme macro. Diffraction, is only a function of the wavelength, i.e. optical or IR are different, and the aperture, once again using a few simplifying assumptions. Wide open apertures give lower diffraction than closed down apertures.

Both blurs are treated independently and the normal practice is to combine them in quadrature, i.e. Total blur is tne sqrt(defocus^2 + diffraction^2). My focus bar shows these values and the blurs, so you can make informed choices. For example, uploading an image to Facebook vs getting a print evaluated in a competition.

If you wish to understand focusing more, you may wish to dip into some of my postings at photography.grayheron.net. Where you can also get my focus bar script.

russellsnr

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #12 on: July 27, 2017, 08:36:43 AM »
Hi Gary, Looked at your site when I asked http://www.magiclantern.fm/forum/index.php?topic=20083.msg187283#msg187283
Did try your Focus Bar script  and afraid  I just could not grasp it.
Thank you for the reply yet again.
Russ

garry23

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #13 on: July 27, 2017, 06:58:56 PM »
Russ

I'll try one my time ;-)

If you are on the ML forum I'm guessing you are interested in taking your very powerful camera to the next level. That is beyond using it in Auto or P mode.

Assuming this is right, I would encourage you to read a little into the basics of photography, eg depth of field, diffraction and exposure Evs etc etc.

DoF is all based around understanding blur, ie on the sensor and in the real world.

If you don't do this, I fear you will keep stumbling through the 'ML stuff'.

If you are struggling with these 'basics', then maybe ML is not for you.

I say the above in the spirit of helping you: not as an insult ;-)

Cheers

Garry

russellsnr

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Re: DOF settings. Simple or Diffraction Aware?
« Reply #14 on: July 28, 2017, 07:12:01 AM »
Russ

I'll try one my time ;-)

If you are on the ML forum I'm guessing you are interested in taking your very powerful camera to the next level. That is beyond using it in Auto or P mode.

Assuming this is right, I would encourage you to read a little into the basics of photography, eg depth of field, diffraction and exposure Evs etc etc.

DoF is all based around understanding blur, ie on the sensor and in the real world.

If you don't do this, I fear you will keep stumbling through the 'ML stuff'.

If you are struggling with these 'basics', then maybe ML is not for you.

I say the above in the spirit of helping you: not as an insult ;-)

Cheers

Garry
Garry I take no insult from any advice, at my age I don't have the time :D I am a manual mode user and do understand  the basics of photography, eg depth of field,  and exposure Evs etc etc but some of the more tech stuff that comes around just does not stick in an old brain. :D ML. for a Canon still image photographer offers a great deal extra that I use and that should already be as standard from Canon. Thankyou for trying to help. Russ
PS, update 28/July/17. Think after some steps forward and a couple back I have the basis of how your script works and a couple test show focus back to front however when I take an image I am getting a warning on the screen 'RAW error- Falling back to YUV overlays" the image looks OK after capture though. (OK found the topic on RAW error)Thanks, Russ