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Olympus OM-D E-M1 Mark II The second Micro Four Thirds camera that offers phase detect focusing so you can use Four Thirds DSLR lenses normally as well a Micro Four Thirds lenses.

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Old 28th April 2017
Walti Walti is offline
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Diffraction calculation

Trying to calculate the "ideal" aperture for the MKii...

Looks like f7.1 is the ideal from the calculations and research I've done... does this sound correct?

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Old 28th April 2017
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Beagletorque Beagletorque is offline
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Re: Diffraction calculation

Ideal for what though?

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Old 28th April 2017
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Re: Diffraction calculation

Balancing the DoF vs diffraction to get the best out of the system, especially for wildlife photography...

However the balance of diffraction vs noise is another consideration owing to the UK weather and the need to up the ISO a bit to get a decent shutter speed at times!

Just been dipping my toes into architectural photography and am struggling to get the best at times, though the high resolution mode and a tripod may be a better way forwards on occasion.
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Old 28th April 2017
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Re: Diffraction calculation

Read this Walti

https://www.lensrentals.com/blog/201...atters-part-2/
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Re: Diffraction calculation

Download a dof calculator for your phone, very handy to check dof and hyperfocals. In terms of diffraction best keep to as low an f stop as possible, assuming your glass is good and the dof is acceptable.
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Old 28th April 2017
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Re: Diffraction calculation

The only relevant diffraction calculation I know is from the Rayleigh diffraction limit giving:
'max resolution on sensor = 2.44* wavelength * f number'

I assume the units for resolution math those of the wavelength, as f number is dimensionless.

I've seen loads of posts about diffraction limited optics etc which don't consider that red light has a much worse problem than the blue.

I don't see how a calculation of any sort can give a optimum aperture. The ideal DOF depends so much on the subject, in some cases a little diffractive softening is worth it for increased DOF, in many others adequate DOF is achievable when diffraction is having no significant affect on the image.

There are other effects changing the image with aperture. Many forms of aberration are reduced by using smaller apertures. The data required to calculate the effects of these are not AFAIK available to photographers. If you're after the ultimate aperture for exhaustive focus stacking (where DOF is not an issue) trial & error is likely to be the best approach. Most lenses are reckoned to be at their best ~2 stops closed down, but the actual value can vary on a lens by lens basis.
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Old 28th April 2017
RobEW RobEW is offline
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Re: Diffraction calculation

According to the article by Roger Cicala which Ricoh posted a link to, if I understand it, the f stop at which diffraction begins to be problematical is dependent on the sensor characteristics (sensor size and pixel size) alone, and doesn't vary depending on what lens you attach.

If we take the approach Cicala describes based on tables 2 & 3, then "a four thirds sensor is becoming diffraction limited by f/11". If we take the approach based on pixel pitch (his table 4) then we would adopt a more conservative limit of f/8 (for a sensor with pixel pitch of 3.8 micrometres)

Of course there are other constraints and trade-offs which may make us want a narrow aperture in some circumstances.

Can I add a question here? How would I know, looking at a photo, if diffraction was compromising the quality? Is it just a rather subjective fuzziness, or is there something specific I can look for by pixel peeping?
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Re: Diffraction calculation

Quote:
Originally Posted by RobEW View Post
According to the article by Roger Cicala which Ricoh posted a link to, if I understand it, the f stop at which diffraction begins to be problematical is dependent on the sensor characteristics (sensor size and pixel size) alone, and doesn't vary depending on what lens you attach.

If we take the approach Cicala describes based on tables 2 & 3, then "a four thirds sensor is becoming diffraction limited by f/11". If we take the approach based on pixel pitch (his table 4) then we would adopt a more conservative limit of f/8 (for a sensor with pixel pitch of 3.8 micrometres)

Of course there are other constraints and trade-offs which may make us want a narrow aperture in some circumstances.

Can I add a question here? How would I know, looking at a photo, if diffraction was compromising the quality? Is it just a rather subjective fuzziness, or is there something specific I can look for by pixel peeping?
I'm trying to understand it myself, as I've noticed that the photos away from wide open tend to not only be better in focus due to the increased DoF but also exposed slightly better (I'm unsure whether this is my imagination or not!)

So when trying to photograph birds I seem to have defaulted by accident to 1/1000s and f8 with the autoISO taking care of the exposure, which seems at the moment to be the best compromise, but I thought I'd look at the defraction limits of the camera to see where this makes a difference, and dependant on how you calculate it (or which website you look at) then the f8 looks to have potential issues f7.1 doesn't, so I thought I'd try a few and see if I can actually see any difference!

I think there's more issues than the camera settings at the moment, the guy holding the camera seems to be the biggest obstacle to excellent photos - it still feels like luck if I get a reasonable shot!
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Old 28th April 2017
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Re: Diffraction calculation

I have done tests myself, which in very simple terms gave the following rule of thumb results:
f/16 Poor, loss of detail, never use unless desperate for extra DOF.
f/11 Acceptable, a little loss of detail. Can use for macro to get more DOF.
f/8 Very good indeed. Almost the same as f/5.6
f/5.6 The best, no loss of detail.

So I'm very happy to use f/8 or wider, I use f/11 for some macro shots, and never use f/16.
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