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Old 2nd August 2019
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F Stop.............!!

Ian made a comment about a photo of mine on the FT user site.

The photo was of "My Porche" which I photo'd at Le Mans recently, and have posted here...……..

https://e-group.uk.net/forum/showthr...highlight=Mans

The comment was that my f stop was 7.1, and that MFT photos show diffraction..

I would say that you probably didn't need to go to f/7.1 though so - maybe f/5.6 and you could have enjoyed a faster shutter speed or a lower ISO setting.

One thing all Micro/Four Thirds users should remember is that past f/5.6 you start to lose resolution due to diffraction.

On the other hand, using a high ISO also has the same effect - whether or not these two factors are mutually exclusive or cumulative; that's a good question and needs answering!


I don't doubt his wisdom, but wonder why this is. I recently took a butterfly photo only to discover afterwards the f stop was 22. The photo worked for me, it might have been a little more colourful though.

And why do we have such a range of Fstops if most are not very good. I see that the 300mm Pro with the new MC2 starts at f8...….which would seem to write off this combination...…….

I think I am a bit still in the old school where the F stop controlled the DoF as much as anything...……….
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Old 2nd August 2019
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Re: F Stop.............!!

Your picture doesn't look unduly soft to me,I'm a little more sceptical about the wisdom.
I've had some shots that apparently "look soft because of defraction" using extension rings for pictures of model cars.
I was stopped down as far as possible to get depth of focus front to back.
Is it soft? I was happy enough but I didn't run through a selection of F numbers to get the widest aperture with the car in focus, I used the "wisdom" that a higher F number would result in greater DoF




Volkswagen Golf by AMc UK, on Flickr




"My Porsche" picture from Le Mans Museum was taken at with the E-PL5 using the 14-42mm 3.5-5.6 R II.

I appear to have used a much lower F number which has resulted in some less dramatic ISO and shutter speeds.
I don't think the car is lacking in depth of focus at f3.7?


ƒ/3.7
17.0 mm
1/80
1250 ISO


I think it's fair to say it's quite dark in there really.




Porsche at Le Mans by AMc UK, on Flickr

According to EXIF in Flickr both our shots were taken "Exposure Mode - Auto". I usually use Program unless I'm specifically choosing an aperture or shutter speed for effect.
Do you know what mode you were in and why you were at those settings?
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Old 2nd August 2019
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Re: F Stop.............!!

Diffraction can be numerically estimated using the Rayleigh criterion for the size of the Airy disk. For closely-spaced objects this approximates to:

x = 2.44 L N

where:

x = size of Airy disk diameter
L = wavelength of light
N = f-stop

Plugging this in for green light (in the middle) and f7.1, we get:

x = 0.009mm

This is still much smaller than the usual circle of confusion used for DoF calculations (0.015mm). In other words, at f7.1, diffraction is not a significant factor.

We don't get an Airy disk larger than the circle of confusion until about f11.

In other words, up to f11 you're fine in practical terms, although if you nit-pick, keep it at f5.6 and below.
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Old 2nd August 2019
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Re: F Stop.............!!

Diffraction limiting of sharpness is a complex subject that depends on many factors, including pixel size and how the image is viewed. There are some calculations on the 'Cambridge in Colour' website that illustrate these points.

For example, the 'simple' calculator at https://www.cambridgeincolour.com/tu...hotography.htm suggests that an MFT camera becomes 'diffraction limited' at smaller openings than f/11 (Olympus now quote this figure also) This, however, assumes that you are viewing a 10"x8" print from 1 foot away.

The calculator in Part 2 of the article at https://www.cambridgeincolour.com/tu...tography-2.htm considers more aspects of image quality and suggests that diffraction effects can become visible at wider openings. For example, an MFT camera with 20MP sensor may show some 'effects' at openings smaller than f/5.2

In my own experience, i have found that using 'stacking' for macro photography, with my 60mm lens set at f/2.8, shows better micro-contrast than when set at f/8. I now use wider apertures whenever possible and rely on 'stacking' to increase the apparent depth of field.
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Re: F Stop.............!!

Yes, stacking is a great technique and better than stopping down for most things - but of course you need a relatively stable platform for it. I took this yesterday with the 8mm fisheye. Wide open at f1.8 and 15 shots:


Schrooms by Paul Kaye, on Flickr
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Old 2nd August 2019
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Re: F Stop.............!!

Super shot, Paul - I've never thought of stacking fish-eye shots
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Re: F Stop.............!!

Quote:
Do you know what mode you were in and why you were at those settings?
Yes I was in Auto Mode onC1 with several other settings.

Why??

My simple rule is that in summer I use a higher stop a there is likely to be more light and Dof benefits. The 12-40 pro just gives and gives. Alas I do get forgetful and in my excitement forgot to open up the aperture. But I think the resulting photo did ok despite me. 👹
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Re: F Stop.............!!

Just curious as to why you’d got the settings you had.
As I said I normally shoot P and scroll from there if needed.
Some of my odder results have been inadvertently leaving A or S mode settings and moving on to another subject.
As long as you’re happy with the image it’s all academic really anyway.
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Re: F Stop.............!!

Just to be clear, I didn't say the shot wasn't sharp but seeing as the shutter speed was quite slow I didn't really think such a small f-stop made sense. DOF wasn't an issue with the composition. I've seen other shots from different photographers that were definitely over-stopped down for no apparent reason and diffraction softness was evident.

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Old 6th August 2019
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Re: F Stop.............!!

My experience with several camera club members who have added or switched to m4/3 from FF gear is that they keep their old habits at first, and don’t take advantage of the dof advantages of the smaller sensor. This results in high ISOs and slow shutter speeds, and not surprisingly they start to moan about their decision.

Telling them to open up by 2 stops comes as a complete revelation.

The second lesson is about Exposing to the Right.

So far I’ve never had anyone still complain after that ;-)
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Re: F Stop.............!!

Quote:
Originally Posted by drmarkf View Post
My experience with several camera club members who have added or switched to m4/3 from FF gear is that they keep their old habits at first, and don’t take advantage of the dof advantages of the smaller sensor. This results in high ISOs and slow shutter speeds, and not surprisingly they start to moan about their decision.

Telling them to open up by 2 stops comes as a complete revelation.

The second lesson is about Exposing to the Right.

So far I’ve never had anyone still complain after that ;-)
Kinda depends on what you want at the time..Could be a disadvantage for some/many situations...………..
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Re: F Stop.............!!



Peacock butterfly taken with an f22 aperture! (Not on purpose,,:-))….F22 1/200 sec and ISO 6400

Whilst its not the best photo I have ever taken, the quality is I guess only just OK. Where is the refraction/defraction that the small aperture is giving....

The high ISO kinda knackers the resolution...………….
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Re: F Stop.............!!



Ox eye Daisy with leaf beetle


by Mark Johnson, on Flickr

Also taken with an f22 but with a better ISO 400...………..
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Re: F Stop.............!!

Quote:
Originally Posted by MJ224 View Post
Kinda depends on what you want at the time..Could be a disadvantage for some/many situations...………..
For sure, but getting them past first base by knowing where 'equivalence' lies in that area makes a huge difference, otherwise m4/3 has one arm tied behind its back.
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Old 7th August 2019
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Re: F Stop.............!!

Hi
So having just purchased an Olympus om-d e-m1 mkii, with thoughts of changing to MFT, I am now wondering if it was the right move.
I have a Canon EOS R and do not seem to have this issue with DOF, the smaller the aperture the better dof and detail, as far as I can see.
Am I confused here?
Roy
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