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  • Welcome to the new site. Here's a thread about the update where you can post your feedback, ask questions or spot those nasty bugs!

It is all in the eyes!

Doug Kerr

Doug Kerr

Well-known member
Hi, Mike,

Mike Shimwell said:
I'm just a bit aware of the constant mantra on the web that implies that diffraction makes a 21Mp sensor less good at resolving detail than a 12...
Click to expand...

Well, and of course we also hear that a 21Mpx camera gives us a smaller DoF than a 12 Mpx sensor camera of the same format size (for equal f/number, focal length, and focus distance).

Best regards,

Doug
 
F

Frank Doorhof

Guest
I never heard that one, that's ridicilous.

To be honest I don't understand the whole DSLRs are now on par with MF DBs, it's a totally different machine all together.
Or is that not what you meant ?
 
M

Mike Shimwell

New member
Frank Doorhof said:
I never heard that one, that's ridicilous.

To be honest I don't understand the whole DSLRs are now on par with MF DBs, it's a totally different machine all together.
Or is that not what you meant ?
Click to expand...

No, I was not commenting on the relative performance of dslrs and digital backs. I've never used a medium format db, so I couldn't in any case. Just reflecting on the fairly common implication that higher resolution sensors are unusable (or at least less useable than lower resolution sensors of equivalent format) at small apertures. Strangely, most of the people who make these comments don't apply them to the 12+Mp crop sensors, which have smaller sensel spacing.

Asher's comment that to get the best we need to open up a little is spot on, but that's just to allow the sensor to resolve all it can.

Now if someone wishes to make an extended loan of a P45+ and medium format system, or Thierry were to find a spare review copy of the HY6 I'd be glad to find out that they can offer higher image quality than a 1Ds3:)

Mike
 
Asher Kelman

Asher Kelman

OPF Owner/Editor-in-Chief
Mike Shimwell said:
Now if someone wishes to make an extended loan of a P45+ and medium format system, or Thierry were to find a spare review copy of the HY6 I'd be glad to find out that they can offer higher image quality than a 1Ds3:)
Click to expand...
Now where are you located? I just want to make sure it goes to a good home, LOL!

I'm still waiting!

You can do well however with a used P20 or P25 or similar from Sinar or Leaf and a Mamiya body. That's what Leonardo uses!

Asher
 
B

Bart_van_der_Wolf

pro member
Mike Shimwell said:
Asher, not trying to teach you to suck eggs, I'm just a bit aware of the constant mantra on the web that implies that diffraction makes a 21Mp sensor less good at resolving detail than a 12...
Click to expand...

Hi Mike,

I don't know where you read that 'constant mantra', but I do occasionally read incomplete 'conclusions' or partial 'truths' (which BTW is not the same as intentional half-truth!) on other forums. Diffraction is just what it is, the choice of sensor design doesn't change diffraction itself. As you correctly stated, a higher sensel density does allow more accurate sampling of the phenomenon.

However, when choosing a 21MP small sensel sensor array, one could assume that most users do so because they could have a need for large format output and thus require per pixel microdetail. In that case it is wise to consider the size of the diffraction spot diameter (which is a function of aperture and wavelength of light).

Doug_Kerr said:
Well, and of course we also hear that a 21Mpx camera gives us a smaller DoF than a 12 Mpx sensor camera of the same format size (for equal f/number, focal length, and focus distance).
Click to expand...

Correct (we hear a lot of stuff, not necessarily true stuff), in the sense that DOF is just what it is (depending on aperture, magnification, focal length, and COC criterion (which itself depends on viewing distance)). The choice of sensel density or sensor array size doesn't change it. All that changes is the sampling accuracy of the phenomenon. However, IMHO there can be a subtle difference as to the per pixel microdetail requirements compared to diffraction effects. Diffraction can negatively affect the best pixels in the DOF zone. Whether that becomes a visible issue depends on viewing conditions and observer.

Bart
 
Doug Kerr

Doug Kerr

Well-known member
Hi, Bart,

Bart_van_der_Wolf said:
Correct (we hear a lot of stuff, not necessarily true stuff), in the sense that DOF is just what it is (depending on aperture, magnification, focal length, and COC criterion (which itself depends on viewing distance)). The choice of sensel density or sensor array size doesn't change it.
Click to expand...

The rationale for the position I mentioned (which I do not endorse) is that we should choose our acceptable circle of confusion diameter (ACoC) based on the sensel pitch of the sensor, since that in fact controls the limiting resolution of the camera. In other words, unless the actual circle of confusion diameter exceeds the inherent resolution, the effect of blurring from misfocus isn't intrusive; conversely, once the actual diameter of the CoC exceeds the inherent resolution, then blurring is intrusive, and thus the blurring from misfocus should be considered "not acceptable" from that point on.

Thus what is "worse" about the DoF performance with the higher-resolution camera is that the blurring more quickly exceeds our (now-increased) aspirations for "sharpness".

But the paradox is when someone contemplates buying a higher-resolution camera (of a particular format size) and is advised that its DoF performance will be worse than the camera he now has!

So of course I do not subscribe to that outlook on choice of ACoC.

Best regards,

Doug
 
B

Bart_van_der_Wolf

pro member
Doug_Kerr said:
So of course I do not subscribe to that outlook on choice of ACoC.
Click to expand...

Hi Doug, we agree.

As I said, the DOF is what it is, the COC either exceeds our output/viewing requirements or it doesn't (IOW it's acceptable, or not). Sampling density, for a given field of view, only influences per pixel microdetail. When the output micro detail is smaller than or equal to visual acuity, things will appear to be in focus.

Bart
 
M

Mike Shimwell

New member
Bart_van_der_Wolf said:
Hi Mike,

I don't know where you read that 'constant mantra', but I do occasionally read incomplete 'conclusions' or partial 'truths' (which BTW is not the same as intentional half-truth!) on other forums. Diffraction is just what it is, the choice of sensor design doesn't change diffraction itself. As you correctly stated, a higher sensel density does allow more accurate sampling of the phenomenon.

However, when choosing a 21MP small sensel sensor array, one could assume that most users do so because they could have a need for large format output and thus require per pixel microdetail. In that case it is wise to consider the size of the diffraction spot diameter (which is a function of aperture and wavelength of light).



Correct (we hear a lot of stuff, not necessarily true stuff), in the sense that DOF is just what it is (depending on aperture, magnification, focal length, and COC criterion (which itself depends on viewing distance)). The choice of sensel density or sensor array size doesn't change it. All that changes is the sampling accuracy of the phenomenon. However, IMHO there can be a subtle difference as to the per pixel microdetail requirements compared to diffraction effects. Diffraction can negatively affect the best pixels in the DOF zone. Whether that becomes a visible issue depends on viewing conditions and observer.

Bart
Click to expand...



Bart (and Doug!)

We are in agreement. My suggestion was not that there is a deliberate attempt to mislead, but that there is a significant amount of incomplete analysis and casual and incomplete testing leading to wrong implications. Also a lot of hearsay. Equally, as you say, the purchase of a 21Mp camera suggests a need for more resolution and, of course, more careful, considered and deliberate technique is required to realise that.

Mike
 
Doug Kerr

Doug Kerr

Well-known member
Hi, Mike,

Mike Shimwell said:
Bart (and Doug!)

We are in agreement. My suggestion was not that there is a deliberate attempt to mislead, but that there is a significant amount of incomplete analysis and casual and incomplete testing leading to wrong implications. Also a lot of hearsay. Equally, as you say, the purchase of a 21Mp camera suggests a need for more resolution and, of course, more careful, considered and deliberate technique is required to realise that.
Click to expand...

All well said!

Best regards,

Doug
 
B

Bart_van_der_Wolf

pro member
Mike Shimwell said:
Bart (and Doug!)

We are in agreement. My suggestion was not that there is a deliberate attempt to mislead, but that there is a significant amount of incomplete analysis and casual and incomplete testing leading to wrong implications. Also a lot of hearsay.
Click to expand...

That's sadly the case. However, this thread presented an opportunity to have an attempt at rectifying some of the misconceptions. A useful article on the subject can be read at Luminous Landscape site. The only niggle I have with that article is that, for large output, their criterion for the size of the blur spot is not as critical as mine (1.5x sensel pitch, on a Bayer CFA sensor with AA-filter).

Bart
 
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