DOF Table for Q2's Summilux 28mm f/1.7 ASPH lens

[Dektol]

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I'm wondering if anyone knows if there is a Depth of field (DOF) table for the Q2 Summilux 28mm f/1.7 ASPH lens. 

If there is, could you please send me a link to it.

Secondly, if the above does not exist, would the data in the Leica Summilux-M 28mm f/1.4 ASPH be valid to use for the Summilux 28mm f/1.7 ASPH lens?

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[jaapv]

Given that DOF is an imprecise variable masquerading as an exact calculation, this should be close enough. You'll find, however, that all DOF tables and scales are optimistic by 1-2 stops, even more  if you crop or print large.

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[01af]

Depth-of-field is a simple concept as long as you just glance over it ... but will become increasingly complex the closer you look into it — which for all practical intents and purposes wouldn't make any sense. So the short answer is: Yes, the Summilux-M 28 mm Asph's depth-of-field table basically is valid for the 28 mm lens in the Leica Q and Q2, too.

As a first approximation, DOF depends on four parameters: image format, focal length, aperture, and distance. But as you probably have guessed by now, that's just a simplification. In reality, there's many more parameters — among them a few elusive ones like kind, grade, and shape of the lens' residual aberration. Fortunately, their effect on actual DOF usually is minuscule so they can safely be neglected most of the time. Anyway — that means that there may be small differences in the depths-of-field of Summilux-M and Q/Q2. After all, the table gives DOF values down to one-millimeter accuracy. So the corresponding table for the Q/Q2 lens (if there was one available somewhere) may differ by a millimeter or two (or three) here and there. Which of course won't make any difference in real life.

[GK James]

Jaapv: When you say "all DOF tables ... are optimistic by 1-2 stops," what do you mean?

Thanks

[jaapv]

That they are based on film (which has a thickness and shows dispersion) and 6x9 cm prints. An A4 print on a digital sensor will show far more pronounced  sharpness falloff.

Also, DOF is a perception and is influenced by contrast ( a misty image will have far deeper DOF) and type of subject. (Hair and eyelashes will seen to be unsharp far sooner than big concrete blocks.)

Everything outside the plane of focus is unsharp. How unsharp? That is for your eye - aided by magnification- to determine.

[wda]

Unless you are a scientist or are engaged on scientific work, does it really matter what data such tables purport to show? I fail to see how they can help improve a photographer's output.

[01af]

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Am 2.3.2020 um 13:19 schrieb jaapv:

Am 2.3.2020 um 12:14 schrieb GK James:

When you say, 'all DOF tables ... are optimistic by 1 - 2 stops,' what do you mean?

That they are based on film (which has a thickness and shows dispersion) and 6 × 9 cm prints. An A4 print on a digital sensor will show far more pronounced  sharpness falloff.

That's a common misconception, caused by excessive pixel-peeping.

In fact, the concept of DOF doesn't depend on the recording medium. Film or digital sensor, that doesn't matter. Also, this '6 × 9 cm print' narrative holds no water. Instead, a 'comfortable viewing distance' is insinuated – which means a distance about equal to the print size (length of diagonal) ... in particular it means: no pixel peeping! So, all those depth-of-field tables or scales on the lenses' barrels are as valid today as they always were.

[jaapv]

I'm not going to chase that particular hare around the forum again... Suffice to say that yours is a lonely voice.

However, you are forgetting that basically there are only two things that affect DOF : magnification throughout the imaging chain and resolution of they eye of the viewer.

Everything else is an attempt to create parameters that  can be caught in a mathematical formula, which will vary from simple to complicated.

So: subject distance, sensor/film format, print size, viewing distance and subjective perception by the viewer will al be determinants for DOF, Focal length is a derivate value.

 

[01af]

vor 15 Minuten schrieb jaapv:

... basically there are only two things that affect DOF: magnification throughout the imaging chain and resolution of they eye of the viewer.

Oh, come on ... you know this isn't true.

.

vor 15 Minuten schrieb jaapv:

... focal length is a derivate value.

Again: a common misconception.

To roll distance and focal length into one parameter, magnification, is a simplification that applies to situations where depth-of-field is narrow (namely, close-ups and telephoto lenses) but doesn't apply generally. So no, focal length is not just a derivative parameter to DOF; it's an elementary one that cannot be replaced by others.

[jaapv]

I disagree. But as we have plenty of threads here, I will not discuss this further. The OP''s original question has been answered in this thread.

[locopek]

I asked Leica for the same data a couple of months ago, and this is what they answered:

 

Quote

The only published lens test data can be found at the end of the attached document.

 

 

 

 

Best regards,
Mark Brady

Technical Advisor

 

Leica Camera Inc
1 Pearl Court, Unit A / Allendale, NJ 07401 / USA

 

So there is not more info available for the 1.7 Summilux.

[Bokeh Street]

On 3/5/2020 at 9:13 PM, wda said:

Unless you are a scientist or are engaged on scientific work, does it really matter what data such tables purport to show? I fail to see how they can help improve a photographer's output.

I think if you are new to M/manual focusing and want to start with zone techniques, it's good to understand for a certain aperture and distance, what you might expect to have in focus - at least until you've shot a few hundred images and get the feel for it.

[clasami]

Am 1.3.2020 um 01:20 schrieb Dektol:

I'm wondering if anyone knows if there is a Depth of field (DOF) table for the Q2 Summilux 28mm f/1.7 ASPH lens. 

If there is, could you please send me a link to it.

Secondly, if the above does not exist, would the data in the Leica Summilux-M 28mm f/1.4 ASPH be valid to use for the Summilux 28mm f/1.7 ASPH lens?

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The table seems a bit optimistic in terms of far distance. It would be good to know which CoC this table is based on. The bigger issue seems to be that the distance scale on the Q2M lens only extends to 2m, and then inifinity. Something I found helpful was a DoF scale shown within the EVF (like Fuji) with an option to switch between Pixel Level DoF and Film Based DoF (like Fuji). Using the DoF scale on the lens of the Q2M leads to lack of sharpness beyond around 100 meters. Not noticable if viewed on a 27 inch monitor w/o magnification.

Edited March 30, 2022 by clasami