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bags27

depth of field of APS C Sensor

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I'm sure this has been discussed many times on this site, so forgive the duplication: my only excuse is laziness.

What is the DoF of a wide open  L 35 f/1.4 (Sigma makes one) or an M f/1.4 on the APS C sensor? IIRC wide open it's something like the equivalent of a 50 f/2.3. Is it the same as that of the TL 35 f/1.4? Or, is the TL lens somehow fixed so that its DoF is equal to a "true" 50mm f/1.4 lens?

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Ken: Someone with more knowledge is welcome to correct me, but I believe the DoF is also subject to the crop factor, so that the TL 35 1.4 renders like a 52mm f/2.1.  Rob

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33 minutes ago, ropo54 said:

Ken: Someone with more knowledge is welcome to correct me, but I believe the DoF is also subject to the crop factor, so that the TL 35 1.4 renders like a 52mm f/2.1.  Rob

Thanks, Rob. I suspect that's right. 

best,

Ken

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1 hour ago, bags27 said:

I'm sure this has been discussed many times on this site, so forgive the duplication: my only excuse is laziness.

What is the DoF of a wide open  L 35 f/1.4 (Sigma makes one) or an M f/1.4 on the APS C sensor? IIRC wide open it's something like the equivalent of a 50 f/2.3. Is it the same as that of the TL 35 f/1.4? Or, is the TL lens somehow fixed so that its DoF is equal to a "true" 50mm f/1.4 lens?

Rob has it right... focal length X 1.5 as well as F stop.

Edited by Donzo98

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2 hours ago, Donzo98 said:

Rob has it right... focal length X 1.5 as well as F stop.

Before I hit the chips and beer, I'd like to understand completely. So does the 35 f/1.4 TL really acts as an f/2 in terms of light?  And does an L or M 35 mm f/1.4 effectively become an f/2 of the CL? I don't think you're saying that.

I think you're saying that the depth of field is roughly equally to one f stop greater but the actual admittance of light remains f/1.4.We're only talking about affecting the DoF, not the realized aperture.

And that means that a 35 mm f/1.4 lens of any sort (L, M, or TL) on a 1/2 sensor doesn't produce the very shallow depth of field that a 50 f/1.4 does on a full frame camera. Right? You'd then need the Voigtlander 35 f/1.2 to do that, I suppose 

Edited by bags27

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Left light gathering alone. F/1.4 is f/1.4 for that matter. 

But your question is about depth of field. To make it easier for comparison, you can use equivalencies. So multiply focal and aperture by the crop factor of any given sensor. Like that you can compare between them. 

No magic with TL lenses. They will obey the law of physics. 

Here Sigma or Summilux-TL 35mm f/1.4 mounted on APS-C camera will act as a 52mm f/2.1 mounted on a 24x36 one. Same field of view and same depth of field. But light gathering capability stays the same as f/1.4 

NB : it does not matter if the lens is made for full frame, MF, m4/3, 1” or APS-C. It’s real focal length and aperture are the numbers to consider and to convert with the crop factor of the sensor. 

Edited by nicci78

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2 hours ago, bags27 said:

I think you're saying that the depth of field is roughly equally to one f stop greater but the actual admittance of light remains f/1.4.We're only talking about affecting the DoF, not the realized aperture.

And that means that a 35 mm f/1.4 lens of any sort (L, M, or TL) on a 1/2 sensor doesn't produce the very shallow depth of field that a 50 f/1.4 does on a full frame camera. Right? You'd then need the Voigtlander 35 f/1.2 to do that, I suppose 

Basically, yes.

Gordon

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Let's forget this light gathering confusion. Yes, the total amount of light will reduce, but the light per square thingie will remain the same, thus the effective aperture will remain the same. Yes, the DOF will diminish, but in real life this will mostly be irrelevant. DOF varies far more with subject distance and subject content.

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21 minutes ago, jaapv said:

Let's forget this light gathering confusion. Yes, the total amount of light will reduce, but the light per square thingie will remain the same, thus the effective aperture will remain the same. Yes, the DOF will diminish, but in real life this will mostly be irrelevant. DOF varies far more with subject distance and subject content.

It is very relevant for me. I mean when comparing apples to apples i.e. with the same subject distance of course. YMMV.

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40 minutes ago, jaapv said:

Let's forget this light gathering confusion. Yes, the total amount of light will reduce, but the light per square thingie will remain the same, thus the effective aperture will remain the same. Yes, the DOF will diminish, but in real life this will mostly be irrelevant. DOF varies far more with subject distance and subject content.

Absolutely correct.

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1 hour ago, lct said:

It is very relevant for me. I mean when comparing apples to apples i.e. with the same subject distance of course. YMMV.

Yes, but even then. Take an image with bright sunlight. Then take the same image on a grey misty day. The DOF will be far more narrow on the sunny photograph.

Image contrast and image frequency (bold shapes vs a busy high-detail photograph) influence DOF much more than the measly mathematical 1.4x by APS-C vs full frame.

I photograph like DOF doesn't exist. Why? because if I print an image to 10x15 cm the DOF will be far deeper and the image apparently sharper all over than my A3+ prints. I need the precise sharpness for my better photographs that I print large.

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4 minutes ago, jaapv said:

Yes, but even then. Take an image with bright sunlight. Then take the same image on a grey misty day. The DOF will be far more narrow on the sunny photograph.

Image contrast and image frequency (bold shapes vs a busy high-detail photograph) influence DOF much more than the measly mathematical 1.4x by APS-C vs full frame.

Again you seem to compare apples to oranges with respect :cool:. Question is not to know how DoF can look like in different weather, distance or whatever conditions but when conditions are the same to shoot the same subject matter with FF and APS-C cameras. I would need a 24/1.4 to replace a mere FF 35/2 on APS-C from this viewpoint. Superb lens but too big for my taste on a compact body. YMMV. 
http://j.mp/30lGPE4

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Depth-of-field is proportional to the linear sensor size. The smaller the sensor, the narrower depth-of-field will be.

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2 hours ago, lct said:

Again you seem to compare apples to oranges with respect :cool:. Question is not to know how DoF can look like in different weather, distance or whatever conditions but when conditions are the same to shoot the same subject matter with FF and APS-C cameras. I would need a 24/1.4 to replace a mere FF 35/2 on APS-C from this viewpoint. Superb lens but too big for my taste on a compact body. YMMV. 
http://j.mp/30lGPE4

Of course MMV. Photography is not about comparing photographs on technicalities. Especially not marginal differences in DOF between image A and B. I can guarantee you that the technical DOF difference between APS-C and FF will be wholly insignificant compared to contrast, sharpening techniques, contrast, texture, print size, print gloss etc. I really don't need to fit my Summilux 24 onto the CL to get Summicron 35 results. In fact, the look of that lens is close to the Summilux 35 on full-frame. That is due to the lens design. A large part of DOF is determined by the way the OOF areas are rendered. The viewer does not really notice a small increase in geometrical dimensions.

 

https://theonlinephotographer.typepad.com/the_online_photographer/2007/11/the-photo-fetis.html
(Plus the first comment ;):lol: )

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21 minutes ago, jaapv said:

[...] A large part of DOF is determined by the way the OOF areas are rendered. The viewer does not really notice a small increase in geometrical dimensions.

Seems like what you're describing here is not DoF but bokeh or OoF rendition. DoF is just a distance based on focal length, f-number and circle of confusion.

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Yes, all areas outside the plane of focus have OOF rendering AKA bokeh, minimally near the plane of focus, maximally at the end of perceived DOF. The OOF/ bokeh determines the subjective phenomenon of DOF. It is not the absolute mathematical approximation, as it is the processing of our brain, in combination with the individual resolving power of our eye that determines the perception of DOF.

You mention the circle of confusion. That is an assumption based on the factors above (amongst others), and thus a variable, set at a given value by convention.

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I have a Zeiss Distagon  M mount f/1.4 that I can use on my CL.  It's a superb lens (and makes me question whether there is any need for me to get the T 35 1.4.  but that's another story.)  Wide open, it has about the same dof as my 50mm Summilux set to f2.0.  If I try adjusting the summilux between 1.4 and 2 (using the electronic finder) I can see marginal changes in dof.  As has been pointed out, other factors like subject distance, lens focal length, degree of enlargement, and even lens resolution at the focal plane, have a larger impact on the picture.  If I wanted virtually nil dof, then I would select something like my 90mm summicron at f2, and use it on any camera.

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6 minutes ago, jaapv said:

You mention the circle of confusion. That is an assumption based on the factors above (amongst others), and thus a variable, set at a given value by convention.

CoC is just a factor of DoF. Nothing new under the sun.

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18 hours ago, bags27 said:

I'm sure this has been discussed many times on this site, so forgive the duplication: my only excuse is laziness.

What is the DoF of a wide open  L 35 f/1.4 (Sigma makes one) or an M f/1.4 on the APS C sensor? IIRC wide open it's something like the equivalent of a 50 f/2.3. Is it the same as that of the TL 35 f/1.4? Or, is the TL lens somehow fixed so that its DoF is equal to a "true" 50mm f/1.4 lens?

Play around with the DoF calculator here: http://www.dofmaster.com/dofjs.html Pick and compare any FF and any APS-C camera. The differences become readily apparent. 

For a little more graphic approach, this one works reasonably well too: https://dofsimulator.net/en/

Essentially, a 35mm lens on the Leica CL nets the same FoV as a 50mm lens on FF. The DoF of a lens on the APS-C format, at any given distance and aperture, is approximately one stop more than a lens with similar field of view at the same distance and f/number setting on FF. 

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