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Kim Dahl

Apeture affecte from fulframe too APSC ?

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A 35mm f/1.4 is a 35mm f/1.4 no matter what camera you put it on.  That much is true.  However:

  1. If you put that lens on an APS-C camera rather than a full frame camera you will get approximately the same field of view as a 50mm lens.  Hence, the crop factor.  Again, with regard to field of view, it will behave like a 50mm lens does on a full frame camera. You didn't change the focal length itself, but you certainly changed the field of view.
  2. With regard to depth of field, the lens again doesn't physically change--it's still an f/1.4 aperture.  However, the subject distance is going to change for a given field of view.  In other words, to get the same picture with a 35mm lens on an APS-C camera, you are going to need to move farther away from your subject than you would with a full frame camera.  By a factor of 1.5x.  Since you are farther away from your subject, the depth of field increased.  It was really due to subject distance, not anything that physically changes in the lens, but the result is still that a 35mm f/1.4 lens on an APS-C camera will generate roughly the same depth of field as a 50mm f/2 lens on a full frame camera for a given field of view.  You're going to back up so that you are shooting from the same distance as that 50mm on full frame, so your depth of field increases. Again, that 35mm f/1.4 on an APS-C camera will generate images that look the same as 50mm f/2 images on a full frame camera.  DOF increased because subject distance increased for a given field of view.  
  3. Here is, perhaps, the trickiest one.  Sensitivity.  Let's compare two sensors with the same 24 megapixels, one APS-C and one full frame.  Let's assume they have the same quantum efficiency (actual sensitivity to light).  The irradiance level coming out of the 35mm f/1.4 lens is going to be the same with both chips.  That is, the amount of light hitting a given chip area in a given exposure length is going to be determined by the aperture.  Since it's an f/1.4 lens on the full frame, it's also an f/1.4 lens on the APS-C camera.  You will end up setting the same ISO and shutter speed on either camera, right?  Right.  But, the pixels are physically smaller on the APS-C size chip.  You're cramming the same 24 megapixels into a smaller chip, so obviously each individual pixel will need to be smaller. In fact, each pixel will have about half the area on an APS-C chip as it would on a full frame chip (rounding slightly).  So, even though each square millimeter of chip receives the same amount of light at f/1.4 regardless of whether it's full frame or APS-C, each pixel does not.  Each APS-C pixel receives half the light of its full frame counterpart.  That means the full frame chip is going to have lower overall noise for a given exposure.  So you get the signal-to-noise ratio in your image of a full frame camera and lens that is a full stop worse in the APS-C camera.  In other words, that 35mm f/1.4 lens shot at ISO 100 on the APS-C camera will give you the same signal-to-noise ratio as a 35mm f/1.4 lens shot at ISO 200 on a full frame camera.  Noisier results out of smaller sensors because each pixel is receiving less light for a given exposure value.  

In summary, a 35mm f/1.4 lens shot on an APS-C camera should give you the same field of view, depth of field, and signal-to-noise ratio as a 50mm f/2 lens shot on an equivalent megapixel count full frame camera.  As long as the subject framing is the same, the perspective should be the same (since that is determined by distance) the depth of field should be the same, and the SNR should be the same since the extra stop of light (f/1.4) will let me set the ISO one stop closer to base ISO, thus offsetting the SNR disadvantage of the smaller pixels.

 

The lens, of course, produces the same cone of light no matter what sensor you couple it to.  Nothing changes about the lens itself--there is no magic involved.  But the result in the photograph from physically moving to get the same field of view with the smaller sensors is that you get essentially the same image in every single meaningful way out of a 50mm f/2 full frame lens/camera combo as you do out of a 35mm f/1.4 APS-C lens/camera combo.  You can consider them equivalent.

 

We've seen this for many years in the other direction.  Anyone remember reading about "Group f/64"?  Ansel Adams?  Cunningham?  Edward Weston?  To get reasonable depth of field--enough for a good landscape shot out of an 8x10 camera--they judged you needed to be shooting at f/64.  Just as APS-C has a somewhat larger depth of field than 35mm (due to the different subject distance required for framing at a particular focal length), a large format camera has a much narrower depth of field.  Hence the requirement to shoot at f/64 to generate the desired "sharpness" across the frame.  It's no different with digital than it was with film.  Group f/64 was came of age in the 1930's.  We're coming up on 100 years that this sort of discussion has been going on.

Edited by Jared

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Completely correct. I would like to make one additional emphasis;The total amount of light received by the sensor is obviously determined by the area of the sensor, but as the amount of light per square millimetre is not changed, the exposure remains the same. A 1.4 lens remains a 1.4 lens regardless of sensor area for exposure purposes.

 

Because of this it is highly confusing to say that a 35 mm 1.4 lens is equivalent to a 50 mm 2.0 lens in every way; it is still a 1.4 lens.

It is more clear to say that the angle of view, DOF and noise behaviour of an APS- C sensor are equivalent to a 1.5 crop on a full frame sensor and leave the lens out of the discussion altogether, as nothing will be changed on the lens itself.

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[...] Since it's an f/1.4 lens on the full frame, it's also an f/1.4 lens on the APS-C camera.  You will end up setting the same ISO and shutter speed on either camera, right?  Right.  But, the pixels are physically smaller on the APS-C size chip.  You're cramming the same 24 megapixels into a smaller chip, so obviously each individual pixel will need to be smaller. In fact, each pixel will have about half the area on an APS-C chip as it would on a full frame chip (rounding slightly).  [...]  

In summary, a 35mm f/1.4 lens shot on an APS-C camera should give you the same field of view, depth of field, and signal-to-noise ratio as a 50mm f/2 lens shot on an equivalent megapixel count full frame camera.  [...]

We've seen this for many years in the other direction.  Anyone remember reading about "Group f/64"?  Ansel Adams?  Cunningham?  Edward Weston?  To get reasonable depth of field--enough for a good landscape shot out of an 8x10 camera--they judged you needed to be shooting at f/64.  Just as APS-C has a somewhat larger depth of field than 35mm (due to the different subject distance required for framing at a particular focal length), a large format camera has a much narrower depth of field.  [...]

 

Interesting thanks but as clear as i understand the matter, not being a techie myself, DoF does not depend upon the number of pixels crammed into a given sensor but on the size of the latter because it determines the value of the circle of confusion taken into account in DoF calculations. When we watch a picture at, say, 30 cm viewing distance (i don't recall the distance taken into account for CoC calculations), be in on a print or a PC monitor, we don't see it more clearly when it has more pixels necessarily because at this very viewing distance, a camera with a 13MP sensor, my M8.2 to take an example, can have a better acutance than a 24MP one for various reasons, a thinner sensor stack in this example. Reason why it is the size of the film or sensor, and not the number of grains (?) or pixels which is taken into account in the calculation of the CoC, hence in that of the DoF. 

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I don’t think Jared is relating pixel count to DOF, rather to noise.

 

Actually the whole discussion is rather silly. A MF photographer will never recalculate the focal length to another format; on 645 everyone knows that 80 mm is a standard lens and 55 a mild wide angle. Nor will he be fiddling with aperture values.

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I don’t think Jared is relating pixel count to DOF, rather to noise.

 

Actually the whole discussion is rather silly. A MF photographer will never recalculate the focal length to another format; on 645 everyone knows that 80 mm is a standard lens and 55 a mild wide angle. Nor will he be fiddling with aperture values.

 

When comparing FF to APS (or FF to MF) as far as DoF is concerned, whatever value one chooses for the FF CoC, there will always be a difference coming from the difference of format and i don't see how noise could make that an FF pic taken at f/1.4 equals or is equivalent to an APS-C one taken at f/2. Both are taken at f/1.4 actually and under the same light, the FF camera with a 50mm lens behaves the same as an APS-C camera with 35mm lens at the same aperture with a different DoF due to different sensors. At least it is the way i've been taking my pics since my first APS-C camera in 2002 or something but again i'm no techie at all.

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An exhausting discussion.  The lens characteristics stay the same, aperture etc.  The crop factor affect the field of view and since one must move closer to or further away from the subject to frame it similarly, the apparent depth of field also changes by the "crop factor".

 

I have been taking images a very long time and one of my most valuable lessons from many photographs is to "learn what your lens sees, don't expect your photograph to reflect what your eye sees when you record the image".  Lenses have individual characteristics as do our eyes.  This is a very good reason to stick with one or a very few lenses and in my case, stay away from zoom lenses.  Just taking photos and learning from the results tells one all that is needed.

 

Just me, perhaps.

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Completely correct. I would like to make one additional emphasis;The total amount of light received by the sensor is obviously determined by the area of the sensor, but as the amount of light per square millimetre is not changed, the exposure remains the same. A 1.4 lens remains a 1.4 lens regardless of sensor area for exposure purposes.

 

Because of this it is highly confusing to say that a 35 mm 1.4 lens is equivalent to a 50 mm 2.0 lens in every way; it is still a 1.4 lens.

It is more clear to say that the angle of view, DOF and noise behaviour of an APS- C sensor are equivalent to a 1.5 crop on a full frame sensor and leave the lens out of the discussion altogether, as nothing will be changed on the lens itself.

Fair enough. The lens, as you said, is still doing the same thing.

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Jared, thanks so much.

Point 3 is exactly what he says in the video and whats was confusing to me. Now it is crystal clear !

No problem. That’s the one a lot of people get stuck on.

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An exhausting discussion. The lens characteristics stay the same, aperture etc. The crop factor affect the field of view and since one must move closer to or further away from the subject to frame it similarly, the apparent depth of field also changes by the "crop factor".

 

I have been taking images a very long time and one of my most valuable lessons from many photographs is to "learn what your lens sees, don't expect your photograph to reflect what your eye sees when you record the image". Lenses have individual characteristics as do our eyes. This is a very good reason to stick with one or a very few lenses and in my case, stay away from zoom lenses. Just taking photos and learning from the results tells one all that is needed.

 

Just me, perhaps.

No, it’s not just you. As Jaapv mentioned we would all be better served just learning how our lenses behave on a given camera. MF photographers don’t worry about equivalence—they just learn their lenses.

 

Like you, I tend to avoid zooms (with ultra wide angles being the major exception for reasons beyond the scope of this discussion). It has nothing to do with the image quality from a good zoom which is more than adequate. Rather, I get lazy with zooms and stop thinking about what I am trying to do. A camera with a zoom, for me, becomes just a way to freeze a memory rather than a way to make a photograph. My brain tends to stop working when I use zooms, and the quality of the pictures suffers.

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Am I understanding this correctly?

 

Using full frame sensor with a 50mm f2 from a distance of 5 feet from my subject will give the same rendering as using an APSC with a 35 f.1.4 from 7.5 feet from my subject.

 

Depth of field will be similar?

 

There will be more noise with the APSC because the pixels are smaller?

Edited by ropo54

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Best practices with each camera will keep you from having to make this comparison.  With the APS-C sensor (CL or Fuji T2/Pro2), I cut back on the maximum ISO that I use, and know that I can't dig as far into the shadows as I can with the M10 or SL when rendering a raw file.  Or when working in manual exposure, I set the full frame camera at ISO 200 to 400 but leave the smaller sensor at ISO 100.

 

Some day, when they figure out how to hold onto 2^14 electrons, generated at a rate of one electron per incoming photon (that's where quantum efficiency comes in) in a 4 micron pixel, we will see base ISOs returning to values like 100 or even 50.  My old 39 MPx CCD digital back, with this sort of dynamic range, has a base ISO of 50, for example.  If you want full dynamic range, you have to wait longer for enough photons to reach the sensor, and the "film speed" goes down.

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When comparing FF to APS (or FF to MF) as far as DoF is concerned, whatever value one chooses for the FF CoC, there will always be a difference coming from the difference of format and i don't see how noise could make that an FF pic taken at f/1.4 equals or is equivalent to an APS-C one taken at f/2. Both are taken at f/1.4 actually and under the same light, the FF camera with a 50mm lens behaves the same as an APS-C camera with 35mm lens at the same aperture with a different DoF due to different sensors. At least it is the way i've been taking my pics since my first APS-C camera in 2002 or something but again i'm no techie at all.

Apart from conflating sensor noise with DOF which nobody on this thread suggested , that is precisely what we have been saying.

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OK folks please help me check my visual acuity and/or mental health if you don't mind.

Here is a 35/1.4 pic shot at f/1.4 on my digital CL. Sorry for the crappy pic ( full size: http://tinyurl.com/y8or5rdf ).
 
CL, 35/1.4, f/1.4:
 
Now here are two 50/1.4 pics shot on my M240 at successively f/1.4 ( full size: https://tinyurl.com/y8pbl39a ) and f/2 ( full size:  https://tinyurl.com/yd864m2x ).
Same light, same shutter speed, same focus point, same iso. 
Please tell me which looks more similar or different to the CL pic above if you don't mind.
 
M240, 50/1.4, f/1.4:
 
M240, 50/1.4, f/2:
 
 

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In terms of depth of field, I'd say the f/2 image from the 50mm looks more like the f/1.4 image from the CL.  Look at, for example, the size of the blue "bokeh ball" just to the right of where it says "Bostitch" on the stapler.  The 35mm f/1.4 and 50mm f/2 have similar defocus.  Or, look at the bar code on the yellow glue stick (if it's a glue stick--whatever that yellow tube is on the right side of the image).  I think this illustrates the point quite well.  The 35mm at f/1.4 on the APS C size camera has very similar depth of field to a 50mm f/2 lens on a full frame camera.  Obviously, since the two lenses have somewhat different ways of rendering, they won't be perfectly identical, but your example seems to me to show the APS-C lens is much closer to the 50mm f/2 than to the 50mm f/1.4.

Edited by Jared

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Am I understanding this correctly?

 

Using full frame sensor with a 50mm f2 from a distance of 5 feet from my subject will give the same rendering as using an APSC with a 35 f.1.4 from 7.5 feet from my subject.

 

Depth of field will be similar?

 

There will be more noise with the APSC because the pixels are smaller?

 

Not quite (though it may have just been a typo on your part--mixing different lenses and different distances).

 

I/we are saying that 50mm f/2 from a distance of 5 feet gives the same field of view and depth of field as an APS-C camera with a 35mm f/1.4 from the same 5 feet.  You wouldn't back up farther with the 35mm since it gives the same field of view as the 50mm.  And, yes, all things being equal the APSC image would be noisier because the pixels are smaller (assuming the same exposure in each).  Since the pixels are smaller, they collect less light in a given exposure time.  In general (ignoring thermal noise, read noise, etc., and just considering shot noise), signal-to-noise ratio = (signal) / (sqrt(signal)).  Less signal = lower signal-to-noise ratio.  Smaller pixels have less signal.

 

One might ask, why don't you just expose the image longer on the camera with the smaller pixels so you get the same signal to noise ratio?  You usually can't.   Smaller pixels not only collect less light, they also hold fewer photons before saturating.  So you'd probably blow out your highlights if you doubled your exposure time to get the same SNR.  Hence, the strange math required by "equivalence".

 

Frankly, if we weren't trying to adapt our full frame lenses to our APS-C bodies, I suspect most of these mathematical gymnastics would just go away.  We'd just learn how a given lens performs on our camera and not worry about what it's equivalent to in full frame.  The problem is, we are used to how a lens behaves on 35mm, so when we shift it over to an APS-C camera we want to know what to expect.  Eventually it will all become intuitive as we spend enough time with each format.  As I said in an earlier post, just as when learning a foreign language the goal is to be able to think in a given language without having to translate back and forth in your head.

Edited by Jared

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Jared or anyone else:

 

My confusion is this:  For example, let's say that I am using a noctilux on an APSc sensor.  

 

At 5 feet of distance from my subject my sensor will capture only the central area of what the lens 'sees'.

 

Now, lets say I step back to 7.5 feet from the subject. While the central area of the lens is still limited by the smaller sensor, by stepping back an additional 2.5 feet I am now capturing a wider area of the scene.  

 

How would this compare/equate to using the noctilux on a full frame sensor at 5 feet distance from the subject?

 

Thanks,

Rob 

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[...] The 35mm at f/1.4 on the APS C size camera has very similar depth of field to a 50mm f/2 lens on a full frame camera.  Obviously, since the two lenses have somewhat different ways of rendering, they won't be perfectly identical, but your example seems to me to show the APS-C lens is much closer to the 50mm f/2 than to the 50mm f/1.4.

 

As far as DoF is concerned we agree of course but DoF is not all photography. I've been using both FF and APS gear for 15+ years and when i had an f/1.4 lens to use it was a 35 on APS and 50 on FF. For both lenses, shutter speeds and apertures have always been the same because there is no significant difference between them besides DoF, sorry to disagree with you.

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Jared or anyone else:

My confusion is this:  For example, let's say that I am using a noctilux on an APSc sensor.  

At 5 feet of distance from my subject my sensor will capture only the central area of what the lens 'sees'.

Now, lets say I step back to 7.5 feet from the subject. While the central area of the lens is still limited by the smaller sensor, by stepping back an additional 2.5 feet I am now capturing a wider area of the scene.  

How would this compare/equate to using the noctilux on a full frame sensor at 5 feet distance from the subject?

 

You mean a Noctilux 50/1 at f/1? If so DoF is very thin there so you won't see a lot of difference anyway. See calculations below. The DoF Master site ( http://www.dofmaster.com/dofjs.htmlhas not been updated to include Leica T or CL cameras so i've chosen an APS-C rangefinder instead, the Epson R-D1 which has been my first crop RF in 2004.

 

 

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