Difference in Angle of View Between Olympus 25mm f/1.8 and Panasonic Leica 25mm f/1.4

Discussion in 'Native Lenses' started by Amin Sabet, Feb 23, 2014.

  1. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    This was already covered in Napier's Part 1 review, but it seems that some questions and misunderstandings remain, so I am adding some supplemental files here for comparison.

    Below are resized images from GX7 images taken with the Panasonic lens (left) and Olympus lens (right), processed from RAW without distortion correction (top) and as processed in camera (bottom):


    As you can see, the files processed without distortion correction (top panel) show very nearly the same angle of view as one another, whereas the disortion-corrected image with the Panasonic lens (bottom left) shows a slightly tighter angle of view than the distortion-corrected image taken with the Olympus lens (bottom right). Which corrected file is closer to a "true" 25mm angle of view is unclear. As you can see, the difference is slight.

    Here are the full-res uncorrected JPEGs, corrected JPEGs, and RAW files for your inspection (note that I had the camera in P mode and auto WB, so f-stop, shutter, and colors were not held constant):

    P1090522-uncorrected.jpg: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P1090522-uncorrected.jpg
    P1090522.JPG: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P1090522.JPG
    P1090522.RW2: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P1090522.RW2
    P1090523-uncorrected.jpg: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P1090523-uncorrected.jpg
    P1090523.JPG: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P1090523.JPG
    P1090523.RW2: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P1090523.RW2

    For the sake of completeness, I repeated the above test using an Olympus E-M1. The results, shown below, were essentially identical:


    And here are the full-res uncorrected JPEGs, corrected JPEGs, and RAW files from this second comparison:

    P2230001-uncorrected.jpg: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P2230001-uncorrected.jpg
    P2230001.JPG: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P2230001.JPG
    P2230001.ORF: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P2230001.ORF
    P2230002-uncorrected.jpg: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P2230002-uncorrected.jpg
    P2230002.JPG: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P2230002.JPG
    P2230002.ORF: https://s3.amazonaws.com/mu43rawfiles/25mm+distortion+comparison/P2230002.ORF
    Last edited: Aug 21, 2016
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  2. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    Hindsight is a wonderful thing - of course, barrel distortion correction is an obvious reason for the different FOV on these two lenses! Nice analysis.
    • Like Like x 1
  3. bg2b

    bg2b Mu-43 Regular

    Dec 22, 2009
    Berkeley Heights, NJ
    The other variable is focus distance. The specified focal length is when the lens is focused at infinity, but many lenses exhibit focus breathing (change of effective focal length when focusing closer). This test shows that both lenses have basically the same angle of view when focused at infinity.
    • Like Like x 2
  4. dougjgreen

    dougjgreen Mu-43 All-Pro

    Jun 5, 2013
    San Diego
    Doug Green
    My results were significantly different from those above - but my results were not shot at infinity - more like 4 feet away.

    I can't replicate them now, because I no longer have the Panasonic 25mm, but suffice it to say that on both my G5 and my E-PL5, shooting a wood panel from a distance of about 3.5 to 4 feet (the distance was standardized between the two because my back was up against a brick column when all of the pics were shot) the Panasonic produced a consistently narrower field of view, by about 2 degrees. The difference with my two lenses was MUCH more dramatic than the corrected JPEG shots shown above. In the Panasonic pictures, the frame included almost exactly 6 panels. In the Olympus pictures, the frame included the same 6 panels, along with about 1" of the next panel on each side. Measuring the width of the panels, The Panasonic was capturing about a 36" wide frame, whereas the Olympus was capturing a 38" wide frame, shot from the same distance. I should add, this difference was clearly visible in the viewfinder as I was shooting these pictures - it wasn't applied after the images were saved as barrel distortion was corrected - unless barrel distortion is being corrected in the viewfinder in real time, prior to saving the image as a JPEG.

    In any case, even if one actually takes as a given the claim that the focal lengths of the two lenses are virtually the same, that fails to explain why, at maximum apertures, the Panasonic is only transmitting 1/3 EV more light than the Olympus, and when both lenses are set to the same nominal stated apertures, the Olympus lens is consistently transmitting 1/3 more EV of light. My comments about the focal length difference between these lenses was an attempt to explain this substantial difference in light transmission. As I stated before, each lens has the same number of elements, the same number of air-glass surfaces, and similar modern multi-coatings, so it would strain credulity to claim that the Panasonic lens was really ~25% less efficient at transmitting light than the Olympus was (which is what the consistent 1/3 EV edge for the Olympus implies). This leaves as the only plausible explanation that the physical apertures of one or both of these lenses is not as stated. Either the Panasonic lens is slightly slower than it's rated f1.4, or the Olympus lens is slightly faster than it's rated f1.8, or both of these are true. In any case, the measured discrepancy is consistently 1/3 EV in total. The observed difference in focal length would only be one possible cause of this. Another is simply that Panasonic has over specified the lens as being faster than it really is. My best hypothesis is that the Panasonic lens is a true f1.5, whereas the Olympus is a true f1.7. The only other explanation is that the nominal apertures are correct, but the Panasonic really is about 25% less efficient at light transmission, and I simply don't believe that, given the similarities of the respective construction of the two lenses.

    The top photo is the Olympus, the bottom the PanaLeica - both shot in JPEG with an E-PL5

    Attached Files:

  5. Serhan

    Serhan Mu-43 Top Veteran

    May 7, 2011
    Per dxo tests, PL 25mm has Transmission T1.7, so it is slower then f/1.4:

    They haven't tested the Oly 25mm yet. Similar 17mm and 45mm lenses have T2, which might be the result for Oly 25mm also.

  6. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Mike Aubrey
    On the contrary, the fact that the Panasonic is an f/1.4 design would encourage, by definition, less efficient light transmission.
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  7. EarthQuake

    EarthQuake Mu-43 Top Veteran

    Sep 30, 2013
    Doug, many lenses actual focal length varies at different focal distances, the focal length of a lens is generally measured by the manufacturer when focused to infinity. Its quite possible that the Oly 25 is more like a 20mm or so when focused to shorter distances. If there is little difference at infinity, this is likely the case.
  8. dougjgreen

    dougjgreen Mu-43 All-Pro

    Jun 5, 2013
    San Diego
    Doug Green
    Except that ignores the fact that both the Olympus and the Panasonic have the same number of elements and groups, and hence the same number of air-glass surfaces. The also have similar modern, state of the art multi-coatings. The REASON that an f1.4 design would tend to encourage less efficient light transmission would be due to it normally involving more elements. But that's specifically not the case here.
  9. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Mike Aubrey
    Ah...if only things were as uncomplicated as that.
  10. dougjgreen

    dougjgreen Mu-43 All-Pro

    Jun 5, 2013
    San Diego
    Doug Green
    They actually are. What causes transmission loss is, primarily, glass to air surfaces - as well as the degree of transparency of each element. But the latter issue is usually pretty consistent across similar types of glass. The only substantive difference between these two lenses architectures (both are 9 element, 7 group lenses with 2 aspherical elements) is that the Panasonic has one element that uses ultra-high refractive index glass. That in itself might make a difference in the transmission efficiency of the lens overall, but it's unlikely that any one single multi-coated exotic UHR glass element would cause more than maybe 2% additional transmission loss, relative to a more conventional glass element, as most individual elements have transmittance efficiencies in the 94-98% range.
  11. T N Args

    T N Args Agent Photocateur

    Dec 3, 2013
    Adelaide, Australia
    call me Arg
    Doug, do it at infinity.

    Plus, look at the uncorrected raw file.

    Or, believe those who have done it for you. https://www.mu-43.com/showthread.php?t=60649

    The answer is: same angle of view.

    You're on the wrong bus, mate.
  12. dougjgreen

    dougjgreen Mu-43 All-Pro

    Jun 5, 2013
    San Diego
    Doug Green
    As I said, the exact same effect that I showed in my photos is also visible in the viewfinder while composing them. So that's not a result of correcting for barrel distortion in the JPEG engine. At least at 3.5 feet, there is a clear difference in the focal lengths of these two lenses, as shown in my pictures - the pictures reflect the composition of the images in the viewfinder as well.

    I can't do the experiment at infinity, because I no longer have the PanaLeica lens. But there is no doubt whatsoever that, at the closer focus point at which this pictures were shot, these lenses are NOT the same focal length.

    I would suggest that the folks who did this test at infinity need to replicate it at closer distances before making the broad claim that the lenses have the same angle of view. At close distances, they clearly do not. I believe that YOU, T N Args, are on the wrong bus, or at a minimum, you seem to believe that all the buses go to the identical destination., when clearly, they do not. How, exactly, would you explain the fact that the image in the viewfinder is clearly a wider field of view with the Olympus lens, than the Panasonic lens, when the subject matter is 3.5 feet away? As you can see in my comparison photos, the field of view difference at 3.5 feet is FAR more dramatic than the prior comparison done at infinity.

    And again, this is actually not the point I was making. The point I was making is that the actual speed differential between these two lenses is noticeably less than the nominal 2/3 of a stop at which they are spec'd. It's much closer to 1/3 of a stop, and whether that's due to a difference in transmission efficiency, or just that the nominal aperture of the Panasonic lens is smaller than it's claimed to be, either due to focal length discrepancy, or simply that the aperture is smaller than it's spec'd to be - the net real world effect is the same, the lens is actually only 1/3 of a stop faster than the Olympus lens, in real world usage. Not 2/3 stop.
  13. Focus breathing.
  14. Petrochemist

    Petrochemist Mu-43 Top Veteran

    Mar 21, 2013
    N Essex, UK
    Not at all!
    The tests show both have about the same FOV at infinity (Doug didn't contest this) but the Olympus is significantly wider than the Panasonic at close focus. This information could be very useful to someone deciding between the lenses.
    The slightly lower than expected light transmission on the Panasonic might also be of interest.
    • Like Like x 1
  15. T N Args

    T N Args Agent Photocateur

    Dec 3, 2013
    Adelaide, Australia
    call me Arg

    What sort of person would that be even slightly 'useful' to?

    I am Australian and perhaps a little too laconic to grasp this.
  16. Wisertime

    Wisertime Mu-43 Hall of Famer

    Aug 6, 2013
    I always wondered if these comparisons are being done "properly". Wouldn't you measure the distance from the Front element, not the sensor? being that the PL is longer physically, that small difference in FOV might need to be accounted for. If you just swapped them on a tripod, it might account for the difference. I'd think if you compared the MU43 and 43 versions of the PL25 the difference might be exaggerated, depending on the methodology. I don't know which is the "correct" way.

    Either way, it's not significant really IMO.
  17. Dramaturg

    Dramaturg Mu-43 Top Veteran

    Jun 7, 2013
  18. dougjgreen

    dougjgreen Mu-43 All-Pro

    Jun 5, 2013
    San Diego
    Doug Green
    In real life, the PL is only about 1/2 inch longer than the Olympus (actually, 14mm, but the front element is more recessed in the Panasonic, so it's maybe 10mm difference - not much). And technically, if the focal length is actually the same, the nodal point is the same distance away, which means that the different physical size of the lenses is not significant. In any case, I'll accept the premise that these lenses have different focal length characteristics at different focus points, and while the lenses may offer a similar FOV at infinity, they do not at closer focus. But that also leads to the conclusion that, at least at closer focus points, the physical focal length also impacts the actual aperture of the lenses. The 1/3 EV discrepancy from what the stated apertures imply that my meter was showing between these two lenses may also be different - and more substantial - at close focus than at infinity.

    And no, I'm not confusing the T-number and the F-stop. I just don't believe that the 1/3 EV discrepancy can be explained on the basis of just different Transmittance Efficiency of the two lenses, given their architectural similarities - i.e. same number of elements and groups, each with 2 aspherical elements, and similar coatings - I can't imagine two such similarly constructed lenses could have transmittance efficiencies that are more than 5-10% different overall, whereas 1/3 EV implies 25% different amounts of light reaching the sensor. I think the difference I observed is much more likely to be due to an actual difference in the size of the physical aperture (which is the ratio of the actual focal length over the diameter of the entrance pupil. The physical f-number gets smaller as the lens focuses closer - which is why extension tubes cause the effective aperture to get significantly smaller. And again, the combination of my results and those reported earlier in the thread, indicate that this changes between infinity and close focus - with the Panasonic getting longer (and hence the real physical aperture shrinking more) at close focus than the Olympus does.
  19. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Actually, that leads YOU to the conclusion you reached but it doesn't necessarily lead others to the same conclusion.

    Well, I would think differently. The problem with extension tubes affecting aperture is not because the F/number gets smaller as the lens focusses closer. The F/number remains constant and it can't change. After all, it's defined in terms of a ratio between the diameter of the aperture opening, which isn't changing as you focus closer, and the focal length of the lens which also isn't changing. What happens is that light exiting the lens at the rear of the lens throws an image circle of a particular size but that size is determined by the distance between the rear of the lens and the sensor. The angle at which the light exits is determined by the design of the rear element. When you introduce an extension tube between the lens and the camera body you move the rear of the lens further from the sensor plane, the light exits the rear element at exactly the same angles regardless of whether there is an extension tube there or not, and because of the increased distance between rear element and sensor the image circle thrown by the lens is increased, just as the size of the circle of light thrown on a wall by a torch increases as you move the torch further away from the wall. Increasing the size of the image circle means that a smaller section of the field of view is thrown on the sensor, hence the magnification, but it also means that less of the light transmitted by the lens is thrown on the sensor and that's why one has to compensate for a loss of transmission compared to what one would expect given the aperture setting on the lens. There is a transmission loss because the sensor now occupies a smaller proportion of the image circle and receives light from a smaller area of the field of view. The size of the physical aperture of the lens is completely unaffected by the use of an extension tube.

    If you're comparing 2 lenses of identical focal length and field of view, both mounted directly on the camera as intended, and the light meter indicates a different exposure is required at the same aperture there are only 4 possible explanations.

    The first is that there has been a change in light intensity between the 2 measurements, easy to occur if you're testing in sunlight and there is some cloud cover which is moving. Ideally you would do your test under conditions where you have complete control over lighting levels and the lighting level can be maintained exactly for the duration of the tests.

    The second is that there are slight differences in the diameter of the aperture opening for each lens. For a 25mm lens, an aperture opening at F/2 should be 12.5mm in diameter. The difference between an opening of 12.4mm and one of 12.6mm is the difference between F/2.016 and F/1.984. It would take a big deviation from nominal aperture diameter to account for a third of a stop difference in transmission but poor quality control and a bad copy of one of the lenses could perhaps result in that and such a fault would probably not be noticed by many in practice. After all, they won't be making the sort of comparison we're talking about and a third of a stop is a small difference in exposure, well within the easy range of adjustment and correction of processing software. It's easy to get a third of a stop difference by simply reframing your composition slightly and including a bit more shadow area or a bit more highlight area.

    The third option is that there is a difference in the transmission efficiency. You consider that unlikely because you don't believe that there would be a significant difference in transmission through a similar number of elements but without testing you really don't know. There was a poster on a totally unrelated forum I sometimes visit who had a signature quote which said something like "In theory there is no difference between theory and practice, in practice there is".

    Fourth, if there is focus breathing going on and the field of view is changing, then that may be due to a change in the size of the image circle which will, of course, alter the amount of light falling on the sensor and that may complicate the comparison at different focus distances.

    Worse, to complicate matters even more, it would be possible for more than one of t those 4 factors to be at play in a single test under natural light outdoors, even for all 4 to be in play in the test.

    I'm sorry but for my money the jury is out on the cause of the third of a stop difference in exposure. There are more factors that could be in play than you have considered and it's possible for more than one of those factors to be in play at the one time. It's not a matter of "x couldn't cause such a big difference so x can't be occurring". X may certainly not be capable of causing such a difference on it's own but that doesn't mean that x is not occurring. There are several possible variables. Neither lens has been tested for accuracy of aperture diameter opening, transmission factor, impact of focus breathing on image circle diameter, and the lighting levels in the test was uncontrolled. No one is in a position to make a categorical statement on any of the factors. All we can say is that there was a difference in recommended exposure with each lens and we don't know why. We have no basis for ruling any one of the possible causal factors in or out of play.
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  20. dougjgreen

    dougjgreen Mu-43 All-Pro

    Jun 5, 2013
    San Diego
    Doug Green
    Actually, the f-number DOES change when you use extension tubes, because the focal length in fact changes. The f-number is the ratio of the focal length over the exit pupil. The focal length is the distance from the focal point of the lens to the sensor. And the focal point is further away when you extend the lens to focus on a closer object.

    A 25mm lens focused at 25mm has a focal length of 25mm, but when you extend it to focus at life-size, your true focal length is now 50mm, because the lens has been moved forward by 25mm to bring an object into focus at life-size. Hence, your actual aperture is now 2 f-stops smaller than if you had been focused at infinity with the same lens opening, because the size of the opening has not changed, but the focal length of the lens DOES change as the focus point changes.

    For convenience of nomenclature's sake, lenses are described by their focal length at infinity focus, but in actual fact, the focal length of any lens increases as the lens is extended forward to focus - unless the lens is specifically designed not to move forward, but rather to focus internally. And in fact, internal-focusing lenses don't respond the same way as other lenses when focused closer. Other lenses increase the magnification as the lens is moved forward, internally focusing lenses may or may not.