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    Lenses FF/APSC

    A good article in the latest magazine....I think a whole series of articles could be written about this subject. It was good to be reminded of the effect of the circle of confusion especially as this could affect APSC images that have to be enlarged more to produce an image of a given size.

    in trying to dispel the belief that DoF is greater on an APSC sensor, I tell people to take an picture on full frame, print it and note the dof......and then trim off the edges of the print with scissors and see if the DoF changes.
    Brian Vickers LRPS

    brianvickersphotography.com

    #2
    Re: Lenses FF/APSC

    Same for apsc gives you more reach....the times I've had to explain that!

    Sent from my SM-N910F using Tapatalk

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      #3
      Re: Lenses FF/APSC

      Originally posted by supergeeman View Post
      Same for apsc gives you more reach....the times I've had to explain that!

      Sent from my SM-N910F using Tapatalk
      Ditto

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        #4
        Re: Lenses FF/APSC

        Originally posted by brianvickers View Post
        in trying to dispel the belief that DoF is greater on an APSC sensor, I tell people to take an picture on full frame, print it and note the dof......and then trim off the edges of the print with scissors and see if the DoF changes.
        The size of the print and the viewing distance does have an effect on our perception of DOF. If you printed the same image at 6x4 and then compared both at the same viewing distance, eg arms length, then the 6x4 will look to have greater depth of field since at that size it's not technically possible to reproduce the same gradation from sharp to soft as you can see in the large print. However if you then move back from the large print until it subtends the same angle of view as the enprint does at arms length the apparent DOF will then be similar to the small print at arms length.
        Nigel

        You may know me from Another Place....

        The new ElSid Photogallery...

        Equipment: Far too much to list - including lots of Nikon...

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          #5
          Re: Lenses FF/APSC

          In terms of the alleged more "reach" with APS-C
          Suppose we take the same image with the same lens on FF and APS-C bodies with the same number of pixels, e.g. the 70D and 6D, both of which have 20.2 megapixels, but on different size sensors. Yes, we can crop in on the 6D image to make the subject the same size as that from the 70D, but only by throwing away a lot of the pixels. The subject may be the same size on each, but the one taken with the 70D will be made up of many more pixels than the one from the 6D. Surely that should mean that we can get better resolution from the 70D image? If we crop in both images even further, then the image from the 6D will lose resolution and detail before the one from the 70D.

          So although we may not actually get more reach with the smaller sensor, isn't the practical effect as if we did? So if we want to take a photo of a small bird from a long distance and need to crop in quite a lot, are we not better off using the smaller sensor, all other things being equal?

          I also find discussion about focal length pretty irrelevant. While 50 mm may still be 50 mm on any body, on the APS-C it gives the same field of view as an 80 mm lens on FF. It's field of view that is relevant to the uses of a lens, not actual focal length. There's little point in putting a 24 mm lens on an APS-C body for wide angle as the field of view will be equivalent to 38 mm and more like a standard lens than wide angle. As I have both type of bodies, I tend to think of everything in terms of FF equivalent rather than actual focal length, it's much more useful and after 30+ years of 35 mm film use, I can look at a subject and think "That looks about right for 24 mm (which means a 15 mm on APS-C)".
          EOS 6D, 6D Mk II, 80D, 70D, 100D, 200D, M50, M100. Canon 10-18, 18 - 55, 55 - 250 IS STM lenses, Canon 16 - 35 mm F4L, 35 mm EF-S macro, 50 mm F1.8 STM, 60 mm EF-S macro, MPE-65 macro, 85 mm F1.8, 200 mm F2.8 L II, M 15 - 45 mm, M 22mm F2, M 32mm F1.4. Sigma 24 - 35 F2 Art, 135 mm F1.8 Art, 17 - 50 F2.8 DC, 105 mm OS macro, 100 - 400 C, 150 - 600 C.

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            #6
            Re: Lenses FF/APSC

            I totally agree Nigel.
            Richard.....I think that is correct too, the point in the article for crop not being quite as good as the FF is that the crop image has to be enlarged more to print it the same and thus the circle of confusion is enlarged that bit more too....the extra pixel density won't help....though its also logical that the extra resolution of the APSC should improve things.
            Brian Vickers LRPS

            brianvickersphotography.com

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              #7
              Re: Lenses FF/APSC

              AFAIK there are three factors controlling DOF. These are the focal length of the lens, the aperture and distance the subject is in front of the lens. There are some "out there" who say DoF is not dependent on the focal length of the lens. Those folks tend to "prove" this by taking images with different F.L lenses and if you compare the results they do seem to show the same DoF. What they usually did is to move the position of the camera to keep the same image size, which is cheating because that is changing two of the three factors at once.
              That said, it means that the DoF on an APS-C body is likely to be worse not better than on FF because you generally use the 1.6 crop factor in choosing a lens. So if you use a shorter lens (e.g. 50 for a portrait) the DoF is greater than for the 85 on FF for the same aperture. Perception is that DoF is different. But like for like the same FL lens on either camera body will give the same DoF. But if you want to match the FF image on an APSC exactly using a 1.6 ratio lens (to keep the same field-of-view image size at the same working distance) you will need a 1.6 greater aperture ... a more expensive lens, if there is one!
              Last edited by neonlamp; 08-10-2017, 20:40.

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                #8
                Re: Lenses FF/APSC

                I found myself still somewhat confused by the "crop factor" debate, so I decided to go back to basics.

                I set up the tripod in the garden and took the two images below of my Backwell Red apple tree. I used my 5D3 and the M5, attached to the 100-400 lens. Both cameras were set to AV, with the aperture set at f8. Both images are full frame, unaltered except for jpg conversion in LR as part of the export process and resizing to 800 tall in Flickr.

                I took the 5d3 image first and adjusted the lens so the the tree filled the height of the frame. Then, without moving the tripod, I uncoupled the 5D3, fitted the M5 (using the Canon M to EF adapter), adjusted the lens so that the tree filled the height of the frame and took the second image.

                I think it is fair to say that the tree fills the same amount of frame in both images (bar very slight differences).

                5D3 Backwell Red by John Liddle, on Flickr


                M5 Backwell Red by John Liddle, on Flickr

                The EXIF tells me that for the 5D3 image I had the lens set at 263mm focal length. Similarly, for the M5 image it was at 164mm focal length.

                263 divided by 164 is 1.6037, or rounded off, 1.6 - I think I recognise that number.

                I seems to me that this exercise shows that for the same lens, photographing the same object, the APS-C camera gives a 1.6 increase in effective focal length.
                John Liddle

                Backwell, North Somerset - "Where the cider apples grow"

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                  #9
                  Re: Lenses FF/APSC

                  To my simple mind, the crop factor effect is simply an "enlargement" of the central image "in camera". It therefore gives the impression of using a "longer lens"!
                  Canon 6D; Canon 760D;Canon G15;Canon 40mm f2.8(Pancake);Canon 50mm f1.8(ii); Canon 17mm-40mm f4L;Canon EF-S 10-18mm f4.5-5.6 IS STM;Canon EF-S 55-250mm f4-5.6 STM lens;Canon 24mm-105mmf4L IS;Canon 70-300mm f4-f5.6 L IS USM;Kenko 1.4x HD TC;Canon 430EX ii flash;Giottos tripod;Manfretto monopod;Cokin P filters + bits and pieces!

                  www.flickr.com/photos/nathaniel3390

                  North Wales where music and the sea give a great concert!

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                    #10
                    Re: Lenses FF/APSC

                    Originally posted by Nathaniel View Post
                    To my simple mind, the crop factor effect is simply an "enlargement" of the central image "in camera". It therefore gives the impression of using a "longer lens"!
                    Exactly. ...there is no real extra focal length...you are still the same distance...the crop sensor enlarges the image....

                    Sent from my SM-N910F using Tapatalk

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                      #11
                      Re: Lenses FF/APSC

                      Originally posted by John Liddle View Post
                      I seems to me that this exercise shows that for the same lens, photographing the same object, the APS-C camera gives a 1.6 increase in effective focal length.
                      Plus if you look at the pictures carefully the background in the M5 image, particularly the skyline, the trees are show more definition showing the depth of field is marginally greater at 164mm than at 263mm...
                      Nigel

                      You may know me from Another Place....

                      The new ElSid Photogallery...

                      Equipment: Far too much to list - including lots of Nikon...

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                        #12
                        Re: Lenses FF/APSC

                        Originally posted by El Sid View Post
                        Plus if you look at the pictures carefully the background in the M5 image, particularly the skyline, the trees are show more definition showing the depth of field is marginally greater at 164mm than at 263mm...
                        Indeed.
                        John Liddle

                        Backwell, North Somerset - "Where the cider apples grow"

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                          #13
                          Re: Lenses FF/APSC

                          Originally posted by supergeeman View Post
                          Exactly. ...there is no real extra focal length...you are still the same distance...the crop sensor enlarges the image....

                          Sent from my SM-N910F using Tapatalk
                          True - and I did not say that there was any real extra focal length - I said that the "effective" focal length was longer.

                          By filling the frame with the subject, each camera has produced the highest definition image it is capable of the apple tree from that distance with that lens, but the M5 has done it with the lens set at a shorter focal length. The corollary of this of course is that the M5 user could, if desired, obtain a similiarly high definition image of a small portion of the subject from that distance, with that lens.

                          If one were to approach this from another direction, one could fix the lens at a particular focal length and then move towards or away from the subject until it filled the frame. The M5 user would find himself standing further away from the subject than the 5D3 user.

                          So although there is indeed no difference in the lens when used on the different cameras, the effective result for the M5 user is that of having a longer focal length lens.
                          Last edited by John Liddle; 27-10-2017, 13:24. Reason: speeling
                          John Liddle

                          Backwell, North Somerset - "Where the cider apples grow"

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                            #14
                            Re: Lenses FF/APSC

                            Originally posted by Nathaniel View Post
                            To my simple mind, the crop factor effect is simply an "enlargement" of the central image "in camera". It therefore gives the impression of using a "longer lens"!
                            Originally posted by supergeeman View Post
                            Exactly. ...there is no real extra focal length...you are still the same distance...the crop sensor enlarges the image....
                            No. Neither the camera nor the sensor enlarges the image. An APS-C sensor captures just the central area of the image that would be captured by a full-frame sensor. It is a crop - no magnification involved.
                            Robert
                            robert@eos-magazine.com

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                              #15
                              Re: Lenses FF/APSC

                              Originally posted by John Liddle View Post
                              True - and I did not say that there was any real extra focal length - I said that the "effective" focal length was longer.
                              So although there is indeed no difference in the lens when used on the different cameras, the effective result for the M5 user is that of having a longer focal length lens.
                              No. Here is a quote from the article I wrote:

                              "Over the years some very misleading phrases have crept into the photographic vocabulary – ‘effective focal length’, ‘equivalent focal length’ and ‘extra reach’. Sorry, but none of these make any sense.

                              We blame Canon (and other camera manufacturers) for this confusion. It all happened with the introduction of EOS digital cameras and the APS-C sensor size. This is significantly smaller than the full-frame format of all EOS film cameras. In trying to transition photographers from the full-frame format to the APS-C format, Canon instruction manuals for APS-C cameras say that the “35mm-equivalent focal length is equal to approx. 1.6 times the marked focal length”.

                              So a 28mm lens used on a full-frame camera becomes a 45mm lens when attached to an APS-C camera? No it doesn’t. When you switch a lens from a full-frame camera to an APS-C camera, all that changes is the field-of-view."
                              Robert
                              robert@eos-magazine.com

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