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Why do mFT lenses focus SO close??
  • Given the "crop factor" and the fact that you will get more bokeh the closer the subject is to the minimum focus distance, why wouldn't the minimum focus distance be farther away? So you can have a subject (say for an interview) at comfortable distance with a 25-50mm (50-100mm eq)? Is this just not possible for some reason? Or are the lenses intentionally made to focus so close, as many manufacturers tout how close you can focus.. We're not all filming flowers...

  • 6 Replies sorted by
  • Also, I am not a huge fan of shallow depth of field, but sometimes (like on commercials, testimonials, etc) it helps and saves a lot of time to be able to just make the background an amorphous blob of light and color.

  • I have big issue understanding complain. As minimum focus distance is just lens design property. All manufacturers fight for smaller values as it makes lens more useful for more people. :-) And it does not really have any bad consequences, no one prevent you to focus further away :-)

  • Well I guess it makes sense from their standpoint, I guess it just sucks from mine haha. Yes I can focus farther but being able to have the subject as close to the minimum focus distance means more blurred out background and not having to open the aperture as much, as the lenses are 2-3x "longer"...

    Hypothetical following: So say I am using a GH3 (2x crop factor) and 5DIII with a 85mm lens that focuses from 1' to 20' (and then infinity) and a low aperture for blurred out background. At 1' the background will be blurrier than if the subject was at 20'. For a portrait, I probably want the subject (let's just say) more than 5' from the camera so I don't creep them out being all up in their face. With the 5D the subject is 5' and with the amount of bokeh that is possible. But it is not possible for me to replicate this shot on the GH3, as the subject would have to be 10' away for the same framing, and the bokeh would be reduced. My only option would be to (if possible) open the aperture more, but if I am shooting video this sucks because I have to worry about keeping focus.

    I understand this is remedial stuff but my point is that it seems manufacturers of mFT lenses don't take the crop factor into account when designing their own lenses. Take the Olympus 45mm 1.8 for example. This a portrait lens (90mm eq), but the min focus distance is 1.5'. First of all, no one takes portraits a foot and a half away from the subject... and if you did, with a micro four thirds camera you would not be able to fit the subjects whole head in the frame. So you have to step back, and lose the full amount of bokeh the f1.8 aperture is capable of.

    I understand they want to appease as many people as possible, but I was not aware insect photographers were such a huge market! haha

  • Yes I can focus farther but being able to have the subject as close to the minimum focus distance means more blurred out background and not having to open the aperture as much, as the lenses are 2-3x "longer"...

    I think you are confused very much. Check http://www.personal-view.com/faqs/camera-usage/general-camera-usage-faq

    Minimum focus distance have nothing to do with DOF (all this "blurred out background" ) :-)

    Take the Olympus 45mm 1.8 for example. This a portrait lens (90mm eq), but the min focus distance is 1.5'. First of all, no one takes portraits a foot and a half away from the subject... and if you did, with a micro four thirds camera you would not be able to fit the subjects whole head in the frame. So you have to step back, and lose the full amount of bokeh the f1.8 aperture is capable of.

    Again, confusion and improper claims. It is not really "portrait lens", as proper design of such lens means that it is not so sharp. You can check portrait lens design on example of Samyang 85mm. And Olympus is used for various tasks, using your approach, as 90mm is also one of most popular macro distances :-) Why minimum focus distance is so large? :-)

    Read FAQ and topics about bokeh.

  • If you step back you will gain bokeh, not lose it because the subject will be smaller in relationship to the total frame. I suggest you actually try it out. The texture of the bokeh will be different, depending on what sort of objects you have in the background. You can calculate the DOF using a fairly simple formula, but I will give you an example. Your 45mm at F1.8 is focused until 5.1 feet at a difference of 5 feet, and 10.4 feet at a distance of ten feet. So you can see that the background will be out of focus even if you double the distance. However, at a mile away, or as you approach infinity, the distance will appear almost the same, but there is no way you would use that lens for a portrait at a distance where the vanishing points merge.

    Subject distance 5 ft

    Depth of field Near limit 4.9 ft Far limit 5.1 ft Total 0.2 ft

    In front of subject 0.1 ft (49%) Behind subject 0.1 ft (51%)

    Hyperfocal distance 248.7 ft Circle of confusion 0.015 mm

    VERSUS Subject distance 10 ft

    Depth of field Near limit 9.62 ft Far limit 10.4 ft Total 0.79 ft

    In front of subject 0.38 ft (48%) Behind subject 0.41 ft (52%)

    Hyperfocal distance 248.7 ft Circle of confusion 0.015 mm

  • EDIT: Corrected typo.

    @theconformist The two other posters are absolutely right. But if you don't want to deal with the formula, here it is below.

    http://www.dofmaster.com/dofjs.html

    You'll notice the calculations do not need to know the minimum focus distance for the lens. All other things being equal, you want the minimum focus distance to be as short as it can be (as long as you don't lose infinity focus on the other end) to be able to use the lens for as wide a range of things as possible.

    Now to get back to your examples with the 85mm lens on both cameras. Here are two very similar DOF/focusing results with about the same framing. Pulling focus in those two setups would be rather similar.

    • 5D Mk III with 85mm at f/2.8

    Subject distance 5 ft

    Depth of field Near limit 4.92 ft Far limit 5.09 ft Total 0.17 ft

    In front of subject 0.08 ft (49%) Behind subject 0.09 ft (51%)

    Hyperfocal distance 279.6 ft Circle of confusion 0.03 mm

    • GH3 with 85mm at f/1.4

    Subject distance 10 ft

    Depth of field Near limit 9.91 ft Far limit 10.1 ft Total 0.17 ft

    In front of subject 0.09 ft (50%) Behind subject 0.09 ft (50%)

    Hyperfocal distance 1117.7 ft Circle of confusion 0.015 mm