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New to group and have a question!

Discussion in 'Introductions...' started by SamJ, Jun 21, 2020.

  1. Chester AP

    Chester AP Well-Known Member

    I was confused by DOF when moving from full frame 35 mm film SLR to half-frame (APS-C) DSLR. The important thing I did not explain above appears to be 'for the same angle of view', for example a 50 mm on the full frame and 24-25 mm on the half-frame. It is often difficult to give a helpful answer without knowing how much technical detail is wanted or will be understood.

    Once the lens on the chosen camera body is compared with its equivalent of a full frame body, the complex arithmetic formulae that also involve the acceptable 'circle of confusion' can be applied to both sensors. Assuming, of course, that the diameter of the 'circle of confusion' which is defined as 1/1500 of the diagonal for both. This was the accepted figure in film days, but I have read suggestions that with modern 40+ megapixel full frame sensors the size should be smaller.

    Terms like 'circle of confusion' are related to the sharpness required in a film negative to produce an acceptably sharp print. Again, this probably isn't the place to go into great detail, but for the curious Wikipedia has a page that looks similar to the section in my 1969 edition of 'The Complete Colour Photographer' by Andreas Feininger, which was were I turned for help in 2008 after looking at the DOF from shots of my APS-C (half frame) DSLR. One difference is that Feininger says that the 'circle of confusion is 1/1500 of the focal length of the camera's 'standard lens' (so 50/1500 mm for a full frame), whereas the Wikipedia entry says 1/1500 of the sensor's diagonal size which is 43/1500 mm for a full frame).

    So, for practical purposes, I think we can say that for the same angle of view a smaller sensor will give greater DOF than a larger sensor if the same lens aperture is used on both lenses. This is also the summary used consistently in AP reviews, particularly of cameras with 'four-thirds' and '1 inch' sensors. Also, smartphones have very short focal length lenses with large apertures, but produce very large DOF due to their minute sensors.

    If I have misunderstood this, corrections would be welcome. But from my own experience, the preceding paragraph matches my experience of using lenses on both 35 mm full frame and APS-C (half frame) camera bodies.

    https://en.wikipedia.org/wiki/Circle_of_confusion
     
    SamJ likes this.
  2. PeteRob

    PeteRob Well-Known Member

    Absolutely. That’s why the first digital compacts wiped the floor with 35 mm film compacts. It wasn’t the cost of film it was the vanishing of oof images, suddenly everything printed at 6x4 was sharp. Cameras in phones are the same and now selective focus is a post-processing step. You have to want to use a camera these days. Personally I’d like bigger sensors in order to use longer focal length lenses for a given field of view because I prefer the results.
     
  3. Chester AP

    Chester AP Well-Known Member

    I suspect the cost of film was important to some people, but as simple (to use) digital compact cameras got cheaper (they were many hundreds of pounds when first available) their success was inevitable. Perhaps the almost universal (not me, for example) love affair with the smartphone and its 'camera' is just the latest version of the snaps vs. photographs debate that Kodak started over a century ago. For 99% of the population, images from a compact camera or smartphone are more than good enough for their purpose, which is being viewed on small screens.

    Whenever the Forum gets a question like 'I've got a smartphone but would like a camera - what type should I get?', many Forum members immediately start discussing the merits if various types of camera, but my first question usually is 'what will you want to do with the images?'. If only ever view them on a small screen, keep what you have. But if you want to get large prints ...
     
  4. RogerMac

    RogerMac Well-Known Member

    The thing about DOF is tlhat it is easy to demonstrate experimental but needs a knowledge of calculus to prove mathemally. If anybody is interested I will send them a scan from my physics A level text book showing the proof (unlikely)
     
  5. Stephen Rundle

    Stephen Rundle In the Stop Bath

    :) how old is the book :)
     
  6. Stephen Rundle

    Stephen Rundle In the Stop Bath

    Let's just agree that FF gives more DOF for the same lens/length/aperture than a crop sensor with the same ......................
     
  7. PeteRob

    PeteRob Well-Known Member

    No. Same lens/length/aperture (and subject distance) produces the same image. It just gets 50% of the area cut off on an APS-C sensor compared to a FF sensor.
     
  8. Chester AP

    Chester AP Well-Known Member

    See post #22 above.
     
  9. PeteRob

    PeteRob Well-Known Member

    Dunno why you're referring me to my own post. There is no inconsistency. A lens will produce what a lens will produce. You just capture a different area from the image circle according to sensor size. If you want the same image on crop sensor as FF, all else being equal, then you have to use a shorter focal length lens and dof will increase. It gets really noticeable when the focal length difference is a factor 6 or so - as for compacts and phones.
     
  10. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    Anything that requires calculus is highly suspect in my opinion. Much simpler to just take a few pictures and see what you get.
     
    SamJ and RogerMac like this.
  11. PeteRob

    PeteRob Well-Known Member

    I was almost tempted to double check as I don’t remember any calculus being involved in the calculation which I remember as a geometric calculation. I’m busy trying to remember some stats at the moment so I let it go.
     
  12. SamJ

    SamJ Member

    Thank you to everyone that contributed to this thread! Some of the answers and opinions were slightly out of my head zone but i followed all the links and learnt a lot!! I'll leave the complications of calculus and maths to another day i think, i may look into a slighly larger sensor camera, bridge or otherwise, but the overall theme of help seems to be to set mine at half zoom and play :) I'll find myself a potato..... when i'm brave i'll post some up for some (ahem) helpful criticism!!
     
    Craig20264 likes this.
  13. Craig20264

    Craig20264 Well-Known Member

    Post and ask away. There are no ego's on these forums. You'll get honest feedback designed to help you achieve your aims. Remember too, there is no such thing as a dumb question. None of us knew anything when we were born. :)
     
  14. Chester AP

    Chester AP Well-Known Member

    It's difficult to know how much detail is wanted when trying to be helpful, but it's sensible to make sure that you have tried to get the best from your current camera before spending money on something different, especially when deciding what to get is not straightforward. Even if some comments may confuse or bewilder, they at least indicate that results can sometimes depend a lot on the physical size of the sensor in your camera. However, a camera with a larger sensor will also be bigger and heavier (as will its lenses), so these factors will be important too. Never buy something in a hurry...

    The potato was only a suggestion, as something about the right size and that will sit still whilst you experiment. Using a digital camera this will only cost you your time and patience - imagine what it was like for older members leaning stuff like this with film.

    Have fun.
     
  15. Snorri

    Snorri Well-Known Member

    Yes the most important advice, have fun.
     

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