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Thread: COF is not confusing

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    Ausphotography Veteran martycon's Avatar
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    COF is not confusing

    But what value to use is a bit puzzling for me. When stacking, the focus distance interval is related to DOF. As I understand, DOF calculation requires a value for COF. I see recommendations for 0.013, and 0.010. Have used this but sometimes think the results sub optimal. Probably my technique is at fault, but should I be using a smaller value. My crude calculations indicate that if COF were to be the size of a typical, fair quality monitor (1024 ? wide), then the COF value should be about 0.003. It means 3 times more exposures, but as that part of stacking is not the greatest time consumer, it would be OK if results were good.

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    Member CathyC's Avatar
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    I realise I am a newbie here .............. but I found your post very confusing what on earth are you talking about, what is COF?
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    Ausphotography Regular enseth's Avatar
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    COF I would imagine would refer to Centre of Field or perhaps Centre of Focus. ie the mid point of the depth of field (DOF)

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    A royal pain in the bum! arthurking83's Avatar
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    I'm thinking it should be CoC(circle of confusion).

    It's a term used for when reproducing images from something small(er) to something larger ... eg a negative to a print.
    Like martycon said, it's used in conjunction with DOF(depth of field) for when trying to predict the actual perception of an image if DOF becomes limited in some way(which it does when you enlarge).

    I've never seen CoC used in conjunction with focus stacking tho .. so we await marty's response as to whether COF is something else.
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    My apologies, it should read COC Circle Of Confusion. That error certainly added to the confusion, sorry.

    - - - Updated - - -

    Sorry COF should read COC Circle Of Confusion.

    - - - Updated - - -

    Arthur you picked it in one, my apologies for the added confusion. Circle Of Confusion it is. When stacking I have been using DOF info to determine the camera movement interval required between exposures (shots). The equation I am using uses the image magnification (sensor size/measured image size) as well as stop number, and a value for COC. It is convenient because there is no need to know where the effective optical center of the lens is. The value for COC is directly related to DOF. Put another way, there is only one distance of perfect focus. DOF determines a zone of acceptable out of focus. COC is used to determine the acceptability of OOF. I suspect that the COC values which are being quoted where I am reading, were used with film in use, rather than digital which readily allows much higher resolution.

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    http://steveaxford.smugmug.com/ Steve Axford's Avatar
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    I think CoC is very useful in understanding why you shouldn't use apertures like f32 if you want the best resolution. I use a Canon 5D III with a 100mm macro and with that I find that f18 is the min aperture I can use if I want the best resolution for full resolution pictures. If I an using video on that camera (or time lapse), then I can go to f22 or maybe f24. If I am focus stacking using f18, then I can use the focus ring to change the focus point. I don't use tables, I experiment and find out what works in real life. I think the key with focus stacking is making it as simple as possible. That way you will use it, CoC is a useful concept in understanding why some things work and some don't. I don't find DoF tables very enlightening.

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