Talk:Circle of confusion/Archive 2

Archive 1

Archive 2

Thanks

I've been teaching myself photography with a Canon SX20IS. This article really helped me. I made a dynamic version of an illustration from this article at http://dbp-consulting.com/Photography/CircleOfConfusion.html If you have time, it would be nice if you looked at it and told me if it's correct or useful. It uses a canvas to draw in so needs a recent browser. It just uses simple thin lens approximation calculations. patrick at dbp-consulting dot com Phorgan1 (talk) 02:05, 31 May 2011 (UTC)

OK, you found out just now that linking it to the article is a more sure way to find out what someone thinks. See WP:EL; these links should be reserved for authoritative comment, not for amateurs who are seeking approval of their understanding. I only read the first bit of yours, but it very blantantly conflates the two usages of CoC, so it's clearly confused. Try again. But don't add it as an EL. Dicklyon (talk) 18:22, 16 October 2011 (UTC)

How can I make it better? Give me a clue? What are the two usages of CoC? Did you like the visualization tool? — Preceding unsigned comment added by Phorgan1 (talk • contribs) 20:11, 5 February 2012 (UTC)

I just wrote on your talk page before noticing that you had spoken up here. Here's the deal: as the page notes, the CoC is the diameter of the fuzzy spot that the lens makes. But CoC is also the tolerable limit on that fuzzy spot. The article here has the "Two uses" section to make clear what these two things are. The page you cited starts out with one and goes into the other, without ever making any connection, as if they were one thing; it's confused and makes no sense. Dicklyon (talk) 00:53, 6 February 2012 (UTC)

Numbers for CoC for various formats

I do not understand how the numbers in the CoC for the formats was calculated:

Using the following code:

import math

FORMATS=[\
    ("Four Thirds System", (13.5, 18), 0.015),
    ("APS-C[2]", (15.0, 22.5), 0.018),
    ("APS-C Canon", (14.8, 22.2), 0.019),
    ("APS-C Nikon/Pentax/Sony", (15.7, 23.6), 0.020),
    ("APS-H Canon", (19.0, 28.7), 0.023),
    ("35", (24., 36.), 0.029),
    ("645 (6x4.5)", (56., 42.), 0.047),
    ("6x6", (56, 56), 0.053),
    ("6x7", (56, 69), 0.059),
    ("6x9", (56, 84), 0.067),
    ("6x12", (56, 112), 0.083),
    ("6x17", (56, 168), 0.12),
    ("4x5", (102, 127), 0.11),
    ("5x7", (127, 178), 0.15),
    ("8x10", (203, 254), 0.22)
]

def coc(w, h, factor=1500.): 
    return math.sqrt((w / 1000. * w / 1000.) + 
                     (h /1000. * h / 1000.)) / factor

def run():
    for f in FORMATS:
        name = f[0]
        frame = f[1]
        f_w = float(frame[0])
        f_h = float(frame[1])
        wiki_coc = f[2]
        my_coc_mm = coc(f_w, f_h) * 1000.
        rel_err = abs(wiki_coc - my_coc_mm) / wiki_coc * 100.
        print "%20s\t%.1f x %.1f\t%.3f\t%.3f\t%.3f %%" % \
            (name, f_w, f_h, wiki_coc, my_coc_mm, rel_err)

I get the following results:

>>> coc.run()
  Four Thirds System	13.5 x 18.0	0.015	0.015	0.000 %
            APS-C[2]	15.0 x 22.5	0.018	0.018	0.154 %
         APS-C Canon	14.8 x 22.2	0.019	0.018	6.382 %
APS-C Nikon/Pentax/Sony	15.7 x 23.6	0.020	0.019	5.516 %
         APS-H Canon	19.0 x 28.7	0.023	0.023	0.234 %
                  35	24.0 x 36.0	0.029	0.029	0.537 %
         645 (6x4.5)	56.0 x 42.0	0.047	0.047	0.709 %
                 6x6	56.0 x 56.0	0.053	0.053	0.382 %
                 6x7	56.0 x 69.0	0.059	0.059	0.413 %
                 6x9	56.0 x 84.0	0.067	0.067	0.453 %
                6x12	56.0 x 112.0	0.083	0.083	0.578 %
                6x17	56.0 x 168.0	0.120	0.118	1.618 %
                 4x5	102.0 x 127.0	0.110	0.109	1.279 %
                 5x7	127.0 x 178.0	0.150	0.146	2.817 %
                8x10	203.0 x 254.0	0.220	0.217	1.469 %
>>> 

The small errors may be due to rounding but the APS-C Cannon and APS-C Nikon numbers seem way off.

Is the problem my code or data in the table?

-- ch@murgatroid.com — Preceding unsigned comment added by 173.11.81.225 (talk) 02:14, 19 June 2011 (UTC)

Your numbers are correct, I think. One wonders where the numbers in the article table came from. Dicklyon (talk) 07:21, 19 June 2011 (UTC)

Ah, here it is, last Nov. I'll back it out. Dicklyon (talk) 07:24, 19 June 2011 (UTC)

I decided to leave those new entries, and put your numbers into them. Dicklyon (talk) 07:26, 19 June 2011 (UTC)

The numbers are correct for the stated format dimensions. But we also need to take a hard look at some of the stated dimensions; for example, with most 4x5 filmholders, the format size is closer to 120 mm x 96 mm, which would give a CoC of 0.102 mm with the criterion of d/1500. As always, I’m having a hard time finding an authoritative source for this information. I can’t speak for Nikon, but the Canon APS-C format has varied from model to model, so we might want to mention this. We clearly think a CoC difference of 0.001 mm for APS-C formats is significant, so I’ve removed a statement to the contrary. JeffConrad (talk) 08:48, 19 June 2011 (UTC)

True, it's a bunch of unsourced stuff. But I don't think list 3-digit numbers implies that we think a difference of 0.001 is significant; two digits would be not enough for the smaller formats (but I agree we don't need unsourced opinions in footnotes). Maybe we should go back to the single generic APC-C entry that we had before. Dicklyon (talk) 15:09, 19 June 2011 (UTC)

I think the unsourced opinion (which I think I originally added) was far closer to the mark than the unsourced (and in some cases, clearly wrong) format dimensions. But the comment didn’t really add anything, so I removed it. Arguably, all of the discrepancies noted above are insignificant in DOFland. But it’s clearly disturbing when the numbers don’t work out for such a simple calculation, so in another sense, such a small difference is significant. Anyway, it still would be nice to get a better handle on some of the format dimensions. I’m not sure we should go to a single “APS-C” format, if for no other reason that Canon or Nikon enthusiasts may quarrel about it. But it seems to me that we don’t need a generic APS-C in addition to the “Canon” and “Nikon” formats. We should bear in mind that, at least for Canon, the “APS-C” format has varied between 22.7 × 15.1 to 22.2 × 14.8, so even the “Canon” format is an average. The LF dimensions are just plain silly, because the opening in the filmholder clearly cannot be as large as the film size; however, as I mentioned, I’m having a hard time finding a reliable source for the dimensions of filmholder openings. JeffConrad (talk) 00:42, 20 June 2011 (UTC)

New Section: CoC in digital photography

Deleted by creator Johnny Swinnen (talk) 23:43, 3 March 2013 (UTC)