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09-26-2009, 10:46 AM   #46
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Wow, interesting but confusing
Maybe it helps to sum it up:

a lens has some parameters which are physically designed/given and measurable/definable:

- focal length
- (max.) aperture
- required registration distance
- (max.) image circle

You can also calculate the DOF for all this lenses and if you calculate it in absolute values (like meters in the field) it will not change.

It's a fact, that all these values don't change, whether you mount them (properly) on a camera with a APS-C, 24x35, 6x45, 6x7 filmbase/sensor. You can mount lenses designed for 6x7 on APS-C if you use adapters to hold the registration distance (if you want to keep the designated focus abilities of the lens) and you can mount APS-C lenses on 24x35 mm K-mount filmcameras, but have to be aware that probably the smaller designed image circle will lead to heavy vignetting in the corners.

But everybody is aware that the use of the same lens does effectively lead to visibly different results on different sensor sizes, even if the lens has had projected exactly the same image on the sensor plane. If you would look at the resulting image at a constant enlargement to the sensor size you could claim that there are no changes, except for the crop of the image from the smaller sensor. But if you consider a comparison at the same viewing/printing size the normal everyday way of doing that there are effective changes. The scale of the depicted objects is different, therefore also the calculated/constant DOF value is visible differently (same value in cm in field at higher enlargement).

I'm sure this is nothing new to anyone here, therefore my surprise over the "confusion" here

Sorry if having been to longish for something obvious


Last edited by MMVIII; 09-26-2009 at 11:16 AM.
09-26-2009, 06:04 PM   #47
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david: about your dilema: i chose the third option: the good old zenitar and defishing software when needed, it's been a year and i am pretty happy so far (the reasons i have stated several times around here, i will only go into details if you think it's worth it for you to think about it). for what it's worth.

jogiba: right. i think it's about one stop, you should get the same with a 200/2.8 on 35mm film (or 135/2 on aps-c?). for the same fov, there is no question about it, i think. some people still seem to be confused about same lens, though

mmvii: i guess there's little chance you can add anything to the confusion at this point, so it can only help, right? . one question regarding your statements: how exactly do you calculate the dof you are talking about? does it not, by any chance, include something specific to the format on which the lens is used, in the formula? like, circle of confusion maybe? . my point is: this is really not a question of "theoretical" versus "practical, everyday" understanding of dof, both theory and practical usage agree in this case (as they should, if the theory is supposed to be any use, btw )

Last edited by nanok; 09-26-2009 at 06:11 PM.
09-27-2009, 10:58 AM   #48
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nanok, yep, true.
Exactly the circle of confusion depends on the sensor size, because this directly relates to the scale by which the projected and captured image has to be enlarged to the commonly assumed size for the presumed normal viewing distance of 25 cm.
Ok, therefore I would have to be more precise by saying, that the circle of confusion, and not the DOF, does not change, because the DOF is a result of the calculation using the mentioned values and it is already considering the resulting image and not the projected by the lens. ;-)
09-27-2009, 11:51 AM   #49
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hm. so if the circle of confusion does not change, what is it that changes? same lens, same distance, same aperture, same format (same circle of confusion), so there is really nothing left to talk about.. . seriously, you cannot keep the coc tied to the lens (in the remote eventuality that that's what you were thinking, though i doubt it ), as it is, obviously, a characteristic of the format used, so yes, the coc does change.

edit: further more, to be very clear: there is no meaningful definition out there (or is there?) about dof connected to the image projected by the lens, itself, only connected to the format (a certain print size at a certain viewing distance, as you mentioned, which are, btw, not arbitrary). dof in direct relation to the image projected by the lens itself is, simply, meaningless. it's like talking about color perception without specifying how the perceiver perceives it (rgb sensor? cmyk sensor? whatever (r)(tm) sensor?), it does make a difference, because, unless you know, that you cannot map spectral values to "perceived color". again: there is no such thing as dof without taking into account a (default) final result, and, thus, format size, the dof concept was invented and defined specifically to serve that purpose (connect a "sensor" + lens + settings to a reasonably predictable final result).


Last edited by nanok; 09-27-2009 at 12:00 PM.
09-27-2009, 11:54 AM   #50
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There seems to be some L.O.C. in this thread.
09-27-2009, 12:03 PM   #51
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blue: does that stand for "some idiot who just won't let go"? you're right i guess, i'll be quiet about it, i think it should be more than enough anyway. sorry for the hijack
09-27-2009, 01:20 PM   #52
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L.O.C. = lots of confusion Hysterical
09-28-2009, 03:22 AM   #53
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oh, that one. right. i still am inclined to thinking my translation is not entirely wrong, though

09-29-2009, 01:16 AM   #54
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QuoteOriginally posted by jogiba Quote
Look at the DOF on a FF Canon 5D MKII made HD video.
Canon Digital Learning Center - Sample EOS 5D Mark II Video: Reverie
This is one hell of a movie. One of the reasons i`m upgrading to a video capable body - my FA31 and FA77, as well as Cosina 55mm 1:1.2 are waiting.
09-29-2009, 08:05 AM   #55
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QuoteOriginally posted by nanok Quote
david: about your dilema: i chose the third option: the good old zenitar and defishing software when needed, it's been a year and i am pretty happy so far (the reasons i have stated several times around here, i will only go into details if you think it's worth it for you to think about it). for what it's worth.
Nanok,

Thanks for the suguestion. I have considered the Zenitar, particularly since my spouse would like to experiment with a fisheye. To save the repeated posting here, I'll look for the threads where you discuss the lens. I do agree that a simple lens design and straight forward PP is preferable to a load of (expensive) glass.
09-29-2009, 11:42 AM   #56
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keep in mind it's not really a proper fisheye on aps-c. if you go that way, you'll need a film body to go with the zenitar, and be able to use it as an actual fisheye. i'll try to find where i talked about the zenitar in more detail (although many others have, so you probably foundtons of info anyway, already)

edit: there's somediscussion here, which might help: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/58948-looking-fisheye-m42-pk.html

Last edited by nanok; 09-29-2009 at 11:58 AM.
10-08-2009, 06:34 AM   #57
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Well, it looks like the 14mm Samyang is being delayed.

Samyang delays shipping of 14mm f/2.8 lens: Digital Photography Review
10-08-2009, 09:49 AM   #58
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QuoteOriginally posted by StephenMerola Quote
Well, it looks like the 14mm Samyang is being delayed.

Samyang delays shipping of 14mm f/2.8 lens: Digital Photography Review
Thanks for the update. I feel bad for folks who pre-ordered...
10-08-2009, 04:16 PM   #59
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QuoteOriginally posted by StephenMerola Quote
Well, it looks like the 14mm Samyang is being delayed.
It's good idea, because this lens has a big problem with flares:
Samyang 14 mm f/2.8 IF ED MC Aspherical review - Introduction - Lenstip.com
10-09-2009, 06:28 AM   #60
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Wow. I did not even know that review existed. I hope they can fix the issue because they have been making some pretty cool lenses lately.
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