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09/27/2003 09:32:34 AM · #26 |
| CoC is determined by how much you plan to enlarge the image. So that is set by how big the original negative/ sensor is and how big you plan to print. 8x10 is often used, but if you plan to print larger than that, you need a smaller CoC for equivalent sharpness. Or if your sensor is smaller, you have to enlarge more to get the same size of print, so again you need a smaller CoC for equivalent sharpness. |
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09/27/2003 10:40:37 AM · #27 |
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09/27/2003 05:16:00 PM · #28 |
You'll have to take into account the viewing distance too (the desired image quality). At a viewing distance of 10", you can aim for about 4 lp/mm for average/good quality, 5-6 lp/mm for good/excellent quality, or 7-8 lp/mm if your eye is more discerning. Most CoC values used in DoF tables use 4 lp/mm (actually less than that).
Once you know E, your enlargement factor (final print diagonal / cropped sensor diagonal), and Q, your desired image quality, you can quickly calculate your CoC (at the sensor) as:
1 / (E * Q).
For example, if I want to print 8x10", my cropped sensor diagonal (for the d60) is 24mm (15x22.5mm cropped to 15x18.75mm), so E is 13.55 and if I use Q = 4, then my CoC is .01845, a familiar value to d60/10d owners. Similarly, CoC(Q=5) = .015mm, CoC(Q=7) = .010mm, CoC(Q=8) = .009mm.
Doubling your viewing distance means you can halve your image quality, thereby doubling your CoC.
So, what about an 11x14" print? E is 18.63, so CoC(Q=4) = .013mm, CoC(Q=5) = .011mm, CoC(Q=8) = .0067mm (can't do it as our pixel size is only .007mm). Maybe 10" is too close to view the print, so we double it. Now our CoC's are doubled too.
The important thing is that CoC is anything but constant for a given film/sensor size, unless you happen to always use the same print size along with the same image quality (at a given viewing distance).
For additional, incredibly comprehensive, spreadsheets, check out //www.accessz.com/ in the Tools section.
Note: I used µm in previous posts where I should have used mm. |
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09/27/2003 05:27:59 PM · #29 |
| It's all Greek to me. I just worry about composition, lighting and the message that I want to convey. Fun stuff!! |
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09/27/2003 10:08:03 PM · #30 |
It all might just be true!
Manually focused, using DOFMaster LE for the palm pilot
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09/29/2003 10:03:09 AM · #31 |
Gordon, that is an excellent example. I believe that focusing on the bridge itself would make the tree in the foreground soft, even stopped all the way down.
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09/29/2003 10:13:53 AM · #32 |
Originally posted by jmsetzler:
Gordon, that is an excellent example. I believe that focusing on the bridge itself would make the tree in the foreground soft, even stopped all the way down. |
Yes it did, even at f22. Also, focusing on the tree made the bridge look soft and out of focus.
The most difficult thing to accept is that when you set the hyperfocal distance and look through the viewfinder, everything looks soft, because the aperture is wide open for the viewfinder, and the focal point is out in 'space' in this case. The DoF preview button is useful to reduce that anxiety.
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10/19/2004 11:31:48 AM · #33 |
| I just got my 20D the other day and have been busy plying with it. I found this article on Hyperfocal Distance but need help to fully understand how to use it on my camera. The A-DEP seems to be useless so is there another way around it? (I only have the EF-S 18-55 at the moment, without DoF markings of course). |
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10/19/2004 11:56:18 AM · #34 |
Originally posted by egillibsen:
I just got my 20D the other day and have been busy plying with it. I found this article on Hyperfocal Distance but need help to fully understand how to use it on my camera. The A-DEP seems to be useless so is there another way around it? (I only have the EF-S 18-55 at the moment, without DoF markings of course). |
Yeah, I was wondering this as well...do you just manually focus back from the subject to where you think you've hit the HF distance? Or do you autofocus on the ground/water that might be between the foreground and subject?
By the way, this has been very informative! |
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10/19/2004 02:02:46 PM · #35 |
Originally posted by miketherock:
i keep reading about the f stops and the apertures, but i couldnt find any of it on my camera...what if i dont have that kind of selection?Does it mean I have a low tech camera? MY cam is olympus d550 zoom... |
With a P&S like your Oly I'm sure you don't have the DEP or A-DEP feature. If you have full manual control of aperture and shutter speed you can calculate the Hyperfocal distance. A very rudimentary method to start with, and at least get an idea of what the results will look like, is to pre-focus on a spot about half way to your main subject. Take a shot focused there, and then do one focused on the subject directly to compare results. The difference will be more noticeable on scenes that have a lot of depth in them, like Gordon's bridge shot. |
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