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10-08-2008, 11:37 PM   #31
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QuoteOriginally posted by Big Dave Quote
Steve,
This is true, but when you use the lenses on a APS_C sensor the DOF is greater for a given field of veiw. I find this helpful for general shooting, but a slight draw for portraits. A larger appeture comes in handy in that case.

Dave
Yes - stressing that this is true for the field-of-view, not for the same lens (same focal length) swapped between a 35mm body and a digital body.

10-09-2008, 12:14 AM   #32
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QuoteOriginally posted by keithlester Quote
You dont focus on the hyperfocal distance itself. You put your infinity mark on one of your aperture marks and are in focus down to the other mark. ...
Hi Keith

Were you speaking with the assumption of using the lens on a 35mm film body? I didn't state it clearly but my question relates to using the lens on a digital body. While what you say is true for a P-FA lens used on a 35mm film camera body, it is not true for the same lens used on a digital SLR with APS-C sensor.

The circle-of-confusion is different for the two, and this results in different depth-of-field for the same lens.

Please don't ask me to explain circle-of-confusion (I think it is very well named!) but there is a good article on Wikipedia that is quite readable, at least the first half. The article does make it clear that the C-of-C figure for 35mm film is different from the C-of-C figure for an APS-C sensor, and it explains why.

There is a good table at Circles of Confusion for Digital Cameras that quotes 0.030mm as the reference figure for 35mm film, and shows 0.020mm as the figure for the Pentax APS-C digitals. These figures are consistent with the range of figures discussed in the Wikipedia article.

If I prepare another table (as above) with the 0.030mm C-of-C figure, it gives me different hyperfocal distance figures compared to the table with the 0.020mm C-of-C figure for digital. With the 31 at f/16 the hyperfocal distance is a meter closer to the camera, and the close-focus point is half a meter closer to the camera, with DoF now extending from 1.02m to infinity (1.52m to infinity for digital). And these new figures match with the DoF marking scale on my lenses. Fine with 35mm film.

However, the DoF scale markings are wrong for digital. And my real-life testing demonstrates this too. To use hyperfocal distance focusing for landscape work, I need a better method than relying on the scale on the lens.

Thanks to all - I've learned a lot in the course of this thread!
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10-09-2008, 11:34 AM   #33
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QuoteOriginally posted by ChrisN Quote
Hi Keith

Were you speaking with the assumption of using the lens on a 35mm film body? I didn't state it clearly but my question relates to using the lens on a digital body. While what you say is true for a P-FA lens used on a 35mm film camera body, it is not true for the same lens used on a digital SLR with APS-C sensor.

The circle-of-confusion is different for the two, and this results in different depth-of-field for the same lens.

Please don't ask me to explain circle-of-confusion (I think it is very well named!) but there is a good article on Wikipedia that is quite readable, at least the first half. The article does make it clear that the C-of-C figure for 35mm film is different from the C-of-C figure for an APS-C sensor, and it explains why.

There is a good table at Circles of Confusion for Digital Cameras that quotes 0.030mm as the reference figure for 35mm film, and shows 0.020mm as the figure for the Pentax APS-C digitals. These figures are consistent with the range of figures discussed in the Wikipedia article.

If I prepare another table (as above) with the 0.030mm C-of-C figure, it gives me different hyperfocal distance figures compared to the table with the 0.020mm C-of-C figure for digital. With the 31 at f/16 the hyperfocal distance is a meter closer to the camera, and the close-focus point is half a meter closer to the camera, with DoF now extending from 1.02m to infinity (1.52m to infinity for digital). And these new figures match with the DoF marking scale on my lenses. Fine with 35mm film.

However, the DoF scale markings are wrong for digital. And my real-life testing demonstrates this too. To use hyperfocal distance focusing for landscape work, I need a better method than relying on the scale on the lens.

Thanks to all - I've learned a lot in the course of this thread!
I was referring to the traditional use of DOF scales with 35mm. Nowadays, if I use them at all, I usually select one stop worse than what I am using. e.g. if I am using F/5.6, I use the scales for F/4. Its fairly straightforward and reasonably close. Mostly, for landscape work, I now use a tripod, the DOF preview facility and a bit of chimping at full mag to make sure the bits I thought should be sharp are sharp.

Hyperfocal was useful on a recent trip to Paris, where I managed to get a higher than usual ratio of keepers using this method, hand-held on an open-top tour bus. I was using a 24mm manual focus lens at F/5.6, so it was a good bet most of the scenes would be sharp enough, and they were.

When I switched to a 100mm lens this was not possible. So all of my detail shots taken with this lens had to be done when the bus was stationary, and by focussing carefully. Possibly less than a half of these turned out to be super-sharp but none showed any signs of shake, so they were just inadequate focussing on my part. I must say I am grateful to Pentax for putting anti-shake in the body of my K10D.

So my experience of Hyperfocal shooting is that it works best with standard to wide-angle lenses, and not at all well with any degree of telephoto. YMMV
10-09-2008, 08:20 PM   #34
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QuoteOriginally posted by keithlester Quote
So my experience of Hyperfocal shooting is that it works best with standard to wide-angle lenses, and not at all well with any degree of telephoto. YMMV
my thoughts too.

However, I'd like to add... the title of this thread is incorrent IMO. Zone focusing is when your lens has icons to indicate rough focus distance. Usually found on older film compacts and indicated by icons to represent a head (close), head and shoulders (not as close), groups of people (bit further away) and mountains (further away!). You guestimate the distance to your subject and select the appropiate setting. I have a Yashica compact (film) that uses this system although it has the distances on the opposite side of the lens as well (need to turn camera upside down to read it though)

Nige.

10-09-2008, 08:32 PM   #35
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QuoteOriginally posted by Big Dave Quote
Hello everyone,
How many of you use zone focusing with your primes? Most of my prime lenses have zone calibrations next to the distance scale on the barrel. I find it very useful, not to have to focus constantly using this feature. It ensures that you don't miss that special shot. It is especially useful in low light where you have a little working distance from the subject. You should try it with your manual focus primes. I think that you will find it useful.

Dave
Hello Dave,

I nearly always use "zone focusing", by using the DOF scale on the lens barrel, with my DA14 because of it's wide angle and landscape capabilities. One of the reasons I was reticent to get the DA12-24 due to the fact that new zooms do not have the DOF scale which I use very much with wide angles.

I do not use the DOF scale as much with longer focal lengths like longer telephotos, but they can still be very helpful especially when trying to figure out what will be in focus at a certain camera to subject distance.
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