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05-29-2011, 11:55 PM   #1
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DA15 goes past infinity

Hi, folks.

I wonder if any other DA15 copy is able to go past infinity. Mine does. The actual infinity focus setting (doublechecked in many ways incl contrast AF and pixel-peeping from focus bracketing) appears to be under the right "o" of the infinity oo mark - the focus ring stop on the infinity side is one millimeter aside.
Other then that I see no issues with my copy so I'm not sure if it worth sending it to service or not (and it appears not to be covered by warranty in my country since it was purchased overseas).

Any input will be greatly appreciated.

Thanks,
Zig

05-30-2011, 12:04 AM   #2
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This is normal. My 15 is exactly the same. Nothing to worry about.

Simply take a look at the DOF scale to verify that this. You can have it quite a bit off the infinity mark and still have infinity in focus, even at f/4.

Last edited by Cannikin; 05-30-2011 at 12:20 AM.
05-30-2011, 12:21 AM   #3
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Cannikin,
Thanks for your input and confirmation on your copy. I won't be that bothered (or, at least, it would be much less) if I didn't notice any difference in the shots which were taken at the actual infinity setting (1mm to focus ring stop; just below the right 'o' part of the infinity sign) and the full focus ring stop in the middle of the infinity mark. But there's a difference (at f4, much less at f5.6) and I see it.

So your take is just to forget it and live with it as is?

Zig
05-30-2011, 12:53 AM   #4
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For an AF lens this is a must. They all go a bit beyond the infinity. Anyway, what's the point in focusing manually to infinity?

05-30-2011, 01:09 AM   #5
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Is there a particular reason why this is bothersome to you? All of my zoom lenses can even go way past the infinity mark itself, as part of a normal manufactured tolerance. This is simply because infinity focus (hyperfocal distance) changes with aperture and focal length, meaning the infinity symbol is nothing more than a rough guideline. If you're using autofocus, it doesn't matter anyway.

The infinity mark on prime lenses is more of a reference for scale focusing, rather than to be lined up directly with. For instance, my FA 77 can't even reach the center of the infinity mark at all, and my DA 35 Ltd can turn past it.

If you're using manual focus, and you want to rely on the distance scale, it's more accurate to scale focus: line up the mark on the DOF scale corresponding to the aperture you're using with the infinity mark, and you can expect to have infinity in focus. This will give you maximum depth of field, and I've verified that the scale is reasonably accurate. That or just use your eyes (and live view magnification if necessary).

Last edited by Cannikin; 05-30-2011 at 01:30 AM.
05-30-2011, 01:32 AM   #6
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Cannikin,
None of the other lenses I owned (or do own now) - whenever MF or AF, zoom or prime - show such behavior. So I was surprised to see it from Limited that some report to be designed and assembled using tighter tolerances and such. So far it's my first and only Limited to own and I'm amazed to see it's ok for this high-grade lens.

Zig
05-30-2011, 02:18 AM - 1 Like   #7
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QuoteOriginally posted by Siegfried Quote
Cannikin,
None of the other lenses I owned (or do own now) - whenever MF or AF, zoom or prime - show such behavior. So I was surprised to see it from Limited that some report to be designed and assembled using tighter tolerances and such. So far it's my first and only Limited to own and I'm amazed to see it's ok for this high-grade lens.

Zig
This is by design. The lenses are functioning exactly as they were designed to do.

And for reference, here's a list of lenses I have verified to turn beyond infinity at the end of the focus ring, regardless of what the infinity symbol says (and most don't even have it at the end of the ring anyway):

DA 15 Ltd
DA 35 Ltd
D FA 100 WR
DA* 60-250
DA 55-300
DA 16-45
Sigma 18-250
Sigma 10-20

Last edited by Cannikin; 05-30-2011 at 03:42 AM.
05-30-2011, 02:20 AM   #8
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Cannikin,
ack'd, thanks.

Zig

05-30-2011, 02:21 AM   #9
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QuoteOriginally posted by cannikin Quote
for the last time, this is by design. The lenses are functioning exactly as they were designed to do.

And for reference, here's a list of lenses i have verified to turn beyond infinity at the end of the focus ring, regardless of what the infinity symbol says (and most don't even have it at the end of the ring anyway):

Da 15 ltd
da 35 ltd
d fa 100 wr
da* 60-250
da 55-300
da 16-45
sigma 18-250
sigma 10-20
dal 18-55
05-30-2011, 05:33 AM   #10
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I have read in several places through the years that lenses can go past infinity to make up for expansion and contraction in different temperatures. Long telephotos can go well past infinity in some instances. It make sense when you think about it. A metal lens like a Limited is certain to expand and contract as the temperatures change. If not, you may not be able to achieve focus at all outside on a hot summer day.
05-30-2011, 06:56 AM   #11
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QuoteOriginally posted by Cannikin Quote
Is there a particular reason why this is bothersome to you? All of my zoom lenses can even go way past the infinity mark itself, as part of a normal manufactured tolerance. This is simply because infinity focus (hyperfocal distance) changes with aperture and focal length, meaning the infinity symbol is nothing more than a rough guideline. If you're using autofocus, it doesn't matter anyway.

The infinity mark on prime lenses is more of a reference for scale focusing, rather than to be lined up directly with. For instance, my FA 77 can't even reach the center of the infinity mark at all, and my DA 35 Ltd can turn past it.

If you're using manual focus, and you want to rely on the distance scale, it's more accurate to scale focus: line up the mark on the DOF scale corresponding to the aperture you're using with the infinity mark, and you can expect to have infinity in focus. This will give you maximum depth of field, and I've verified that the scale is reasonably accurate. That or just use your eyes (and live view magnification if necessary).
One reason for wanting infinity focus with a hard stop is that it is very fast and easy to focus on far away things when shooting landscapes. If it also happens to be night, so that auto focus does not work and you cannot see well enough in the viewfinder to focus manually, a hard-stop for infinity focus is very useful. I have a couple of old manual lenses with this, and I like it very much.
05-30-2011, 05:19 PM   #12
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QuoteOriginally posted by Siegfried Quote
Cannikin,
None of the other lenses I owned (or do own now) - whenever MF or AF, zoom or prime - show such behavior.
Really? I've never heard of a lens that doesn't. What lenses do you own?
05-30-2011, 09:41 PM   #13
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Teles are allowed to focus past infinity by design to compensate for the change of temperature. However, I doubt this is the case for wide angle if one looks at how precise old time wide primes are. What I believe is that modern AF lenses were allowed to focus past infinity because of possible loose QC. Imagine what will happen if the camera wasn't calibrated precisely with a lens that stops right at infinity? The combo might not be able to hit infinity at all and the camera AF will complain (BF has the same effect). Also, adjustment for wides like 15mm is so fine it only takes 0.1mm to throw the image OOF. Just observe how much the rear element travels with the focus ring travels 1mm from infinity mark and you will see. Moreover, the famous Japanese QC in the 80's is history. Nowadays, "good enough" is the key. I just done adjusting the infinity of my DA14 and the amount of movement was so little it was almost impossible to be dead on. I have to rely on my calipers with 0.02mm increment to get it right. Factory workers just don't have the time to be picky like I do. Now the focus distance mark is useful at last and 1 metre really means 1 metre.

Last edited by wlachan; 05-30-2011 at 09:50 PM.
05-30-2011, 10:23 PM   #14
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QuoteOriginally posted by Marc Sabatella Quote
Really? I've never heard of a lens that doesn't. What lenses do you own?
Marc,
In that sentence I was referring to Tokina AT-X AF270, Tokina AT-X AF280PRO, MC Helios 44K-4 (3 different copies from different sources with different backgrounds in their history), MC Helios 77K, Seikanon 28/2.8 macro (pk-A). I have sold and don't have an access right now to DA50-200 and FA28-105, but I don't recall those copies to be able to go past infinity either.

A friend of mine who went into Nikon land gave me his D90 with 50/1.4 bla-bla-bla (all I know: it's the most recent version with SDM/HSM/UMC-whatever motor inside) and kit zoom 18-135 to play for a while and although I'm not that positive on the zoom, but that prime doesn't go beyond infinity for sure.

Since it's a common coin to consider Pentax Limited series being something of premium grade and 'assembled to higher standards with tighter tolerances' (most of us have seen this phrase a lot, haven't we?) then I was really surprised to discover my DA15 being able to no accommodate those tight tolerances as far as I understand them. Not that much, but nevertheless.

Bottom line:
- thanks for all your inputs, I acknowledge I understand that it's ok for most lenses to go beyond infinity (more or less)
- I can live with it
- I'm not ok with it
- it's not going to service (at least right away and only for this feature discovered)

Thanks,
Zig
05-31-2011, 03:08 AM   #15
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QuoteOriginally posted by Marc Sabatella Quote
Really? I've never heard of a lens that doesn't. What lenses do you own?
I can add the SMC M 50 F/1.7. When used with the ME Super it came with, the split prisms align nicely when you look at something far away and turn the lens all the way to the stop. As far as I know, the camera in question has a properly calibrated focusing screen (it has taken pictures with proper focus during many years of operation). I have also used it with my K-5, and turned the ring all the way to infinity to take pictures of buildings that were far away. Those pictures came out sharp in the middle at F/1.7 even when pixel peeping. So with that lens, turning to the stop gives nicely aligned infinity focus - perfect and very usable for nighttime landscape photography. Also very usable in the daytime, since precise infinity focusing can be done so much faster and without any effort.
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