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10-23-2007, 06:34 AM   #16
m8o
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thePirate... I can confirm that mine too likes to be a hair, ever so slightly, under infinite focus for the best sharpness. Here's the catch, and I have to re-do the test a third time wiriting down everything as I go this time to be sure. It appears in the viewfinder that infinite focus is the sharpest; when I tick back a hair it seems less sharp. But in the computer there's a slight edge to the one that was a tick back. Don't quote me on that yet. I need to be more scientific now that I saw that, writing down my shots as I go.

thnx for the link Bart.

10-23-2007, 09:10 AM   #17
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Yes, thanks Bart. Waiting for you to verify your findings m8o... I think Stephen G may have had a point in asking me to test the lens on a film body before taking any action. I have a nagging feeling its not the lens at all, but the camera. I'd hate to 'tinker' and then discover I couldn't achieve infinity at all on a future body. I may just stick with my 'adjustment' for now and wait for a future body to force my hand once and for all.

Afterall, it still can acheive infinity. I just wonder how many people out there are thinking this lens isn't a great performer at infinity but don't know the secret...
10-23-2007, 08:25 PM   #18
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Lens Testing

QuoteOriginally posted by thePiRaTE!! Quote
I think Stephen G may have had a point in asking me to test the lens on a film body before taking any action.
If you want to test this lens with a DS, I would love to help as I am considering this lens but want to see it in person.
Did you get the lens hood? $69 seems outrageous.
10-23-2007, 08:32 PM   #19
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That could work out well, thanks for the offer. I'll PM you and we can arrange details. The hood is included with the 125, no need to fork out the extra dosh. Its only necessary for the other lenses in the series. FWIW, I have the hoods for both the 125 and the 180 and haven't used them at all, even in daylight. For any possible minor gains, the additional size and encumbrance doesn't make it worth while (to me).

10-26-2007, 05:34 PM   #20
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For anyone who happened to be following this thread (namely the few Voigtlander lens users out there amongst us) - I find it worthy to mention that after doing some testing, I have discovered that the Voigtlanders are not alone in this 'issue'. To begin, I will say that the 125 is the most pronounced in the 'touch-back for infinity' trait - enough so to draw my attention to it - but ALL my lenses have shown at least a modicum of improvement in sharpness by doing this. I now believe my K10 body isn't properly assembled to exact standards, as Wlachan had alluded to.

Its not all bad as I can still get the results by doing the little adjustment, but it means I'll be assuming focusing responsibilities at all times when shooting infinity just to be sure of the result.

FWIW, I would recommend that any K10 user try and shoot infinity at max rotation with any lens, and then a slight (VERY slight) kick back into the throw and take the shot again. Zoom in and see if you don't find that the detail is sharper on the adjusted shot. I don't know if its just my unit, or if they are all like this. Try it and see? Please let me know here if you do, I may persue an adjustment on my body instead if I am alone in this.

Thanks,


Kelly.
10-27-2007, 07:56 AM   #21
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A relevant thread over at the other forum:
MF lenses at infinity: Pentax SLR Talk Forum: Digital Photography Review

I also have the Voigtlander, and find that both my 125 and 180 focus a bit beyond infinity as well.
10-27-2007, 12:27 PM   #22
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I think you are on the right trail now! I gave the 18mm-55mm 'kit' lens a try. I set my K10D to manual focus, turned it full pin and took a pic. Then I tuned it back ever so slightly and took another pic. The proof is in the puddin'! I will give my other lenses a similar try, but this one is very obvious. The pictures are cropped slightly different but you get the idea.

Both shots are taken through a window on a drizzly, dark day. (Just for the record, it's not my house! My neighbor has chosen his front lawn as an appropriate place to park his bass boat.)

Last edited by J.Scott; 11-23-2007 at 05:13 AM.
10-27-2007, 12:41 PM   #23
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I believe all AF lenses are designed to go a little beyond infinity (hmm, beyond infinity, an interesting concept!) so the AF can go past and then come back a little to lock on. Probably a safe margin built in to compensate for all the things talked about here--manufacturing tolerances, temperature changes, wear, etc.--and I would guess that it's a larger margin than MF lenses. I've never noticed this issue with any of my MF lenses until now, but it makes sense that the infinity stop cannot be so exact for all the lenses to cover all the variables that affect focus, and going past a little bit is much better than not quite making it, therefore manufacturing tolerances probably start at infinity and go past, rather than have plus or minus around infinity.

10-27-2007, 01:07 PM   #24
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"To infinity - and Beyond!" To quote Buzz Lightyear.

I tried my MF 50mm f1.7 and at full rotation it is at perfect infinite focus. Hopefully others will try their MF lenses to compare results.
10-28-2007, 03:09 PM   #25
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"infinity and beyond" <---lol, nice 1.

Thanks for the tests J.Scott, it gives me a feeling that perhaps its just the way things are, rather than that my equipment is faulty in some way. I fully admit I am quite new to photography, but it would seem to me that a lens should have some indication that it was intended to 'over-focus', if indeed it were by design. Only my Sigma 15mm fish eye intentionally allows for scrolling past infinity in its markings.

My suggestion - for the sake of accuracy and new photographers everywhere; just a little red tick mark past infinity to give a clue to this no-man land. It didn't take me long to figure out, but it shouldn't be something that needs to be figured out as I see it, especially when impressions of lens quality can be formed by a single image in a shop.

I'll still be curious to note other results as well, or if this effect is as pronounced on a film body. Anyone have one they'de care to test the same thing on?
10-28-2007, 09:36 PM   #26
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In astronomy, true infinity is a measurement of an infinite distance that cannot be expressed easily in any other way. Light emitted from these distant objects is said to be traveling parallel to each other. When we focus a telescope to view distant objects in space we first focus on the moon. If we focus on any object on earth, even an object that is 10 miles away, it will not be a truly infinite focus, and the images that we get would be out of focus. By focusing on the moon we can get a reasonable infinite focus.

Before you condemn your lens or camera I suggest you check your focus on the moon. I think you might find that your lens will be closer to infinite focus.


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10-29-2007, 05:37 PM   #27
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God bless Stephen Gandy - my Voigtlander 125mm f2.5 Macro APO-Lanthar arrived today! Shipped only last Wednesday from California and in my sweaty palms Monday afternoon; what a beautiful lens! It is clearly the most expensive and heaviest lens I own.

Of course I had to try and see if, like most of it's kin, it has to be turned back a tick from full focus to be perfectly in focus. It is true - it has to be turned back ever so slightly. Hopefully I will have some time to test-drive it this week and show off some pictures.
10-29-2007, 07:51 PM   #28
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Welcome to the club! These are great lenses, and I'm sure enjoying mine. The 125 is quite large, especially on my little *istD! The 180 and 90 are much smaller. I'm thinking about getting a katz-eye screen to help speed up focusing. It looks like the infinity focusing issue is pretty common, at least on this last batch that Cosina made up all in KA mount. I'm going to try focusing on the moon as Joe1955 suggests.
10-30-2007, 07:02 AM   #29
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I understand what Joel is saying for sure. I noticed an appreciable difference in the focus point between something 1000 feet away vs. something about 1 and 1/2 miles away. You'd think both were @ equal 'infinity' in-focus points on the barrel, but not quite.
10-30-2007, 10:22 AM   #30
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I'll set out to determine this new possiblity in my case. Perhaps then its not focusing past infinity, but just not all the way there given the subjects distance. Interesting, I feel a little smarter everytime I come back here guys - thank you for sharing you time and knowledge. Tests forthcoming!
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