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03-04-2010, 03:48 PM   #1
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Focus at infinity

I was looking at a person's pictures of the constellation Orion the other day and it said that he "focused" at infinity. What does this mean and how do you do that? I have a k-x and the kit 18mm - 55mm lens and a DA 50mm-200mm lens.

03-04-2010, 03:51 PM   #2
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Infinity is marked by that laid over figure "8", on the focus distance marks. When doing sky photos, it will get you close, then tweak the focus to get it perfect. Some lenses will turn past the infinity point.
03-04-2010, 10:42 PM   #3
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Also remember to switch your focus to manual mode. Cameras are terrible at autofocusing at the sky.

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03-05-2010, 08:33 AM   #4
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I don't see an infinity symbal on the kit lens or am I dense. If there is no symbal can the lens still be focused at infinity?

03-05-2010, 08:43 AM   #5
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Yes. You will find infinity turning the focusing ring all the way to the longest distance. The lens will stop there but as wildlifephotog mentioned, some lenses may be able to go a slight bit further.
03-05-2010, 08:46 AM   #6
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yes, but who knows where infinifty actually is. aim at something distant but land-based, and manual focus on it, then don't touch the focus or zoom after that.

you might have some luck using autofocus to grab infinity on a distant target, and then switch to MF, and don't touch the lens after that point.
03-05-2010, 08:49 AM   #7
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QuoteOriginally posted by veebs2 Quote
I don't see an infinity symbal on the kit lens or am I dense. If there is no symbal can the lens still be focused at infinity?
You're dense Check the focusing ring (the ring closest to the front of the lens); it has a scale in meters and feet starting at 0.25m/0.82ft (in orange) followed by 0.35m/1.15ft and increasing to 2m/7ft. After that, there is the infinity symbol.

Data taken from an DA18-55mm ALII
03-05-2010, 10:03 AM   #8
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No, the OP is not dense. There are no scale markings on the DAL kit lens. That is one of the differences between the DAL and the AL II kit lenses.

03-05-2010, 10:08 AM   #9
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QuoteOriginally posted by kiwibird Quote
No, the OP is not dense. There are no scale markings on the DAL kit lens. That is one of the differences between the DAL and the AL II kit lenses.
So, that's another thing that's different but never actually gets mentioned except for the absence of the hood and clutch-focus and the plastic mount.
That's good info.
Pentax should have actually put the marks in as how much would it saved them leaving it out. I'm sure not a lot.
03-05-2010, 10:12 AM   #10
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QuoteOriginally posted by GerryL Quote
So, that's another thing that's different but never actually gets mentioned except for the absence of the hood and clutch-focus and the plastic mount.
That's good info.
Pentax should have actually put the marks in as how much would it saved them leaving it out. I'm sure not a lot.
Probably would have cost them an extra $5 per unit to have a calibration machine measure the focus of the lens and apply the silkscreen correctly. Perhaps although the optical quality of the DAL matches the more expensive version, the construction quality lags behind and it's not possible to calibrate the lens to a specific distance scale?
03-05-2010, 10:16 AM   #11
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These things are mass produced and I wouldn't think they have to calibrate each lens.
Manufacturing standards nowadays are very precise and calibration may be done at the start and everything done automatically after that.
There would be random sampling every now and then to check quality but that would be it.
The only thing they would actually save on is the additional ink for the silkscreen process.
03-05-2010, 10:25 AM   #12
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QuoteOriginally posted by kiwibird Quote
No, the OP is not dense. There are no scale markings on the DAL kit lens. That is one of the differences between the DAL and the AL II kit lenses.
Therefore my reference to the AL-II. Thanks for that info.

@ veebs2
Sorry for the insult
03-05-2010, 12:48 PM   #13
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Don't worry about it...no insult taken since i am dense about a lot of things!
03-05-2010, 05:47 PM   #14
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QuoteOriginally posted by GerryL Quote
These things are mass produced and I wouldn't think they have to calibrate each lens.
Manufacturing standards nowadays are very precise and calibration may be done at the start and everything done automatically after that.
There would be random sampling every now and then to check quality but that would be it.
The only thing they would actually save on is the additional ink for the silkscreen process.
My money's still on a calibration issue ... there's actually additional cost to not ink the focus ring on the DAL version... if the DA and DAL are the same lens except for no hood and plastic mount, why not use the calibrated focus ring on all of them, instead, Pentax has a printed focus ring and an unprinted ring, and the additional time overhead to load the correct ring for a certain X number of unit production run.

Sorry to the OP for going off-topic here
03-05-2010, 06:23 PM   #15
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At night use a bright star to manually focus lens; this is infinity focus. If infinity focus is set with another method, tip: use gaffers tape to prevent focus ring from turning (but remember to remove tape before using autofocus or lens AF mechanism may be damaged!) If tape isn't used, or star is used to focus, remember to re-check focus before each series of shots; in the dark, many nightsky photographers have accidentally and unknowingly bumped the focus ring and subsequent photos were out-of-focus as a result.

Every step in manufacture has a labor cost; silkscreening focus rings is more than one step, making a screened ring cost maybe multiple times the cost of unscreened ring.
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