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Old Apr 10, 2009, 9:15 PM   #1
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The other issue I had noticed on Sunday with the 18-250 lens was that when I was trying to photograph anything at a long distance at 250mm I could not focus. Either in AF or manual. In manual, it was as though I needed to be able to turn the focus ring more, but it wouldn't go.

I went out at lunch today to a cemetery with rows of stones and experimented. I'd center focus on something in the way distance and shoot at 18mm at largest aperture, med and smallest. Then, try the same shot at 250mm at largest, med and smallest aperture. It would focus lock fine on 18mm, but no matter what I tried to focus on for 250mm it wouldn't lock. If I switched to manual, I couldn't turn the focus ring enough to get it to focus.

But, if I left it at 250mm and tried to focus on something closer it worked fine. Or, if I moved down to as far as a little over 100mm at the far distant object it would work fine in auto and manual.

This is where I think I screwed up. I did the same test with my Tamron 70-300 lens and it gave me pretty sharp photos that locked quickly on focus at 300mm considering I was hand holding (elbows propped on top of my car). I was thinking once I got home that it wasn't really a true equalized test since, of course, the 300mm would be able to get me out farther.

So, before I try again tomorrow at a farther distance for the Tamron lens, two things. First, am I worrying about something that doesn't exist? Maybe it's just not possible to focus on something at long distance. Second, any other factors I should be considering when doing this if first question isn't true.

I have read some of the links from the post a few days ago on the AF discussion. Trying to find objects that are dark against light with a definite line (although, could have done better than a cemetery with gray stones and green grass).

Below are two images. One at 18mm, 1/20 sec, F16, AP, spot metering, spot AF, auto focused. Second one at 250mm, 1/15 sec, F16, AP, spot metering, spot AF, manual focus. SR is on for both.

I'm sorry in advance if I'm asking a stupid question. I just don't get this.

Patty
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Old Apr 10, 2009, 9:16 PM   #2
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I was always focusing on the very center of the image on the stone in the way back of this "lovely" scene. I was centering on the edge of the stone on this one.
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Old Apr 10, 2009, 9:23 PM   #3
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Hmmm, could the lightness of the area be part of the problem. Here is another photo of a dark stone taken at 250mm, 0.5 sec, F45, AP, spot focus and metering, manual focus. Could the darkness of this stone be what's making it easier for the camera to focus? This stone is the one to the right of the one I was taking in the first image. It is actually a little bit farther back (maybe 1/2 foot) than the lighter stone.

Patty
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Old Apr 10, 2009, 9:59 PM   #4
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Oh My Gosh!
Patty, there is a big hole in the roof of your car!
:shock:
oh wait, that's a sun roof...

about your lens... I'm no expert on lenses but, it sure sounds like you're doing everything right. I can't see any reason for your problem as far as what you're focusing on. My guess is there is a problem with the lens. :-?
GW:bye:
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Old Apr 10, 2009, 11:05 PM   #5
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Patty

I agree with GW. Sounds like a problem with the lense. The only other thing to try is to put the lense on the K100 and try it.


Phil
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Old Apr 11, 2009, 12:09 AM   #6
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If it will not focus in manual, it should be a problem with the lens, and not the camera, so it should be no different on your K100 - Phil's suggestion is a good one.. A zoom lens should focus at all distances at all focal lengths (except at macro settings which this lens doesn't have), especially at distance at extreme telephoto settings - distance is where long focal lengths are intended to be used the most! If this lens is like the Tamron, it has a zoom lock on the camera end of the zoom ring that only engages at the 18mm settting - set your lens as far as you can turn it at that end of the range and then engage and release the lock several times to make sure it isn't binding the mechanism - I doubt if this could be responsible for bad focus, but give it a try and see what happens.
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Old Apr 11, 2009, 8:09 AM   #7
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Thanks, GW, Phil and penolta.

Yeah, I really gotta do something about that hole. It's raining today!:-)

Okay, I put the lens on the K100 and the same exact thing happens. I can focus at ~100mm, but not farther. Either in manual or AF. We used a very tiny bit of rubbing alcohol to clean off the contacts and still no change.

Looks like I'll be driving back to Boston and looking for another lens. Let's hope this guy keeps his promise that I had two weeks to get back to him. I really do like this lens otherwise. When it does focus, the images are great. And, I really like the idea of only taking one lens on vacation or back and forth to work every day.

Patty
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Old Apr 11, 2009, 8:28 AM   #8
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Hi Patty

Sorry to hear that it is the Lense. One other thing I May Suggest is this. No idea if its a good thing To do on a Lense( Dont think It would hurt Anything). However a Little trick on Cell Phones With battery issues is to use a pencil eraser to Clean the Contacts. Its has helped me a few Times as my Phones Aged.



Phil
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Old Apr 11, 2009, 8:40 AM   #9
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So, you are saying use an eraser instead of the rubbing alcohol? I'll give it a try. I've just e-mailed the guy sending him a link to these photos and see what he says. Hopefully he keeps his promise of letting me return it. Unless we can find some other reason this is happening. Or, a way to fix it. It would be interesting to try a different 18-250 lens and see what happens. I know the local Hunt's store doesn't have one. Or, didn't a few weeks ago. I doubt any other place around would have it to try it.

Patty
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Old Apr 11, 2009, 10:41 AM   #10
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Patty,

If your coming to the Boston area I would be happy to let you try my Tamron 18-250 as it is the same lens as the Pentax for all intents and purposes except has 6 year warranty. If Hunts Photo is out of stock on the Pentax ask if they have the Tamron. There is a Pentax lens quoted as being brand new and in box for $350.00 in the marketplace in PentaxForums.com

Lou

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