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08-17-2010, 04:01 PM   #16
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QuoteOriginally posted by RioRico Quote
MoiVous' technique is exactly the opposite of aerodave's. And this article says not to bother, either way.

But the question arises: How to clearly distinguish the parfocals from the varifocals? Other than by screwing with the focus, I mean.
The easiest way is to look at the price tag. If you can do that without having a heart attack, it`s a varifocal.

08-17-2010, 08:47 PM   #17
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QuoteOriginally posted by baldrick Quote
The easiest way is to look at the price tag. If you can do that without having a heart attack, it`s a varifocal.
Well said! That's about right.
08-18-2010, 05:21 AM   #18
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QuoteOriginally posted by SpecialK Quote
Regardless of anything else, that does not seem right.
AF and wide angles.

in a nutshell, AF will be iffy with wide angle lenses.

here's a good article to read.

Mastering Wide-Angle
08-18-2010, 12:41 PM   #19
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QuoteOriginally posted by opiedog Quote
AF and wide angles.

in a nutshell, AF will be iffy with wide angle lenses.

here's a good article to read.

Mastering Wide-Angle
Showing 75 feet at 25 feet is way beyond "iffy".

08-18-2010, 08:05 PM   #20
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QuoteOriginally posted by SpecialK Quote
Showing 75 feet at 25 feet is way beyond "iffy".
Showing 75 feet at 25 metres, on the other hand, is pretty close!
08-19-2010, 08:44 AM   #21
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QuoteOriginally posted by SpecialK Quote
Regardless of anything else, that does not seem right.
I actually didn't think that through when I posted it. The discrepancy is not that much, it's probably closer to a 20ft discrepancy and this only happens at 18mm and when I am trying to focus on something that is further than 50ft away. Focusing on something close (withing 20ft) or anything when zoomed in from about 25mm and on, will be accurate. My original concern was for the 18mm end and long distances.
08-19-2010, 09:27 AM   #22
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QuoteOriginally posted by KxBlaze Quote
I actually didn't think that through when I posted it. The discrepancy is not that much, it's probably closer to a 20ft discrepancy and this only happens at 18mm and when I am trying to focus on something that is further than 50ft away. Focusing on something close (withing 20ft) or anything when zoomed in from about 25mm and on, will be accurate. My original concern was for the 18mm end and long distances.
FWIW, my pentax 12-24 sometimes lands between the 7ft and Infinity mark when focusing at infinity.

the image comes back sharp anyway.
made very little or no difference when i manually move the focus closer to the infinity side.

i have the same issue with my 18-250 tamron. when focusing at 18mm it's pretty iffy. i sometimes have to manually adjust the focusing ring.
08-19-2010, 10:27 AM   #23
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QuoteOriginally posted by opiedog Quote
FWIW, my pentax 12-24 sometimes lands between the 7ft and Infinity mark when focusing at infinity.

the image comes back sharp anyway.
made very little or no difference when i manually move the focus closer to the infinity side.

i have the same issue with my 18-250 tamron. when focusing at 18mm it's pretty iffy. i sometimes have to manually adjust the focusing ring.
My images come back sharp too, this "problem" was more annoying than anything and I just wanted to make sure that my new lens wasn't a piece.

08-19-2010, 12:41 PM   #24
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yes, it was quite disconcerting for me at first and i was even wondering if this is a Pentax issue but thankfully, no.

sometimes i zoom in to telephoto, get the focus and zoom back out to wide. it's not very accurate since most zooms are varifocal, but it works for me anyway.

i use the AF button instead of the shutter button for AF, so this is easy.
Zoom in, press AF button, zoom out, press shutter.


YMMV
08-20-2010, 05:30 AM   #25
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It sounds like the focusing on the OPs lens is more than just a varifocal problem - it may need professional attention.

My Tamron 18 - 250mm does the same thing but regardless of whether i rely on the camera to catch focus at 18mm or zoom out, catch focus at 250mm and then hold the focus back to 18, my 18mm shots look the same - DOF at 18mm covers a lot of sins and the Tammy is not sharp enough to show the difference.
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