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08-13-2009, 10:04 AM   #16
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A quick question, did you have tungsten lights when you did your focus chart tests. There has been some threads that indicate that tungsten lights can cause ff, especially with Tamron
https://www.pentaxforums.com/forums/660108-post18.html

Best regards,
Haakan

08-13-2009, 11:13 AM   #17
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QuoteOriginally posted by Haakan Quote
A quick question, did you have tungsten lights when you did your focus chart tests. There has been some threads that indicate that tungsten lights can cause ff, especially with Tamron
https://www.pentaxforums.com/forums/660108-post18.html

Best regards,
Haakan
Nope, everything was natural outdoor light,
Brian
08-13-2009, 11:22 AM   #18
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six of one, half dozen of the other

QuoteOriginally posted by kenyee Quote
It's the lens...I went through 3 copies of it on my K10D before giving up. It'd either BF or FF at the wide or tele end and I didn't have focus adjustment. Try calibrating it for 50mm and live with it or get another lens and see if you get lucky in Tamron roulette ;-)

You can dig up my old thread on this in the lens forum...
I'd like to think so, but it works so well on the K100 and noticeably less well on the K20, regardless of AF Adjustment. I'm starting to think it's the interaction of this lens @ 75mm with this camera that may simply not work. I'm not looking to blame anybody, just find a solution.

And it may be that the solution is to (a) get a new lens for the K20, or (b) send the K20 back and keep the Tamron on the K100. It works out to about the same amount of money. In terms of cameras, the K20 is just excellent in so many ways, with so many additional features, I'm leaning toward (a).

Thanks for the input,
Brian

Last edited by FHPhotographer; 08-13-2009 at 11:42 AM.
08-13-2009, 11:43 AM   #19
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QuoteOriginally posted by FHPhotographer Quote
Well, I took your advice set the AF Adjustment (several settings but -10 looked the best), and reset it to the default of +/-0, and took shots of a focus test page for both. This is the result
I'm assuming those are crops, and you really did focus on the center where you were supposed to?

Anyhow, at the posted size, I see only a small discrepancy - both images show the center line within the focus zone, just further forward in one than the other. A difference of millimeters. It would seem pretty clear that this is not related to whatever was going on in the bush shot.

QuoteQuote:
it's still coming out soft @75mm contrasted with 28mm, and it gets softer at longer distance,
I'd consider the possibility, then that that's how sharp this lens is (or isn't) at these focal lengths and distance, and that it isn't a focus problem at all. Although by most accounts it's great there, so perhaps you have a dud lens. hard to tell at the posted size.

08-13-2009, 12:42 PM   #20
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Am I "seeing" more with the K20?

QuoteOriginally posted by Marc Sabatella Quote
I'm assuming those are crops, and you really did focus on the center where you were supposed to?

Anyhow, at the posted size, I see only a small discrepancy - both images show the center line within the focus zone, just further forward in one than the other. A difference of millimeters. It would seem pretty clear that this is not related to whatever was going on in the bush shot.



I'd consider the possibility, then that that's how sharp this lens is (or isn't) at these focal lengths and distance, and that it isn't a focus problem at all. Although by most accounts it's great there, so perhaps you have a dud lens. hard to tell at the posted size.
Okay, I show my ignorance here, but... I know folks talk about needing higher quality lenses to take full advantage of the higher resolution cameras, but does it work the other way as well, i.e., a higher end camera shows the limitations of a lower quality lens? If that's the case, am I not "seeing" the Tamron softness on the 6mp K100 that is now being "seen" on the K20? Is the lens really delivering the same data on both cameras?
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08-13-2009, 03:33 PM   #21
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QuoteOriginally posted by FHPhotographer Quote
I know folks talk about needing higher quality lenses to take full advantage of the higher resolution cameras, but does it work the other way as well, i.e., a higher end camera shows the limitations of a lower quality lens? If that's the case, am I not "seeing" the Tamron softness on the 6mp K100 that is now being "seen" on the K20? Is the lens really delivering the same data on both cameras?
Yes, barring a focus irregularity, the K100D and K20D are seeing the same image at their sensor. But the K20D records it in more detail. If the lens itself doesn't provide enough resolution to withstand that kind of scrutiny, you'll see it viewing at 100%. But compare both images at the same size and it should be similar. I'm guessing the lens should be good enough that it looks the same when viewed at 100% on the K100d and similar size on the k20D, and if you zoom in a little further on the K200D, you'll see even more detail, but at some point you'll be zooming past where there is any more detail to see, and it will just start looking soft.

It's actually the exact same phenomenon behind my comments about not being able to tell much from the small samples posted here. They aren't "zoomed in" far enough to see how sharp or soft the lens really is. Viewed as thumbnails, virtually *all* images look razor sharp. Only when displayed large enough can you make fine distinctions. And the K20D lets you zoom in further, and thus make finer distinctions, than the K100D.

But that doesn't mean you should use a lens on the K20D just because it starts to show its limitations once you zoom in on an image beyond how far you could have zoomed in with a 6MP camera. If you are just planning on viewing full screen, it should look just as good coming from either camera. And at any given print size, the image will look as good or better coming from the K20D as from the K100D. So what if it doesn't look so hot at the theoretical maximum size from the k20D? You couldn't have come anywhere near that size with the K100D.

BTW, do be sure you have similar sharpening settings set in your camera/software when doing these comparisons!
08-13-2009, 07:47 PM   #22
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Pilot error, pilot error, pull up!

QuoteOriginally posted by Marc Sabatella Quote
Yes, barring a focus irregularity, the K100D and K20D are seeing the same image at their sensor. But the K20D records it in more detail. If the lens itself doesn't provide enough resolution to withstand that kind of scrutiny, you'll see it viewing at 100%. But compare both images at the same size and it should be similar. I'm guessing the lens should be good enough that it looks the same when viewed at 100% on the K100d and similar size on the k20D,
Well, the devil is in the details and I was getting some of 'em wrong.

Finally I've gotten the 100% cropping correct, cranked in a -7 AF Adjustment on the K20, and here are the results of the same shot, same settings @100% using first

the Tamron 28-75 on the K100...

and then the Tamron on the K20...

So what say you now, they look pretty close to me in terms of the Tamron AF, but I see more detail (as I'd hoped) from the K20. The next question, of course, is how much more could I get out the K20 using perhaps the FA 77mm,
Brian
08-14-2009, 12:28 PM   #23
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Yes, what these pictures show is just how much a difference the pilot makes :-). I look at that 100% crop from the K20D and say, wow, just how much better do you *need* it to be? And will whatever difference you get be worth $600 or whatever the FA77 goes for?

08-14-2009, 02:51 PM   #24
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Marc's said it all.
You've probably got all the detail you ever need.
The 77ltd wouldn't add much in terms of detail, though it may render colours and contrast better - it's the X-factor that makes all 77ltd owners call it 'magic'.
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