[eva2000]

After posting my comparison photos between Sigma 18-50mm f2.8 EX DC Macro and Tamron 17-50 f2.8 lens, some folks have commented that my Tamron lens might be front focusing. So I did some tests and seems it maybe it's the case as i'm definitely getting front focusing when using Auto Focus mode, while in Manual mode it's fine.

I tested Tamron 17-50mm f2.8 lens at 45 degree angle and approximately 38cm distance from lens to target.

I tested Auto Focus @F2.8, F4.0, F8.0 and Manual Focus @F2.8, F4.0, F8.0.

AF Point = Center
SR = Disabled
2 second Timer set

All bullet point listed/linked images imported as DNG RAW into Lightroom 2 and 100% crops exported as JPEG 70%.

• Auto Focus @F2.8 (50 mm > 1/13 sec at f / 2.8 | ISO 125)
• Auto Focus @F4.0 (50 mm > 1/5 sec at f / 4.0 | ISO 125)
• Auto Focus @F8.0 (50 mm > 0.6 sec at f / 8.0 | ISO 125)
• Manual Focus @F2.8 (50 mm > 1/10 sec at f / 2.8 | ISO 125)
• Manual Focus @F4.0 (50 mm > 1/5 sec at f / 4.0 | ISO 125)
• Manual Focus @F8.0 (50 mm > 0.8 sec at f / 8.0 | ISO 125)

Here's resized @540pixel width JPEG @85% quality without sharpening

Auto Focus @F2.8 vs Manual Focus @F2.8

Auto Focus @F4.0 vs Manual Focus @F4.0

Auto Focus @F8.0 vs Manual Focus @F8.0

So is this front focusing ???

Tried the same tests with newspaper/magazine text and stationery objects around the house and similar results - Auto Focus was focusing in front of the point I had targeted. Manual focus didn't have any problems.

Didn't have any probs with my Sigma 18-50mm f2.8 EX DC Macro lens.

I only received this lens on Friday Deember 12, 2008 last week. Grounds for replacement/repair/exchange ?

Thanks in advance for any suggestions or comments you can provide

George


Update: I tested Sigma 18-50mm EX DC Macro f2.8 lens the same way and did some new tests to compare Tamron 17-50mm f2.8 lens in AF vs MF vs Sigma 18-50mm EX DC macro f2.8 lens in AF. As you can see Tamron 17-50mm f2.8 definitely front focuses i think!

Tested settings:
The focus point was the green MENU icon's middle cell/box (out of the 3 cell divided boxes).

• AF point = Center
• ISO = 125
• Aperture priority
• DNG RAW imported into Lightroom 2 exported as JPEG at 85% quality - resized not cropped.

1. Tamron 17-50mm @50mm f2.8 AF vs Tamron 17-50mm @50mm f2.8 MF
2. Tamron 17-50mm @50mm f2.8 AF vs Sigma 18-50mm @50mm f2.8 AF
3. Tamron 17-50mm @50mm f4.0 AF vs Tamron 17-50mm @50mm f4.0 MF
4. Tamron 17-50mm @50mm f4.0 AF vs Sigma 18-50mm @50mm f4.0 AF
5. Tamron 17-50mm @50mm f8.0 AF vs Tamron 17-50mm @50mm f8.0 MF
6. Tamron 17-50mm @50mm f8.0 AF vs Sigma 18-50mm @50mm f8.0 AF

Tamron 17-50mm @50mm f2.8 AF vs Tamron 17-50mm @50mm f2.8 MF

Tamron 17-50mm @50mm f2.8 AF vs Sigma 18-50mm @50mm f2.8 AF

Tamron 17-50mm @50mm f4.0 AF vs Tamron 17-50mm @50mm f4.0 MF

Tamron 17-50mm @50mm f4.0 AF vs Sigma 18-50mm @50mm f4.0 AF

Tamron 17-50mm @50mm f8.0 AF vs Tamron 17-50mm @50mm f8.0 MF

Tamron 17-50mm @50mm f8.0 AF vs Sigma 18-50mm @50mm f8.0 AF

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Last edited by eva2000; 12-18-2008 at 10:18 PM.

[solisti]

Yep, seems like front focus. Try it also in different light (tungsten vs. natural light etc..).

IMHO the grounds for repair or replacement are there, especially if you bougth it online, you can send it back and have your money back (at least here it is so, you don't really even need a reason to send item back during the two first weeks).

May I ask why you need both the Sigma and Tamron?

[avian]

Yep, seems like front focus. Try it also in different light (tungsten vs. natural light etc..).

IMHO the grounds for repair or replacement are there, especially if you bougth it online, you can send it back and have your money back (at least here it is so, you don't really even need a reason to send item back during the two first weeks).

May I ask why you need both the Sigma and Tamron?

Definitely try different light. I thought my 50-135 was severely front focusing (indoors testing the first night after receiving it). During outdoors daylight conditions it was no where near as bad (though still present).

[jsherman999]

Does the K200D have a debug mode that allows AF adjustment like the K10D does?

Since you're an overclocker, I assume you'd like to tweak the firmware on the body for this lens!

[Marc Sabatella]

So is this front focusing ???

Are those crops? You do know you need to actually center the focus target and make sure the camera is using the center focus point, right? And these look have quite a bit of what looks like perspective distortion - were you shooting at the widest angle setting, or or did you perhaps not have the chart perfectly flat?

Assuming you set up the tests correctly and these are indeed just crops, then yes, looks like very clear FF, but it's hard to tell from the pictures if the test was done correctly.

Didn't have any probs with my Sigma 18-50mm f2.8 EX DC Macro lens.

I only received this lens on Friday Deember 12, 2008 last week. Grounds for replacement/repair/exchange ?

Did you test the Sigma in the same way, or is it possible you simply didn't notice any problems? I ask because it is usually not really clear whether problems with focus are caused by the camera or the lens (either or both could conceivably be at fault).

[eva2000]

Yep, seems like front focus. Try it also in different light (tungsten vs. natural light etc..).

IMHO the grounds for repair or replacement are there, especially if you bougth it online, you can send it back and have your money back (at least here it is so, you don't really even need a reason to send item back during the two first weeks).

May I ask why you need both the Sigma and Tamron?

Definitely try different light. I thought my 50-135 was severely front focusing (indoors testing the first night after receiving it). During outdoors daylight conditions it was no where near as bad (though still present).

Yeah i tried in daylight and shade as well as in room with 30W CFL Daylight bulbs rated for 150W same front focus but at different degrees of severity but it definitely still existed. I got Tamron out of curiosity/LBA

Does the K200D have a debug mode that allows AF adjustment like the K10D does?

Since you're an overclocker, I assume you'd like to tweak the firmware on the body for this lens!

unfortunately K200D doesn't have AF adjustment like K20D

Are those crops? You do know you need to actually center the focus target and make sure the camera is using the center focus point, right? And these look have quite a bit of what looks like perspective distortion - were you shooting at the widest angle setting, or or did you perhaps not have the chart perfectly flat?

Assuming you set up the tests correctly and these are indeed just crops, then yes, looks like very clear FF, but it's hard to tell from the pictures if the test was done correctly.

Did you test the Sigma in the same way, or is it possible you simply didn't notice any problems? I ask because it is usually not really clear whether problems with focus are caused by the camera or the lens (either or both could conceivably be at fault).

The bullet listed linked versions are 100% crops, the inline images are resized 540pixel versions both show front focussing in AF mode.

[netuser]

Where do one find this test sheets for printing and test own lens ?

[eva2000]

Focustestchart.com download

[netuser]

Focustestchart.com download

Many thanks

[Miserere]

Where do one find this test sheets for printing and test own lens ?

I prefer these. Much easier to set up.

[eva2000]

no probs netuser

I prefer these. Much easier to set up.

I printed those on A4 and seemed too small ??? are they meant to be printed on larger paper sizes ?

[Marc Sabatella]

The bullet listed linked versions are 100% crops, the inline images are resized 540pixel versions both show front focussing in AF mode.

Maybe I'm missing something, but the links in your list appear to be the exact same images as the inline ones - imaes that don't even show the focus target. So again, I must ask - did you actually center your camera on the focus target at the center of the target, or on the markings to the side as it appears from the posted images? If the latter, then these tests are meaningless.

The focus point was the green MENU icon's middle cell/box (out of the 3 cell divided boxes).

These tests are meaningless also. *You* might have wanted the camera to focus on that, but there is absolutely no way to force the camera to do so - tha subject has far too much *else* going on to compete with that button. Even using center point, the button below the menu button would be a perfectly legitimate area for the camera to have chosen.

Stick to well-designed, correctly used focus test charts. If you want to use other subjects, it is absolutely imperative they be as well-controlled as the test chart - there must not be *anything* else that is *anywhere near* the thing you want the camera to focus on. A piece of string stretched horizontally across on a plain colored table, for example, could work fine. But not if there is also a salt shaker right in front of that piece of string for the camera to potentially choose instead!

[yzuo]

I had the same problem with this lens mounted on my DS and haven't had a chance to try it on the K20D which I just received.

[eva2000]

Maybe I'm missing something, but the links in your list appear to be the exact same images as the inline ones - imaes that don't even show the focus target. So again, I must ask - did you actually center your camera on the focus target at the center of the target, or on the markings to the side as it appears from the posted images? If the latter, then these tests are meaningless.



These tests are meaningless also. *You* might have wanted the camera to focus on that, but there is absolutely no way to force the camera to do so - tha subject has far too much *else* going on to compete with that button. Even using center point, the button below the menu button would be a perfectly legitimate area for the camera to have chosen.

Stick to well-designed, correctly used focus test charts. If you want to use other subjects, it is absolutely imperative they be as well-controlled as the test chart - there must not be *anything* else that is *anywhere near* the thing you want the camera to focus on. A piece of string stretched horizontally across on a plain colored table, for example, could work fine. But not if there is also a salt shaker right in front of that piece of string for the camera to potentially choose instead!

They're centered for focuschart but curious (noob and all) why the Sigma was able to AF to correct spots for both tests and not the Tamron if that was the case ? I tried it with lots of other test targets and Sigma always focused on what I wanted but Tamron not once did - always in front of target from f2.8-4.0 ??

[Marc Sabatella]

They're centered for focuschart but curious (noob and all) why the Sigma was able to AF to correct spots for both tests and not the Tamron if that was the case ? I tried it with lots of other test targets and Sigma always focused on what I wanted but Tamron not once did - always in front of target from f2.8-4.0 ??

Could well be that the Tamron has an FF problem - unless you were testing in tungsten light, in which case the ztamron might be fine, and the Sigma might have a *backfocus* problem that the tungsten light is masking.

That's for the focus test charts. When I say the results were meaningless for the remote control, I mean they were meaningless- no point trying to assign any meaning to them. The camera will focus on whatever it pleases. Could be totally coincidence that it chose the "right" button when the Sigma was mounted - ther'e absolutely no way to know, so there is no point even thinking about it.