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12-15-2007, 05:58 PM   #1
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My Tamron 28-75 2.8 arrived...

I've been waiting for this lens for nearly a month. I guess i'll give you guys a guick review of my first impressions. I do have complaints however.

Lens construction and quality feels amazing.
Fairly tight zoom ring (i like)
Performance on my K100D, focussing is fast and i think it's a little quieter compared to the kit lenses (18-55 & 50-200), the shutter sounds quieter too.

Complaints:
focussing is off. I've taken about 100+ shots with it today, in various circumstances. I don't know how to describe it but auto-focus does do its job and it locks on, but after i take the shot, the object i focused on, turns out blurry (70mm & 2.8). Things behind the object turn out relatively crisp however. I gotta change the aperature to about 8.0 or smaller to get a sharp image. I don't know if this is called Rear focus or Front focus - probably the former.

I bought this item off ebay. so i emailed the seller back. damnit, i probably wont' have it back for xmas now either....

I'll post a sample of what i mean. I would like someone else with the same lens to post an image so i can compare. I'll post everyting at f/2.8 cuz it seems like that's where the prob is most apparent.


Last edited by Tingchaleun; 12-15-2007 at 07:53 PM.
12-15-2007, 06:30 PM   #2
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same shot of what i mean...

So i'll explain what i did.

camera was placed just over one meter away from the object, and at a 45 degree angle to the ruler. I used a tripod, 2sec timer. iso400, 1/45s, 70mm @ f2.8. I autopfocused on the 6 (the hole in the ruler by 6")... and quite obviously 8" seems to be more infocus...

is there anything i can do to fix this?

Last edited by Tingchaleun; 02-16-2008 at 03:25 PM.
12-15-2007, 09:42 PM   #3
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Does nobody care? Or is the nature of my post typically talked about?
12-15-2007, 10:41 PM   #4
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Noone has replied because there's nothing wrong! it looks fine, talk about it all being in your head. AF is never going to be millimeter precise, yours is as good as it gets

12-16-2007, 01:29 AM   #5
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Hi Tingchaleun-

I had a related experience with an SMC-M manual lens recently, and I was told essentially the same thing. Stop complaining, focus is never 100% accurate, example photos aren't real life, get out and take pictures instead, etc. But there IS a problem, and I can see it in your photos clear as day. Too much front focus. In my case it was a back focus issue, but the basic result is the same: everything looks great in the viewfinder, but the focal plane in the resulting photo is off.

I dealt with it in two ways: more focusing practice (focus improves substantially if I rotate into focus from the left rather than the right) with the manual lens, and I returned my K10D to Pentax (still under warranty) to have the sensor alignment checked. They also adjusted and calibrated the autofocus circuit. Though I don't think the latter did much for focusing with the manual lens, since then I've noticed a slight improvement in focus with my kit 18-55.

If you search around for "back focus" (though you're correct, your lens is front focusing), you'll find many references to this problem. It seems certain lenses cause more problems than others, and some individual camera/lens combos are idiosyncratic also. My guess is that, barring any sensor misalignment or other camera issues (did you notice this problem with other lenses?), a different copy of your 28-75 would work just fine... Good luck!

Kerey
12-16-2007, 02:27 AM   #6
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There is too many details in your example picture. You do not know which one of them is used by sensor for focusing. Focus sensor is actually quite large....

You get an aidea how large the sensitive are of one sensor is:
- select center sensor (only)
- select AF-C
- put for example very skinny candle to the table, or stick or whatever, but it must have small tip and there must be distant background behind it
- focus to the candle tip, keep shutter button half pressed
- start moving your camera so that the tip goes farther from center focusing sensor, focus snaps to the background immediately when candle tip is away from sensor area

You will notice that you cant focus to the very tiny details because of the size of sensor.... sensor "see" all details within the sensor area as one.
12-16-2007, 02:53 AM   #7
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I also have this lens. At f2.8 I do experience some front focusing but this is more apparent at dim lighting and tungsten lighting/stage lighting. but come to think of it, a f2.8, the depth of field is too shallow and it is understandable that the lens will misfocus a little. I usually go with f3.2 or f4.
12-16-2007, 05:23 AM   #8
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hi, looks like front focus to me, so is a problem. but i would do a lot more testing at different focal lengths / aperatures / and distance to object to make sure if it was consistant then I would return the lens for recalibration etc

Phil

12-16-2007, 06:33 AM   #9
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On the surface, it appears the lens is front focusing.

A couple of thoughts, both predicated on DOF:
  1. The focus sensor indicator could be off position, so you think you are focused on the 6 but in fact are focused on the eight. Which focus sensor were you using? At that close focus, if you used center sensor, and recomposed, there might not be enough DOF to cover the minute change in focus distance. All AF systems rely on DOF to some extent to get the lens in focus "good enough". The DOF at f2.8, and close focused is razor thin, so if focus is off, you see it more readily.
  2. What type of of lighting did you use, Tungston lighting can also fool the AF sensor a bit.
If none of the above apply, then the lens is indeed front focusing and should be returned to the seller. There have been some examples of this lens FF/BF. Mine BF ever so slightly. It is not enough to bother me. F2.8 the lens is a bit soft for me. Improves considerably at f3.5, and you get that much more DOF. It's not much, but seems to be enough to keep my subjects in focus.
12-16-2007, 06:45 AM   #10
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Hi --

Well, I can't tell from the two photos you've posted whether there is a serious back- or front- focus issue. But I'll take your word for it that (1) you know what you're doing; (2) that you've done real-life tests & not just angled-ruler-tests (and under various lighting conditions); and (3) this problem seriously affects your real-life ability to use the lens. Based on those assumptions, my advice would be either to return the lens, or to see if there's a warranty from Tamron that you can somehow avail yourself of and get Tamron to fix it.

Now, I just read that you bought this off E-bay. I don't know what that means precisely -- whether you bought it new from a genuine store, or used from an individual. If the latter, I would say that wasn't the best idea. This lens -- which I have -- has quite a reputation for quality-control issues. But if you got a good one, it would be worth its weight in gold. Thus, I decided that the only way I'd buy one is if I could actually try it out first on my camera (or, if I couldn't do that, to buy it from some place with a solid reputation & easy return policy).

Good luck!
12-16-2007, 06:57 AM   #11
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QuoteOriginally posted by roscot Quote
On the surface, it appears the lens is front focusing.

A couple of thoughts, both predicated on DOF:
  1. The focus sensor indicator could be off position, so you think you are focused on the 6 but in fact are focused on the eight. Which focus sensor were you using? At that close focus, if you used center sensor, and recomposed, there might not be enough DOF to cover the minute change in focus distance. All AF systems rely on DOF to some extent to get the lens in focus "good enough". The DOF at f2.8, and close focused is razor thin, so if focus is off, you see it more readily.
  2. What type of of lighting did you use, Tungston lighting can also fool the AF sensor a bit.
If none of the above apply, then the lens is indeed front focusing and should be returned to the seller. There have been some examples of this lens FF/BF. Mine BF ever so slightly. It is not enough to bother me. F2.8 the lens is a bit soft for me. Improves considerably at f3.5, and you get that much more DOF. It's not much, but seems to be enough to keep my subjects in focus.
I'd agree with Roscot. It's hard to tell for sure from the shots you've posted but I think the lens has an issue. To be totally sure you should download the following:

http://focustestchart.com/focus21.pdf

and do a controlled test shot using a tripod or camera support. If the lens proves to be off, I'd get a refund and return it. There's enough of these coming on the used and new market to get another copy.

I have one of these lenses and frankly it's a great lens. A tad soft wide open but that's to be expected with any zoom.
12-16-2007, 07:28 AM   #12
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BTW, you commented earlier that everyone ignored the thread. Just a thought for the future. If you have an issue you need help with it's better to put that in the title. "Help Lens won't focus" etc. I ignored the thread myself because it just sounded like and announcement of new ownership. I only looked at it because there were some responses and figured something must be going on here.
12-16-2007, 04:23 PM   #13
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Thanks for all the comments people. I've taken everything into consideration.

1) I have tried the lens in various situations. I am finding it hard to be satisfied with the image at all (preset - indicated on the lens) focal lengths + @f/2.8. Like i said before, i have tried at different aperatures, and this SEEMS to fix the problem, but if you think about it, it only seems so because it covers a deeper depth. The sample images you see above are taken with my flash. I have also tried take pictures with no flash (in tungsten light, outdoor natural light - same results)

2) I tried to compare the images with my other kit lenses (18-55 & 50-200). The result is, even these lenses produced better images, although their max aperature is 3.5/4 - not an exact comparison can be made, but generally i can see the difference. I have never had any focussing related problems before using this lens. So i think this eliminates issues with my focussing sensor in the body.

3)I bought this item from an ebay store in Japan - i contacted them and they are going to repair it. For future reference, i bought it from "matsuiyastore". They sent me the product, but the warranty and other documents (excluding instruction manual, box) was all in japanese. I can't send it to Tamron USA. Strang thing is, the bottom of the box says "UPC code for USA and CANADA ONLY", but everything inside is Japanese...
12-16-2007, 05:59 PM   #14
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For Your Interest, Here is another Set-up

This is a comparison between the new Tamron Lens and my DA 50-200

Last edited by Tingchaleun; 02-16-2008 at 03:25 PM.
12-16-2007, 06:00 PM   #15
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hmmm.. that's really hard to make out isn't it? the actual file is fairly large, so i had to cut it down by a lot. But anyway, the "black lines" you see across the loonie says "focus HERE" - which indicates where i had focused with my camera. You can see that with the DA 50-200, it was spot on, while with the tamron, it was definitely off. Each loonie is about an inch and a half away from the next loonie.

Last edited by Tingchaleun; 12-16-2007 at 08:12 PM.
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