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DPChallenge Forums >> Hardware and Software >> Tamron SP AF 28-75mm f/2.8 XR Di for Canon 20d
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Showing posts 1 - 16 of 16, (reverse)
AuthorThread
 05/01/2006 06:51:59 AM · #1
Hi all,

I just bought this lens on all the good reviews it has recieved. I was wondering if anyone had a good way of testing he lens to make sure it is good quality.

I did the brick wall test and looked at the photos at a 100% and 200% crop, but have nothing to compare them to. If anyone has these photos or any other way of testing the lens I would greatly appreciate the help

Thanks
Rich
 05/01/2006 07:05:00 AM · #2
I just ordered that same lens... should be in this week and I will shoot some comparisons with my kit lens. Since the Tamron is so much faster, it's kind of like comparing apples and oranges though.
 05/01/2006 07:30:50 AM · #3
I am having a hard time comparing this lens to my kit lens as they are not very similar at all. I was hoping someone could give me a single lens type of test that could help me decide if it is a dud or not. I was also hoping someone with the lens could give an idea where the lens is the sharpest and where it is not very good.

Thanks
Rich
 05/01/2006 07:37:47 AM · #4
I don't know about comparing it to other lenses like that but my husband has one and he swears by it. I know at least one other person who has one and swears by it as well. It is a good lens and I have heard that as far as image quality goes, it is not too far behind the Canon 24-70 2.8 L which costs a small fortune. If you go to fredmiranda.com and click on reviews and find the lens, sometimes posters post links to comparisons like that.

June
 05/01/2006 07:41:39 AM · #5
I tested mine by taking a shot of a newspaper taped to a wall at 28mm and 75mm so that it just filled the frame, using various aperatures. Nothing really scientific, but the were all sharp. I find its gets a bit sharper at about F5.6.
 05/01/2006 08:56:18 AM · #6
Cheeky,

When you look at the photos and say they are shap, what percentage of a crop are you look at them?

Thanks
Rich

05/01/2006 09:12:00 AM · #7
imatest. You can compare the scores with other peoples' copies. I have the results for my 28-75 on 20d around here somewhere if you want to compare.
 05/01/2006 09:41:07 AM · #8
To get a fair comparison you need another lens within (or close to) the Tamrons focal length of 28-75mm. A 50mm prime would be a good candidate, if you have one.

Then shoot the same subject at f2.8, f5, and 5.6 (you could do more, but its really a waste of time after f5.6, cause if you can't tell by then....) Once you're done, compare the shots and see how well the lenses match up.

All the shots from the same apertures should look VERY similar one another. Even if you a comparing a prime to a zoom. If they don't then there is likely a problem with the lens that looks worse.

If you don't have a similar lens with f2.8 available, then trying to compare yours using someone elses chart is rather silly, IMO. Just take some shots at f2.8 and see how the look. If you are unsure whether or not what you are seeing is any good, post some full-size crops and we'll tell ya.

05/01/2006 09:54:16 AM · #9
I find the results I get with my Tamron to be very nice and sharp, even wide open. You buy a f2.8 lens so you can shoot it at f2.8, right?

I don't shoot pictures of test patterns and newspapers, I leave that for the measurbators.
 05/01/2006 11:42:42 AM · #10
cresus,

I would really appreciate it if you sent me the comp files for this lens. I would like to know how mine compares with similar lenses.
Mcmurma,

I will post some good size crops for peoples opinions.

Thanks
 05/01/2006 11:48:17 AM · #11
i think the only way to really test for sharpness is to compair it to a prime lens you know is sharp. That being said i've not heard about quality control problems with this lens. Are your pictures looking sharp enough for you? If they are, don't worry about it.
 05/01/2006 12:09:14 PM · #12
Sorry for not getting back to you sooner thndrdrag, I usually look at 100% and 200% If you wanted to get a bit more sosphisticated you can download test sheets to take pictures of. I just had a look and I cant find the old one I did, no point really holding onto them.
 05/01/2006 01:09:51 PM · #13
Thanks all for your suggestions,Am I to understand this correctly then: If I have a 20-90 Kit lens I can test @ 50mm with an Apt. 5.6 on both lenses and should get similiae results?

Thanks
Rich
 05/01/2006 02:21:34 PM · #14
One thing you CAN test for effectively is focusing issues, like "backfocus". If you have a "bad" copy of the lens, it most likely has a backfocus issue. In other words, the focus is set at 36 inches but on examination you see that 33 inches away is the point of sharpest focus, whatever. You can test this by shooting a yardstick at an angle. Focus precisely on a number in the middle then blow the picture up and see where the actual sharpest point is.

That's a rough simplification, but such an approach will isolate focusing problems. Be sure you do it with the correct AF point selected, and do it also in MF. Focus issues in MF may be caused by the eyepiece adjustment on the camera, though. If the AF shot is on-focus, then you have a standard by which to adjust the eyepiece so MF matches.

R.
 05/02/2006 07:00:09 AM · #15
Hello all,

I took a bunch of test shots last night with my new lens. well after cursing at it for 15 minutes for lack of sharpness I remembered I was shooting in RAW format and needed to do the post processing. I would like to let you know I am happy with this lens except at 75mm where it seems to fall off a bit. But oveerall I am happy.

Thank you all for your help once again. For all your suggestions and ideas.

Rich
 05/02/2006 07:10:03 AM · #16
Anyone got any idea whether this lens is sharper or softer than the 50mm f/1.8?

That's another lens that is very cheap that you might want to consider comparing with.

I recently had some trouble with a focus issue on my lens and I am now a firm believer in testing lenses as Bear_music mentioned.
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