What does IQ means?

[KenRC51]

CA = chromatic aberation, PP = purple fringe.... they are the same things. It's where the highlight meets the dark area and you see purple bands.

What does it do and why is it important? How do you test for this? Sorry or so many questions. I find that people in the forum are really quick in response and friendly

Btw, this tamron 17-50 f/2.8 is my second copy. My first and second copy was bought from Samy Camera. The first copy I think I got a displayed copy (the salesmen told me it was new). I looked new but have a few finger print on the front and back of the lens. Also the lens hood did not fit, it was a lens hood for another lens. I was not happy with this, so I took it back to Samy Camera for a exchange. The customer services was good, they exchanged it with no hassle and questions asked.

Once I got the second copy of the lens I tried it on my D90 and found out that the second lens (the new one) focus a lot quicker and a little bit more quitter. I do some times wonder if I still have a bad copy. How do I test my lens to see if it is a bad copy? Since I am a newbie I do not know what to look for and know something is wrong by look at the pic or the sound of the lens. Can some of you more experienced photographer tell me how? thanks

[K1W1]

CA generally shows up as a purple edge between areas where there is a big difference in contrast. The edge of a branch against the sky is one example where it often shows.

Good lens show no or almost no CA. Bad lens show lots of CA and ordinary lens show CA under certain circumstances that can always be recreated (same f stop and subject for example)

The good news is that most modern post processing software has controls to remove or at least minimise CA. Also newer cameras such as the D300 (not sure about the D90) also automatically handle CA and remove it as they they are processing the image so you no longer see it as often in your shots.

[tim11]

A lens with finger marks and mismatched caps can't be new. Very likely it's the demonstration version which should be classified as used. The Tamron 17-50 is very good generally.

Here is a sample of CA or PP. You see it clearly when viewing an image 100%.


I did my own test recently because I suspect the lens is faulty because I couldn't get the sharpness I am used to; since the images I had from that faulty lens were soft and blurry mainly. I put the camera on a tripod and did a few shots in this thread.. As I said, I read a few reviews and if my lens behave in similar characteristics as expected in the reviews then I accept it's a good lens.

[KenRC51]

A lens with finger marks and mismatched caps can't be new. Very likely it's the demonstration version which should be classified as used. The Tamron 17-50 is very good generally.

Here is a sample of CA or PP. You see it clearly when viewing an image 100%.


I did my own test recently because I suspect the lens is faulty because I couldn't get the sharpness I am used to; since the images I had from that faulty lens were soft and blurry mainly. I put the camera on a tripod and did a few shots in this thread.. As I said, I read a few reviews and if my lens behave in similar characteristics as expected in the reviews then I accept it's a good lens.

Oh I see what you mean. I have not seen any of my pictures looking like this. So you think I should put my camer with the new lens on a tripod to take a pic and then crop it 100% to see if the picture is still clear?

[tim11]

I only did the tripod tests because I had reasons to suspect the fault. Looking hard for evil then you will see evils. All lenses have some CA in similar circumstance unless yours isn't consistent with reviews which should only be used as a guide.

[fionndruinne]

IQ is totally subjective. At different points in your journey as a photographer you will have various standards as to what classifies as "good" IQ, and that's perfectly natural. Judge whether your current glass is satisfactory, and work from there. There's no need to get hung up on IQ unless you are yourself certain you ought to be.

[KenRC51]

How do I test for distortion? Do all lens have distortion?

[GoneTomorrow]

Oh I see what you mean. I have not seen any of my pictures looking like this. So you think I should put my camer with the new lens on a tripod to take a pic and then crop it 100% to see if the picture is still clear?

A good test for CA/PP is to take the same kind of shot Tim posted: areas of extreme contrast, like the leaves here against a white overcast sky. They're also more prevalent at wider angles and in the corners.

How do I test for distortion? Do all lens have distortion?

Two kinds of distortion: barrel and perspective. Barrel is when straight lines (buildings, picture frames, etc.) are curved by the lens, and perspective is when objects are "stretched" in a sense and warped. Perspective distortion is only a problem for really wide angles < 20mm or so.

Example of perspective distortion. This shot is at 10mm, notice the wall clock:

[tim11]

Ken, What are you doing to yourself?
You approach photography from the wrong angle. Yes all lenses have distortions to some extend with some less than others, depending on designs. And there are different kinds of distortion.
If there is a reason for you to suspect your copy is bad then by any mean test it. If you notice half the image is blurry or can't get sharpness then test it. Otherwise, just enjoy taking the photos; don't get too paranoid with a possible bad lens that you have no reason to believe anyway.

[jcon]

I agree completely with Tim.