Lens Sharpness

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sooyeshun

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Hi recently I bought a lens for myself (2nd hand from gumtree). It 100% free from cosmetic damage. So I assume the previous owner is a careful owner.

It is Tamron 28-75mm f/2.8 DI LD ASP for my 450D
This is my 1st lens upgrade from my kit lens 18-55mm IS f3.5-5.6.
After shooting a bit. I cant find why the Tamron 28-75mm is rated sharper than my kit lens in slrgear.com
From everywhere I read on the internet, Tamron 28-75 is a very sharp lens.

How to compare both? I tried shooting both constant at 35mm with f3.5,4,5.6, 7.1, 8

I wonder how to determine who's sharper. They looks the same in terms of quality with my limited experience on sharpness.

Tamron with f2.8 open wide is very soft. By enlarging the image from my camera. I can it its very soft, details looks burry. I tend to shoot about f3.5 unless I'm struggle with indoor light, i'll use f2.8.

Any clue?
 
to test this, I'd whack it on a tripod and then in good light shoot at a scene across the street with house numbers in it..
or at a biscuit tin with words on it , specifically from my experience
then just change the aperture and shoot again
you should be able to see any improvement in sharpness
I found my tamron was pretty good but sharper at f4-6 than f2.8..which is to be expected
 
For most lenses the optimum sharpness is around 2 stops down from wide open. Try shooting at f 5.6 and see if it gives better performance. I'd also use a fairly high shutter speed, even on a tripod.

I would also use a subject that has lots of detail and contrast to ensure that the focus point is spot on
 
The 18-55 IS kit lens is very sharp! You could put it up against a £1000 lens and if you shoot at a mid-range f/number and check the centre of the image, it will be impossible to tell the difference.

With the Tamron you are paying for the f/2.8 aperture, which is a lot faster than your kit lens, and full frame coverage, which you don't need. Don't expect greater sharpness because you quite likely won't get it.
 
All these while i was told, i get what i paid for. a 18-55 IS is just about £100 +- .
So I decide to give it a try on Tamron 28-75mm f2.8 . I wanted faster lens with zoom. FOr portraits and body shoots. with nice bokeh effects.

Till now i still like my kit lens. =)
 
sooyeshun said:
All these while i was told, i get what i paid for. a 18-55 IS is just about £100 +- .
So I decide to give it a try on Tamron 28-75mm f2.8 . I wanted faster lens with zoom. FOr portraits and body shoots. with nice bokeh effects.

Till now i still like my kit lens. =)
Click to expand...

You do get what you pay for, if you consider the economics of what you're buying.

The Canon 18-55mm f/3.5-5.6 IS is cheap because it is a modest specification lens, economically constructed (which doesn't always means badly made) and sold in vast numbers by the world's biggest camera company. It is scale economies that really brings the cost down.

The Tamron 28-75mm f/2.8 is completely different, and much more ambitious. It is f/2.8 throughout, ie two stops larger than the kit lens at 55mm and beyond, which is four times brighter. This is very difficult optically, and quite often lenses that are just one stop brighter are double the cost (eg Canon 70-200 f/4 and f/2.8 zooms).

It is also covers full frame sensors, which are 2.5x larger than crop format, which is another large optical hurdle.

All in all, that's a lot to ask for the price and I'm not surprised it is a bit soft at f/2.8. In fact I would guess that the kit lens beats it just about everywhere, especially at 18mm ;) However, the Tamron is going to be better at f/2.8, at 75mm and on a full frame camera.

A lens that does this spec with less compromises is the Canon 24-70L 2.8, and is priced accordingly. Another lens that is similar to the kit zoom but with f/2.8 throughout is the Canon 17-55 2.8 IS, and that too is less compromised. But also expensive.

You do get what you pay for.
 
sooyeshun said:
So, beside the way Chappers mentioned to test both lens, is there any others?
Click to expand...

There are lots of ways to test lenses, for different reasons, but the best way by far in this instance is to shoot the same subject side by side with the two lenses. Identical subject and settings for each, then compare them directly together.

Shoot a distant target to reduce potential focusing errors, field curavature etc. Car number plate is good, road signs, street signs, shop front etc. Bold graphics with some fine detail is a good combination.

Use a fast shutter speed to eliminate camera shake, and increase ISO if you need to get that. If the light changes between shots it will wreck the comparison - bright sun makes things look sharper, over cast and it looks soft.

All lenses are best at mid-range f/numbers, in the centre of the image. And worst at lowest f/numbers in the corners.

Also look out for distortion and vignetting. Both lenses will have some of that.
 
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