How sharp is tack sharp?


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shgfun

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Sep 19, 2007
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#1
Newbie here, never tested lens sharpness although bought two lens already.

I shot some thing printed out on a plain paper posted on the wall, and compared my two lens mounted on a tripod, close distance with an angle at f8, here are the results of 100% crop and no sharpening:

canon 50/f1.8 lens


tamron 18-250/f3.5-6.3 lens


It doesn't fit my idea of tack sharp, and I also don't see a big difference between the two. Did I get a bad copy of canon or good copy of tamron? Or did I do the test wrong?

Please advise.

Also when you purchase a lens, how do you test it on site for sharpness? If it is not sharp, say a bad copy, do you change it at the store or go to the custom service.

TIA.

Jiang
 

ykia

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Apr 23, 2005
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#2
Can't tell if the lens is "not sharp" or it's back/front focussing.

First download and print the focus test chart (http://www.dphotojournal.com/download-free-focus-test-chart/).

Put the chart in a well lit area (outdoors, near window, lights all on).

There are instructions on how to use and read the results in the PDF file.

Set your camera to AV mode and choose the lowest AV value (eg. F/1.8 or F/3.5) so the the DOF is very shallow.

Fire off 10 shots and repeat for the next lens.

Upload the pics to your PC and review it at 100%.

If it's spot on for most, then you can eliminate focussing issues.
 

Oct 21, 2007
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#3
ok i am still new to all this so can't comment on any lens or anything

but from my view i see the 'I' of the cannon one more blur than the one of the tamro
 

scenar

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Aug 23, 2005
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#4
your shutter speed is way tooo low. the EXIF for the 1st pic is 1/6s
it is difficult to obtain a sharp pic @ such low speeds except with mirror lockup and a steady tripod.

to test for sharpness u should be shooting @ much higher shutter speeds or with flash.

I did not check the EXIF for the 2nd pic, but i suspect that it is just as slow if not slower.

Get your photographic basics right first b4 obsessing over lens sharpness and equipment, which is the atmosphere perpetuated in many online forums and magazines
 

shgfun

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Sep 19, 2007
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#5
Can't tell if the lens is "not sharp" or it's back/front focussing.

First download and print the focus test chart (http://www.dphotojournal.com/download-free-focus-test-chart/).

Put the chart in a well lit area (outdoors, near window, lights all on).

There are instructions on how to use and read the results in the PDF file.

Set your camera to AV mode and choose the lowest AV value (eg. F/1.8 or F/3.5) so the the DOF is very shallow.

Fire off 10 shots and repeat for the next lens.

Upload the pics to your PC and review it at 100%.

If it's spot on for most, then you can eliminate focussing issues.
Thanks, ykia. I'll try that tomorrow with better lighting as scenar suggested.

ok i am still new to all this so can't comment on any lens or anything

but from my view i see the 'I' of the cannon one more blur than the one of the tamro
I was focusing on letter H, so this might due to some back or front focusing issues that ykia pointed out.

your shutter speed is way tooo low. the EXIF for the 1st pic is 1/6s
it is difficult to obtain a sharp pic @ such low speeds except with mirror lockup and a steady tripod.

to test for sharpness u should be shooting @ much higher shutter speeds or with flash.

I did not check the EXIF for the 2nd pic, but i suspect that it is just as slow if not slower.

Get your photographic basics right first b4 obsessing over lens sharpness and equipment, which is the atmosphere perpetuated in many online forums and magazines
Hello scenar, thanks for the tip. I did mount the camera on a tripod and used remote release. I'll try better lighting conditions to reduce the necessary exposure time for my next test. FYI, I am not so over obsessing over equipment, although we all want something good in general. :) I'm just trying to understand the sharpness issue, so I can be better prepared next time purchasing lens, as I have seen so often on reviews about some 'bad' copy lens.
 

cantaresg

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Feb 23, 2007
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#6
In any case, if you are testing for sharpness, you should mount your camera and lens on a tripod, use mirror lock and shutter release. This will prevent camera shake, so you can be sure that any blurness is due to backfocusing or lens not sharp.
 

shgfun

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Sep 19, 2007
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#7
Following ykia pointed out earlier, did the test on focusing first using the test sheet, under following conditions:

Used a tripod and remote release for this
manual exposure (still have trouble getting the paper really white)
test sheet printed out with my 'low-end' inkjet printer (may cause problem?)

here are the test examples of 100% crop:
Tamron:

Canon:


It seems that focusing is all right from 8-10 pictures taken with the two lens, not that far off. But at wide open of f/1.8 of my canon 50mm lens, it looks quite soft, it improves when I stop down to f4 as one would expect.

Is the softness with my lens wide open acceptable or did I have a bad copy? Please advise if you have done similar tests.

Thanks.

Jiang
 

SolBadGuy

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Nov 5, 2006
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#8
i dun own the canon 50mm 1.4, so i dunno how sharp it is supposed to be. however, most lenses are not "tack sharp" when wide open, although IQ may still be acceptable..
 

shgfun

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Sep 19, 2007
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#10
i dun own the canon 50mm 1.4, so i dunno how sharp it is supposed to be. however, most lenses are not "tack sharp" when wide open, although IQ may still be acceptable..
Hehe, I only have 50mm 1.8. And you are right about the statement.

Just wondering whether the IQ I posted above is in the normal range for a prime lens such as 50/1.8 with pretty good reputation.

You are comparing f1.8 vs f4.5, why not both set to the same setting. :dunno:
I was testing the focusing issue that is why I set max aperture. Below is a picture taken with canon 50mm with f4.5 also:
 

#11
I was testing the focusing issue that is why I set max aperture. Below is a picture taken with canon 50mm with f4.5 also:

Your canon 50mm is better/sharper than the tamron look at the right edge of the line top right down and notice the very slight purple color.

YMMV
 

shgfun

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Sep 19, 2007
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#12
Hello Longkangman, I agree on that. But then this is not such a fair comparison, as canon has stopped down a few stops, while tamron is shot at wide open (although 4.5 @ 50mm):(
 

#13
Hello Longkangman, I agree on that. But then this is not such a fair comparison, as canon has stopped down a few stops, while tamron is shot at wide open (although 4.5 @ 50mm):(
I assume you know what you are doing the test. :dunno:
The dist of both img is not the same. etc...

Thot the tamron one wide open is at f3.5 and f6.3 .
 

shgfun

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Sep 19, 2007
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#14
I assume you know what you are doing the test. :dunno:
The dist of both img is not the same. etc...
Actually I may NOT :embrass:

I was shooting around both lens closest focusing distance, the size difference maybe related to that and/or different magnification of the two lens (I mean they are not life size macro lens, it is possible to have diffrent magnification, right?)

Tamron goes to f4.5 max at 50mm, it is 3.5 at wide end.

Thanks for helping out.
 

ykia

Senior Member
Apr 23, 2005
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#15
One more thing shgfun : Do you have a filter attached to the lenses? Try removing them.

From the F/1.8 sample, looks like the 50mm is focussing a bit to the front, but even then the image is not "tack sharp". There might be a slight lens mis-alignment as the right looks sharper than the left, assuming you've got the setup correct.

Might want to go down to CSC to ask them to check. I think they may not charge for diagnosis.
 

shgfun

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Sep 19, 2007
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#16
One more thing shgfun : Do you have a filter attached to the lenses? Try removing them.

From the F/1.8 sample, looks like the 50mm is focussing a bit to the front, but even then the image is not "tack sharp". There might be a slight lens mis-alignment as the right looks sharper than the left, assuming you've got the setup correct.

Might want to go down to CSC to ask them to check. I think they may not charge for diagnosis.
No filters attached. I don't even have one for my 50mm actually.

It is probably a little bit front focus, but not much, at least according to the test sheet instruction suggest. Regarding right sharper then left, not sure I see that, but was it due to the right being closer to the center where I focus plus maybe somewhat small tilt etc.? Don't know.

So you do think the lens sharpness wide open is somewhat below par, I guess. Maybe I shall pay my first visit to CSC.
 

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