When the lens is not sharp


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shgfun

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Sep 19, 2007
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#1
I recently tried to test my lens sharpness, please see the post here:
http://forums.clubsnap.org/showthread.php?t=321903

It seems that my 50mm/f1.8 lens is not sharp wide open.

So here comes the question: when we buy lens at the shop we can't really do the sharpness testing (need a PC to view the 100% crop). So if we found out later at home after some tests that the lens is not sharp, is it possible to do exchange at the shop? Personally I thought it might not be possible here in Singapore. Then what do we do? Any ideas or experience?

Thanks for viewing and helping.
 

a.c.e

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Jul 27, 2007
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#2
did you try your lens at other aperture range? let's say f8.
ha, i always think that my 50 f1.4 not sharp untill i read some books, it say my lens will be sharp after f4.
 

ExplorerZ

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Jan 9, 2006
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#3
I recently tried to test my lens sharpness, please see the post here:
http://forums.clubsnap.org/showthread.php?t=321903

It seems that my 50mm/f1.8 lens is not sharp wide open.

So here comes the question: when we buy lens at the shop we can't really do the sharpness testing (need a PC to view the 100% crop). So if we found out later at home after some tests that the lens is not sharp, is it possible to do exchange at the shop? Personally I thought it might not be possible here in Singapore. Then what do we do? Any ideas or experience?

Thanks for viewing and helping.
1st of all, are you sure that your lens is not sharp is due to a bad copy (ie. mis-aligned elements) or due to the nature of the lens...
its pointless to exchange or even cherry pick a copy if the lens nature is soft wide open.
like what a.c.e have said, not all lens are naturally good wide open
 

Dream Merchant

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Staff member
Jan 11, 2007
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#4
I think some of the larger stores will usually offer a 1-for-1 exchange within 7 days if everything looks brand new (box not squsahed, lens not dirtied etc). Just ask before buying.

The thing about a lot of equipment is that there's nothing that can be labelled as 'perfect'. It's a matter of balanced compromises.

Also, I apologise in advance for 'rocking the boat' by what I am about to share.

I hate to say this, but don't expect miracles from the ef 50mm 1.8 MKII. It's a budget, entry-level lens. It's fun and easy to use and can be reasonably sharp and wonderful when stopped down. What I would call 'Cheap n Cheerful!', not particularly sophisticated, refined or eloquent.

If you want razor sharp from wide open, and the speed, and affordable price all combined, one way is to look at the old all metal and glass manual focus 50mm 1.7 or 1.8 lenses from brands like Zeiss or Olympus. I haven't tried other brands, so I can't comment. Again, a matter of balanced compromises. You loose AF and have to meter and shoot stopped down.

From my own non-scientific tests and what my eyes saw, my previous (cheap - I sold it here for $75. Typically, they go for around $180) OM 50mm 1.8 wide open at 1.8, right out to the extremes edges, whacked my $500+ ef 50mm 1.4 stopped down to 1.8! Having said that, if I didn't have the OM 50mm 1.8 to compare, the ef 50mm 1.4 wide open looks superbly sharp, and it is consistent across the apetures. My OM 135mm 3.5 wide open resolves more details than my ef100mm macro stopped down to 3.5.

Even some super expensive 50mms are a little soft wide open, especially the 1.4s or 1.2s, and that again is a balanced compromise. Those lenses were primarily designed to be light-gathering machines when used wide open. They are usually razor sharp stopped down a little. Macro lenses were designed to be razor sharp from wide open, but are slower.

However, there's absolutely no harm taking your lens down to CSC with your AF test charts you shot and having it checked or exchanged. BTW, all the charts seem to be shot at an angle, and not straight-on.

CHEERS!
 

shgfun

New Member
Sep 19, 2007
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#5
Thanks a.c.e. and ExplorerZ.

It certainly helped when I stopped down to 4.5, but was just wondering whether someone owns this lens did similar test.

Also trying to understand the common practice when someone indeed encounters a 'bad' copy.

P.S. Going through many sites, found this one, http://www.pbase.com/accl/ef50, seems that it is kind of soft wide open also. Maybe I should just drop this topic.
 

shgfun

New Member
Sep 19, 2007
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#6
Hello Dream Merchant,

Thanks for very detailed info, appreciated.

Regarding the angled shot, it was supposed to be around 45 deg, as I was trying to check if it is focusing correctly.
 

Dream Merchant

Moderator
Staff member
Jan 11, 2007
9,659
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#7
You're welcome shgfun.

I was referring to the left/right angle, not the elevated 45 deg angle. ;)

Anyways, try taking the lens down to CSC and 'wonder' aloud how a Canon prime lens can perform soo badly lor.
 

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