Settle this bet please...

tofu_girl · 21st June 2005

Hi everyone, I'm hoping someone here can settle a bet for me.

So I'm over at my friend's apt and he's playing with my 50mm f1.8. After about 20 or so shots...he uploads them to his computer and we notice the pics taken at 1.8 to be a little soft. So we decided to take some test shots after I mentioned his hands always seem to be shaky when around me...(he didn't enjoy that too much

)

We took pictures of his crumpler bag with the focus centered right on the logo. Pics we're taken on a tripod with AF on. Full Sized pics shown below...

http://www.i-levelmedia.com/test/crumpler_1.8.JPG
http://www.i-levelmedia.com/test/crumpler_2.8.JPG

The pics to me seem to be what you'd expect...a little soft at 1.8 but much sharper at 2.8.

His contention is that the pictures are equally sharp but at a different focus point...basically saying the AF is a little off. So even though we centered focus on the logo, he seems to think the orange lining on the top right is in focus and equally sharp on both pics. I think he's full of crap personally...and can't admit being wrong.

What do you ppl think?

Also...how are other ppl's 50mm 1.8's out there? Should the picture we took be sharper at 1.8?

nightwolf75 · 21st June 2005

believe this question was asked numerous times b4, most recently last month. see http://forum.clubsnap.org/showthread...highlight=50mm

the ans - DOF.

eikin · 21st June 2005

can't view the 2.8 picture

EDIT: ok, can view now

tofu_girl · 21st June 2005

Originally Posted by nightwolf75

believe this question was asked numerous times b4, most recently last month. see http://forum.clubsnap.org/showthread...highlight=50mm

the ans - DOF.

I'm talking about a simple bet btw a friend and mine...how was this question answered numerous times before if it's subjected only toward my lens?

Obviously DOF is what causes the softness...but shouldn't the logo in focus be sharper than the orange lining above? Please read carefully before answering.

eikin · 21st June 2005

actually i don't quite understand the bet, so you're saying your friend has shaky hands?

anyway i use the 50mm as well, NW pointed out the answer, the DOF @1.8 is significantly lower than @2.8. i usually use the lens @2.2 though, which i feel gives me enough control of the DOF

eikin · 21st June 2005

Originally Posted by tofu_girl

I'm talking about a simple bet btw a friend and mine...how was this question answered numerous times before if it's subjected only toward my lens?

Obviously DOF is what causes the softness...but shouldn't the logo in focus be sharper than the orange lining above? Please read carefully before answering.

the logo is slightly bulging outwards, so if you focus at the centre of the logo, the orange lining (that happens to fall in the same plane as the centre of the logo) will of course be in focus as well.

tofu_girl · 21st June 2005

Originally Posted by eikin

actually i don't quite understand the bet, so you're saying your friend has shaky hands?

anyway i use the 50mm as well, NW pointed out the answer, the DOF @1.8 is significantly lower than @2.8. i usually use the lens @2.2 though, which i feel gives me enough control of the DOF

my friend is basically saying that my AF is not accurate since the logo (the part we aimed at) was softer than another part of the crumpler bag (lining above the logo).

tofu_girl · 21st June 2005

Originally Posted by eikin

the logo is slightly bulging outwards, so if you focus at the centre of the logo, the orange lining (that happens to fall in the same plane as the centre of the logo) will of course be in focus as well.

So your contention is that the logo and lining are equally sharp then...

nightwolf75 · 21st June 2005

Originally Posted by tofu_girl

I'm talking about a simple bet btw a friend and mine...how was this question answered numerous times before if it's subjected only toward my lens?

Obviously DOF is what causes the softness...but shouldn't the logo in focus be sharper than the orange lining above? Read carefully please before answering.

fyi - in case anyone dunno wat DOF means.
http://www.luminous-landscape.com/tu...ries/dof.shtml

actually, the pics are not a good comparison in terms of sharpness. its no fault of the lens. 1st pic is focused more likely at the bottom of the logo while the 2nd pic is focused more on the center. if u folks really wanna bet, mount on a tripod, use the center AF and shoot at the same point.

would be nice if u could show as the Exif data too.

btw, i did read ur post carefully. and, with all care and due consideration to ur question, i will respectfully answer that any comparisons of lens sharpness shld be done with more care to the setup and considerations to the technical specs of wat a lens can or cannot do, as eikin has kindly pointed out.

eikin · 21st June 2005

Originally Posted by tofu_girl

So your contention is that the logo and lining are equally sharp then...

the part of the logo that happens to fall in the same plane as the lining, the logo is not flat, somemore you are not shooting directly in front of the subject but at a tilted angle

nightpiper · 21st June 2005

its a lens thing. difficult & expensive to make a lens thats sharp corner to corner & max aperture & at the same time keep the lens to a small size (think canon 50mm F1.0). many big aperture lenses look a little soft when wide open. i dun think there's anything wrong with the pics.

some say the centre portion is best thats why consumer DSLRs have a smaller sensor to tap on the centre sweet spot. if u own a full frame DSLR, the softness is more obvious & corner softness is very evident.

tofu_girl · 21st June 2005

Originally Posted by nightwolf75

fyi - in case anyone dunno wat DOF means.
http://www.luminous-landscape.com/tu...ries/dof.shtml

actually, the pics are not a good comparison in terms of sharpness. its no fault of the lens. 1st pic is focused more likely at the bottom of the logo while the 2nd pic is focused more on the center. if u folks really wanna bet, mount on a tripod, use the center AF and shoot at the same point.

would be nice if u could show as the Exif data too.

btw, i did read ur post carefully. and, with all care and due consideration to ur question, i will respectfully answer that any comparisons of lens sharpness shld be done with more care to the setup and considerations to the technical specs of wat a lens can or cannot do, as eikin has kindly pointed out.

Well as I stated above...the pics WERE taken on a tripod. The picture taken at 2.8 was on AI Focus...the lens was then changed to MF so that no focal change was done before taking the 1.8 pic. And yes, center AF was used for the 2.8 picture.

eikin · 21st June 2005

Originally Posted by tofu_girl

my friend is basically saying that my AF is not accurate since the logo (the part we aimed at) was softer than another part of the crumpler bag (lining above the logo).

so is your friend saying that you can't focus correctly?

tofu_girl · 21st June 2005

Originally Posted by eikin

so is your friend saying that you can't focus correctly?

The AF on my 50mm f1.8 lens...by the way, my friend took the 2 pics above...

eikin · 21st June 2005

Originally Posted by tofu_girl

The AF on my 50mm f1.8 lens...

so your friend is saying that the lens can't focus correctly?

nightpiper · 21st June 2005

can i complicate the matter a bit more?

it cud be due to backfocus or frontfocus. steeping down the aperture increases the DOF so the F2.8 pic look sharper.

tofu_girl · 21st June 2005

all Exif information should be included with the jpg. But if you can't view it...what would you like to know?

denniskee · 21st June 2005

may i propose you do a focusing check (back, right on, front) on the lens before any comparison is made? esle i cant see the base line of this comparison.

Rocklance · 21st June 2005

I have no answers to offer, just want to add some observations:

- In both photos, the logo is indeed at the center (roughly near the left armpit of the guy).

- Composition of both photos are identical, neither the camera nor the bag moved. (To confirm, I superimposed one on the other and made the front one half transparent.)

- The photos were taken 14 seconds apart, not too likely that much has changed.

- To my naked eyes, the 2.8 is much brighter than the 1.8. Obviously the exposure time is different since the aperture is different (1/60 for the 2.8 and 1/160 for the 1.8), but it's still surprising to see such brightness difference. (Was the bag near a window such that the periodic dimming of the sun made a difference?)

- The 2.8 photo was obviously sharper at the center, you can even see bits of dust on the rubber logo. Such details were mostly lost on the 1.8. The other logo on the left (the zipper tab) is roughly on the same pane and similar sharpness/focus issue can be seen.

- The aperture is different, so DoF is different. But since focus is on the center spot, the logo there should be in focus and the rest may blur away due to DoF. Doesn't seem so in these shots.

By the way, a question, when AF is on the center spot, any idea how big this 'spot' is? Obviously it wouldn't be just one pixel. If it is big enough that it covers part of the cloth material, the camera may be focusing more on the cloth, which has a weaving pattern that's perhaps higher contrast. And if the intensity of the sunlight changes, it could confuse the camera.

Anyway, that would just explain these 2 test shots. Tofu_girl already observed softness at 1.8 before taking the test shots, so it seems more likely to be a lens characteristic (rather than sunlight, AF focusing, DoF etc.)?

freelancer · 21st June 2005

Originally Posted by tofu_girl

I'm hoping someone here can settle a bet for me.

[snip]

The pics to me seem to be what you'd expect...a little soft at 1.8 but much sharper at 2.8.

The Canon 50/1.8 is known to have some issues with the focus accuracy at F1.8. It is the way the lens AF motor system is designed. If you were to take 3 images at F1.8 in succession (tripod mounted, cable release), you will be amazed to find perhaps one or two image in good focus and another soft.

This is not just my observations. If you do a search at dpreview Canon Lens forum, there was a similar discussion I posted almost 2 years back and look at the response from one of the lens "guru" there on the subject

21st June 2005	#1
tofu_girl New Member Join Date: Jun 2005 Posts: 20	Settle this bet please... Hi everyone, I'm hoping someone here can settle a bet for me. So I'm over at my friend's apt and he's playing with my 50mm f1.8. After about 20 or so shots...he uploads them to his computer and we notice the pics taken at 1.8 to be a little soft. So we decided to take some test shots after I mentioned his hands always seem to be shaky when around me...(he didn't enjoy that too much ) We took pictures of his crumpler bag with the focus centered right on the logo. Pics we're taken on a tripod with AF on. Full Sized pics shown below... http://www.i-levelmedia.com/test/crumpler_1.8.JPG http://www.i-levelmedia.com/test/crumpler_2.8.JPG The pics to me seem to be what you'd expect...a little soft at 1.8 but much sharper at 2.8. His contention is that the pictures are equally sharp but at a different focus point...basically saying the AF is a little off. So even though we centered focus on the logo, he seems to think the orange lining on the top right is in focus and equally sharp on both pics. I think he's full of crap personally...and can't admit being wrong. What do you ppl think? Also...how are other ppl's 50mm 1.8's out there? Should the picture we took be sharper at 1.8?

21st June 2005	#2
nightwolf75 Moderator Join Date: Dec 2003 Location: in bet MORE diaper changes... Posts: 14,592	believe this question was asked numerous times b4, most recently last month. see http://forum.clubsnap.org/showthread...highlight=50mm the ans - DOF. __________________ When did ignorance become a point of view? - Dilbert budget AD/ROM shooter, anyone?

21st June 2005	#3
eikin Moderator Join Date: Apr 2004 Location: 東京 Tokyo Posts: 10,920	can't view the 2.8 picture EDIT: ok, can view now __________________ APAD

21st June 2005	#5
eikin Moderator Join Date: Apr 2004 Location: 東京 Tokyo Posts: 10,920	actually i don't quite understand the bet, so you're saying your friend has shaky hands? anyway i use the 50mm as well, NW pointed out the answer, the DOF @1.8 is significantly lower than @2.8. i usually use the lens @2.2 though, which i feel gives me enough control of the DOF __________________ APAD

21st June 2005	#17
tofu_girl New Member Join Date: Jun 2005 Posts: 20	all Exif information should be included with the jpg. But if you can't view it...what would you like to know? Last edited by tofu_girl; 21st June 2005 at 11:11 AM.

21st June 2005	#11
nightpiper Member Join Date: Oct 2003 Posts: 1,801	its a lens thing. difficult & expensive to make a lens thats sharp corner to corner & max aperture & at the same time keep the lens to a small size (think canon 50mm F1.0). many big aperture lenses look a little soft when wide open. i dun think there's anything wrong with the pics. some say the centre portion is best thats why consumer DSLRs have a smaller sensor to tap on the centre sweet spot. if u own a full frame DSLR, the softness is more obvious & corner softness is very evident.

21st June 2005	#16
nightpiper Member Join Date: Oct 2003 Posts: 1,801	can i complicate the matter a bit more? it cud be due to backfocus or frontfocus. steeping down the aperture increases the DOF so the F2.8 pic look sharper.

21st June 2005	#18
denniskee Senior Member Join Date: Oct 2003 Location: bukit batok Posts: 4,214	may i propose you do a focusing check (back, right on, front) on the lens before any comparison is made? esle i cant see the base line of this comparison. __________________ photography makes one sees things from all angles.

21st June 2005	#19
Rocklance New Member Join Date: Jun 2005 Posts: 16	I have no answers to offer, just want to add some observations: - In both photos, the logo is indeed at the center (roughly near the left armpit of the guy). - Composition of both photos are identical, neither the camera nor the bag moved. (To confirm, I superimposed one on the other and made the front one half transparent.) - The photos were taken 14 seconds apart, not too likely that much has changed. - To my naked eyes, the 2.8 is much brighter than the 1.8. Obviously the exposure time is different since the aperture is different (1/60 for the 2.8 and 1/160 for the 1.8), but it's still surprising to see such brightness difference. (Was the bag near a window such that the periodic dimming of the sun made a difference?) - The 2.8 photo was obviously sharper at the center, you can even see bits of dust on the rubber logo. Such details were mostly lost on the 1.8. The other logo on the left (the zipper tab) is roughly on the same pane and similar sharpness/focus issue can be seen. - The aperture is different, so DoF is different. But since focus is on the center spot, the logo there should be in focus and the rest may blur away due to DoF. Doesn't seem so in these shots. By the way, a question, when AF is on the center spot, any idea how big this 'spot' is? Obviously it wouldn't be just one pixel. If it is big enough that it covers part of the cloth material, the camera may be focusing more on the cloth, which has a weaving pattern that's perhaps higher contrast. And if the intensity of the sunlight changes, it could confuse the camera. Anyway, that would just explain these 2 test shots. Tofu_girl already observed softness at 1.8 before taking the test shots, so it seems more likely to be a lens characteristic (rather than sunlight, AF focusing, DoF etc.)?