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Author Topic: optimum aperture for my 3 Canon lenses  (Read 4250 times)

Philmar

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optimum aperture for my 3 Canon lenses
« on: July 08, 2010, 01:47:20 pm »

I have 3 Canon lenses and am interested in finding out what the optimum aperture is for sharpness.

I know lenses are weakest when wide open and also when stopped down (due to diffraction). I fully understand that aperture has an effect on DOF. But supposing one were not concerned about DOF i.e. when taking shots of a painting or a wall (straight on) and it was guaranteed to fall in to any of the aperturesí DOF. Which aperture gives most sharpness? or does it depend on subject distance?

I own a 24-70 L, a 10-22 EFS and a 70-200 L IS. What are the sweet spot apertures for these?
If it is relevant, I shoot with a cropped sensor 30D.

Is there a website where this has been tested and results chronicled? A handy table? a rule of thumb? a collection of old wive's tales?

And YES, I know Google is my friend but it doesn't seem to be liking me today. In fact my first google search pointed me towards a Ken Rockwell link. I've been reading review after review for these individual lenses but no joy.....

ErikKaffehr

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« Reply #1 on: July 08, 2010, 02:14:08 pm »

Hi,

In general I would say that most lenses perform best at f/8. Center can often be slightly better at f/5.6.

Here are some lens test sites:

http://www.photozone.de
http://www.slrgear.com
http://www.dxomark.com/index.php/en/Lens-w.../Compare-lenses

Note: Photozone tests compensate for field curvature.

Best regards
Erik


Quote from: Philmar
I have 3 Canon lenses and am interested in finding out what the optimum aperture is for sharpness.

I know lenses are weakest when wide open and also when stopped down (due to diffraction). I fully understand that aperture has an effect on DOF. But supposing one were not concerned about DOF i.e. when taking shots of a painting or a wall (straight on) and it was guaranteed to fall in to any of the aperturesí DOF. Which aperture gives most sharpness? or does it depend on subject distance?

I own a 24-70 L, a 10-22 EFS and a 70-200 L IS. What are the sweet spot apertures for these?
If it is relevant, I shoot with a cropped sensor 30D.

Is there a website where this has been tested and results chronicled? A handy table? a rule of thumb? a collection of old wive's tales?

And YES, I know Google is my friend but it doesn't seem to be liking me today. In fact my first google search pointed me towards a Ken Rockwell link. I've been reading review after review for these individual lenses but no joy.....
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Erik Kaffehr
 

Greg D

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« Reply #2 on: July 08, 2010, 02:15:02 pm »

Quote from: Philmar
I have 3 Canon lenses and am interested in finding out what the optimum aperture is for sharpness.

I know lenses are weakest when wide open and also when stopped down (due to diffraction). I fully understand that aperture has an effect on DOF. But supposing one were not concerned about DOF i.e. when taking shots of a painting or a wall (straight on) and it was guaranteed to fall in to any of the aperturesí DOF. Which aperture gives most sharpness? or does it depend on subject distance?

I own a 24-70 L, a 10-22 EFS and a 70-200 L IS. What are the sweet spot apertures for these?
If it is relevant, I shoot with a cropped sensor 30D.

Is there a website where this has been tested and results chronicled? A handy table? a rule of thumb? a collection of old wive's tales?

And YES, I know Google is my friend but it doesn't seem to be liking me today. In fact my first google search pointed me towards a Ken Rockwell link. I've been reading review after review for these individual lenses but no joy.....

Just test it yourself.  I answered this question for my lenses by taping a dollar bill to the wall, levelling the camera on a tripod, and shooting at apertures from wide open to about f16 over a range of focal lengths and at several different focus distances, then looking at the results on screen.  Pretty much answers the question, at least for closer focus distances, and it's easy enough to test the same way in the field for longer distances.
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Philmar

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optimum aperture for my 3 Canon lenses
« Reply #3 on: July 08, 2010, 05:20:18 pm »

Philmar

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optimum aperture for my 3 Canon lenses
« Reply #4 on: July 08, 2010, 05:47:35 pm »

Quote from: grog13
Just test it yourself.  I answered this question for my lenses by taping a dollar bill to the wall, levelling the camera on a tripod, and shooting at apertures from wide open to about f16 over a range of focal lengths and at several different focus distances, then looking at the results on screen.  Pretty much answers the question, at least for closer focus distances, and it's easy enough to test the same way in the field for longer distances.

Yes, of course. Personally I am a photo-hobby/enthusiast not a professional looking to create for-publication prints or wall hangings for clients.
Probably testing is the best solution. I asked here because in my photographic journey I am just learning about diffraction and how this makes lenses weaker at the smaller aperatures. So before I launch myself in to a 3 hour experiment I thought a few minutes on the ol'internet might garner time saving answers.

maybe a few examples will explain why i am asking.

For example the other day I saw an interesting pattern in my citiy's office towers. When I took this snap I choose the shutter speed of 1/320 (using the reciprocity rule) because I calculated it was the minimum shutter speed I could work with shooting at 200 mm on a crop sensor 30D.

This resulted in the largest DOF (my intention) but may have resulted in a f-stop where defraction caused a loss in sharpness. Now if I had known what the sweet spot was for the lens I might still have had sufficient DOF and had a sharper photo.

Likewise, when I encountered this shot I realised DOF wouldn't be an issue even if shot at 200 mm with the 70-200

or this shot taken at 70mm with the 24-70

So my think at that time was to shoot wide open at the max f 4 and f2.8 respectively so as to minimize possible camera shake. I didn't know that lenses were not as sharp wide open. If I'd known the lens' sweet spot then i could have selected that aperture (assuming it didn't invite problems due to camera shake).

I am just exploring ideas that, though new to me, have probably been part of the pros' mental calulations. If I can avoid a controlled testing of my lenses, then all the better.

feppe

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optimum aperture for my 3 Canon lenses
« Reply #5 on: July 08, 2010, 05:57:35 pm »

Doing your own tests is well worth the effort. When I finally did mine, I understood the limitations of my lenses much better.

Quote from: Philmar
For example the other day I saw an interesting pattern in my citiy's office towers. When I took this snap I choose the shutter speed of 1/320 (using the reciprocity rule) because I calculated it was the minimum shutter speed I could work with shooting at 200 mm on a crop sensor 30D.

If you're referring to the rule for handheld shutter speed of 1/[FF equivalent focal length], it's too loose for digital cameras and pixel peeping, and easily gives blurred shots - so that might be one reason you didn't get sharp shots. I recommend faster shutter speed, and/or taking multiple shots and picking the sharpest.

tokengirl

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« Reply #6 on: July 08, 2010, 06:03:07 pm »

If you are seeking the best possible answer for your particular three lenses, then self-testing is the way to go.

However, I think it would be a shame if you started obsessing over it.  Your Flickr site is terrific, you have a great eye.  THAT is what matters, not whether your lens is microscopically sharper at f8 than at f5.6.  I say use the aperture that gets you the depth of field that you want in the image and bugger the rest.  Seriously.
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Philmar

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optimum aperture for my 3 Canon lenses
« Reply #7 on: July 08, 2010, 06:07:05 pm »

Quote from: feppe
Doing your own tests is well worth the effort. When I finally did mine, I understood the limitations of my lenses much better.
He he he - you guys really are gonna grind this lazy bugger in to doing these tests aren't ya    

Quote from: feppe
If you're referring to the rule for handheld shutter speed of 1/[FF equivalent focal length], it's too loose for digital cameras and pixel peeping, and easily gives blurred shots
Yes that's what i was refering to. I assumed if you took the aperture and multiplied by 1.6 (the crop factor) that the reciprocity rule would still apply to crop DSLRs.  

i'm not saying that i get blurred shots. i'm saying that in certain instances that if I had known of the sweet spot that i could have taken shots that were sharper since in a few instances I chose to shoot wide open or with max DOF when the sweet spot would have been more appropriate. But you do raise the point that it may be camera shake rather than diffraction at play in those instances.
Thanks!!
« Last Edit: July 08, 2010, 06:09:07 pm by Philmar »
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feppe

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« Reply #8 on: July 08, 2010, 06:13:09 pm »

Quote from: Philmar
Yes that's what i was refering to. I assumed if you took the aperture and multiplied by 1.6 (the crop factor) that the reciprocity rule would still apply to crop DSLRs.

It does, but we have much higher requirements for sharpness than in the film days the rule was created due to 100% pixel peeping and larger prints - and people are likely more critical as well.

Schewe

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optimum aperture for my 3 Canon lenses
« Reply #9 on: July 08, 2010, 07:12:45 pm »

Quote from: Philmar
I have 3 Canon lenses and am interested in finding out what the optimum aperture is for sharpness.

Most lenses are optimal stopped down 2-3 stops from wide open.
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Ed Blagden

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« Reply #10 on: July 09, 2010, 02:58:50 am »

Quote from: tokengirl
If you are seeking the best possible answer for your particular three lenses, then self-testing is the way to go.

However, I think it would be a shame if you started obsessing over it.  Your Flickr site is terrific, you have a great eye.  THAT is what matters, not whether your lens is microscopically sharper at f8 than at f5.6.  I say use the aperture that gets you the depth of field that you want in the image and bugger the rest.  Seriously.
+1 To that.

Yes, for all lenses there will be an optimal aperture, but you will only see the difference between the optimal aperture and others if you are shooting on a good heavy tripod, using Mirror Lock-Up, with a cable release or self timer.  For hand-held shooting the effects of small camera vibrations, even if you are using the 1/focal length x 1.6 rule, will be much greater on sharpness than the lens performance at this or that aperture.

Remember, Aperture is mainly a creative tool to increase or decrease the depth of the focal plane, and you should use it that way.  If you want a faster shutter speed then just crank up the ISO.  As you said earlier you are not looking to make publication prints or wall hangings.  If all you are doing is posting to the web and making small-ish prints then don't sweat it.  

Ed
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Philmar

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optimum aperture for my 3 Canon lenses
« Reply #11 on: July 09, 2010, 11:41:07 am »

OK - thanks everyone for talking me down off of the pixelpeeping ledge!!
I don't really have to do the tests since it looks like they are available online. I can compare lenses and test charts here:

http://www.the-digital-picture.com/...ensC...=0&Lens=404

Yeah I guess you're right. This really only is noticable at a pixel peeking level so I'll sweat the big stuff instead. And from now on when I am confronted with shots where the DOF is not an issue (like the ones above) I will now stop down a few stop from wide open (assuming camera shake doesn't become an issue). And I'll be more leery of the rule of reciprocity for DSLR.

Thanks for the important context, everyone!!

Greg D

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« Reply #12 on: July 09, 2010, 01:12:38 pm »

Quote from: Philmar
OK - thanks everyone for talking me down off of the pixelpeeping ledge!!
I don't really have to do the tests since it looks like they are available online. I can compare lenses and test charts here:

http://www.the-digital-picture.com/...ensC...=0&Lens=404

Yeah I guess you're right. This really only is noticable at a pixel peeking level so I'll sweat the big stuff instead. And from now on when I am confronted with shots where the DOF is not an issue (like the ones above) I will now stop down a few stop from wide open (assuming camera shake doesn't become an issue). And I'll be more leery of the rule of reciprocity for DSLR.

Thanks for the important context, everyone!!

By the way, I think the shots you posted are great.  Whether they're tack-sharp or not, they're very interesting photos.

-Greg
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