Canon 70-300 is f4/5.6 usm 60d blurry and soft photos

[Robodot]

I brought this up a few weeks back without any real solid answer so I thought i would provide one to anyone who might be interested in putting a full frame lens on a crop sensor camera like i did.

I independently came to a conclusion by testing further, this lens was only sharpest at 300mm with F9+. I recently found out that many, many, many people who own this lens came to the same exact conclusion. as I did.

So i dug a little more (trying to decide to keep Canon or go to another brand) this is what I discovered:

When you use a full frame lens (EF) on a crop sensor camera, not only do you multiply the crop factor for the focal length, you also must "multiply the aperture" by that crop factor.

So on my lens, instead of being a f4/5.6 as Canon states is really a F6.3 / F9.

what does this mean in the real world, you will not be able to separate the subject from the background or use in lower light levels without noise.

[Waddizzle]

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@Robodot wrote:

I brought this up a few weeks back without any real solid answer so I thought i would provide one to anyone who might be interested in putting a full frame lens on a crop sensor camera like i did.

I independently came to a conclusion by testing further, this lens was only sharpest at 300mm with F9+. I recently found out that many, many, many people who own this lens came to the same exact conclusion. as I did.

So i dug a little more (trying to decide to keep Canon or go to another brand) this is what I discovered:

When you use a full frame lens (EF) on a crop sensor camera, not only do you multiply the crop factor for the focal length, you also must "multiply the aperture" by that crop factor.

So on my lens, instead of being a f4/5.6 as Canon states is really a F6.3 / F9.

what does this mean in the real world, you will not be able to separate the subject from the background or use in lower light levels without noise.

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Uh, nope.  I do not think so.  

There is a very simple test to debunk that theory.  Put the lens on a full frame camera, adjust for proper exposure, and take a photo.  Now, put the lens on a APS-C body, dial in the same exposure, and take a photo.  Guess what happens?  Of course, both shots will be properly exposed.  If the aperture crop factor existed, the photo taken on the APS-C body should be underexposed.  But, it will not be.  

This rumor arises from a simple misunderstanding of physics.  Suppose light is falling on a full frame sensor with a given intensity.  Now suppose that same light intensity is falling on an APS-C sensor.  Guess what happens?  Of course, the smaller sensor will receive fewer photons than the full frame sensor, and the ratio of the difference will be the same as the ratio of their total surface areas, which just so happens to be the crop factor.

[ebiggs1]

"When you use a full frame lens (EF) on a crop sensor camera, not only do you multiply the crop factor for the focal length, you also must "multiply the aperture" by that crop factor."

Total nonsense!  Where do you people come up with this stuff? 

 Totally agree with, my friend, waddrizzle on this one.

"Uh, nope.  I do not think so.  

There is a very simple test to debunk that theory..."

However there is even an easier way to see it.  Place a sheet of letter size paper on the table, shine a light on a 6 1/2" circle drawn on that paper. Now draw a 4" inch (1.6 crop) circle on it. SHine the the light again.  Each circle was equally exposed. The light that falls outside of either circle is simply wasted. It effects neither exposure.

It always comes back to the fact that a lens is a lens is a lens and it is always the same lens.  It matters not which or what camera you use it on. A lens can not change its physical characteristics unless a mechanical modification is made. They are what they are.

[Robodot]

I like the word "Photons", has a nice ring to it.

[Waddizzle]

BTW, many consumer priced telephoto lenses are not their sharpest at minimum aperture.  

I have a Sigma 150-600mm “C”, which is a little soft at minimum aperture, but razor sharp at f/8.  But, I perform AFMA adjustments on it at minimum aperture because the DOF becomes too wide at narrower apertures like f/8 to make the test meaningful.

[ebiggs1]

"... is a little soft at minimum aperture, but razor sharp at f/8.  But, I perform AFMA adjustments on it ..."

One caveat, AFMA does not make a lens any sharper. It simply moves the critical focus point closer or farther from the film plane. Again, back to that fact a lens is what it is and it always will be. Unless mechanical mods are done, of course, goes without saying.

[Waddizzle]

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@ebiggs1 wrote:

"... is a little soft at minimum aperture, but razor sharp at f/8.  But, I perform AFMA adjustments on it ..."

One caveat, AFMA does not make a lens any sharper. It simply moves the critical focus point closer or farther from the film plane. Again, back to that fact a lens is what it is and it always will be. Unless mechanical mods are done, of course, goes without saying.

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There you go again.  It is time once again to take you to school, my friend.

Your caveat  that AFMA does not make a lens any sharper is correct, simply because that is not what AFMA does.  Your observation that “a lens is what it is .... unless mechanical mods are done,” is also correct.  It does go without saying.  

But, you consistently fail to connect the last dot, which I truly find quite baffling.  AFMA corrects the camera to the lens, not the lens to the camera.  You frequently tell people that Canon can do this calibration for you.  Why do you not understand that Canon has given the user the capability to do it himself.

It must be said that your negative comments and observations regarding AFMA totally ignore manufacturing tolerances.  Your conclusions are based upon the false assumption that every lens is identical.  Not every lens is identically.  

There will always be some slop in how well parts are machined.  When you combine several dozen parts, the cumulative error can be significant, which is another concept that you have demonstrated that you fully understand.

So, I ask.  What is the difference between lens variations due to manufacturing tolerances and making mechanical modifications to a lens?  Of course, there is no difference.  Every lens is ever so slightly different from its’ brothers in a very small way.

You also exhibit a failure to grasp the fundamental nature of how AF works.  Autofocus is not performed by the lens.  AF is a process controlled by the camera body, which makes a given set of assumptions on how the lens behaves.  A process control engineer might describe the camera/lens AF system as a PID control loop.

Sometimes, these baseline set of assumptions of lens performance is INCORRECT due to an accumulation of variations in manufacturing tolerances.  These variations can be corrected for by making an autofocus micro-adjustment, AFMA, iwhich are made n the camera, not the lens.

So, no, an AFMA does not make a lens any sharper.  It tunes the lens AF control loop in the camera.

[Waddizzle]

Oops, I forgot to connect the final dot!  As I said, AFMA is a tuning process in the camera, not the lens.  

Mirrorless cameras do not offer AFMA, because they do not need [it].  A mirrorless camera uses its’ image sensor for focusing.  It will focus on what the lens sees, which creates very sharp photos when you use a sharp lens.

A DSLR does not [normally] use the image sensor for focusing.  It uses a separate AF sensor for focusing.  Sometimes, there is a slight difference between what the AF sensor sees and what the image [sensor] sees.  The difference could be the camera body, which you could adjust for.  Most people adjust AFMA “per lens”, which allows them to correct for both camera and lens tolerances at the same time.

And, there you have it, the final dot.  AFMA does not make a lens sharper.  AFMA calibrates what the AF sensor sees with what the image sensor sees.  I do not know what is so hard to understand about that.

[ebiggs1]

"...AFMA is a tuning process in the camera, not the lens."

Thanx so much for confirming the fact AFMA does not make a lens any sharper although affirmation from you was not sought after nor desired. No matter how you try to spin it, that simple fact remains.  The lens is as sharp as it will ever be when it is constructed unless a physical or mechanical alteration is made.

[Waddizzle]

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@ebiggs1 wrote:

"...AFMA is a tuning process in the camera, not the lens."

Thanx so much for confirming the fact AFMA does not make a lens any sharper although affirmation from you was not sought after nor desired. No matter how you try to spin it, that simple fact remains. 

The lens is as sharp as it will ever be when it is constructed unless a physical or mechanical alteration is made.

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Thank-you, but you still do not understand AFMA.  No one believes AFMA makes lenses sharper, except for you.  Where you get this misplaced belief that everyone else does not understand AFMA is baffling coming from someone as experienced as you. 

“The lens is as sharp as it will ever be when it is constructed unless a physical or mechanical alteration is made.“

This statement is a declaration that you truly do not understand what AFMA does.  You are projecting that which you do not understand onto everyone else.  I just explained it, so there is no need to explain it again.  I had thought that i could help enlighten you about AFMA, but I see I was mistaken.