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


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.



I think Robodot creates his posts just so you two can argue.  Seems you are both saying the same thing.  BTW you both seem very knowledgeable and I do enjoy your posts.

@CaliforniaDream wrote:

I think Robodot creates his posts just so you two can argue.  Seems you are both saying the same thing.  BTW you both seem very knowledgeable and I do enjoy your posts.

We are saying the same thing, that being AFMA does not improve lens sharpness, but for very different reasons.  


I think AFMA is a good feature.  it can improve the AF performance of the overall camera/lens focusing system.  Not all lens and camera bodies are manufactured perfectly identical.  The AFMA allows you to compensate for the variations due to tolerances.


He admittedly does not bother with using AFMA.  He thinks everyone believes AFMA improves lens sharpness.  Since lens charpness cannot be improved, then AFMA is just something to make people feel better about the gear, and does not improve the focusing performance.


When he says that once a lens is manufactured, its’ sharpness cannot be improved.  I would beg to differ.  In the previous post, I briefly touched on the subject of a control loop.  


What is a control loop?  Think of thermostat on the wall that controls the heating furnace in a home.  You dial in a setpoint temperature.  The thermostat sends a signal to the furnace to ignite.  The furnace controls the mechanics involved in lighting the furnace.  It simply obeys the commands [Flame On] and [Flame Off].  


When the furnace ignites this starts a forced air fan system, which blows warm air throughout the house,  The wall thermostat on the wall reads this air temperature, which it uses to determine when turn off the flame when the proper temperature is reached.  Because nothing is perfect, the temperature will overshoot the mark a bit, and miss the setpoint.  


In theory, a cooling correction system could kick in, but most thermostats just shut down the furnace.  Smart thermostats collect data.  They look at the setpoint, how long the furnace ran, and how far actual temperature overshot the setpoint.  They use this data to compute the thermal momentum of the home, and will turn off the furnace a little sooner to reduce the amount of overshoot of the setpoint.

The control loop is formed by the thermostat input, the setpoint of the temperature controller, and the furnace providing heated air, which is detected by the thermostat.  The goal is set ambient air temperature in the house at the thermostat setpoint temperature.  Additional control loops are contained within the lens to control the focusing motors, which is done through firmware in the lens.


The camera and lens when combined form their own type of control loop.  Instead of a temperatare, the user dials in a focusing distance.  Instead of measuring temperature the the temperature controller is measuring focus.  Instead of lighting a furnace and controlling a fan, focusing motors are activated to move the focusing lens elements.  The goal is to set focus at a set distance from the camera.


The lens and camera each have a role in reaching the focus setpoint.  In the case of a home thermostat, it computes the thermal momentum of a home, and over the course of a couple days of heating cycles, it will be able to hold the temperature in the home at the setpoint, or in other words, achieve a temperature lock.


But, a thermostat only works with one house, while a camera works with multiple lenses.  The role of knowing the physical momentum and inertia of the focusing motors and lens elements falls on the lens.  The camera tells the lens forward or back, but the lens actually carries out the command.  


Some lenses are able to move focusing elements better than others.  Some lens focusing systems may get into a tug of war with the image stabilization system in the lens.  My Sigma 150-500mm was really bad at this.  I usually had to turn off the Optical Stabilization in the lens.  I sold it for the newer 150-600mm, which improved the OS tendency to fight when the lens refocused, but it still created soft images, most especially above 500mm focal lengths.


I could get sharper images with the 150-600 by manually focusing at an area where I knew my subjects would be i.e. I would focus at the first base bag, and wait for the play at first base.  I could even focus at 600mm and get razor sharp images, but I could net get them with the AF system in the camera.  Making an AFMA adjustment could not correct, but eventually Sigma did.  Sigma released new lens firmware, which had completely rewritten AF and OS algorithms.


EOS 6D2017_10_221791-2.jpg


That is how sharp my 150-600mm lens has become.  Here is a crop of the left side of the photo.


EOS 6D2017_10_221791.jpg


Shot with a 6D.  Pretty amazing, I think.

"The right mouse button is your friend."

"Robodot creates his posts just so you two can argue."


Not hardly. I do not consider wadrizzle a legitimate person to argue with. I basically ignore him or her. I simply tell it like it is.


AFMA is simply a procedure that allows the camera to correct for small errors with front or back focusing misalignment. Nothing more, nothing less. It does nothing to the lens at all. The lens is as sharp as it will ever be no matter how many thermostats you try to throw at it. The AF system in the camera can't alter the lens, but it can control what is happening behind the lens in the camera.  I.E. move the focal plane. However even this system is not perfect. DOF influences it and angle to subject does also. How fast, how open, a lens is, is another factor. Slow small aperture lenses do not benefit from AFMA as much as faster larger aperture lenses do. These conclusions come from years of actual photographic experience. When a person buys an expensive camera then becomes an overnight success, a keyboard jock if you will, they often fall to Internet conclusions.

EOS 1DX and 1D Mk IV and less lenses then before!

I would have to agree with ebiggs1 about what AFMA really does.  The way a lens focuses is a feed back loop, which has nothing to do with AFMA.  AFMA only changes the settings of that feed back loop.

"... but I see I was mistaken."


That is the first step to recovery. Admitting you have a problem.

EOS 1DX and 1D Mk IV and less lenses then before!

is that a f4 lens and are you using a crop sensor camera?


@Robodot wrote:

is that a f4 lens and are you using a crop sensor camera?

I take it that you are still not convinced that aperture crop factor does not exist?

Okay,  Do not take our word for it.  Go see for yourself.  Buy a light meter and read the instruction manual.  Or, you could go visit a leading manufacturer’s web site, like Sekonic, and download an instruction manual.  It does not matter which model.  You can go for one of the digital models, but the inexpensive analog meters are simpler to use, and really drive the point home.


Exposure can be looked at as a way to describe light intensity striking an object, or a surface.  A light meter measures the intensity of light falling on its sensor, and can display the measurement as a camera exposure setting, or as an Exposure Value, or both.


Back to the instruction manual.  You do not really need to read it cover to cover.  I just want you to notice something abut light meters.  A light meter does not care what type of camera you have.  There is no provision to enter a crop factor for aperture.  Look for it in the manual, if you want.  You will not find it, no matter which manual you read.


The meter does not care if you have a full frame digital sensor, or an APS-C digital sensor.  A meter does not care if you are using a digital camera, a 35mm film camera, or a medium format film or digital camera.  All of those cameras would use the same exposure settings when given identical shooting conditions.

"The right mouse button is your friend."

I am sure all of you are right, I am just trying to figure out why my lens is only sharp at 300mm at f9. when i purchased it Canon says it is a f4/5.6 which i thought was the aperture settings I could use, thats not the case.


That really limits what I can do with it. I went by the f stop rating on the lens figuring at 5.6 I would get clear and sharp photos at 300mm.


So in looking for answers I ran across this video by Tony.


it just happens his formula of including the crop factor into the aperture rating too works out to be f9, which is where this lens is sharp.

I think that video I saw had more to do with field of view and depth of field, I reckon.

here is the link to video from Tony explaining it better:
click here to view the gallery