# Best way to test gear (notably lenses)?



## Mitch.Conner (Aug 21, 2014)

So I just read this post. Wow. That sounds terrible. I realize that you can get bad copies of lenses, but I had never heard of FoCal until that thread.

I own a 5D3, the included kit 24-105, and I just ordered a 24-70 f/2.8 II IS. Before that I used an S95, and before that a Konica Minolta 5D (although I still use this occasionally even today). I've never tested any gear aside from just taking photos with it.

Do most people use some type of test to see if their gear is up to spec? If so, what's the best way to do it (preferably that doesn't break the bank)?


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## davidcampbellphotography (Aug 21, 2014)

A cheap way to test your lenses is to use a book shelf and compare images subjectively.

-Make sure all the books in the shelf are level, an easy way to do this is to get a long steel ruler, place it against the bookshelf frame, then pull the books forward against the ruler.
- Set up your camera/tripod to that for each focal length (zoom or different prime lenses) have the same field of view. 
-Use a remote to minimise vibrations of you touching the camera.
- Use Liveview with the 10x (or highest magnification setting) to manually focus on the book in the center of the frame. If you do not use liveview, you should manually focus the lens and leave it on manual focus.
- Start with the widest aperture (e.g. f2.8). This will give you the narrowest depth of field and give you an idea if your lens has field curvature at the corners. Some lenses will appear soft in the corners, this is not necessarily due to lens sharpness but the focal plane is actually a curved plane.
-Take shots through the aperture range, don't change the focus. You want to understand the change to any field curvature. As you stop down, your depth of field will increase and your corners will become sharper both due to field curvature and also lens aberration will be improved. I recommend either using aperture priority to maintain the same exposure, or use manual mode and adjust the shutter speed to maintain the same exposure when you stop down.
-Repeat for each focal length.
-Import the files into your RAW converter
-If you have a grey card in the shot, correct the white balance.
-Now this may be controversial, but myself and my photography mentor, believe it is better to apply optimal capture sharpening in the RAW converter to correct for the anti-aliasing filter of the camera. This is particularly important when comparing different camera systems with different AA filters and sensor resolutions. Now many people will say that you should not apply any sharpening and compare all images as unsharpened, but this is not real world practice. After all, you don't leave your nice photos you take unsharpened. I think this way of thinking has come about by many online lens test reviews where the person has not optimally sharpened the RAW file and has over done it. Sharpening is a skill that takes a lot of practice and a good eye to get it right, but once you have YOUR sharpening workflow figured out, you should be able to consistently apply it to any image. Of course this comes down to practice and experience. Let the flame war begin! (To those people that disagree, that is fine, you can adjust the method to suit how you feel about it).
-I reccomend you rename the files to include the lens, focal length and aperture setting e.g. 24-70f2-8_24mm_f2-8
-One you have all the images, it is just a matter of comparing them side by side.

The advantage of the books is that they generally have very good printing of the text on the spine, particularly if they have dust covers rather than a textured hard cover.

Another trick you can do, is check the RAW file size in windows explorer or the mac equivalent (finder? not a mac user, but you will work it out). You will notice that if the lighting and exposure is the same for all shots, the file size will be different. This is because the sharper/more in focus shots will have more high frequency information that translates to a larger file size. This will give you a fast way to find the optimum aperture for that sensor resolution as it file will have the most data and remove some of the subjective element. It will also let you see where your diffraction limit is as the file size should drop off as you stop down too much.
This technique is used by astrophotographers to find the sharpest focus image or best tracking for their equatorial mount out of a bunch of test shots.

Now the only issue this method will have is that some lenses may perform better at different focus distances. E.g. infinity vs minimum focus distance. But it is a good start and you will learn a lot in the process with out spending any money. Just your time.

If you are able to pick an area of your bookshelf that you have read everything, you might be able to leave it set up for when you buy another lens in the future.

Happy lens testing. Hope my method helps.

David


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## neuroanatomist (Aug 21, 2014)

From the guys who's livelihood depends on it...

http://www.lensrentals.com/blog/2010/11/how-to-test-a-lens


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## ifp (Aug 21, 2014)

This one is another good read.

http://www.lensrentals.com/blog/2014/02/setting-up-an-optical-testing-station


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## Mitch.Conner (Aug 23, 2014)

Thanks guys. I'll read the articles by LensRentals.

As for the method posted above, davidcampbellphotography - why should I sharpen the images when testing a lens? Why wouldn't it be better to leave the images as is for comparison?

Also, I'm a little lost on that method. What would I be comparing my images against to know if the lens is performing as it should be?


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## Mt Spokane Photography (Aug 23, 2014)

Testing lenses is a minefield.

First of all, they usually focus differently at different distances, testing at a distance of 50X focal length usually, but not always works best. Its a good idea to test at three or more different distances to see if its a serious issue.

If you can use some flat surface like a brick wall, and make certain you are perpendicular to it, the results can reveal some things like a decentered lens element. The image will be out of focus on one edge while the opposite edge is sharp. Rotate the camera and if the oof edge follows the rotation, you have found a issue. Using star charts can find the issue as well.

I like and use FoCal, but it requires a careful setup, and paying attention to factors that affect your results. Its good to understand those factors that affect the AF system since they apply to normal shooting.

As others have noted, Lens Rentals tests all of their lenses as they come back into stock, and they have learned to make adjustments to many of them. They keep teasing a service for individuals who want their lens tested. However, they are not going to adjust a lens, just test it.

I think that their business is growing so fast that they will not have the capacity to do this.

Canon has a superb facility, and the software to detect lens issues and fix them, but its time consuming and expensive. They do not give you before and after results, and only adjust a lens to be in spec, they do not adjust it to be as good as possible. Some lenses will never be extremely sharp due to the glass manufacturing tolerances, so some are better than others. This is a result of the state of the art. The tolerances involver are far beyond the capability of direct measuring equipment, so indirect methods must be used, and, in the final analysis, the expensive big whites have lens groups selected and graded to get a near perfect match.

Then, there is the lens mounts, which can bend slightly, and the body. Sensors must be adjusted to align perfectly with a lens mount, and be the correct distance away.

I happened across a factory service manual for my old 5D classic, it has the methods and specs for aligning the critical items in the body. Shims are used to tweak things.


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## Mitch.Conner (Aug 23, 2014)

Mt Spokane Photography said:


> Testing lenses is a minefield.
> 
> First of all, they usually focus differently at different distances, testing at a distance of 50X focal length usually, but not always works best. Its a good idea to test at three or more different distances to see if its a serious issue.
> 
> ...



I don't have a brick wall, but I do have a brick patio. I think my camera mount would let me flip it to be perpendicular to the floor. Would that work?

What is an "oof edge"? Was that meant to be "roof"?

I realize some lenses aren't the sharpest. I don't expect my EF 24-105 f/4L IS USM to be the sharpest lens, but I'd like to know that it's doing what it's supposed to do. 

To be honest, I'm much much more concerned about the new Canon EF 70-200 f/2.8L IS USM that I have coming my way.

If it wasn't for the ridiculous bargain that the 24-105 was buying it through the kit, I'd sell it. The 70-200 I expect some real sharpness from.

I've seen this chart used repeatedly online. Would it help me with this task, and is it worth $225?

The 70-200 is just the first lens. I'm waiting until Photokina to make further buying decisions. I waited to buy the lenses for my 5d3 because supposedly this year was going to be the year of the lens and I figured I could take the time to get acquainted with my new camera.


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## Valvebounce (Aug 23, 2014)

Hi Mitch. 
OOF edge is an out of focus edge, basically meaning a lens with an off centre element would be sharper from the centre to one edge and less sharp from the centre to the other edge (or top to bottom). 

Cheers, Graham.


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## Mitch.Conner (Aug 23, 2014)

Valvebounce said:


> Hi Mitch.
> OOF edge is an out of focus edge, basically meaning a lens with an off centre element would be sharper from the centre to one edge and less sharp from the centre to the other edge (or top to bottom).
> 
> Cheers, Graham.



You beat me to editing my post this morning. Out of nowhere, when I woke up a few minutes ago it hit me, OOF = Out Of Focus. How embarrassing!

Thanks though.


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