Canon 500mm F4 L ii overexposing at narrower aperature settings

[steve_z]

Lens: Canon 500mm L ii

Problem statement:

I notice that if I shoot at f8 or higher fstop that the resultant picture is more and more overexposed by about one fstop for every fstop raised. I think that the aperture is not closing to narrower than about f5.6

What I have done to investigate:

1. I used both R5 and 80D and noticed the same issue

2. When looking down the lens while I use the Depth of Field Preview button, I notice that the aperture opening does not get narrower than what I see at f5.6 as I increase the fstop to f11, 16, 22. The opening is closed to about 1/4 inch around the opening. Occasionally, I saw the aperture close more (about every 5 to 10 times I pressed the DoF Preview button), but it was not consistent. I used the same camera settings on a different lens and saw the aperture closing more and more as I changed the fstop, so I don't think it is the camera settings.

3. I tried a series of shots in manual mode at constant ISO, evaluative metering with no exposure compensation. I varied the fstop f5.6, f8, f11, f16, f22. For each shot I set the shutter speed so the exposure meter was at zero. The histogram on the R5 showed exposure that was consistent with the exposure meter. What I saw when looking at the actual picture and associated histogram was that the exposure was overexposing for each fstop change. To measure this, I changed the shutter speed to create a picture that looked properly exposed and had a histogram that looked similar to the histogram before the picture was taken. In all cases, as the fstop went from f5.6 to 8, 11, 16, 22, that a shutter speed at the same as that at f5.6 had the picture in proper exposure.

Checking the EXIF showed the fstop that I requested. There was no indicator in the EXIF about the aperture being more open.

4. I tried spot metering, different ISO, and a different camera (an 80D in live view mode) as well. All behaved as noted in #3.

5. The lens contacts looked clean and there were no error messages, but I swiped them lightly with isopropyl alcohol swab to make sure they were clean. Results stayed as noted in #3.

6. I called Canon support to review these results, and they recommended sending in for repair of aperture but did not have an idea how much this might be.

So, couple of questions:

1. Does anyone think it could be something different than the physical lens aperture? If so, what tests could I do to determine this? 

2. Anyone have this happen to them and have insights into how much this might be to fix?

Thank you.

[Hazel_T]

Hi steve_z,

Since the same thing is happening with multiple cameras that does indicate there is an issue with the aperture diaphragm in the lens. Typically if it was an issue with one of the cameras or with settings it wouldn't be consistent on multiple camera bodies. We would recommend sending the lens in for repair.

The full estimate is not written until the technician has the lens in hand for inspection. Prior to sending it in we are able to let you know what the current labor rates (in August 2022) are to repair this lens model. The labor rates to repair the EF 500mm f/4L IS II USM lens are $179 for minor repairs, $269 for standard repairs, and $359 for major repairs. The full estimate will also have charges for tax and shipping.

The Canon U.S.A., Inc. online repair portal allows you to set up service in a few simple steps. The repair portal gives you the ability to set up service for multiple pieces of equipment at once, and to receive a repair estimate in the majority of cases, depending on your model and issue. The portal also allows you to upload images or videos that will assist us in repairing your product. You can also select how you wish to be notified of the progress of your repair. The portal's service history section allows you to view all services that have been performed on any of your camera or video products since January 7, 2020. 

Please follow the link below to access our online repair portal to arrange for service:

https://mycanon.usa.canon.com/signin

Instructions for Accessing and Using the Online Repair Portal

You will need to access or create your My Canon Account.

If you already have a My Canon Account and your product is already registered, simply click on the “Get Repair Services” link on the left menu and follow the onscreen instructions to arrange for service for your product.

If you have a My Canon Account and your product is not registered, you must register your product first. Click on the “Get Repair Services” link on the left menu, then click on the “Register Product” link on the right. After your product is registered, click on the “Get Repair Service” link on the left menu and follow the onscreen instructions to arrange for service for your product.

If you do not have a My Canon Account, you will need to create one. After you create your account, click on the “Add Product” link to register your first product. After your product is registered, click on the “Get Repair Service” link on the left menu and follow the onscreen instructions to arrange for service for your product. 

Once you have completed the repair request, you will have an opportunity to print a copy of the request for your records. This request form will also contain shipping instructions and an address label that you will attach to the outside of your shipping box when mailing your equipment for repair.

[wq9nsc]

A sticking aperture assembly is not that uncommon and it sounds like that is the issue.  Sometimes the issue will clear, at least temporarily, with exercise but given what you have done it has already been exercised so it is time for it to go in for repair.

Until the technician has the lens in hand, a firm estimate can't be provided because the problem could be the assembly blades sticking (most likely) but it could also be controller related.  And if the technician finds other issues then the service center would want to address those while the lens is apart.

If you aren't a member of CPS, you should seriously consider joining.  In addition to the other membership benefits there are also discounts on repairs.  I own several of the L series long primes from the 200 through the 800 and they get a CPS cleaning and checkup when needed.  I have found the service to always be excellent and well worth the price, particularly when you consider how much you pay for these Canon L series long primes.

Rodger

[ebiggs1]

" I called Canon support to review these results, and they recommended sending in for repair of aperture but did not have an idea how much this might be."

They will give you the cost before they do the work for your approval.

[steve_z · Accepted solution]

Thank you everyone. 500mm is in for repair - new aperture motor was needed.