Overexposure with increasing f stop

I have had a Tamron SP 150-600mm f/5.-6.3 di VC for several months and have loved it. I have used it with my Nikond500 with great results for all kind of nature shots. I typically shoot in manual mode, with iso on Auto, adjusting the exposure compensation as needed. In the past few days, if I try and shoot with the aperture over f11, the image is overexposed. As I INCREASE the aperture, it just gets brighter and brighter. I have had to decrease the exposure compensation to the most extreme (-5.0) and still overexposed. The shots are of my same yard, birds, etc. that I have done for a few years so I typically know what shutter speed, etc. to set my camera on. I even tried resetting my nikon D500 to factory settings in case I messed with something in error.

 

I did try my nikkor 70-300mm lens which I haven't used since getting the above lens and it does not do this but it is a much shorter lens.

 

Any idea other than my lens needs repair what might be going on? Thanks for any help.

Try the lens on another body and see if the same thing happens. Even a borrowed body will do, just to isolate the problem to the lens itself. I'd first suspect an errant setting in the camera controls for this type problem, or possibly an incompatibility between the older spec Tamron lens and the newer D500. Best option is to try it on several camera bodies and make sure the problem occurs consistently before assuming it is the lens. You might also check the Tamron website to see if there is a software upgrade for that lens to assure compatibility with the D500.

 

FYI: I own that lens and it works flawlessly on my D7100 and D5100, though it is currently in the shop due to the internal AF mechanism having failed.

If you could clarify a couple of points, that would be helpful:

In the past few days, if I try and shoot with the aperture over f11, the image is overexposed.

Do you mean, “if I try and shoot with the aperture setting at f/13; f/14; f/16; f/18 . . .etc., the image is overexposed.”

 

As I INCREASE the aperture, it just gets brighter and brighter.

Do you mean, “as I move the aperture smaller, from f/11 through to f/16, it just gets brighter and brighter.”

 

***

 

In any case, as well as trying the Tamron Lens on another camera, another test to do is set your camera with your Tamron Lens pointed at a wall where there will be no light variation – either open shade or direct sunlight on it.

 

Use Matrix metering; Manual camera mode; Zero Exposure Compensation; and set the ISO MANUALLY to a setting which allows the Camera’s TTL meter to indicate a “correct exposure” of near f/8 @ 1/400s.

 

Then make series of images of same area of the wall, MANUALLY adjusting ONLY the Aperture and Shutter Speed in a series of exposures as per:

 

f/5.6 @ 1/800s

f/8 @ 1/400s

f/11 @ 1/200s

f/16 @ 1/100s

f/22 @ 1/50s

f/32 @ 1/25s

 

You can make images using the intermediate Apertures and Shutter Speeds, if you like.

 

This test will determine to an extent beyond some reasonable doubt, that the Lens’s Aperture/Iris are working correctly – if all the images appear to have the same exposure.

 

WW

Assuming that the original post is being read right, and the image becomes brighter when the aperture is closed down, I suspect that this might happen if the camera is set on an automated mode (which would include manual mode with auto ISO), if the lens has a sticky aperture. The camera's meter will presume that the lens will stop down, and expose accordingly.

 

One thing to try might be to set the camera in fully manual mode, with Auto ISO off, and set the meter to expose correctly with the lens wide open. Now stop it down, changing nothing else, and see if it changes (including depth of field). If the lens is working correctly stopping down should result in visible underexposure. If it stays the same I'd suspect the diaphragm of not working.

The D500 has a depth of field preview button. You should be able to verify in a general way if the diaphragm is working as intended. remove the lens cap and point the back of the camera towards a light, well-lit object. Turn the camera on and put it in "A" mode. while looking through the objective lens, move the diaphragm through its full range in steps using the command dial. After each click turn, activate the preview button and observe if the diaphragm has changed size. You should be able to see it move through its entire range.(You must release and re-press the preview button each time you change the aperture setting.) Note, this is only a gross check of operability, but it will give quick feedback as to whether or not the camera and lens are connected and communicating.

If you could clarify a couple of points, that would be helpful:

Do you mean, “if I try and shoot with the aperture setting at f/13; f/14; f/16; f/18 . . .etc., the image is overexposed.”

 

Do you mean, “as I move the aperture smaller, from f/11 through to f/16, it just gets brighter and brighter.”

 

***

 

In any case, as well as trying the Tamron Lens on another camera, another test to do is set your camera with your Tamron Lens pointed at a wall where there will be no light variation – either open shade or direct sunlight on it.

 

Use Matrix metering; Manual camera mode; Zero Exposure Compensation; and set the ISO MANUALLY to a setting which allows the Camera’s TTL meter to indicate a “correct exposure” of near f/8 @ 1/400s.

 

Then make series of images of same area of the wall, MANUALLY adjusting ONLY the Aperture and Shutter Speed in a series of exposures as per:

 

f/5.6 @ 1/800s

f/8 @ 1/400s

f/11 @ 1/200s

f/16 @ 1/100s

f/22 @ 1/50s

f/32 @ 1/25s

 

You can make images using the intermediate Apertures and Shutter Speeds, if you like.

 

This test will determine to an extent beyond some reasonable doubt, that the Lens’s Aperture/Iris are working correctly – if all the images appear to have the same exposure.

 

WW

I hope this posts at the right place as first time posting on this site. Thanks for all your help! In trying the above things, I found that the diaphragm was not working. In trying the series of exposures that William Michael recommended, as well as per Matthew Curie. They didn' t have the same exposure at all. Also, when I put it on "A" mode, I noticed regardless of what f stop I chose, the shutter speed didn't change. I did remember to try the recommendation of using a different body and tried it on my d5000. Yep, same thing happened. Tamron said it was under warranty of course, and "replaced the aperture apparatus" and it should be in my hands today. Those were all great tests I now know to use in the future....I couldn't figure out what to turn off or leave automatic to isolate the problem. (And, I did actually have a firmware update for Nikon I had no idea about. So I appreciate that info even though it didn't fix this issue.)

Good!

Glad that the problem has been identified and I expect that you are excited about getting you lens returned in full working order.

Go make some nice photos.

 

WW