Greetings,
I have a Canon EOS Rebel T5 which is in excellent condition. I mated it up with a recently acquired Sigma 70~300mm 1:4~5.6mm APO Macro Lens. Please bare with me because I am trying to describe my problem. The lens fits perfectly, no problem there. I should also mention that I have a Sunpak external flash, made exclusively for my T5. It also is in excellent condition. When practicing to learn how these two guys get along, I noticed something very peculiar. Here are my settings: 1/125s, F/4.0, ISO 100 and shooting in Manual Mode. I should mention that I have never had a problem with this flash, in fact I like it better than some of the speedlights that Canon offers.
Okay, at these settings, my photographs came out a little underexposed, again using the external flash. Now, here is the weird part. The more I shut down the lens, the more overexposed the photographs turned out. I increased the number for the f/stop setting all the way down to f/25 and again, grossly overexposed. Then I decided to increase the shutter speed to 1/800s, and left the other settings alone. When looking through the viewfinder, I noticed the shutter speed automatically adjusted itself to 1/200s and at this speed, the flash would not flash. I reset the shutter speed to 1/160s, the flash worked but the image was horrible. I then decided that perhaps I was too close to the subject and I then moved farther back. There was a little change, but nothing to write home about. The flash unit does have a diffuser which I did use and it turned out alright. The question is of course, why are the exposure settings changed prior to taking the photo? I can upload the photos here which will show the EXIF data. I do like the images I get with the Sigma lens. The auto-focus is very accurate, however it is slow so just a minor inconvenience. Thanks for the help. The batteries are all fully charged and I did clean all the contacts. Also, why are the lens settings working erroneously?
Tony
Last edited by Tonytee; 04-29-2018 at 08:44 PM.
Reason: Additional Information.