Sigma 17-50mm F2.8 lens issues

[haiti954]

Hello folks. I need help with the Sigma 17-50mm F2.8 lens which i bought 2 months ago. I bought it because i heard the light condition will not keep changing while recording videos, well that's not the case for me because my videos change from dark to bright or vice versa. I use Canon EOS 77D in manual mode but maybe i am not doing something right, can i get some help because i'm still learning those things about iso or exposure or aperture. Thank you

 

[USAFRet]

Hello folks. I need help with the Sigma 17-50mm F2.8 lens which i bought 2 months ago. I bought it because i heard the light condition will not keep changing while recording videos, well that's not the case for me because my videos change from dark to bright or vice versa. I use Canon EOS 77D in manual mode but maybe i am not doing something right, can i get some help because i'm still learning those things about iso or exposure or aperture. Thank you

Exposure Lock (AE) is what you're probably looking for.
http://learn.usa.canon.com/resources/articles/2011/autoexposure_ae_lock_article.shtml