I just purchased a rebel t7. It has video capabilities and I there's not a whole lot in the book about doing videos. And I'm wondering how can I get it to so that I can take the video through the viewfinder. Doing the video using the screen doesn't help if it's sunny out cuz then I can't see what I'm trying to video. Also there is this diatric adjustment knob that the book says nothing about what it's supposed to do. Thank you
You won't be able to use the optical viewfinder when shooting video. Video mode requires the mirror to be in the locked-up position so the sensor can be continuously exposed to the image passing thru the lens. Other model cameras that use an electronic viewfinder will allow you to see your scene thru the viewfinder since they don't use a reflex mirror like a DSLR does.
Some cameras may allow you to add an accessory electronic viewfinder to the hot shoe, but I can't say for sure if you can do this with a Canon T7.
The dioptric adjustment is used to clearly focus what you see thru the viewfinder depending on your corrected or uncorrected vision. It's like focusing a pair of binoculars to obtain the best focus specifically for your eyes.
Thank you. Do you have any suggestions as to other cameras that use an electronic viewfinder for video?
Less expensive than a new camera, but not quite as convenient, would be a Hoodman Loupe.
Depending on where you bought the camera, and if you bought it as new, is it possible that you could return it in exchange for a different model?
I don't know if this would work satisfactorily for you but the T7 has a fixed LCD screen. A T7i or T8i (as well as a several other models) has a tilt-swivel LCD screen. I don't shoot a lot of video with my 60D but when shooting outdoors I can usually open the LCD to the side and swivel it to an angle that reduces glare from the screen.
You can even swivel it down flat and it can be used like a waist level viewfinder. I find it works especially well this way when shooting on a tripod at below eye level. It's also easier to use your hand or body to shade the LCD if needed when the light is coming from directly above you.