I currently have a Canon Rebel T7. I’m wanting to upgrade my lens to help gain better quality photos for my photography business im starting up as a side. I’ve heard good things about the “Canon - RF 35mm F1.8 Macro IS STM Macro Lens for EOS R” However I know i don’t have that camera. Is there an adapter I could buy to get this lens, if so could someone help me pick when one I am supposed to get or another lens for portraits for my camera. Thank you in advance!
The answer is no -- the RF lens mount has a short flange distance, and RF lenses can not be adapted to long-flange cameras like EF or EF-S. You can read more about this here, if you're interested: https://moonblink.info/MudLake/gear/lenses
For your camera, you should be looking for EF-S lenses, since it's an EF-S camera; but EF lenses will also fit and work well. EF-M and RF will not work.
As for what lens to pick, there are plenty of options. But for portraits I think most folk would pick a longer focal length than 35mm. With a lens that wide, to fill the frame with a face shot, you are going to have to be very close to your subject, and they're going to look like a clown. 50, 75 or 85mm might be more appropriate. But since zooms these days are pretty good, why not go for versatility and get a zoom? That way you can set your camera-subject distance to what it needs to be and still shoot different framings.
As Atticus wisely said, you can't use an RF lens won a DSLR, also to echo his comment, I would recommend the versatility of a zoom. If you can afford it the EF-S 17-55 IS STM is a brilliant lens as it has a constant aperture of f/2.8. Another would be the Ef-S 15-85mm IS USM lens, which has been called 'the secret L lens' for it great quality. Finally, if you are looking at zooms, the EF-S 18-135 IS STM or USM lens is a good kit lens, so it is not expensive, highly versatile with good optics.
If you want to stick to a fixed focal length lens, the the 'Nifty Fifty' 10mm 1.8 STM lens is going to be a good possibility - sharp and cheap. On your crop sensor T6, the field of view will be reduced by the sensor, making the result look like an 80mm lens took the image, which is a good focal length for portraits. Finally, the EF-S 60mm f/2.8 macro lens is great for closeups, but also a great portrait lens, and on your camera its FoV will seem like that of a 100mm lens, again a great portrait range.
Lot's of lens choices. As to the focal length, it depends on distance to subject. The reason we pick a slightly longer FL is to keep a reasonable distance from the subject so as not to be right in their face. Given the same AOV any lens will yield the same perspective. It only become the "clown" look when that AOV can not be achieved. This is usually do to a wall in the studio where further distance to subject is impossible. A 35mm lens on a T7 gives what most would call a normal looking FL or close to what the human eye sees. On a full frame format camera this is generally considered to be the 50mm lens.
So what FL works best for a T7, probably something in the 50mm FL range. The EF-S 17-55mm f/2.8 IS USM Lens is a great choice. Any FL beyond 55m is going to be as much as a challenge as to little FL and I would avoid it. The old tried and true EF 50mm f/1.8 STM Lens another good choice. The key here is choose something in, or close to, 50mm FL range.
" I’m wanting to upgrade my ... photography business im starting up as a side."
As important as gear, perhaps even more important, is your ability to edit your shots. If you are truly interested in doing this you need to get and learn Photoshop. That's period!
Also I would include a plan to upgrade your T7 as soon as possible. The oblivious choice there is the new R series cameras. I am not saying you need to go out and do that tomorrow but maybe after a few jobs are in the books. You should be able to know if it is go or not.
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