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Old Jul 13, 2018, 11:44 PM   #1
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Default Canon 85 mm?

I have a Canon Rebel T3i.

The lenses I have are these:

Sigma 10-20mm F4-5.6 EX DC
Sigma 17-50mm F2.8 EX DC OS
Sigma 18-200mm F3.5-6.3 DC OS


I just saw a very good deal on a Canon EF 85mm f/1.8 USM.

Would this be a good addition for portraits?

Update: The reviews I've read were kind of mixed: I read references to the T3i's sensor size. I believe that because of the sensor size, this will actually be like using a 135 mm.

Is it still a good choice for portraits?

Last edited by dg27; Jul 14, 2018 at 10:54 AM. Reason: clarification
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Old Jul 14, 2018, 1:21 PM   #2
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The Canon EF 85mm f/1.8 USM is sharp in the center, but the edges don't sharpen up until you stop down to f/4 or more. That makes it ok for portraiture, since sharpness in the edges and corners isn't important. It's also low in distortion, vignetting and chromatic aberration.

On a 'Full Frame' body, a good focal length for a portrait lens is from 85mm to 135mm in order to avoid the effects of perspective distortion. Your T3i has a 'crop factor' of 1.6X which gives a 85mm lens a '35mm equivalent' focal length of 136mm, which is close enough to the upper limit that it'll be fine.
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Old Jul 14, 2018, 2:39 PM   #3
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Is it used?
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Old Jul 14, 2018, 3:13 PM   #4
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Default Canon 85 mm?

Thanks, TCav,

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It's also low in distortion, vignetting and chromatic aberration.
I was worried about chromatic aberration in particular since I saw that mentioned in a review

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Your T3i has a 'crop factor' of 1.6X which gives a 85mm lens a '35mm equivalent' focal length of 136mm, which is close enough to the upper limit that it'll be fine.
Thanks. I wonder whether a 50 mm (X 1.6 = 80 mm) would be a better choice for portraits (that is the only thing I am getting this for). I can get a comparable 50 mm for slightly less than the cost of this.

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Is it used?
No--brand new, with a few filters thrown in.

Last edited by dg27; Jul 14, 2018 at 4:18 PM. Reason: correction
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Old Jul 14, 2018, 7:59 PM   #5
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No--brand new, with a few filters thrown in.
At best, the filters are probably worthless, and at worst, they may be damaging to your image quality. That's the case whenever they throw filters in for free.
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Old Jul 14, 2018, 11:36 PM   #6
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At best, the filters are probably worthless, and at worst, they may be damaging to your image quality. That's the case whenever they throw filters in for free.
Good point. I always buy my own aftermarket filters anyway. Thanks.

But what about 50 mm versus 85 mm?

With the 1.6 conversion would a 50 (= 80) be an OK choice for portraits?
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Old Jul 15, 2018, 6:17 AM   #7
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With the 1.6 conversion would a 50 (= 80) be an OK choice for portraits?
50mm is too short to avoid perspective distortion in typical head-and-shoulders portraits. This can result in a seemingly enlarged nose and compressed ears.

On the other hand, there are lots of different kinds of portraits, and whatever lens you use to take portraits is a portrait lens. A 50mm lens is fine for "environmental portraits", when you back away from the subject to include some of the environment in the composition.

Your Sigma 18-200 covers both 50mm and 85mm. Why don't you experiment with that for a while. Don't worry about achieving a shallow Depth of Field with a large aperture. Just set the lens for either 50mm or 85mm and see if you like the compositions you get.
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Old Jul 15, 2018, 8:56 AM   #8
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Default Canon 85 mm?

Thanks for all the very helpful info, TCav.

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Your Sigma 18-200 covers both 50mm and 85mm. Why don't you experiment with that for a while. Don't worry about achieving a shallow Depth of Field with a large aperture. Just set the lens for either 50mm or 85mm and see if you like the compositions you get.
That's the lens I normally use; I'll experiment with your suggestion.

(I just wondered whether I'd get better results with a fixed lens.)
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Old Jul 15, 2018, 4:52 PM   #9
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(I just wondered whether I'd get better results with a fixed lens.)
The Sigma 18-200 OS suffers from a lot of field curvature, so the edges and corners will be blurry at the maximum apertures of f/4.8 at 50mm and f/5.3 at 80mm. The Canon 85/1.8 is sharper in the edges and corners, but the larger aperture means the more shallow depth of field. If you'll be shooting in front of a backdrop, there won't be a lot of difference, but if you plan on using a real background, the 85/1.8 will let you determine how much blur you want it to have.
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Old Jul 15, 2018, 6:07 PM   #10
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Default Canon 85 mm?

Thanks, TCav. This is very helpful.
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