Difference in same focal lens picture quality

Hello, I want to ask, please what's the difference in picture quality between two lens of the same focal lens but at different apertures. For example, what's the difference in picture quality of a Canon 85mm f1.8 at f1.8 and a Canon 85mm f1.2 at f1.8. Are there any difference in picture quality even though they are of the same focal length and aperture and why?

To answer a question with a question: A Ruf modified sports car has a top speed of 200 MPH. A Mack dump-truck has a top speed of 83 (made up) MPH. Is there any difference in their cornering ability if both are traveling at 40 MPH?

Different products, made for different purposes, to different specifications.

Bassat's response has me scratching my head. Aside from 85/1.8 focusing faster and can handle moving subjects better, the purposes of both lenses are the same. The difference is who the market is for each lens.

To more directly answer the question - A discerning eye can pick out differences in the image:

• Typically, a lens wide open at its largest aperture will be a little soft. That said, the 85/1.8 is soft wide open and the 85L is sharper and f1.8. 85L is already sharp at f1.2, by the way. That's also due to the higher grade optics.
  
  
• The rendering of color may be a bit different, but you may not notice unless you compare side by side. I do find that my 85L gives me a more overall subjective feeling of punchier colors than my old 85/1.8.
  
  
• Also hard to notice is the difference in bokeh. The 85L has generally more pleasing and creamier bokeh at f1.8.
  
  
• I also remember more chromatic aberration from the 85/1.8. There is still some on the 85L, but less and in fewer situations.
  

Optically, no, no difference. Both same focal length and aperture with render identical results, however, as mentioned above, lens quality plays a huge roll in the final image and the f/1.2 is just a better all around lens designed differently so you may see quite a difference between the two lenses just because of the design of the lens. DOF and FOV might be the same but color, sharpness, bokeh, micro contrast, vignetting and such can be quite different.

SLRLounge's comparison. Scroll down for f1.8 comparisons.

https://www.slrlounge.​com/canon-85mm-prime/

They are the same... The difference is... Now THAT is funny.

The 85 1.8 is good for a start, but I soon got tired of the purple fringing.
The 85 1.2L is often used for full body shots at f1.2 for the 3D like pop and dreamy modelshoots.
The sky is the limit being able to go back to f1.2, this lens sucks light like any other lens, exept an old f1.0

Nathan wrote in post #18041420
SLRLounge's comparison. Scroll down for f1.8 comparisons.

https://www.slrlounge.​com/canon-85mm-prime/

TDPR has test carts as well to make this comparison. http://www.the-digital-picture.com …omp=0&FLIComp=0​&APIComp=0

OP, the differences will vary between all lenses, so I wouldn't draw results from a single pair of primes. It will also vary by aperture as you stop it down. Differences in aperture blades will cause different bokeha. There's no black and white answer here.

Back to the car analogy presented earlier in the thread, any two cars traveling at the same speed will get to the same destination at the same time. However, one may get you there in a lot more comfort, luxury, sport, or style.

I would like to upgrade my 85/1.8 but there is such a massive jump in price going to the 1.2 L II combined with the fact that the AF is much slower and I would definitely be throwing action at an 85mm lens that it doesn't make me want to make that jump. And now Tamron has the 85 VC which I darn near bought last trip to the local camera shop and Sigma has the 85 rumored out soon.

I really wish Canon would come to play in the more prosumer market. Discontinue the 85/1.8 and replace it with two lenses. Have one be a $250 85/2.0 nifty 85 kind of thing and then have a miny L for around $600-900. Give it IS and f/1.4-1.8 with L optics and fast focusing to compete with Tamron and Sigma. Canon offers two levels of L zooms in the f/4 and f/2.8 options, why not offer two levels of a prime in the under 200mm market?

FEChariot wrote in post #18041992
and then have a miny L for around $600-900. Give it IS and f/1.4-1.8 with L optics and fast focusing to compete with Tamron and Sigma. Canon offers two levels of L zooms in the f/4 and f/2.8 options, why not offer two levels of a prime in the under 200mm market?

I'd like a 85 f1.4 IS with L optics and fast focusing for $600 too.....

Good luck finding it.

Just 6 examples of 85mm lenses. Including the 70-200 2.8II they range from 8 lens elements to 23 and from no special elements to aspherical, low dispersion, fluorite elements. If using f2.8 for all 6 and the zoom at 85mm, you just have to expect some differences in image quality. I think image characteristics is more accurate as quality is subjective unless you just want to pick one specific characteristic, for example sharpness. Even then centre, mid and corner sharpness is usually measured so the top performer is again subjective.

EF 85mm f/1.8 USM
9 elements in 7 groups without any special elements

EF 85mm f/1.2L USM
8 elements in 7 groups including one ground and polished aspherical lens element.

EF 85mm f/1.2L II USM
upgraded anti-reflective lens coatings

Tamron SP 85mm f/1.8 Di VC USD
13 elements in 9 groups
The SP 85mm F/1.8 employs LD and XLD low dispersion glass elements to correct critical aberrations.

Sigma 85mm F1.4 EX DG HSM
11 elements in 8 groups
1 SLD glass element and 1 Aspherical element

EF 70-200mm f/2.8L IS II USM
23 elements in 19 groups (1 Fluorite and 5 UD elements)

delta0014 wrote in post #18042059
I'd like a 85 f1.4 IS with L optics and fast focusing for $600 too.....

Good luck finding it.

Well I was thinking the bottom part of the $600-900 range would make it more of a twin to the existing 35/2 IS and the upper end would be enough for L build similar to the 100L and then it would probably not be 1.4 and be 1.8.

Specs aside, if canon released a $600-900 upgrade to the 85/1.8, I'd be all over it.

Test results from photozone.de tests of lens on 20MPixel FF body:

Vignetting:
0.58% at f/2 with 85 f/1.2 vs. 1.73% at f/1.8 with 85 f/1.8

MTF rating:
at Center: 3604 line-pairs at f/2 with 85 f/1.2 vs. 3082 line-pairs at f/1.8 with 85 f/1.8
at Border: 2577 line-pairs at f/2 with 85 f/1.2 vs. 2916 line-pairs at f/1.8 with 85 f/1.8
at Extreme: 2581 line-pairs at f/2 with 85 f/1.2 vs. 2888 line-pairs at f/1.8 with 85 f/1.8

I thought the same too that's why I liked the post. Getting to the same destination at the same time can be related to the capturing the image and luxury and style can be linked to for example bokeh.

Great responses out here. Thanks everyone for your input