Yes, Yair is correct.
I use this nifty calculator courtesy of Capture Integration to work out all my lens conversions.
http://www.captureintegration.com/2009/02/03/focal-length-equivalent-calculator/
I wish the answer was an absolute with only one "right" answer. But there are several nuances to consider.
Aspect Ratio Matters
First, our calculator only considers the diagonal of the frame (regardless of aspect ratio). Many of our clients don't like the 3:2 aspect ratio for vertical headshots and crop almost all of their 35mm dSLR headshots to 4:3. If you always crop to 4:3 your 85/1.2 is roughly a 135mm on a 36x48mm sensor (aka 1.1 crop MF) since the MF will capture 4:3 natively.
The X Factors
When selecting a mainstay portrait lens the focal length (relative to sensor size) is very important but it's not the
whole story. The working distance to the model (and it's impact on both you and the model), the draw, the ease/speed/accuracy of focusing, the max usable/sharp aperture, the out of focus rendering, and even the physical size of the lens (how heavy, emotional impact: intimidation or intimacy) all play a role in which lens is the best overall mainstay for you.
Lens Niches
It's also not the case that the lens manufacturers all seek the same priorities at the same equivalent focal lengths. The Canon 85/1.2 and the Phase One 120/4 AF Macro are not duplicates of each other. If anything the 150D/2.8 or 110LS/2.8 are closer to the 85L as far as intended use/market goes.
Biased By Limited Selection?
You love the 85L, but you selected it amongst lenses fairly spaced out (assuming you were choosing from amongst L series primes). The 50L was presumably too short and the 135L presumably too long, but if you were instead handed a 75mm, 80mm, 85mm, 90mm, and 95mm would you still have picked out exactly an 85mm?
You've concluded that 85mm is ideal, but maybe instead you should consider the equivalent of a 50L equivalent too wide and the equivalent of a 135L too long and be open to anything between those two.
Budget Matters
The
Phase One 150/2.8 D (approx. US$3.5k) is my favorite lens on any system. For some that lens falls well within their budget - for others it does not. If you are trying to stick to a tight budget you'll find many on the forum ready, willing, and able to help recommend legacy lenses like the Mamiya 150mm f/3.5 which are darn good but cost a fraction as much.
The [lens which is the closest mm equivalent] and the [lens which fits your budget] may or may not be the same thing.
Moral of the Story
So by all means use our calculator to get a sense of the numeric equivalency (that's why we made the calculator after all) but if possible, don't stop there. The numbers are important but there is no substitute for your own hands on experience actually taking pictures.
A better overall question might be "I shoot studio portraits with a 5DII and 85mm and love the results. Here are a few of my favorite portraits I've taken with this rig [insert a picture or two]. Here is what I love about them [insert reasons here]. I'm thinking of switching to a 36x48mm sensor and am considering X platform. My budget is around [insert budget]. Based on this information what lenses in those systems would you suggest I look at?"
Then take those responses and do anything you can to get the suggested lenses in your hands to see how they feel to you. Full disclosure: this is a very biased/self-interested suggestion to make since, as a dealer, we frequently set up such evaluation rentals for our customers across the country.
Phase One P40+ with 150mm at f/3.2
Doug Peterson
(e-mail Me)
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Head of Technical Services, Capture Integration
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