Is 85mm really ideal for portraits?

Discussion in 'Beyond the Basics' started by adamhiram, Sep 28, 2020.

  1. Quassaw

    Quassaw TPF Noob!

    Joined:
    Aug 25, 2020
    Messages:
    22
    Likes Received:
    10
    Location:
    Manchester
    Can others edit my Photos:
    Photos NOT OK to edit
    The distance from the focal point to the image plane is known as (indeed, defined as) as the 'focal length'. If the object is at infinity then a 50mm lens will focus on the image plane at 50mm from its optical centre. Nothing at all to do with a camera. 1/v +1/u = 1/f and all that. A 50mm lens is a 50mm lens - nothing more, nothing less. Cast an image from a 50mm on to a wall, and you'll get exactly the same image from a lens designed for a m4/3 camera, a crop-sensor camera, a 'full-frame' camera, a 120 camera - indeed any camera, or a 50mm magnifying glass, a 50mm enlarger lens. Some lenses will vignette more than others, but that's nothing at all to do with the focal length of the lens.

    You need to understand that the 'distortion' (the 'big nose' or 'flat features' effect) has got nothing at all to do with the focal length of the lens, it's entirely due to the distance between the optical centre of the lens (or, near enough, the camera) and the model. Using a bigger or smaller sensor/film, or shorter/longer lens has no effect on the distortion PROVIDED THE DISTANCE BETWEEN THE MODEL AND THE CAMERA DOES NOT CHANGE. Of course, with a 4x5 camera you'll get the frame filled differently than a crop-sensor camera, but that's a different consideration. A 120 film camera usually had a 'standard' lens of 75mm or so, a 35mm SLR would have a 50mm as standard, and an APS would have a 35mm lens as standard, because all three would fill the frame to a similar amount, so you'd tend to stand the same distance from the model to take the same shot - but it's the distance that determines the perspective, not the length of the lens. If you still don't understand, try drawing some ray diagrams.


     
  2. Soocom1

    Soocom1 Been spending a lot of time on here!

    Joined:
    Feb 27, 2006
    Messages:
    2,868
    Likes Received:
    1,237
    Can others edit my Photos:
    Photos NOT OK to edit

    Couple of things here.

    1: The registration distance is the distance from the mounting of the back of the lens to the image plain. The focal distance is the distance from the image plain to the focal point.
    50mm is 50 mm is 50mm regardless of lens or camera.

    2: The IMAGE CIRCLE also contains a sweet spot where there is least amount of distortion. The closer the focal distance the smaller the sweet spot and thus that sweet spot translates to a smaller area on the subject that can be described as non-or least distorted. This is a simple optical fact.

    3: The registration distance is designed to allow for a full image circle. Thus the further away from the image plane the larger the circle. Again a simple matter of physics here. This also translates to a smaller or larger sweet spot based on the image size vs. focal distance. (Think full frame vs. APS). Or as I have done a great deal of shots with...
    Med. Format lenses on APS C and H sensors. The end result is a highly undistorted image with very wide angle lenses allowing for extremely shallow depth of field and a helluva lot of light.

    Try it some time.

    But go ahead and put a 50mm mirrorless on a SLR or a 50mm SLR lens on a mirrorless without an adapter.

    have fun!
     
  3. Quassaw

    Quassaw TPF Noob!

    Joined:
    Aug 25, 2020
    Messages:
    22
    Likes Received:
    10
    Location:
    Manchester
    Can others edit my Photos:
    Photos NOT OK to edit
    I'm glad you agree with me. But the registration distance is not really to do with the size of the image circle - Nikon APS and FF SLRs have the same registration distance - most (but not all) DX lenses have a smaller image circle than is needed for FX, but with the same registration distance! Mirrorless cameras have a shorter registration distance because there is no need for a mirror box. Crudely, Nikon could make a lens for a Z6 by taking a D850 lens and gluing a bit of aluminium to it, and it would work exactly as it did on the D850. Indeed, that what the FTZ is - a hollow aluminium tube with some electrical contacts. Fitting a native Z6 lens on to a D850 is just as easy in theory - all you need is a hacksaw. However, one big advantage of the mirrorless with its short register distance is that short focal-length lenses don't need as many compromises inherent in retrofocus designs. But yes, I could remove the mirror box from a D850 with a hacksaw and make a Z6 lens work on it - but it seems a rather expensive project.

    But enough of theory - can it be done? Yes. I make very crude lenses, and my single-element 72mm lens works on ALL of my (IL) cameras - NEX, Z6, D5100, Petri - completely ignorant of which camera it was designed for (because in reality it's a magnifying glass and a variety of Pringles tubes).

    And if you want a really, really simple proof of what I say, make a pinhole, put it on a camera, and take a picture. Add some extension tubes, and take the same picture. The 'focal length' will have changed, but the two pictures will have exactly the same perspective, albeit that the first one will show a bit more of the image.
     
  4. Soocom1

    Soocom1 Been spending a lot of time on here!

    Joined:
    Feb 27, 2006
    Messages:
    2,868
    Likes Received:
    1,237
    Can others edit my Photos:
    Photos NOT OK to edit
    which is WHY they are called CROPPED sensors.


    OK...
    I can place a magnifying glass on a camera and make it work..
    That's not the point.

    The dynamics of lens construction and camera design has specific advantages.
    the reg. distance is based again on the image circle aspect. There are adapters to fit 35mm lenses on Med. Format mirrorless. It can create an image circle and work, but in most aspects has no infinity.

    But the aspect here is back to the OP.
    The portrait lens of 85mm in this argument is based on 35mm camera design. (mirrorless or not.)

    85mm has specific design aspects that make it more favorable (as pointed out in another post) mostly to european and Western tastes.
    This includes typ. (though not always) a larger and faster lens, a narrower FoVV and less distortion int he sweet spot but allowing for a larger amount of light.

    Original 85mm lenses from the 1960's have smaller elements and in some cases not as a dynamic range effect. this is why they are preferred. it makes for a nice compromise.

    Having discovered the 135mm by accident in the 1980's I came to find the overall image quality heads and tails above a standard 50 or even 58mm (Rokkor lens) that I had inherited from the ol' man.

    The problem there is the distance needed to make a clean image. More distance, narrower FoV and a smaller sweet spot translated to a good portrait but alot of lighting adjustments.

    Again, why I prefer Med. Format.
     
  5. Rickbb

    Rickbb No longer a newbie, moving up!

    Joined:
    Jul 31, 2020
    Messages:
    190
    Likes Received:
    106
    Location:
    Central North Carolina USA
    Can others edit my Photos:
    Photos NOT OK to edit
    Back in my film days I’d shoot bust shots, (waist up), with a 105 or a zoom at about 120. It looked better and let me get back far enough to make the sitter more at ease.

    I’m pretty much the same on my crop sensor D90, zoomed out to get some distance and flatten the perspective a bit. It just looks better, IMHO.
     
  6. adamhiram

    adamhiram No longer a newbie, moving up!

    Joined:
    Feb 6, 2015
    Messages:
    679
    Likes Received:
    429
    Can others edit my Photos:
    Photos OK to edit
    This totally makes sense, and I'm a little embarrassed this wasn't obvious to me from the start. Of course two photos taken from the same distance with the same lens will have the same perspective; the crop sensor will just be a cropped image. It actually feels silly even typing this.
     
  7. adamhiram

    adamhiram No longer a newbie, moving up!

    Joined:
    Feb 6, 2015
    Messages:
    679
    Likes Received:
    429
    Can others edit my Photos:
    Photos OK to edit
    These are excellent points, which were echoed in some of the reading I did prior to typing this post. I guess I've gotten so used to the 135mm look (or rather the perspective it gives when standing at the appropriate distance to fill the frame), so the full frame 85mm perspective looked a bit different to me. It makes sense that the perspective from 12' away would different than 6-8'.

    I also didn't think of the cultural preference aspect of it, which is absolutely something important to consider. You also made an excellent point about the subject appearing in a way that is familiar to them. I presume that applies to portraiture in general - we typically see people from 6-8' away, so seeing their image flattened from a more distant perspective might not be as familiar or pleasing. Thanks for sharing!
     
    • Like Like x 1
  8. adamhiram

    adamhiram No longer a newbie, moving up!

    Joined:
    Feb 6, 2015
    Messages:
    679
    Likes Received:
    429
    Can others edit my Photos:
    Photos OK to edit
    I am still very interested in trying out 105mm or 135mm on a full frame body. I've become accustomed to that perspective, and I've gotten used to shooting from that distance using 85mm on a crop sensor, so that's not a big deal either. The catch is there are no native Z-mount options other than a 70-200, and nothing on Nikon's roadmap. I am curious how I would like shooting with Sigma's F-mount lenses in this range, although they are quite large and heavy, especially the 105mm. As I mentioned in my original post, the visual of this monster lens on a small mirrorless body is a bit comical, and I'm not sure it's something I'd want to carry around all day, but for studio work or on a tripod it seems quite usable. Definitely some food for thought!
     
  9. JBPhotog

    JBPhotog No longer a newbie, moving up!

    Joined:
    Mar 26, 2018
    Messages:
    709
    Likes Received:
    299
    Location:
    Canada
    Can others edit my Photos:
    Photos NOT OK to edit
    I suggest you have a look and feel of the Nikkor AF-S 105mm f/1.4E ED as if performs better than the Sigma and isn't as bulky. Some would say it has the same qualities as the Nikkor AF-S 200mm f/2G ED VRII.

    Regarding FL for portraits, personally I am a fan of the 105mm for head and shoulders shots as the perspective on facial features produces natural results. However, I have also shot many head and shoulders with my Nikkor 70-200 f/2.8G VRII and even my Nikkor 300mm f/2.8G VRII. Don't let anyone tell you you can only use a specific FL, you are the creator do what serves your vision.
     
  10. photoflyer

    photoflyer TPF Supporters Supporting Member

    Joined:
    Nov 15, 2017
    Messages:
    1,140
    Likes Received:
    1,525
    Location:
    Washington D.C. Area
    Can others edit my Photos:
    Photos OK to edit
    If you told nothing else but that I was to go shoot portraits I would take my 85 on full frame for three reasons:

    1 I just like it

    2 I don't like the 50 for portraits

    3 I don't have a 105, 135 or 200 ( and my 70-200 2.8 is just to intrusive for candids but could be great in studio)

    Oh, and the 24-105 f 4 is a bit slow

    But, I think you will find others who would much prefer the shorter or longer lenses and have great results to back their preference. Yes, distortion is a factor but I think we see it because we're looking for it. Unless it is extreme, l think the average viewer is drawn to other elements of a good image.

    Ultimately it is what you're comfortable with and what you have experience with.
     
    • Like Like x 1
  11. adamhiram

    adamhiram No longer a newbie, moving up!

    Joined:
    Feb 6, 2015
    Messages:
    679
    Likes Received:
    429
    Can others edit my Photos:
    Photos OK to edit
    Thank you, I appreciate the insight. I've read that the Sigma 105mm is a bit sharper and costs about $500 less, so that's interesting that you mention that the Nikon version performs better. Then again the Sigma is also a lot heavier and the massive front element probably makes it more even intrusive than the 70-200 you commented on. Hopefully I can get my hands on one or both of these to try out in the next few months and see if it's something I want to pick up. While I am used to the working distance that comes with 135mm (85mm on 1.5x crop sensor), I never liked being that far away, and in most cases it created a challenge of finding a space that long outside of my home studio.

    As a side note, I have always had zooms and they sat on the shelf most of the time anyway. With the price tag on the Z-mount f/2.8 zooms, I'm certainly in no rush to go that route.
     
    Last edited: Sep 29, 2020
  12. adamhiram

    adamhiram No longer a newbie, moving up!

    Joined:
    Feb 6, 2015
    Messages:
    679
    Likes Received:
    429
    Can others edit my Photos:
    Photos OK to edit


    Thank you, this is very helpful. I figured the slight distortion couldn't be a big deal if it is so many people's go-to for portraiture. I am in the fortunate position of having just switched to full frame, and have the opportunity to reconsider my lens strategy. I still have my 50mm and 85mm f/1.8 primes, so there's no immediate need to go out and purchase anything, but I am definitely eager to try out some other focal lengths.
     

Share This Page