As always I enjoyed the in depth approach you take when approaching a question. I dont really have a prefrence, for me it's more a matter of fitting the lens to the application. In studio I don't need fast glass as my aperture rarely drops below f/5.6. With sufficient floor space and FOV I can routinely shoot head and shoulders kids and adults at 105mm. When I get into the more elaborate "set" shots 50mm is my go to. Using a technique I learned from a Joel Grimes video, I'll sometimes use the perspective distortion of a 28mm to "enlarge" the arms, muscle on men. In studio bokeh isnt so much a concern, but sharpness is. Outside, it depends on the application, if I'm shooting ambient the legacy f/1.8 135mm is a good choice because of its buttery OOF and smooth transition between zones, as are the FA 100m 2.8, the 77mm f/1.8, LTD, and the legacy 50mm f/1.2. Many times it comes down to a choice based on FOV and space between the subject/subjects.
The problem with the right lens and distance has to do with converting a 3D image to 2D on paper or a screen. In our brain, these issues are compensated for naturally. Noses are still larger than ears closer up than they are far away. But our brain understand this issue and adjusts accordingly and "sees" the nose at the correct size. It just like Keystoning effect on buildings. When we look up at a building, the top edges are closer to each other than at the bottom. But our brain sees in 3D and adjusts accordingly mentally. But once you record that image a a 2D surface, film, screen or print, the lengths look different and the lines seems to converge. Or the nose seems bigger. So with noses, you stand further back and zoom in with a longer lens. With Keystoning, we keep the lens and film or sensor surface parallel to the building's surface.
You raise a really good point - for studio work I typically live between f/5.6 and f/8 as well. For the test shots used in this post, I used my variable aperture 70-300 lens, which seems plenty sharp once stepped down. In fact a number of people still use headshots I took with it a few years ago before I decided to pickup an 85mm prime. For outdoor use though, I definitely have a use for a wide aperture tele/portrait lens.
Subjectively, I always much preferred working in the 135mm range on full frame for portrait work. First, I did this with a 70-200 and eventually with a sigma 135 ART. Anything below 100mm or so never seemed to give me the results I enjoyed. I don’t have a scientific breakdown of the reasons, though I suspect it relates to longer focal lengths making it easier to obtain background separation. Obviously this doesn’t matter much in the studio, but that was never my domain so I don’t have experience there to speak of. If I could only have one lens for portrait work these days, it would be a 70-200 2.8 for the raw versatility that it brings to the table. Alas, I don’t shoot portraits any longer so it’s not something I spend much time worrying about.
Personally, I think it depends on the portrait type. If I am shooting on a typical backdrop 50 is my go-to. (sigma 50 art). I actually photographed a school today and brought both my 85 art and my 50 art....as much as I wanted to use the 85, it was too tight and I switched back to my trusty 50. I have used a 50 for school portraits for over 5 years and I think it's the best for headshot/background shots. I think for outdoor shots or sessions where you have more room to move around I might use my 85. I think its important as a portrait photographer to have a wide variety of focal lengths in your bag
@adamhiram another consideration for you to think about is aspect ratio. You always hear "fill the frame" but what do you do when you've "filled the frame" on a sensor with its 3:2 aspect ratio, and Mom wants an 8x10 (5:4) or an 11x14 (14:11) Your beautiful image is going to be missing something, or you spend some quality time in PS adding length/width, so you can crop to the correct ratio. A better option for me is a little pre-planning (choice of focal length and required FOV) for the anticipated final image so I have room to crop.
There is an easy fix for shooting in 5:4 aspect ratio if the plan is making typically sized prints. Set your Image Area in the Shooting Menu and choose 5:4, crop marks will be visible and your image captured will be cropped to that aspect ratio. Its always a good practise to leave a bit of breathing room around your subject unless of course you are in tight.
Thank you all for the great feedback. I've been happy with my Nikon 85mm f/1.8 since I got it a few years ago, and I'm leaning towards replacing it with the Z-mount version, which is significantly sharper, less prone to flare, and does much better with chromatic aberration. 105mm seems like a good compromise between longer focal length and comfortable working distance - I've had some challenges using an 85mm on a crop sensor in tighter spaces, which is roughly equivalent to 135mm on full frame. However the high price of the Nikon lens and the absurdly large size of Sigma's offering probably make this a no-go. 135mm seems like a a good 2nd option to have if I hold onto my 85mm. The lens size (at least for the Sigma) is more reasonable, and I'm pretty used to that working distance. Thanks again, and I'll try to follow up if I make any decisions in the future. From everyone's experiences, it sounds like there's really no wrong answer.
The lens length does not effect compression, camera subject does. A 35 mm lens will have the same compression as an 85 at 7 feet. You can just crop. Want to see this without a lens, stand at the bathroom sink against the counter. Look at your nose, take a step back and watch it look smaller. Take another step back, smaller again, another the same. What is ideal is what is your vision of compression and what you feel is proper for a particular face. Only you know your vision. With my ample italian probiscus, I want you back 10-12 feet. At 15 feet I have a michael jackson nose. Chose the compression from the distance you like then chose the lens for the angle of view you desire. This is the same for any other photography but has been forgotten with so many folks using zooms and just standing in the spot they first see the shot, zooming and shooting. Setting perspective should be done before lens selection if possible. My choice for a head and shoulders 8-10 feet distance and a 100 or 135. There is compression but not excessive for my taste. I trained with 2 photographers who charge 45 grand for a wedding. They used the 85 for 3/4 couple shots during the day. I listen to folks that get paid that kind of money.
Sorry, but this is quite incorrect. To prove it, shoot the subject with them at the same size on-camera at 24mm and then again at 105mm. Huge difference due to the focal length.
Your definition of registration is different from that I've met all over the place in the past, both on-line & in print, and doesn't describe a constant distance let alone a feature of the lens. Registration is usually used to mean the same as back focal length, the distance of the image plane from the mounting flange of the lens. The minimum distance of the image plane from the focal point (ie along the lens axis) is dependant on the distance being focused and the lenses focal length. When focused at infinity the image plane passes throught the focal point (by definition), When the image size is the same as the subject size (1:1 macro) the image plane is one focal length behind the focal point, by the time the subject is at the front focal point the image distance is at infinity.