[Jonathan Mac]

When most people talk about "portrait" focal lengths they mean, possibly without even realising it, traditional studio portrait focal lengths. That means you need a certain distance from the subject in order for them to feel they don't have the camera in their face, and for that I have found the most appropriate focal length (on APS-C) is 70mm (105mm equivalent). Of course, this will depend on what sort of results you want.

For more informal portraits in a real social environment, which I like much more, I find something wider to give much better results. The best "portrait" lens I've ever used is the DA 35mm f/2.8 limited, which is just over 50mm equivalent.

50mm fits between these two scenarios and I would say is more useful in the second than in the first, but that's very subjective.

[BrianR]

But for anything other than headshots, you need to be like a mile away. It's a big problem: you don't get strong bokeh/isolation unless you're reasonably close. But you have to back up sooo far with anything over 75mm on APS-C that you lose that bokeh unless you shoot at f/2, and even then it's not as strong.

This doesn't make sense to me? If all you change when switching to a longer focal length is your distance to the subject to keep the same framing of your subject, your background should now have more absolute blur, be a smaller cross section of the background (possibly less colour variation), resulting in better subject isolation. There are good examples under the "background blur" section here: Depth of field. Though talking about "Distance Compression", there are half-body portrait examples here: Depth of Field Explained (scroll down to "Focal length and Distance Compression").

Do you have any examples to illustrate what you're saying?

[Saltwater Images]

More portraits are done at around that FL than any other, SI - it's what phones are equipped with.

The issue with selfies is they're taken at arm's length.

There are bridal portraits done with 14-24 and 16-35 ultrawide zooms.



There is no such thing as compression due to focal length, SI.

That's a myth, no matter how widespread.

Wow Clackers, that's two unscientific assumptions. Does that mean the earth is flat too:-)

When working in a small interior space with several members in a bridal party to get into a shot - there is no choice but to utilize a wider lens. Wide angle lenses create extension distortion AKA wade-angle distortion. If you would like to learn more about compression distortion and extension distortion these links may be helpful:
- https://en.wikipedia.org/wiki/Perspective_distortion_(photography)
- What is Lens Compression and How to Use It In Your Photos

Joe Sinnott at the School of Visual Arts in New York has an excellent video about choosing a portrait lens. In the video Joe also explains wide-angle and compression distortion as well as the impact they have on portraits. Here's a link to the video:

You Tube

You Tube

[Wheatfield]

But for anything other than headshots, you need to be like a mile away. It's a big problem: you don't get strong bokeh/isolation unless you're reasonably close. But you have to back up sooo far with anything over 75mm on APS-C that you lose that bokeh unless you shoot at f/2, and even then it's not as strong. But the PDAF system loses accuracy as you get further away (because measuring distance becomes more error prone), so you're more likely to end up out of focus. For the precision you need to focus at f/2 with a long lens, that's not so good.





Just to provide reference, I have to shoot all of my boudoir with a 55mm lens. Even in my home, with a reasonably large bedroom, there's simply not enough room for a 77mm (K-1) for much other than head and shoulder shots. Something shorter than the classic portrait lenses is indeed needed.

If you can get back 15-20 feet, full lengths with a 70mm on APS-C are perfectly feasible. Depth of field is a product of reproduction ratio.
Pretty much your entire post is wrong.

[MadMathMind]

This doesn't make sense to me? If all you change when switching to a longer focal length is your distance to the subject to keep the same framing of your subject, your background should now have more absolute blur, be a smaller cross section of the background (possibly less colour variation), resulting in better subject isolation. There are good examples under the "background blur" section here: Depth of field. Though talking about "Distance Compression", there are half-body portrait examples here: Depth of Field Explained (scroll down to "Focal length and Distance Compression").

Do you have any examples to illustrate what you're saying?

The strength of the blur is dominated by the ratio of the focusing distance and the distance to background. The focal length and aperture matter as well, but it's that ratio that really matters. Here's an example. FA77 on the K-1 and the K-5iis. Both shot at f/2.8.

K-5IIs and FA77


K-1 and FA77


And just for fun, here's the K-1 and the DA*55 at f/2.8:


For the first shot, I was 11' away and about 9' away for the K-1. With the 55, I was about 6' away. My framing isn't identical and you can see I was closer with the K-5 shot. For the same framing, I probably need to be 12' away on K-5. You might expect

While the wall at the far back seems to be blurred about the same in both photos, the blur is much stronger closer to the vacuum with the K-1 and FA77. Look at the wall on the right, where it goes back into doorway. In the K-5 shot, you can make out some lines on the molding near the floor. The carpet just behind the vacuum has some definition while on the K-1 shot it's much blurrier and you can't see the fibers. The crumbs on the carpet are much better defined in the K-5IIs shot. The isolation is not as strong, even though the same frame (within a few inches) and focal length was used.

Now look at the shot with the DA*55. It has about the same level of blur as the K-1 shot. It was taken quite a bit closer. The focal length is much shorter yet we still have the same strong blur. What we take from this is the focusing distance is what matters the most.

Tony Northrop has his thing about "equivalent f-stops." What he argues is that you need to divide the f-stop by the crop factor as well. I think his math is a bit off on that but you can see he's not incorrect that you need to adjust the f-stop to compensate for the greater distance you must be. And indeed, here's one with the K-5IIs and FA77 at f/2.2:



We see a very similar level of blur with as we do with the K-1 here. We had to back up 33% and we had to go down two thirds of a stop.


---------- Post added 12-17-16 at 01:12 PM ----------

If you can get back 15-20 feet, full lengths with a 70mm on APS-C are perfectly feasible. Depth of field is a product of reproduction ratio.
Pretty much your entire post is wrong.

Magnification, and hence reproduction ratio, changes as you get further from the lens. For simple lenses, the two are related by



d_i is the distance from the lens to the image. As you back up more, you'll magnify things in the "foreground" less than the background and have less image compression. Alteratively, as you get closer, you magnify things that are close more than things that are farther. This effect is more gradual with longer focal lengths. Hence, the reproduction ratio decreases on APS-C and that's why you don't quite get the same isolation/compression and why shorter focal lengths don't distort like they do on FF. You can fill a frame with a person's face at 30mm without causing issues on APS-C. Do the same on FF and they will look strange. This is why.


And getting back 15-20 feet is a challenge in many cases. Try doing that in a crowded walkway or a small room. If you've got an extra 20' in your studio....can I come shoot at your place? We've got like 12' at the most. If you have infinite space, sure, but I rarely used my FA77 on crop because I didn't have the room in most cases. Now it's my most used lens on the K-1.

[clackers]

Joe Sinnott at the School of Visual Arts in New York has an excellent video about choosing a portrait lens.

Then Joe's students should ask for a refund, if that's the teaching they pay for, SI.

Lens compression (a shortening of the foreground and background relationship) is nonsense, and he and you are contradicted by your own links.

The Photography Life article admits that "Lens compression does occur when you take a picture with a telephoto lens, but it is not because of the lens or its focal length. It is because we tend to stand farther away from our subjects when we use a long lens."

In fact, the writer fails to control variables, and the demonstration photos involve not just a change in focal length, but a change in shooting distance. He also conflates "compression" with "perspective distortion" - these are two different effects.

I think your Wikipedia article explains best:

Note that linear perspective changes are caused by distance, not by the lens per se – two shots of the same scene from the same distance will exhibit identical perspective geometry, regardless of lens used. However, since wide-angle lenses have a wider field of view, they are generally used from closer, while telephoto lenses have a narrower field of view and are generally used from farther away. For example, if standing at a distance so that a normal lens captures someone's face, a shot with a wide-angle lens or telephoto lens from the same distance will have exactly the same linear perspective geometry on the face, though the wide-angle lens may fit the entire body into the shot, while the telephoto lens captures only the nose. However, crops of these three images with the same coverage will yield the same perspective distortion – the nose will look the same in all three.

(Emphasis mine).

You've seen Sandy's portrait of his daughter with the DA21.

Here are two of mine with that FoV, and a third done with the FoV of the DA15!

[Sandy Hancock]

Wide angle lenses create extension distortion AKA wide-angle distortion.

No. They don't. Getting too close to your subject does that.

Maintaining a reasonable camera to subject distance is all that is needed to avoid perspective extension for portraits. If you are the typical 2-3 metres away from your subject and you want a tight head shot, use a longish telephoto. If you want a classic head and shoulders shot, by all means use a short telephoto. If you want If you want a full body shot with some background interest, use a moderate wide angle. If you have a subject who is self-conscious about a large nose, stand further back to change the perspective - a longer lens will now be necessary to get the right framing, but it is not the *cause* of the perspective compression.

Choose the right focal length for the job. That will not always be your classic short telephoto.

[BrianR]

The strength of the blur is dominated by the ratio of the focusing distance and the distance to background.

It definitely matters, but this this is not so strong that using a wider angle will create more background blur. See the examples in the links from earlier. As you move to a longer focal length (and have to step back), the ratio of the focusing distance to the background gets closer to 1 but the absolute blur of the background increases.

See also this background blur calculator which covers the case of keeping the subjects framing the same: How much blur? - A visual background blur calculator

FA77 on the K-1 and the K-5iis. Both shot at f/2.8.

You've introduced sensor size as another factor...how about we keep it simpler?

Now look at the shot with the DA*55. It has about the same level of blur as the K-1 shot. It was taken quite a bit closer. The focal length is much shorter yet we still have the same strong blur. What we take from this is the focusing distance is what matters the most.

I would have said the background of the K-1 + 77mm has more blur than the K-1 + 55mm. Not by much (the focal lengths are close), but line up the trim in the hallway and flip back and forth, to me the 77mm version is blurrier.

Here's a more extreme example that I think illustrates a few things for this thread:



My aged Tick action figure (his torso has faded) stands about 40cm from the background. The framing of the Tick is (almost) the same in each, all are shot at f/4 on a k5iis. The only changes were focal length and where I stood. To me the background blur and separation are higher as I moved up in focal length. Do you not agree?



Unrelated to the background blur, you can see the "Compression" effect from standing further back. The background is made up of little 1cm squares, the larger grid is 5cm squares. The Tick is about 15cm.. as we move further back, the grid behind him gets closer to lining up with his true height.

You can also see how a longer lens makes it easier to select a part of the background to help with separation. Wide angles see everything - this is both annoying and awesome.

The perspective change is also dramatic, at 14mm I'm up in his grill and his chin looks relatively enormous compared to the 300mm taken from a few feet back. Obviously, 14mm would be ideal for the Tick since his chin is so heroic and should be emphasized, but not all subjects will agree.

I've posted this shot before, but it's an example of what 14mm will do in a head shot. I like to keep my friends close. Really close. Uncomfortably close. So they will tell you this is an accurate portrayal of the size of my nose in real life:





I keep my smelly friends a little further away, and I'll look more like this to them. The framing not as tight and @50mm, so the camera is a good deal further back resulting in an ample, but hopefully not comical, nose (where did I put that 300mm?):

[Sagitta]

One of my best lenses for doing 'across the table' portraits is my Sammy 35mm.





The Sigma 10-20mm isn't that bad either on the, er... long end.

[UncleVanya]

FA 31 Limited


FA 35 on K-3



DA 40 Limited (SMC) on K-3






FA 77 on K-3




DFA 100 on K-3


DA* 200 on K-3




---------- Post added 12-18-16 at 12:48 AM ----------

I think my point is simply that you can get away with a lot of different lens focal lengths for portraits on APSC. Working distance and intended framing together will rule the day.

[BATMON]

Just picked up the Pentax Silver 70mm today. Cant wait too get shooting!

[NZ_Ross]

Just picked up the Pentax Silver 70mm today. Cant wait too get shooting!

I trust you will enjoy, it is a nice lens. Please share the results of your efforts

[HudsonShooter]

Just picked up the Pentax Silver 70mm today. Cant wait too get shooting!

da70mm is great get ready for some nice shots.

[Cambo]

the 10-17 Fisheye Zoom is wonderful for selfies...









or Portraits....








Cheers,
Cameron

[UncleVanya]

the 10-17 Fisheye Zoom is wonderful for selfies...


or Portraits....


Cheers,
Cameron

And crazy realistic too... LOL. I love these.