[kangamel]

For head and shoulders portraits is there a lot of difference between 28mm and 35 as far as distortion. I know if I photograph my son at 18mm I cant recognise him

[stillshot2]

The rule of thumb is usually 85-135mm for portraits, so the higher the better.

[HenrikDK]

Second above. Traditional portrait lens is 85mm - on cropped that would be around 55mm. 50 and up should work pretty well. I prefer 77mm - just so happens I have a lens of that focal length

[jatrax]

As above, the "portrait" lens from Pentax for APS-C is the DA*55mm or the DA*50-135. You can do quite well with an older 50mm for general portraits, for head shots you need to be 70 - 100mm.

[kangamel]

thanks for the quick replies I understand a longer focal length is more flattering for portraits, and I have 50mm and a 50-200, but 50 is too long for my everyday use. What I am wondering is if there is going to be much more noticeable distortion from a 28mm prime that is not present from a 35mm when capturing a face at close distance. I know neither are normal portrait lengths, I want wide, but without too nuch distortion when I get close up to people. I have a 28mm and wondering if a 35 would give nicer close ups, while still wide enough to not needing to back away for everything else.

[baro-nite]

The issue is not the focal length per se, it is how close you are to the subject. You'll get the same perspective (same proportions of facial features) using, say, a 28mm lens as you will with a 135mm lens, if the subject distance is the same; if you cropped the shot from the 28 to the same angle of view as the 135, you'd have trouble telling the two apart (other than the greater resolution of the uncropped shot). The reason 55mm is a good focal length for portraits on APS-C is that for a head-and-shoulders framing you are a suitable distance from the subject. 28mm is a good choice for a full-length portrait.

[HenrikDK]

Not sure there is a answer to your question... 35mm would have less distortion, but doubt there is much of a material difference. Stepping back and cropping would probably be much easier/impactful! If it is important to you, try it out in a controlled setting.

[stillshot2]

It all depends on what you want to achieve... if you want to get "close up" such as filling the frame with the person's face at 35mm, you will get an out of focus background but they will have the "fat nose" look. If you back up from the subject and crop afterward you will lose the subject isolation from the background and some detail from cropping but the subjects face will be less distorted. I personally notice that filling the frame with a subjects face even at 50mm will be a little distorted, hence the 85-135mm rule of thumb. So... for best results you either need to buy a zoom that covers 35-85mm or simply switch lenses to a different focal length. Sadly, a 35mm fixed focal length lens can't "do it all."

[Just1MoreDave]

The best way to answer the question for yourself is to grab a patient test subject and take some shots at 28mm and 35mm. The 18-55 zoom should be good enough for this. Then you have actual shots to compare and judge by your own standards.

For me, I think 35mm is fine. I will use 28mm when I stray from "portrait" to "candid". I think people used to looking at cell phone shots are already used to seeing this sort of distortion, so it depends on who's looking. A lot of cell phone cameras use lenses that would be 22-24mm on APS-C.

[Tan68]

I agree with using the zoom lens to test out different focal lengths.

Both the 28 and 35 are 'normal' on APS-C as 42/55 on FF.
I kinda like 28 more on APS-C

But you want an always on lens that can be used for portraits close. Of course, the 35 will show less but is it significant? Zoom lens test!

As pointed out, the longer lens is better/traditional for tight/close portraits. With your wider lens, though, you should have more background included with your subject... So, you will have a different look for same subject size.

People say they use the 35 for portraits but I never asked if they meant tight or most of body. If the distortion is acceptable to you and you like the look/feel of the 28/35, why not ?

[RGlasel]

I think people used to looking at cell phone shots are already used to seeing this sort of distortion

For comparison, the iPhone 4 had an equivalent focal length of 29 mm, the 4S, 35mm, the 5, 31mm. The 5S has a slightly longer focal length than the 5 (4.12mm vs. 4.10mm) but a larger sensor so less of a crop factor, resulting in an equivalent focal length of 29.7mm. On an APS-C Pentax camera, the 28mm K-Mount lens has an equivalent focal length of 42mm, the 35mm lens, 52.5mm. I thought it was interesting that the lens speed of iPhone cameras has been steadily increasing, going from f2.8 with the 4, to f2.2 with the 5S. DOF is still pretty long compared to lenses on APS-C cameras with the same aperture. Which leads me to my counterpoint to your statement that people are used to the distortion they see in cell phone shots. I think they are only accepting the limitations of cell phone shots because any picture taken with a lousy camera is better than a picture not taken. Never mind the wide angle distortion, the much longer DOF in every shot makes every cell phone picture a flat, unrealistic representation of whatever the photographer saw in his or her eye. The 50% increase in crop factor from FF to APS-C is nothing compared to the 756% increase with the 1/3.2" sensor used in most cell phones. Which didn't stop Apple from promoting the 5S because the pixels on its sensor are one tenth of a micron larger than the pixels on the 5.

[Na Horuk]

What I am wondering is if there is going to be much more noticeable distortion from a 28mm prime that is not present from a 35mm when capturing a face at close distance.

One other thing you can do is look up the specific 28mm and 35mm lens you are thinking about on review sites and see their measured distortion.
There is also a difference between distortion and perspective. Basically, to have your subject fill the frame, you will have to come much closer with the 28mm lens, which emphasizes the perspective and makes the person look even more round.
tl;dr: yes, 28mm is noticeably wider and worse for portraits than 35mm, which itself isn't perfect for such usage.

Anyway, Pentax isn't selling a 28mm lens right now (only zooms that have that range), so the DA 35mm f2.4 and FA 35mm f2.0 are the only choices. But both are a great lens. Sharp, fast AF, good low light performance. But! For closeup portraits 35mm is still not very flattering. It makes faces rounder. Especially with children, because they are small and you have to come closer. 35mm is good for photos where the hole person is in the photograph and some of the environment. Honestly, for actual portraits I would suggest DA 50mm f1.8 or DA* 55mm if the budget permits (top notch portrait lens). The DA 50mm f1.8 is very cheap now, too, under $200. Used its even cheaper. Or the Pentax M 50mm f1.7, which can be found for under $60, if you don't mind using a manual lens.
Simply switch camera to portrait mode or Av mode (f-number down between f1.8 or f2.8) and you will have nice portraits.

[Tan68]

By distortion, I gather he does not mean curvature of image field but the 'round face' look you mention that is usually a feature of being closer to the subject. A different perspective to use 28mm and have same size subject as with 35 where 28 gives more distortion... same word but different intention with its use, I think :^)

I call it the 'big nose effect'. Most devastating are the wide angle shots with legs and arms that can be much closer to the camera than a nose... makes arms and thighs look large...

[Na Horuk]

Yep, as Tan68 said!
Perspective is when features look out of proportion. Distortion is when straight lines are no longer straight. Distortion can make a person's forehead seem elongated, if its in the corner of the frame for example. Perspective on the other hand makes the person's nose look large and their ears small by comparison, but the shapes stay normal. Only distances between them get exaggerated and the things that are near appear much bigger than those that are only a little bit farther away

[kangamel]

Thanks everyone,

yes, 28mm is noticeably wider and worse for portraits than 35mm,.

thanks Na Horuk, that is exactly what I was asking, although all the answers have been informative. I have a F 28mm f2.8 and I also have a 50mm, one is a bit hard on faces the other doesn't fit enough in the frame for my use, maybe 35mm is worth a try next.