[careaga]

I have a K-50 and have been toying with the idea of getting an 85 mm lens for portraiture. At B&H I was looking at some K mount lenses (manual) and it said they were for full frame and were equivalent to APS-C Focal Length: 127.5 mm. I understand that my K-50 isn't full frame and I have read about the math used to convert full frame (lens length) to APS, which might as well be Chinese to me, math not being my strong suite.
My question is this: I have a 135 mm manual lens that works well with my K-50. Would I be wasting money on getting a lens so close to what I already have? Bear in mind I am NOT a pro. I am barely an enthusiast.
Any help/advise would be greatly appreciated.

[pschlute]

Focal length of a lens is a property of a lens only. Putting that lens on aps-c or full frame does not change the FL.

Your proposed 85mm lens will not look like a 127.5mm lens. It will look like a 85mm.

Focal length "equivalence" is misunderstood, and in my view very unhelpful, but here goes anyway.....

Take a 85mm lens , put it on a full frame camera and you get a certain magnification and field of view when the image is viewed say on your computer screen at full screen view. Now put the same lens (still 85mm) on a smaller aps-c sensor. The lens produces the same image circle and magnification on the sensor. But because the aps-c sensor is smaller, less of the field of view is recorded. Now when you view the aps-c image on your computer screen in full screen view you see a narrower field of view and the subject of your picture is larger. The image is only larger because it has been "enlarged" more in order to fill your screen as it has a narrower field of view.

If you have only ever used aps-c cameras ignore FF equivalence...it is irrelevant. I shoot FF now, I used to shoot aps-c, and before that 35mm film. I have no need at all to know what my lenses "equivalence" are in Medium format camera terms as it is irrelevant.

Hope this helps

[jatrax]

My question is this: I have a 135 mm manual lens that works well with my K-50. Would I be wasting money on getting a lens so close to what I already have?

Doing the math your 135mm has the same field of view on your K-50 as a 200mm lens. So not all that close.

Traditionally portrait focal lengths were 85mm to 135mm (on 24x36 film) but that is not a hard rule. You need to 'do the math' on any lens you are considering in order to make sense of things. The numbers for APS-C would be 56mm to 90mm giving you roughly the same field of view as 85mm to 135mm lenses on a full frame camera.

Personally I think 85mm is a bit longish on APS-C but as I said there is no hard rule, use what works for your style. The Pentax DA*55 f/1.4 is the standard portrait lens for APS-C by the way. Which closely matches the 85mm lenses field of view on 24x36.

[careaga]

Doing the math your 135mm has the same field of view on your K-50 as a 200mm lens. So not all that close.

Traditionally portrait focal lengths were 85mm to 135mm (on 24x36 film) but that is not a hard rule. You need to 'do the math' on any lens you are considering in order to make sense of things. The numbers for APS-C would be 56mm to 90mm giving you roughly the same field of view as 85mm to 135mm lenses on a full frame camera.

Personally I think 85mm is a bit longish on APS-C but as I said there is no hard rule, use what works for your style. The Pentax DA*55 f/1.4 is the standard portrait lens for APS-C by the way. Which closely matches the 85mm lenses field of view on 24x36.

OK, so I had the math completely opposite? Figures.
I have a 50mm f 1.7 which is super sharp so I'm thinking I'll stick with that. Like I said, I am not a pro and money is not something I have to toss around needlessly.
Thank you for you input.

[D1N0]

There are no portrait lenses. There are only portrait photographers

[rich14]

I have a K-50 and have been toying with the idea of getting an 85 mm lens for portraiture. At B&H I was looking at some K mount lenses (manual) and it said they were for full frame and were equivalent to APS-C Focal Length: 127.5 mm. I understand that my K-50 isn't full frame and I have read about the math used to convert full frame (lens length) to APS, which might as well be Chinese to me, math not being my strong suite.
My question is this: I have a 135 mm manual lens that works well with my K-50. Would I be wasting money on getting a lens so close to what I already have? Bear in mind I am NOT a pro. I am barely an enthusiast.
Any help/advise would be greatly appreciated.

Using the 85mm lens on your APS-C camera will give you a field of view similar to that of a 127mm lens used on a full frame camera. 127mm is in the range of focal lengths generally considered to be the "portrait range" for full frame. That range is generally about 100-135mm for full head portraits. Standing about 4 feet from your subject, his/her head will just about fill the vertical dimension of the frame with pleasing perspective for a portrait.

So, yes, the 85mm on your camera will work well for portraits in terms of perspective and image size and will be toward the long end of focal lengths for this purpose.

Your 135mm lens on your APS-C camera is functioning about like a 210mm lens would on a full frame camera, in terms of the field of view. That is, it's giving you the view and "image magnification" of a medium-long telephoto lens.

Rich

[swanlefitte]

All lenses are the focal length they say, period. The way they look on different size sensors is different. The 85 is 85. The 135 is 135. If you use them on apsc they will look different than on full frame.
You here alot how 85mm is the "best portrait " lens. Thats basrd on full frame. Alot of people disagree with that opinion but on apsc that would be 56mm. So you want the 55 1.4 by that metric.

[BWG]

I have a K-50 and have been toying with the idea of getting an 85 mm lens for portraiture. At B&H I was looking at some K mount lenses (manual) and it said they were for full frame and were equivalent to APS-C Focal Length: 127.5 mm. I understand that my K-50 isn't full frame and I have read about the math used to convert full frame (lens length) to APS, which might as well be Chinese to me, math not being my strong suite.
My question is this: I have a 135 mm manual lens that works well with my K-50. Would I be wasting money on getting a lens so close to what I already have? Bear in mind I am NOT a pro. I am barely an enthusiast.
Any help/advise would be greatly appreciated.

If you can afford it, get the DA70 f2.4.
And don't worry about crop factor unless you go full frame someday in the future. Then, and only then will you notice the difference.

[ronniemac]

As has been mentioned above, the DA* 55 F1.4 is considered to be a very good lens for portraiture. Continuing with the F1.4 theme because it enables shallow depth of field therefore good subject isolation from background with a smooth bokeh, the FA 50mm 1.4 is worth considering. If budget is tight, consider the DA 50mm F1.8, it is sharp in the central area and excellent value for money.

Although I have these lenses, my favourites for portrait on APSC has always been the DA 70 F2.4 Limited. A better lens in this mould is the FA 77 F1.8 Limited, but it's pretty costly and I have only used it on the K-1.

I find it difficult to single out one of these lenses as a recommendation for you, partly because I don't know your budget, partly because I don't know how you like to shoot. It would be a good idea to look at the users' lens reviews in this forum where you will see good examples of what each lens is capable of.

[AstroDave]

I have a 50mm f 1.7 which is super sharp so I'm thinking I'll stick with that. Like I said, I am not a pro and money is not something I have to toss around needlessly.

I think you will find that a very nice portrait lens. Work with it for a while. If you ultimately feel you need something longer, then consider something in the 70-85 range.

[Alex645]

I have a K-50 and have been toying with the idea of getting an 85 mm lens for portraiture.

My question is this: I have a 135 mm manual lens that works well with my K-50. Would I be wasting money on getting a lens so close to what I already have? Bear in mind I am NOT a pro. I am barely an enthusiast.

There is no harm (other than price and sometimes size) using a FF lens on APS-C. The opposite is usually not the case and you may have vignetting or sharpness issues on the edges and corners.

My advice would be to get the 85mm IF you think there may be a K-1 in your future one day. If not, I would recommend the Pentax DA 50mm f/1.8. It's so affordable and an incredible value. Your 135mm is a bit of a longer prime for portraits, and the 50mm would be an excellent short prime.

Pentax smc DA 50mm f/1.8 Lens 22177 B&H Photo Video

If you're lucky enough to have 8x the budget of the price of a new DA 50mm, then the Pentax SMCP FA 77mm f/1.8 Limited is the gold standard.

Pentax Telephoto SMCP-FA 77mm f/1.8 Limited Series 27980 B&H

[Sandy Hancock]

Yes, your 50mm lens is an excellent focal length for general portraiture on a crop camera - roughly equivalent to the fabled FA77 on full frame.

The gap between 50 and 135 is quite a big one though. Do you have a zoom lens to cover it? If you're looking for a prime to do the job though, something in the 70-90mm range would be perfect. In Pentax land, even the Takumar, K and M fastish 85's are often quite expensive; they are also rather thin on the ground. The Samyang/Rokinon 85/1.4 is freely available, comparable in price, faster, and comes with a new lens warranty. The DA70/2.4 limited might also be worth a look - it's tiny and renders beautifully, but it's more expensive, even second hand.

But for all that, D1N0 got right. I have made decent portraits with a crop camera at focal lengths from 21mm to 300mm. Factors such as light, timing, technique and connection with your model are more important than focal length.

[quant2325]

If you are “barely an enthusiast” consider the following:
1. How close do you want to be to your subject? If you want a nice headshot of your teen kid or spouse, who cares? They aren’t going to be intimidated if you are close to them. I generally shoot with a 70mm or a zoom on an APS-C for headshots and portraits, but I could easily get by with a 50mm if I didn’t have other lenses.
2. Is the lens sharp enough? Generally, most Pentax 50mm lenses, even the manual ones, are plenty sharp for portraits.
3. What do you want to do with the background? If you are shooting at f/8 on a white background it doesn’t matter. If you want the background of an outdoor scene to be totally blurred, you would want a 135mm (something around 200mm FF equivalent) shooting wide open (or close to it) to blur out the background.
4. If you are “barely an enthusiast,” use what you have and learn to take great photos with it! Then consider spending money on more glass. You will learn faster if you spend $ on a reflector or two, a couple of umbrellas or softboxes, etc. If you have the $ for lenses, spend it and have fun. If you don't have the $ don't worry about using what you have.
5. Have fun! With basic lenses, you can take photos as good as the pros. The post-processing may not be as good unless you learn to use software, and there is skill in getting the perfect expressions, but you can get great results without spending a ton of money on equipment. Remember, many of the iconic portraits over the past 100 years came from equipment that is worse in terms of IQ than what you are using.

[gm4life]

Go with the DA 55 SMC * awesome portrait lens... And a great low light lens too. If you can't swing it a DA 50 SMC is a good value too.

[TheOneAndOnlyJH]

I have a K-50 and have been toying with the idea of getting an 85 mm lens for portraiture. At B&H I was looking at some K mount lenses (manual) and it said they were for full frame and were equivalent to APS-C Focal Length: 127.5 mm. I understand that my K-50 isn't full frame and I have read about the math used to convert full frame (lens length) to APS, which might as well be Chinese to me, math not being my strong suite.
My question is this: I have a 135 mm manual lens that works well with my K-50. Would I be wasting money on getting a lens so close to what I already have? Bear in mind I am NOT a pro. I am barely an enthusiast.
Any help/advise would be greatly appreciated.

Ignore what they say about equivalence, it is just an 85mm lens and that's it. You can pretty much ignore full frame equivalence math if you aren't switching between different systems, just get used to what focal length means in terms of your camera and you'll be fine.

Full frame equivalence math only came about because people were used to how their lenses performed on film (full frame, a.k.a. 35mm 'sensor' size) and wanted to wrap their heads around how lenses would perform on their new digital cameras with smaller sensors. A good analogy would be to think of it like inches and centimeters. If you think well in terms of inches, you take measurements in centimeters and convert them to inches so the information is easier for you to wrap your head around, or vice versa. (Just like you might convert someone's height measurement from 175cm to 69 inches or 5'9" since that's the format you are used to seeing.) If you never switch between systems, you never need to worry about the math. (Though if you do switch to full frame in the future, you'll probably have a good understanding of what focal lengths mean on APS-C and you may end up doing the math in reverse.)

These ranges aren't set in stone and everybody has different tastes, but here's a rough guide:

Ultra wide angle.....10mm (APS-C) / 16mm (Full Frame) .................... Creative architecture, landscapes, starry skies, etc.
Wide angle lens.....18mm (APS-C) / 28mm (Full Frame) ..................... Commonly used for landscapes, group pictures
Normal lens...........35mm (APS-C) / 50mm (Full Frame) ..................... 'Normal' being closest to the way you see the world with your eyes
Portrait lens......50-90mm (APS-C) / 70-135mm (Full Frame) .............. 'Portraits' can range from full body to head shots, so the range is quite subjective.
Telephoto lens.... >70mm (APS-C) / >100mm (Full Frame)