[reivax]

I'm taking some portraits later this week and I was debating on whether or not to use my Pentax FA 50 1.4 or to use my Sigma 17-50 2.8. I was pretty set on using the prime, but for curiosity's sake, I decided to look up some test scores on lenstip. I have to admit that I'm a little surprised at seeing the zoom had better scores than the prime. Is this accurate?

I've always tried to use primes when I do any kind of portraits, but if the Sigma is actually going to give me better results, then I'm not sure why I would want to use the 50 mm. I know the prime is a lot faster and it's also more compact, but if I don't need to go to faster than 2.8 and weight/space is not an issue, why would I want to use it over the Sigma? I am hoping that I'm reading the tests wrong and that someone can enlighten me. I am really disappointed to see those results. I really did expect the Pentax to perform better.

Pentax
Pentax smc FA 50 mm f/1.4 review - Image resolution - Lenstip.com

Sigma
Sigma 17-50 mm f/2.8 EX DC OS HSM review - Image resolution - Lenstip.com

[normhead]

You need to try them out an see which results you like better. I wouldn't avoid using a zoom because it's a zoom, I don't have that particular bias, but I especially wouldn't pick a portrait lens based on resolution. Portrait lenses should be picked on rendition… in my day portrait lenses were intentionally a bit softer with better out of focus rendering.

[SpecialK]

Easy. You have the lenses - take sample shots and choose :-)

Why rely on a number, or us?

[maxfield_photo]

I find that sharpness is vastly overrated especially for portraiture. I'm not saying it's unimportant, but often times I end up softening the skin in post. What is important is the focus. You know that focus scale that's printed on most primes that shows the "zone of acceptable focus"? It's hogwash. In portraiture there is only the point of critical focus, everything else is out of focus. The point of critical focus needs to reside somewhere between the tips and the base of the eyelashes. Yeah, it's that small.

The Sigma may in fact be sharper that the Pentax 50, you have to remember that that lens is a decade old. You see the same thing from Canon and Nikon, some of their zooms out perform their primes, and 50mm in particular seems to be problematic. But I can almost guarantee that the 50mm Pentax will focus more accurately than the Sigma zoom. f/1.4 makes the difference between in focus and out of focus very apparent (particularly if you use a split prism focusing screen). Like others have said, since you own both lenses, try them out a see for yourself.

[SyncGuy]

You need to try them out an see which results you like better. I wouldn't avoid using a zoom because it's a zoom, I don't have that particular bias, but I especially wouldn't pick a portrait lens based on resolution. Portrait lenses should be picked on rendition… in my day portrait lenses were intentionally a bit softer with better out of focus rendering.

Sonnars.... *ouch*!

[reivax]

I went ahead and performed the most unprofessional test I could think of and tested both lenses out at 2.8; 4; & 5.6. All images were taken with manual settings (to ensure everything was as identical as possible). All shots were handheld and ISO was set at 3200 (didn't want flash to alter colors, etc).

At 2.8, I think I like the Pentax more, after that, I think the Sigma renders colors a lot better than the Pentax.

[reivax]

Do the colors look desaturated to anyone else? They shouldn't... Could photoshop have rendered them this way? On my computer, the images look fine. They colors are really off after uploading them to this site.

[normhead]

The Pentax out of focus areas seem to be rendered about a stop ahead of the Sigma images, the Pentax @ ƒ4 looks closest to the Sigma @ f 2.8. Given that the Sigma is a slower lens… by 2 stops, that's a 3 stop disadvantage when looking at the out of focus areas. But I have no idea how important that is for you.

[reivax]

It's got to be some setting in Photoshop that I don't know about. I exported the image through Lightroom and everything looks fine now... Any help with this would be greatly appreciated. Thanks. Here's the correct rendition.

[reivax]

The Pentax out of focus areas seem to rendered about a stop ahead of the Sigma images, the Pentax @ ƒ4 looks closest to the Sigma @ f 2.8. Given that the Sigma is a slower lens… by 2 stops, that's a 3 stop disadvantage when looking at the out of focus areas. But I have no idea how important that is for you.

Wow, I hadn't even noticed that. That is a pretty significant difference. And this is why I wanted your guys' opinions. Thanks. Anything else you notice?

[Joojoo2010]

Looks to me that in FA50 pics focus is more in front than sigma pics and this will explain most of different background blur ratio.

I believe that my FA50 gives better IQ than any of my zooms in 50mm...including also tamron 17-50,28-75...sigma 17-50 i do not own but i do believe FA50 will be better than any zooms in 50mm for pentax...but difference can be very little only.

[Canada_Rockies]

Wow, I hadn't even noticed that. That is a pretty significant difference. And this is why I wanted your guys' opinions. Thanks. Anything else you notice?

Given that the focus seems to be slightly different, if you have a body that allows focus adjustment, try adjusting the 50 to focus better. You can pay for super fancy gizmos, but a ruler at an angle should do the job.

[Na Horuk]

A reason for the odd colours might be the colour space setting, on your camera and in the software that you use to edit files. You probably want them all to be set to sRGB, its a standard that works well for sharing online.
Personally I prefer to use primes, and at f1.4 you can get a lot of background blur/subject isolation. Just make sure the person's eyes (or at least the one closest to the camera) is in perfect focus. Primes also kind of force you to frame more creatively. With zooms people often just stop in front of their subject and then zoom a little and take a shot. With a prime, you might be forced to take a step back or forward, and suddenly you will think about crouching a little or leaning to the side.. maybe its just me, though. Lots of people get great results from zoom lenses, I dont want to put anybody down.

[reivax]

Given that the focus seems to be slightly different, if you have a body that allows focus adjustment, try adjusting the 50 to focus better. You can pay for super fancy gizmos, but a ruler at an angle should do the job.

I've never really had any issues with focusing on the FA 50. I didn't really pay too much attention to where I focused on the plant. I was more concerned with color rendition, but now I'm wishing I would have. I will definitely pay more attention to my focus points. Maybe I do need to adjust it.

Would that inch or two difference in focus point really make that much of a difference in how out of focus the background is? I know it does make a difference, but a full stop?

[reivax]

A reason for the odd colours might be the colour space setting, on your camera and in the software that you use to edit files. You probably want them all to be set to sRGB, its a standard that works well for sharing online.
Personally I prefer to use primes, and at f1.4 you can get a lot of background blur/subject isolation. Just make sure the person's eyes (or at least the one closest to the camera) is in perfect focus. Primes also kind of force you to frame more creatively. With zooms people often just stop in front of their subject and then zoom a little and take a shot. With a prime, you might be forced to take a step back or forward, and suddenly you will think about crouching a little or leaning to the side.. maybe its just me, though. Lots of people get great results from zoom lenses, I dont want to put anybody down.

I use sRGB for everything. My editing programs are Lightroom 5 and Photoshop CS6. I've never had an issue like that with any other image I've edited on Photoshop, it seems to be this particular file only. I'll look into the settings to see if something got changed. Thanks.