[vladan]

I have K-3. I am to use it for shooting my paintings (no glass), mostly outdoors. Which lens should I buy?

[Ptr_Mrtn]

Normal prime focal length, 35mm give or take. The 35mm limited macro has almost no distortion, and can focus plenty close for even a small painting. If your budget isn't so large, the normal da 35mm 2.4 should be perfectly acceptable

[Homo_erectus]

I digitize my girlfriends watercolors and I use a 105mm Macro. You'll want good light and a tripod and maybe a laser level for best results. There are some fantastic videos on youtube that show how museums do this. I highly recommend watching them.

[CristiC]

Since the subject is flat I would recommend prime macro lenses.
SMC Pentax-D FA 50mm F2.8 Macro
SMC Pentax-A 50mm F2.8 Macro
but first choice would be the SMC Pentax-DA 35mm F2.8 Limited Macro
Maybe a manual focus lens like Samyang 85mm F1.4 used at F5.6 provides the sharpness needed across the frame and is very usable for portraits too.

[Ishpuini]

Some photographers use (tilt-)shift lenses to photograph paintings. Partly because it's not always possible to mount a camera dead center in front of the canvas, partly to control reflections from external light sources, both of which can be compensated for by shifting the lens. I suppose if you want to document your own paintings you'll have full control on how to mount them in front of your camera, so this may not be relevant to you.

Macro lenses may indeed be the best choice if you can mount the camera exactly in front of your work.

The size of your paintings will determine the preferred focal length. The smaller your work the shorter working distance you need and the longer focal length you can use. The bigger your work the further you'll have to move back and the sooner you might need a wide angle lens.

One important thing to consider is not related to lenses, but to white balance. If you shoot outside, putting you work in the sun may cause unwanted reflections, and putting it in the shade will result in a white balance that may be too blue. It's probably a good idea to include a grey card in a series or just inside the camera's frame but outside the picture's frame. If you shoot RAW, this will allow you to set the correct white balance in post processing. Alternative it to use manual white balance and meter it off a grey card before taking the picture of your work.

hth, Wim

[emalvick]

A gray card is very important.

I shoot a lot of paintings in galleries and museums as well as some I've painted myself. I've not used a macro lens (seems like a good suggestion though), but I do try and stick with a focal length between 30 and 85 mm as much as possible to minimize distortion. I occasionally use a CPL if there is glass involved. I don't worry as much about shooting straight on. Glare can be an issue per the CPL suggestion, and at museums getting that type of shot can be difficult. Rather, I always compose wider than I need to and try to stay within 15 degrees of normal (straight on) and utilize Photoshop or other software to adjust for distortion as much as possible.

It sounds like a recipe for trouble, but I've been surprised at the results I can get. I've shot further out of plain with success too, but I've also had failures. Regardless, I find adjustments for orientation are almost a guarantee to be necessary.

[johnyates]

I have K-3. I am to use it for shooting my paintings (no glass), mostly outdoors. Which lens should I buy?

Get the longest lens that is usable with the working distance you have available. This will help minimise the inevitable slight errors in getting the sensor plane parallel to the painting. I think a 100mm macro would be a very good choice if you have the space.

[Homo_erectus]

The 105mm macro I use works very well. In the past I have used many different lenses and actually most work well enough as long as you can get square to the plane of the painting. Longer lenses work better because you can fill the frame and be far enough away that you aren't making shadows with the lens, camera or your body.

I use a gray card as well, I forgot to mention it in my previous post.

[6BQ5]

I would recommend a macro or telephoto lens of some kind. They tend to exhibit less distortion. Maybe lens corrections in software make up for the distortions well enough. Why not avoid them in the first place though, right?

[TaoMaas]

Some photographers use (tilt-)shift lenses to photograph paintings. Partly because it's not always possible to mount a camera dead center in front of the canvas...

Yes! You want to make the back of your camera as parallel to the painting as possible. That way, you don't distort it through key-stoning.

A gray card is very important.

Yes! A custom white-balance is almost a "must" because you want the colors as accurate as possible.

I would use a moderate lens, if I were you. If you get too close with a wide lens, you'll distort the proportions of the painting. If you stand too far back with a long lens, you may compress it too much. However, if you have to choose between a long lens and a wide lens...go with the longer lens.

[vladan]

I'll set for the DA 35mm F2.8 Limited Macro. Yes, I will be using the gray card, my tripod, and I am good with Photoshop. By the way, I am currently using Sigma "Art" 35mm f/1.4 DG HSM, borrowed it from a friend.
Thank you all.