If there's something I love more than weird cameras, it's weird lenses.

And this one's a weird one.

No, the title isn't a typo… I'm not confused, and I don't mean the Pentax 17mm f/4 fisheye, which is quite normal and generally well-regarded for what it is.

Today I'm talking about its secret cousin that nobody talks about, the fixed-focus 18mm pancake lens:

It's really very pancake-y!

This little guy starts at f/11 and you can stop it down to f/16 or f/22. No half-stops here. Why? Well, there's no bladed diaphragm. When you turn the aperture ring, the lens swaps in one of three little Waterhouse stops, fully formed with a perfectly round iris.

So it's super tiny, fixed focus, and has Waterhouse stops. Definitely weird!

And it's m42 — without the usual Pentax aperture pin — meaning it's a preset lens, which makes focusing difficult on a DSLR without liveview, but it can be used anywhere and everywhere.

But how's the image quality? Because that's what really matters.

Well, if you're looking for seriously sharp wide angle for serious photography, you don't want it. Literally any other lens will put it to shame.

But if you like character… you've come to the right place.

Here's a series of unedited shots at f/11, f/16, and f/22 respectively:

f/11

f/16

f/22

At f/11: Nothing is sharp. Nothing. There's a hint of sharpness about the palo verde bush to the right of the wooden pole — the center of the lens — but it's just a touch and the area is very small. Also it's quite far away! You'd think at f/11 with an 18mm lens, you'd already be into the hyperfocal zone. You'd think wrong.

That said, the unsharpness is quite dreamy and pleasing. I continue to be shocked by how low the aberrations are in this lens.

At f/16: Some sharpness! Or at least the sensation of sharpness. All frame edges are still somewhat blurry, the corners especially so. The vignetting has become greater and also a bit weird. I'm not sure about the tan-pink at the bottom right… will have to do more testing to see if this was a quirk of the scene/lighting or an ongoing thing.

At f/22: Pleasingly vintage sharp! Of course the far corners are still blurred and there's that weird tan vignette at the bottom right. But the body of the photo has a really pleasing feeling of depth… how can a super-wide have 3D pop, much less at f/22? I don't know, but it does seem to have it.

Note that this is on full-frame… I haven't tried it on APS-C yet, but I did try it on 4/3 and the effect of diffraction was pretty damn high. It gave a neat vintage effect at f/16 though, but objectively not as "good" as on the full-frame Sigma fp.

More samples

Surprisingly low distortion for the age of the optical formula, I think:

Be sure it's fully screwed in and stays that way… or else you get a pseudo-macro effect like this one below; note the tiny branches in focus in the front. Unless you want that kinda thing! Very Holga-esque. My copy likes to come unscrewed when I change the aperture.

Its character converts beautifully to b&w with clarity, toning, etc. Below is the original and then black & white using my own "Infrared toned" preset. The one issue is that the natural haze on the leftmost mountain ridge turns into what looks like a bad sky mask… I didn't use masks at all. Oops! Need to go back and work on that manually.

Below is a test shot on my Olympus e400 Four Thirds camera (a half-frame sensor). Note that despite the "bad edges" being well cropped off, there is a noticeable increase of chromatic aberrations/fringing, and that "vintage lithograph postcard" vibe, and loss of the 3D pop. I like this very much personally but I'm perverse; I wouldn't recommend this lens for small sensors, generally.

My first opinion: Awesome!

I love it on full frame. Can't wait to take it out and play with it some more!

But I also love the Lomography aesthetic; I heavily used my film Holga and Diana back in the day and they were among the few cameras I never sold or donated after I "gave up" photography due to my illness, and I carted them through an international move, twice.

If you're looking for a wide angle bargain and you like sharp and normal rendering, keep walking. For that use case, it's not so much a "compromise" as a disaster.

But if you like unique and interesting looks and don't mind fiddling… it's well worth getting, if you can find a good copy for a fair price.

Also: keep in mind, I live in the second sunniest city in the United States, and it only misses the number one spot by 1 or 2 days. So, especially with a camera that excels at high ISO, this lens' f/22 sweet spot is not a problem for me. Maybe you are not so lucky with light.

Shopping advice

These lenses are rare-ish, and they're also prone to internal separation. I wouldn't buy a copy with internal separation. The separation appears like yellow smears around the edges or lots of little bubbles around the center.

I paid about $160 for mine, with no visible separation and with caps and original leather case, and that seems about fair.

Currently listings are at $250-400 on eBay for lenses with lots of separation, exactly what you don't want — and that price is ludicrous.

This is a lens to set alerts for and wait.