The Light Slide

fun with photography


Research: Adapting Pentax Auto 110 lenses with aperture

Posted by Amy Hoy on

The Pentax Auto 110 lenses are little jewels: tiny, beautiful, and they take lovely photos. Best of all, they're usable on other cameras. Personally I've adapted them to my Pentax Q and Samsung NX mini.

Pentax Auto 110 70mm

The one downside? They lack apertures. For simplicity, and size, the aperture is controlled inside the body of the tiny Pentax Auto 110 camera. Kinda the opposite of the lens-mounted Pentax Q leaf shutters…

I've shot the 110 lenses wide open, but I've also inserted little Lensbaby aperture discs (affiliate link) into the adapters to stop down. Which works!

But this leaves the diaphram sitting pretty far back behind the rear lens element, which isn't ideal, optically. And the Lensbaby aperture discs were not made for the Pentax lenses, so they don't actually stop down all that far.

But now I am thinking seriously about using these tiny little gems on the Fujifilm X-E1 that is winging my way. Shockingly (!) even the 18mm lens will cover an APS-C sensor.

So I did my thing and dove into research mode… and found that photographer Jean Poitier has quite cleverly made the 18mm f/2.8 into a seriously sharp, nearly pan-focal lens.

He came up with a new kind of hack to stop it down all the way to f/8 (which the Lensbaby discs don't reach, I think).

Here are the example photos he's posted from his lens hack:

Jean Poitier's photos

Hôtel de Ville
Chambord - n° 2
`
Chambord - n° 5
Sitting alone

Seems like a lot of chromatic aberration in this last one, which does give me a little pause. Maybe less would be had mounting the apertures at the rear, or even front? But the black and white results are stunning…

The technique

And here's how he did it… all excerpts are from Jean's posts on a thread over on the PentaxForum:

[I tried different techniques,] First was to use a paper hole reinforcer that I had Sharpie blacked-out ... sticky-side stuck to the rear element housing. Another method is to use black rubber plumbing washers/grommets that are attached as well to the rear of the lens.

My preferred option was to open the 18mm and insert a DIY aperture disk (thick black paper with hole via a small hobby punch) between the front and rear elements ... just like a movable aperture, but static and maybe about f/8+ at my best guess-timate.

I may try to go smaller inserted DIY aperture on the 18mm ... I have a second copy which could be used, but I am happy with my first efforts

— comment

I opened the 18mm lens and inserted a DIY aperture disk using black electrical tape with a small hole punched in the center ... the smaller than normal hole punch was from a hobby store.

I did this on my own and I have never seen any Web videos about this intervention.

Maybe I should make another one with more of the pin-hole type aperture and document the intervention for this thread. Give me a bit of time ... as I remember, the disk is snug inside because it is squeezed between the lens housing halves.

— comment

my hole punch was a kind of scrap-booking item… [a regular hole punch is much bigger than f/8]

Questions remain:

  • is there a better way to do it than buying a specialty scrapbooking punch?
  • how tough is it to open up & reassemble the lens?
  • is it better to have the iris inside the lens (like most lenses) or behind the lens (as in the actual Pentax Auto 110 camera)?

But chances are that I will be trying it after a little more thinking.