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Pentax 110 lens with aperture control

T

turbo

Guest
A day off, a bunch of camera parts (size 00 shutter + Pentax 110) and an idea.


The finished product will screw into a C-mount adapter, provide infinity focus and f-stops from 2.8 to 11 and a smidge. The 50mm lens will not fit in the adapter. The bottom picture was taken with the 18mm at f8.
 
C

ChrisJ

Guest
I've been looking for a way to do this myself, even wide open the lenses are good, stopped down they would be really good.

Where did you get the shutter mechanism?

Chris
 
T

turbo

Guest
The shutter was off of a Konica I, a Konirapid shutter, but any
size 00 shutter will work. I started to use a compur shutter from a
Kodak but the aperture lever was behind the shutter so could not be
accessed when mounted.
 

woodmancy

Subscriber Member
The shutter was off of a Konica I, a Konirapid shutter, but any
size 00 shutter will work. I started to use a compur shutter from a
Kodak but the aperture lever was behind the shutter so could not be
accessed when mounted.
Briliant

Keith
 
R

Ranger 9

Guest
VERY spiffy build!

Am I correct in thinking you removed the actual shutter assembly (blades, master ring, timing geartrain, etc.) from the shutter housing, and just used the diaphragm assembly?
 

pentacon6

New member
I used to think that no 00 shutter is too small for homemade lens. Now you find a new value of that. Good job!
 
V

Vivek

Guest
Awesome! I might have a few shutters around. :)

The 18/2.8 (especially stopped down, sample is real nice) kicks the Oly-D 17/2.8 in terms of performance (flatter field and no CA).
 
T

turbo

Guest
Yep, stripped the shutter of everything but the housing and aperture. Mounted the 110 mount flange to the shutter's speed dial retaining ring and glued the ring to the shutter body.

The shutter mounting thread is the same diameter, but a different pitch. That's OK though because you don't screw it in very deep (about 1/2 turn). Use the shutter mount ring and shim/grind to adjust infinity focus.

I made the mistake of gluing the flange assembly to the body without the lens mounted, so there was not enough clearance between the flange and shutter to mount the lens. Since the flange can be removed, I shimmed the flange to provide the needed clearance.

One thing missing is a DOF scale. Have to judge sharpness in the finder. In the attached photo the focus was on the truck front tire.
 
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simplebot

Guest
That's awesome! I also built one, but I used an iris from an old broken pentax 50mm lens, and mounted it into the c-mount adapter. I wasn't able to achieve infinity focus due to the bulk of the mechanism, so I've kind of shelved it for now, unless I need to do some close up photography.
Here's a pic:

I don't have any f-stops set, so I just wing it for DOF through the viewfinder. It's fun, but not very usable right now. Congrats on yours!
 

m3photo

New member
Re: Adapter for sale

Would you be interested in selling your adapter?
echols
I'd also be interested in having a pre-made diaphragm adapter for PENTAX-110 lenses - anyone up to it? On the G1 they're certainly good even at f/2.8, I reckon the 18mm could be an excellent street lens with the possibility of stopping it down.
 
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turbo

Guest
Would you be interested in selling your adapter?
echols
I don't have any more defunct shutters to build another adapter. I collect and rebuild 50-80 year old German cameras which frequently use the compur #00 shutter. I find that a lot of the cameras I buy for parts end up being repairable. I'm the only person I know that can end up with fewer parts after buying a parts camera. Sigh!

Maybe one of the adapter makers will see the interest in this and build an aperture Pentax-110 mount. Hmmmm. Maybe I should start buying 110 lenses.

turbo
 

madmaxmedia

New member
Could you just stick a black disk with a hole into the c-mount adapter, to at least be able to stop it down to a preset aperture?

If that is possible, then you can at least switch between 2.8 and say f8 for lots of DOF. Not exactly convenient, but a nice option I think.
 

m3photo

New member
Re: Black disk

Could you just stick a black disk with a hole into the c-mount adapter, to at least be able to stop it down to a preset aperture?

If that is possible, then you can at least switch between 2.8 and say f8 for lots of DOF. Not exactly convenient, but a nice option I think.
Funny that, I was thinking of exactly the same thing driving to work this morning! F/8 as it happens is what I usually stop down to to get the best out of most lenses.
 

PeterB666

Member
Maybe one of the adapter makers will see the interest in this and build an aperture Pentax-110 mount. Hmmmm. Maybe I should start buying 110 lenses.

turbo
Quite probably a good idea. The way C-Mount lenses and OM lenses have increased in value since MFT isn't funny anymore (unless you already have what you want).
 
T

turbo

Guest
Could you just stick a black disk with a hole into the c-mount adapter, to at least be able to stop it down to a preset aperture?

If that is possible, then you can at least switch between 2.8 and say f8 for lots of DOF. Not exactly convenient, but a nice option I think.
Waterhouse stops. Back in the days when the lens cap was your shutter, one of the ways to change f-stop was with thin metal sheets with different sized holes that were slipped into a slot behind the lens.

You could cut 3x5 cards to size with an f-stop (and painted Sharpie black, of course) and tape it to the back of the adapter. That should work.
 

madmaxmedia

New member
Great! I will start playing around with aperture disks, as soon as I get my hands on a 110 lens. The 18mm 2.8 is really the only Pentax one I want, not sure if there are any other good ones from other cameras.
 
C

ChrisJ

Guest
The only problem with this approach is that the actual diameter of the f stops is dependant on the focal length of the lens. The physical aperture diameter is just focal length divided by f number.

So for the 18mm lens they would be;-

f4 = 4.5mm

f5.6 = 3.21mm

f8 = 2.25mm

f11 = 1.63mm

f16 = 1.125mm

Whereas the apertures for the 24mm lens would need to be;-

f4 = 6mm

f5.6 = 4.28mm

f8 = 3mm

f11 = 2.18mm

f16 = 1.5mm

For the 50mm and 70mm lenses - well you can work it out yourself.

For the 20 - 40mm zoom it would be high on impossible to get the right aperture.

Whether any of this actually matters is a moot point really, by making an aperture disc with a diameter of 2.75mm it would be wider than f8 when used with the 18mm lens and smaller than f8 when used with a 24mm lens. If you used it with the 50mm lens it would be an effective aperture of f18! But you would still get the increase in DOF, in fact you would get the same DOF as a 21mm lens at f8, but your shutter speed would be slower!

It all ties together (I think!) and the hours spent in the optics lectures I attended (over 50 years ago) is finally paying off.

Chris
 

madmaxmedia

New member
Thanks Chris, I was just wondering what size the hole should be- I am mainly interested in the 18mm lens anyway and will probably end up just making just a f8 disk for now.

I actually ended up winning a auction for Pentax 110 and both 18mm and 24mm lenses though (and a couple of filters to boot). So your info is very helpful. Thanks!
 
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