Home
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

Building an adaptor for the Pentacon 80mm projection lens
View previous topic :: View next topic  


PostPosted: Mon Sep 11, 2017 9:30 am    Post subject: Building an adaptor for the Pentacon 80mm projection lens Reply with quote

The Pentacon 80 lens is a  projection lens for 35mm slide projectors. It is the successor of the Diaplan 80mm f/2.8 (that was made of metal), the Pentacon’s body is all plastic.  It does not have any iris to control de light. Its  body has a groove along it to allow focusing when placed in a projector. It does not have any coating to protect against flare because the light is supposed to come opposite to what it comes in any camera lens. Not very fancy to be used on a camera for such limitations.

But it has some powers:

- It's a Cooke triplet design (three elements of single lenses) that could provide a special bubble bokeh and a vintage look to the pictures, similar to the Trioplan 100mm but with smaller bubbles.

 

- Very lightweight (75g) that allows for a simple plastic adapter to use it.

- Good resolution (common on the projection lenses).

- Covering the full frame 35mm sensor.

So I decided to build my own adapter using my 3D printers. The target was to have the widest focusing range possible (from macro to infinity if possible) and a standard mount that could be used in most of the current digital cameras (mirror or mirrorless). Since I had several adapters to the L39 screw I decided to use it as the lens mount. So the barrel had to have a L39 screw on the base and a cylinder that would hold the lens, with some kind of guide for the helicoid groove. It took me several iterations until I reached something usable.

This is the barrel being printed on my M Prime One printer, the screw is printed on the top to ensure accuracy. I used black PLA and layers of 0.1mm (higher layers do not provided enough resolution for the L39 mount screw). As you can see in the back of the barrel, there is a hole to place the screw that will fix the lens in position.



And this is the barrel once printed:



To guide the lens along the barrel I used a M4 screw with Allen head, and a M4 nut. The screw fits well inside the groove of the lens. I also printed a knob that fits tight on the head of the allen screw, it has to be glued in place. I used some Superglue gel.



The nut is placed inside the barrel. To ensure tightness, i did cast the place for the nut a bit narrower than needed and then forced the nut inside with the help of the heath from the tip of a soldering iron. (No Superglue inside the lenses, the vapours can damage the optics)




 

This ensure that once cooled, the nut will remain in place.

Since the lens has no coating at all, a shade would be needed, so I printed one that fits on the front just by pressure. It took me several iterations to find the right diameter size to allow fitting and keeping well in place. It's a matter of tenths of millimeter



Then putting all togheter: Make the screw protruding a bit inside the barrel and align the groove with it, screw in a little (being extremely careful of not using excessive pressure to avoid damaging the lens) and finally placing the shade in place:



Once this done, just screwing in the L39 adapter gives an usable lens. Tested on a NEX-F3, a Samsung NX210 that sport APS-C sensors. Next steps will be trying on u4/3 and FF.

At this time I can focus macro (don’t know yet the macro relationship) but it cannot reach full infinity, but quite close. (around 100m far). A difficulty is the narrow DOF. An 80mm lens with 2.8 aperture gives no much DOF).

Next steps (beside the testing on other cameras) will be trying to modify the adapter to hold some kind of removable fixed iris (a circle with a hole inside) to reduce a bit the DOF, because the results are very promising.

Selfie on the NEX-F3



The lens on a NX210 Samsung camera:



And some samples:

Missed focus but good for showing wich bokeh can be attained.



Close focusing:



Farthest focusing:



More testing to be done on u4/3 and FF cameras.


Last edited by Jesito on Fri Sep 15, 2017 7:09 am; edited 1 time in total


PostPosted: Mon Sep 11, 2017 8:08 pm    Post subject: Reply with quote

Advanced DIY 😳


PostPosted: Tue Sep 12, 2017 1:02 am    Post subject: Reply with quote

nice result.
the green part make it like toy though.


PostPosted: Tue Sep 12, 2017 8:50 am    Post subject: Reply with quote

Nicely done, certainly much lighter than my solution!


PostPosted: Tue Sep 12, 2017 9:15 am    Post subject: Reply with quote

hoanpham wrote:
Advanced DIY


Thanks for commenting, Hoan.
Not so advanced. Nowadays most of the teenagers have access to a 3D printer and do things far more complex... ;o)


Last edited by Jesito on Fri Sep 15, 2017 7:10 am; edited 1 time in total


PostPosted: Tue Sep 12, 2017 9:17 am    Post subject: Reply with quote

IAZA wrote:
nice result.
the green part make it like toy though.


Yes, it does. It's the only colour I had available, and I thought all black would be too dark.
Anyway, it's not more than a toy ;o)


PostPosted: Tue Sep 12, 2017 9:37 am    Post subject: Reply with quote

kds315* wrote:
Nicely done, certainly much lighter than my solution!


Thanks Klaus. Do you mean the one you published in your Blog around 2015? (the one with a M65 and a M42 helicoid?).
That one is much sturdy and configurable... It was a source of inspiration for my adapter for the enlarger lenses, (Pentax-k helicoid instead).

I like the 3D printing process because it's really quick from the idea to the prototype, many times usable prototypes.
But if one wants somethig really strong and durable, nothing like your solution.


PostPosted: Fri Sep 15, 2017 7:03 am    Post subject: Reply with quote

A couple of shots with the lens mounted on the EOS-M:





PostPosted: Fri Sep 15, 2017 9:08 am    Post subject: Reply with quote

Jesito, is the lens clear inside? It lacks a bit contrast (and also sharpness) if I may say.
At least I expected that.


PostPosted: Sat Sep 16, 2017 4:26 am    Post subject: Reply with quote

kds315* wrote:
Jesito, is the lens clear inside? It lacks a bit contrast (and also sharpness) if I may say.
At least I expected that.


Hi Klaus,

Thanks for commenting
Yes, I think so. The lens is brand new, we got a batch of three of them (for some other colleagues) and they came well packed, wrapped on strong paper. Never used before, for sure.
The pictures were taken handheld. In my laptop's monitor they look reasonably contrasted. I agree on the overall sharpness that could be related to focusing problems from my side, my sight is not as good as it used to be. (Years do not forgive). I'll try more samples, this time on a tripod. It can be also some problem with the bright surface of the plastic inside the barrel.I thought in painting it with a matt dark grey paint. There is a lot of room for improvement there...
At least, I see the one of the banana tree right in both sharpness and contrast. Do you see it right?.
Kind regards,
Jes.