Triplet 2.8/78 adaptation for DSLR camera

11/11/2014 - 10:56
Triplet 2.8/78 adaptation for DSLR camera




This is the simplest anastigmatic. Cooke triplet was a major advancement in lens design. It widely used in inexpensive cameras. But despite its simplicity, lens of this design has an interesting character.

Cooke Triplet design

Cooke triplet optical design (picture taken from Wikipedia) So it makes sense to mount the lens on the camera. Here is shooting examples. In addition we will wipe dust off and blackened elements edges. Let's get started …  

 

Disassembling Triplet 2.8/78

Unscrew the lens unit from the body, I used hit my arm plastic tube. Inserted into the front lens mount, and twisted counterclockwise. And get this view. Disassembling Triplet 2.8/78

Next, unscrew lens unit of the barrel, without barrel, it is very small.

disassembling Triplet 2,8/78

Now take out the elements. Between them are black metal rings for support for the desired distance, as well as act as a diaphragm.

 

Note:

When removing the elements note as negative lens element. It is very similar to a symmetric, so the reassembly can be confused and and put it wrong. disassembling Triplet 2,8/78

Disassembled Triplet 2,8/78

 

Edge-Blackening

Edge-Blackening helps to reduce stray light, that scatters off of the edges of an element. In fact, the diaphragm acts as a blackening without skipping more unwanted glare. Since the lens is designed for the overhead projector, the manufacturer does not bother so as to enhance the image contrast. Take a permanent marker and paint the edges of the front and rear elements. If there is dust on the lens, it can gently wipe. After edge-blackening reassemble elements back to the barrel. Be careful Cooke triplet requires careful assembly, any even small deviations from the optical axis, so that's fraught with consequences shown in the photo below.

 

What happens if you assemble a negative element inverted

When you get the wrong lens assembly with all sorts of strong optical defects such as spherical aberration, coma, drop in sharpness from the center of the frame. Of course, the picture becomes more expressive, but consider whether it is necessary to you?

wrong reassembled Triplet 2,8/78wrong reassembled Triplet 2,8/78

Halos are somewhat like meniscus lens design

wrong reassembled Triplet 2,8/78wrong reassembled Triplet 2,8/78wrong reassembled Triplet 2,8/78

Some attracts such an unusual picture. But such a lens focusing is difficult.

 

Focusing mechanism for Triplet 2.8/78

To lens could focus, you must attach it focusing mechanism. This can be done in several ways, one can firmly insert the lens into the tube and get the focus mehanism of the "Trombone" type. You can even make DIY helicoid. But I seemed these methods are not very comfortable or labor intensive. So I used it for the donor helicoid from the Helios 44-2. For these purposes, I bought a shabby Helios 44-2, and get out of it lens unit, leaving only the helicoid. Aperture I decided not to leave, because the values ​​of 2.8 at a focal length of 78mm is sufficient for portraits. The all beauty of the Triplet in bokeh. Cover the aperture, and will dry sharp picture is not much different from the usual lenses. The more correctly put a diaphragm between 2 and 3 element too much trouble.  

 

Adaptation Triplet 2.8 / 78 for the camera

So, to install the lens in the Nikon we need to cut off a portion of the back of the tube to get the desired flange distance. Rear segment by my approximate calculations was 68.5mm. I decided to leave the front part of the native barrel, because it has a good hood, as well as constructive. In order to adjust the flange distance is necessary to cut the back of the case, a tube with a screw thread. According to my calculations, it turned out that it needs to be shortened in the 35mm. Take a hacksaw and saw off the excess. It is important that the interval was not imperfections, otherwise you will get a tilt of the optical axis. For a flat housing segments can be used as a pipe cutter. Next screwing lens unit back to our barrel, and fasten to the helicoid. To secure the front part to the helicoid, I cut the puck out of cork 20-liter water bottles. Its diameter due to friction on the well-kept helicoid. In a puck, I cut a round hole by rear element size so this washer also need to center respect to the holes in the helicoid (it is a bit larger). adapted Triplet 2,8/78

Now my lens has a blue stripe. Like a red stripe on the Canon L series :).

 

Now our lens ready for shooting

To attach it on Nikon I used M42-Nikon adapter. Well, a few test shots. Shootings without post-processing. Only resize. Also read Triplet 2.8/78 Review with more sample shootings.

Triplet 2,8/78 samplesTriplet 2,8/78 samplesTriplet 2,8/78 samples





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