Material for adapting the lens from the Soviet telescope ZT4-20x50 specifically for Radozhiva prepared a reader nicknamed Iskander.
Alteration ZT4-20h50
foreword
The pipe ZT4-20x50 was given to me as a gift more than 20 years ago. It consists of three steps. The lens is a glued two-lens achromat, seated in a plastic first stage, fixed with a plastic ring with a thread, with a wrap-on anti-skeleton hood. The second stage is a metal tube, which was tightly included in the first, but for 20 years of operation it was very loose. The third stage - also metal, contains a wrapping system of three optical elements. It ends with a thread for fitting an eyepiece with a focusing device in the form of a wide corrugated ring.
The scale of the tragedy
Due to the general looseness of the system, after reading the magazines "Science and Life", I decided to build a telescope out of it. I removed all the lenses of the turning system from the third stage, cut off the excess, pushed the third stage into the second, gluing it tightly with epoxy. Focusing it at infinity, I also filled the compound of the first and second stages with epoxy. The pipe turned out to be shorter in length, rigid, monolithic, but gave an inverted image. An additional projection eyepiece corrected these shortcomings, along the way bringing the magnification to 60X. In this form, but without a projection eyepiece, I photographed the Moon, attaching a Canon soap dish with a XNUMXx zoom to the eyepiece.
Alteration ZT4-20h50
Newtonian classic
Realizing that the extra optical elements in the form of an eyepiece and a 13-lens soap dish are unlikely to improve the picture quality, I decided to test this lens in the "Newtonian focus", when the image from the lens directly hits the matrix. In my opinion, this is the perfect solution. Looking ahead, I will say that the real aperture such a system is several times higher than the aperture of most modern photographic lenses ... corny because of the small number of lenses. I suspect that aperture modern multi-lenses are VERY overpriced, despite the ultra-modern antireflection coatings.
Achromat + DSLR, and between them - plastic.
I didn't want to spoil, cut, sharpen the original pipe, so that it would be possible to return everything to its place. So I started sculpting the lens barrel from scratch. Since the lens diameter is 52 mm, I took a piece of PVC pipe with an outer diameter of 50 mm (white) as the inner pipe, it is quite rigid, with thick walls. I glued a flange to it, to it - an M42-EOS mount adapter with a chip (of course, at this stage, at least roughly alignment must be observed!). At the first test stages I used Globus nitroclay, but the adapter was constantly torn off, but the glue remnants were easily cleaned off. At the final stage, I glued the adapter with silicone sealant, and for reliability I advise superglue or screws.
Alteration ZT4-20h50
The outer tube is my special love and sex. To begin with, I took a plumbing coupling (it is produced in gray with two rubber seals, an inner diameter of 50 mm, a length of about 90 mm), took out the oil seals. To this clutch I used a semblance of a frame with a lens. To make it clear, I did this to evaluate the real tube stick out and the minimum focusing distance. Realizing that the length was not enough, I bought another pipe of the same format called "expansion coupling". After cutting off all the excess from it, about 150 mm remained, after gluing these pipes - the total length of the outer pipe turned out to be about 220 mm. I focused with simple translational movements of the outer tube. The first pictures showed that there is no contrast, and the pipes must be blackened inside. The inner tube was painted with silicone matte black paint. The picture has changed dramatically! With the blackening of the outer pipe, I had big problems, even the paint of the marker starts rolling and sticking during friction, so I advise you not to paint, but immediately select the color blacker.
Alteration ZT4-20h50
Helicoid - Easy!
When cutting the same pipe, I made a marking in a spiral, with a step of about 30 mm, cut it with a hacksaw for metal, cleaned it with sandpaper and put on the resulting “serpentine” on the outer pipe. Since the “serpentine” extended and increased in diameter, an even spiral groove was formed with a width of about 4 mm and a depth of 2 mm. Then he poured superglue into the groove.
Alteration ZT4-20h50
Alteration ZT4-20h50
After I made a leash attached to the inner pipe, at its end there is a small pin that fits into the groove of the helicoid. It can be replaced with a metal bolt in the future.
Alteration ZT4-20h50
Alteration ZT4-20h50
Alteration ZT4-20h50
Alteration ZT4-20h50
I chose the position of the leash, focusing in the rear position on the moon, and then moved it a couple of millimeters back for a reserve, and glued it, as a result, I got a small jump to infinity.
Installation Features:
- Focal Length: 330mm
- Lens Diameter: 50mm
- Relative Hole: 6,6
- Total length from the bayonet plane: 300 - 383 mm
- Focusing Outer Tube: 83 mm
- Focusing distance: from 3 meters to infinity
- When focusing from MDF to infinity, the outer tube makes 2 turns
- Focusing through the viewfinder is inaccurate, so it’s better to focus through Live View
Sample photos:
You will find more reviews from readers of Radozhiva here.
The author of the review article is great! And his work is worthy of respect. Of course, if you have a certain amount of money, you can shoot from a satellite. But to do it yourself and so that others can show and pass on experience is a high level.
Rodion, there is no logic. In a photomultiplier, the subject of photography is a film. Photo paper is a sensor. Light travels from the film (object) to photographic paper (sensor). There is a correct path of rays. Classic supermacro, when the image of an object (photographs on paper) in linear dimensions is larger than the object itself (film). What are you confusing. Oh, yes, and who has verified that the quality will be worse when the lens is flipped? Okay, the dispute is not on the topic of the article, I will try this and that, it is interesting to compare.
Actually very cool. To assemble from plumbing and lenses something that in principle is capable of photographing in itself is already a good task.
in terms of the quality of the photos themselves - well, in principle, the moon on 70-200 f4 Nikon's lens was much better for me (for d5200 a carcass). Well, he was bought for a lot of money, how can you compare something.