Homemade 280mm Telephoto Lens

I tried to build a cheap telephoto lens, I managed in it although mine has some limits, there is a reason why commercial lens are really expansive...

Step 1: Material

Material I used:
-Reflex body cap (for my Nikon D40 the BF-1A) 5 euro
-Magnification lens (diameter 10cm, focus about 280mm) 5 euro
-PVC pipe reduction D=10cm to 5cm 2 euro
-PVC pipe D=10cm 1 euro
-PVC maintenance joint for 10cm pipes 9 euro
-Self adhesive black velvet (and optional black rugged self-adhesive)
-some screws

I also used a saw, a drill and a threader and screwdriver.

Comments

[Eternal_Tristan]

You will have better luck using an "achromat" lens, like the one's used for telescopes. These are composed of two lenses sandwiched together specially configured to reduce the problems caused by chromatic aberration, which is what you are seeing with all the different red and blue colors in your tests shots. Try something like this: http://www.surplusshed.com/pages/item/l2196.html

[rimar2000]

Very good work.

Since you have a lot of manual skill, I suggest some alternatives for improvement this:

1) buy a cheap pair of binoculars, for those Chinese or Taiwanese, and use one objective. Maybe you need to mount the lens on cardboard.
2) You can enhance easily and cheaply the spherical aberration of your cheap lens: take a flat glass, an o-ring with outer diameter equal to or slightly lower of the lens; build a sandwich lens / o-ring / glass; fill the space between the lens and the glass with clean glycerin or alcohol; seal the joints with silicone.
You can replace the o-ring whit a seal of car's oil filter, but you must wash it very well.
The result will be not perfect, but will be better.

[landimatteo]

thank you, I already tried with the binocular lens, but was little and only 140mm and with cyan dominance. the other advice sounds interesting but the idea of have a liquid that could flow through a leak in my dear D40 doesn't sounds good.

[BobS]

Cyan dominance means it was probably coated red. It blocks certain wavelengths. Use brass polish and lots of time& effort to remove the coating!

[landimatteo]

it actually is red coated. but I won't ruin the lens polishing it...

[rimar2000]

NOOOO!!! Please don't do it!!

"...In all modern lenses the surface is coated to reduce abrasion, flare, and surface reflectance, and to adjust color balance..." ;
"...Today, most lenses are multi-coated in order to minimize lens flare and other unwanted effects. Some lenses have a UV coating to keep out the ultraviolet light that could taint color...";
"...The introduction many years ago of optical coatings, and advances in coating technology over the years, have resulted in major improvements, and modern high-quality zoom lenses give images of quite acceptable contrast,..."

(http://en.wikipedia.org/wiki/Photographic_lens)

[rimar2000]

1) 140mm is something. I guess you can obtain greater and better cheap binoculars. 2) Color is easy to correct, but spherical aberration is almost impossible. 3) If you seal correctly the ensemble, you must not fear a leak. But anyways, the project is yours, not mine ;)

[BobS]

A 7 X 50 binocular front element has a focal length of about 250 mm. It is nicely (reasonably) corrected, as it is an achromatic lens (element). It is quite fast, about f5. Use this in your tele lens, and the results will be far better!!!

[landimatteo]

if I find one suitable binocular or scope I would try.

[BobS]

A 5x lens should mean a focal length of 50 mm. 250 mm = 1x, 1m would be 1/4X, etc.

[landimatteo]

This has not much sense... my lens is 280mm and was described as 5X.
according to your theory a 280mm focus would be 0,89X
<1 X means that the lense don't magnify but reduce the image, but positive lenses magnify so its always >1X.
For binoculars, microscopes and telescopes the Ax has a meaning, the focus of lens is A times the focus of the eyepiece. but in single lenses?

something similar to what you say is diopter= 1/(focal length in meters) so 1000mm is +1, 200mm is +5, 400mm is +2.5, 100mm is +10

[lemonie]

What distance was the cap at when you photographed it? L

[landimatteo]

It was about 20m far I think but I'm not sure. It is only 1,35x-1,4x compared to my nikkor 200mm. I wasn't focusing on magnification but on light. My Nikkor is F5.6, my homemade lens is F2.8 without diaphragm, F3.5 with 8cm hole and F4 with 7cm hole.

[lemonie]

Not knowing too much about these things, I'm impressed that you got that from 20m! L

[landimatteo]

I took a look to my house map and I think I overextimated distances. I think that 7-10m for the hat and 20m for the tyre, but I'm still not sure.

[gmoon]

Ha! I love this! While somewhat optically flawed, it would still be very useful for artistic effects. You'll never get rid of the aberration and distortion with a "simple" lens, of course. Have you thought about placing the aperture between the lens and the camera body? Maybe even add a little slot to insert apertures of different sizes...

[landimatteo]

I know that with a single lens I will never correct aberrations, I hope in the future to correct a little if I will be able to find spare lens, the hard is that it's really hard find lens with charatheristics I'm looking for without buy them in a specialist and expansive shop. Also the lens I used was described as "5X" lens instead 280mm focus or +3.6 or so...imagine going around looking for a specific lens, even harder is find negative lenses. I though about something like the rear filter-holder in some supertelephoto I saw in Internet/magazines but, since the main part of the costs are concentrated in the "pipes", at the moment I don't want to cut the pvc.