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A $5 1000mm telephoto lens
Lens: 1000mm x 30mm f33 Camera: Pentax k-x Photo Location: Adelaide South Australia ISO: 400 Shutter Speed: 1/125s Aperture: F32 
Posted By: marty-0750, 04-12-2014, 10:36 PM

Ok , the only part that is $5 is the lens element itself - a simple plano-convex 30mm x 1000mm (from Surplushed Surplus Shed) fitted into a cardboard tube.

The rigging is made for stuff lying around the garage while the tripod and bellows is equipment I happen to already have. The bellows is more a convenience and an over-sized draw tube between the camera and telephoto tube will do the same for focusing.


A simple lens suffers from chromatic and spherical aberration. But this lens has a long focal ratio - f33. This helps to reduce chromatic aberration. As you can see it is not that bad for a $5 lens though some red-purple fringing is still evident.


However, processing with some selective hue tweaks in Paintshop Pro reduces apparent chromatic fringing and with some sharpening produces a rather acceptable image!


This unprocessed, uncropped image of the moon shows some colour fringing around the lunar limb but hardly noticeable.


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04-12-2014, 10:40 PM   #2
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Wow !

Impressed.
04-12-2014, 10:52 PM   #3
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I like it! I admire your ingenuity (but it might be a bit cumbersome for birding). My first telephoto experiment some 40 years ago was a Busnhell Spacemaster telescope taped to projector stand. I didn't have an adapter so I just looked through it using my Exa SLR with Tessar 50/2.8 and got a shot of the Orion Nebula. Like yours, it the result was OK and the experiment a lot of fun. I would like to see your moon shot processed.
04-12-2014, 11:02 PM   #4
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I picked it was in South Australia - the Stobie pole! A truly wonderful invention of one of my classmate's grandfather. They are really convenient to design into power line supplies. My first proper job.

I think we described that pole top arrangement as a E1122 (variation) for cost clerk purposes. It is over 30 years, so someone may be able to correct me - I might have the number wrong. The variations are the addition of the light fitting and the LV connections to a customer.

Actually - pretty good image, not that much different to what I was just getting with my Rubinar 1000/10 mirror which even with the K3 improved viewfinder is a bit of a challenge to focus. It is good to see the hexagon bolt heads and rust stains.

What do you vary to focus it?

04-13-2014, 12:56 AM   #5
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You mean James Cyril Stobie B.E? He use to be a member of the Astronomical Society of South Australia. His "stobie poles" were infamous among the members in that they supported the streetlight rigs that often annoyed observers with their light pollution.

The "telephoto lens" is really a 17th style telescope I made so that I could see what the astronomers of the era "saw" - before the invention of the achromatic lens.
_

For focusing the tube slides along the v-shapes. It is held against a perforated lens cap at the end of the bellows. The elastic band maintains tension.

_

The business end of the telescope. The lens cell with the 30mm plano-convex.

_

The telescope with a Huygens eyepiece (set of two plano-convex lenses). So, the telescope is entirely non-achromatic, no coated lenses. It performs rather better than I would have expected.

_

A snapshot of the moon taken hand-held through the eyepiece at 26x with a Canon compact camera. Shows more detail than in direct "telephoto" mode.

Last edited by marty-0750; 04-13-2014 at 01:04 AM. Reason: typos
04-14-2014, 01:05 AM   #6
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Love places like that. Thanks for filling in the story. I have bought odd lenses from them and they don't charge a fortune to post to Australia like Edmund/Thorlabs do.
04-14-2014, 01:24 PM   #7
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Very cool.
04-14-2014, 04:46 PM   #8
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I'm impressed that you managed to keep it "long lens white" too.

04-19-2014, 06:29 AM   #9
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QuoteOriginally posted by dcshooter Quote
I think you might have forgotten to attach the image!
Strange? I can see it on the post on my screen

Anyway, deleted that post and trying again....

Here's another taken today. A little bit more care in focusing and some post sharpening puts that extra snap to it. Seeing effects give it that slight ripple look in parts. At f33 photos are limited pretty much to bright daylight but also provides a decent depth of field.

Last edited by marty-0750; 04-19-2014 at 06:44 AM.
04-19-2014, 12:39 PM   #10
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What was the temperature when you took the image just attached? How far were you from the sign and the building behind?
04-19-2014, 07:36 PM   #11
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QuoteOriginally posted by tim60 Quote
What was the temperature when you took the image just attached? How far were you from the sign and the building behind?
Measurements with google maps indicate the sign is 200 meters away (650ft) from my camera location and the house behind another 20 meters (65ft) The forground bushes are about 20 meters (65ft) in front. That is, the depts is around 40 metres. (130ft)

Temperature as recorded by Bureau of Meteorology for the time stamp of the image (11:38am 19 April) 19C (66F). Thermals from the paved road by the sign probably produced the seeing effects.
04-19-2014, 07:49 PM   #12
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QuoteOriginally posted by marty-0750 Quote
Measurements with google maps indicate the sign is 200 meters away (650ft) from my camera location and the house behind another 20 meters (65ft) The forground bushes are about 20 meters (65ft) in front. That is, the depts is around 40 metres. (130ft)

Temperature as recorded by Bureau of Meteorology for the time stamp of the image (11:38am 19 April) 19C (66F). Thermals from the paved road by the sign probably produced the seeing effects.
Thanks. I have found 20C was about scintillation limit for 1000mm at distances like that. I guess the elevation of the road got fairly near the edge of view. The DOF looks about what I would expect from a regular 1000 mirror lens. Impressive bit of kit you built there. My 1000mm also offers macro, it focuses down to about 4m but the results are a bit weird. (Astringent persimmons being dried, after peeling, last weekend from about 4.5m. They are about 2" across.)
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04-20-2014, 05:07 AM   #13
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Thanks. That promoted me to go to the lake and try close up of these birds. Some passer-bys were intruiged by the "tele-lens contraption" and queried its operation.

Chromatic aberration is most obvious at contrasty boundaries like the breast and background of the sea gull. Distance = 10 meters. The residual aberration casts a slightly dreamy "portrait" effect over the photos.




04-20-2014, 06:13 AM   #14
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ha and wow I would love to see you get through airport security with that
04-20-2014, 12:47 PM   #15
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Your lens is impressive.
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