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DIY focal reducer

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#1 ccs_hello

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Posted 18 September 2010 - 12:02 AM

Have done that before using bino objectives like this and this pic
Posted Image
now using a different set of old lenses: achromat from Edmund Scientific fl=80mm diameter=46mm.

Here is the achromat itself:

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#2 ccs_hello

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Posted 18 September 2010 - 12:04 AM

First edge blackening

Also for fun, I drew this pic
Posted Image
on Halloween in '04 on "edge blackening" subject and used in this CN thread.


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#3 ccs_hello

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Posted 18 September 2010 - 12:15 AM

Now need adapter body

Left is for inserting into a C/CS mount video camera (compression fit, not using CS mount's 1"-32tpi thread).
Right is for a 1.25" imager inserting into.

The larger end is 2" to go into OTA's focuser.

Finding the right bottle is not easy :) :).

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#4 ccs_hello

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Posted 18 September 2010 - 12:17 AM

Lens about to be inserted into the adapter body

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#5 ccs_hello

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Posted 18 September 2010 - 12:19 AM

Now fit into the videocam

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#6 ccs_hello

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Posted 18 September 2010 - 12:20 AM

Front view

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#7 ccs_hello

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Posted 18 September 2010 - 12:23 AM

Direct front view, the CCD sensor surely looks larger.

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#8 NeoDinian

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Posted 18 September 2010 - 08:11 AM

Wow. Nice job.

How far did you set the lens to the chip, and how's it held in place?

You said finding the right bottle was tough, so..... What kind of bottle is it?

#9 ccs_hello

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Posted 18 September 2010 - 10:37 AM

Jeff,

(Over the counter) medicine pill bottles :).
The left one is tricky (it is used to test your sharp observation :) )

The fourth post showed the lens was wrapped around with scotch tape as the shim before inserting into the adapter. I can fine-tune the position. The lens has a f.l. of 80mm, so if the lens mid-point to CCD distance is 40mm, I got 0.5x but I have to move the focuser drawtube inward by 40mm.

The degree of freedom is mainly constrained by how much inward movement focuser drawtube can offer. I purposely get the short focal length achormat, choose larger diameter lens, and larger adapter size for this very reason. 0.34x is possible in one of my refractor (required inward movement -104mm !!). Play with this formula to check:
http://www.wilmslowa...formulae.htm#FR

It will be using a type-1/3" CCD imager thus vignetting wil not be a problem.

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#10 ccs_hello

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Posted 18 September 2010 - 10:39 AM

This is the other adapter with a 1.25" imager attached.

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#11 ccs_hello

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Posted 18 September 2010 - 10:40 AM

Direct front view of the above arrangement.

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#12 RickShelton

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Posted 19 September 2010 - 12:51 PM

Let me guess,,, one of those "5-hour" energy bottles?
Fill us in please,,

Rick

#13 ccs_hello

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Posted 19 September 2010 - 01:33 PM

Rick,

The left bottle actually is two bottles (smaller one inserted into the big one) glued together :).

It is very hard to find a 1" to 2" step-up bottle :) :).

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#14 Lightning

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Posted 20 September 2010 - 03:18 AM

Thread bookmarked... thank you Sir!






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