A new type of Newtonian collimator (DIY)

dcnicholls · #1 06-12-2006, 12:52 AM

The "Krupa Collimator" as originally described in ATMJ in 1993 didn't quite work. Here's how to make one, and make it work, using scrap parts and a cheap commercial lens: http://www.dcnicholls.com/krupa

DN

bojan · #2 06-12-2006, 10:56 AM

Just what I needed :-) Will try to build and report here asap -)

iceman (Mike) · #3 06-12-2006, 11:27 AM

Great article!

It looks like a normal cheshire/sight-tube though, as long as your mirror is centre spotted? It is effectively the same thing?

janoskiss (Steve H) · #4 06-12-2006, 11:55 AM

Mike, it's the same thing as the barlowed laser, except it uses a LED instead of a laser, and if I understood correctly (after a quick skim through) the screen is translucent so it's easier to view than a screen placed at the 'wrong end' of the focuser.

Starkler (Geoff) · #5 06-12-2006, 12:12 PM

Going by the fact that ambient light needs to be quite low to see a shadow on a barlowed laser, I dare say that this Krupa collimator would only be able to be used in darkness.

dcnicholls · #6 06-12-2006, 12:18 PM

Yes, jaonoskiss is right. It's not a sight tube or Cheshire, but a "view through" equivalent of the Barlowed laser. The short focal length lens gives the observer a magnified view of the back of the LED, and, through the transparent disk, the focused image (shadow) of the centre spot.

DN

dcnicholls · #7 06-12-2006, 12:30 PM

Quote:

Originally Posted by Starkler

Going by the fact that ambient light needs to be quite low to see a shadow on a barlowed laser, I dare say that this Krupa collimator would only be able to be used in darkness.

It depends on how bright the LED is. It's easy to use at normal daytime indoor light levels, using a Jaycar 2800 mcd red LED (cat. No. ZD104) with a 150 ohm resistor in series with three 1.5 volt A76/LR44 button batteries. This may be a wee bit bright at night, so a refinement might be to drop the current by switching in a second resistor (or a small potentiometer).

The only trick in using it is to get the eye centred in the field of view, otherwise you see black "blobs".

DN

iceman (Mike) · #8 06-12-2006, 08:11 PM

It's a very nice article, David. It would make a great addition to the Projects and Articles page. I'll PM you

dcnicholls · #9 06-12-2006, 08:32 PM

Quote:

Originally Posted by iceman

It's a very nice article, David. It would make a great addition to the Projects and Articles page. I'll PM you

Good idea. See my PM reply.

DN

Garyh · #10 08-12-2006, 01:18 PM

I have to make one!!, just curious instead of a 30mm lense why not make it so that you can throw in a 20-30mm eyepiece in the top tube?
Cheers Gary

dcnicholls · #11 08-12-2006, 10:39 PM

That might well work, provided you have an eyepiece that can be used as a magnifier. Something simple like a Ramsden might work, but none of the more modern eyepieces I tried would focus the back of the LED (not even a 1966 vintage 25mm Kellner). It's essential to see both the LED and the collimation ring sharply.

DN

johnno · #12 09-12-2006, 01:58 AM

Hi DN,

That is a very interesting article,Many thanks for posting it.

I am sure many members,Myself included, will find it very usefull.

Regards.John

dcnicholls · #13 13-12-2006, 04:32 PM

Note: I've just added some new dimensions to the construction diagram (Figure 3, red figures), based on a second model I made. I've also added a bit more text. The newer dimensions work slightly better (for someone without glasses), but either works well.

DN

dcnicholls · #14 15-12-2006, 09:11 PM

The article is now available on this site, in the Projects and articles section

DN