bahtinov racquet

[rowan46]

I have been trying to chase details of a mask used for collimating a sct its appears to be some kind of hartmann variant. Whilst looking I came across a bartinov racquet. here instead of blacked out card fishing line is used to form the bars theoretically giving more light throughput and enabling focus on fainter stars. I was wondering If this would be a better design on a small sct thus compensating for the small apparture. Has anyone used one of these?

[barkis]

There is no mask I'm aware of that will support collimating the SCT.

Unless that one in your first thread does so.

There is a laser collimating tool, but it ain't cheap.

In your last thread, you covered the same subject, in which you said the diffraction rings were concentric. Observing a star with a medium power eyepiece, as you moved toward focus, would show a flaring off to one side if collimation was less than perfect. If you are unable to focus the star to a point, bearing in mind that being a small aperture telescope, coupled with the central obstruction, will give a star the appearance of being slightly bloated. This will be exacerbated by the scope not being at ambient temperature, the seeing is garbage.

If your scope performed fine on previous occasions, then it can't be a serious problem, and should be traceable.

[rowan46]

sorry barkis this thread is about the focussing i made a bahtinov mask to assist with focussing some while ago I ws just wondering wether this variant ie the bahtinov racquet would be better on a small sct. as for the other mask there have been a few references in other forums but the only pattern I can find is for an 8" sct I may try and scale that down and see if it works. I put this thread out to see if anybody had used the bahtinov racquet and how it performed. again many thanks for your help

[barkis]

You can make your own Bahtinov mask. There is a programme out there, that will generate the mask for you. You supply the scope details, put the numbers in the appropriate boxes, and a file will be created. It ha to be opened in Gimp, or some other programme, and the mask will appear. You can print it out, and make one using it as a template. You could use thin metal, plastic, or even cardboard for the mask. Spray it Matt Black and away you go.

These masks are a series of slots, which you have to cut out with a Stanley knife, or exacto Knife. You will know what to do when you see it.

I hope someone can provide a link as to where the Mask generating programme can be found.

You could aalso try Ebay. Do a search for Bahtinov Mask, and something will pop up. Write and ask if they can do one for your telescope. They are not too expensive to buy, especially the small ones.

Ron.

[angusb1]

The site Barkis is talking about is Astrojargon

[glowjet]

Might I suggest you have a look in the public domain for a primer written by Chris Lord on : "Franhofer Diffraction and its affect on aperture masks", where he strips down the Bhatinov mask to point where three simple strips of material are placed across the scopes aperture to give as good or better results to aid focusing with web cams or digital cameras and, of course, very simple to make, should be very easy to experiment with a small SCT with strips between 1.5 to 2.5mm in width.

John.

[m.tweedy]

Is this any good if you want to make one

http://www.focus-mask.com/Free_Templates.html

To buy one try this

http://www.stayfocused.eu/accessories/bahtinov-masks.html