Bahtinov focusing mask on my 250 newt?

[palatine]

ive just got one and wondered do you have to align the mask perfectly with the centre of teh scope? It just has 2 holes in it and i have put some fixings in teh hang it off teh end of teh scope but its no centered.

TIA

ira

[michael.h.f.wilkinson]

If my understanding of the optical processes involved is correct, the alignment is not critical. I haven't tried using one well off axis, however

[The Titan Calibos]

I used mine wednesday night whilst a star was travelling through my view (not tracking) and it worked perfectly.If you have bought a good quality mask for the exact size scope you use then the 2 screws should be enough and centre the mask automatically.

[palatine]

thank you gents... if the skies ever clear i'll put it to good use

[tferrari]

I've changed the angle relative to my refractor's dewshield while viewing through liveview on a DSLR. I've never noticed any difference worth mentioning. Slap it on the scope and focus.

[glowjet]

The Bahtinov is a devise meant to cause an obstruction to a wavefront of light, so as to create an observable diffraction pattern at the point of focus. So long as it is positioned to obstruct the light path, somewhere across the aperture of the scope, is all that is required. Obviously positioning the mask centrally is a logical process, but the exact centre is not necessary.The resulting diffraction pattern will always lie on the optical axis of the scope, even if the mask has been position some way off centre

[palatine]

thanks again for all your comments chaps... i'm still waiting for a clear night tho.... lol