I'm the new boy!

[SeedyF]

Hello and welcome from me too :

[SeedyF]

Hello and welcome from me too

[glowjet]

Hi Russell,

A very warm welcome to SGL, focusing : make a 3/16" Y out of black card and put this across the aperture of the 125, it does not have to be on dead center, bend the corners and stick it with a little blue tack, locate and point at a bright star, you should find that when the scope has reached exact focus your screen should show X formation diffraction spikes, with a vertical bisecting the precise center, the vertical moves left and right as you move in and out of focus, if the arms of the cross are a little faint then make the arms of the Y a little wider, this should brighten the X at the expense of making it smaller and thicker, if the whole image is to short and thick, then reduce the width of the Y, experiment is the order of the day. Its some time ago now but one of the forum members had great success with some round black rubber, approx 1mm-2mm thick, he just knotted three lengths together and stretched them over the aperture of the scope in the form of a Y, HTH, enjoy the forum.

John.

[phillc]

Hello Russell and a warm welcome to SGL.

phillc

[Russell.D71]

Thanks very much for the warm welcome and hope you all have clear skies.

[Russell.D71]

Cheers John,

Will have a go at what you have advised, also just to add l have a astro engineering focus-master lite. Is this suitable do you think?

All the best Russsell

[michigander]

Welcome to SGL, Russell!

Dana

[glowjet]

Sorry Russell I missed your response, the Focus-Master lite has been on the go since 1619 when it was invented by Christopher Scheiner, after that it was more commonly known as the three hole Hartman mask, a lot of Astronomers had difficulty in finding the point of precise focus, then a number of years ago a Russian, Parvel Bhatinov came up with an alternative, which is now widely regarded as the best focusing aid there is, it is readily available on the market but a little complicated to make yourself, a very respected Astronomer, Chris Lord undertook an in depth investigation into the diffraction spikes produced by the mask, (he has published this as a PDF file) and this resulted in the basic Y pattern, being less restrictive it allows more light to enter by as much as 1f stop, works in the same manner but produces brighter results, and of course very easy to make, as I pointed out one forum member was very creative and used round solid rubber to great success, there is a formula for calculating the width of the of the material and it is relative to the focal length of the scope, I am sure details for the Bhatinov mask can be found in the forum archives, in the end it is down to experimentation, start of with the arms and leg of your Y at 3mm and work from there, if the arms of the X are a little weak in brightness in the diffraction pattern, then just make them wider, it is, never the less very accurate and will give you that precise point of focus which you want. You may ask why such a simple thing is not readily mentioned, I think its because its not well publicized, most go for the established B mask and then buy one or get busy with scissors and knife to make one from the many computer diagrams available, not realizing that there is a much more simple design giving the same result.

John.