DIY Bahtinov Mask

[xx Ash xx]

Hi,

I'm attempting to create a DIY Bahtinov Mask...

I'm using the website http://astrojargon.net/MaskGenerator.aspx to generate the template and I'm using a Helios Skywatcher 150 with the following spec:

f=1000m

d=150mm

The total diamter of the enitre tube is 175mm

Just to be on the same side as i'm a little unsure of what is meant by "Clear Aperture", can somebody a lot more knowledgable than I am advise on what numbers I should be using in the generator?

Thanks

[dephelis]

I've come across a few differing interpretations of 'clear aperture'. As far as the Bahtinov generator goes, this should the diameter of your primary mirror, so 150mm in your case.

[xx Ash xx]

Thanks, taking into account the total diameter of my tube and including the f=1000mm & d=150mm

When the mask is printed off, i'd expect the whole template to be 175mm wide but it isn't. It comes out to 1500mm wide.

[xx Ash xx]

Thanks, taking into account the total diameter of my tube and including the f=1000mm & d=150mm

When the mask is printed off, i'd expect the whole template to be 175mm wide but it isn't. It comes out to 1500mm wide.

Nevermind, it was me..... Sorted now !!

[dephelis]

Glad it's all sorted

[xx Ash xx]

No,thought i'd got it but something still isn't right.I just can seem to get the correct dimensions for the Mask.

I'd made a miscalculation and the total diamater of my tube is 194mm. Therefore, my scopes spec is

Focal Length =1000mm

Aperture =150mm (Primary Mirror Diameter)

Tube Diameter = 194mm (Resulting in an Edge Thickness of 44mm)

So, taking measurements into account, I'd expect the total mask diamater to be 194mm with the slits being 150mm in diamater.... However, when printed the mask is coming in at about 10mm short in covering the front of my scope.

I've tried different edge thicknesses but I can't get my head round it.

I'm saving the .svg file, then opening it with Inkscape, using Inkscape to save as a .png and then printing off.

[xx Ash xx]

Hi,

Anybody out there that can point me in the right direction or am I reading too much into it......

[Bizibilder]

Have you scaled the print on the printer? 194mm is outside the normal margins for A4 printing and the printer may be "scaling to fit") - you'll find the tick box in "Printer Properties".

[nigelg]

import the image into a program such as PhotoShop, then scale image to 107% save and reprint.

Nigel

[glowjet]

You can of course use a Y mask, as plenty on here have done, just make a plastic Y to the same dimensions of the bars of the Bahtinov, will work just the same and less cutting, try one, should not take long to make and worth the experiment

John.

[BargeGazer]

From your dimensions I think you may have the wrong figure for edge thickness. As you have both diameters for tube and aperture the thickness should be half the difference. The formula wants aperture Diameter but Thickness is difference in Radii.

At least that was where I went wrong when looking at one formula.

David