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arad85

Bhatinov masks... generic or specific...

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I need a Bhatinov for my C80ED. Given the cost and the other favourable mentions here, I'm going to order from Stay Focused. They offer either a 80-100mm generic mask for £10.50 or a tailored up-to 100mm mask for £15.

Does anyone know if there is there any difference in performance between the two when used on a C80ED? It's not the money (although it is nearly 50% more expensive) it's more the fact that I'd probably have to wait a few weeks for the custom one. Or is the 80ED focuser not that accurate being R&P?

Thanks in advance

Andy

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Hi Andy,

No specific experience with a generic vs a "bespoke" mask, however, the masks are specific for each optical arrangement.

You can make your own however for as little as £1.75 which is what I did.

GoTo: astrojargon - Bahtinov Focusing Mask Generator: Version 0.4

Enter the following details:

Focal Length (in mm), Clear Aperture (in mm) and Edge Thickness in mm.

You can also enter the thickness of the structural bar and the diameter of the central obstruction (for Maks and SCTs).

If you scroll down this page, there are further options that you can specify.

This YouTube video shows the mask in action:

Note that these two URLs ARE NOT the same as those published on page 82 of August's Sky At Night magazine. These work!

Zaph

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I made one out of Cardboard for my ED80 and it worked fine. It was only to see what you could get away with really. I think others have laminated card.

Neil C

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The basic Cross pattern with the moving central line seems to be generated even with non optimal designs... the difference seems to be in the actuall make-up of the line...at some extremes it breaks down into a series of dashed lines or ..

I did get a load made at one time laser cut steel optimised for specific scopes...

Peter...

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Polystyrene pizza bases !
Don't eat pizza :) I'm on a low-carb diet (and it's working too!! :))

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I cut mine out of a plastic folder cover. It works great, but the tabs I made to elastic it to my scope all broke off, so now I just hold it up! Not as easy, but it still works, until |I can find a new way to attach it!

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I want to get a mask for my 8" SCT but dont know whether to get for made for F10 (Native focsal length) or F6.3 (Focal length that will be most used for imaging with a reducer), does anybody know?

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I'm dangerous with a Stanley knife so bought a generic one for my C80-ED from Mr Stayfocused. It works fine. I wouldn't bother with the custom as it's only for focusing. i.e. if it does the job fine why pay more?

Put some white paint on the pins though in case you drop them in the dark

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Thanks oceanheated... Already ordered it - also realised that the external diameter of the C80ED dew shield is 110mm so I'd have to have paid for the larger custom made one.

Great idea about the white paint though :)

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I have made 2 so far and the one for my refractor the original slots were so small and numerous I knew it would drive me nuts cutting so many out, so I changed the input data so I got a few nice wide slots, bottom line it works fine, I have a nicely homemade job for my ED refractor and a simple thick paper one for my SNT based on a 6" SCT printed up to 10" that works fine as well.

So to get a usable mask you don't need to be too precise on the details, just a number of slots at the correct angle mucks the incoming light enough to give the required focusing pattern.

BTW the technical term ...mucks = causes diffraction patterns

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I'm not so sure that focal ratio is that critical in the design calculations, but as Peter says it gives you cleaner lines in defraction pattern.

I made one for the 10" newt, based on one of Peters drawings. I've used it with the DSLR at f/6.3 but also with the QHY5 with both 2x and 3 x barlows and it gives perfect focus with all these setups.

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I'm not so sure that focal ratio is that critical in the design calculations, but as Peter says it gives you cleaner lines in defraction pattern.

I made one for the 10" newt, based on one of Peters drawings. I've used it with the DSLR at f/6.3 but also with the QHY5 with both 2x and 3 x barlows and it gives perfect focus with all these setups.

Snap !

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Mine, for a 10" SCT and a 80mm Equinox, are printed on photo paper and laminated, before tackling it with a scalpel.

Both work extremely well.

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Ordered a generic one Thursday late pm, arrived this Morning (Monday) well packaged recorded delivery. Brilliant :)

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I went and used the first website link, entered info, downloaded 'saved' to PC, but it won't open, it's a .svc file???

Read somewhere you need the GIMP program to open up the file, help???

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It seems to generate an SVG file, which can be opened in IE or Firefox quite happily (you may have to agree to installing a plugin of some description...)

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yeah tried opening it up in IE but then it closes IE and goes back to the download tab pop-up??

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Thanks arad85.

Just downloaded Adobe add-on [sVG] and it now opens in IE, still have a problem now that it's not showing it to scale???

Am not having a very good day am I lol :-D

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Sometimes IE resizes images. If you hover over it,does the cursor change to a small magnifying glass with a + in it? If so, left click inside the image....

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Naaa, it's not doing the old +/- magnifiying glass thing, it's litterally one size. Tried printing, A3 printer [here in work], but it appeared squished [oval].

Read it can be exported as a dxf file, works AutoCAD, but can't seem to save it as this file??

---

Ignore above, just been playing round with print settings and think I've managed to get it right...... watch this space :)

Thanks mate.

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Is there a mask generator that delivers a jpeg file for printing?

This svg format is doing me ead in!

I'm sure the answer is on sgl somewhere, tried searching but couldn't find it.

cheers

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