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Focussing mask...


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In the precious few minutes of clear skies last night, I decided to go for a widefield shot of the whole of Orions Sword. So swapped the DSI to the GSO and the QHY8 to the WO72 with field flattener.

This meant I had an ideal opportunity to reset the focus on the WO72 using the slinky looking bahtinov focussing mask, which was kindly supplied to me by Peter (Psychobilly). Its a precision laser cut steel affair, with very nicely and accurately cut apertures in it.

But do they work ? :p

The OTA was pointed at Capella. At first, being well out of focus, the image on screen was a replica of the mask. Winding the focus in reduced the image in size, but the pattern stayed the same.

Then, all of a sudden, the six pointed star appeared. And this is where the mask really came into its own. When the star is perfectly focussed, the star has a symmetrical pattern, slightly out of focus, and one of the outer spikes moves. You soon learn which way needs turning in or out.

Apparently the masks are made to suit your exact configuration, including focal reducers etc, so to test that the focus really WAS in focus, I removed the mask and replaced it with a wire crosshair. The images off the camera showed that focus really was spot on.

I for one am in the habit it seems of wasting many a night with a slightly out of focus setup. I hope that when I have a Bahtinov for each of my OTA's, that this will be a thing of the past.

All in all the mask proved to be very effective, very useful, and best of all very EASY to use :hello2: , i'd thoroughly recommend them.


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Thanks for the report TJ... since I had them made I haven't had a single clear night to try mine out... :p

I'm quite happy to keep drawing mask templates for anyone who wants them ... they will be third order designs thought as the first order ones require more precise cutting...

I have no idea of production costs at the moment but that being worked on - cost will be highly dependent on volume...so no decision has been taken about wether they will actually be produced yet...

The M72's were produced because I need one for my scope and they ran me 3 for nothing :hello2:

I am looking to get "retailer" status on the forum so that its obvious that I have an interest in any discussions involving the masks...


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Just used mine again tonight.

The variation between "spot on" and "just a tiny wee little bit out" is very obvious when using the mask. I'm talking about 1/12th of a turn on the slow focus knob!

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The prorotype run will be these masks...they have been "allocated" to people for trials after discussions with the individuals involved. This run is being used to get some idea of the production costs etc... i'm calling in a big favour to get them made by a local engineering company and it will probably cost me in the future...

Celestron 6SE SCT

Celestron CPC800 SCT

Celestron CPC925 SCT

Meade ETX105 Mak

GSO 8" f4

Meade 10" LX f6.3 SCT

Meade 10" LX f10 SCT

Skywatcher 190 Mak Newt

Skywatcher 200 Newt

Skywatcher 250 Newt

Skywatcher ED 80 Pro Ref

Skywatcher EQ 66 Pro Ref - also WO ZS66

William Optic Megrez 110 Ref

William Optic Megrez 72 Ref

Skywatcher EQ 120 Pro Ref

Skywatcher EQ 80 Pro Ref

William Optic FLT102 Ref

Meade 12" LX f10 SCT

Meade 12" LX f6.3 SCT

They will be laser cut form 1mm mild steel plate - and supplied "flat" the mounting tabs would need to be folded to grip the OTA Dewshield - paint finish is beign worked on but thast by a company that dont owe me any favours - so chances are the samples will be provided unpainted...or painted with matt black spray with the "warning" that the paint will crack on the fold - easy to touch up.. proper finish should void this eventually...

I did supply CAD data to a few people who were going to get them made themselves but had hardly any feedback... I have also had very little feedback about the other masks that I posted on the forum...thanks to those who have posted back :hello2:

To produce "professional" masks the measurements need to be very accurate which is why to date the only masks that I have had laser cut are for scopes which I have myself...


Once again thanks to George for bringing the mask design to the attention of the forum in the first place...

Glad your getting a chance to use it TJ... :p

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Great report TJ - thanks for taking the time to report back. Thanks also to Billy (Pete?) for all the effort he has put in over the last two months or so in developing and understanding the design process. I read the whole original post this afternoon trying to get some background on the topic - yes, all 5 pages of it!

Now, where's my measuring tape, WO Megrez 90 dims about to be PM'd in Mr Billy's direction.


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Owning something a bit different to everyone else has it's downsides, however Billy kindly posted a mask for the Cape and I have to echo what TJ has said about the transformation from mask image to six pointed "star" .

Quite remarkable, quick and very reliable !!

I used mounting board for mine and sprayed the white side black.

Hats off and 3x cheers to Bahtinov and Peter(Billy)

Karlo :thumbright:

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I read the whole original post this afternoon trying to get some background on the topic - yes, all 5 pages of it!


You want to try reading the Cloudy nights thread... now that cooked my brain for a while...

Thanks for the feedback guys its much appreciated...

But dont for get Mr Bahtinov for putting the info in the public domain and our very own "George" for bringing it to our attention in the first place...


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