[SOLD] Super cheap Bahtinov mask cut for you. Choose from MDF or Acrylic

[erick (Eric)]

I have added two little knobs, top and bottom, to add in placing and removing the mask from inside each OTA. First use last night - neat!!

[roddz (Rodd)]

Hi Mike could I please order 3 Masks.
The first 2 in 2mm Acrylic, both for 100mm refractors.

1: 100mm 800mm FL 118mm diameter
2: 100mm 500mm FL 116mm diameter

the 3rd in 3mm acrylic for a Vixen VC200L

3: 200mm 1800mm Fl 218mm diameter, aprox 75mm central obstruction.
Thanks Rodd
roddz@spin.net.au

[vk2emq (John)]

Mike,

I'd be interested in getting some Bahtinov masks, however on doing some research in forums here and elsewhere about possibilities for automated focussing I came across references to the Carey variant of the Bahtinov Mask -

http://www.iceinspace.com.au/forum/s...ad.php?t=45396

http://en.wikipedia.org/wiki/Carey_mask

This appears to offer superior indication of "perfect" focussing compared to the Bahtinov mask on which it is based, however is much more difficult to fabricate, requiring much thinner substrate base material for the mask.

Could you please advise if it would be cost effective for you to fabricate a Carey Mask ?

best regards,

John vk2emq

[ozstockman (Mike)]

Hi John,

I would be happy to make Carey masks especially if there is any interest in them. However as we discussed it with George on the 2nd page of this topic material used for them should be 1-1.5mm thick. So far I couldn't find anything not expensive and thinner than 1.5mm. I will check with my current acrylic supplier if they have any plastic that is 1-1.5mm thin.

I am about to get more powerful laser with 3 times bigger working area than I have now. It means that I will be able to cut out bigger masks(up to 20") and will be able to do it faster. So may be I can try some plastic I didn't have a success before. It didn't work as my laser cut it very slow and it melted. Now if more powerful machine will cut it faster it might work.

Regards,

Mike

P.S. Since to my equipment update my current 50W laser must be sold. It won't be cheap as these types of equipment are very expensive. However considering its price when its new mine will be a few times cheaper. If anybody is interested in it please pm me.

[mithrandir (Andrew)]

Originally Posted by ozstockman

I would be happy to make Carey masks especially if there is any interest in them. However as we discussed it with George on the 2nd page of this topic material used for them should be 1-1.5mm thick. So far I couldn't find anything not expensive and thinner than 1.5mm. I will check with my current acrylic supplier if they have any plastic that is 1-1.5mm thin.

Can you do cuts at an angle like this sectional view? It would get the thinner edge, but require two passes. Or does the mask require both corners to be at 90 deg?

[ozstockman (Mike)]

Sorry for the delay Andrew.
No, my laser cannot do angle cuts. It cuts at 90 deg only.

I have got some thin plastic from my supplier. It's about 1.5mm thick. However I haven't tried it yet and it's clear. I asked them for something suitable for picture frames and that all they sell that is thinner than 2mm. They don't have it in any other colour but may be it's possible to spray paint it in black.

[Marty]

Hi,

I have a CPC1100 and Hyperstar setup want to get a Carey Mask made.

My research indicates that there are a few ways of using a Mask with Hyperstar..... Mounted on the end of dew shield, a split hollow center mask, or take the camera off and fit a hollow centre mask over the Hyperstar.

I imagine that mounting on the end of the Dew shield would be the fastest when needing to refocus due to Temp changes, but is it as accurate?

If using the Dew shield mount, the end of the Dew shield is ~400mm from the OTA and ~200mm from the camera.

So would I use a central obstruction in this case? and what size obstruction? same diameter as the camera (EOS 550D) or less considering it will be 200mm away?

I am also a bit concerned about the weight of 3mm MDF/Acrylic mask and that the dew shield might just flop off the end of the scope. It's a Kendrick Zap Cap made from ~1mm black ABS plastic with a Velcro seam and rubber non slip heater strip, so not able to handle much weight without slipping.

I noticed from reading this thread that you are constantly on the hunt for new materials; so what is the lightest material you currently have that may do the job? is MDF/Acrylic still the only options? or have you found some thinner ABS plastic now?

George Carey - "In an earlier post there were comments that a Carey mask from 3mm acrylic was not so good and needed a thinner material. I have now done some experiments with my 10" reflector and 3mm acrylic and it is perfectly OK. Previous trials were with a 6" scope.
I suspect that some of my disappointing results were due to poor tracking. Have a look here http://www.btinternet.com/~gfcarey/careymaskten.htm
for some examples."

Ozstockman (Mike)- "Thanks George for letting us know about results with 3mm thick Carey mask.
I will try to cut one for myself and test it shortly."

Just wondering, did you get a chance to test yet?

Regards,

Marty

[GeorgeC]

I am using a Carey mask made from 3mm acrylic on a 10" scope with no problems. I was having difficulty before, but I now think that that was due to a rather poor mount. I have an ASA DDM60 now which remains rock steady during a 20 second exposure. The diffraction spikes are good and sharp. If your mount moves around at all the spikes get smeared and are less distinct.
For my 6 inch scope I still use a paper card Carey mask which is quite thin (<1.5mm). It gets a little warped if I leave it in the observatory for a while but still works well. Here is an example:

http://geoastro.comeze.com/masks/6mask.jpg

[Marty]

Hi George,

Good to hear 3mm is ok now

Do you have any ideas about mask center obstruction sizes and how they might be relevant when mounted out on the front of a dew shield with a Hyperstar inside?
Or would I be better getting a 2 part split mask made and popping it straight on the OTA?

[GeorgeC]

A central obstruction should be no problem. Obviously if the obstruction is very large you will get dimmer spikes. A mask that is in two pieces (I assume you mean that when you say 'split mask') will not be a good idea. The angles involved in a Carey mask are such that any error in getting the two halves fitted together will destroy the accuracy. You judge focus by comparing the very narrow separation in left/right spikes and a fraction of a degree error would make this impossible. This would also apply to the Bahtinov mask.
If the two halves were cut precisely and fitted together without any gaps then it could work. Perhaps..

[Carl]

Hi Mark
Noticed your thred re making Banhotov masks.
Are you still doing them? I live in North East Victoria. need mask for 80ed
and C8 scopes

Cheers Carl

[Carl]

Hi Mike
The thread seems a bit old. Are you still making them. I need 2

Cheers
Carl

[ozstockman (Mike)]

Hi Carl,

I have just replied to your email. I can still make 5-10 masks for small scopes of 2mm thick black acrylic but I run out of 3mm for big scopes. Since these days there is much less offers for masks coming from ISS I have been thinking to stop selling masks after I run out of all 2mm thick acrylic that I have now in stock.
Only if there is at least 8-10 people who want 3mm thick acrylic masks for big scopes it will be worth for me to update my stock for 3mm thick black acrylic panels.

If anybody wants 3mm thick MDF masks instead of one cut out of 3mm thick black acrylic I can do them anytime. I cut out a lot of stuff of 3mm -18mm thick MDF everyday and I always have MDF in stock

Cheers,

Mike

Originally Posted by Carl

Hi Mike
The thread seems a bit old. Are you still making them. I need 2

Cheers
Carl

[Logieberra (Logan)]

Hey guys

How important is it for the mask to be perfectly centred (in relation to the primary mirror / lens)? I've fitted my 10" mask to the newtonian, and when I look through the focuser - the centre lines of the mask do not line up perfectly with my secondary vanes - indicating she's off perhaps 5mm.

What's the science behind it? Will this be fine, and make no difference? Or should I re-drill?

Cheers.

[GeorgeC]

I did some experiments with the Mask simulator. It showed that there was no noticeable effect of have the mask off centre.
Have a look at http://geoastro.comeze.com/careymask.htm down the page a bit. This was for a Carey mask but I am sure the Bahtinov would produce the same result.
George

[Tandum (Robin)]

I had a 10" mask hanging from the top of an 8" scope using tape last week-end and it worked fine. ie: 2" of the mask was hanging off the bottom of the 8" scope.

Mike has just sent me a new mask for the 8" scope and it fits like a glove. Thanks mate.

[Logieberra (Logan)]

That's a relief! Good Info. Thanks guys.

[ozstockman (Mike)]

3mm black acrylic is back in stock. Moreover from now I can do solid masks with OD up to 59cm in diameter.

[stephenb (Stephen)]

Hi Mike, I've sent you a PM sent re: a DSLR mask

[stephenb (Stephen)]

Has anyone mounted on to a DSLR lens? Any thoughts on the best method? My idea was to buy a cheap screw-on filter, perhaps take out the glass itself and mount the Bahtinov mask in place of the glass.

(Sorry if this is out of the terms of reference with the classifieds, but there seems to be a lot of justified discussion on this product).

Regards,
Stephen