Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Revolutionary new way of focusing! No less!

This topic has been archived. This means that you cannot reply to this topic.
517 replies to this topic

#126 Tomal

Tomal

    Mariner 2

  • -----
  • Posts: 267
  • Joined: 24 Mar 2008

Posted 04 September 2008 - 08:09 PM

My advise: don't worry about the details. Make one from cheap material and try it out.


I second that!

#127 snowdragonusa

snowdragonusa

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 04 Sep 2007

Posted 04 September 2008 - 09:51 PM

Wow! What a sensation this little guy is! I wasn't sure what the inventor's last name was so I just stuck with Pavel. However, Bahtinov Mask really is appropriate.

So... The Amazing Bahtinov Mask it is! :)

Anyway, I just sent out an email to the folk who wanted a scalable drawing I had down on my first design. I modified the drawing to work a little better for a refractor since those scopes do not have the center obstruction to worry about.

I did make a bit of a blunder though. I had asked folks to send me their aperture sizes instead of the full scope opening. oops :foreheadslap:

In any event I hope you all find even better and more inventive ways to make, cut, paste, tape, glue (oh, maybe not glue), sew, tack, or otherwise adhere your new Bahtinov Masks to your scope.

A HUGE thanks again to Dennis for first introducing us all to this incredible new focusing aid. And of course, we need to heartily thank the inventor of this awesome design and for his generosity at giving this knowledge to us open source!

Thank you Mr. Bahtinov!!!


Here is the refractor modification.

Attached Thumbnails

  • 2624610-small Refractor Bahtinov Mask.jpg


#128 Galaxyhunter

Galaxyhunter

    Mercury-Atlas

  • *****
  • Posts: 2,881
  • Joined: 02 Jan 2006

Posted 04 September 2008 - 09:58 PM

O.K. Just so I understand the formula correctly, FL*3 / 175(mean)= the total width. Then the width is divided into a slot & a bar? My scopes FL is 2024. So that would be 2024*3=6072 /175=34.6mm. The slot would be 17mm & the bar would be 17mm, correct?
Does the first 20° slot intersect the circle center, cause from what I can tell, it looks like the two angeled slots intersect short of center, Or is this not critical?
Does the number of slots matter? :question:

#129 Nocturnal

Nocturnal

    Surveyor 1

  • *****
  • Posts: 1,850
  • Joined: 14 Sep 2005

Posted 04 September 2008 - 09:59 PM

Did you put the center strap off-center on purpose? I put mine in the middle. I suspect it doesn't matter but I'm curious if you had a reason.

Here are some pictures of my prototype and focus images:

http://gallery.tungs...p?g2_itemId=816

#130 snowdragonusa

snowdragonusa

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 04 Sep 2007

Posted 04 September 2008 - 10:03 PM

O.K. Just so I understand the formula correctly, FL*3 / 175(mean)= the total width. Then the width is divided into a slot & a bar? My scopes FL is 2024. So that would be 2024*3=6072 /175=34.6mm. The slot would be 17mm & the bar would be 17mm, correct?
Does the first 20° slot intersect the circle center, cause from what I can tell, it looks like the two angeled slots intersect short of center, Or is this not critical?
Does the number of slots matter? :question:


Nope - leave the 3 out unless you are getting very small numbers (i.e. small focal lengths).

Yours would be 2024/150-200 = 10 to 14 mm. Now take that number and divide by 2 so you would have an alternating 5mm cutout and a 5mm strip etc.

#131 snowdragonusa

snowdragonusa

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 04 Sep 2007

Posted 04 September 2008 - 10:06 PM

Did you put the center strap off-center on purpose? I put mine in the middle. I suspect it doesn't matter but I'm curious if you had a reason.


Naw, not really. I just quickly reworked my existing drawing to lessen the overall light blocking. The off center bar does not affect anything. It just makes a center brace for the overall structure and 'covers' where all the cutouts would otherwise meet.

#132 Nocturnal

Nocturnal

    Surveyor 1

  • *****
  • Posts: 1,850
  • Joined: 14 Sep 2005

Posted 04 September 2008 - 10:23 PM


Naw, not really. I just quickly reworked my existing drawing to lessen the overall light blocking. The off center bar does not affect anything. It just makes a center brace for the overall structure and 'covers' where all the cutouts would otherwise meet.


Cool, thanks. I noticed when I refocused just now (DeepSkyStacker Live was showing a slight increase in FWHM) that there is a bit more focus travel from just outside to just right than I want. I'll have to look at optimizing this a bit more to see if I can make the pattern 'sharper'.

#133 snowdragonusa

snowdragonusa

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 04 Sep 2007

Posted 04 September 2008 - 10:25 PM

I'll have to look at optimizing this a bit more to see if I can make the pattern 'sharper'.


Yup, I am guessing that is where the focal length formual may come into play.

#134 Gus_Smedstad

Gus_Smedstad

    Surveyor 1

  • *****
  • Posts: 1,538
  • Joined: 02 Jul 2006

Posted 05 September 2008 - 08:23 AM

I glued the paper mask on a piece of foam board

Good idea. I was thinking about my struggles with my cardboard Hartman mask, and when you mentioned this I remembered I had a big piece of leftover foam board from a different project. I'll probably still have trouble cutting it out, but not like dealing with corrugation.

- Gus

#135 Nocturnal

Nocturnal

    Surveyor 1

  • *****
  • Posts: 1,850
  • Joined: 14 Sep 2005

Posted 05 September 2008 - 08:30 AM

Good idea. I was thinking about my struggles with my cardboard Hartman mask, and when you mentioned this I remembered I had a big piece of leftover foam board from a different project. I'll probably still have trouble cutting it out, but not like dealing with corrugation.

- Gus


Cutting a circle in foam board is tricky, especially when you're impatient to try things out :) Mine was 5mm thick so it worked OK with a thin and narrow X-acto blade.

#136 Gus_Smedstad

Gus_Smedstad

    Surveyor 1

  • *****
  • Posts: 1,538
  • Joined: 02 Jul 2006

Posted 05 September 2008 - 08:53 AM

I'm thinking I'm going to make a square mask, with tabs for the edges of the OTA. I don't want it to ride on the mirror / spider vanes anyway, so if it's on the outside, why does it have to be circular?

- Gus

#137 Nocturnal

Nocturnal

    Surveyor 1

  • *****
  • Posts: 1,850
  • Joined: 14 Sep 2005

Posted 05 September 2008 - 08:56 AM

I'm thinking I'm going to make a square mask, with tabs for the edges of the OTA. I don't want it to ride on the mirror / spider vanes anyway, so if it's on the outside, why does it have to be circular?

- Gus


It doesn't need to be round at all :) I just wanted it to fit the dewshield on my refractor. Post a pic of what you came up with!

#138 snowdragonusa

snowdragonusa

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 04 Sep 2007

Posted 05 September 2008 - 10:06 AM

I'm thinking I'm going to make a square mask, with tabs for the edges of the OTA. I don't want it to ride on the mirror / spider vanes anyway, so if it's on the outside, why does it have to be circular?

- Gus


Really the only reason would be to conserve on material if you are working with more expensive stuff. Also to optimize the amount of cutting you are doing.
But if you have extra material and time why not square, or triangular, or perhaps oblong! :grin:

#139 Gus_Smedstad

Gus_Smedstad

    Surveyor 1

  • *****
  • Posts: 1,538
  • Joined: 02 Jul 2006

Posted 05 September 2008 - 10:19 AM

I imagine that any material we'd make a mask from would be rectangular initially. So if you're making it a circle, the savings of material would only give you neigh-useless corner pieces. And I'm thinking square because I'm clumsy and I imagine the cutting will be easier.

I'd think the main reason to go with a circle is that it's much, much more aesthetic.

- Gus

#140 cvedeler

cvedeler

    Vanguard

  • *****
  • Posts: 2,203
  • Joined: 20 Dec 2005

Posted 05 September 2008 - 11:20 AM

Mine ain't pretty, but it sure is good.

I made mine from a plastic For Sale sign. I grabbed the image Adam was kind enough to post here, scaled it to fit the outside of my dew shield, printed it, taped it on the back of the plastic sign and with the help of a straight edge and a razor blade cut out all the parts.

I went with the thin plastic sign as I knew all those cuts would be a chore and I wanted it to cut easy. After it was all cut up it was much more flimsy than I had anticipated. That was fixed by using Popsicle sticks and a glue gun. As a testimony to the wide tolerances of the design, one of the popsicle sticks blocks most of one of the openings. I had some old plastic window blind parts that act as angle bars I glue gunned on with some black felt that hold the mask to the dew shield. It works great as long as the scope is pointed up. Luckily for my design, that is where most of the stars are. :grin:

I didn't worry about the size or spacing. I just scaled Adams image to fit my scope. The details of this design aren't that important I think as mine worked flawlessly as advertised. $2.50 for a For Sale sign and 30 minutes of my time and, vola a highly precision focusing instrument.

Attached Thumbnails

  • 2625478-IMG_3020-800.jpg


#141 cvedeler

cvedeler

    Vanguard

  • *****
  • Posts: 2,203
  • Joined: 20 Dec 2005

Posted 05 September 2008 - 11:22 AM

Here is the front.

Attached Thumbnails

  • 2625480-IMG_3021-800.jpg


#142 John Wunderlin

John Wunderlin

    Vendor - Spike-a Focusing Mask

  • *****
  • Vendors
  • Posts: 2,456
  • Joined: 01 Oct 2004

Posted 05 September 2008 - 11:25 AM

Who says that's not pretty!?!? It's tricked out! Love it.

#143 Nocturnal

Nocturnal

    Surveyor 1

  • *****
  • Posts: 1,850
  • Joined: 14 Sep 2005

Posted 05 September 2008 - 11:34 AM

Here is the front.


Excellent!

#144 Tomal

Tomal

    Mariner 2

  • -----
  • Posts: 267
  • Joined: 24 Mar 2008

Posted 05 September 2008 - 12:01 PM

Here is my Bahtinov mask, it ain't pretty, but it works. I cut it out from some cardboard and made a holder from some "dew cap material". It goes on like a dew cap and works great!

Attached Thumbnails

  • 2625556-mask.jpg


#145 snowdragonusa

snowdragonusa

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 04 Sep 2007

Posted 05 September 2008 - 12:24 PM

Nice work folks! Looking good!

Chris - Have you tried removing the Popsicle stick that is blocking the middle slit to see if there is a difference in the clarity of the center diffraction spike? I am curious if there will be a difference.

Cheers!

#146 jgw12936

jgw12936

    Apollo

  • *****
  • Posts: 1,103
  • Joined: 28 Mar 2007

Posted 05 September 2008 - 12:29 PM

I tried one too, will give it a test run tonight. Scaled the drawing (Thanks Snowdragon!), printed, glued it to a piece of cardboard from the back of a pad of notebook paper, cut a plastic container lid that is a close fit, done. Cost $0. If I like it, I plan to buy John's...
Jim

Attached Thumbnails

  • 2625595-001-jpeg.jpg


#147 cvedeler

cvedeler

    Vanguard

  • *****
  • Posts: 2,203
  • Joined: 20 Dec 2005

Posted 05 September 2008 - 01:39 PM

Nice work folks! Looking good!

Chris - Have you tried removing the Popsicle stick that is blocking the middle slit to see if there is a difference in the clarity of the center diffraction spike? I am curious if there will be a difference.

Cheers!


Well, do to my super high tech design ;), the Popsicle stick is integral to the integrity of the unit. Removing it would weaken the structure such that it will not hold a uniform flat shape, essentially bowing like a Pringle potato chip upon installation. You see, my design team (my 2 year old and 6 year old daughters), after minutes of R&D came up with a design that holds on to the dew cap via tension gripage. This was a compensation to slightly poor placement of the plastic angle bits. In the field it turned out to be a feature which renders a nice grip unlikely to fly off in the wind. But as a result places undue tension through the center of the unit requiring the 4 spoke pattern of Popsicle sticks to hold it flat and provide ample gripage. I suspect the curved slats of a Pringle potato chip would render a very interesting defraction pattern. :grin:

#148 cvedeler

cvedeler

    Vanguard

  • *****
  • Posts: 2,203
  • Joined: 20 Dec 2005

Posted 05 September 2008 - 01:49 PM

I just got a quote back from a local sign company that can cut via a water jet for my design. They want $93! I may be getting one of yours John depending on how well my high tech one holds up.

#149 snowdragonusa

snowdragonusa

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 04 Sep 2007

Posted 05 September 2008 - 02:00 PM

:funny:

#150 snowdragonusa

snowdragonusa

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 04 Sep 2007

Posted 05 September 2008 - 02:03 PM

I tried one too, will give it a test run tonight. Scaled the drawing (Thanks Snowdragon!), printed, glued it to a piece of cardboard from the back of a pad of notebook paper, cut a plastic container lid that is a close fit, done. Cost $0. If I like it, I plan to buy John's...
Jim


Hey Jim, let me know how that refractor style mask works out! I am really excited to see if it works better for a refractor than the SCT design.


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics