Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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Fourstars-- good job. That looks like it was a lot of work. You show great skills to make this with a scroll saw.
David(greeps) I assume by narrower cutout you are referring to more as well as narrow, so yes it will brighten up the spikes to allow you to focus on a dim star. But in reality it is more practical to make cuts that are comfortable and easy to cut. Plus very narrow cuts tend to get flimsy and could bend or break.
You can also use a longer exposure time to focus on a dim star, so don’t worry too much about cutting narrow slots.
Did you read all 23 pages?  That must have taken a while. I’ve read them all too, but not all at one time.
One more tip- if you have a binoviewer you can use the mask to balance the focus between the two eyepieces.
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Meade LXD75-SN-8, SN-10, C11
DSI Pro
Canon XSi 450D unmod
www.spike-a.com Bahtinov Style Focus Mask
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g__day
super member
Reged: 06/19/07
Posts: 109
Loc: Sydney
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Rather than cut one out - why not simply print it on A3 paper than quality photocopy to thick clear acrylic?
I did it that way for a C9.25 - works beautifully - cost all up $2
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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Quote:
Rather than cut one out - why not simply print it on A3 paper than quality photocopy to thick clear acrylic?
I did it that way for a C9.25 - works beautifully - cost all up $2
We (John and I) printing on clear transparencies. You do get a nice diffraction pattern, but the clear transparency changed the focus just slightly. You can confirm this using software that will read FWHM.
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Meade LXD75-SN-8, SN-10, C11
DSI Pro
Canon XSi 450D unmod
www.spike-a.com Bahtinov Style Focus Mask
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greeps
member
Reged: 02/04/06
Posts: 52
Loc: Chattanooga, TN
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Thanks, Jerry, for the reply. I did play around with the exposures the other night. I found with a bright star a reduced exposure gives a better image for focus. It reduced the size of the central star in relation to the spikes and allowed made it easier to judge when the spikes were centered. I didn't try it on a dim star with a longer exposure.
I did read all the posts but it was 2 sittings and it did take a while. It's good stuff, though.
Does the screen absolutely need to go over the front of the telescope or could a smaller version be placed elsewhere in the imaging path? I'm wondering about a reduced 1.25" version on a 1.25" clear filter to allow use remotely by rotating that filter/screen into the optical path as we do with color filters. It could be made accurately with a photo etch technique.
I've found yet another way of making a screen for a larger telescope, this one is for an 8" f/6 Mak-Newt. I used a router and a pattern bit. I printed the pattern and contact cemented it to a 1/4" MDF. I rough cut the openings with a band saw to remove most of the waste. I don't have a surrounding support on this one so to avoid closed slots, sawed through the edge of the filter so the slots are now open (looking like a fish skeleton) but leaving a bit extra on the ends of the bars to glue to a supporting ring later. I cut some strips of MDF the same width as the bars on the screen. Next I placed the strips on the black stripes on the screen and held them in place and drilled 1/8" registration holes through the strips and the bars, then inserted 1/8" registration pins to keep the MDF strips securely in place. Using a router and a 1/4" pattern bit with the bearing following the strips, it was easy to route straight lines to clean up the rough sawn slots. It worked pretty well. I wasn't able to go deeply into the "V"s with the router so cleaned those portions up with the band saw. I squared the rounded corners with a razor. After removing the strips and registration pins, I filled the 1/8" holes with some wood putty. It turned out pretty well. The screen is rigid and it didn't seem to take that much longer than the smaller one I cut from Kydex. I'll stain it black and seal it with some polyurethane, then affix a supporting ring.
Edited by greeps (12/27/08 12:27 PM)
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kingjamez
scholastic sledgehammer
Reged: 10/03/06
Posts: 991
Loc: Washington D.C.
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Greeps:
If you don't put the mask over the front of the scope, how are you going to remove it without disturbing the camera?
-Jim
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C8 on Atlas with EQMOD
ETX125 UHTC
Celestron Onyx 80mm
Meade Walmart 60mm guide scope
Canon Xsi Modified w/IDAS LPR
Gen 3 NightVision Eyepiece
Aspiring Optician
Watch my Wiimote control Atlas:
http://www.youtube.com/watch?v=PnmkygmGNiM
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greeps
member
Reged: 02/04/06
Posts: 52
Loc: Chattanooga, TN
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Quote:
Greeps:
If you don't put the mask over the front of the scope, how are you going to remove it without disturbing the camera?
-Jim
Hi Jim,
If it is an element in the filter wheel, it would rotate into the imaging path just like any other filter.
As you may know, with monochrome cameras, at least 4 filters are usually used for each target, a luminance (clear), a red, a green, and a blue. Software causes the filter wheel to rotate a different filter into the light path with each exposure. The 4 exposures can be combined for a color image. The filter changes do not disturb the camera, the telescope, and if the filters are parfocal, it doesn't disturb the focus.
My filter wheel has room for 5 filters. Currently there's a hydrogen alpha filter in the 5th spot. I could remove that. If the mask can be used in this position, a tiny image of the mask could be placed on a clear filter.
As you may also know, unattended telescopes are controlled remotely, either live or through scripts, or a combination. The photographer may be as close as the nearest building or half way around the world. The problem with these masks is that they must be physically placed on the telescope and removed prior to imaging, not a problem if you are sitting at the telescope, but a big problem for a truly remote imager. If one of these masks could be placed on a filter in the filter wheel, the remote operator could rotate the mask filter into the light path just like any other filter, focus with a series of exposures, then rotate the conventional filters into the light path just like usual. It would remove the need for the operator to be at the telescope and there'd be no disturbance of the camera.
David
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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Interesting idea David. I think that lines on the filters would not work. The spots on the filter such as dust are very far out of focus and show a large donut. So I think the lines would also just be too distorted to create diffraction spikes.
If you do test this idea, I would love to hear the results. Please post what you find.
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Meade LXD75-SN-8, SN-10, C11
DSI Pro
Canon XSi 450D unmod
www.spike-a.com Bahtinov Style Focus Mask
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greeps
member
Reged: 02/04/06
Posts: 52
Loc: Chattanooga, TN
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I'm not sure the donut analogy makes sense to me. I think the mask has to be well out of focus to work. It's well out of focus on the front of the telescope and if anything, it's closer to focus on the filter but still well out of focus.
I was hoping you'd have an idea if it would work. I wonder if we could get an idea by putting a fine line in an X pattern on a filter to mimic a spider and seeing if it causes spider type diffraction spikes.
David
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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David, I don't think I would waste a filter. If you want to see if your theory is sound, just cut a small piece of a screen window just the size of a filter and place that in your filter wheel. I will be very surprised if you see any diffraction spikes.
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fourstars
sage
Reged: 07/12/06
Posts: 365
Loc: Wild West.
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The filter idea is great if it works. I would think that as long as your in the light cone you would get the same result. FL would be the same? Light waves behave the same?
I bet most imagers would start focusing this way!
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Staring off into space is highly underated!
Edited by fourstars (12/28/08 12:17 PM)
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greeps
member
Reged: 02/04/06
Posts: 52
Loc: Chattanooga, TN
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Quote:
David, I don't think I would waste a filter. If you want to see if your theory is sound, just cut a small piece of a screen window just the size of a filter and place that in your filter wheel. I will be very surprised if you see any diffraction spikes.
Hi Jerry,
I don't have an extra filter to waste. The screen idea might work. Actually what I was thinking about was using a little flexible adhesive and attach two fine wires to the rim of a clear filter. The adhesive will peel off and bring the wires with it. I'd be careful not to touch the surface of the filter with the adhesive.
If it works, I can look into a photoetch type paint. The problem is going to be to try to find an inexpensive filter that's parfocal with the filters I already have. If the filter isn't parfocal I don't think it will be useful.
David
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NebulaCowboy
member
Reged: 12/05/08
Posts: 35
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Anyone found a place online to waterjet the disk out cheap ? What did it cost ? even if it was local
Dave
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jilldwr
super member
Reged: 02/17/06
Posts: 151
Loc: Ontario, Canada
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Well, there's this place here and free templates here for starters. I bought a mask for my 90mm Apo for $20.
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Celestron C8/ 90mm Flourite Triplet/6"F5 Newt-Astrograph/WO66
Losmandy GM100/ Custom Designed GEM
Orion Autoguider/ Canon 350T DSLR/ Stiletto Focuser
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NebulaCowboy
member
Reged: 12/05/08
Posts: 35
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I ordered one from him. THANKS
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Trebor777
Hazy
Reged: 01/04/08
Posts: 1159
Loc: Connecticut - U.S.
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Quote:
Well, there's this place here and free templates here for starters. I bought a mask for my 90mm Apo for $20.
Me too, just ordered one yesterday. They're making one for my 10"- (SN10 F/4)
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- Randy
Telescopes (Solar too), Eyepieces, Mounts, Filters, CCD Cameras,
Astronomy Accessories, My Eyes, My Mind (Sometimes) and Hopefully Clear Skies.
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ChrisofAmpthill
newbie
Reged: 02/17/07
Posts: 1
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A truly amazing thread with brain waves from Russia and unstinting contributions from arround the world.
Have followed all the contibutions and have printed off two versions for my F1100mm 150mm refractor with differant slot widths using the X3 factor. Before making one I have not been able to resolve a question re the relationship between the left hand slots and angled slots. In some posts the RH and LH slots appear to meet on the central bar and in other posts they appear to diverge between the middle and the top or bottom. Apologies for being long winded, have I missed something, is it unimportant.
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greeps
member
Reged: 02/04/06
Posts: 52
Loc: Chattanooga, TN
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Quote:
Before making one I have not been able to resolve a question re the relationship between the left hand slots and angled slots. In some posts the RH and LH slots appear to meet on the central bar and in other posts they appear to diverge between the middle and the top or bottom. Apologies for being long winded, have I missed something, is it unimportant.
It doesn't matter. The important things are that there are 3 sets of slots and that they are angled appropriately. The actual configuration of the slots, whether they meet, whether there is that triangle without the slots, and the central circle just doesn't matter. I suspect each different configuration you see here will slightly affect the brightness of the diffraction spikes and the more "open" space (space devoted to openings) you have the brighter, but the bottom line is that it doesn't matter. You'll adjust your exposure based on the brightness of the star and the brightness of the spikes anyway, so you'll compensate, and a design that causes an exposure change of a half second or so just doesn't matter.
They all work and they're amazing. I'd suggest you just pick any of the designs you like and go for it. I'm sure that once you try it you'll be hooked, just like the rest of us.
David
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FarmerDave
sage
Reged: 09/07/07
Posts: 412
Loc: Northern Virginia
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Quote:
They all work and they're amazing. I'd suggest you just pick any of the designs you like and go for it. I'm sure that once you try it you'll be hooked, just like the rest of us.
David
Gosh, David, you make it sound like a cult or something. 
David
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Celestron C6/C9.25/CG-5GT Mount
Orion 80ED/EON 72/Supercharged Atlas EQ-G
Garrett Optical Signature Series 10x50
Canon XTi (soon to be modded)/Canon 40D (unmodded)
Meade DSI/Meade DSI Pro/Philips SPC900N
1944 Ford 2N/1948 Ford 8N
Bahtinov Mask Generator * AstroCataLink * 40DShutterCount
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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That would make You(FarmerDave) one of the cult leaders.  
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Meade LXD75-SN-8, SN-10, C11
DSI Pro
Canon XSi 450D unmod
www.spike-a.com Bahtinov Style Focus Mask
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FarmerDave
sage
Reged: 09/07/07
Posts: 412
Loc: Northern Virginia
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Quote:
That would make You(FarmerDave) one of the cult leaders.
Me? Nah, I'm just an enabler. 
Dennis, Adam, John and you are the real culprits on this thread.
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Celestron C6/C9.25/CG-5GT Mount
Orion 80ED/EON 72/Supercharged Atlas EQ-G
Garrett Optical Signature Series 10x50
Canon XTi (soon to be modded)/Canon 40D (unmodded)
Meade DSI/Meade DSI Pro/Philips SPC900N
1944 Ford 2N/1948 Ford 8N
Bahtinov Mask Generator * AstroCataLink * 40DShutterCount
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