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  #21  
Old 27-05-2019, 08:25 PM
Averton (P and C)
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Hi Ray, the fishing line mask looks better & better. Love the photo
Clare & Peter
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  #22  
Old 27-05-2019, 08:46 PM
Sunfish (Ray)
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Thanks. It is a little rough but works . I may try the embroidering hoop which I used for a solar funnel projector screen and which would provide a neater finish, like a racquet.

Nylon line, plastic and timber may be more forgiving I think than other materials. Making one on your own cnc sounds like fun.

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Originally Posted by Averton View Post
Hi Ray, the fishing line mask looks better & better. Love the photo
Clare & Peter
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  #23  
Old 27-05-2019, 09:32 PM
Sunfish (Ray)
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I note your dxf for the 5 inch has 2mm bars which seems admirably fine. But then 2 mm spaces also where I have 6.5 mm spaces. Does the small spacing work or would much wider spacing allow more light?
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  #24  
Old 28-05-2019, 09:53 AM
Averton (P and C)
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Hi Ray, The mask we made from that dxf is working really well for us but we have no experience of using any other so it can probably still be improved. The idea of one to one ratio of bars to spacers was just taken from the on-line generator but letting more light through could be an advantage. At the moment our biggest issue is improving our tracking but we can try some more ideas for masks next time we are looking at focusing. Our "to do" list just grows faster than we can keep up with
Clare & Peter
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  #25  
Old 28-05-2019, 12:34 PM
Sunfish (Ray)
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Well if it works , keep with it. I found that more light was essential on a refractor but the SCT is more forgiving.

I am also unsure why some masks leave the uncut parts filled rather than empty, which would also block light and possibly require more magnification , like a Duncan collimation mask which requires a 5mm eyepiece.

Good luck with the tracking and guiding. There is always more to do.

QUOTE=Averton;1430412]Hi Ray, The mask we made from that dxf is working really well for us but we have no experience of using any other so it can probably still be improved. The idea of one to one ratio of bars to spacers was just taken from the on-line generator but letting more light through could be an advantage. At the moment our biggest issue is improving our tracking but we can try some more ideas for masks next time we are looking at focusing. Our "to do" list just grows faster than we can keep up with
Clare & Peter[/QUOTE]
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  #26  
Old 16-06-2019, 07:52 PM
Wavytone (Nick)
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The bars can be as thin as you dare, any width will cause diffraction. I think the only reason bars were thick was so they would be reasonably durable if cut from relatively fragile materials like card, MDF or ply. Laser-cut plastic should work pretty well.
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  #27  
Old 09-07-2019, 03:26 PM
Averton (P and C)
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We recently purchased a cheap DSLR camera and found that with the wider FOV our original mask was blocking too much light as Ray suggested. So we decided to make a laced mask ala Ray's. This has proved to work very well with the DSLR. Attached is the dxf file for the outside frame. If you use DXF2GCODE the dxf file layers automatically creates your drill files and routing files, of course you will need a tool change between layers. The construction layer roughly shows the lacing pattern but the pictures should clarify the details. There is also a single sub with the mask in position showing the diffraction spikes. (note the one star on the bottom left of the pic which is clearly different focus to the rest is a double star)
Thanks Ray.
Clare & Peter
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Click for full-size image (Bahtinov mask laced 001.jpg)
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Click for full-size image (Bahtinov mask laced 005.jpg)
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Click for full-size image (Bahtinov mask laced 006.jpg)
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Attached Files
File Type: zip bahtinov 5 inch laced version.dxf.zip (6.2 KB, 41 views)
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  #28  
Old 15-07-2019, 09:38 PM
Sunfish (Ray)
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I have been away on an instrument building course so I missed this.

Looks a lot neater than my old plumbing fitting and rough drill holes.
I am glad to works.

The instrument building workshop has shown me some techniques and tools could help me build a better version. I am working on a modification. A work in progress.

I have found with some filters such as UHC or Oiii I can not see the diffraction pattern clearly. I am not sure if any one else has this problem.
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  #29  
Old 02-08-2019, 02:05 PM
Sunfish (Ray)
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Resolved the UHC / NB refractor fishing line Bahtinov visibility. Just turned the gain to maximum and the zoom to 150. A little fuzzy but clearly visible.
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  #30  
Old 03-08-2019, 08:46 AM
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rcheshire (Rowland)
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This works for me at short focal lengths.
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  #31  
Old 04-08-2019, 05:03 PM
Sunfish (Ray)
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I assume you are showing the difference between the out of focus shot at the top and the in focus at the bottom? I tried a similar all through line pattern without the change in angle at the centre line generated by the online generator. It seemed not to show enough difference between in and out of focus diffraction for me.
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  #32  
Old 07-08-2019, 09:50 AM
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rcheshire (Rowland)
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Perhaps a wider splay on one side would be preferable. The double star is apparent.
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