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Old 29-10-2019, 05:58 AM
poider (Peter)
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Bahtinov mask

Just a quick question on bahtinov masks if I get one for my camera lenses does it matter for varying focal lengths, should i make one for each length?
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Old 29-10-2019, 01:53 PM
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xelasnave
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I have tried mine used for the 80mm on the 115 mm a d it seemed ok..the only reason I did not use it for a full session was the distance from the lappy to the scope meant I had to walk from one to the other for each adjustment..so I blew up a bright star a d stood at the scope to adjust...I suspect it should work on different FLs at this stage.
Alex
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Old 29-10-2019, 04:41 PM
poider (Peter)
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Thank you Alex, I don't use a laptop... yet
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Old 29-10-2019, 07:17 PM
poider (Peter)
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Do I need a laptop to use a bahtinov mask?
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Old 29-10-2019, 08:11 PM
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iborg (Philip)
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Hi

I think a laptop can help, because it makes for a larger image, but, so long as you can the three spikes well enough you should be fine.

Philip
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Old 29-10-2019, 08:11 PM
Imme (Jon)
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No to the laptop....as long as you can see the picture on camera screen
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Old 29-10-2019, 08:31 PM
Sunfish (Ray)
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Depends on the scope. My c8 is easy to use a Bahtinov mask cut from sheet plastic to a pattern created by the generator available online with 5mm bars.

Live view on a DSLR on a bright star shows a pattern easily.

The 100mm refractor is a bit harder and requires a very bright star , full zoomed in live view and a very fine Bahtinov mask to be able see the diffraction pattern.
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Old 29-10-2019, 08:33 PM
Dennis
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My experience has been that I have struggled to get a reliable focus on lenses smaller than 100mm focal length, even when using the x10 magnified Live View on the rear LCD.

The diffraction spikes were just too small to interpret with any confidence. This was using a Bahtinov Mask designed for a 102 mm aperture instrument.

Cheers

Dennis
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Old 29-10-2019, 08:45 PM
poider (Peter)
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Thank you all I have seen the mask generator, I use a 10 - 20mm lens, a 50mm lens, a 18-300mm lens and a 150-500mm lens, mainly the 150 to 500mm so if I generated a mask what would the focal length be that I would generate it to?
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Old 30-10-2019, 01:22 PM
Sunfish (Ray)
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You might try my fishing line model which works very well on 100mm F8 lense. As shown in the attached image. Also see a version made by the Avertons which is the same thing fine tuned and they provide a dxf file. I will se if I can find a PDF.

http://www.iceinspace.com.au/forum/s...7&postcount=27

With a refractor the bars and spacing needs to be as fine as you can, 1 mm bars or fishing line is ideal. I posted a dxf in that thread.

When I say 100mm that is the diameter of my old manual NIKON F8 800mm lense and also my ancient Pentax 67 f4 400mm. Have not tried a smaller diameter lense but maybe your 500 is big enough. I think live view full zoom focus is good enough for shorter focal length wide field work. I think my live view zoom is 10x
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Last edited by RB; 30-10-2019 at 03:58 PM.
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Old 19-11-2019, 09:12 PM
BadSean (Sean)
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Quote:
Originally Posted by Sunfish View Post
You might try my fishing line model which works very well on 100mm F8 lense. As shown in the attached image. Also see a version made by the Avertons which is the same thing fine tuned and they provide a dxf file. I will se if I can find a PDF.

http://www.iceinspace.com.au/forum/s...7&postcount=27

With a refractor the bars and spacing needs to be as fine as you can, 1 mm bars or fishing line is ideal. I posted a dxf in that thread.
That is a VERY neat solution.

I've found that chunky line bahtinov masks didn't make things as easy to focus as I would have liked when using a camera lens (the panasonic leica 100-400mm, and olympus 40-150 f2.8) with live view between 5x and 14x.

I'm going to try the fishing line mask for my camera lenses. Hopefully I get better results.

If the mask I have sent to print for my RC8 doesn't work out, I will definitely be trying out your fishing line method for that too.
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