saadabbasi
member
Reged: 08/23/09
Posts: 46
Loc: Pakistan
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Hello everyone,
In a few weeks time, I intend to shoot with my 80-200mm F2.8 on my Nikon D40. Naturally, I'm worried about focusing. When I did some wide-field work, I just taped the lens to infinity after autofocusing during the day.
I'm thinking that I'll need a much more critical focus this time around. My googling led me to the Bahtinov mask generator and I generated the following image:
The focal length I put in was 200mm and the aperture was 71mm (200/2.8).
What I'm worried about is that will this work? The lines seem very narrow to me and I'm not sure how I'll be able to cut it precisely.
Any advice would be appreciated.
For the record, I do not have live-view on my camera.
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Falcon-
sage
Reged: 09/11/09
Posts: 241
Loc: Gambier Island, BC, Canada
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I just took your 200mm and 71mm figure and pluged them in to a mask generator and found that reducing the "bahtinov factor" option from 150 to 50 gave a more reasonable looking result.
I have not used one of these to focus yet, so I can not be sure changing the Bahtinov Factor option is the proper solution, but it appeared to be so based on the description next to the option on that page. Try that!
- Sean
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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saadabbasi
member
Reged: 08/23/09
Posts: 46
Loc: Pakistan
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Yes, that does seem manageable. And will it work on a F2.8 200mm lens?
Also, whats the best way to go on about making one? What materials would work best and whats the best way to cut it?
Edited by saadabbasi (11/07/09 08:53 PM)
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jcham21
sage
Reged: 12/02/07
Posts: 358
Loc: Tucson, Arizona
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I shoot with a Canon 200mm F2.8L lens and this is the Bahtinov Mask I use to focus:
I printed the pattern on a transparency using my printer and used a Sharpie to color in the black lines. I also cut out the portions that let the light through the mask.
I used the 66ED template found here: http://www.focus-mask.com/Free_Templates.html
Here is what the diffraction pattern looks like through my mask and the 200L:
James
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James
Canon XTi
Canon EF 200mm f/2.8L II Camera Lens
Celestar 8
Main Astrophotography Gallery
Comet Lulin Gallery
How To Make a 6" F/15 Refractor
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Falcon-
sage
Reged: 09/11/09
Posts: 241
Loc: Gambier Island, BC, Canada
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Quote:
Yes, that does seem manageable. And will it work on a F2.8 200mm lens?
Sure - I produced it using the 71mm you specified as the correct aperture in your first post. I recommend that you produce your own version though using the same settings to make sure the image scales correctly when you print it.
Quote:
Also, whats the best way to go on about making one? What materials would work best and whats the best way to cut it?
Well I do not know about the BEST way, but inspired by this thread I just made my own! I used a plastic file folder for the material. This is what I did:
- I used that mask generator to build the mask for my lens (a 300mm f/4)
- printed that on plain paper
- taped the paper to a rough cutout of the plastic from the file folder
- cut the slots with a razor blade
- I then cut little tabs on the edges to use to hold it on to the lens.
My cuts are not particularly precise, and as it is cloudy I could not test it, but here is what it looks like (It is held on by tucking the tabs under an elastic band around the edge of the lens):
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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Falcon-
sage
Reged: 09/11/09
Posts: 241
Loc: Gambier Island, BC, Canada
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And here it is again.
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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Falcon-
sage
Reged: 09/11/09
Posts: 241
Loc: Gambier Island, BC, Canada
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I hope you do not mind me hijacking the thread a little bit... I kept going and made Bahtinov Masks for two more of my lenses, and calculated what I would need to make for my 4.5" newt.
In this image, from left to right is:
- Old Minolta MD 50mm f/1.7 on a 2x teleconverter on a MD to EOS converter making a 100mm f/3.4. Odd, I know, but it works!
- My inexpensive Canon 75-300 f/ 4-5.6 (mask set for 300mm @ f/5.6)
- A friend's 300mm f/4 L IS lens on temporary loan to me... oh how I wish it was mine!
The mask for the funky MD setup fits right inside the filter threads and is my best mask of the three. Now I just need a clear night to test these with....
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Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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amateur
sage
Reged: 06/15/06
Posts: 301
Loc: The Netherlands
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Here is how I solved it for the 80-200mm using a 3D printer.
The lines are just 1 mm wide. If you make them wider you will not see the first order diffraction peaks, that are needed for accurate focusing. It cost me about 10$.
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Falcon-
sage
Reged: 09/11/09
Posts: 241
Loc: Gambier Island, BC, Canada
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amateur - THAT is a nice mask! Wish I had access to a 3d printer!
--------------------
Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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amateur
sage
Reged: 06/15/06
Posts: 301
Loc: The Netherlands
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Anybody has access to a 3D printer via the web:
Shapeways site
By the way, you can accurately predict what the Bahtinov pattern will look like, using any and mask and any lense using the Maskulator (simulation software).
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Falcon-
sage
Reged: 09/11/09
Posts: 241
Loc: Gambier Island, BC, Canada
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That is a cool service. I am going to pass that on to a few people for sure!
But of course I should revise my previous statement and make it "I wish I had access to a 3d printer at no cost"  There is alas a reason my only good lens is borrowed and I spent $1.29cdn on materials to make 4 masks...
--------------------
Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
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saadabbasi
member
Reged: 08/23/09
Posts: 46
Loc: Pakistan
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Thanks for all the responses.
jcham, that is an extremely elegant solution! How wide are your cuts? Do you have trouble with focusing or do you find that your focus is always spot on?
I don't have access to a 3D printer (I also don't live in the US, so shipping will be costly if I order via the web) and I'm not sure if I can find laser cutting or anything like that either. So I suppose I'll have to DIY this stuff.
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Monkey Trumpets
member
Reged: 11/17/07
Posts: 22
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I have the Canon 70-200 F4 L, and have been wondering....Is it possible to use the mask with the lens hood in place?
Thanks-
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jcham21
sage
Reged: 12/02/07
Posts: 358
Loc: Tucson, Arizona
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Quote:
How wide are your cuts? Do you have trouble with focusing or do you find that your focus is always spot on?
The slits are 4.5mm wide. The focusing routine might be made more accurate with a smaller spacing. I don't have trouble with focusing. With my current mask, my photos turn out fine. It works well enough for me.
James
--------------------
James
Canon XTi
Canon EF 200mm f/2.8L II Camera Lens
Celestar 8
Main Astrophotography Gallery
Comet Lulin Gallery
How To Make a 6" F/15 Refractor
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Falcon-
sage
Reged: 09/11/09
Posts: 241
Loc: Gambier Island, BC, Canada
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Quote:
I have the Canon 70-200 F4 L, and have been wondering....Is it possible to use the mask with the lens hood in place?
I was wondering the exact same thing about the Canon 300L I have here... I *suspect* that it will indeed work or else newtonians with their somewhat random amount of tube past the secondary might have issues with bahtinov masks - but I could be wrong. I would test it and let you know, but see only rain in the 7 day forecast here 
--------------------
Tasco 11TE-5 'Lunagrosso': 4.5" Newtonian, 900mm f/7.9
Meade DS-2114S: 4.5" Newtonian, 1000mm f/8.8
Galileoscope: 50mm Achromatic Refractor, 500mm f/10
Tasco EQ-2-like mount w/ clock drive
Celestron CG-5GT mount
|
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