517 replies to this topic

[Joselo]

This is truly "REVOLUTIONARY"
Has anyone made a mask for an FSQ106ED ?
One more thing, I would really like for this invention to be patent, and protect the inventor's rights.
DO NOT LET THE CHINESE STEAL THIS, they are experts in copyright infringements, and will make more money than you can imagine, believe me.

[Nocturnal]

This is truly "REVOLUTIONARY"
Has anyone made a mask for an FSQ106ED ?
One more thing, I would really like for this invention to be patent, and protect the inventor's rights.
DO NOT LET THE CHINESE STEAL THIS, they are experts in copyright infringements, and will make more money than you can imagine, believe me.

I think you may want to read up on patent law a bit before you post messages like this. How can the Chinese (or anyone else) *steal* something that's out in the open and freely available to everyone? Mr Bahtinov did not patent his invention and we should all be thankful for that. Near as I can tell anyone can make one for him/herself or produce thousands of them to sell to anyone who wants one.

[snowdragonusa]

I have a 2800mm fl scope. I often image with a 2x barlow and I sometimes image with a 3.3 fr.

924mm ~= 4-6mm
2800mm ~= 14-18mm
5600mm ~= 28-37mm

I need 3 different masks right? I don't understand the angle relationship--do the 3 need different angles as well?

Anyone starting to get an idea of how far off your focal length can be before problems start?

Brian

Hey Brian,

So far I don't think there is a huge difference in the spacing so long as it is close. The 924mm FL from the FR can be adjusted with the 3*924/150= ~18mm (9mm cut, 9mm spaced)
That is just about same measurement for the native FL of 2800mm
The real question comes into effect with the use of a barlow. My suggestion is to try it out. I am going out tonight to a star party and will try my 2x and 3x barlows with my mask and see if there is any difference.
My guess is that there will not be.

I'll post back tonight or tomorrow.

Cheers!

[snowdragonusa]

Here is an image using the focus mask.
Focus is to easy with it.

Regards

Mark

http://astronomy.qte...1-SiiHaOiii.jpg

Great image Mark!

[groz]

One more thing, I would really like for this invention to be patent, and protect the inventor's rights.

It's kind of late for that, the photos are published, the description is published. Unless somebody filed for patents prior to publishing, then the net is already full of 'prior art'.

The USPO will surely issue a patent if somebody files in the usa, but that's only because they dont research applications. The resultant patent wont be worth the paper it's written on, because the first attempt to enforce it will result in prior art being shown in court, and the patent wont hold up. There's more than ample prior art on the net already. Any patent issued on this will only have value if the filing is dated prior to the original publications of the concept by pavel. Anything filed after that, is worthless, even if the patent gets issued.

[Mark Sibole]

Thanks Adam,
Ive found focus is almost impossible to miss with the mask.

Mark

[snowdragonusa]

Hmm, you say 'almost impossible' did you have some issues?

[Mark Sibole]

I never say impossible cause something can always go wrong in this hobby lol.
Lets just say you can reach focus in less than 5 minutes with a 99.8 percent chance of getting perfect focus.
The .2 percent is usually human error.
I used the design for the refractor and it worked great.

Mark

[Tomal]

I nominate this thread for "Best Threads in CCD Imaging & Processing", anyone with me ?

[snowdragonusa]

I second that nomination!

[raf1]

Aye. I believe the Bahtinov mask will raise the quality of all astro images and increase the joy we get from this obsession (I mean hobby).

And my wife says I can't focus, hah!

Ron

[Joselo]

I just hope whoever makes money out of this invention, will hold tribute/nomination to the true inventor. I believe strongly in fairness and equality, that is all I can say for now.

[Gus_Smedstad]

Going square paid an unexpected dividend.

I wasn't really sure how I was going to seat this on the telescope. What I settled on was some thick pieces of foam tape intended for weatherstripping, that I just happened to have lying around. This stuff has adhesive on the back, and the triangular bits at the corners of the mask made ideal attachment points. I put a couple of layers on, and placed them inward from the ideal location so that there's a slight friction fit with outside of the telescope. Since they're soft foam and very elastic, it's easy to attach it to the scope with a firm grip.



- Gus

[Dubboy]

Thank you, Dennis, for sharing this "revolutionary new way of focusing".
And thank you, Adam, for posting the work you have done in testing the method. I copy/pasted your refractor pattern to Photoshop and sized it to fit the cell that I made for a Hartmann mask.
Last night was clear with "not so nice" seeing and transparency.
I used the Bahtinov mask on a Megrez 110 (focal length 655mm...f/5.95) in visual mode first and the results were great.
I then attached my Canon 350D with a 2.5x angle finder. If I remember correctly, the first,out-of-focus star is Vega and the fainter, closer-to-focus star is Alpha Ophiuchus (mag 2.09).
It was very hard to see the focusing pattern in the camera's finder so I adjusted focus until the faint "line" was sharp. My results are shown below. You can see that the first exposure is slightly off but the second is pretty close. The "test" images below that were taken at closer-to-focus. M13 at 30sec and M27 at 150sec. Both are unguided.
Because the camera viewfinder does not clearly show the focusing pattern, I'll still have to "shoot and check" but it will be a lot more accurate.
A big "HOORAY" to Pavel Bahtinov for sharing this with the astro community.

"Jerry-rigged" test mask



Out of Focus


Closer-to-focus


M13...30 seconds


M27...150 seconds

[snowdragonusa]

Hey Don, looks like your photos on PhotoBucket are password protected and cannot be accessed publicly.

[Dubboy]

Hey Don, looks like your photos on PhotoBucket are password protected and cannot be accessed publicly.

Hey Adam,
Thanks for the correction. My bad!!!
I went back and "cleaned up" my Photobucket album, deleting some pics...didn't know it would effect my post.
Can you see them now?
(

[jgraham]

The image below shows my original modified Hartman mask on the right and my first draft of a Bahtinov mask on the left, both are from my SN6. The respective focusing pattern (an average of 0.1sec exposures of Altair using my DSI Pro) is shown below each mask. The pattern from the Bahtinov mask is much brighter and it is much easier to judge when the best focus is achieved.

This example Bahtinov mask was cut from black foam core art board using 5mm slots and slats. The angle of the reference slots are +/-20 degrees from the centerline (40 degree total internal angle).

My next task is to make a mask for all of my telescopes and see how well this works visually.

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[snowdragonusa]

Hey Adam,
Thanks for the correction. My bad!!!
I went back and "cleaned up" my Photobucket album, deleting some pics...didn't know it would effect my post.
Can you see them now?
(

Looks great Don!

[Scott Mitchell]

OK, I'll jump in too. I made my mask last night. I used a scaled version of Adam's graphic (thanks again Adam!). I scaled it up to a 9" diameter which resulted in 6mm openings. I went the for sale sign route since I happened to see them while I was at Home Depot getting something else ($1.40 for materials isn't bad). I actually like the material, although it does result in a funny looking mask on one side. The plastic is not too tough to cut and it has a decent amount of rigidity once mounted. I squared it off instead of cutting out the circle and super glued it to a cross stitch circle that I have previously used for my hartman mask.

And the results? It works pretty well! I could clearly see the middle diffraction spike moving to the center between the outer diffraction spikes. I was unable to resolve the 6 small circles when in focus like Dennis' original pictures. So a great improvement over my old hartman mask, but the focusing tool in the latest Meade Envisage seems to let me be a little more precise.

Here's my lovely work of art:

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[blueman]

I read the thread and it seems a very interesting design
It seems to me that it works by a sort of interference pattern caused by the vertical line opposed by the 20° line to each side.
For masks I have been making and using string masks for a while. I wrote an article that was published about the various types of masks and included the cross hair string mask as my favorite.
So, I thought, why not try a string mask and see if the intersecting lines are the actual important thing.
This Bahtinov mask design though very nice and pretty too, is not an easy one to make. Thinking that there might be an easier solution I made this new string mask.
Hopefully I will be able to give it a try soon. A lot of Moon, but it may be worthwhile to just do something that would allow me to spot a bright star and look at it with the mask in place.
When I know something I will post again.
Blueman

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[Luke S]

This method is fairly similar to something I have used for quite some time. If you have a newt or anything with a central mirror held with wires etc. you don't need to add anything, if you have a SC that doesn't have the support structure I have just put a piece of masking tape, running across the center of the aperture (not touching the correcting plate, just held up on each edge by the telescope tube). Then to focus, find a reasonably bright star and take a long enough exposure to get diffraction spikes, out of focus the diffraction spikes will be split, in focus they become one. Simple, effective and costs a roll of masking tape.

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[wr-astro]

... I'm not clear at this point whether this is a major improvment over an ordinary Hartman mask which has 6 diffraction spikes. The triangular version gives 18 diffraction spikes, which is really unusable, ...
- Gus

Hi Gus

If the Hartman mask has round holes then there should be no real diffraction spikes (if nothing else like a spider vane causes them).

If the Hartman mask has triangular holes there should be just 2 (on both sides) * 3 (number of sides with differing orientation) * 3 (number of holes with differing orientation) = 18 diffraction spikes if the sides of the triangles point all in different directions. If you use equilateral triangles with sides that point in the same direction one will get just 2 * 3 * 1 = 6 diffraction spikes. Then it mainly matters just in regards of the brightness of the diffraction spikes if one uses just 2 or more of the equilateral triangles with aligned sides. I never understood why some guys recommended or used non-aligned triangle sides when they switched from round to triangular holes.

[isramirez]

A mate in Mexico, Pedro Gonzalez, created his Pavel mask for only $8USD, look


He is performing tests in his Maksutov as soon as weahter conditions improve here


Believe now is the proper time for chinese guys to contact Pavel Bahtinov and make the masks available at low costs for anyone around the world... $5USD maybe $6USD? or free if you gets a new scope?

[snowdragonusa]

Now that is one nice looking Bahtinov Mask!!!

[Gus_Smedstad]

If the Hartman mask has round holes then there should be no real diffraction spikes

Of course not. Originally I was using circles, but after reading about the advantages of diffraction spikes for determining exact focus, I put a toothpick wrapped in electrical tape across each hole. This was a big improvement.

If you use equilateral triangles with sides that point in the same direction one will get just 2 * 3 * 1 = 6 diffraction spikes.

The problem there is making sure the triangles are precisely aligned so the spikes overlap to give you just 6 instead of 18 spikes. The circle-and-toothpike solution was easier.

- Gus