The Bahtinov Mask - focusing becomes a joy!

[steppenwolf]

Hi Graham, I use software tools like FWHM and HFD for focussing my CCD camera but there is a tiny problem with these - in the typical seeing that we get in this country, the numbers can jump about all over the place so it is not always obvious when you have a true reading from that split second of exposure - the Bahtinov mask tends to 'smooth' the fluctuations out. For me though, its true value is with a self contained DSLR rather than with a CCD camera.

[Pixie]

OK Steve, that makes more sense. Many thanks.

Graham

[Tim]

I would add something to that. The Bahtinov mask will get you to the same point that FWHM or other techniques use, in a fraction of the time. Also it is not so seeing dependant. As has been said, you can see rightaway which direction to move the focusser.

Also, should the focus point move when the locking screw is tightened, you can see exactly how much and in which direction, making it much easier to correct. Software focussing will give you no idea about that.

On Steve's excellent pics above, if they were taken through my 8" newt, there is a very very tiny movement of the focusser required between those points, but only the central position is really truly focussed.

It would be very interesting to test them in reverse, ie, use software focussing first, then pop a mask on and see how accurate it is.

I use the FWHM utility of Nebulosity, to zoom in on a bright star, but rely on the masks to show perfect focus.

Wouldn't be without the masks now.

TJ

[centroid]

Breaking News!!!

I used my little homemade Bahtinov Mask 'in anger' tonight, and have to say, that I'm impressed.

Dave

[RobH]

I would add something to that. The Bahtinov mask will get you to the same point that FWHM or other techniques use, in a fraction of the time. Also it is not so seeing dependant. As has been said, you can see rightaway which direction to move the focusser.

Also, should the focus point move when the locking screw is tightened, you can see exactly how much and in which direction, making it much easier to correct. Software focussing will give you no idea about that.

On Steve's excellent pics above, if they were taken through my 8" newt, there is a very very tiny movement of the focusser required between those points, but only the central position is really truly focussed.

It would be very interesting to test them in reverse, ie, use software focussing first, then pop a mask on and see how accurate it is.

TJ

I completely agree TJ.

On Sunday night I was out until the wee hors with the TMB, which I don't have a mask for yet.

The wind was force 7 + and seeing was pretty bad. Trying to focs in those conditions with the software routine in Maxim was a non-starter, and I didn't get perfect focus at all that night.

I've tried the SCT in similar conditions, and focus using the mask was a doddle.

I have tried it in reverse as TJ mentions, and, in good seeing and not being blown about, the mask showed the software to have achieved perfect focus, so, they both agree with each other, but the mask is many times quicker.

Cheers

Rob

[beamer3.6m]

So Psychobilly.

How much for one of these as I have no way of making one myself.

[centroid]

Have a look here:

http://stargazerslounge.com/index.php/topic,38443.0.html

Dave

[ncjunk]

Just to give an idea as to what you can get away with here is a picture of

my "blue peter" mask. 2 bits of card glued together with a print out of the template.

cut out the holes with a craft knife and then taped it really badly to the scope.

I am amazed to say it worked although I dont expect the mask will be very long lasting.

I will attach the photos of the focusing to show the spikes when i can.

Neil C

[ncjunk]

Here is one of the shots of what the above cardboard mask produces.So I would say you don´t have to be really accurate with this.Although I would still like one like psychobillys at some point.

Neil C

[Psychobilly]

I will no longer be able to get masks produced cheaply unless I buy in minimum quantities of 10 per design - I was hopign to have been able to mix and match but thats no longer an option... so its cardboard plastic and knives again i'm afraid...

Billy...

[nightfisher]

I bought a bahtinov mask nearly a year ago, and never got round to trying it, untill the other night, a real wow moment to see how easy perfect focus can be gained in such a short time....credit to Pavel bahtinov

[Psychobilly]

Just a note this thread is nearly 3 years old...

If anyones looking for ready made mask then I would check out the ones from FLO

http://www.firstlightoptics.com/bahtinov-focus-masks.html

Peter...

[nightfisher]

I did not notice how old this thread is

yes Flo are stocking them, looks like i will be ordering one for my 180 skymax

[Jgw]

Hi Steve, glad that tool helped...I also use this.

.... Bahtinov grabber for any camera Niels Noordhoek’s weblog

Great wee tool..

Cu John

[gcraib]

Bought a Bahtinov mask earlier this year and the results were superb.

it really helps you obtain good focus if you are not sure (ie poor seeing or scope shake) and I've yet to use it with the DLSR but will be expecting it to really help there as the live view can be a bit of guess work otherwise.

[sabin_fota]

this is my home-made Bahtinov mask for my Celestron C6 XLT (I wanna sell this too), an very, very useful little thing .

I have another one for my WO Megrez 90mm APO, it is the most important piece of gear, because without it the whole work is in vain.

The specifications are calculated here : astrojargon - Bahtinov Focusing Mask Generator: Overview