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Quatermass

Good by Bahtinov hello the Lord mask amen!

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Having just got my evostar ed80 and not having a suitable Bahtinov mask for it I was going to make a smaller version but then I found this great article on the forums about making a much easyer and better mask The Lord Mask

First read this article by the chap who says this..

I trust this primer in Fraunhofer diffraction demonstrates how the Bahtinov mask

functions, and how a superior mask consisting of a 'Y' shaped bar serves exactly

the same purpose, but to better effect.

So save yourself the time and effort in making a Bahtinov mask, or save your

money. Instead make a 'Y' shaped mask. Perhaps you could recognize the man

who pointed out this economical alternative and christen it the "Lord" mask

http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/Fraunhofer-primer.pdf

So armed with this info I then set about making my own.

You will need an old DVD case a craft knife and pencil.

First mark out on the dvd case your circle using the dew shield from you ed80

2012-03-10%252012.04.04.jpg

Next mark out a cross in the centre in pencil

2012-03-10%252012.09.37.jpg

Next mark out the Y shape using a 20% angle for the top bars

2012-03-10%252012.15.13.jpg

When that is cut out you can also cut out the middle section of the DVD case the bit that holds the DVD that just happens to fit nice and snug around the outside of the Dew mask if you cut it carefully with a craft knife then stick your Y shape on it with some black tape and you have neat little Y shape Lord Mask that clips on an off the dew mask with ease.

Job done and cost nothing to have a focusing mask for your ed80.:)

2012-03-10%252013.00.11.jpg

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Blimey. Looks like a lot less work than making a bahtinov.

As accurate?

Gonna give it a go.

Sent from my X10i

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Very interesting - have you tried it yet, and (if so) how did you get on?

Cheers,

Peter

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Blimey. Looks like a lot less work than making a bahtinov.

As accurate?

Gonna give it a go.

As accurate yes and far quicker to make one then making a Bahtinov Mask, took me 25 minutes to knock that one up :hello2: or you can pay out 13.00 quid for a Bahtinov mask if you like :)

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How did you find it on faint stars? Without the repeating refraction of multiple slits, I am led to believe this is where the Y mask falls down?

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Very interesting - have you tried it yet, and (if so) how did you get on?

Cheers,

Peter

Only just made it but I have read on the forums of others that are using it and they say it works just as good if you read the article by the chap it will convince you that it is as accurate and is much brighter then a bahtinov mask. Got to be a time saver as well if you going to make one.

Recently there has been a good deal of enthusiastic chatter on Cloudy Nights and

Stargazer's Lounge and other astronomy forums about a focusing mask invented

by Pavel Bahtinov. Bahtinov masks, as they have come to be known, have been

produced én mass by keen astrophotographers, and commercial enterprises.

The Bahtinov mask produces three principal diffraction spikes, a vertical spike

flanked by two spikes inclined ~20º. The spikes cross on axis at the focal plane.

Shift the focus and the vertical spike shifts off-axis.

Lets see how the separate parts of the Bahtinov mask behave. First the horizontal

rungs.

Carry on reading from here in the article and it all makes sense..

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How did you find it on faint stars? Without the repeating refraction of multiple slits, I am led to believe this is where the Y mask falls down?

Page 8 on the article ..

Note the same diffraction pattern, except much brighter (because less light is

blocked). This mask will act in precisely the same way as the Bahtinov mask. Shift

the image away from the focal plane and the central spike will translate

orthogonally.

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Page 8 on the article ..

Note the same diffraction pattern, except much brighter (because less light is

blocked). This mask will act in precisely the same way as the Bahtinov mask. Shift

the image away from the focal plane and the central spike will translate

orthogonally.

Doesn't really answer my question given the star being used is ridiculously bright.

When you do test it out, I would be very interested to know how it fairs on faint star fields with no bright stars :)

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I will test it out tonight if the clouds play nice again but most of the time I focus using a bright star any way as the view port in my Canon 350D is very small. I use it to get a rough focus before putting on a Bahtinov Mask I would not choose a faint star to focus with normally though as I tend to focus on a bright star then move to my chosen target for imaging. Will give a full report on the results but others on the forum have said it works well for them and it sure beats cutting out a Bahtinov Mask.

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Saturday night... Stumbled across this thread and just had to do it. Will test later when the storm has passed :)

/per

saturday.jpg

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Happy to report it works great on medium and bright stars and I allways focus on a bright star any way. Was able to focus in a matter of minutes and image is nice and sharp lovely jubbly :)

Sent from my GT-S5670 using Tapatalk

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Well now, here's a thread with the magic word in it. The blue touch paper is lit. Hold onto your hats.

Olly

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I think they're both useful. In theory I think the Bahtinov mask produces a stronger image than the Lord Y because of the larger number of slits. In practice it can sometimes reduce the light levels so much that the image is difficult to work with. At least, that's my experience.

I have wondered if perhaps one is more suited to slower focal ratios and the other to faster, but I've done no experimentation to check. Neither have I tried third order Y masks or even masks with a small number of slits. I'd love to spend some time investigating these things, but somehow given the rarity of decent nights that sort of thing gets forgotten in favour of actually viewing or imaging when one does come along.

James

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I love it easy to make and works just fine will post an image of it in a mo..:)

Sent from my GT-S5670 using Tapatalk

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5ac5c1bb-d04d-d4e6.jpg

not a great photo just a quick snap of the view from my camera and the picture was taken with thin cloud.

Sent from my GT-S5670 using Tapatalk

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Cant recall one in the pdf link above but having used a bahtinov for 2 years and testing this one out tonight theres nothing in it as far as I can see except saving time and money and that I am happy about.

Sent from my GT-S5670 using Tapatalk

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Very interesting.

What happens if you zoom right in on the core?

Using Ha or S2 or Oiii filters you tend to get a series of dots with a bahtinov mask, and by zooming in on the centre of the pattern it is easy to separate the dots and get perfect focus. How does the Y mask look close in?

Cheers

Tim

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Really good QM, simple to make and gives good results, congrats:)

Edited by starfox

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As we have no clear sky (again) and I need one for my APO 80, here's my attempt.

Having made two bahtinovs, this was miles easier to make (about 20 minutes). Just need the clouds to pass now......

Thanks for the tip :):icon_salut:

post-19169-133877745135_thumb.jpg

Edited by earth titan

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Is there a recommendation to the Y width to aperture?

Focal length rather than aperture. Bahtinov's original guidelines still apply. Bahtinov said (afair) that the minimum width for a bar and a gap was focal length / 200 and the maximum focal length / 150. To get the size for the bars in your Y mask you need to adjust for the fact that you don't have a gap by dividing those values by 2.

If you have a short focal length scope and those numbers turn out awkwardly small you can create a "third order" mask by first multiplying the focal length by three and working from there.

James

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As we have no clear sky (again) and I need one for my APO 80, here's my attempt.

Having made two bahtinovs, this was miles easier to make (about 20 minutes). Just need the clouds to pass now......

Thanks for the tip :):icon_salut:

you might find it needs to be on the front of the dew shield like this..

2012-03-10%252013.00.11.jpg

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you might find it needs to be on the front of the dew shield like this..

2012-03-10%252013.00.11.jpg

Piccie doesn't show it too well, but this is on the dew shield which slides back and forward...

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Hi all. I experimented with the Carey mask a while back and found the Bahtinov to be far superior. After reading this thread today I made several for my William Optics Megrez 102 varying in width of the bars in 3mm, 5mm, 7mm, 9mm, 11mm, 13mm and 15mm. I went outside tonight and tried every one of them on Jupiter then Bettleguise and all I could see was a big blurry ball with some very faint spikes but I could not distinguish when I reached focus. With a Bahtinov mask no problem at all on either target.

I was using my 450D with live preview on the LCD screen and x10 magnification.

I am not just saying this because of what I do for a living, I really truly believe the Bahtinov to be a much better and surer way of get focus.

I don't know, maybe I have done something wrong with the Lord masks I made, but I measured the angles exactly.

Keith

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