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Quatermass

Good by Bahtinov hello the Lord mask amen!

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Hi Keith I used my lord mask again tonight and didnt have any problems with it at all it did the job really well so very strange that yours are not working, I think making the bars thinner gives you longer spikes and shorter spikes if you make them to thick mine are 5mm. I am also mounting them on the end of the dew shield. But hey does it really matter if it works for you it works if not use a bahtinov mask I use both but am quite happy using the lord mask on my ed 80.

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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

Just before I get the craft knife out!

So for a 200P (1000 F5) we are talking between 2.5 and 3.3, or a third order mask of 7.5 and 10mm ?

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Here's one I made earlier (untested) made from tie-raps (zip ties).

post-32860-133877745941_thumb.jpg

post-32860-133877745949_thumb.jpg

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I use a programme called 'Bahtinov grabber' to assit with focusing - Wonder whether you could still use this programme with a Y mask. Personally, I'd not be without the programme now as it makes focussing much easier than looking at a screen with the pattern on it.

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Tested mine last night and it works a treat.

Happy days.

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Impressive results.

I have to say, despite owning Bahtinov masks for all my scopes, I rarely use them. FWHM works for me :)

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Here's one I made earlier (untested) made from tie-raps (zip ties).

Well, I can honestly say my tie-rap version did nothing at all, no spikes visible at all. So I'll try making the legs wider.

I presume these spikes don't depend on their also being a spider (holding the secondary mirror) in the optical path, because the SCT does not have a spider.

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An old camping mat wrapped around the end will give you a quick dew shield or a bit of card board I think yours is not working because it needs to be away from the middle part of your scope that its currently sitting on putting a 6inch gap in front of it and placing it there should work for you.

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An old camping mat wrapped around the end will give you a quick dew shield or a bit of card board I think yours is not working because it needs to be away from the middle part of your scope that its currently sitting on putting a 6inch gap in front of it and placing it there should work for you.

Thanks Quatermass, I'll try that the next time their are stars in the sky - might be a while before I report back (with images of it if it werks).

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Sure it will work Cath it was just the way you had it on your telescope that was blocking its defraction effect works great on mine and easy to use as well. Lets hope we get some nice clear skies for you soon.

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going to give this a go, for my camera lens's just 2 questions

can i use the same mask for all the lens as they are all generally the same shape

(see lens in my sig)

and what dimensions would be good to use?

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I dont think it matter that much just a y shape with the y part at 20 degree angles should be fine

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I have a couple of Keith's Bahtinov masks and, to be honest, I am certainly not looking to change them.

Olly

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I have used Y-masks on all my scopes (and a couple of camera lenses) and have found them easy to use, but then, I always use a nice bright star to achieve focus. Never worried too much about angles or thicknesses - maybe if I did they would work even better, but they do me ok at present.

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I've heard of Mr Lord's Y mask but the same effect is achieved with three sticks or rods across the scope aperture as a double-Y as below to create the required stellar diffraction pattern:hello2:

post-33671-133877750221_thumb.jpg

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Couldn't be bothered with crossed 'sticks' but did a folded Y mask eg 'arrow' mask in card [below] and will test tonight and report - the diffraction should[?] be identical to a Y. :)

Dual pic shows mask in two slightly different positions eg 'point' centred and

decentred so I could replace scope cap

;)

ps: the original Y thread on CloudyNight was in June 2009 so has it taken nearly 3yrs to Cross the Pond?:)

post-33671-133877751094_thumb.jpg

Edited by nytecam

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gonna give making one a go today does any one know how i can do the angle with out a protractor :)

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Did some 'arrow' mask [pics earlier here] star tests last night on my set-up [12" f/3.7 SCT via f/3.3 FR+ SX Lodestar-C cam] and wholly unimpressed:mad: It only worked on bright first mag stars and still uncertainty as to precise focus via the diffraction pattern seen on the laptop.

I'll stick to my focusing against faint stars in field in a download loop which, for me, has worked fine over the last decade.:)

I note on reading Mr Lord's primer for the first time, there are no actual star images therein - just computer generated graphics. My reference to '3 crossed sticks' and 'folded Y' that I called an 'arrow' mask that I used are there and equally 'effective' even if it doesn't work for me:rolleyes:

I left the arrow mask over my scope last night to image SN2012au and aw where both at mag 13 etc the mask and its 'effect' are completely invisible :) Interesting if shortlived experiment for me.

Edited by nytecam

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I think the reason there not working for you is because you dont have the mask on a dew shield away from the surface of the telescope, I have no problems with mine at all and it work well for me.

Mask in front of lens on dew shield

2012-03-10%252013.00.11.jpg

And my results

Y%2520mask.JPG

Your mask is on the surface interrupted by the middle part of your telescope.

82980d1332347584-good-bahtinov-hello-lord-mask-amen-arrow-mask1.jpg

Edited by Quatermass

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For those thinking of making one of these mask I would say if your using an evostar ed80 like me and you do what I have done it will work and making a bahtinov mask is a pain, this is much easier to make. I made 3 Bahtinov Masks for my 200p they work fine as well but for my evostar making a smaller Bahtinov Mask compared to making the Y mask was a no brainer the y mask is easy to make and it works, and to the question of will it work on faint stars my answer is I never use a faint star to focus on so I don't mind. The Y mask gets my vote for being easy to make and for working with my normal set up. I cant see it working on a SC telescope though it has to be on a dew shield 4 inches away from the main lens, if I am wrong please correct me but when its mounted on telescope with out a dew shield it fails.

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I cant see it working on a SC telescope though it has to be on a dew shield 4 inches away from the main lens, if I am wrong please correct me but when its mounted on telescope with out a dew shield it fails.

Hi Quatermass

Yes I haven't been able to try it again as yet on my 6SE SCT, I get very few chances to use a scope (once every 2 weeks if I'm lucky). Hopefully this weekend I'll get a chance (if the sky is clear) and will post back the results with the Y mask on the end of the dew shield. I think the dew shield I have is about 10" to 12" long.

Edited by Cath

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Here is one taken on my 8SE last night - Y mask hanging on the front of the dewshield, which extends 28cm from the front of the dovetail bar (resized to 50%).

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Hi Cath

Schmidt-Cassegrain telescopes seem to have that central part that obscures the mask I might be wrong but it seems that if the mask is obscured by it then its not going to work, on my refractor the mask sits in front of the main lens about 4 inches away and its not obstructed by any thing this may be why SC users are having issues with the Y mask.

Hope you get some clear sky viewing soon it was thick fog in suffolk last night.

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