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New Focusing Aid

George

By George
in Imaging - Discussion

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Psychobilly

Psychobilly

Posted
Posted

My Russian is not very good so i'm tryign to find an english explanation of the scaling process. I have spoken to the co-owner of the firm that have the laser cutter this morning and he has said if I can get him the drawing as a DXF or DWG then he'll price it and make me a couple of prototypes (one for the 8" and one for the 66mm to try....

I will keep you posted...

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Psychobilly

Psychobilly

Posted
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I have read through the design rules on the cloudy nights forum and have got the mask drawn in Autocad for use on a CPC800 at F10 and F3.3

8192_normal.jpeg

(click to enlarge)

The two holes small holes will have M3 x 10 threaded inserts for fixing handles the two cutouts allow the mask to pass the pegs used for holding the front cap onto the scope.

Will try and get one cut tomorrow...

Got to draw the one for the "66" next...

Billy...

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Psychobilly

Psychobilly

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Should have the "prototypes" in stainless hopefully by mid week or friday at the latest...all I'll need then is the weather to test them :clouds2:

I could get them made in small(ish) batches but will need to know dimensions focal lenghts etc to get them designed for other scope/reducer combos...

Looking into costings for different materials/finishes etc

Billy...

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RichieJarvis

RichieJarvis

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Very cool - I'd like 2 - one for my 6" Newt, and one for the ZenithStar 66...

As far as mounting, I made a triangular Hartmann mask for my old LX200R - worked very well - the mount mechnism was as simple as 2 screws which hung over the tube. As the scope is pointing up, and normally not directly up, the 2 screws simply hung the mask over the end of the tube. This also saves having to man-handle the scope too much when attaching/detaching the mask.

Just a thought!

Cheers,

Richie

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NiteGawper

NiteGawper

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How precise does the calculation have to be for various scope lengths etc??

The reason I ask is that I have an f/8 150mm TAL-2 with a focal length of 1200mm so I can work out the size of the mask for that.

But my other scope is a 250mm (10") f/6 Dob - but I don't actually know the focal length. Is there a way to calculate the F/L??

And how important is the F/L when asking the mask??

Cheers,

NG...

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Andrew*

Andrew*

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How precise does the calculation have to be for various scope lengths etc??

The reason I ask is that I have an f/8 150mm TAL-2 with a focal length of 1200mm so I can work out the size of the mask for that.

But my other scope is a 250mm (10") f/6 Dob - but I don't actually know the focal length. Is there a way to calculate the F/L??

And how important is the F/L when asking the mask??

Cheers,

NG...

The focal length is the aperture multiplied by the focal ratio. So 250mm x f/6 = 1500mm.

I don't think the focal length is totally vital to making a successful mask, so work out the width of the slits optimised for both scopes - i.e. using a f/l of 1350mm in the formula.

Andrew

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Psychobilly

Psychobilly

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Just give me the focal length and the relevant measurements and i'll knock up the templates in Autocad and post a preview on the forum...

I will hopefully have the first two designs cut in stainless for me in the next day or so - all i need then is a clear spell to check them out.

The CPC one mounts inside the front corrector plate cell with a central hole to clear the secondary mount.

The SWE66 one fits to the front of the dewshield...the tabs bend back to hold it in place..

Describe what you want with measurements and i'll do my best to get them drawn up in a day ot two...

You can't really scale the designs for different apertures you have to do the calcs and work from there...(this is all based on what I have read elsewhwere and I have yet to try out the designs)

Billy...

Forgot to add the slots can be samller when the masks are precision made if your going to cut them from card etc then you really need to use the one with the "3rd order" slots - again based on what I have read elsewhwere to make it easier to cut..

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Andrew*

Andrew*

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PB, would you at all mind doing a drawing for an 8" f/5 (1000mm f/l) for me (and many others with this scope?

You should be charging for this!

I don't think the focal length is totally vital to making a successful mask, so work out the width of the slits optimised for both scopes - i.e. using a f/l of 1350mm in the formula.

Of course that would mean 2 different apertures - d'oh! :withstupid:

Andrew

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Psychobilly

Psychobilly

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Much cheaper version, http://home.comcast.net/~dandkmccrady/Articles/FocusMask/FocusMask.htm

:clouds2: Think about it!! I really can't see the results of this being any different to be honest.

Correct me if i'm wrong, but isn't this a bit of an expensive gimmick?

Jeff.

They needn't be that expensive...

I do all the "cad" work myself minimising the programming time....

An 8 foot x 4 foot sheet of 0.8mm stainless is round £50 and you can get a load out of that...especialy if you nest different sized masks onthe sheet.

If you laser cut using compressed air rather than nitrogen it helps keep the cost down but with some

"staining" of the metal around the cut..

If you can get away with unfinished stainless then thats obviously cheaper...

It will be interesting to see how they work the "videos" show how they masks allow you to get critical focus very easily. I have tried rough cut masks and they are ok.. the precisely cut stainless ones I have had made in the past are much better as you get very good merger of the sub "images" at focus.

I am extremely fortunate in that I get my "prototypes" cut for free...I always offer to pay for materials and machine time but usually a contribution to the Coffee fund is all thats required...

Billy...

1000mm F5 comming next as soon as someone posts the OD of the OTA :)

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Psychobilly

Psychobilly

Posted
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Billy - Thank you! :notworthy:

I'll give it a spin at the next opportunity. Question: Why is there no central circle?

Cheers

Andrew

It's for a refractor....

I'll need a rough diameter for the central obstruction for the 8" 1000mm f5

There's no need charge for knocking up the templates as I want to see if these "designs" actually work...

And keeps me out of mischief on damp nights...

so get them all in before the weather changes :clouds2:

Hope this link works...

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2544487/page/0/view/collapsed/sb/5/o/all/fpart/all/vc/1

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Psychobilly

Psychobilly

Posted
Posted

Thats better...

8253_normal.jpeg

(click to enlarge)

Will do some more tomorrow night...

Billy...

Third order again so less cutting...

Note this will overlap the sides of an a4 sheet when scaled but all the slot detail will fit the page.. I haven't added anything for mounting it either...

I'll have to check the ED80 one I might have forgotten to halve the result :clouds2:

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