Baader Hyperion question

[Uranium235]

I will be taking delivery of a Hyperion 17mm EP in couple of days, and ive just one question in regard to Eyepiece Projection using my DSLR.

I already have the fine tuning rings, adapters and T2 extenders ready, but I having trouble with the tricky subject of focus.

If I were to focus the EP perfectly without the camera, lock the focuser, then carefully re-attach the EP with the camera at the basic lens > CCD distance of 50mm - would I need to re-focus?

This is because using a Bahtinov mask through my cams viewfinder is a bit of a depressing experience... but it works great with an EP. Im finding myself having to mess about taking subs before i start anything useful - just to check the focus.... iffy collimation isnt helping either (so I ordered a laser collimator too).

Thanks in advance

[glowjet]

The Bahtinov Mask has been the subject of recent discussion in other threads, research on the subject of the mask has brought to light some interesting facts, two of the most interesting are that the grid of bars produces a multi-order spike of lesser intensity due to energy loss, and secondly that a simple Y will produce the same diffraction pattern except be much brighter, the mask will act in just the same way as the Bahtinov mask, move the image away from the focal plane and the vertical spike will translate right or left as you move in and out of focus, if you make up a new mask of the Y pattern, the width of bars being the same as your Bmask or in the region of 3mm to 4mm wide out of say black card just to experiment, you may find the resulting image can now be focused in your cams viewfinder.

John.

[Uranium235]

Is there an online generator for the Y mask? As im not sure of the angles involved for that one (3x120deg?)... I wouldnt know where to start! If anyone has made one for a 6", a printable template would be most useful

Thanks for the suggestion, I will have a go at it.

[glowjet]

It is just a straight forward Y, the two angled arms 40° apart, the whole lying across the center of your aperture, as to the width of the arms this can be open to experiment, the general guide is the fatter the arms the brighter the diffraction spike, in reality the brightness of the spike will be a function of the bar width / aperture ratio, the information on the new type of mask has only just come to light so as yet no templates or on line generators have been established, what is quite amazing there is no hard and fast rule in the design, in accordance with Fruanhofers Principle and Babinet`s Principle a single bar placed anywhere across your aperture will produce a diffraction spike on the optical axis, with three bars, of which two are angled and one vertical, the vertical bar will always move to the right or left until focus is achieved, when it will lie on the center of the optical axis splitting the two angled bars, when making the design one must also bear in mind that diffraction spikes are always perpendicular or at right angles to the bar, as a start I should angle the bars as suggested and make them some 5mm wide for starters, but at the end of the day any angle, length or width of bar will produce spikes, so long as the above principles are borne in mind, I hope this helps to make things a little clearer.

John.

[TopHouse]

It does if you're Polish!

[Uranium235]

Thanks glowjet... well explained!

Then I guess I could just print off a massive "Y" from Word or Photoshop? And if that fails, I will literally just draw it and then print it off.

I know one thing though, its going to be hell of a lot quicker to make!

On a side note, will a mask work with a QHY5/PHD? It would be a nice option to be able to fine tune my guidescope for better tracking.

[glowjet]

Where a plane wavefront, in this case light, is constrained to enter a finite aperture, the light makes contact with all points of the aperture perimeter to produce secondary radiators,( Huygens Principle ) where these secondary wavefronts reinforce or nullify one another, diffraction patterns are produced hence the airy disk,

with the QHY5 the only way to find out is to experiment, to see if you can produce a diffraction pattern, taking into account the points I have mentioned in mask design I am sorry if these explanations sound a little complicated, but you should see the maths associated with the basic principles.

John.

[glowjet]

I just had a thought Uranium, you will be using Baader Hyperion's with Fine Tuning Rings, I have just taken delivery of some rings, re-checked on the info and found that if you use them with a 2" diagonal you need a stop ring to prevent damage to the mirror with the 1.25 nose piece on the end, just thought it worth a mention in case you were not aware of the problem.

John.

[Uranium235]

Already on the case mate, Ive managed to safely mount it in the focuser with the help of a 2" extention tube. Ive also done it without the 2" ext too, but the primary group of lenses on the Hyperion would be way too close to the secondary mirror to get focus I think (not enough out travel). Thats a shame tho cos the 2" extention I have doesnt have the same 2" safety ring that you get on the EP, so ive gotta be super-careful and make sure everything is tight - it would be a bit of a wounder to have the ep and cam fall out and smash into a thousand pieces!

Its looking like clear skies tonight (if a little windy), so I will give it a test drive with the Y mask and see how it performs. Oh btw, have I done the mask right? Thanks for the help man

[glowjet]

That looks good, but you might need to make the arms less wide, it should , however, give you bright spikes but short ones, you might try making the arms less wide, I would suggest between 5mm and 8 mm, you can but experiment to find the one which gives the best result for focus and brightness, well done so far.

John.