Very long spikes!

[Spica]

Hi. Noticed a new thing the other night, when visually looking at Vega in dead center of the 26 mm Meade SP Series 4000 (5 elements - Japan version) EP through my Nexstar 130 GT, I had four spikes ALL across the field of view. I never noticed this before, and it seems like Vega and it's bright magnitude is the only star that causes this. I've looked at Vega before and never experieced it earlier.

Is there any flaw on the optics after all, or is it just normal from time to time depending on the atmospheric conditions?

It was kinda neat experience but weird!

[Capricorn]

It will be diffraction spikes caused by the spider holding the secondary in position.

Can be one of the problems of a reflector.

[ecosse]

Yeh diffraction spikes, I get them when looking at Jupiter kinda annoying but bearable. Does anyone know if flocking reduces this any? I know you can't completely get rid of it but can it be made less?

[Spica]

Good stuff. Heard of diff spikes, but never realized they'd be so prominent! Interesting. Found a site explaining the diffraction difference in tubes with 4 vanes, 3 vanes and an arch vane as opposed to none.

If one had only one vane, which i assume is possible, would they be non existence by then? Have never seen a scope with only one vane though.

If I see a pretty picture with spikes on the stars, can i then make the assumption the 'scope used for the photo is a reflecting one? Or are spikes in photos caused by a different phenomena?

[Gina]

One vane will give you two diffraction spikes. 180 degrees apart and at right angles to the vane.

[arbacia]

Spikes are concomitant to the Newtonian design. They are not a flaw, but a consequence, a characteristic, of the design.

Nothing wrong with it. However, spikes has a positive side: they can help to focus.

Probably will be only noted on bright stars, but all the stars show spikes (at least if a enough sesitive camera is used)

Patricio

[rfdesigner]

It was lovely to get rid of them on mine by adding an optical window.... better planetary contrast, less muck inside the scope, no spikes on images.

As far as I can tell I have the only 12" windowed newt, so not a terribly common thing to do.

Derek

[Trull]

When I upgraded my own design, I used three curved vanes to support the secondary - which have drastically reduced the spikes. Pretty easy to do.

I used hacksaw blades, and brazed them into cut bolts for adjustability.

I like the idea of an optical window - which would be easy to build, although you could go tilted and use correctors to achieve the same effect.

[ollypenrice]

It was lovely to get rid of them on mine by adding an optical window.... better planetary contrast, less muck inside the scope, no spikes on images.

As far as I can tell I have the only 12" windowed newt, so not a terribly common thing to do.

Derek

Very interesting indeed. I would love a Takahashi Epsilon for fast deep sky imaging, but not with starfields full of square stars and little diff spikes. An optical window had occurred to me for this scope... I wonder.

Olly

[arbacia]

An optical window should be made of polished optical glass. A two sides polished. perfectly flat optical glass is very expensive [extremely expensive indeed, just look at the cost of newtonian secondary mirrors!].

Then, why care to get optical quality polishing the surface of both mirrors just to use lower quality optical surfaces in the loght path? Why don't use directly a Mak-newtonian or a Schimdt-Cassegrain?

Patricio

[rfdesigner]

An optical window should be made of polished optical glass. A two sides polished. perfectly flat optical glass is very expensive [extremely expensive indeed, just look at the cost of newtonian secondary mirrors!].

Then, why care to get optical quality polishing the surface of both mirrors just to use lower quality optical surfaces in the loght path? Why don't use directly a Mak-newtonian or a Schimdt-Cassegrain?

Patricio

I was supremely lucky to get David Sindon to make me mine, at a very reasonable price concidering that one side isn't actually perfectly flat. One side needs to be polished to conteract the variations in the refractive index of the glass. Only a job for someone who really knows what they're doing.

Derek