Annoying 4 point "reflections" on brighter objects

[ChrisThePuma]

Hi All

I am very confident my scope is properly collimated (checked star shapes when out of focus, and can see a very circular reflection complete with 3 mirror "clips" etc) - but when looking at brighter objcts (Venus, Jupiter etc) i get an annoying 4 pointed star like effect from the planet (see very crude drawing)

I have fiddled with the secondary supports to see if it is these but whatever i do they alwars stay the same - these dont come out in the snaps i take through the lense with my camera, but make "visual looking" slightly annoying because of these "reflctions" (if this is what they are)

Any idea on what causes these and if i can overcome them?

thanks

chris

[Psychobilly]

I guess you have a newt...

In which case they are Diffraction spikes caused by the spider vanes that hold the secondary mirror...

Not a lot you can do really...

Some manufacturers used curved vanes...

Peter..

[Kedvenc]

It's the diffraction pattern from the spider (secondary supports) and I believe there is not much you can do about it.

[JamesF]

I'm fairly sure you're talking about the diffraction spikes caused by the spider supporting the secondary mirror. Without changing the design of the telescope they're pretty much unavoidable. I'm surprised they're so bad on planets though.

James

[haitch]

It's the diffraction pattern from the spider (secondary supports) and I believe there is not much you can do about it.

Make an aperture mask so you only use part of the aperture without anything crossing it on bright objects or buy a refractor, SCT or Mak?

Make sure the supports are parallel to the light path to minimise their effect.

[Marine Bio]

Just my personal opinion but I actually quite like the diffraction spikes often seen in astrophotography taken on these sort of telescopes. I think on pictures of clusters like the Pleiades it really adds something to the image. I'm sure there are many more who will disagree however.

[182570]

That's one of the reasons to buy a refractor:headbang:

[haitch]

Just my personal opinion but I actually quite like the diffraction spikes often seen in astrophotography taken on these sort of telescopes. I think on pictures of clusters like the Pleiades it really adds something to the image. I'm sure there are many more who will disagree however.

First thing I should say is I do love my dob and yes, they look ok on stars but for planets they are a pain the butt as they tend to smear out some of the detail.

[Karen]

That's one of the reasons to buy a refractor:headbang:

No it isn't. It's one of the reasons to buy a Maksutov.

[Marine Bio]

First thing I should say is I do love my dob and yes, they look ok on stars but for planets they are a pain the butt as they tend to smear out some of the detail.

Agreed. Stars ok, they can look pretty. Not at all pretty on planets.

[brantuk]

"No it isn't. It's one of the reasons to buy a Maksutov"

Nope - it's one of the reasons to get one each of everything lol

[jimmyjamjoejoe]

Some manufacturers used curved vanes...

Peter..

Do they create diffraction spirals?

[haitch]

Do they create diffraction spirals?

Diffraction smears... Curved vanes can, if well implemented, make visible diffraction patterns disappear but it is still there only spread around causing a general reduction in contrast. If they are curved they are actually longer so there is really more diffraction. In fact every edge in the light path causes diffraction.

[Zachariah]

I only seem to see this on bright planets like Jupiter and Venus when using a low power ep. Up the magnification and it goes.

[Moonshane]

certainly is the diffraction spikes but I tend to look at the planet not the spikes! as you say, it's only an issue with the bright planets, certainly not the moon or anything relatively faint.

I also use the masking trick on my 16" dob. this effectively creates an apochromatic 6.7" f11 refractor, if you needed a reason to buy a bigger newt!

[LukeSkywatcher]

Only the brighter planet (Venus) cause me to see the spikes. Jupiter meybe to a degree.

Nothing else.

[Caldwell 14]

That's one of the reasons to buy a refractor:headbang:

Yes amazing isn't it, a little bit of CA and its the end of the world, Coma, spikes, mushy veiws, poor culmanation and poor contrast are greated with a shrug of the shoulders.

[haitch]

Yes amazing isn't it, a little bit of CA and its the end of the world, Coma, spikes, mushy veiws, poor culmanation and poor contrast are greated with a shrug of the shoulders.

But only on around 3 objects. I'll stick with my 14" of aperture for the rest! (I've got an ETX90 for those 3)

[Moonshane]

not sure what newts you have been looking through but I am not surprised you don't like them if they were as described.

all three of my scopes have none of the characteristics you mention. (ok they have spikes on bright objects at full aperture)

[haitch]

Diffraction, like many aberrations, is something of a personal issue. I can generally live with it, others seem not to notice it where as others really struggle. My old Darkstar dob could do with a better spider but even so it's not a huge issue for me.

I hardly noticed it before owning a Megrez 88 for a while.