Diffraction spikes on planets- do they disturb you?

[JeremyS]

I’m interested in hearing people’s experiences with diffraction spikes when observing planets with a scope fitted with a spider.

I find with my Mewlon 210 the 4 diffraction spikes on Jupiter and Mars a bit disturbing. I’m used to observing with refractors and SCTs wHich obviously don’t produce spikes. I wonder if it’s especially associated with  Cassegrains. Newtonians display them, but are they as prominent?

I wonder what others find and whether it’s distracting.

There was a bit of a discussion on Mr Spock’s CC6 thread but it looks like  he got fed up and locked it. Some have commented, for example, they are less prominent on the Mewlon 180, with its 3 veins and 6 diffraction spikes. What about other Cassegrainians?

[HollyHound]

I do find the diffraction spikes on my Mewlon 180 are noticeable on planets, but (as you already mentioned) they are much less prominent in the 180, as it has three spider vanes, and so when they “double up” they become six fainter spikes.

They really don’t bother me that much, and are not visible on the moon, which is where I mostly use the Mewlon.

I also see them on my Dob, but again not bothersome.

Do you find yours very disturbing.

[JeremyS]

4 minutes ago, HollyHound said:

 

Do you find yours very disturbing.

Just a bit distracting. The more I try to ignore them, the more prominent they become. Over time, I have become acclimated to them quite a lot.

[Captain Scarlet]

Yes on my 12” Newt, they are very prominent indeed. More like diffraction _stripes_. Suiter thinks they do disproportionate damage to contrast on a planet, arguing that every morsel of brightness creates its own spikes, which directly overlay the bits of the planet right next to it, and so on. And the heavier shorter spikes produced by thicker vanes are especially damaging as very little of the diffracted light gets thrown outside the planet’s disc. I can’t help thinking all this when using my newt on planets, and it bothers me. On stars, I’m less bothered.

Cheers, Magnus

[NGC 1502]

I would prefer diffraction spikes not to be there, but it’s one of the consequences I can deal with using a regular Newtonian.

The advantages of a Newt greatly outweigh those diffraction spikes, and they’re only seen on the brightest of objects.

All types of scope are a compromise, it’s a case of deciding what you can live with and what you cannot.

Ed.

[ScouseSpaceCadet]

Newtonian diffraction spikes when observing planets drove me to refractors. I appreciate I'm losing resolving power but I'd rather have a higher contrast cleaner view.

[PeterStudz]

I’m no expert but diffraction spikes on planets in my 8” Dob annoy me! But I find it depends on a number of factors - magnification, dark adaption, time of night, target altitude, light pollution… And I’m usually able to find I way that on practice it doesn’t bother me. 

However, I’ve only had noticeable spikes on Jupiter, Mars and Venus. Jupiter only at low magnification, and for that a variable polarising filter can get rid of them. Or simply upping the power. Mars I always use a variable polarising filter. Not only does this help with any spikes but more importantly I find that the filter improves contrast and allows me to see more. For Venus, if at all possible, I prefer to observe during daylight - no spikes then. If I must observe Venus at night then I use a filter to cut down the spikes. Planets during twilight I really enjoy and of course no spike issues then. 

[John]

I've owned plenty of newtonians with conventional spider vanes over the past 40 years so they must have shown diffraction spikes around brighter targets but I can't recall thinking them annoying BUT that was some time ago. My 12 inch dob, which was my only newtonian for around a decade, had curved vanes so the diffraction was there but dissipated across the field of view rather than concentrated into spikes, and I came to appreciate that - it's impact / distraction seemed somehow lessened.

Since that 12 inch scope, I have owned a few other smaller newts which had conventional spider vanes and found myself not liking seeing the diffraction concentrated into spikes again- maybe my "tastes" have changed or maybe I'm less able to "look past" them now 

I'm currently considering another scope that does have secondary vanes and will, presumably, show some diffraction spikes although I'm told that the 3 vane design (Mewlon 180c) shows them less distinctly than a 4 vane setup.

Given complete freedom of choice I guess I would prefer a large aperture design that shows a "spikeless" view but the reality is that I'm not able to either afford or handle a 7 inch refractor. I guess a maksutov-cassegrain or maksutov-newtonian might dispense with them as well so are alternative options.

Apart from high quality apochromatic refractors, there are bound to be some compromises with the views through a telescope I suppose. We are all seeking the "Mary Poppins" views in larger apertures though - "practically perfect in every way" 🙂

From feedback on different scope designs I've read on forums, I suspect personal tolerance of this varies observer to observer as it seems to for false colour and other issues. 

 

 

Edited May 27 by John

[rl]

Having owned many Newtonians I've never been really bothered about diffraction spikes that much visually. I find them more annoying in photography.

The JWST sports some of the worst diffraction spikes I've ever seen...nobody seems to mind!

[josefk]

i'm on record on here a few times moaning about them with my Classical Cassegrain. I'm ambivalent when they appear across bright stars (they can sometimes even make a nice aesthetic change) but they are ruinous to my appreciation of Mars and Jupiter (unless viewing Jupiter in at dusk or dawn).

For planetary observing i appreciate the "in orbit" sensation (sharp planetary disc with black sky) and the planet width diffraction "beams" of my Cassegrain put a scope in between me and the planet in a way that i can't get passed/ignore. I knew within 5-seconds of first light with the Cassegrain on Mars that it was going to cost me anther scope without vanes.

[Mr Spock]

With the 12" on Jupiter they are extremely prominent. However, I cut the brightness down with a variable polariser and so don't see them. 

A (very) poor drawing to show what I mean, but you get the idea. Left without, right with polariser.

[bosun21]

Having owned quite a few Newtonians over the years I was never bothered nor really noticed diffraction spikes. However after reading a few threads on the question I now do indeed notice them, and find myself actively looking for them. This was one of the reasons I bought a 180 Maksutov for high magnification planetary observing minus the diffraction spikes. I now primarily use my 10" Synscan dobsonian for observing everything else where they are far less noticeable. Planetary imaging however isn't really affected by diffraction spikes as far as I have noticed so the 10" dobsonian can redeem itself in this regard. Love them or loathe them it's a penalty we pay.

[PeterStudz]

1 hour ago, Mr Spock said:

With the 12" on Jupiter they are extremely prominent. However, I cut the brightness down with a variable polariser and so don't see them. 

A (very) poor drawing to show what I mean, but you get the idea. Left without, right with polariser.

This is a good way of illustrating it and exactly what I found. In fact on Mars it was a revelation. Without a variable polarising filter, even if ignoring the diffraction spikes, Mars was a small featureless shimmering disc. With the VP filter it was transformed into a small beautiful sphere with subtle features. Plus the added bonus of no visible diffraction spikes 😀

[josefk]

4 minutes ago, PeterStudz said:

This is a good way of illustrating it and exactly what I found. In fact on Mars it was a revelation. Without a variable polarising filter, even if ignoring the diffraction spikes, Mars was a small featureless shimmering disc. With the VP filter it was transformed into a small beautiful sphere with subtle features. Plus the added bonus of no visible diffraction spikes 😀

Now you (both) tell me! 🤣

[Mr Spock]

Try a variable polariser and violet filter on Venus and you might see some cloud detail instead of a dazzling blur and diffraction spikes 

[Louis D]

Planetary diffraction spikes really only bug me when they cover up a moon I'd like to observe.

[magnahrl]

I have been observing planets since -74 with a Cave 8" f/4,5 Newt and since -08 with an Orion UK 8" f/6. Honestly I notice the spikes but they don`t disturbe me at all. I also observe planets with "spikeless" C8, 6" mak and 3,1" and 4,7" refractors. I don`t  even think of the difference. My main concern is how good (or bad) the scope optically really is. I have had my CC8 too short time for any opportunity to observe planets. Looking forward to it!

Magnus A.

[IB20]

Yes and yes. I would say I’ve always struggled to get consistently fantastic views of particularly the gas giants with the 8” dob. I find the overall excess brightness and diffraction stripes/bands really detracts from gathering visual information. I’ve tried filters but it never seems as pleasing as using my 3-5” fracs. Mars weirdly is superb in the dob and assume the spikes are less prominent due to the higher magnifications that I can use.

[PeterStudz]

50 minutes ago, IB20 said:

Yes and yes. I would say I’ve always struggled to get consistently fantastic views of particularly the gas giants with the 8” dob. I find the overall excess brightness and diffraction stripes/bands really detracts from gathering visual information. I’ve tried filters but it never seems as pleasing as using my 3-5” fracs. Mars weirdly is superb in the dob and assume the spikes are less prominent due to the higher magnifications that I can use.

Interesting, with my 8” Dob I’ve found almost the complete opposite! The only diffraction spikes I’ve had on a gas giant (whatever the magnification) has been Jupiter at low power. But it’s been easily illuminated by using a variable polarising filter. Saturn I’ve never seen spikes. 

However, Mars, even at x375 (which is the practical limit even if conditions allow) does show diffraction spikes. Again a VP filter cuts them off and has the bonus of improving contrast. 

Just a note:- I have tried colour filters on planets and find them practically useless. For me all they do is change the colour of the planet. They might take away a little glare, but a VP filter is better at that. 

One other thing I have noticed - when viewing planets do not get your eyes adapted to the dark. I’ll often look straight at my phone screen just to make sure. Better still, going inside the house for a short break with all the lights on. Often, when I get back out, I can see more. I’m in Bortle 7 and the light pollution generally helps with planetary. Occasionally I’ve viewed a planet(s) as the sun has come up. There’s always an optimal view for a few minutes during twilight. Far better than during the dark. And of course during this point in twilight there’s no spike issue. 

[IB20]

2 hours ago, PeterStudz said:

Interesting, with my 8” Dob I’ve found almost the complete opposite! The only diffraction spikes I’ve had on a gas giant (whatever the magnification) has been Jupiter at low power. But it’s been easily illuminated by using a variable polarising filter. Saturn I’ve never seen spikes. 

However, Mars, even at x375 (which is the practical limit even if conditions allow) does show diffraction spikes. Again a VP filter cuts them off and has the bonus of improving contrast. 

Just a note:- I have tried colour filters on planets and find them practically useless. For me all they do is change the colour of the planet. They might take away a little glare, but a VP filter is better at that. 

One other thing I have noticed - when viewing planets do not get your eyes adapted to the dark. I’ll often look straight at my phone screen just to make sure. Better still, going inside the house for a short break with all the lights on. Often, when I get back out, I can see more. I’m in Bortle 7 and the light pollution generally helps with planetary. Occasionally I’ve viewed a planet(s) as the sun has come up. There’s always an optimal view for a few minutes during twilight. Far better than during the dark. And of course during this point in twilight there’s no spike issue. 

Saturn less so in regard to diff spikes but the brightness washes details out and makes seeing the supposed improved resolution increase less easy, particularly the CD. My local seeing doesn’t seem to support high mag on these targets in the dob, it’s one of the reasons I moved to smaller aperture quality fracs. I wonder if Mars worked so well due to it being higher in the sky, maybe heat loss from my patio has less affect when the tube is pointing vertically? Or perhaps it was just a case of great seeing made me ignore the diffraction spikes? 

I’d welcome seeing nice big and bright diffraction stripes on Uranus and Neptune, probably need a 50” for that. 😅

 

[Whistlin Bob]

Nice topic. I came here to say that when I use a 14" dob, the spikes don't bother me, but the other effects of diffraction really impede the quality of the image and cause a frustrating loss of detail. I find an aperture mask gives a far superior view. However, reading the thread I'm now wondering why I've only tried my VP filter on the moon. Definitely going to try it on planets when they're next up at a sociable time. And this is why I love SGL!

[dweller25]

I see the 6 spikes in my Mewlon 180C

But I am not disturbed 🤪

[StevieDvd]

I don't have these issues being a refractor user but I did see this video from Cuiv the lazy geek which may interest some of you:

https://www.youtube.com/watch?v=tj-gDFrYnG8

 

[Louis D]

This thread on CN about diffraction pattern simulations might be an interesting read for some.