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Is it normal to get glare from Jupiter?


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6 minutes ago, Stu said:

Have a look at lower powers and see what you see. It seems like it may be an eye sensitivity thing. In terms of physics they are there, but it seems some see them, some don’t. I don’t believe it is the scope making the difference (assuming standard 3 or 4 vane spiders)

I'll need to have a proper look.  I try to ignore them, I seem to recall that they were less like what you'd see with a diffraction spike like in an image and more like a solid band.  They're definitely from the vanes, but they done taper as they get away from the planet (as far as I can remember)

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I was looking at Venus a few nights ago with the 12". Even with a 30mm eyepiece there were no spikes, just a small overbright disc with some even, all around scatter from the eyepiece. At that magnification, x51, I could clearly see the phase. At higher magnifications there was also nothing. When I used my variable polariser to cut down the brightness there was a lovely disc with some faint cloud detail.

I have no clue what some people are seeing *scratches head*

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1 hour ago, Ratlet said:

I'll need to have a proper look.  I try to ignore them, I seem to recall that they were less like what you'd see with a diffraction spike like in an image and more like a solid band.  They're definitely from the vanes, but they done taper as they get away from the planet (as far as I can remember)

Yep, as has been mentioned before they are broad bands or blades of light which are the width of the planet. They are much less well defined than spikes from bright stars as they are spread out more.

Ideally you obviously just ignore these and focus on the object you are trying to observe!

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28 minutes ago, Mr Spock said:

I was looking at Venus a few nights ago with the 12". Even with a 30mm eyepiece there were no spikes, just a small overbright disc with some even, all around scatter from the eyepiece. At that magnification, x51, I could clearly see the phase. At higher magnifications there was also nothing. When I used my variable polariser to cut down the brightness there was a lovely disc with some faint cloud detail.

I have no clue what some people are seeing *scratches head*

I assume you see diffraction spikes off bright stars in your dob?

Even though you don’t see them on planets Michael, do you accept that according to the laws of physics, they do exist?

I found this example here, not totally natural feeling but gives an idea:

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1 hour ago, Stu said:

I assume you see diffraction spikes off bright stars in your dob?

Even though you don’t see them on planets Michael, do you accept that according to the laws of physics, they do exist?

I found this example here, not totally natural feeling but gives an idea:

I’ve never seen an image of Jupiter like that ever. Regarding the stars I honestly can’t recall seeing them there either, either that or I didn’t notice. I will now be looking for these after reading this thread. I truly hope I don’t start seeing these spikes as it would ruin it for me.

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I can't  say that I've ever noticed such pronounced diffraction spikes as that image in a four vane system, maybe a photo accentuates them.  For me, diffraction spikes are a minor penalty for being able to use a larger telescope than a refractor.    🙂 

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4 minutes ago, Peter Drew said:

I can't  say that I've ever noticed such pronounced diffraction spikes as that image in a four vane system, maybe a photo accentuates them.  For me, diffraction spikes are a minor penalty for being able to use a larger telescope than a refractor.    🙂 

I think they are more pronounced in the image Peter, agreed. This conversation has turned into something I didn’t intend, but as a ‘seeker of truth’, my only goal was to establish that they exist (due to physical laws) regardless of their variability of visibility depending on circumstances or observer.

The key aim actually is to ignore them and focus on the target itself! 👍

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12 minutes ago, Stu said:

I think they are more pronounced in the image Peter, agreed. This conversation has turned into something I didn’t intend, but as a ‘seeker of truth’, my only goal was to establish that they exist (due to physical laws) regardless of their variability of visibility depending on circumstances or observer.

The key aim actually is to ignore them and focus on the target itself! 👍

I think ignoring them must have been my subconscious strategy,  I'll look for them next time I get the chance.      🙂 

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1 minute ago, Peter Drew said:

I think ignoring them must have been my subconscious strategy,  I'll look for them next time I get the chance.      🙂 

I’m going to be really unpopular now if the ‘non see’ers’ suddenly start seeing these 😱🤪🤣

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Oh dear I hope it doesn’t become one of those things “you can’t unsee”.

My own experience is that the stripes are more prominent and longer than shown in that photo.

The spider diffraction is destructive to contrast in a planet. Returning to the “many stars each with spikes bundled together” analogy, and combining it with the fact that thicker vanes produce shorter brighter spikes, you get that each point within the planet is overlapped by all the diffraction thrown from the neighbouring areas in the planet.

What you want to try to achieve is long, thin spikes (from each “planet-pixel”) so that the diffraction from each point is thrown _beyond_ the disc. To do that, you need vanes to be as thin as possible, and accurately straightened up to present as small a profile to the sky as possible. And, if possible, 3 vanes is better than 4 as it results in 25% less total diffraction.

Apols, I’ve perpetuated the slightly-off-topic theme 😬

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4 hours ago, bosun21 said:

’ve never seen an image of Jupiter like that ever

My 15" under great seeing shows more than the image in the photo. 300x is a magic minimum for Jupiter IMHO and large aperture really brings out detail and colour. The Binotron 27's/15" have given me views that is etched right into the brain .

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4 hours ago, Stu said:

but as a ‘seeker of truth’, my only goal was to establish that they exist (due to physical laws) regardless of their variability of visibility depending on circumstances or observer.

They are always there, no question.

A great thread years ago down in the physics section IIRC highlighted the ability of the brain to "fill in information". It is possible and I think likely that some observers wont see them because the brain is already tuned not to see them. It wants to keep the image the way it thinks it should be IMHO.

The laws of light and physics state the diffraction spikes have to be there, regardless if an individual sees them or not.

Great response on this Stu, Gerry

 

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3 hours ago, jetstream said:

It is possible and I think likely that some observers wont see them because the brain is already tuned not to see them.

On the other hand people see what isn't there due to expectation bias...

This will be my last post. I can see more and more SGL turning into another forum where there are constant disagreements and highly opinionated views. There have been several threads like this recently. Not very SGL in my view.

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7 minutes ago, Mr Spock said:

On the other hand people see what isn't there due to expectation bias...

This will be my last post. I can see more and more SGL turning into another forum where there are constant disagreements and highly opinionated views. There have been several threads like this recently. Not very SGL in my view.

That will be a great loss to the forum.  You've done loads to help further my enjoyment of the hobby and understanding of how to squeeze every last drop from the limited dark skies we get.  I'm sure there is a slew of others who feel the same way.

I understand your feeling though.  I've always found the discussions here to be more relaxed and sociable than other forums and is a large part of why this is the forum I mostly post on.

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All telescopes, refractors and reflectors suffer from diffraction effects caused by anything in the light path. With a refractor the diffraction is caused by the edge of the lens cell. In a system with a secondary obstruction, both the edge of the mirror and the edge of the secondary produce diffraction paterns, hence the brighter first diffraction ring in reflectors and Cat's. I see diffraction spikes every time I use a Newtonian. It's simply the nature of the beast. A single vein spider will produce a spike that crosses the full field, and a double vein will create double the diffraction. A three vein will create six spikes, and a four vein, although appearing to produce four spikes, actually produces 8, they simply overlap. It's the edge of an object that produces the diffraction pattern, so thin vein spiders still produce the same diffraction effects, though the fractionally reduced distance between the diffraction effect may be less obvious. Even curved veins don't eradicate or reduce the effect, they just smear it.

The glare around a planet can be produced by diffraction, but also by oil on the eye lens of the eyepiece from eyelashes, especially when there is minimal eye relief.

Most often though it can be the result of mist or ice particles in the atmosphere.

Edited by mikeDnight
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I think the way to reconcile that some cannot see them off a planet is that there will be a certain level of LP which will extinguish the bands. It’s no coincidence that the two here who have said they generally see _bolder_ stripes than the above photo also happen to be the ones to have 21.8 skies: @jetstream and me. The level of LP to render them invisible may not be very high. Also Jupiter in particular has I suggest a similar overall colour to that of LP.

Cheers, Magnus

Edited by Captain Scarlet
typo
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1 hour ago, mikeDnight said:

All telescopes, refractors and reflectors suffer from diffraction effects caused by anything in the light path

Great statement Mike.

 

1 hour ago, mikeDnight said:

The glare around a planet can be produced by diffraction

This too.

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I personally dont find anything controversial with regards to diffraction and diffraction spikes. Accepting that the spider has an effect potentially as glare on a planet or whatever goes a long way to sorting out if there any additional causes of glare in our control IMHO. If a few other causes of glare, stacked together and added up in a newt the view can be a very washed out, undesirable one.

An example is a 200mm f3.8 that initially caused massive glare among other things. After a bit of work it is a high contrast large DSO getter.Knowing how much glare is normal really helps- and its not much in practise IMHO. Assuming the mirror is low scatter etc etc.

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I suppose Michael not being aware of the spider diffraction in his reflector, is a lot like me not seeing the CA in an achromatic refractor. I know its there but it doesn't generally bother me if its well controlled, so I don't look for it.  I do think discussing diffraction in this thread was only meant to be helpful, and although a minor diversion, it is quite important, and potentially linked to the op's question.

 

Edited by mikeDnight
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