112 replies to this topic

[Magnetic Field]

Yes, but sadly, Saturn (and Jupiter) are REALLY low in my sky for the next years -  or next five or so years in Saturn's case. I can only hope to get a few mediocre views this year. A really sharp view is unlikely.

 

 

Clear skies!
Thomas, Denmark

Denmark is even higher than most parts of the UK.

 

Saturn and Jupiter are even lower in your sky.

 

I am probably for 4 or 5 weeks in August on the continent on holiday where Saturn and Jupiter will be higher in the sky than in the UK.

[David Gray]

Addressing the premise (I hope.......) of this Thread:

 

“How many bands on Saturn can you see in your 3" and 4" apochromat". – and referencing my 415mm (16.3”) Dall-Kirkham performance...........Some points........(lengthy – sorry).

 

For meaningful comparisons we need to note that Saturn’s atmosphere is more changeable than the casual observer realises.  Currently some of the belts NEB(N) and what I think is a NTrB (N Tropical Band) seemed faded in unison since last apparition.  Most prominent mid-latitude belts being the NTB and the NNTB; the latter defining a seemingly extended NPR which also seems less banded this apparition. The definition here is Belts/Bands dark/dusky, Zones bright/light.

 

The so-called Hexagon is not a feature in itself and is simply the long-known NPC (North Polar Cap) that has been found to show a hexagonal shape.  Calling it the Hexagon (an unfortunate trend recent apparitions) can look like claiming to actually seeing (very tricky visually) that shape is being claimed.

 

The Cassini Div. is not always black all round....first off, often lightened by light leaking through where it crosses the globe; a perceptive observer with excellent optics might catch that.  That apart it is not devoid of ring particles which when viewed further from the ansae extremities take on a lighter aspect due to the foreshortened particle-bunching.  In fact in larger scopes and in very good conditions some lightness in the whole division becomes apparent giving a slate-hued effect – much as Ring C.  A lot of the blackness is actually contrast-induced with the bright defining A/B rings.

 

Somewhat confirming that is when I have caught it in moderate seeing in bright twilight – sun on the horizon – Cassini looking very black in a light field (16.3” D-K,270X) but must be a contrast effect it looking darker than the sky.  Then again in similar skies but near perfect definition I saw it very similar in intensity to Ring C: deeply slate-hued – lighter than the Globe Shadow on the ring (ShG/R).  In dark skies that shadow still looks blacker/no-slate to me than the division – even when more narrow than the Cassini and in very good definition.

 

As to the Encke Gap (IAU) we need be very cautious of that seeming detected as a similar effect is caused by that narrow brighter edge of Ring A giving an apparent dark – contrast-induced - line   In fact the whole planet can be a minefield of contrast effects. When I’ve seen it in pristine conditions there is a more sureness that contrast effects are not the main player but even then, some level, still involved I feel......gut-feel!

 

Also the broader Encke Minima, more of a band, can take on a sharp linear appearance against the lighter inner Ring A irradiating against Cassini.  No denying there are real features there, but just happen to lay where dark/light interfaces play their tricks......

 

Unfortunately lower-res apertures can fall into that with their seeming pristine/crisp views.  That brighter dark-sky-contrasting Ring A rim has some connotations with the Terby Spot; that notorious contrast-effect, that imagers also suffer, against the globe shadow (ShG/R).  Tried to find decent clarifying Link but maybe others will succeed – like many things now: seemingly fading into the mists............thus we encounter confused newbies (and not-so newbie!)  

 

The attached is a couple of better views (confident-Encke) when the planet was riding high here.  The ring south-face on view and the SPC in evidence – no hexagon-shape ever reported for that.

 

The Encke gap these recent apparitions (& Ring B minor divs.) I’ve recorded a few times and more muted and far fewer times than those hi-alt south-face views not because of any differences twixt the faces.......Simply because even with, the less frequent, steady air low down, we northerners have to contend with viewing through a much longer path of airborne particulates which will often damage contrasts and fine detail regardless of steady seeing.  What I call the second seeing effect: *The crispness factor*; when all else comes good that gets to be the decider.

 

I might need to edit this tomorrow - off to bed to catch Saturn in the morning.........

 

 

 

[Sasa]

Here is another sketch of Saturn, not from me but from my favorite observer of the past W. Tempel through his personal Steinheil 108mm refractor

 

https://www.research..._fig6_238023570

[Asbytec]

To my way of thinking, it's all about contrast and the state of Saturn's atmosphere at the time. Generally, however, a small aperture can capture the more distinct belts David shows in his sketches as they are high enough contrast. I point to image Sasa shows above to support that claim. I believe the image notes the equatorial belt, the north equatorial belt (southern part of it, anyway), and the faint temperate belt just below the (maybe) polar cap. So, yes, our observations can resemble David's sketches, it is the same Saturn we're all observing after all. It should be similar. 

 

David shows these features (on a given night) very distinctly. But, he also shows some belts that have much lower contrast beyond the contrast reach of a smaller aperture...actually out of reach of our eye because that detail may well be resolved in the small aperture image. The equatorial belt in David's 2002 sketch is weak, but it's seen against the lighter hues of the equatorial zone. I'd think we could eek out that higher contrast feature when the belt is more prominent offering just enough contrast in the telescope's afocal image presented to our eyes.

 

The other softer belts are certainly there, you can take a digital image of them to prove that. However, the contrast is too low for our eye unless a larger aperture is used. A larger aperture has better contrast on those image scales, especially when magnified to suit our acuity. So, on a given night, it's possible to see a lot of what David sketches in a small aperture, just not as well unless we have super human acuity by genetics or training.

 

Seeing matters, too, as we all know. High contrast features can survive some amount of seeing, soft contrasts cannot...not even in a large aperture. They come and go in a large aperture, but are not really possible in a smaller one, regardless. But, here's the kicker for me. I'd bet much of the detail David sketches is resolved in the image of a smaller aperture. To me, if the detail is there, then there is a chance of hope we can struggle to see it because it is there to be seen. So often failing to do so, of course, but that's our physiological limitation failing us. Knowing this offers hope that someday, if we strain hard enough and push our selves, well just maybe...not.  

[Asbytec]

That's an interesting attachment Norme. The Enke division has often raised eyebrows, especially in a small aperture scope, in which it is arguably impossible to resolve width wise. However, linearly its  feature I regularly see, just inside the outer edge of the A ring. Often it is lost if the atmosphere is turbulent or the scope is warm, and only rarely do I see it in both anse though I do have some sketches showing it in both. The minima tends to be more central to the A ring and more of a shadowy feature to my eye. The attachment makes an interesting comment about sketching and seeing the Enke division, and also about the importance of good optics in the last paragraph. I know it might seem counter intuitive, but I feel smaller aperture scopes with sharp optics can really work to advantage in less than perfect conditions, as they seem to see through the seeing with relative ease. And using a binoviewer makes things much easier to discern too! ☺

 

Thanks for your interesting post and the attached article too!

 

Mike

Yes, I saw that comment on quality optics and suggested magnification for 10" aperture or less. It is a 'linear' (sic) feature and certainly resolution is more likely with such high contrast thin lines. And you're right, it does raise eyebrows when folks see it in less than about 10" aperture or so.

 

I'd think nothing is impossible, so I do not rule it out. It's probability I guess, and probability is quite low but not zero. So, if it's not zero, then it's possible with all the conditions mentioned: quality, on the ansae, the best moments during the most excellent seeing, sufficient magnification, luck, etc.

 

If you are seeing something near the edge, that is where the Enke gap is as you say. Yes, toward the center of the A ring is the Enke minimum. I've seen the minimum many times. Only once I thought I may have seen the Enke gap, but I was quickly talked out of it - for shame. Wrote it off as a diffraction effect, which it may have been...in my case. Cannot rule that out. 

 

I am a believer in "infinite resolution" (sic), it really is just a matter of contrast right up to the 100% limit. I've seen high contrast features smaller than the Airy disc, sometimes much smaller as Cassini is. So long as the contrast is transferred to the afocal image, we stand a chance of seeing it. At small image scales, linear or otherwise, those probabilities fall off quite dramatically approaching (but not necessarily reaching) impossible unless contrast transferred to the image does hit zero for all intents and purposes. Then there is nothing to see.

 

Yea, I try not to doubt, but sometimes I raise my eyebrow and make sure folks know the Enke minimum is nearby and not to confuse the two. The Enke gap is not that easy, but it is highly unlikely...which is what convinced me to rule out my possible sighting. Playing the odds. But, if you are seeing a thin dark line near the edge of the A ring, that's where the gap is. If we see something where it's supposed to be, there's a chance we saw it. 

Edited by Asbytec, 21 May 2019 - 05:43 PM.

[Cpk133]

When I look at Hubble images of Saturn and see how fine the Enke gap is, I'm not at all surprised that I haven't been able to detect it.  I figure from my latitude, there's enough atmospheric dispersion to make it impossible anywhere but the tiniest part of the ansae, toss in a bit of haziness and it's gone.  As far as color goes, I have no problem seeing banding and colors even with a 60mm achromat.  For some unknown reason, I've never sketched Saturn but that's going to change this opposition (when these pesky clouds get out of the way).

[starman876]

Surprised the folks with super seeing have not chimed in on this thread to report what they see. 

[David Gray]

Huh!  Surprisingly, contrary to what I said about possible editing my last post (#77), not caught sight of anything so far – in spite of the haste to bash it off so to get to bed for Saturn this a.m........worrying!

 

Anyhow; seeing not great for Saturn but far from ‘white’/blank/featureless – white & featureless in not great seeing (i.e. albeit usable) would suggest too bright to me.

 

Now I have to decide on staying up tonight for Jupiter (where the buzz is the GRS might be unraveling!) – or early night for Saturn-a.m. – candle-burning both ends in prospect....

 

Just to say something about those 2002/03 sketches/views:  there would have been a degree of ‘glare’ swamping of softer features in play as these were non-binovu (mono only).  (Bino-ing from 2004); also no apodizer: that earlier version a bit too dimming for effective use on Saturn.

 

I agree with Norme about the detail being there in even small apertures – some often incipiently beckoning at the respective aperture-reach.......Back in the 1960’s I had a great 10” (f/8) Newt (mothballed) and time again as I was saying to the then BAA Saturn (A.W.Heath) (rough quote):  *So often in the best conditions I sense a wealth of detail just out of reach – as though through a haze. [absent or less opaque on crisper Jupiter]* 

 

The D-K went some way to getting some of that: getting >200 transit timings (CMTs) of mostly fine/subtle structure during the 1990s and early 2000s apparitions where with the later binoviewer and better apodizer might have given more certainty to untimed more fleeting/suspected stuff.  Hubble and the Cassini Mission showed us that structure and the overlying haze.

Edited by David Gray, 22 May 2019 - 05:02 AM.

[Magnetic Field]

Huh!  Surprisingly, contrary to what I said about possible editing my last post (#77), not caught sight of anything so far – in spite of the haste to bash it off so to get to bed for Saturn this a.m........worrying!

 

Anyhow; seeing not great for Saturn but far from ‘white’/blank/featureless – white & featureless in not great seeing (i.e. albeit usable) would suggest too bright to me.

 

Now I have to decide on staying up tonight for Jupiter (where the buzz is the GRS might be unraveling!) – or early night for Saturn-a.m. – candle-burning both ends in prospect....

 

Just to say something about those 2002/03 sketches/views:  there would have been a degree of ‘glare’ swamping of softer features in play as these were non-binovu (mono only).  (Bino-ing from 2004); also no apodizer: that earlier version a bit too dimming for effective use on Saturn.

 

I agree with Norme about the detail being there in even small apertures – some often incipiently beckoning at the respective aperture-reach.......Back in the 1960’s I had a great 10” (f/8) Newt (mothballed) and time again as I was saying to the then BAA Saturn (A.W.Heath) (rough quote):  *So often in the best conditions I sense a wealth of detail just out of reach – as though through a haze. [absent or less opaque on crisper Jupiter]* 

 

The D-K went some way to getting some of that: getting >200 transit timings (CMTs) of mostly fine/subtle structure during the 1990s and early 2000s apparitions where with the later binoviewer and better apodizer might have given more certainty to untimed more fleeting/suspected stuff.  Hubble and the Cassini Mission showed us that structure and the overlying haze.

I apologise for being off topic. But you mentioned the GRS:

 

But I posted this right now on a new opportunity that comes up with Jupiter's Great Red Spot (GRS):

 

https://www.cloudyni...rger-telescope/

 

 

Are you also observing Jupiter with your Dall-Kirkham?

Edited by Magnetic Field, 22 May 2019 - 06:56 AM.

[David Gray]

Jupiter :  Just yesterday posted this.............a 3-inch view but of course am mainly using the D-K. 

 

 https://www.cloudyni...u/#entry9381457

 

                             ...................................                                ...............................

 

Indeed all the planets with the 16.3":   Mercury to Neptune (plus Jupiter's big 4)

 

Put this montage together of particularly good views 2014/15.  Main file not to hand but.....

 

From top left Mercury; two of Venus below then in order up to Neptune bottom right.

 

I normally use various filters (some stacked) with Venus but confined to white-light here.

Edited by David Gray, 22 May 2019 - 08:13 AM.

[Magnetic Field]

Jupiter :  Just yesterday posted this.............a 3-inch view but of course am mainly using the D-K. 

 

 https://www.cloudyni...u/#entry9381457

 

                             ...................................                                ...............................

 

Indeed all the planets with the 16.3":   Mercury to Neptune (plus Jupiter's big 4)

 

Put this montage together of particularly good views 2014/15.  Main file not to hand but.....

 

From top left Mercury; two of Venus below then in order up to Neptune bottom right.

 

I normally use various filters (some stacked) with Venus but confined to white-light here.

Pln Sktch Mont II.jpg

Your Venus rendering is very impressive (I would say outstanding).

 

I often observe Venus in daylight from my window if I can find her with my Vixen Mini Porta (and the rubbish new built windows that cannot be fully opened; I am often too lazy to walk over to cul-de-sac Orchard a 5min walk away):

 

https://www.cloudyni...-the-1st-floor/

 

Are you observing Venus through daylight?

 

Edit: Okay I suffer from eye floaters. Probably a rubbish idea. But  the reason why I want a Borg 89ED: the max tube size of the Borg is 105mm. The tube diameter of the Vixen VMC 110L is 125mm. The Borg would give me more wiggle room while peeking through the window struts.

 

Edit 2: I have never seen brownish hues on Venus in my small telescopes. Grey scales if any. I wonder what aperture we would need to see your colour rendering. Are you using special filter on Venus? When I was a teenager I took part in the German Venus watch programme (at that time with a false-colour heavy Vixen 4" f/10 achromat). Sending in my monthly compiled drawings and observations.

Edited by Magnetic Field, 22 May 2019 - 08:49 AM.

[David Gray]

Yes daylight: mid-afternoon at eastern elongations; and normally an hour or so pre-sunrise to late morning. 

 

It is searingly bright even with the sun up and even with the Binovu + apodizer – thus considerable

filtering (stacking) to bring more certainty to very subtle features.

 

This thread shows some offerings (Posts #1 & #10) and gives the gist of what I seek.

 

https://www.cloudyni...5-with-filters/

 

Window observing: done a lot of that with the 3"......tripod tipped against the sill to get the tube

well out (altaz. mount) back in the 60s - it worked well enough..........

[David Gray]

Sort of on/off topic here but these sketches were by the well-known (or once was!) comet & nova hunter/discoverer George Alcock.

 

https://www.britastr...urnal_item/5752

 

The full article for members only but it relates how they were dismissed as fanciful by some *prominents* in the BAA.  Thus driving him to abandon submitting planetary stuff and turned comet/nova work instead.  His Jupiter – and other planet sketches were later confirmed as accurate.

 

1952 observations: note the size of the GRS – the wealth of detail apparent is because there was an SEB Revival – seen 3 of these events myself, spectacular!

 

Oh yes the 4” refractor he used had a triplet objective.

 

https://en.wikipedia...i/George_Alcock

 

http://martinmobberl....uk/Alcock.html

Edited by David Gray, 22 May 2019 - 11:50 AM.

[mikeDnight]

Yes, I saw that comment on quality optics and suggested magnification for 10" aperture or less. It is a 'linear' (sic) feature and certainly resolution is more likely with such high contrast thin lines. And you're right, it does raise eyebrows when folks see it in less than about 10" aperture or so.

 

I'd think nothing is impossible, so I do not rule it out. It's probability I guess, and probability is quite low but not zero. So, if it's not zero, then it's possible with all the conditions mentioned: quality, on the ansae, the best moments during the most excellent seeing, sufficient magnification, luck, etc.

 

If you are seeing something near the edge, that is where the Enke gap is as you say. Yes, toward the center of the A ring is the Enke minimum. I've seen the minimum many times. Only once I thought I may have seen the Enke gap, but I was quickly talked out of it - for shame. Wrote it off as a diffraction effect, which it may have been...in my case. Cannot rule that out. 

 

I am a believer in "infinite resolution" (sic), it really is just a matter of contrast right up to the 100% limit. I've seen high contrast features smaller than the Airy disc, sometimes much smaller as Cassini is. So long as the contrast is transferred to the afocal image, we stand a chance of seeing it. At small image scales, linear or otherwise, those probabilities fall off quite dramatically approaching (but not necessarily reaching) impossible unless contrast transferred to the image does hit zero for all intents and purposes. Then there is nothing to see.

 

Yea, I try not to doubt, but sometimes I raise my eyebrow and make sure folks know the Enke minimum is nearby and not to confuse the two. The Enke gap is not that easy, but it is highly unlikely...which is what convinced me to rule out my possible sighting. Playing the odds. But, if you are seeing a thin dark line near the edge of the A ring, that's where the gap is. If we see something where it's supposed to be, there's a chance we saw it. 

Of course it may not actually be the Enke gap I've been seeing Norme. As David mentioned in one of his posts above, there's a high chance it could be simply a contrast feature at the outer edge of the A ring. All I'm sure of is that I have seen the feature so many times in my various refractors over the years, that I'm confident something is going on at that point on the ring. 

In my observations, often the outer edge of Cassini's division seems softer than the edge against the B ring, but again that too may be down to contrast. Radial streaks in the A ring and radial spokes in the B ring can be seen quite regularly too. I've often noticed a bright polar spot and wonder if that may be due to aurora? Who knows?? I just draw what I see! 

[David Gray]

There is definitely a division (Encke Gap) there at sub-res for most amateur scopes (inc. mine)

somewhere up the aperture range it should manifest in very good definition as a

sharp black line.  In the 16.3" its more of a dark softish very narrow 'pencil' line.  Using the

BAA Intensity Scale 0=bright 10=black when I catch it it ranges 6.5 to 8.5: the

better the definition the darker.

 

Somewhere down the aperture range maybe there is an interplay: a 'juggle' in the

seeing tremors - real and ringer reinforcing each other - sort of...........

 

But I suspect 6" and below more of it contrast......maybe.....

 

Dave.

Edited by David Gray, 22 May 2019 - 12:10 PM.

[Asbytec]

Of course it may not actually be the Enke gap I've been seeing Norme. As David mentioned in one of his posts above, there's a high chance it could be simply a contrast feature at the outer edge of the A ring. All I'm sure of is that I have seen the feature so many times in my various refractors over the years, that I'm confident something is going on at that point on the ring. 

In my observations, often the outer edge of Cassini's division seems softer than the edge against the B ring, but again that too may be down to contrast. Radial streaks in the A ring and radial spokes in the B ring can be seen quite regularly too. I've often noticed a bright polar spot and wonder if that may be due to aurora? Who knows?? I just draw what I see! 

I have sometimes wonder about not drawing what you see. What I mean is, we sometimes see illusions and some form of mental or optical affects that are not real...apparently. But, we see them none the less. One that comes to mind is the greenish contrast hues on Mars. I know these are illusion, so I do not sketch them as green features. But, I also know I am fooled sometimes, just not often when or what affect is fooling me. I do not have a library of illusions in my mind to cross check my observations. So, I agree, sketch what we see, regardless, and maybe it'll get sorted in the wash.

 

As for the A ring and Enke division, yea I have gotten some hints that something is going on, too. Tantalizing hints of Enke. But I am always talked out of it, as David says, some quick jitters in the seeing which I have seen happen with star images. Or something, some small vague contrast effect possibly the interplay of light and dark involving Enke. Anything other than the Enke division in a modest aperture of modest quality.  But, who knows for sure. I know the rapid image shift is some seeing conditions, even excellent seeing, is real and the effect can be similar to a lucky snapshot of Enke. So, for me, the sighting remains tantalizingly close but no cigar. I wish I could say I've seen it, but my argument is not strong enough to argue back with any credibility.

 

I have yet to see the spokes or any radial streaks. Normally those are reserved for larger apertures with better contrast on those scales. However, I am sure the spokes are present in the image as a low contrast detail that might be eked out by keen observer and a high contrast afocal image. That's certainly possible. Aurora, yikes! If any scope (observer) can do any of it, certainly a large quality refractor can with a keen observer at the controls. Together, this offers the best chance of seeing detail at the margin. Even a modest obstruction, some aberration, or weak coatings, etc., can push detail at the margin beyond the margin to be picked up, again, by a larger aperture by an intrepid observer.

 

Again, these details are certainly large enough to be "resolved" in a modest aperture and are present in the image, it's just a matter of object and image contrast and personal acuity...and seeing, and high contrast optics, and whatever. Nice segue back to the belts on Saturn, because this holds true for them, as well. 

 

It's all fun, pushing ourselves to the limit of our perception of the telescopic image and returning safely home totally sane and not corrupted by the dark side. Sometimes we see some strange things in the hinterlands at the limits of our perception. Sometimes they are real, sometimes illusion, and sometimes imagination. But, we see them and sketch them, regardless, without knowing but believing they are real. It's a hazard to our hobby we have to endure as observers. The beauty is, we can actually learn to trust ourselves out beyond the horizon of our day to day reality and come back with a real story to tell of rings, and gaps, and of belts. That's observing.

Edited by Asbytec, 22 May 2019 - 07:57 PM.

[Bomber Bob]

Surprised the folks with super seeing have not chimed in on this thread to report what they see. 

Lots of reasons for me:  2+ straight years of cloudy nights.  No 4" APO.  Maybe a half-dozen Saturn views in my vintage Vixen FL80S, and no sketching.  Can't recall if I posted any observing reports, either.

 

I had to search back to June 2017 to find any Saturn photos, and these were with achromatics.  First is with a 1960s Lafayette Galactic 76x910, and the second with my 1950s Edmund 100x1500:

 

 

Used my ASI120MC for both.  In fact, the Galactic's was my very first attempt with this camera, and I didn't nail focus.

[BGazing]

Before anyone lobs stones at me: this is not a confrontational post. And this is not a post refractor vs reflector.

 

 

I observed Saturn 2 weeks ago low on the horizon under bad seeing with my Vixen VMC 110L (magnifications: 130x, 170x and 210x).

 

I saw 1 equatorial band (again bad seeing and low at the horizon).

 

 

Someone made a sketch of hot new Saturn with his 40cm Dall-Kirkham reflector:

 

https://www.cloudyni...m/#entry9369266

 

 

Does your 3" or 4" apo ever show more than 1 or 2 bands on Saturn?

Try using ADC (stick a barlow before it) and you will 

a) suddenly see 'better seeing'

b) the picture will clear up of dispersion and will be less mushy and with more detail.

As for the question, I will check it with my refractors and let you know, has been quite a while since I have last seen Saturn.

[gnowellsct]

2. And this is more a question for the Dall-Kirkham owner: why the 40cm Dall-Kirkam if I can get the fantastic Saturn view with a 4" apochromat.

What would a 5" apochromat show?

The larger scope gets to the higher magnification with a larger exit pupil, greatly improving ease of viewing.

The larger scope intrinsically does more stuff, besides Saturn. One reason apo owners are so fixated on planets is a lot of deep sky is pretty feeble...territory north of 11th or 12th mag. There is of course a distinction between detection and actually having something to view.

Difference between what people have the artistic skill to draw and what they see. Limits to the drawing medium and artist's skills tend to equalize apertures.

Decreasing marginal returns. It would take 20 years to get a good grip on lunar details in a 3 inch apo. Sixteen inches shows more, period. But it reminds me of a hotel I was in where the breakfast counter was about eighty feet long. It would have taken two weeks to sample the cheeses let alone fruits meats pastries. Sometimes a more restricted offering is a blessing. I have scopes from 81mm to 356mm but don't really want the 356mm on the moon. Not yet anyhow. It's too much to take in. This is probably why some of CNs best sketchers prefer smaller instruments. The smaller aperture filters out mind numbing details that would take forever to draw. And of course developing the skill puts a premium on frequent viewing and ease of set up.

With Saturn you're increasingly looking for subtleties which you won't even notice till you've spent a lot of time at smaller apertures.

A five inch apo is great but you see more in larger apertures. Color saturation improves.

Best way to understand these differences is to bolt an apo on to a larger instrument or set up side by side. But there are decreasing marginal returns. The first three or four inches of aperture show at least one everything there is to see in the sky. Saturn's ring can be seen at 40mm aperture at 20x. So why does one need a three inch?

[gnowellsct]

This has become an interesting thread. More controversy than I would expect to see in such a simple post. I am sure this will get more interesting

Cmon, it's the refractor forum

[Asbytec]

Cmon, it's the refractor forum

So, let's get busy.

In any case, a modest APO is not going to show what the large DK shows in the sketch in question. Couple of belts, a couple of zones, some nice rings and a polar hood. Maybe a few or several moons.

[starman876]

So, let's get busy.

In any case, a modest APO is not going to show what the large DK shows in the sketch in question. Couple of belts, a couple of zones, some nice rings and a polar hood. Maybe a few or several moons.

That is a good point.  Saturns moons really start to show themselves in a large aperture scope. 

[Rich V.]

That is a good point.  Saturns moons really start to show themselves in a large aperture scope. 

You can still pick out five of Saturn's brightest moons in an 80mm, though.  I haven't seen the sixth brightest,  Enceladus, in my 80mm but I've heard reports of others seeing it in a 100mm.

 

Rich

[gnowellsct]

That is a good point.  Saturns moons really start to show themselves in a large aperture scope. 

Well let's put it this way.  In a 4" apo at 200x you are dimming out.  That's just all there is to it.  When you dim out colors become less vivid.  Less vivid colors means less things to see.

 

About ten or eleven years ago I had the FS128 set up on Jupiter at 300x and conditions were just mind blowingly good.  I was in awe of what that 128 was doing.  Then I walked over to my C14...

 

...and spent most of the rest of the time with the C14, it was just obviously bringing in much much more.  There were more details and the colors were strikingly vivid.

 

Saturn's rings have very subtle coloration differences so eyeballs are going to be a big part of what gets seen.  If you have early cataracts or congenital color blindness (which in the usual case is one of degree, not these people are color blind and these people are not) there are some things that are going to elude you.

 

I score top tier on color tests but one of my best observing buds and my own son do not.  This sometimes is evident when I'm jumping up and down about the details in Jupiter's festoons or the exquisite gossamer details in solar prominences (h-alpha).  H-alpha is really tough on people who are red-impaired.    

 

This increase in detail with aperture has repeatedly been the case and why my favorite way to use an apo is with an SCT attached.  

 

Sometimes the difference aperture makes is striking other times you have to pay attention.  Let's say your four inch is showing some random set of lunar details which we symbolically represent thus

 

/o--\X

 

you switch to your ten or fourteen inch and see

 

/.o--\'X.

 

That's a big deal to get that extra detail, but also an example of what I mean by decreasing marginal returns.  The first three or four inches show you 90% of what there is to see.  The next ten inches show you the same view at an easier exit pupil (which definitely matters, for long viewing sessions), and if you're paying attention you'll see that a few details that are not in the first set.  But you are getting a big honking eyeball full of lunar details and the fact that a few are missing from the smaller scope doesn't really detract from the fact that you're having a rocking good time.

 

AND NOW A WORD FROM MY PERSONAL OBSESSIONS.  It is to be noted that aperture differences are only significant holding the steadiness of view (the mount) constant.  As has been shown  a pair of 7x50 non-stabilized binoculars shows less than half the detail of a pair of 10x30 image stabilized binoculars.   It is pointless to discuss aperture differences if this is not taken into account.  Many of the "my apo beats the dob/sct" stories may readily be due to the tendency of larger optics to have less stable mountings than the smaller ones.   And if you can't afford a good mount for your large optic you're wasting your money.  Get the best mount you can afford and size the optic to the mount.  WE NOW END THIS MESSAGE SPONSORED BY MY PERSONAL OBSESSIONS.

 

But, holding steadiness of the mount constant, it is to be remarked (as I often have) that the jump from the human night adapted pupil to a 3 or 4 inch aperture (and even less) is epochal.  It opens up the sky.  You can see galaxies, globulars, doubles, rings of Saturn, GRS on Jupiter, emissions, reflection, and dark nebulae; everything there is to see, in sum.  To get an equivalent jump in aperture, you need to go from roughly 4 inches to 80 inches.  From this we can observe that virtually all amateur instruments, even though a 25" "blows away" a 15", are marginal improvements over the first three or four inches.  And three and four inch telescopes kept professional astronomers busy for two centuries give or take.

 

Greg N

Edited by gnowellsct, 19 June 2019 - 01:38 PM.

[Eddgie]

My   observations with 4" Apo (Televue 101) were very much in line with Roberto and Allen's drawings. 

 

The major problem I have with a small aperture like this for planetary is that I can't get enough scale before the image dims, and when I go too high, what little color I can see is far more muted than with larger apertures.

 

My best views were not as good as David's image shown above, but much closer to that than most of the 4" drawings I see here.  Those observations were made with a 12" dob with really good mirrors, and a 14 with fairly good mirrors.  In these scopes, the colors I can see make the various bands more easily separated out because, well, there are colors. 

 

The drawing by David and Roberto though are pretty close to what I have seen in most small scopes.   The MN56 was perhaps a tad bit better than the TV101 because the image was a bit brighter and a bit more color was seen.  The difference was super subtle, but that tiny little extra bit of color did make it look like there was a tiny bit more banding detail. 

 

Saturn is a very colorful planet.  The colors are mostly muted pastels (green, pale yellow and slight blue tint and peach),  but there is a great deal of it and this color contrast makes what looks like a single band in a smaller scope where things seem more monochromatic (to me) into two or three bands.  If they all look like a muted smokey color, the tend to merge together.  Many of these bands would otherwise be visible in a 4" scope because they are wide enough to be resolved, but for me, they look more smokey grey than pastel.  Not enough of my  cones are firing in a 4" scope I guess. 

Edited by Eddgie, 19 June 2019 - 04:48 PM.