Improving Planetary Views

[chrispj]

I've had a few good sessions over the last week or so, mostly watching Jupiter and Saturn as they are visible at a reasonable hour,  and also splitting doubles courtesy of Ag's rather good new book. 

 

I'm using my Bresser 102/1000 refractor,  on a Skytee 2, with my current shortest eyepiece being a Pentax XW 7mm. Jupiter I can discern the larger colour bands,  very occasional brief hints there might be narrower bands and the four main moons (highlight being a transit I think of Ganymede last night). Saturn I  see the rings as a single entity,  the planet as a fairly uniform disc and the shadow of the planet on the rings. Not even a hint of the Cassini division. Jupiter seems to have something of an aura around the edges which i would think must be due to brightness and diffusion/ dispersion through the glass (I've looked and i can't see any smears on the lens!).

 

I have something of a quandary where to go from here to improve things.  The obvious would be to step up to my 10" Dob but that has the fundamental problem that it's not high enough to see the planets over the garden fence! Other options seem to be in a more or less similar monetary ballpark so I'd be really interested to know what others think. 

 

1. Higher magnification eyepiece; obviously a smaller exit pupil - how low can you go before this is likely to be problematic?  Also I'm not sure realistically how much more I can push it before it will be too much for the scope. Continuing my XW/Delite theme isn't overly cheap either (i like the eye relief being a glasses wearer) as they don't pop up 2ndhand that often (but cheaper than options 2 or 3).

 

2. Better glass; there's the odd tempting item that pops up,  like the 80mm StellaMira in the classifieds recently. Better glass = clearer image/ more detail/ higher possible magnification? But less aperture = less light and shorter fl so smaller image for a given eyepiece... Hmmm.

 

3. More aperture, faster goal ratio; again in the classifieds there's items like the Starwave 152 f5.9 at a not unreasonable cost. Focal length similar to my Bresser so not dissimilar magnification,  lower f number so a larger exit pupil for a given eyepiece so easier to use shorter eyepieces/Barlow what I have already...

 

4. Binoviewers; like hen's teeth secondhand. 2 eyes better than one, brain processing etc. More fiddly for my wife to come and take a look as she does like to for a few minutes sometimes. Tempting out of curiousity.

 

5. Anything else?

 

Any ideas/ thoughts appreciated. Also any ideas on how any of the above might improve splitting of tight doubles - is this a magnification issue or do i really want better glass...?

Thanks all!

[johninderby]

Longer focal length is an advantage for lunar / planetary or doubles.

Sounds like a mak or classical cassegrain would be a good move for better planetary views as they are planetary specialists although excellent on small DSOs and doubles.

The StellaLyra Classical Cassegrain is a great planetary scope and very reasonably priced. The SW maks have rocketed  up in price recently so not such a good buy new. The CC cools down very quickly and not having a corrector doesn’t suffer from dew. I have both the 6” and 8” CC and use the 6” for a grab’n’go setup. The 8” is a lot heavier but would be fine on a Skytee but also costs more.

https://www.firstlightoptics.com/telescopes-in-stock/stellalyra-6-f12-m-crf-classical-cassegrain-telescope-ota.html

 

[Franklin]

Stick with the 4". The planets are not very high up at the moment and the atmosphere plays havoc with the seeing, like looking through boiling water!. If Saturn and Jupiter were up higher in the sky your scope should easily show the Cassini Division and plenty of detail on Jove. As far as Mag goes the 142x is fine for Jupiter with its larger disc but Saturn could benefit from 200x. Again it all boils down to conditions. Low elevation, bad seeing and maybe even collimation? The Bresser achros usually have decent optics, I've owned several in the past, but if chromatic aberration is visible then that will lower contrast as well. You could try a yellow filter to control this or a more expensive Contrast Booster filter which I would recommend to use with all achros when used at high mags. Having said all of that I can say that the upgrade to ED glass DOES make a huge improvement over traditional achromatics and also binoviewing just makes everything stand out more again. I've always had achros and recently got a 100ED and binoviewers and the improvements have just blown me away! Saving up for a Fluorite now, when will it ever end!

[Tiny Clanger]

5 Anything else

Time , conditions, and patience.

Time : if you don't already sit down to observe, try it , your eye stays in the right place more easily. It also means you can relax and persist more easily,  try to spend half an hour or more studying a target, moments of better seeing will show glimpses of detail, and your brain will start to put them together to assemble a view.

Conditions : sometimes you look at a planet with a high magnification and it is fizzing like a soluble aspirin or bouncing around ... turn your attention elsewhere, no detail tonight, the seeing is awful . One night , one magical night to come, the air will be steady and you will be able to push your 'scope to it's best possible view . One night last month the sky here was so steady the Cassini division (which I'd previously seen as a vague thing) was like a precision engraved black groove, almost unbelievably clear for me to see for nearly an hour. Well worth the dozens of hours of fuzzier views and hoping ! The gas giants are low in our skies at the moment, so far from ideal, the light from them has to struggle though a greater thickness of atmosphere than that from a higher object.

Patience  ... see time & conditions above 

Give your 102 a while to show you the best it can in the favourable conditions (which have to happen sometime .... eventually .... ), I know what you mean about the garden fence/dob thing, up on a tripod makes my 127 mak a far better bet for low objects vs trees and fences than my heritage dob.

The highest mag I have managed on the planets most of the time with the mak is 187x (with an 8mm eyepiece) and 250x on that one exceptional night. 250x does push the (f12 ish) mak into exit pupil /  eye floater territory for me,  approximately 0.5mm exit pupil . Your 'scope is what,  f10 ? a 5mm eyepiece (or a barlowed 10mm if you already have one ? ) might be OK, it depends on your eyes though ...

Heather

[chrispj]

Thanks all.

The CC is an interesting idea John,  i have always loved a classic refractor so i hadn't considered one before. Another thing to ponder...

 

I have a lot of floaters (i can see them right now, nevermind when i look through a telescope), hence the concern about exit pupil and thoughts turning towards binoviewers. My observing eye gets tired quite quickly as well, which they might help. As does the rest of me,  I should sit down,  such an obvious thing,  instead of wobbling back and forwards bouncing off the eyepiece!

 

 

[johninderby]

I have an 80mm f/15, a 100mm f/13 and a 125mm f/7.9 so I too love my refractors 🙂

I have been impressed by the views through the CC6” too and it gives great views for the money. Probably not quite as good as my 125mm APO refractor but a small fraction of the price and has it’s place in my scope line up.

 

[Tiny Clanger]

11 minutes ago, chrispj said:

Thanks all.

The CC is an interesting idea John,  i have always loved a classic refractor so i hadn't considered one before. Another thing to ponder...

 

I have a lot of floaters (i can see them right now, nevermind when i look through a telescope), hence the concern about exit pupil and thoughts turning towards binoviewers. My observing eye gets tired quite quickly as well, which they might help. As does the rest of me,  I should sit down,  such an obvious thing,  instead of wobbling back and forwards bouncing off the eyepiece!

 

 

Exit pupil is going to be a big factor for you then , and a 'scope with a long focal length for planetary detail is going to have to have a big aperture so you get an acceptable focal ratio/exit pupil . Which is expensive !

I've read that binoviewers allow the brain to do its customary trick of taking the two views (one per eye) and editing out the random and irrelevant anomalies ( the floaters) , but if you see them even without a telescope (and presumably using both eyes ! )  , maybe they are unlikely to be the answer .

[johninderby]

Binoviewers aren’t for everyone. Many love them but for some they just aren’t good. As I have weaker vision in one eye using binoviewers or binoculars is an unpleasant experience and gives no where near as good views as just one eye.

So very much an individual thing.

 

[chrispj]

6 hours ago, Franklin said:

 but if chromatic aberration is visible then that will lower contrast as well. You could try a yellow filter to control this or a more expensive Contrast Booster filter which I would recommend to use with all achros when used at high mags. 

I hadn't considered chromatic aberration, not knowing anything much about it or how it appears until just now. It is evident to an extent on Jupiter by the time i get to 100x with the Bresser 102 and more so with the 7mm. I will most likely try a filter in the short term, though I suspect I'll be keeping an eye on the classifieds for a Cassegrain type or an ED refractor (though not this month!).

[Franklin]

Achromatics can't quite focus all the wavelengths of light at the same point, so the violet/blue light is a little blurred when the other wavelengths are in focus, even more so in faster scopes. Having a longer focal length helps control this aberration, that's why all the old classic refractors were so long and awkward to mount. A simple Wratten yellow filter works by cutting out the blue light all together, but of course it also turns everything yellow. Though it will sharpen up the contrast as it will remove the unfocused violet/blue light. I've observed with achros for 40 years and have now just got an entry level ED that uses FPL51 glass and the improvement is very noticeable. Saving up for some proper fancy glass now.

[John]

I think you would find the planetary views with an F/9 ED 100 refractor (eg: Skywatcher ED100) somewhat of an improvement over your current achomat. I moved from a good achromat (100mm F/10 TAL) to the ED100 and noticed that the ED scope was sharper, more contrasty and supported higher magnifications.

No disrespect to the TAL 100 which is a very good achromat but the ED doublets are a step up in my opinion.

 

[Franklin]

Totally agree with the above and they come up on the used market at very good prices.

[IB20]

7 hours ago, Tiny Clanger said:

5 Anything else

Time , conditions, and patience.

 

Bingo! There have been nights where I have seen stunning planetary images with both 3” & 8” scopes and others when boiling, wobbly views surrounded by secondary colouration made observing the planets a waste of time. 
 

[nfotis]

On 12/10/2021 at 18:06, chrispj said:

Thanks all.

The CC is an interesting idea John,  i have always loved a classic refractor so i hadn't considered one before. Another thing to ponder...

 

I have a lot of floaters (i can see them right now, nevermind when i look through a telescope), hence the concern about exit pupil and thoughts turning towards binoviewers. My observing eye gets tired quite quickly as well, which they might help. As does the rest of me,  I should sit down,  such an obvious thing,  instead of wobbling back and forwards bouncing off the eyepiece!

 

 

For floaters, it's my understanding that slower scopes (f/12 or f/15) are less susceptible to these.

At least, I see lots of floaters on my C9.25, but none on my Skymax 180.

N.F.

 

[Tiny Clanger]

22 minutes ago, nfotis said:

For floaters, it's my understanding that slower scopes (f/12 or f/15) are less susceptible to these.

At least, I see lots of floaters on my C9.25, but none on my Skymax 180.

N.F.

 

It's all to do with exit pupil, f5 scope with 5mm eyepiece, = 1mm exit pupil, probably no danger of floaters spoiling the view. f15 scope, same 5mm ep, exit pupil = 0.33 mm, floaters galore 😞  I start to find floaters unpleasantly intrusive on bright targets at  0.5m exit pupil

https://www.cloudynights.com/topic/693848-eye-floaters-and-eyepiece-type/

Heather

[nfotis]

Well, a f/15 scope like my Skymax 180 doesn't need a 5mm eyepiece (the lowest I have gone is a 7-21mm zoom EP, and it was quite pleasant, because even the Moon wasn't excessively bright).

Your mileage may vary, of course, but the longer focal distance in scopes means you don't have to push much in the eyepiece front.

Since I am more of a photographer than observer, though, I claim no expertise on this matter.

For planetary, my ideal suggestions are:

C9.25, Classic Cassegrain 8", Skymax 180

Or a step down:

C8, CC6, Skymax 150

N.F.

 

[Tiny Clanger]

10 minutes ago, nfotis said:

Well, a f/15 scope like my Skymax 180 doesn't need a 5mm eyepiece (the lowest I have gone is a 7-21mm zoom EP, and it was quite pleasant, because even the Moon wasn't excessively bright).

Your mileage may vary, of course, but the longer focal distance in scopes means you don't have to push much in the eyepiece front.

Since I am more of a photographer than observer, though, I claim no expertise on this matter.

For planetary, my ideal suggestions are:

C9.25, Classic Cassegrain 8", Skymax 180

Or a step down:

C8, CC6, Skymax 150

N.F.

 

My post was a mathematical example of how focal ratio and exit pupil are related, no more than that.

[Nik271]

In most situations going for 0.3mm exit pupil is too much, I think only the Moon is an exception. 0.3mm exit pupil means using magnification more than 3 times the aperture in mm which is very rare and most scopes will not support it. I think 0.5mm exit pupil is more reasonable.  

Edited November 8, 2021 by Nik271
typos

[neil phillips]

Cant comment on the classical cassegrain as i havent tried one yet. But soon will. But i have tried a lot of scopes in my time 16" dob. 8/3/4 dob  8" SCT meade 7" F15 Mak  a poor C11 

102 starwave refractor. 127 l bresser refractor Briefly 10" meade SCT To name a few. The best planetary scope by far. one i still use today and get the best results from so far. ( And more inconsistently a 12" skywatcher newtonian)

Is a Orion 245mm F6.3 Newtonian. Newtonians with superb mirrors will in my opinion cost per inch beat most scopes. No ED 80 could compete even remotely with a long focus Newtonian of fair size. With quality mirror. The views can be razor sharp with resolution to match. 80mm EDs is just not big enough unfortunately. Nice for there size. But only for there size. 

In your shoes. i would likely get either a 7" Mak possibly 8" classical cassegrain ( will be trying one of those very soon myself  ) A 6" orion F8 1/10th pv newtonian. A 8" F8 1/10th pv orion Newtonian. On a budget a skywatcher 6" F8 Newtonian. Or stella lyra F8 or bresser F8 6inch Newtonians. As a aside been very impressed over the years from what ive seen with Celestron C9.25 Either matching or nearly matching my somewhat larger Orion. 

There are reasons long focus Newtonians tend to do better generally. Producing somewhat sharper more contrasty views that snap into focus. With a good mirror the views can truely be razor sharp My 10" 1/10th pv F6.3 ( nearly a planetary scope, certainly better than the F4.7 version) well collimated is a force to be reckoned with. I have a Antares 1/30th secondary on this. And it totally rocks

Some planets this year that you have been viewing. So you can get a idea of what i have had to deal with elevation wise. And how my Newtonian has cut through the low elevation. If my experiance tells me anything then these are my thoughts. The only thing i truely would love to try and never have is a C14 but then thats a monster with its own problems, not least of which is the 7 grand price tag. These Orions can be picked up secondhand for around £500

 

Saturn this year

Edited November 9, 2021 by neil phillips

[neil phillips]

6 hours ago, nfotis said:

Well, a f/15 scope like my Skymax 180 doesn't need a 5mm eyepiece (the lowest I have gone is a 7-21mm zoom EP, and it was quite pleasant, because even the Moon wasn't excessively bright).

Your mileage may vary, of course, but the longer focal distance in scopes means you don't have to push much in the eyepiece front.

Since I am more of a photographer than observer, though, I claim no expertise on this matter.

For planetary, my ideal suggestions are:

C9.25, Classic Cassegrain 8", Skymax 180

Or a step down:

C8, CC6, Skymax 150

N.F.

 

Btw CC6 is not 6" CC8 is 7.3 in size, and also larger central obstruction than claimed by GSO 

[johninderby]

CC8 is actually about 7.5” as later  measurements have proven. Also don’t go by the photo on FLOs site as they have used the RC photo and not the CC with it’s much smaller central obstruction..

Ignore the CN “test” as it is a load of total nonsense and the conclusions are just not what I and many others have actually found to be true. 

Edited November 9, 2021 by johninderby

[neil phillips]

22 minutes ago, johninderby said:

CC8 is actually about 7.5” as later  measurements have proven. Also don’t go by the photo on FLOs site as they have used the RC photo and not the CC with it’s much smaller central obstruction..

Ignore the CN “test” as it is a load of total nonsense and the conclusions are just not what I and many others have actually found to be true. 

Interesting John. I stand corrected. What measurements were done in the UK that prove this ?  Ok from info in the UK  how big is the CC6. And what are the central obstructions of both scopes by percentage. Apparently some feel the flashlight test is accurate, i am guessing this may not be so then. Quite pleased to be honest John. My new scope next week has just grown a little. Exactly what i want to hear

Edited November 9, 2021 by neil phillips

[johninderby]

Later posts on CN have corrected the aperture. As more user experiences have been posted online they seem to mirror my experience.. That original review / test on CN continues to baffle me as some of rhe conclusions are the opposite of what I’ve found. Was it bias or perhaps a CC that had been knocked out of collimation during shipping.🤔

https://astronomytechnologytoday.com/2020/01/03/gso-eight-cassegrain/

Specs from Orion website.

CC6”

Secondary mirror obstruction: 58mm

Secondary mirror obstruction by diameter: 38%

Secondary mirror obstruction by area: 15%

CC8”

Secondary mirror obstruction:  68mm

Secondary mirror obstruction by diameter:  34%

Secondary mirror obstruction by area:  12%

Edited November 9, 2021 by johninderby

[neil phillips]

Not sure about that John. On this review. From CN they claim GSO themselves commented and said this

GSO 8-inch TRUE CASSEGRAIN - Telescopes - Articles - Articles - Cloudy Nights

With the advertised high-reflectivity mirrors, the GSO should have roughly the same magnitude penetration and image brightness as the C-8.  I contacted the dealer, Agena Astro, to explain the situation, and they immediately queried GSO  for the technical details.  The response was detailed and quite interesting.

The design of the telescope is a compromise that gives priority to high-power lunar and planetary performance.  With the relatively short-focus parabolic primary mirror, a large secondary that would degrade image contrast would not be desirable.  The solution: Use a smaller secondary [still a roughly 33% obstruction] and reduce the effective aperture of the scope to 7.34

inches(186.5mm).  According to the factory specs, the 100 percent illumination circle is 15mm.

Edited November 9, 2021 by neil phillips