178 replies to this topic

[scooke]

The point of calling slow newts planet killers is that they give killer views of planets. A high F ratio is inherently better for high power views. A slow scope with excellent optics will give better views of planets than a fast scope with equivalent optics. This is a fact that owners of fast scopes need to accept.

I'm in the camp of thinking that a planet killer is any scope, regardless of f-ratio, type, or configuration, that has the capability of delivering a killer view of the planets.  As others have said, realizing that view has more involved than just the telescope itself; managing thermal issues, seeing, collimation, viewer experience, etc. all factor into what is seen but reducing the variables to just the telescope itself, it could be anything of sufficient aperture.  I do think that while smaller scopes can give excellent images of the planets for their size, if you don't have at least 6" of aperture and preferably 10" of aperture, you are unable to realize the resolution available on the best of the best seeing nights.  Having said all that, my best views of Jupiter and Saturn ever were with a 18"F3.75 Starmaster.  I think the additional aperture also helps a lot when using high magnification to see the smallest lowest contrast details.  The additional light just helps make the difference even if the larger aperture is seeing limited.

[BDS316]

I had a 6” F8 Discovery dob that had an excellent mirror. But my SW 100 ED was close enough that I sold the dob for the convenience of the refractor. But going from a 6” F8 to an 8” F8 or 9 dob puts you into an entirely different league. I would put my 8” F9 against any 5” APO refractor. That said, I still want a 5” APO refractor.

Since we already know that your 8 inch f/9 is just as good or better than a 5 inch APO on planetary and lunar, you might be better off with a 4 inch APO rather than a 5 inch.

 

Wider max actual field of view

lighter and more portable

more well suited to terrestrial viewing

Edited by BDS316, 24 January 2020 - 11:07 AM.

[Galicapernistein]

Since we already know that your 8 inch f/9 is just as good or better than a 5 inch APO on planetary and lunar, you might be better off with a 4 inch APO rather than a 5 inch.

 

Wider max actual field of view

lighter and more portable

more well suited to terrestrial viewing

I already do, a SW 100 ED. My portable F9. But a 5” triplet in a shorter F ratio has its own appeals.

Edited by Galicapernistein, 24 January 2020 - 11:25 AM.

[Galicapernistein]

I'm in the camp of thinking that a planet killer is any scope, regardless of f-ratio, type, or configuration, that has the capability of delivering a killer view of the planets.  As others have said, realizing that view has more involved than just the telescope itself; managing thermal issues, seeing, collimation, viewer experience, etc. all factor into what is seen but reducing the variables to just the telescope itself, it could be anything of sufficient aperture.  I do think that while smaller scopes can give excellent images of the planets for their size, if you don't have at least 6" of aperture and preferably 10" of aperture, you are unable to realize the resolution available on the best of the best seeing nights.  Having said all that, my best views of Jupiter and Saturn ever were with a 18"F3.75 Starmaster.  I think the additional aperture also helps a lot when using high magnification to see the smallest lowest contrast details.  The additional light just helps make the difference even if the larger aperture is seeing limited.

When I say a high F ratio is better for high power views, I should specify (and I will from now on) that I’m talking about smaller newts. Bigger mirrors can obviously compensate for many issues by sheer resolving power. An 18” F8 might provide better views, but the atmosphere will only allow so much power, and an 18” F8 would require a ladder I wouldn’t want to climb. The bigger exit pupils they provide are a definite improvement over smaller scopes. There’s no arguing that a big, fast newt packs a lot of performance into a relatively small package, and for serious galaxy hunting they can’t be beat. 

Edited by Galicapernistein, 24 January 2020 - 12:39 PM.

[turtle86]

I'm in the camp of thinking that a planet killer is any scope, regardless of f-ratio, type, or configuration, that has the capability of delivering a killer view of the planets.  As others have said, realizing that view has more involved than just the telescope itself; managing thermal issues, seeing, collimation, viewer experience, etc. all factor into what is seen but reducing the variables to just the telescope itself, it could be anything of sufficient aperture.  I do think that while smaller scopes can give excellent images of the planets for their size, if you don't have at least 6" of aperture and preferably 10" of aperture, you are unable to realize the resolution available on the best of the best seeing nights.  Having said all that, my best views of Jupiter and Saturn ever were with a 18"F3.75 Starmaster.  I think the additional aperture also helps a lot when using high magnification to see the smallest lowest contrast details.  The additional light just helps make the difference even if the larger aperture is seeing limited.

I agree. I have an AP 130 GT, and it's as good as a 5" apo can get. It certainly gives great planetary views, but it simply can't compete with my 18" Starmaster in terms of resolution, at least where I observe.

[Magnetic Field]

When I say a high F ratio is better for high power views, I should specify (and I will from now on) that I’m talking about smaller newts. Bigger mirrors can obviously compensate for many issues by sheer resolving power. An 18” F8 might provide better views, but the atmosphere will only allow so much power, and an 18” F8 would require a ladder I wouldn’t want to climb. There’s no arguing that a big, fast newt packs a lot of performance into a relatively small package, and for serious galaxy hunting they can’t be beat. 

I don't think you know what you are talking about.

[Galicapernistein]

I don't think you know what you are talking about.

Possibly. I have no experience with big, fast newts. But if they’re not good with galaxies, I would be surprised.

[CHASLX200]

If i had to have one last planet scope, it would be a 20" F/6 Dob.

[a__l]

Well, I think it's work, so we'll have to agree to disagree on this.

For me, this is a clear hobby (building, testing optics, etc.)
We all strive to expand our horizons of knowledge, not stopping there.
Homo sapiens 
(Lat)

[Asbytec]

There is always something better out there. The Hubble certainly kills planets, as does the Keck. Kill Planets with what you have using whatever aperture, pray for good seeing, attend to cooling and collimation, and bring your experience to the task. Minimize the variables and improve our skill. To me, that's where it's at. After all, killing planets is really about seeing them as being killed. Etched in the sky and in our minds. I'm sure we've all done it. 

Edited by Asbytec, 24 January 2020 - 08:10 PM.

[a__l]

This is not about equipment in which billions have been invested.
Observations with eyes are a subjective substance. Or maybe if there was another telescope nearby (with the same aperture) he would have "killed" better (!)
If you come up with such ideas, it is advisable to confirm this with something more objective.

[Asbytec]

Or maybe if there was another telescope nearby (with the same aperture) he would have "killed" better (!)

 

If you come up with such ideas, it is advisable to confirm this with something more objective.

Yes, maybe he is. Or maybe he's not. If any of the variables are not optimum, can one say they are killing planets? A 200mm APO under the jet stream, a C14 in sub zero temps and at the dew point, a poor quality obstructed scope under great tropical seeing, a miscollimated 8" Newt, a newbie observing Jupiter though a 6" APO at an outreach, a C8 at a star party, or even a skilled observer viewing Jupiter or Mars at 90x, for instance. 

 

Objective is nice. I believe the small white ovals against a soft grey belt make a good standard. Last time I checked, there were about 9 of the more prominent ones. I have seen 5 of them over time in a 6" scope, sometimes more than 1 at a time. A 12" can probably do all of them, so much for that standard unless the actual count is measured 0 to 9. I am sure Jupiter being etched requires no explanation as we've all seen it. I've seen it. Being etched is probably not a subjective thing, we know it when it happens. Okay, so maybe if Jove is etched, we're killing it?

 

Yes, throwing the Hubble into the discussion was an extreme example of something being better than the rest of us. In reality, and all else equal (or not), a 20" f/3 is better than anything I have. But, does the fact someone has something better preclude me from killing planets, too? Don't we all get a trophy? (LOL being facetious). 

 

Is killing planets really all about large hand crafted unobstructed apertures costing many thousands of dollars? If so, then we'd all better toss in the towel and never speak of it again, because the Hubble is professionally made costing billions and sets the bar too high for any of us. It's like none of us can kill planets, except we say we do. And I believe it. Alexander (Sasa) kills Jupiter in a small refractor, my gosh he sketches a lot of detail rivaling larger apertures. I believe we've all killed planets because everything came together and we were there to see it.

Edited by Asbytec, 24 January 2020 - 11:42 PM.

[dhferguson]

Cheers,

The OP did not state how much effort he/she was willing to exert. There are several factors that comprise a "planet killer." These are: optics configuration and quality, comfort and ease of use, and storage & setup. Let us look at each but first, how much money are you willing to spend and would you really use a large & heavy instrument?

Newtonians of 8-12.5" aperture are the most cost effective. I agree with others that perhaps the easiest/cheapest way to a planet killer is to buy a mass-manufactured Dob and have the primary refigured. First, though, you may want to replace the secondary with a high quality mirror from the likes of, say, Antares and see if you are happy. The MTF of any obstructed scope degrades significantly when the diameter of the secondary minor axis exceeds 20% the primary diameter. Thus, you will want such a small secondary, which if you also want a 1 deg or so field with only minor vignetting for DSOs, means f/4.5 or greater. So a 12.5" with f/4.5 or greater can yield fabulous planetary detail. However, the mirror must be supported properly (check with the freeware program PLOP), the mirror must be allowed to thermally equilibrate (I set mine up at dusk ... a fan is a good idea too), and collimation needs to be spot on. Incidentally, mass manufacture SCTs have central obscurations of roughly 35% so planetary contrast aperture-for-aperture is less than with a Newtonian.

Dobs will work but, personally, I hate "nudge nudge nudge" when observing at high power. Also, I've yet to observe with a Servo-Cat (or like) or Poncet platform that doesn't have some level of vibration or other issues. One solution--and this is lots of work--is to acquire a "classic" Astrola, Optical Craftsmen, Parks etc. mount, clean up or refurbish (as needed), then replace the crummy OEM polar drive with a Byers (used only, eBay), Opti-Craft, etc. drive. You need to acquire rotating rings for the tube, which with an observing chair magically converts a GEM Newt from a torture device to the most comfortable of all telescopes to use. I did all of this and prefer my optically superlative 10" to my optically very good 14.5" Dob for planets. The scope is a beast but rolls easily on casters from the garage. Or, for a GEM mount, you can spend kilobucks on a Paramount or A-P mount, your choice.

Another good option if a lighter and more transportable scope is desired is a 100-150mm ED or triplet refractor. Most evenings the seeing will dominate anyway. You can mount up to a 130mm refractor on an AVX class mount but larger apertures will require a more substantial mount. Me personally, I have a Stellarvue Access 125mm ED/AVX which I take out about half the time (mediocre seeing, moon near full) and use nearly exclusively for planets, the moon, and double stars.

Happy observing always,

Don

[a__l]

No need for a many of words. Show StarTest during the "kill"
This will tell a lot about your statements. Thereafter you can reason what you saw on Jupiter (or Mars).
For example, I was curious to see 20 f/3, which is the best. Why can't I see this, that’s the question?
But I see a many of Chinese examples, which are much cheaper for the price and people publish this without any problems.

[Asbytec]

No need for a many of words. Show StarTest during the "kill"
This will tell a lot about your statements. Thereafter you can reason what you saw on Jupiter (or Mars).
For example, I was curious to see 20 f/3, which is the best. Why can't I see this, that’s the question?
But I see a many of Chinese examples, which are much cheaper for the price and people publish this without any problems.

I am not sure I follow. But, if I told you my 30% obstructed Chinese scope star tests apparently near 1/6 PV of lower order spherical, is reasonably smooth to the level of seeing, no coma corrector, is well collimated and thermally stable, sources of astigmatism were dealt with using Lockwood's article on round stars, under Pickering 7/10 seeing, and observing Jupiter at 0.5mm exit pupil using a 60 degree well corrected apparent field of view while nudging the scope every 30 seconds or so, then you know everything you need to know? 

 

I might agree, the question may be "Why can't I see this?" The other question might be, "Can anyone else see it"? I mean, planet killing is about seeing more than the other guy, right? So, there is only one winner in this game, he who sees the most wins the coveted title of "Planet Killer". If "Why can't I see this?" means my obstruction dampens contrast transfer, then I assert so does lesser seeing conditions. Or anything else in the wobbly stack, including our own experience and acuity. How does one reconcile all of those variables into planet killing unless they are all tamed and we are observing side by side on that night. To my way of thinking, it's not a contest. It's the view. 

 

But, I do appreciate the interesting exchange of ideas, rather than a heated argument with bad feelings and locked threads.  

Edited by Asbytec, 25 January 2020 - 12:16 AM.

[a__l]

I am not sure I follow. But, if I told you my 30% obstructed Chinese scope star tests apparently near 1/6 PV of lower order spherical, is reasonably smooth to the level of seeing, no coma corrector, is well collimated and thermally stable, sources of astigmatism were dealt with using Lockwood's article on round stars, under Pickering 7/10 seeing, and observing Jupiter at 0.5mm exit pupil using a 60 degree well corrected apparent field of view while nudging the scope every 30 seconds or so, then you know everything you need to know? 

 

Any exploitation of a professional tool begins with the publication of a customer report on the test measurements. For example, a 6-meter telescope (I once published an interferogram on CN) was tested for six months with the stars. Based on these tests, it was decided to leave the old mirror, and put the new, which millions spent on, in a box.

I am not writing that it is necessary to test with expensive devices, but to make a star test and publish it is not a problem for anyone.
The more this happens, the better. For all.

[Asbytec]

...but to make a star test and publish it is not a problem for anyone. The more this happens, the better. For all.

Okay. Please don't misunderstand, I believe a quality optic matters.I know the obstruction has an effect, that aperture rules, and seeing favors smaller apertures. I also believe a diffraction limited scope can do a fine job. I just believe, based on my experience, that all this and more matter for high resolution imaging. It's how well we bring our particular mix of variables to bear that matters most. 

 

For example, I have a mass produced obstructed scope, not the ideal planet killer, but I also have reasonably good seeing (or better), thermal stability, and very good collimation which is essential for planet killing. It could be better with an unobstructed quality optic and a larger aperture, but on balance of all the variables equals a fine image. On player has a full house and someone else has a flush. Both are potential winning hands composed of different cards. 

 

Other's mileage will vary, some better some worse some times. I'm not complaining about my best views, because it's not always that good. But sometimes it is that good, sometimes we are dealt a straight flush or better. 

[bridgman]

My impression was that the "planet killer" term might have been overtaken by events, in the sense that it pre-dated availability of inexpensive Chinese apo's and (I'm less sure about this part) high quality fast Dob's.

 

When I was first getting into observing a "planet killer" was an *affordable* scope that was great for planetary observing, which at the time meant either a long FL achromat or a long FL Newtonian/Dob. Typically it would be a scope chosen primarily for observing within our solar system, although it could be used more generally.

 

These days we have more options and I'm less sure that the "planet killer" term makes sense anymore.

[Magnetic Field]

Okay. Please don't misunderstand, I believe a quality optic matters.I know the obstruction has an effect, that aperture rules, and seeing favors smaller apertures. I also believe a diffraction limited scope can do a fine job. I just believe, based on my experience, that all this and more matter for high resolution imaging. It's how well we bring our particular mix of variables to bear that matters most. 

 

For example, I have a mass produced obstructed scope, not the ideal planet killer, but I also have reasonably good seeing (or better), thermal stability, and very good collimation which is essential for planet killing. It could be better with an unobstructed quality optic and a larger aperture, but on balance of all the variables equals a fine image. On player has a full house and someone else has a flush. Both are potential winning hands composed of different cards. 

 

Other's mileage will vary, some better some worse some times. I'm not complaining about my best views, because it's not always that good. But sometimes it is that good, sometimes we are dealt a straight flush or better. 

Can someone please comment on post #96 in this thread.

 

Is my post #96 a red herring.

 

 

Thanks

[Magnetic Field]

My impression was that the "planet killer" term might have been overtaken by events, in the sense that it pre-dated availability of inexpensive Chinese apo's and (I'm less sure about this part) high quality fast Dob's.

 

When I was first getting into observing a "planet killer" was an *affordable* scope that was great for planetary observing, which at the time meant either a long FL achromat or a long FL Newtonian/Dob. Typically it would be a scope chosen primarily for observing within our solar system, although it could be used more generally.

 

These days we have more options and I'm less sure that the "planet killer" term makes sense anymore.

This probably part explains it.

 

People always forget that the world moves on (although there hasn't been a big fundamental breakthrough within the last 100 years  in the field of the only true science that we call physics) and things change and get technically better.

 

Combating lore an myth is a futile pastime (as the refractor forum here is a prime example).

Edited by Magnetic Field, 25 January 2020 - 01:01 PM.

[Galicapernistein]

Why?

 

It cannot be the reason that a faster scope is more prone to collimation issues.

 

I fail to understand why people think a slow scope is better for planets.

 

Edit:

 

A 20" f/5 vs 20" f/10 with the same optical error and flaws interferometrically measured at focal point. So, why should I use the 20" f/10 for observing the planets? For the same magnification is it the choice of eyepiece which would favour the f/10?

I think your last point may be partly correct when it comes to smaller, slow Newtonians. With a 3.5mm eyepiece, I can comfortably use 540x in my 8” F9. In my 10” F 5.6, it would only get me 400x. But with a 3.5mm eyepiece,  a 20” F5 would get over 700x. Would there be any advantage to having a 20” F10 and getting over 1400x with a 3.5mm eyepiece? Probably not.

[Darren Drake]

The only real advantage is the secondary obstruction could be somewhat smaller.  The difference however would be insignificant and not worth the extra length of the tube and need for an insanely large ladder.  The f5 would be dramatically better given those factors.

[Jon Isaacs]

I think your last point may be partly correct when it comes to smaller, slow Newtonians. With a 3.5mm eyepiece, I can comfortably use 540x in my 8” F9. In my 10” F 5.6, it would only get me 400x. But with a 3.5mm eyepiece,  a 20” F5 would get over 700x. Would there be any advantage to having a 20” F10 and getting over 1400x with a 3.5mm eyepiece? Probably not.

 

A Barlow eliminates the need for short focal length eyepieces.. 

 

Jon

[Galicapernistein]

A Barlow eliminates the need for short focal length eyepieces.. 

 

Jon

Barlows may be useful with fast refractors, but I’ve never been satisfied with the views they provide in Newtonians.

[Defenderslideguitar]

Absytec said.....planet killing is about seeing more than the other guy, right?.....     

  yes it is about seeing more ...detail...........it is about seeing more than I ever have before...

   Planet killing is a cool title    i like it   but as shown throughout the thread    so many variables are in play

    And I can tell you that for some of us it is just that magical night of excellent seeing when things all fell into place for whatever reason...................Like when I saw Jupiter and Saturn with my 1990 Tak FC-100  and got the best views  I had ever seen in my limited experience

 

  Of course   then when I was at Stellafane and looked through some of the big dobs for the first time  it was  a real   

eye opener..

A closed tube 10 inch Dob  f-8  would be a great step up for me     seeing more than I have before      I think at my level of experience      a good started Dob size

Edited by Defenderslideguitar, 26 January 2020 - 09:01 AM.