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jmoore
Carpal Tunnel
Reged: 10/01/03
Posts: 1959
Loc: Beaufort, NC
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Let's assume the goal is to get the best planetary looks possible. What would give better views...a top-quality 4-6" APO, or a big (say, 12-18") top-quality reflector?
Let's divide this question in two sections. First, consider APOs only. It seems that there are many of you out there who absolutely LOVE your 4" APOs...beautiful, crisp, high-contrast images from edge to edge in the field of view. BUT, since planets often look best at higher powers (e.g., >200X), isn't a 4" scope often limiting? Also, since resolution is a function of aperture, aren't there features you simply can't see with a 4" APO? I guess I'm having a hard time believing that the optical quality of these 4" scopes can overcome their aperture "deficit". Shouldn't at least a 5" or 6" APO be considered necessary for getting the best high-mag planetary views money can buy?
Now, comparing the choice APO to the big reflector. From what I read, it almost seems like dogma that APOs are best for planets, while Dobs are best for deep-sky...period. But it seems to me that, in theory, a top-notch 15" reflector would be the better scope to have for both deep-sky AND PLANETARY viewing (ignoring portability or astrophotography needs). The big aperture would resolve finer planetary details, and it would presumably give the same contrast as at least a 5" APO. Am I leaving out some reason that the APO would still be more desireable for planetary viewing?
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Hardin 12"
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Ron B[ee]
Tyro
Reged: 04/27/03
Posts: 4720
Loc: CA
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Well, in my opinion, what's best for you or me may not be best for others.
My 4-inch APO is alas only 4-inch. In my opinion, the 4-inch aperture is a barest minimum for a good view of the planet (sometimes too much barest to bear  . My 8-inch Discovery PDHQ f/6 Dob with very good mirror shows more details on Mars, showed the pit crater on the Lunar dome much easier plus showing many more teeny rilles, more details on Saturn (Cassini as easy gap), more with the glimpse I had of Jupiter on morning recently. Simply put, there are some features that I can see with the 8-inch that I just can't see with my 4-inch. In spite of this, I love  my 4-inch APO nonetheless. It's very quick to be deployed and cooled down (especially with my busy impromptu viewing lifestyle); whereas, my 8-inch needs cooldown time period (I plan to get a fan for it)!
There are nights (seems to be many evenings on Mars recently) where high magnification was impossible in either of my scopes, both of which seems to reveal the same amount of details. The view through my 4-inch APO on Mars looked "calmer" (i.e. the rim doesn't vibrate so much). However, when I masked down my 8-inch to 4-inch, I got a similar "calmer" look as well but with a loss of resolution! Upon closer scrutiny, I saw that because the 8-inch gathers more light than the 4-inch and has better resolution, many of dimmer vibrating rims became really dim and very hard to see with my 4-inch and my masked 8-inch; so it's because the 8-inch simply shows a brighter view of every features and thus is more of a perception. Perhaps, this is why some people mistakenly think the 4-inch shows the planets better, I don't know. Furthermore, in my humble opinion, if you plan to use a telescope at 125x-150x on the planets, you're wasting aperture. At this low power (low power for the Dob , I cannot discern the difference between my two scopes (except the brighter view). But when that 5mm Radian went it and I get to 250x, 300x, and beyond, if the seeing cooperates, I get more than my money's worth from the Dob.
Lastly, take a look at this review of the 10" Teleport. I think the author made very good points about planets and aperture.
http://www.cloudynights.com/reviews2/teleport.htm
In my opinion, a high quality Newtonian with small secondary (my is only 19% obstructed is also a planetary scope. Don't believe what I say. Just look at what the highly skilled and famous observers use for observing the planets.
As an asides, my 4-inch APO is on a driven mount and its much better to view the planets this way; you free yourself completely to focus on the planets, look for minute details and sketch. I've nearly had it with nudging the Dob and I intend to get an EQ platform for it.
In summary, people who pick or wanna pick a 4-inch APO should pick it for the right (personal) reasons and not be misinformed or succumb to a 4-inch deep myth .
Ron the 4-inch Tall Evangelist B[ee]
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5-inch Tele Vue NP127 APO 
4-inch Tele Vue TV-102 APO 
Edited by Ron B[ee] (11/12/03 04:35 PM)
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eric moerman
super member
Reged: 11/08/03
Posts: 279
Loc: belgium
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Hello to everybody,I would like to tell someting that happend last summer here(in belgium) on a local star party.This star party was held near a public observatory that houses a 20cm(8")F10 apo-refractor.I was there to with my personal telescope that i have build myself(it stil not finishd  )My telescope is a 12,5" F7newt.,mirror and sec.are from mr.R.F.Royce.In the afternoon we where looking at the sun with the 12,5 and the 8".After a while some people started running back and forward between my telescoop and the apo.Also one of the owners came over to have a look and left again without saying anything.Some people started telling me that they could see more detail in my telescoop than in the apo,someting i finded difficult to believe until my good friend camo over to me,al excited,the same.Unfortenetly i dint have the chance to go and have a look for myself because it started to get cloudy by that time  Im very sure that a newtonian that is build proparly, with the same care and attention to detail as a apo will be almost always as good as a apo (or bether).The problem is that most newtonians are build on a budget.You cant compare a 10000$apo whit 1000$ newt.thats not fare.Invest in a very good mirror,good focuser,and by or build a good tubus that is proparly baffeld and blackened and you wil have a apokiller newtonian.Thats the way i did it and im very pleased about the result.Look at the way the people from Parralax instr.and Lightspeed telescopes build there newt.thats the way to do it if you want the highest performance.Yes they are expensive but compare them to the same size apo,they are real bargains!Ofcourse newt have some other smal problems like cooling isseus but that are problems that can be dealed with.Portabilety is another problem but i suppose that a 8"F10 refractor is not so portabel anymore to.So,YES,i do think that newt.are the way to go if you want to look at the planets.I think you need at least 6" aparture to have a dessent look,and that's just where (affordebel)apo's stop.One day i will build a 6"F15 newt 
Ps:sorry for my bad spelling  Newtons rule Apo's 
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NuroSlam
sage
Reged: 10/02/03
Posts: 241
Loc: Carrollton, TX
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An off axis newt would be even better, nothing better then 0% obstruction. Like the DGM 9 inch Off-Axis Newt
http://users.erols.com/dgmoptics/cad9.htm
Slam
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Ralph
Telestar 60mm, 395 EQ Mount, WeeCam
You fear me now don't you?
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Anonymous
Unregistered
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Hey Eric,
You must be using a French Belgium keyboard. I've had headaches with them in the past trying to type in English. I agree with the opinions given so far - although, in my experience though the most important factor is the observer. Sometimes no matter how much aperture or exotic glass/design you may have an untrained eye will have a difficult time teasing detail out of high/low contrast objects. But with that said, I think some of the best planetary views I've seen were with a Starmaster 14.5
BTW- Eric, I'm going to be in Brussels for three weeks in Dec., can you give me any information on local star parties or clubs. Thanks.
Sam
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eric moerman
super member
Reged: 11/08/03
Posts: 279
Loc: belgium
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Hello Sam,unfortenetly there is not someting like a star party scene here in belguim.We have only one that name worthy and that one is in august.also the clubs are not like they are in america,most clubs are buzy with teoretical stuf and dont doe so much observing at al.Me and some friends however do go out observing as much as possibel to some relative dark place(for belgium norms!)and you are welkom to join us ofcorse.But i have to tell you that december is one of the worst months in belgium(most cloudy nights).your ofcorse also welcom just to make a visit to my place so you can see how it is to a amateur astronomer in belgium 
Greatings,eric.
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Anonymous
Unregistered
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For my 2 cents.......
On a dollar basis, you can't beat a Newt. For the price of an APO, you can buy a high quality Newt with a premium mirror that has much, much more aperture. So even though it is an obstructed system, a dollar equivalent Newt will still show more contrast, be capable of more magnification, shorter exposure times, take filters better (more light to throw away), etc.
But as we know, "money isn't everything." The Newt will require constant tweaking for optimal collimation. It will be much larger and heavier than a dollar equivalent APO. This means more setup time, more dragging stuff around, heavier stuff to drag around, etc. With proper care, the optics of an APO should last a lifetime. A Newt will need re-coating from time to time. If you're using a GEM, the eyepiece of a Newt will turn up at weird angles sometimes, requiring you to rotate the tube while avoiding having it fall out of the rings. (Those Parks rotating rings look nice though a bit pricey.) The eyepiece of an APO is always pretty much in the same place.
So for pure viewing, on a dollar equal basis, a good Newt wins hands down. It's really no contest. But for many people, when all the other factors are considered, an APO is a better choice.
I sure wish I could afford one!!!!
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Anonymous
Unregistered
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Eric,
Thanks for the invitation. My girlfriend and I have an apartment in Ixelles. We'll be around from the 15th of Dec. to early Jan. Maybe we'll get lucky have have a few clear nights.. I can always hope and bring my binoculars and ED80 if it fits in our luggage.
Sam
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