Telescope for planet veiwing?

[Andy38416]

Evening all,

I'm currently looking at purchasing a new scope with the main focus being on viewing planets. I currently own a heritage 130p, but was looking to upgrade to something better with a stable mount, not a dob. Budget being about £300-£400. Also space is a little bit of a problem at the moment too so didn't want anything huge.

i was looking at the Skywatcher Evostar 120 or the Celestron Omni XLT 120, are these good scopes or am i missing something?

just after a bit of help and advice really, don't want to spend money on something needlessly and who better to ask.

thanks

Andy

[nightfisher]

here goes:

for planet work a Mak is near as dam king, a skymax 127 will really do the job, and if you can get it on the AZ4 mount it will be real stable

[rowan46]

Here's another option for you

http://www.firstlightoptics.com/slt-series/celestron-nexstar-127-slt.html

no false colour like the evostars and the mount is good enough for webcamming.

[Andy38416]

I must admit I didn't think of Mak's, the goto is appealing but do I not loose anything in the quality of the scope etc, normally people try and advise to stay clear of goto's for some reason.

If the Mak's will be better it would be worth me looking, plus a little smaller than a refractor in size.

[Ags]

There's nothing wrong with maks. There's nothing wrong with goto.

[tich]

I've looked at Jupiter with a 127 Mak & I can say the detail it was showing was awesome. I agree that there's nothing wrong with GOTO's when you get used to setting them up & if you prefer to go manual star hopping then there's nothing stopping you, just when you find your target the mount will keep tracking it.

[rowan46]

It's really deep space that some frown on goto if you want apparture on a budget it makes sense to spend most of the money on the optics. but there is nothing inherently wrong with goto and the maksutov design is very very good on planets. yes refractors are better but you are talking either apo's or large very long focal length achromats in my opinion a 5" mak is better than a 5" short achromat An f14 or so achromat is great on planets and the moon an f8 or so will show a fair bit of ca especially with larger apparture a 5" mak will not show much if any ca

[Andy38416]

Thanks, will have a look at the 127 range of Mak's, the celestron model seems preferable to me, though I know they are basically the same thing.

Thanks for everybody's quick and above all useful help.

[JD75]

If I may sneak a question in, how do the Maks perform on DSOs? I appreciate that they're not going to compete with, say, an 8" reflector, but I'm primarily interested in looking at the planets but would like to be able to cruise about a bit more and see what's out there. I'm hoping to get a look through one soon, but any thoughts you folks have would be much appreciated.

[knobby]

If orion neb is an 8 through my 10"dob... Its a 5 through my SW127 mak .

Not sure if that helps but its difficult to quantify

[dweller25]

Of All the scopes I have owned here is how I would rank them for planetary performance......

1. 10" Dob - a bit too heavy for my back.

2. 8" Dob - best all rounder by far - cheap too :-)

3. C8 - surprisingly good on the planets.

4. 5" Achro - but I did not like the chromatic abberation - and filters DO NOT remove it.

5. 180mm Mak - refused to cool down !!!

6. 127mm Mak

In my opinion a very cost effective setup with excellent planetary performance would be an 8" Dob with three wide field eyepieces.....

a. x170 for Mercury, Venus, Jupiter and the Moon.

b. x200 for Jupiter and Saturn,

c. x240 for Mars and Uranus.

So assuming you did the right thing and bought a 8" F/6 Dob (which takes up much less space than an Evostar 120 ) and a 7, 6 and 5mm eyepiece you will be set up for years of planetary viewing

Just my two penneth.

HTH

[Andy38416]

Isn't the 200p a bit of a beast? I don't really fancy another dob, I know my 130p is quite a small dob but would like something with slow motion or tracking ideally, just as making small movements with my dob can be frustrating sometimes.

Will have to have a good think before splashing the cash

[Mr Fiery Jack]

Get a 4 inch achro on an AZ4, for that money and you won't go far wrong.

[Mr Fiery Jack]

You can get a 4 inch Celestron refractor on their version of the EQ 5 for that money and for not much extra to add a drive,

[rowan46]

Of All the scopes I have owned here is how I would rank them for planetary performance......

1. 10" Dob - a bit too heavy for my back.

2. 8" Dob - best all rounder by far - cheap too :-)

3. C8 - surprisingly good on the planets.

4. 5" Achro - but I did not like the chromatic abberation - and filters DO NOT remove it.

5. 180mm Mak - refused to cool down !!!

6. 127mm Mak

In my opinion a very cost effective setup with excellent planetary performance would be an 8" Dob with three wide field eyepieces.....

a. x170 for Mercury, Venus, Jupiter and the Moon.

b. x200 for Jupiter and Saturn,

c. x240 for Mars and Uranus.

So assuming you did the right thing and bought a 8" F/6 Dob (which takes up much less space than an Evostar 120 ) and a 7, 6 and 5mm eyepiece you will be set up for years of planetary viewing

Just my two penneth.

HTH

That sounds about right in performance but the op stated he didn't want a dob and comparing a 5" to an 8" isn't a very fair test. The only fair comparison was between either the 8" dob and the sct 8" or the achromat and the 5" mak so the choice is between false colour and no false colour that's a judgement call some people can live with it. I hate it so for me I put the 5" mak above the 120 evostar.

[Andy38416]

I'm now completely torn between the Celestron Omni XLT 120 or the Nexstar 127 SLT. Both exactly the same price at £359.

I got an email from a provider saying the views through both of the above would be no different (contrast, mag etc) than my 130p Hertiage, surely this can't be true? I'm not expecting a massive jump but would have thought it would be noticeable.

[dweller25]

I will check it out for you ........

[dweller25]

Here are the numbers for the three scopes you mentioned.

Assuming full cool down and perfect collimation of each scope .......

The key factors in planetary performance are resolution and contrast transfer. An easy way to calculate CT is to subtract the size of the secondary obstruction from the size of the primary mirror - basic but it will be close, so ......

Scope.................Resolution (arc secs).............Contrast equivalent (to a perfect APO)

Omni 120.........................1.13.......................................120mm - lots of chromatic aberration

Nextstar 127.....................0.91.......................................99mm - no CA

Heritage 130.....................0.89......................................112mm - no CA

So the best overall scope in terms of resolution and contract is your Heritage - your supplier is giving you good advice.

To see more than the heritage shoes you would need another 25mm of clear aperture - so around the 135mm area - a Celestron C8

HTH

[rowan46]

theoretically he is right and as Dweller25 on a previous post in this thread shows a larger apparture gives better views on planets. You canna change the laws of physics. But the refractor gives better contrast than a small dob as it has no central obstruction and an f12 mak gives better magnification both of which are desirable traits when planetary viewing. they also both come on mounts which allow you to track planets at high magnification easier than pushing a small dob round. Either a 5" mak or achro will give better views on planets than a 5" f5 newtonian especially as the newt is on a dob base and the other 2 are mounted. if you can find an older f15 achro refractor of about 100mm aparture for that price it will i feel give you the best of both worlds nearly ca free and good magnification those old achros are real planet killers

[Capricorn]

Reflectors tend to be a little less contrasty, however the 120 refractors will have a little CA and some SA from the edges so it is a case of take your pick.

If the 130P is f/5 then you will get magnification a bit easier from the 120+127.

The 127 will have a narrower field of view, makes it a little more difficult to get things actually in view, although a 32mm plossl helps.

So whatever you go for you compromise somewhere, which compromise is for you to decide.

Personally I would have dropped down to an Evostar 102 and bought an eyepiece like one of the BST's, being the same basic lens as the 120, it is smaller diameter there is less CA and SA and less cost. It gathers less light but planets are generally bright enough to not worry about.

[Ags]

The mak has a big advantage over a dob-mounted f5 newt... Although the newt is theoretically sharper in the dead center of the field of view, this advantage is lost as soon as the planet drifts off-center, as typically happens with a dob. The reason isthat all newts suffer from coma, a smearing of the image that increases quickly from the center of the FOV. Maks are equally sharp across the whole FOV, and the one you are looking at is on a tracking mount so it stays in the middle of the view anyway.

From what I've read I would think one of the best budget planetary scopes is the 150PL, it is F8 so its central obstruction is negligible and the effects of coma are much reduced. It comes on a EQ3 mount, which is more bulky than the mak 127 mount and also might be a little underpowered for a long scope like the 150PL.

[rowan46]

Here are the numbers for the three scopes you mentioned.

Assuming full cool down and perfect collimation of each scope .......

The key factors in planetary performance are resolution and contrast transfer. An easy way to calculate CT is to subtract the size of the secondary obstruction from the size of the primary mirror - basic but it will be close, so ......

Scope.................Resolution (arc secs).............Contrast equivalent (to a perfect APO)

Omni 120.........................1.13.......................................120mm - lots of chromatic aberration

Nextstar 127.....................0.91.......................................99mm - no CA

Heritage 130.....................0.89......................................112mm - no CA

So the best overall scope in terms of resolution and contract is your Heritage - your supplier is giving you good advice.

To see more than the heritage shoes you would need another 25mm of clear aperture - so around the 135mm area - a Celestron C8

HTH

Here's me eating humble pie I have looked through the mak the evostar and the heritage on planets and to my eyes I thought the heritage the worst of them it's probably a function of the mount. another scope that I haven't tried but gets excellent reviews is the tal 100 by many reports it is much better colour corrected than the evostar

http://www.firstlightoptics.com/tal/tal-100rs-refractor-optical-tube-assembly.html

[Ags]

Dweller25, I must say I have seen different formulas for resolution giving quite different results. And i have read elsewhere that the 'subtract central obstruction' formula is just plain wrong. According to Damian Peach, the contrast achieved by an obstructed scope can be much worse, slightly better, or roughly equivalent to an unobstructed scope, depending on the kind of contrast being observed.

We also have to factor in practical considerations - the newt is a parabolic mirror ( hard to manufacture accurately) and the mak is made up of spherical surfaces (easy to manufacture to a high standard).

If I had to choose between a 130 dob (which I doubt can be collimated accurately) and 127 mak on a driven mount with goto, I would definitely pick the mak!

[Andy38416]

Thanks for everybody's calculations and advice on this, it has helped.

I think for me the choice is now between the 127 Nexstar or buying nothing and sticking with my 130p dob for now. With my budget being between £300-£400, anything much bigger (apart from another dob) starts to really increase in price.

[Ags]

Perhaps wait a while for now, and see if you can get a chance to look through some of these scopes yourself.

You could look at getting a BST Explorer eyepiece for viewing planets, these have a wider field of view than plossls, so you will not need to push the scope so frequently, and the BSTs are nice EPs. I think they were recently rebranded Starguiders.