Jump to content

Planets (specifically mars) - get a new refractor or stick with newt?


Recommended Posts

  • Replies 36
  • Created
  • Last Reply

Assuming the scopes are pretty much similar aperture I'd go with the refractor; I have one of these for purely visual use. The TAL100RS is a really excellent scope in its size bracket and an absolute bargain for the money, in my opinion. Some people get some very interesting results using it for photography too, for example see:

I've not had any experience with the Celestron though.

Link to comment
Share on other sites

Assuming the scopes are pretty much similar aperture I'd go with the refractor; I have one of these for purely visual use. The TAL100RS is a really excellent scope in its size bracket and an absolute bargain for the money, in my opinion. Some people get some very interesting results using it for photography too, for example see:

http://stargazerslou...ing-for-laughs/

I've not had any experience with the Celestron though.

Thanks, the celestron is just a random scope picked out of thin air to compare. Any better 100-114 newt would do.

Really like the look of the TAL. I figure the fact of no secondary obstruction means I get more light? ie the whole 4" with the TAL vs 4.5"newt-(minus)2"secondary=2.5" of light gathering...?

Link to comment
Share on other sites

TBH, for planets it's hard to see past a Mak-Cass or SCT due to their long focal length relative to their aperture. For example a 5" mak-casses made by Intes Micro and Skywatcher both have a focal legnth of about 1.5 metres which is a third longer than the TAL100.

BTW, central obstructions cover a small amount as a percentage, nothing to worry about.

Tony..

Link to comment
Share on other sites

Tony makes a good point, and a lot of SGLers really rate the skywatcher skymax 127 mak and its equivalents for plantetary. I suppose it depends what else you may want to do with this scope. The field of view in Maks/SCTs is generally smaller than newts and 'fracs of equivalent aperture. Central obstruction I believe would not be that much of an issue for planetary work, but on a 4" mak the obstruction can be quite large, relative to the aperture. This may be more of any issue if you wanted to do other work with the scope (DSOs for example). Not sure if I read whether there any issues getting DSLRs to focus in smaller Maks? Someone will correct me I'm sure if not.

Link to comment
Share on other sites

If i had to buy all over again i would still find it a hard choice between the 4" frac, and 5" mak, i guess the mak would win in a full head to head, but the tal might prove just that little more versatile, and it looks like a classic

Link to comment
Share on other sites

For serious planetary imaging all that matters is aperture. That generally means using an SCT or a Newt, most other types of scope are just too small to have the resolving power that you want. Though you may not want to go as far as what I think of as serious planetary imaging and there is a lot of fun to be had with a cheap webcam and a smaller scope.

For visual work, a large aperture is not such a big requirement and the mak is a fantastic scope.

Cheers,

Chris

Link to comment
Share on other sites

For imaging forget anything long, the long focal length, folded or not, means that any tracking errors are amplfiied, as are any alignment errors. Also means the scope has to be on an equitorial.

People image with short f/5 and f/6 scopes for a reason.

To see Mars you need: Good light gathering, good magnification and a lot of luck. Without all 3 forget any idea of a good view. Good contrast is also useful and a refractor delivers that.

The Tal with a 5mm eyepiece will give 200x, for Mars 250x would be better. Owing to the magnification you need to collect light, you are spreading the collected light out as lot. 100mm diameter may not be enough. Would be a lot easier if you decided to pick Saturn = Tal + 8mm eyepiece is good on Saturn.

Link to comment
Share on other sites

For serious planetary imaging all that matters is aperture. That generally means using an SCT or a Newt, most other types of scope are just too small to have the resolving power that you want. Though you may not want to go as far as what I think of as serious planetary imaging and there is a lot of fun to be had with a cheap webcam and a smaller scope.

Cheers,

Chris

c14 by any chance chris :grin: i have a mak180 and its a pretty capable scope.i have also seen plenty of good images with large dobs as well.

Link to comment
Share on other sites

For imaging forget anything long, the long focal length, folded or not, means that any tracking errors are amplfiied, as are any alignment errors. Also means the scope has to be on an equitorial.

People image with short f/5 and f/6 scopes for a reason.

To see Mars you need: Good light gathering, good magnification and a lot of luck. Without all 3 forget any idea of a good view. Good contrast is also useful and a refractor delivers that.

There seems to be some confusion here between deep sky imaging and planetary imaging. Doing planetary imaging at f/5 or f/6 would be a waste of time, f/20 to f/40 is nearer the mark depending on the target and folded optics are ideal.

Cheers,

Chris

Link to comment
Share on other sites

c14 by any chance chris :grin: i have a mak180 and its a pretty capable scope.i have also seen plenty of good images with large dobs as well.

He he, yes a C14 is getting pretty close to idea. :grin:

True, I was not thinking of some of the monster sized maks out there, the mak180 does indeed have enough aperture to produce great images. When I said newt I was referring to the large dobs, I would not want to try and mount a 10" newt any other way.

Cheers,

Chris

Link to comment
Share on other sites

As Capricorn notes - for visual on Saturn the Tal and an 8mm (BST in my case) is a good combination.

There was a gap in the cloudy conditions last night and I was looking at Saturn - crisp (though small) view. It was still quite light and the seeing wasn't great so no surface details (there may have been a band in the northern hemisphere or it may have been my imagination) or details on the rings but it was very easy to see the gap between the rings and the planet. Titan was clear but no other moons. My wife isn't into Astro but even she was impressed.

Mars has been a bane with this scope - it's not easy as it is and the only EP I have that is greater power than the 8mm is the supplied Tal 6.3mm - I haven't been able to resolve anything with that particular EP yet. It may be the seeing has never been good enough or it may be the EP (someone else may be able to make more comment on the stock 6.3mm EP).

Link to comment
Share on other sites

mars is a tough target even with a c14 unless its somewhere near opposition.it is a quite small target compared to jupiter and even saturn.

I agree completely, I found that Mars was quite disappointing visually through my C14 and it only really gave up its secrets when it was imaged.

Link to comment
Share on other sites

If you're after visual then you'll get better views more easily if you upgrade to an >8" Newtonian. It is around this aperture at which telescopes become seeing limited on almost all nights in our skies. The further you go below about 8" the more often you'll be reaching your telescope's resolution limit before you reach the atmosphere's. Going larger than 8" won't mean you'll be able to use higher powers on planets on a given night but it will mean you'll get a brighter image with more lively colours.

Link to comment
Share on other sites

Mars wont be back till 2014 and is quite dissapointing at ep compared to Jupiter due to app size

i agree with the aperture does matter for viewing and imaging planets so

i'd stick with 114 newt and upgrade to 8"+ scope either tracking dob or sct, or newt,

will give best improved results

James

Link to comment
Share on other sites

The mak sounds and looks great. Forget mars methinks then, I want to keep aperture down to a minimum but with maximum detail/resolution/contrast. (anti-aperture-fever)

I need a travel scope as such to show my friends the sky. Planets and super bright dso's are our targets. No need for galaxys.

Link to comment
Share on other sites

The mak sounds and looks great. Forget mars methinks then, I want to keep aperture down to a minimum but with maximum detail/resolution/contrast. (anti-aperture-fever)

I need a travel scope as such to show my friends the sky. Planets and super bright dso's are our targets. No need for galaxys.

I understand the need for portability but keep in mind that it's aperture that gives you resolution. The reason for this is that the larger the aperture the smaller the point spread function. It doesn't matter if it's a Newt, a Mak, or a refractor: they all work the same way in the end. The way to get the most detail is to have enough aperture to ensure your scope is comfortably within the seeing limit. Contrast is affected by a bunch of things such stray light, coating quality, and optical quality.

Link to comment
Share on other sites

I'd go for the Mak.

I get better images with my SCT than I ever did from my refractor. Unless you get a good refractor, you will end up with a blue ring around the subject. Although not impossible to remove, it makes it more difficult.

Link to comment
Share on other sites

I am no imager but my best ever visual observations of Mars came this year with my 16" f4 dob which was masked to 170mm (f11). I used a Baader Neodymium filter and on occasions magnifications of 300x (more usually 200x-250x). detailed views were constant and solid at these magnifications with the occasional ping into crisp sharpness. polar caps, Syrtis Major and even clouds over Olympus Mons were seen regularly. at full aperture the detail was still there but seeing meant that the image was a lot brighter (= less contrast) and less stable. my 6" f11 also provided great views but never really matched the masked 16".

I think that you'd be hard pushed to beat a 6" f8 newt unless you spend a lot more money.

Link to comment
Share on other sites

I'd go for the Mak.

I get better images with my SCT than I ever did from my refractor. Unless you get a good refractor, you will end up with a blue ring around the subject. Although not impossible to remove, it makes it more difficult.

This is where i get confused. I have a 90mm refractor (Celestron 90EQ). Its F/L is 1000mm (f11). I also have a 200mm SCT (Celestron 8SE). Its F/L is 2032mm (f10?).

Its been a few years since i observed planets such as Jupiter and Saturn with the refractor and in my minds eye i seem to remember the views with this scope being better then the views i am getting with the SCT, on these planets. Views with the SCT are very good, i just seem to remember being happier with the refrac.

Do you think my mind is playing tricks on me about this? I was new to scopes when i used the 90EQ.

Link to comment
Share on other sites

I know what you mean....I have had various scopes and on the planets and moon the refractors always seemed to be the weapon of choice.

I now have a Mak which is a great planet killer, however there is still something about refractors that i cannot put my finger on.

No idea why!

Link to comment
Share on other sites

I have no reason to remember the views of planets through my 90EQ fondly and being better, because to be honest i found using the scope a real pain in the backside because of the EQ mount and the bulkiness of the whole setup.

Yet,

I also have a Heritage 130P (Dob) and have viewed the same planets and cant say i was as impressed.

Basically, for some reason, in my mind the best views i have ever had of the planets was with my 90mm refractor.

It makes no sense.

I can only think it was because i was new to using scopes and those memories of observing the planets have stuck in my mind as the best ever.

Mars is always pants no matter what scope i use. This year i had one good view of Mars. Its a fickle planet.

Link to comment
Share on other sites

It's definitely worth setting them up side by side to be sure, though. Certainly memory can play tricks on you. In theory your SCT should be better (assuming it's well collimated) since you'll be able to get it to substantially higher powers than the refractor. Things don't always work out that way, though. Differences in optical quality, cooling issues, etc, may result in the smaller scope producing better views. Got to just try and see.

Link to comment
Share on other sites

I can only think it was because i was new to using scopes and those memories of observing the planets have stuck in my mind as the best ever.

Yeah, I have that happen too. First time I see an interesting object I remember it as being better than it was. But maybe you weren't impressed by the views through the 130p because of an optical issue. If the mirror had a bad edge, for example, that will really screw up the contrast.

Mars is always pants no matter what scope i use. This year i had one good view of Mars. Its a fickle planet.

Indeed, yes. I only managed a couple of good views too. Jupiter's slowly returning, though, so plenty to look forward to!

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.