Equipment confusion

[Xiionn]

Hi, I am getting back into what was a childhood obsession given to me by my grandfather. Many a night we would look at the moon and planets with his 70mm refractor.

Recently My 8 year old has been asking me about the stars and constellations, and listens with actual interest when i point out the various objects in the night sky so i have taken the scope out and serviced it to use it. Trouble is its very old and the mount is frankly rubbish now with a lot of movement, glass isnt so great with some pitting etc. So i have decided to upgrade and buy a new scope with a solid mount.

My question is, what type of scope to buy. For looking at mostly planets and the obvious wonders in the sky with my children would i be better off with something like a Skywatcher 127 Maksutov with a focal length of 1500, or a 120mm refractor with 1200mm focal length? They have roughly equivalent apertures and useable magnifications.

I have been told that Refractors are better for crisp sharp images... but the 127 is heralded as better for planets.

I know much of the sky by sight, but i know virtually nothing about equipment.

Thanks,

Rich

[x6gas]

Personally I would go for the 'frac... though I don't own a Mak, I do have an SCT but I am a recent convert to refractors and I can now see what all those 'frac fans have been banging on about.

That said, I have an 11" SCT and a 90mm 'frac so perhaps unsurprising that the latter is easier to use (quicker to cool down, no collimation issues, lighter and easier to handle etc).

[umadog]

Well, sharp views are better for planets

Quite a while ago I ceased to believe this "better for plants" stuff attached to particular designs and/or focal lengths (with the possible exception of small scopes with large central obstructions) . The quality of the optics and the ability of the user to align the telescope (should it need it) matter much more. Things need to be considered on a case by case basis. In this instance, you are talking two telescopes with more or less identical apertures. The difference being that the Mak has a ~35% central obstruction by diameter. Obstructions over about 25% are significant with those below about 20% being insignificant (i.e. you wouldn't notice it). At over 30%, you're going to notice a difference compared to an unobstructed scope of the same aperture (in theory, anyway. I can't say I've done a head-to-head comparison with two such scopes). Furthermore, at these smaller apertures the contrast is limited to a much greater degree by the scope than by the atmosphere. So I reckon the refractor would win, assuming the optics were comparable.

The refractor should produce more contrasty views and it won't have nearly the cool-down problems of a Mak. You'll get a wider field of view too. You will likely notice the chromatic aberration on the refractor, though. The Mak is more compact, though. So it really depends...

[pel]

I fancy a SW 127 Mak myself, they look great and do a brilliant job on the Planets.

[nightfisher]

I would say either the 127 mak, or a Tal100rs refractor, i know the tal is 20mm down on aperture but has less false colour than the evostar 120

[tjr]

Well I personally own a 127 Mak and can report that it is an excellent scope, very good on the planets and moon and better on DSOs than I was hoping. It will certainly serve you well.

However, part of my decision in getting this scope was its compact size allowing me to get it out and about often. If I was faced with your choice - and without my concern - I might quite fancy the frac.

Are you looking at the SW Evostar 120 by any chance? It is comparable in price to the SW Mak127, but without GOTO.

[Bizibilder]

I love my Evostar 120 - the only time I have had a problem with it was observing Venus which did show quite bad colour fringing but Venus is very bright!! I have used it on the Moon and had exellent views and the planets as well where it has performed very well - the colour fringing being neglegable (and I don't use a "fringe-killing" filter). It has a good field of view with a low power eyepiece for scanning the stars.

If you get a decent 2x barlow for it then you will have an excellent and easy to use scope for better views of the planets.

[Xiionn]

I have looked at the 100R and assumed that it would be better to go bigger on the aperture...probably a common mistake but being a photographer i assosiate aperture with cost and value.

I have been looking at the following scopes with much confusion.

200mm Dobsobian, ruled out because i want to track objects easily for periods of time with my 8 year old.

127 Goto systems from Celestron and Skywatcher, simply because my 8 year old could probably use it to tour the sky with little knowlege and it will automatically track...this is a big plus point and may decide it to be honest.

120 Refractors from both Skywatcher and Celestron. Out of the two i was leaning towards the Celestron Omni XLT 120 out of the two.

The thing that gets me is the goto mounts, to get a bigger scope with a computerized mount the cost goes a bit silly! They do a 102mm refractor with goto mounts for £300 ish, but to get a 120 refractor suddenly its twice that.

I would like ideally to get a comuterized mount for the sake of my 8 year old. But a larger scope is suddenly £££

[Ags]

The Mak is a lot smaller than a 120mm refractor. A small mak on a goto mount works very well with children, in my experience.

[Xiionn]

The thing that worries me is the mounts, is the goto mount on the 127 going to be sturdy enough? A lot of people poopoo anything less than an EQ5 mount for virtually anything!

Just how hard is it to track an object well manually with an EQ5 mount with slow controls, or is a motorised mount essential for astrophotography and long viewing windows?

[tjr]

The goto mount that comes with the Skymax 127 is sturdy enough for visual use. If the wind gets up it can shake around a little, and focusing can make it wobble for a couple of seconds. That's with legs extended too, if you keep them retracted then stability is greatly increased.

I had an amazing view of Saturn last night with the Skymax and goto mount. The view was stunning and the mount tracked accurately for about 2 hours at high magnification with few and minor adjustments. Can't really fault that setup!

[ronin]

I would suggest the refractor, mainly because it has a wider field of view, so it is easier to get the things in sight. Not a lot of use if they do not appear in the eyepiece.

You might get a bit more magnification from the Mak but I see little advantage in it. The other factor being Maks are good on planets, well yes, so are most scopes if selected with a measure of common sense, but how many planets are there ?

Mercury and Venus are not exactly exciting, small and cloud covered respectively, Mars is a pain so you have just Jupiter and Saturn.

When people go on about which mount it is usually because someone will want to delve into astrophotography or they will obviously consider a bigger scope in the future.

The principle being buy a big enough one now. The EQ5 is fairly solid however and is a lot easier to pick up and transport then the HEQ5.

Remember that the eyepieces at come with whichever scope will soon be insufficent and you will want 2 or 3 additional ones.

Mention this as I see the Evostar 120 on EQ5 comes out at a few pounds under £400, an additional few eyepieces would make up another £100 and a set of motors another £100 again. So ultimately £500.

[tjr]

Hi Ronin. In your experience are refractors that much better for viewing non-platetary objects than maks? The reason I ask is: if i were to supplement my mak with a second scope and get say a 80-100mm refractor, would I notice much of difference between the two in the views they yield?

[Ags]

Hi tjr, in my experience a small reFractor or a small mak are equivalent. The mak has a smaller field of view, but still gives a wide enough field of view for 99% of DSOs. Unless you have a VERY expensive refractor, the mak will give better views, sharper across the field with no false color and eyepieces will be performing at their best.

As far as planets go, Jupiter is amazing, so is Saturn, and I have to disagree with Ronin regarding Mars - Mars is the most gorgeous sight through a telescope, the detail is subtle but wonderful. Probably I can appreciate the sight more because I am using a mak :-P...

Venus is good too in a serene sort of way. There are many people who do almost exclusively planetary observing. Unlike boring old DSOs planets actually change from night to night, even hour to hour.

If you want to view DSOs you would probably be best served by a reflector, but unless it is a goto or tracking dob it would be hard to involve a child. Aperture is important partucularly for clusters. In any 4 or 5 inch scope, a glob like m13 will be faint with barely resolved stars. In a 10 inch scope the same cluster is a mass of relatively bright stars. Or to put it differently: in my 4 inch mak m57 is a tiny ring of (greenish?) gas, but in an eight inch scope the nebula would be twice as large (whilst retaining the same surface brightness).

[umadog]

You know... With a keen 8 year old you may be ok without the tracking and so could go for aperture instead. I've shared views of Jupiter through my non-tracking 10" with a 6 year old. The trick is not to use excessively high power, where the planet zooms through the FOV. You can probably go as high as about 100x without needing to push the scope too often for them. If the child is keen they will soon learn how to push the scope themselves. If you're observing DSOs at lower power, the tracking is more or less a non-issue. You'll get better no DSO views with larger aperture, that could afford if you don't buy tracking.

It all depends on the child, though. Some will tolerate this stuff but others won't. Of course, without goto you will have to do the finding until they're a little older. Then again, you'd probably be present anyway and finding stuff together is part of the fun. It also shows kids how one does things oneself, rather than asking a machine to magically do something. There isn't a right answer, just remember that no goto can work too.

[tjr]

Ags, thanks for that very clear explanation. I imagine the OP found this usefull too.

[Ags]

tjr, I actually do own a small refractor as a travel scope as backup for my equally small mak. Taken to very dark skies the refractor (a cheap little ST80) gives superb views. One thing the ST80 can do that my Mak can't: it can get to an exit pupil of 5mm (albeit at a magnification of 16x). That means it can show objects much more brightly (but much smaller) than my mak can - giving me my best view of the Orion nebula. If I could get a 65mm EP for my mak it could show the same view, but such an eyepiece does not exist and even if it did the view would be vignetted by the mak's baffle tube.

Sadly I can only use an exit pupil of 5mm under dark skies, so at home in a city I stick to the mak and to planets, double stars and so on.

[Xiionn]

All good stuff...

The thing that puts me off about reflectors is collimation. I understand that with a Mac or fractor you often only have to do this once. The chances are high that i will never take the scope anywhere but the garden as i live in a light poluution free wilderness..so does this mean that a reflector wont need collimating so much, or is it still a ritual needed.

For this reason i am leaning towards refractors and possibly macs. The refractor or equivalent value will have the same if not greater light gathering due to no central obstruction as i have recently been informed.

Im guessing in the future i will probably buy a 250 sized dob specifically for looking at DSO's...

Decisions decisions

[Tiddles]

I love the combination of a Dob and Hyperion zoom EP. If you step away from the EP and lose your planet, zoom out and re-centre. Simples!!

I'm sure any child would find nudging a simple AltAz mount far more intuitive and easy to understand than polar alignment RA and DE with an EQ mount.

The views of all DSO's and indeed the number to be seen will improve with aperture.

8" Dob and Hyperion zoom, £450 oh and you'll be wanting to make a solar filter for the Venus transit, +£20.

Added, I check the colimation of my 6" Dob every session with a quick star test. I've done it once since new and it regularly gets carted around thrown in the car.

[Ags]

It is not really true that the CO of a mak cuts out much light - even a big obstruction only removes 10% of light, an amount of dimming you would not be able to detect visually. On the other hand, a mak also reflects the light off three mirrors in comparison to the single mirror in the frac's diagonal. Each reflective surface is cutting an additional 10% of light, so it all adds up. And if you really want to, you can get a 99% reflective dielectric diagonal... If my math is right, my 102mm mak has the light gathering power of a 90mm frac.

[umadog]

The light loss by a big obstruction isn't the problem: like you say, 10% is negligible. The potential problem comes from decrease in contrast caused by an >30% obstruction. Whether that's a problem in practice depends, I would guess, on the instrument's aperture (i.e. what power per inch you're typically using), what you're comparing it to, and your seeing limits.

[Xiionn]

Just been looking at various second hand sites including ebay and not much around that i can see.

Leaning towards the 127 mak, or 120 Skywatcher frak, or 150 omni cg4 celestron, or 200p eq5 skywatcher...

Or may just buy something second hand if it comes up

[Ad Astra]

I have both a 120mm Apo refractor and a 127mm mak - both are of the Orion USA make, so I guess I can chip in on this a bit.

I find the Mak to be just wonderful for lunar and planetary views, it is also much smaller and lighter and very easy to use as a portable scope you can take along almost anywhere.

For the very best view, though - you simply cannot beat the unobstructed refractor. Crisp, very little chromatic error (color fringing), and practically a bottomless well of magnification. I easily split the rings of Saturn the other night with a non-motorized EQ mount (slow-motion tracking is very easy with a single knob on this type of mount - even at magnifications over 200x!) I was also able to get 5 of Saturn's moons, too. For the Mak, either of these feats are difficult to replicate. Not to say that I don't get nice views, but the finest details that make you say WOW! are just a bit out of reach due to loss of contrast and sharpness from the central obstruction.

The refractor will also do much better with a camera than the the Mak will. It will also reach and pull in deep sky stuff that is beyond the Mak's abilities.

Bottom line - if you want maximum portability - take the Mak. If you want the optimum visual quality - take the refractor. My favorite is the refractor every time, although the Mak will fit in the back seat, mount on a camera tripod in an emergency, and can fit under an airline seat - none of which the refractor is good at.

By the way - no collimation issues for either one. The Mak's secondary mirror is actually a silvered section of the front corrector lens. Since it is part of the glass - there is nothing to adjust. Pretty much the same as the refractor - with a bit of care, they never need adjusting.

Hope that helps a bit!

Dan

[JonnyK]

I recently bought a celestron 127mak with goto and so far I have been blown away by it, it's easy to use, the quality of the ota is outstanding and the mount so far has been faultless. The option of being able to control the scope through the computer is also very appelaing to me, something I will try out further down the line.

[Xiionn]

I have looked around a bit, am i right in saying that if i buy an EQ5 mount that later on i can add motor control to this fairly easily...but i cant add any computerised function to that setup and would have to buy a dedicated computerised mount?

The engineer in me thinkgs this cant be so, as once something has motors a simple computer controller should be able to link to them easily, but i cant see any goto upgrades for an EQ5 mount on any store listings.