Everyone had a newt?

[Hemi]

G'Day All!

Ive never had a newt (on any mount), just my C925 SCT and a 102 refractor.
Should I get a newt, am I missing something, even if its just a right of passage?

Ive always felt guilty about never having had a newt, or never ever having had to collimate two mirrors etc etc.:P

Should I get a newt? Always thought about a 16in SW DOB, but im small, and its.....BIG. I like my comforts and so a refractor and an SCT are just....comfortable.

What do you think?:question:

Cheers


Hemi

[jamespierce]

There is nothing magical about newts ... but refractors and schmid-cass style scopes don't scale up as well once you get past 11 or 12 inches. A 16 inch dobsonian is a pretty special size for a telescope, big enough to enjoy lots and lots of faint objects but still somewhat managable.

[Startrek]

I wouldn’t use anything else for visual and AP
My 8” f5 blows me away for astrophotography and my 12” Goto for visual is unbelievable
Check my photos in the beginners AP section
Cheers from a newt lover !!

[brian nordstrom]

:thumbsup:I have a 10 inch f10 Newt and with its 20mm secondary is bar none the best platetary scope I have ever looked through , a friend at the time's 152mm f12 AP super planetary APO could not compete at all , our clubs C14 had no chance as well .

The only down size was that the eyepiece was nearly 2.5 metres up , but a good solid set of steps fixed that , OH :eyepop: it was definatly NOT portable ...

Brian.

[mental4astro]

Hemi,

The BEST scope is the one that gets used.

If you are happy with what you have, then you a blessed! :)

Why would you feel "guilty"???

Your question seems to me more about justifying you getting big aperture than what a "Newtonian" entails.

Why not get a BIG SCT then?

There is soooo much hype, demonizing and scaremongering about collimating Newts that it is astounding. It is only aligning the mirrors, nothing more, nothing less. And ALL the hype exclusively stems from the word ""collimation" :scared: :scared: :scared3: :scared3: :eek: :eek: :scared2: :scared2:

There is nothing demonic about the collimation process. Remember that a Newt is a scope where the optics are not rigidly held in place, but in spring loaded mechanisms, so if subjected to vibrations, say from a car or setting up and taking down, things can move. And any movement is only very small. Ok, so you need to tweak a screw or two 1/16th of a turn, big deal! The optics will not be horribly misaligned. It's done at the start of your session and you know that if you spend the 2 min that it will take AT MOST, the scope will be performing its very best for you! :)

Don't make "collimation" your excuse for not getting a big aperture if that's what you really want. More significant is do you have the space to store it and a car to transport it if you need to. Those are much more pressing issues to consider.

Alex.

[RyanJones]

Honestly, I love my newt. Having said that, 90% of my astro is photography. If that is the avenue you wish to persue then id say get one. Everything is a balance though. I do find AP easier in bad light pollution with my SCT. Every scope has it's pluses and minuses. As mental4astro says, the best scopes are the ones you use.

[Startrek]

One important thing to consider is Cost !!
Newts do give the biggest bang for the buck
Refractors are great but can be expensive particularly if your not all together happy with the one you choose to buy
My 2 cents added .......

[Merlin66]

Hemi,
I've built and used many Newtonian's over the years - from a 6" f8 (back in 1966) through 18" Dobbies and almost every aperture in between.
I used a great 12" f5 for many years, visually searching for Super Novae.

I feel the "sweet spot" for a Newtonian is a 10" aperture, and around f6 (easy on the eyepiece)

[Renato1]

The best views I have ever had of Jupiter and Saturn bar none and by a long shot, were through the 10" dob of a fellow club member (and other club members also agreed it was the best they'd seen). He used a Panoptic in a Powermate for the eyepiece, and had designed and optimised the telescope as a planetary telescope using the best parts available. Only problem was that his primary mirror alone cost more than either my SCT or my 14.5" dob. Hard to buy his set-up off the shelf.

The best views of the planets I've ever seen with my telescopes is in my 14.5" dob. Only problem there was that the times that occurred were few and far between - it was always at the end of a long observing session out in the country, where the telescope had cooled down and atmosphere had become excellent.

If you want a big dob, you'll want one that you can handle, and not be a grinding exercise.

Before doing that though consider - have you actually looked at most or all of the objects listed in say SkyAtlas 2000 with your 9.25" SCT?

On the other hand, if you really wanted to pick off all the DSOs in the Large Magellanic Cloud listed in Herald Bobroff AstroAtlas, you really need something bigger than your SCT.
Regards,
Renato

[doppler]

I guess a 10"f5 or 8"F6 newt is the perfect in-between scope at 1200mm focal length (C925 SCT @ 2350mm and 102 refractor @ 660mm)

Rick

[Ukastronomer]

:) :) :)

[Hemi]

Thanks everyone for some great perspectives.

James, I agree there is probably nothing more magical about a newt over any other, they are all magical. I’ve just never had the magic from a newt, as I’ve never owned one.

Doppler, I get a nice in between fL with the 6.3 reducer on the C925. Wouldn’t the 10 or 8in newt be too similar in aperture to it?

Hah, Ronato, very true, I’ll never see everything that I can with either of my 2 scopes, but sometimes you want to see something differently. Like driving to work in a faster car.:)

Startrek, your images are amazing, I’ve seen everyone. I’m very tempted.:question:

Hey Alex, words of the wise, as usual. Totally agree. That’s why I only have 2 scopes, and my c925 never really gets deposed off the AZEQ6. I am totally smitten with it. Not really guilty, but always thought that “proper” astronomers had newts. (Excuse me Galileo!). I would love a 16in DOB I think....guilty as charged of aperture fever.

It’s meant to be the first weekend of the dry season here in Darwin. It’s not rained in a while, and I was looking forward to the new moon. But the clouds have rolled in out of nowhere and the heavens have opened.:( and I only mentioned buying a new telescope!

Hope it’s better for you guys, wherever you are.

Hemi

[brian nordstrom]

Here is a shot of my 10 inch f10 I have rebuilt this scope many times over the years , It's now in 2 pieces ( OTA , they clip together ) on a Dobsonion mount . The silver bit's in this photo .

Brian.

[Ukastronomer]

100% agree, but for me it was, many years ago I rushed in, like many thinking I know best, and bought a 120mm Acromat, this was 15 years ago, sold after a month, then I bought a 8" observatory class newtonian, again thinking I knew what I wanted, waste of £2k, sold, came back to Astronomy two years ago and spent SIX months asking questions on this and other forums, re bought a refractor and have never looked back, but got the right one this time.

Buy in haste, repent at leisure

[Ukastronomer]

I've never owned a Ferrari but I don't miss or want one, or had any envy

[Hemi]

Thanks Jeremy,
It’s nice that we all are different.:)
I think a newt will give me a different experience of this hobby, than my current scopes. For me that’s what it’s about I suppose. That’s why I like to observe, image, sketch, use binos, have a go at a few simple ATM/DIY projects etc. (I’m terrible at all of them, I might add!).....”resistance is futile”, (I think your a Dr Who fan Jeremy?), so a newt is inevitable.

Cheers

H

[MPS]

I have a 10' dob, great scope, great views. Has the old school feel which I like as well as the room to tinker with it. Great complement to the various ' mirror' collection

[mental4astro]

One thing I never, ever, want to do is not respect people's different $$$ they have available to spend. There's plenty of good but expensive gear, and rattling off those Brand names is easy. I try a different approach, to find those gems hidden among the modestly priced gear, and discuss those. Not everyone can afford to drop $1000 on an EP, but with some thought given to the scope/scopes you have, there may be $200, $100, or even $50 eyepiece options that will do a stonking good job.

My quip of getting a big SCT was meant tongue in cheek. There is a huge price difference between a 16" Skywatcher dob and a 16" Meade SCT... :rolleyes: Not to mention logistical.

Hemi, if you ate considering a light bucket, then of course a big Newt/dob is a special beast. I have dobs from 114mm to 17.5", and each fulfills a particular niche for me. Tonight for instance, I'm going to my dark site at Katoomba Airfield (first time in 3 years :D ) and I'll be taking my 17.5" dob & my 8" f/4 dobbie too. There are things the 8" can do that the 17.5" can't, so I will exploit both.

Is there an astro association in Darwin you can join? I know the weather systems of the tropics plays havoc with astro, but hopefully there is a modest astro group happening. Maybe someone there has a big light bucket you can look through before laying down your money, and also come to see what it takes to wrangle it from set up to take down.

As Jeremy said "Buy in haste, regret at leisure" - great line! :D

Alex.

[Outcast]

Hey Hemi,

This is kinda close to my heart so; I'll pop my perspective in here for ya.. maybe it will help...

When I first got into Astro approx 11 years ago... everyone said.. buy a Dob, best bang for buck... & you know what; they are absolutely right but... in my situation at the time I wanted light and portable, easy to pack up & transport, yada, yada, yada... so, I bought an 80mm APO refractor secondhand to keep the price down..... huge difference hey??

Was I disappointed... nope, not at all, it met the brief... it was light, portable easy to handle in & out of my house... it got used... The views in my very much beginner opinion were outstanding...

Then I wanted more.. I wanted aperture... I knew I could get an 8" or 10" dob at a great price but..... they were big, they were cumbersome, I had to learn how to collimate one.. so... I bought an 8" SCT, again secondhand to keep the price down... I love my 8" SCT... the views were a step up in wow factor from the 80mm... I thought... I have everything I'll ever need here... & so stupidly I sold the 80mm, invested some money in some relatively good quality eyepieces... am I disappointed.. not on your life.. recently had it out under truly dark skies for the first time & observed some things for the first time that I could not have gotten with the 80mm...

However, I still wanted bigger but, I still look at big dobs (the generally commercially available ones) & think... I can't be bothered lugging that in and out each night or packing it into the car.. 6 months ago, I enquired on the cost of a pretty much custom made dob that gave me aperture but, packed down small.. ah, now we are talking... but, at the time.. the cost was a huge impediment to me...

Recently, things changed, some money has come to me so now, I have a custom made 12" dob on order & I cannot wait to get my hands on it... Would I like bigger... sure but, then that comes with a cost & 'portability'... yada, yada, yada..

I share this with you only because this is my journey to gaining aperture... your reasons might be different, your finances might be different & your attitude towards portability, convenience may be different but, this is my journey... so, if it helps you way up the pro's & con's then that's awesome... if lugging a 16" collapsible dob in and out isn't a consideration or, money is no object to gaining relatively lightweight, truly portable aperture.. then good luck to you... no jealousy intended...

What's the view like in a large(ish) aperture dob.. no idea... I'll let you know in a few months when I finally get to look through one.. sadly we don't have a club up here so, no opportunity to try before I buy.. but, hey... I'm pretty sure it will be pretty damn good... :D

Cheers

[Hemi]

Wow, thanks again everyone, I am always humbled by the responses.

Hi Outcast, thanks for sharing your take on this. Alas, cost is most definitely a consideration. And I should stress again that it’s going to take some tectonics to shift my 925 off the mount. My first scope! After years of armchair observing. I would of course love to have the “big dob”, but ultimately would like just to have a newt to view through, whatever size, mass produced or custom or even ATM. I’m lucky, in that I have a semi permanent setup. So a big dob would be mostly setup, ready to go.

Alex, there aren’t any Astro societies in Darwin :sadeyes: I will get down to a star party interstate at some point. I’m completely opposite of the buy in haste philosophy! It takes me forever to buy anything of substance. Too much cogitation at times. But it’s served me well so far...very few regrets with my current two scopes. Although I wish I had researched a bit more about focal reduction on the ES102. But I wasn’t thinking of imaging back then.

I’m very tempted by an 8in newt, or having a go at building a simple 6in. ( not the grinding bit,:eyepop:)

:) H

[Merlin66]

Hemi,
If you’re serious about building a 6” I have a very good 6” mirror and a diagonal and focuser just needing a tube and assembly.
Drop me a PM if you’re interested.

[Outcast]

I can completely understand why mate... the wow factor of an 8" SCT is pretty damn good... 9.25" would be a step up again...

[sil]

Spot on right there.

If you want to know the horrors of a manual EQ mount with a Newt then go for it. Its what newbies see as being a typical telescope and they can be impressively large for little cost. So its a con and people quickly find its a poor choice and get put off as a result. Refractors, Newtonians, Dosbonians and Cats all have there place in astronomy for various reasons, Hense they are commonly found. Learn what the figures actually mean and what the strengths and weaknesses of each type are and you start to understand why there are choices and why no single type rules them all. They each rule something. If you have scopes that do what you need then thats all that matters. Collimation isn't too difficult, again learn what the adjustments do . I think most problems people really have with newts is down to the tripod mount that they came with. But with a good mount already a newt OTA is no problem and it may even be worth you picking up a good fast second hand newt to experience for yourself what a "fast" ota delivers as opposed to what focal length gives you with what you have got.

[Hemi]

So it seems I spoke to soon! The tectonics have moved and the C925 has been shifted (at least temporarily)...(Houston we have a problem thread)!

Pros and cons of the SW 10in F4 vs F5 (price aside)? Purpose would be a multi use scope: EAA and visual.

Not sure of the correct etiquette, and if I should have started a new thread for this....apologies!

Mould free optics and clear skies!

Hemi

[mental4astro]

10" f/4 vs f/5 - coma is the only main difference. It is much more aggressive in an f/4 instrument than f/5.

Best way to relay this is with my own experience with my Newts from f/4 to f/5.

For EEA using a small chip, say 1/3" size, at f/4 there is no coma to be seen. As the chip gets larger, coma will begin to appear, but really for EEA it may or may not be a concern for you. With my 1/3" chip camera, I don't use a coma corrector, and certainly at f/5 even less need to so.

Visual, the only time I use a coma corrector is with my f/4 Newt when using 30mm and 24mm 82° eyepieces. Not vital, but it does clean up the image especially with the 30mm. But remember, I am using eyepieces specifically designed for Newts, in my case these are Explore Scientific EPs, so there is no astigmatism present, only coma. TV eyepieces are also brilliant in Newts. If you use EPs not designed for Newts, any aberrations seen with them in an f/5 Newt will be much more prominent at f/4. Careful eyepiece selection becomes more important with very fast focal ratio Newts.

I hope this helps you.

Alex.

[Ukastronomer]

Actually I am a Babylon 5 fan

[doppler]

If you are after a multipurpose newt you could get a dob 8" or 10" and then add some tube rings and mount it on your eq6. I use my 10"f5 for imaging and as a visual scope on its dob base.

[xelasnave]

I have a 6 inch 8 inch and twelve inch all f5 and think they are wonderful.
I have not used the eight for visual but have used all for photos.
Don't be put off by folk complicating the job of adjustment.
Alex

[Startrek]

I totally agree with Alex
I have a 6” f6 for AP , an 8” f5 for AP and a 12” f5 for visual ( all great scopes in their own right)
As for imaging I’m totally in awe of what my new 8” F5 can do, it too me 6 months to decide to upgrade but I’m glad I took the advice of many experienced IIS members , Alex included
As for the EQ6-R mount it’s flawless , so smooth and tracking is superb, my guiding numbers on this mount are way lower than my HEQ5
Good advice doesn’t cost anything !

[Hemi]

Thanks for the advice again....
Ok im thinking the 10in F5. Similar aperture to the c925, but very different focal length of course. Should be a good balance of AP and visual. The F4 worries me a little as my first newt in terms of coma, picky collimating, and tricky focusing....have not bought a telescope for 3 yrs so very excited 😆

Mould (or mold) free optics!

Hemi

[mental4astro]

Hemi,

It is wrong to say that an f/4 Newt is more "picky" of difficult to collimate. This is a common complaint though from owners of these fast Newts that are mass produced. What these have in common is they are all poorly manufactured, using components that are undersized or of poor material selection or poorly prepared. It is a real shame as the material choices made by the mass production manufacturers is just to save a few cents per scope, but it means that there are now thousands upon thousands of pages on the net dedicated to fixing their cockups, :rolleyes:

What is never heard is of collimation problems with all those big dobs or high end Newts that are f/4 and faster! What these all have in common is they have all been designed and built using the appropriate materials.

I have two 8" f/4 Newts, one is a dedicated visual instrument that I made, the other is a solid tube OTA I can couple to a dob mount or pop onto a gem. The solid tube is a GSO scope, but I've modified the secondary mirror holder and made the primary mirror cell myself. No collimation issues with either scope than with any other Newtonian.

244402 , 244403

Also, collimation is far more critical for photo than for visual, as our eyes are not just an active part of the optical train, but also very adaptive, which cameras are not.

There is some good news though about the very fast mass produced scopes. There are some simple mods that can be done to fix what really should have been implemented by the manufacturers. If you want to know what these are I'm happy to explain them. These will cost only a few dollars, which if these had been done at the factory would have cost only cents... :rolleyes: :rolleyes:

Alex.

[Hemi]

Hi Alex, I would be very interested in knowing what the mods are. I was thinking the SW 10in black diamond F4.

Hemi

[gjr80]

Keen to hear about this too.

Gary

[JeniSkunk]

Add me to the list of interested folks as well, Alex.

[ngcles]

Hi All,



Never a truer word said.

So good in fact, I'll say it again: The telescope that's best for you, is the 'scope you will use most.

There is absolutely no point at all in getting any telescope that's going to sit in a corner, gather dust and make you feel guilty that you aren't using it, but instead prefer another. Everyone's cup of tea is a bit different.

Yes, Newtonians, unless they are permanently mounted do need to be collimated before use. Would knowing that you had to tune a guitar before you can play it put you off buying a guitar? I mean, tuning a guitar is such an incredible hassle, it takes ages and ages and is so, so fiddly.

Like most things in life that are skill-based (as opposed to talent-based) collimating any telescope takes just a bit of learning but really isn't hard at all with the right tools. The more you do it, the quicker you will get at doing it and before long, it takes no more than a minute or few to get right.

One thing I will take issue with Alex here (in a later comment) is about the difficulty of collimating an f/4 as opposed to, say, an f/6. I guess you are technically correct here Alex: It is no harder to collimate faster f/ratios, but the reality is, slower f/ratios are more tolerant of slight mis-collimation than fast ones. At say f/6 a newtonian that is slightly off perfection will be hard to pick from one that's spot on. At f/4, the tolerances between great and yuck become exceedingly small.

As others have said, guilt should never play a role in choosing a telescope. There are good reasons to pick a big-un, there are good reasons to pick a little-un. There are good reasons to pick a Newtonian, there are good reasons to pick a Schmidt-Cassegrainian or a refractor. Where the balance point is, will depend on how you rank (and how much weight is accorded to) the following factors: cost, ease of portability, ease of use, image fidelity, light-gathering and your own life-circumstances..

Best,

L.

[Chapstick]

The first scope I used was a 8" dob which I found very uncomfortable to use, not my cup of tea. I've since had SCT's, refractor and mak-newt all on CGEM which for me at least was the key to enjoying these scopes. I think if I went back to a dob it would have to be around 18-20" for it to have a more comfortable EP location for my height.

[Wavytone]

Hemi, no I’d say you aren’t missing anything by not having a newt...

For many the reason to buy or make one is simple - they are a way to satisfy aperture fever on a low budget.

Personally I made 5 in my early years - the first two while in high school then as struggling student. At that a time a C8 was way over my budget, a 3” Unitron was hot stuff and we all lusted after the 4” Unitrons fully equipped. But a simple well-made f/7 8” newtonian was vastly superior.

Then John Dobson arrived and big cheap light-buckets were all the rage. Either that or you had an SCT, typically 8-10”. This remained the case for 20 years.

Despite the many significant changes in the last 10 years the big newtonians (dobs) remain cheap and effective if what you want is a light bucket. What the changes amount to is gear you could once only dream of now being affordable for amateurs, facilitating many other things.

[Hemi]

Thanks to everyone who has commented on this thread.

I am surprised (maybe not!) that no one posted saying that they've never had a newt (and why) and apart from Jared, no ones also said that they dislike them....hmmm I really feel justified in buying one to find out for myself :)

Cheers

Hemi

[xelasnave]

Hemi.
My eight inch Newtonian Telescope cost under five hundred dollars and added to that figure was the cost of a coma corrector which was around three fifty I think...with additional tube rings the thing still cost under a thousand dollars...new.
There is little to fault with it.
And I have still not adjusted it.
Even a six inch does a fine job...I used one for years and would still be using it but I wore it out☺.
You could start with a long fl six which will see you there for about three fifty bucks but I bet you will be happy if you go for the eight.
F5 or F4? Mine is F5 and fast enough for me. I have no experience with a F4 but I doubt they are beyond management.
Alex

[Wavytone]

Oh I know someone who never did - he opted for Unitron refractors, then a C8. And another with a 130mm APO.

[ngcles]

Hi Wavytone & All,



I don't think it is helpful to characterise a large Newtonian as little more than a cheap "light-bucket".

Sure, inch for inch they are inexpensive compared to many other designs but a well made, optimised Newtonian with a sensibly sized secondary mirror are exceptionally high-contrast telescopes (second only to a refractor). As a planetary instrument, I'll back a moderate f/ Newtonain against anything apart from a similar-sized refractor.

Best,

L.

[Wavytone]

If in sydney you should meet the MK91 one night. The premium maks also beat newtonians of the same aperture. There are larger maks from APM, TEC and AP optimised for resolution. Expensive yes, but not as expensive as the comparable refractor.

Sure you could line up say a 18"dob, maybe that would resolve the Encke division in Saturns rings, maybe not. But the MK91 does.

[ChrisV]

So what's extra good about the Mak-newts Nick? I'd be interested to know as I'm thinking of upgrading from my gso newt some time - I was thinking of one of the TS optics UNC carbon fiber jobs. But I keep hearing about mak- newts ...

I started off with a newt in my teens. Built one with my brother - it was great except we couldn't afford a decent mount. We gave up pretty quickly. Took me 40 years to get back into it!

[Outcast]

I've never had a Newt... :rofl:

I am however, in the process of rectifying that... I have one of Mental's 12" lightweight/portable dobsonians on order....

And, I cannot wait to get it.... :eyepop:

Cheers

[Wavytone]

Chris,

For the 5"-7" aperture range mak-newtonians are underrated, IMHO. The basic geometry is the same as any newtonian, ie can have a smallish secondary, however the use of spherical surfaces means no coma, and a flat focal plane is possible. Nirvana for visual observers and not bad for imaging, either. Secondly the big corrector effectively closes the OTA so the mirror coatings will last a very long time if it is well cared-for.

In particular Intes garanteed their complete scopes to 1/6 or 1/8 wave, something very few manufacturers ever did. When properly collimated, these scopes do perform extremely well.

Another aspect to consider is that Intes built theirs like a T34 tank optimised for maximum contrast - a full steel tube OTA in battleship grey with internal baffles, and a screw-on black dewcap with more baffles. The original Intes Crayford focusers were very agricultural - worked but very crudely made. Heavy, but they last. A long time.

And in case you don't know, Intes ceased production a few years ago so these scopes are now only available secondhand. The big downside was their cost, and that they were (are) only viable in apertures around 5" - 7" - the Intes 130mm MN56 being the baby, vs the Skywatcher 190 being the largest in this country. Intes made a few 8" and 10" versions but none exist in this country AFAIK.

The alternative is a newtonian with coma corrector of one kind or another near the focal plane. This solution is cheaper but inferior, and there's no practical limit on the aperture (big cheap mirrors are available).

[ngcles]

Hi All,



While I agree that the Maksitov design eliminates coma, coma only becomes truly obtrusive in a Newtonian when the f/ is very short (ie f/5 and faster) and the star is far from being on axis -- ie when using a wide visual field at low power.

A Newtonian with a coma corrector the only other solution ???

What about a "slowish" Newtonian -- like one I used to own a 10" f/6.2 (1570mm f.l) with a 46mm 18% central obstruction? At f/6.2, I concede the tube wasn't "short" and needed a good mount to bear its mass and length, but the planetary images were absolutely stunning.

A 27% obstructed 9.1" Intes Makistov isn't a "smallish" central obstruction -- it is moderate verging on large and will affect contrast particularly on planetary images. This is settled physics -- though people still tend to try and argue it away with their own perceptions at the eyepiece or some form of argument from authority. You can arger' with me son but you can't arger' with figures -- as Foghorn Leghorn was wont to say.

In a perfect (unobstructed ) telescope, 84% of the incoming light will make it into the centre of the Airy disc and 16% into the surrounding diffraction rings. This effect is caused by the wave nature of light, the circular shape of the entrance pupil (aperture) and nothing else. If you introduce a central obstruction first and then progressively increase it in diameter more and more light is redistributed from the central disc and into the rings. At a 20% obstruction a further 8% is re-distributed -- ie 76 -v- 24%. by the time you get to 30% an additional 16% is re-distributed from the disc to the surrounding rings -- ie 68 -v- 32%. The difference between say my old f/6.2 and your Intes is about 10% more energy illuminating the rings rather than the central disc.

So how does this affect a visual planetary image? Well the image of a planet you see in the eyepiece is a mosaic of adjoining/overlapping airy discs and the more energy/illumination there is in the rings, then the less contrast you will perceive because the rings overlay the adjacent discs.

http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/c-o%27s.html

If you are doing planetary observing coma is no issue at all -- the planet is in the centre of the field and you are using a narrow field with a small exit pupil. Nobody observes planets out near the edge of the field. Coma only become obtrusive at low f/ratios at very low power.

One of the nice things about building a Newtonian from the ground up rather than buying one off the rack is you can deliberately optimise various attributes by changing focal lengths and secondary obstructions.

In the U.S (in particular) there is a strong movement (fashion?) toward large ultra-fast Newtonians. If you want a 24" telescope **and** you want to observe with both feet on the ground **and** you want increased portability that's fine -- but there is a price to be paid for that -- a much increased secondary mirror **and** coma **and** decreasing tolerance of slight mis-collimation (and much increased fabrication costs for the mirror). If people want to pay that price, that's their business and its a matter of priorities I guess. But here's the thing: It is a price that must be paid no matter how you argue it -- that's simple physics

My latest 'scope is the first one I never designed and had no part in building, a 25" f/5 "classic" Obsession. The price I have to pay for exquisite image quality (with a 14% central obstruction -- almost negligible) is a fairly narrow native field (smallest low power is x104 and 48 arc-minute field), poor portability and being several steps up the ladder nearly all the time.

Many people are not willing to pay that price but I do not need portability. I observe in my front paddock 80m from the house and the 'scope moves only 5m fully assembled from storage to observing. My own personal view is that the exquisite image quality exceeds the nuisance value of trips up and down the ladder. That was my choice to pay that price rather than the other one: 31% obstruction at say f/3.2 (7" secondary) producing decreased image quality + vastly increased mirror fabrication cost + zero tolerance to mis-collimation.

But to re-iterate -- there are a lot of very good and attractive reasons to own a Maksutov -- or for that matter a Newtonian, a Refractor or indeed a Schmidt-Cassegrainian. Maksitovs are excellent performers for several applications and they are very good general use telescopes, but given a 27% central obstruction, they are not super-outstanding planetary performers compared to similar-sized 'scopes with a much smaller or better no obstruction.

Best,

L.