Maksutov Cassegrain vs Dobsonian

[bluesilver]

Hi,  sorry if this has been asked before,  i did a search but didn't find anything,  so thought it best to ask.

 

In regards to viewing planets,   I currently have a 16 inch Dobsonian  (400p)   and i was interested to know how it would perform against the Skywatcher 180/2700 Maksutov Casserain.

Will the 180/2700 Maksutov Casserain give me a larger clearer view than the Dobsonian will?

I am talking about viewing say Saturn or Jupiter at both the same time or night,   So amusing i had both setup right next to each other.

Currently i can get away with a 10 mm eyepiece in the Dobsonian before things get a bit fuzzy. (180 X)

Will the 180/2700 Maksutov Casserain allow me to get a larger image through the eyepiece before it gets fuzzy or will it still only be able to produce around the same size image that i am currently getting through my Dobsonian?

 

I use to have a 10 inch Dobsonian and found that it could also only take around a 10 mm eye piece before things got a bit fuzzy ( 120 X)

 

If the  180/2700 Maksutov Casserain will handle a 10 mm eye piece it would give me 270 X

 

Only asking as i have been offered a good price on a 180/2700 Maksutov Casserain,  but unsure if it will give me better views of planets that what i am currently getting.

I also realise the 180/2700 Maksutov Casserain has a much narrower filed of view,  so thinking this might also help in larger magnification.

Any information would be greatly appreciated.

Thanks.

 

 

 

 

 

[alan potts]

Well I do have both but my Dob is 18 inches. I would say that apart from the fact that the Mak is on a guided mount which at least stops the need to nudge, that's where any advantage ends. My Dob gave me the best view of Jupiter I have ever had showing so much more than even my 12 inch SC. The image was bright, sharp and so much deatil. Don't get me wrong the 180mm Mak is a good scope but for me is maybe sort of a match for a 5 1/2 inches area refractor but no match for a 16 inch.

This getting fussy could be cool down of the mirror or local seeing, I have often used X400 on my Dob and X300 on my Mak on planets though I tend to stick to x180-200 on Jupiter and up to x250 on Saturn, I often find on any scope less is more.

Alan 

[dweller25]

The planets have been quite low for us in the UK for a while so they will not stand high magnification well - For example I normally observe Saturn at x200 but this year x120 gave the best view in the same scope.

A 7” Mak will be no match for a 16” Newtonian. You could experiment by making an off axis mask to mimic a smaller diameter scope.

But planets need the resolution large apertures bring so You may want to save your money and stick with the great scope you have.

For the very best planetary views your scope will need to be well collimated, fully cooled and the seeing needs to be good - this is the biggest problem in the UK with the ever present jet stream 😏

Edited November 21, 2019 by dweller25

[johninderby]

The 16” dob will win on the views it can produce however you also have to consider the convieience factor. The 180 mak will be a lot more convieient to set up and use. I used one on a Skytee II alt az mount and it was just so quick to set up. Also being long focal length cheaper eyepieces perforn well.

On the downside the mak will take a while to cool down and produce it’s best views but it is small enough to leave the OTA in a shed or garage to cool down. Also maks are dew magnets and this can be the biggest downside. 

Replaced my 180 mak with an 8” classical cassegrain which has zero dew problems, quick cool down and takes higher mag than the mak. Performance is in a different class to the mak on lunar / planetary and reminds me of my old 12” dob.

So the mak would not compete with the 16” dob performance wise but would compliment it and would get used a lot.

[Geoff Barnes]

Hi again @bluesilver, I know you are in Tasmania but even so, not far from me in Melbourne, and with Jupiter and Saturn at 75 degrees altitude I have no problem observing at 300x with my 12 inch SW Dobsonian on good nights of seeing and the views are quite sharp.

Obviously at 200x the images are brighter and a tad sharper but still very good at 300x. I have on a few good nights pushed up to 375x and even 500x on rare occasions and then things become a bit fuzzy.

If you are getting fuzzy views at only 120x or up to 180x it suggests to me that your collimation may be off, or your primary mirror is not at ambient air temperature, I can't think of any other reason, your views should be tack sharp at those magnifications.

[ollypenrice]

I always found the need to hand-track the Dob to be quite a big negative on the planets. For this reason I might be temped by the Mak.

Olly

[Geoff Barnes]

12 minutes ago, ollypenrice said:

I always found the need to hand-track the Dob to be quite a big negative on the planets. For this reason I might be temped by the Mak.

Olly

Yes, at the high powers I've been observing it would be hopeless without the tracking feature of my GoTo Dob, which is precisely why I chose it.

[chiltonstar]

My 180 Mak gives me the best view at x190 for Jupiter, x270 and x350 for Saturn and Mars, although the low altitude of Jupiter and Saturn, and the dust storm on Mars have reduced the detail quite a bit this last year. I like the convenience of the Mak, its shortness cpd with a long newtonian design and the lack of diffraction spikes and coma (I gave up on newtonians for this reason). It is also virtually collimation-free, unlike newtonians!

For me, cool down time and dewing have rarely been issues after I insulated the tube with an aluminised polystyrene sheet from B&Q; planets are ready to view within a few minutes, and the front corrector plate stays virtually dew-free because of the residual heat trapped in the tube and the thermal inertia of the corrector (the finder scopes still dew up though!).

For planetary viewing, the 180 Mak will sit on a moderate sized EQ mount (modified Vixen SP in my case) which helps enormously for seeing planetary detail, or for quick sessions I use my SkyTee2 AZ mount. The shortness of the tube means my left hand can cover the Alt and Az slomo knobs and keep the target in view - difficult with a long tube design.

Chris

[Stu]

Given the altitude of the planets for you 'down under' currently, your 16" should be delivering much higher powers as Geoff suggests. Many moons ago, I viewed Jupiter through a 16" under pretty poor conditions and it was excellent; the additional resolution is well worth having if your seeing conditions will sustain the magnification.

Regarding tracking, most of the time I use a tracking EQ mount when I observe planets or the moon, as I find it allows steadier views and uninterrupted observing. With a manual dob you could consider buying or making an EQ platform which will give you around 45 minutes tracking between resets. Very simple to use and again, helps eliminate vibrations when nudging the scope regularly.

[John]

You have had some great replies already

Your 16 inch dob should be providing superb planetary views from your location at 200x - 250x or more. I would suspect that a collimation check and adjustment might be in order.

I find tracking at high power no problem with my undriven 12 inch dob. I do use eyepieces with wide fields of view though, which helps

200x - 300x tracking is entirely possible with my dob using the "nudge-let drift, nudge-let drift, etc, etc" approach.

[Peter Drew]

Having both would be ideal,  is the 180Mak available for a "try before you buy" arrangement?      🙂

[MimasDeathStar]

3 hours ago, Stu said:

Given the altitude of the planets for you 'down under' currently, your 16" should be delivering much higher powers as Geoff suggests. Many moons ago, I viewed Jupiter through a 16" under pretty poor conditions and it was excellent; the additional resolution is well worth having if your seeing conditions will sustain the magnification.

Regarding tracking, most of the time I use a tracking EQ mount when I observe planets or the moon, as I find it allows steadier views and uninterrupted observing. With a manual dob you could consider buying or making an EQ platform which will give you around 45 minutes tracking between resets. Very simple to use and again, helps eliminate vibrations when nudging the scope regularly.

That's such a lovely looking setup! That platform reminds me of Halfords Gadget Blue which is the colour I spray just about everything! 

[joe aguiar]

the only problem I find those tracking dob bases are expensive about $500 plus taxes $565 total. That's as much as the whole scope itself like a 8 to 10" dob.

I would never buy an accessory that cost as much as the scope itself. an ep is different you can use that on every scope  you have but that base would be for only that scope most people don't have multi-dobs.

but this is my view on these tracking bases maybe if they were $100 then I can see that

joejaguar

[johninderby]

Easy and very cheap to buil your own EQ platform. There’s not a lot to one really.

https://www.instructables.com/id/Equatorial-Platform-for-the-North/

Edited November 21, 2019 by johninderby

[Stu]

10 minutes ago, joe aguiar said:

the only problem I find those tracking dob bases are expensive about $500 plus taxes $565 total. That's as much as the whole scope itself like a 8 to 10" dob.

I would never buy an accessory that cost as much as the scope itself. an ep is different you can use that on every scope  you have but that base would be for only that scope most people don't have multi-dobs.

but this is my view on these tracking bases maybe if they were $100 then I can see that

joejaguar

Well I've got a couple of dobs it is useful for, and it can also be used with a tripod and refractor or even for long exposures with a DSLR and widefield lens. Not just a one trick pony, and as John says, quite possible to build one yourself for much less.

[joe aguiar]

ok I see where you coming from, that looks similar to the az4.

I norm just buy eq mounts I like the eq4 to eq5 it holds a decent amount size scope reflectors to reflectors to scts. But to me its just easier to track even if you don't have any drives on a eq mount BUT I just ordered 3 dual axis drive with battery pack and hand controller for 3 of my eq mounts and they were $138 each. I guess I could have just got 1 and just use each ota on it BUT I like to have a mount for each scope I own.

Anyway I guess what I was saying in my case a dual axis drive with controller and battery pack is about $150 (with tax) which is a small % of the whole scope and mount package WHERE with  the dob verion costs 100% of the scope.

to me doesn't make sence but if you have 2 dobs and a az4 type mount then I can see where it fits your needs well.

joejaguar

[joe aguiar]

On the original topic

when I had my 16" dob I never tried it on the planets or moon I only used it for deep sky, being f4.5 and only being a push/pull dob tracking at high powers were not ideal. so I manilly used it for low to med to med high powers BUT not very high powers or the item would leave the ep fov.

Normally planets need high power viewing with tracking to be ideal or atleast with slow motion controls.

Also being f4.5 had lots coma from the 80% out to the edge, so taking this into consideration if someome used this kinda scope for high planet views, the item will be out the fov even faster maybe 15 sec before its into the outter coma part.and if your not collimated 100% the image will degreed fast. Being this fast even a few % off does a lot in the image.

I also had the meade LX200 7" makf/15 UHTC OTA without the extra counter weight in mirror since it wasn't the fork mounted kind. So its not the Skywatcher version but its similar size. I had some of the best views of Saturn from this scope once cooled. Problem was cooldown was good from 1 to 2 hrs but was perfect after 2 to 3 hrs which is a long time, wven with a fan and intake air. So I would wonder how other brands /makes like the orion/SW without intake air and fans would cool , maybe even way longer.

 

[bingevader]

8 hours ago, John said:

I do use eyepieces with wide fields of view though, which helps

Those itty bitty little TV things? 

But in all seriousness, my very slow but steady move to 82° EPs is making a great deal of difference.

[Ben the Ignorant]

15 hours ago, bluesilver said:

In regards to viewing planets,   I currently have a 16 inch Dobsonian  (400p)   and i was interested to know how it would perform against the Skywatcher 180/2700 Maksutov Casserain.

You need to assess your local turbulence before you spend money and get more gear to store and handle. Make a 150mm off-axis mask for your 400, its reaction to turbulence will be similar to that of a 180mm scope. The obstruction and larger diameter of the 180mm will make it a bit more sensitive to air motion but the off-axis mask costs no money and yields some good info.

Also, as others have said, the powers at which your dobs break down seem kinda low so your scopes probably need a little refining of the collimation.

[John]

I'm wondering if there are some other factors at play here

@bluesilver said that he previously had a 10 inch dobsonain which seemed to top out at 120x before things got fuzzy.

Maybe some localised issues that are affecting seeing conditions ?

[bluesilver]

Thanks heaps for all the replies,  greatly appreciated.

I should of mentioned that the 16 inch Dobsonian is a collapsible GOTO, Skywatcher brand.

I might just be unlucky on the nights i am viewing the planets as the collimation is pretty spot on.

I am very lucky to get any decent views through the eyepiece with a 5 mm eyepiece,  I am using Televue eyepieces,  so views should be good.

Unfortunately it is not a try before you buy with the 180/2700 Maksutov Casserain,  i was just offered a good deal from a shop that includes a Skywatcher AZEQ6 tripod.

I don't travel with the 16 inch Dob,  but got it on a trolley platform that only take a few minutes to setup.

If the image through the eye piece is going to be larger and better with my Dob,  i might be better of with the Dob, 

I was just thinking of the 180/2700 Maksutov Casserain as it could possibly be a good scope for doing a bit of astrophotograpghy with if it also gave better planetary views,  but now thinking after reading through the replies,  I might be better of with a refractor for astrophotography work.

 

 

[Louis D]

That Skywatcher mirror might not have the best figure.  Having looked through 12" to 18" Dobs with Pegasus, Nova, Royce, Raycraft, Swayze, and Zambuto mirrors, I know that the planetary views can be spectacularly good at 200x to 300x with steady seeing, which Australia, like Texas, is more than capable of providing.  You might want to seek out a local astronomy club to see if one of its members could double check your scope for you.

[Limerick John]

The best planetary views I have seen were with my 12" Dob. I found them better than through my 11" SCT, as the cool down period is quicker there are no tube currents. That was from Sydney where the local seeing can be exceptional at times. Back in Ireland with the same scope and the low altitude of the planets it is mostly mushy images with the odd night of average/ decent seeing. I rarely push it beyond 120X.

Syywatcher scopes are pretty good. What does a star test look like through your scope (in and out of focus). Are there nice concentric rings on both sides of the focus or is it mushy? Make sure the scope is fully cooled down before doing this. use a high powered eyepiece and a green filter if you have one.

[russell slusher]

I don't know why people are not mentioning it.  With a large Dob that is an F-4.5 you need a coma corrector. GSO (in Taiwan) makes a very good 2" coma corrector. They make them for several different brands. I bought one for my 14" Dob.  AgenaAstro sells them. for $115.  I recently bought a 180mm Maksutov.  I'm going to do a side-by-side comparison viewing of the planets when we get some clear sky.

[Louis D]

On 24/07/2020 at 17:55, russell slusher said:

I don't know why people are not mentioning it.  With a large Dob that is an F-4.5 you need a coma corrector. GSO (in Taiwan) makes a very good 2" coma corrector. They make them for several different brands. I bought one for my 14" Dob.  AgenaAstro sells them. for $115.  I recently bought a 180mm Maksutov.  I'm going to do a side-by-side comparison viewing of the planets when we get some clear sky.

I have the GSO coma corrector, and it works great in my 8" f/6 Dob, but I need to take it out for highest power work with planets because it seems to add a bit of spherical aberration on axis.  The views are definitely sharper on axis without it.  I have noticed the same thing with my TSFLAT2 in my ED and APO refractors.  Highest power views are sharper without it in the optical path.