Why are Maks so good on planets ?

[Mr Spock]

The best view I had of Saturn (when it was overhead), was through an OMC-140. That has an aperture of 140mm and a primary of 150mm. I expect a Skymax 150 would be similar in size - can anyone confirm this?

[johninderby]

2 minutes ago, Mr Spock said:

The best view I had of Saturn (when it was overhead), was through an OMC-140. That has an aperture of 140mm and a primary of 150mm. I expect a Skymax 150 would be similar in size - can anyone confirm this?

The Skymax 150 is about 142mm. The OMC 140 I had was a bit of a frustrating scope. Super sensative to seeing conditions. When seeing was great it gave great views but in average seeing was disapointing.

[Mr Spock]

1 minute ago, johninderby said:

When seeing was great it gave great views but in average seeing was disapointing.

Agreed. Mine was an early one with better than 1/8th wave optics. On a good day star images were perfect; on an average day they were mush. I've never had a better view of ε lyr than I had on one of the good days.

A lot of that was down to me not understanding how difficult Maks are to cooldown. On a night where the temperature was dropping it never quite reached equilibrium.

[johninderby]

My OMC140 was the carbon fibre tube with 1/10pv optics. Eek just took at look at OOs current prices and they don’t show the 1/10pv option price. 🙀🙀🙀

Edited July 23, 2019 by johninderby

[John]

1 hour ago, johninderby said:

The Skymax 150 is about 142mm. The OMC 140 I had was a bit of a frustrating scope. Super sensative to seeing conditions. When seeing was great it gave great views but in average seeing was disapointing.

140mm is the figure that I've seen elsewhere for the effective aperture of the Synta 150 mak-cassegrain.

Over the years I've read very varied reports of the Orion Optics OMC 140's. Some superb and a few somewhat less so.

With regards to the secondary obstruction size, as I understand it, the actual reflective part of the secondary is part of the obstruction but there is also a flared light baffle which adds to the overall obstruction.

My personal preference in the maksutov type scopes is the maksutov-newtonian. They have longer tunbs than the folded cassegrain type designs of course but can have very small secondary obstructions resulting in truly "refractor like" images. 

 

[Mark at Beaufort]

@johninderby- John have you undertaken an observing session with your Bresser MC-127 Mak/Cass. I really fancy a light weight Mak/Cass and the Bresser seems a slightly better choice than the Skywatcher Skymax 127.

[johninderby]

Mainly on lunar and Jupiter so far but impressed with this little scope. Have owned a Celestron 127 and a Skywatcher 127 mak in the past so have something to compare it with.

The full aperture does give it that tiny bit more resolution and with the longer focal length the optics seem just a bit sharper with better contrast. It’s not a very big improvement but it is a noticeable improvement. 

So it’s a more expensive scope than the Skymax but you are getting a slightly better scope. Lots of cheap second hand Skymax 127s around but very few second hand Bressers.

 

Edited July 23, 2019 by johninderby

[Mark at Beaufort]

25 minutes ago, johninderby said:

Mainly on lunar and Jupiter so far but impressed with this little scope. Have owned a Celestron 127 and a Skywatcher 127 mak in the past so have something to compare it with.

The full aperture does give it that tiny bit more resolution and with the longer focal length the optics seem just a bit sharper with better contrast. It’s not a very big improvement but it is a noticeable improvement. 

So it’s a more expensive scope than the Skymax but you are getting a slightly better scope. Lots of cheap second hand Skymax 127s around but very few second hand Bressers.

 

Thanks for that John. I assume that the quality of the star diagonal is not that great so an upgrade would be a good idea. Because the OTA has a SCT screw I would guess that a diagonal with a SCT screw would be safer. It seems that all SCT diagonals are 2" with a 1.25" adapter. I wonder whether you can use 2" EPs without vignetting?

[johninderby]

Yes the diagonal is the typical plastic cheapie one. I’m using a Baader T2 prism. The scope has a standard SCT thread on the back. The baffle tube is just under 28mm diameter.

I’ve been playing around with different focus knobs. I’m about to fit a flanged bearing where the focus shaft passes through the rear cover and also fit the rubber knob off a Skymax 180. Details to be posted when the bits get here.

Edited July 23, 2019 by johninderby

[Mark at Beaufort]

3 minutes ago, johninderby said:

Yes the diagonal is the typical plastic cheapie one. I’m using a Baader T2 prism. The scope has a standard SCT thread on the back. The baffle tube is just under 28mm diameter.

I’ve been playing around with different focus knobs. 

Thanks John - brilliant answer

[paulastro]

Agree with all the positive points folks make about Maksutovs, particularly for lunar and planetary observing.

For me, it is evident after using many telescopes over a long period of time that the 'big three' in respect of planetary performance, with the best being first are as follows. (that is comparing same aperture scopes)

1  Apochromatic refractor.

2  Maksutov-Newtonian.

3  Maksutov.

For visual observing, this is a gimee as far as I'm concerned.  As pointed out by others, on any given night in first class seeing (very rare) a larger aperture of other configurations of first class optical quality may be a better choice.  However, it is far, far more often that a smaller aperture scope from 'the big three' will outperform larger scopes of other optical systems.

The main work horses up at The Astronomy Centre (Todmorden) are two 16 inch SCs, and for the multi uses the scopes are used for this is not surprising.  It is still often the case though that a 4 inch apo (or more) will give the better view of the Moon and planets. 

I'm sure Peter remembers years ago when we took a 16inch SC to Kelling when Mars was favourably place and it gave superb views of Mars, in fact I will readily admit that in the excellent conditions we had that morning - it was the best view of Mars I have ever had.  Likewise, many many years ago I had the best view of Saturn I have ever had using an 8.5 inch f6.3 (I think) Newtonian with top grade optics by David Hinds.  Having said this, to me these are exception that proves the rule.

It's not for nothing that people using other optical systems sometimes state that on a particular night when their telescope performed particularly well that the images were 'apo or refractor like'.  

Now I just have to hope Peter will allow me to visit TAC still !  😱 

 

[Ben the Ignorant]

2 hours ago, John said:

the actual reflective part of the secondary is part of the obstruction but there is also a flared light baffle which adds to the overall obstruction.

This baffle can be removed, as professional optician Davide Sigillò has done, obstruction went from 37% to 29%.

http://www.davidesigillo.eu/test_10.html

I'll translate the relevant paragraphs:

Io una volta smontata la cella avvitata al tubo che contiene il menisco ed il secondario ho rimosso il paraluce che è semplicemente incollato con una specie di adesivo spugnoso circolare. L’ostruzione, avendo calcolato la riduzione effettuata, scende con questa modifica sotto il 29% e una volta puliti li specchi (polverosi in questo esemplare) e rimontato il tutto l’ho puntato di nuovo sul cielo.

 

Incredibile sembra di guardare con un altro strumento!!

Immagini più brillanti, più contrastate e più luminose, l’ostruzione non si avverte più come prima, le immagini stellari sono più piccole e secche ed i pianeti e la luna mostrano più dettagli e contrasto.

Unico neo togliendo il paraluce si introducono ovviamente dei riflessi interni che possono essere eliminati montando dei diaframmi nel tubo o nel focheggiatore.

 

Once the cell that contains the meniscus and the secondary has been unscrewed, I removed the baffle which is simply glued with a ring of some kind of spongy adhesive. The obstruction, having calculated the reduction, shrinks down to less than 29%, and once the mirrors (dusty in this case) were cleaned I pointed it at the sky again.

 

Incredible, it feels like observing with another instrument!

Brighter and more contrasty images, the obstruction is not noticeable like it was, stellar images are smaller and tighter, and the planets as well as the Moon show more details and contrast. The only minus is the removal of the baffle introduces internal reflections that can be eliminated with ribs in the main tube or focuser tube. 

[johninderby]

I’m not a fan of removing the baffle. It’s there to reduce stray light so what little you might gain in reducing central obstruction you lose in susceptibility to problems with stray light. It costs money for the manufacturer to fit the baffle so if it wasn’t needed they would save a few pence by not fitting it in the first place.

I get the feeling that some people that have done the mod think it makes a big improvement because they’ve gone to the trouble of removing it. Just read a post on CN of someone who refitted the baffle and couldn’t tell the difference.

Edited July 23, 2019 by johninderby

[Ben the Ignorant]

I reduced the secondary housing on my 130mm f/7 newtonian and contrast improved, just looking at the darker areas of pine trees at dusk made it clear more leaves and shades or colors were visible. The guy who couldn't tell the difference probably didn't have experienced eyes.

These are the only pictures I got now, the spider job is not finished on these photos.

About that stray light, adding a coat of rough black paint and/or ribs to the outer and inner tubes takes care of most of it, and accepting the larger obstruction is also a compromise, anyway.

[andrew s]

While not about Maks or visual, have a look at Thierry Legault's site. As well as stunning high resolution images his Technical section has the results of his studies on types of scope, obstruction impact, focus and collimation. He uses a refractor as well as catadioptic telescopes and in my view gives a very balanced perspective. 

www.astrophoto.fr. in English.

Regards Andrew 

 

[Vox45]

36 minutes ago, andrew s said:

While not about Maks or visual, have a look at Thierry Legault's site.

He has published a very good book as well 

ISBN-13: 978-1937538439

https://www.amazon.fr/Astrophotography-Thierry-Legault/dp/1937538435

[John]

Just for info, the Meade mak-cassegrains (eg: the ETX range and the old Meade 7 inch mak-cass) do seem to operate at their full stated aperture. They have oversized primaries. I've not been a big fan of Meade products over the years but I have heard that the optics of their mak-cassegrains are rather good.

 

[jetstream]

36 minutes ago, andrew s said:

While not about Maks or visual, have a look at Thierry Legault's site. As well as stunning high resolution images his Technical section has the results of his studies on types of scope, obstruction impact, focus and collimation. He uses a refractor as well as catadioptic telescopes and in my view gives a very balanced perspective. 

www.astrophoto.fr. in English.

Regards Andrew 

 

I like this statement by Thierry

" These results are valid only if the instrument is optically good and properly collimated. If it is not the case, the MTF curve is squashed, the resolution limit is lowered and the loss of resolution affects all the objects, including high contrast objects like the Moon "

 

It amazes me how it seems so many are intimidated by collimation and it makes me wonder how many newt (SCT too) owners are really missing their scopes performance.

Because the true planetary performance of any telescope, represented by the MTF graph, is absolutely dependent on optical quality we can only compare telescopes of equal optical specs if we want to get a meaningful comparison. A great place to start understanding this is to compare a refractor with 1/4 wave spherical aberration vs a 1/8 wave newt with a 20% obstruction.  My point is real world comparisons need to take individual scopes characteristics into account vs generalizing about telescope "type" ie Mak, refractors etc.

and in all this miscollimation or poor focus destroys everything from start to finish with respect to the quality and amount of detail seen.

[paulastro]

3 minutes ago, John said:

Just for info, the Meade mak-cassegrains (eg: the ETX range and the old Meade 7 inch mak-cass) do seem to operate at their full stated aperture. They have oversized primaries. I've not been a big fan of Meade products over the years but I have heard that the optics of their mak-cassegrains are rather good.

 

John, many years ago I owned one of the Meade 7 inch Maks, and a friend of mine also had one for some time.  As I said, it was a long time ago, but I remember thinking the optics were good also, though it was too long ago for me to make a comparison to more modern incarnations.  I also remember it was very heavy, and not unusually took a long time to cool time.  I seem to remember that it had a weight at one end of it to aid with the scopes balance some how.

Generally in modern incarnations I think the various 127mm models are rather good, great for the roving planetary and lunar observer.

[John]

5 minutes ago, jetstream said:

It amazes me how it seems so many are intimidated by collimation and it makes me wonder how many newt (SCT too) owners are really missing their scopes performance....

I agree Gerry - from some of the SCT performances that I've seen I tend to agree. Trouble is, it seems impolite to suggest that the scope might be out of collimation if it's not yours !

I feel that maintaining accurate collimation is a routine part of telescope ownership and operation in the same way that tuning is part and parcel of owning and playing an instrument.

 

[andrew s]

@jetstream absolutely right. I could not agree more.

Regards Andrew 

[John]

Just now, paulastro said:

John, many years ago I owned one of the Meade 7 inch Maks, and a friend of mine also had one for some time.  As I said, it was a long time ago, but I remember thinking the optics were good also, though it was too long ago for me to make a comparison to more modern incarnations.  I also remember it was very heavy, and not unusually took a long time to cool time.  I seem to remember that it had a weight at one end of it to aid with the scopes balance some how.

Generally in modern incarnations I think the various 127mm models are rather good, great for the roving planetary and lunar observer.

One quirk of the Meade 7 inch mak was a whopping big counterweight to balance the tube. Apart from adding weight this also slowed down cooling I believe. A popular modification is to remove this weight. Meade adopted the same thing with their sonotube dobs - massive great weight just behind the primary. Not such a great idea !

 

[nightfisher]

9 hours ago, Mr Spock said:

The best view I had of Saturn (when it was overhead), was through an OMC-140. That has an aperture of 140mm and a primary of 150mm. I expect a Skymax 150 would be similar in size - can anyone confirm this?

When Mr Spock decided to part with this OMC 140 i snapped it up, this was many years ago, i kept it for about a year but as others have said,  it seemed this model was very prone to under performing on average nights, then when seeing was very good the scope would amaze me.

I have owned a huge amount of scopes, seeking that "Holy grail", amazingly i found it after re purchasing a skymax 127, i had purchased this scope at a time when i had a nice Tal 100rs and a skymax 150 so the poor little 127 did not really get used and i sold it on, then a few years and many scopes later i had the chance to buy this back, its now my only scope and i really like it, if any thing happened to it i would have to have another 127

[Carbon Brush]

An excellent thrwad raising many good and interesting points. Thank you to all the contributors.

Ref John...

My personal preference in the maksutov type scopes is the maksutov-newtonian. They have longer tunbs than the folded cassegrain type designs of course but can have very small secondary obstructions resulting in truly "refractor like" images. 

My Intes Micro MN78 (7" dia & F8 in round figures and small obstruction) gives tremendous views. It almost never gets taken off the observatory mount.
Then again at around 20Kg for the OTA, a quick scope swap to compares views is not a snap decision. It isn't grab n go!

David.

[Rob]

I would imagine the Bresser Mak is a reborn Meade ETX?. I owned both the SW127 & ETX125 OTA's the ETX I had was a white tube with metal machined rear plate SCT thread. Its performance was stunning!.

The Bresser Mak is on my wish list!

Rob