Mak, Cas or Frac?

[pbyrne]

Hi guys

 

I am looking to perform more lunar observations, with a little planetary thrown in, in the scope stakes, I am considering one of the following and would appreciate any thoughts or experiences that you may have.

150mm Maksutov.

150mm Classical Cassegrain.

100-110mm ED Refractor.

Each scope has its pros and cons. 

The Mak, has the longest focal length, however, there is the question of cool down time due to the heavy meniscus mirror and it susceptability to dew.  The Skywatcher version comes with diagonal, eyepiece and finder.

The CC does not have the same cool down issue as the Mak, due to a lack of a meniscus mirror, it also comes with a R&P focuser and there are no worries about dew build up.  There is no eyepiece, finder or diagonal.

The ED is smaller in aperture, it does benefit from not having loss of light due to the design of the above pair having the secondary systems, again, there is no finder, diagonal and eyepiece.  Then there is the cost.  Am I correct to state that a doublet will be more than enough to cut down on potential false colour?  

A lack of a finder, diagonal and eyepiece are not an issue, as I already have them all.  The scope will sit on a Skywatcher HEQ-5 and though not inititially a consideration, I may want to dabble in lunar photography at a later date.  

 

Thanks for looking.

[Nik271]

What is the seeing  on average in your location? The 150mm scope will  give you quite a bit more resolution, down to 1 arcsecond, but it is no use if the seeing does not support it.

The frac in the 100mm apertue is the most versatile. I have a 100mm ED doublet with FLP-51 glass, i.e. the cheapest doublet availble. I can easily go to x180 magnification and there is very little purple colour and only on extrmely bright objects (Venus, Sirius), interesting I don't see it on the Moon. I think a 100mm FPL 53 at F7 will show no discernible false colour at all visually at anything.

I also have 127mm SW Mak (which is 120mm actual aperture) and also 180mm SW Mak. Cooldown time is not really an issue on the 127mm, but it is on the 180mm.

For planetary my 127Mak beats my 100mm refractor in good seeing, despite the central obstruction. For planetary and visual this is my go-to scope. I recently split Mu Cygni with it, which pleasantly surpised me. My average seeing does not usually support the extra resolution of the 180 Mak, mind you it is still better in almost any condition, but not by much.

So I would guess that the 150mm Mak will blow away a 4 inch refractor if the seeing supports it and from what I've heard of the 150mm Cassegrain that one may do even better.

The refractor will be lighter and more portable though,and of course no annoying dewing  (in the Mak) or diffraction spikes (in the Cas).

So....not an easy choice. Bottom line from me: if you have good seeing go for the 150mm scopes, otherwise get a nice FLP53  100mm doublet.

 

Nik

 

 

Edited August 18, 2023 by Nik271

[Cosmic Geoff]

What is your budget? Is weight or bulk a constraint?

You could add a Newtonian to that list.  

Why have you ruled out a Schmidt-Cassegrain?

For planetary observing, the bigger the aperture, the better (seeing permitting).

[Elp]

The refractor will be the sharpest with highest contrast, seeing plays a large factor on the final visual acuity as the 150s will give you more mag and resolution. From experience with scopes that I've owned the best crispest views I've had go in this order, apo refractor, Newtonian, acro refractor, SCT.

Edited August 18, 2023 by Elp

[bosun21]

What’s it doing in the binoculars thread 🤔.

[inedible_hulk]

I have the SkyMax 150. None of the reflectors or refractors I’ve owned have come close for planetary or lunar. Though it is rather a one trick pony in that respect.

I use a DIY camping mat dew shield and a dew band, and dew hasn’t been a problem. Cool down times can be significantly cut down by keeping the scope somewhere cool and by planning ahead. Have it out cooling whilst you set up the mount etc.

If you go down the imaging route, you will eventually find that you need to add an additional focuser for the fine focus. As far as I’m aware, there isn’t an upgrade for the stock focuser. 
 

[Roy Challen]

2 minutes ago, bosun21 said:

What’s it doing in the binoculars thread 🤔.

Binoscope?😉

[bosun21]

2 minutes ago, inedible_hulk said:

. As far as I’m aware, there isn’t an upgrade for the stock focuser. 

There’s several Crayford style focusers that fit on the 150 and 180 but not for the 127.

[JeremyS]

If it’s just moon and planets then go for aperture in closed tube: Max.

 

[vlaiv]

I'd go with classical Cassegrain.

I have 102 Mak and I put it to test once on Jupiter against simple 100mm F/10 achromat and achromat pulled ahead despite having residual color.

I expected Mak to perform just a tiny bit better than achro, but it was the other way around.

This shows two things:

- Skywatcher Maksutovs have some sample to sample variations of course, and it really depends how lucky you get.

- That particular Maksutov design is a bit of a tradeoff. Maksutovs should really be F/15 or slower and ones by Skywatcher are Gregory Maksutov type. They have secondary aluminized spot on back of corrector plate and not separate mirror. This limits how well corrected particular scope can be - and they are a bit too fast at F/12. This tells me that design itself is probably capable of being better performer then these particular executions by Skywatcher.

On the up side - they are affordable for what they offer.

[Stu1smartcookie]

Juat to put my opinion in , i have both the 127 bresser Mak and a 150mm Classical Cassegrain and i find the class cass a better scope ( not just for the increase in apperture ) 

The minimal cooldown time , the nice focuser ... but its quite a heavy beast compared to the mak and its oh so back heavy with those extension rings and the focuser . 

Still it is a lovely scope and has already given me fine views of Saturn this year

 

[RT65CB-SWL]

Similar to @Stu1smartcookie, except mine is a C6 and a ‘re-modded’ ETX105...

[Paz]

I would vote for the larger aperture first of all, it will suffer from poor seeing but seeing comes and goes and can be managed to some extent, a small scope can't ever increase its aperture and resolving power.

If it is just for planets and lunar I would vote for the maksutov due to the small central obstruction and no spider vanes, but I agree with the comments about getting a f15 Mak or longer and you have to think through and be realistic about cool down times.

[inedible_hulk]

 

4 hours ago, inedible_hulk said:

As far as I’m aware, there isn’t an upgrade for the stock focuser. 

 

Apologies, I should have been clearer. Unlike some SCTs, there isn’t (to my knowledge) a third party microfocuser which directly replaces the telescope’s focuser. btw, if there is one, I’d love to know.

[vlaiv]

14 minutes ago, inedible_hulk said:

 

Apologies, I should have been clearer. Unlike some SCTs, there isn’t (to my knowledge) a third party microfocuser which directly replaces the telescope’s focuser. btw, if there is one, I’d love to know.

I'm not entirely sure you'd need dual speed focuser for telescope that slow.

Here is a handy table:

If MCT has focusing screw with standard pitch - say even 1mm pitch (but 0.75 or 0.6mm would be more realistic) - it would take half a turn of such focuser to move across critical focus zone at F/15

[RT65CB-SWL]

5 hours ago, inedible_hulk said:

I have the SkyMax 150. None of the reflectors or refractors I’ve owned have come close for planetary or lunar. Though it is rather a one trick pony in that respect.

I use a DIY camping mat dew shield and a dew band, and dew hasn’t been a problem. Cool down times can be significantly cut down by keeping the scope somewhere cool and by planning ahead. Have it out cooling whilst you set up the mount etc.

If you go down the imaging route, you will eventually find that you need to add an additional focuser for the fine focus. As far as I’m aware, there isn’t an upgrade for the stock focuser. 
 

 

34 minutes ago, inedible_hulk said:

 

Apologies, I should have been clearer. Unlike some SCTs, there isn’t (to my knowledge) a third party microfocuser which directly replaces the telescope’s focuser. btw, if there is one, I’d love to know.

An alternative idea for a microfocuser maybe a helical focuser. I have this type... https://www.firstlightoptics.com/adapters/baader-125-t2-helical-focuser.html and you will need one of these too... https://www.firstlightoptics.com/diagonals/baader-nosepiece-125-t2.html

Edited August 18, 2023 by RT65CB-SWL

[pbyrne]

Thanks for the replies.

This is why this hobby is so fascinating, and frustrating, there are recommendations for all three scopes.

I live in Bortle 6 skies, the seeing is attrocious, LED streetlights everywhere.  

The reason I have not considered a SCT, is that I had a Celestron C6 some years back, and for some reason I just could not come to like it, I think it was the mirror shift, but I sold it soon after.  I want to stick to the 150mm size because I believe that it is the best portable size, the Mak can go up to 180mm, but that comes with an even longer cool down time and how will the view be improved with an extra 30mm?  

I love the look of the refractor, but at this moment, it is down to either the Mak or the CC.

More thinking required.

[RT65CB-SWL]

5 hours ago, inedible_hulk said:

I have the SkyMax 150. None of the reflectors or refractors I’ve owned have come close for planetary or lunar. Though it is rather a one trick pony in that respect.

I use a DIY camping mat dew shield and a dew band, and dew hasn’t been a problem. Cool down times can be significantly cut down by keeping the scope somewhere cool and by planning ahead. Have it out cooling whilst you set up the mount etc.

If you go down the imaging route, you will eventually find that you need to add an additional focuser for the fine focus. As far as I’m aware, there isn’t an upgrade for the stock focuser. 
 

 

35 minutes ago, inedible_hulk said:

 

Apologies, I should have been clearer. Unlike some SCTs, there isn’t (to my knowledge) a third party microfocuser which directly replaces the telescope’s focuser. btw, if there is one, I’d love to know.

An alternative idea for a microfocuser maybe a helical focuser. I have this type... https://www.firstlightoptics.com/adapters/baader-125-t2-helical-focuser.html - you will need one of these too... https://www.firstlightoptics.com/diagonals/baader-nosepiece-125-t2.html

Edited August 18, 2023 by RT65CB-SWL

[Mr Spock]

If I had a choice of 150mm scopes it would be the CC. I had a 140 Mak once. The optics were great (it was 1/8th pv) it really needed a lot of cool down time despite being kept in a porch. On nights where the temperature was falling rapidly it never did reach equilibrium. I did have my best ever view of Saturn with it (high up in Taurus) but I never really got a lot of use out of it.

To throw a spanner in the works my Starfield 102mm was a much more capable scope.

[inedible_hulk]

7 minutes ago, vlaiv said:

'm not entirely sure you'd need dual speed focuser for telescope that slow.

In my experience of twiddling a small knob moving the big mirror on the 150, and trying  various tricks like clothes pegs and bottle tops, I’d say yes, it would really benefit from a dual speed focuser. Or perhaps just a better focuser. But that’s just my experience with the 150, which appears to have very little weight.

8 minutes ago, RT65CB-SWL said:

An alternative idea for a microfocuser maybe a helical focuser.

Thank you, I’d had been wondering if this was worth a try.

[Captain Scarlet]

3 hours ago, Paz said:

I would vote for the larger aperture first of all, it will suffer from poor seeing but seeing comes and goes and can be managed to some extent, a small scope can't ever increase its aperture and resolving power.

If it is just for planets and lunar I would vote for the maksutov due to the small central obstruction and no spider vanes, but I agree with the comments about getting a f15 Mak or longer and you have to think through and be realistic about cool down times.

Sadly the skymax does not have a small obstruction. Although the central spot and baffle on the corrector are indeed small, the CO is actually defined by the retaining ring on the primary mirror, which seems to be much larger than it needs to be. Consequently the CO comes to about 33%.

[mikeDnight]

Get the ED refractor!  No cool down worries, no spider diffraction, no collimation issues, and a good ED doublet will be essentially colour free visually, and will give razor sharp views.

Edited August 18, 2023 by mikeDnight

[Bivanus]

"100mm FPL 53 at F7 will show no discernible false colour at all visually at anything."  - True dat ! Just looked thru mine a bit , FPL53/Lanthan doublet , no violet - or other coloured flowers - garden.

"I love the look of the refractor, but at this moment, it is down to either the Mak or the CC." - not a fan due to collimation HOWEVER having to choose I would most likely go for the CC but you do you.

[JeremyS]

There is only one certainty in life: if in doubt go with the frac 😊

[Knighty2112]

Owning all three types of scope at some point (but still have the ED ‘fracs) I would definitely go with the ‘frac.