I've had enough of newtonian stars

[spaceboy]

OK so the title says it all. If money were no object and I had a big enough obsy my ideal scope would be an 8" f/7 apo refractor. The more I use refractors the more I enjoy those little balls of light with those beautifully concentric circles. Nights of good seeing and transparency rewards me even more leaving only those pin points of light. (and purple halo but I can live with that)

While I have scopes from 120mm to 254mm I think 200mm seems to offer up enough to keep you interested while not being too much of a handful. An 8" apo is never going to happen with out winning the Euro millions so what alternatives at an affordable out lay are available ??  

I have no experience with coma correctors but I wonder if this will help any with the star quality itself as I think the problem lies with actual diffraction caused by the secondary and not eyepiece aberrations or coma. This seems the cheapest option open to me and it could be used in both my 8" & 10" newts. I also wonder if as a cheap fix swapping my secondary supports for curved or circular would benefit me any or is it a mix of several things, thermals in the tube etc that makes Newtonian stars little balls of fire ??

I am a little apprehensive regards SCT and MAKs as they have such long focal lengths and are prone to dew which agreeably can be sorted using heaters but brings with it a need for power. I did once own a TAL 200k which gave good stars and a quick cool down time with no concerns of dew due to the open tube design but again a focal length of 2000mm meant wide field views were out of the question. How do SCT stars compare to refractor stars and is the some what larger central obstruction going to reduce contrast dramatically? I know MAK's offer up some super sharp stars but the cool down time of the skymax 180 along with its f/15 focal length means this is not an option for me.

I admit I have always wanted a 120ED after stupidly  letting go of my EVO 120 achro but while I do enjoy the views you can get from a sub 6" scope I feel it always leaves me wanting on anything other than the moon. My 150P newt performed well seeming to cope better than my larger Newtonians no doubt as it was smaller and less effected by thermal currents, seeing etc. I know from having an ST102 that small scopes punch through the seeing far better than larger scopes so again I wonder if the 120ED may in the longer run offer more quality observations even if I am left wanting for a bit more aperture ? Despite my first experiences with ca back in the day I have since grown used to it and find it far more acceptable than the little balls of fire I put up with in my newts.

I guess I am asking for miracles here as nothing seems to come cheap in astronomy and I'm sure from my post you can gather some confusion in my mind to a solution to tick all the boxes. I admit there is a little apprehension there also as my intension is to whittle down my scopes to a grab and go/ solar scope (already covered) and a main scope that gives me nice clean stars. If I get it wrong I could be left with regrets as we all know what it's like when you can't distinguish that new deep sky object and the dreaded aperture hunger bites.

I guess there is the Maksutov-Newtonian just shy of 200mm ?? again there is the need for power (dew control) and a need for hefty mount at 10KG although I have that covered depending on my focusing vibrations OCD.

 

 

 

[michael.h.f.wilkinson]

I wonder if seeing isn't in part to blame. My 80mm APM triplet gives beautiful stars at 60x with the Delos 8mm, but at 65.5x in the 8" SCT (with the 31T5 Nagler) they often appear as tight, or even tighter. If you go to the same exit pupil (Nagler 12T4 and Delos14 are closest) the stars look less tight, because magnification is much higher, and seeing (plus diffraction from the central obstruction) cause this at the much higher magnification used (145-169x). I have looked through a TEC140. Great scope, but if seeing is bad, you really get no benefit from the excellent optics.

As an affordable alternative to an 8" refractor, a very slow 8" Newtonian with small secondary could work well. An 8" F/8 would need a secondary smaller than 20%. Below that the diffraction effects are very small. The spikes from the vanes would be there, of course. Alternatively, a Mak-Newt with small secondary obstruction can give outstanding images, with no spikes.

[spaceboy]

I know in the past I have had stars very similar to a refractor when using my 150P. This was a night of exceptional seeing though as I was splitting some rather close doubles.

Refractors and I guess closed tube scopes in general just seem to offer cleaner stars more of the time. I know that larger apertures do suffer when it comes to star quality as they tend to magnify the atmosphere in the process and most large scopes are often newts so maybe I am being a little down on newts as being the problem. But with no experience with MAK - Newts do they suffer similar atmospheric effects being reasonable large aperture ??

[John]

The closest to "refractor like" stars that I've got from a non-refractor came from a russian 6" maksutov-newtonian. I believe that the 190 mak-newts also put up very tight star images.

 

[spaceboy]

Did you own that scope John? I admit I think I am leaning towards a Mak-newt. May have some sitting on my hands while watching the classifieds though as they ain't cheap new

[Bodkin]

6 minutes ago, John said:

The closest to "refractor like" stars that I've got from a non-refractor came from a russian 6" maksutov-newtonian. I believe that the 190 mak-newts also put up very tight star images.

 

I have a six inch Intes mak Newt and it does provide excellent views with tight stars across a pretty flat field.  Eight inch versions from Intes Micro are pretty expensive new and rarely come up secondhand (I am looking myself). If the 190MN from Skywatcher can produce similar kinds of results it would be a bargain.

[Mr Spock]

The best I've had came from an ⅛λ 140mm Mak I used to have. That one put most of the light into the airy disc - barely any diffraction rings at all.

[John]

57 minutes ago, spaceboy said:

Did you own that scope John? I admit I think I am leaning towards a Mak-newt. May have some sitting on my hands while watching the classifieds though as they ain't cheap new

I have owned an Intes 6" F/5.9 mak-newt but I was recently considering the Skywatcher 190 MN so I consulted my friend Alan (Potts) who has owned one for quite some time. His feedback was very positive on the scope and it's "refractor like" virtues.

I was not able to proceed back then but the scope is still on my "I'd like to own one" list 

 

[spaceboy]

A while back one came up on ABS for around £450 which I thought was a fair price yet it seem to be on there for a while. I remember whishing it would hurry up and sell as I'd always fancied one. So your not the only one who has missed out John. Although if I bought everything I fancy owning I would be in a whole heap of debt by now  Alas I will have to keep those eyes peeled yet again and hope I stumble across one in my budget. It's odd as I am not all that concerned by coma or CA but just lately I find the little Newtonian balls of fire tedious and much prefer refractor stars. So much so I often pack away my 10" in favour of my ST120 or the handful EVO150. I know my collimation is spot on in the newts and the scope is or should be at an ambient temp but I just don't see nice little balls of light.

[Stu]

Good advice already Nick. If it were me, I would probably go for one of the two suggested already ie an Orion Optics f8 8" with 1/10th wave optics and curved vane spider, or an MN190.

The 8" would be a bit of a handful on an EQ mount, so I reckon dob mounted on an EQ platform would be best. Perhaps an AZEQ6 in Az mode would cope?

The MN190 is a heavy beast from what I've heard, plus 'needs' a focuser upgrade from standard (ok, benefits from) and I've read of collimation challenges but I'm sure it gives fabulous views.

Both these scopes are on my 'would like to own at some stage' list

http://scopeviews.co.uk/OrionOptics200Dob.htm

[nightfisher]

Just to buck the trend slightly, i would suggest the 150 pro mak, or if your mount can stand it the 180 pro (though thre 150 is the Cinderella of the range)

Stars in this scope are perfect plus its very good for double stars (think 6" f12 APO without the price tag)

but i guess i am biased  

[spaceboy]

54 minutes ago, Stu said:

Good advice already Nick. If it were me, I would probably go for one of the two suggested already ie an Orion Optics f8 8" with 1/10th wave optics and curved vane spider, or an MN190.

The 8" would be a bit of a handful on an EQ mount, so I reckon dob mounted on an EQ platform would be best. Perhaps an AZEQ6 in Az mode would cope?

The MN190 is a heavy beast from what I've heard, plus 'needs' a focuser upgrade from standard (ok, benefits from) and I've read of collimation challenges but I'm sure it gives fabulous views.

Both these scopes are on my 'would like to own at some stage' list

http://scopeviews.co.uk/OrionOptics200Dob.htm

 

I'm still not totally convinced even an f/8 newt is going to give me refractor stars no matter how good the optics? I get that a slower newt will be more forgiving regards edge performance but it is focused stars in the centre that I find the issue. Yes they sort of come sharp as a point of light but not like they do in refractors. Recent threads have given me food for thought regards stars in general. We always nit pick eyepiece performance yet a lot of "errors" can be due to scope design. Coma in fast newts, diffraction spikes, CA, field curvature, SA etc. EP selection can improve no end on all of this but not compensate for the limitations of the scope design so either coma correctors or field flatteners are required. It got me thinking is there one good performing scope out there that isn't going to cost the earth, has the aperture and gives the views people often sought after through eyepiece or fluorite refractor purchases.

I do think if a MN190 comes up at the right price I will have a new scope in my collection and a clear out of newts. It will sit on my EQ6 so mounting shouldn't be an issue although TBH I think the Ercole is capable. I agree the focuser looks pants but again it is easy enough to swap out. Not too sure about collimation so that may be the deal breaker if I don't find something on the net to suggest an easy solution.

29 minutes ago, nightfisher said:

Just to buck the trend slightly, i would suggest the 150 pro mak, or if your mount can stand it the 180 pro (though thre 150 is the Cinderella of the range)

Stars in this scope are perfect plus its very good for double stars (think 6" f12 APO without the price tag)

but i guess i am biased  

Tut Tut Jules

 

3 hours ago, spaceboy said:

I know MAK's offer up some super sharp stars but the cool down time of the skymax 180 along with its f/15 focal length means this is not an option for me.

 

[ollypenrice]

The TEC 140, second hand, is not entirely nuts on price and is about as good as it gets unless you are a Cloudy Nights Fundamentalist bent on holy war. But a slow Newtonian has to be a good idea, too. They are entirely out of fashion but fashion is fashion. (Think platform soles.) A 200mm F8  Newt with curved spider vanes could put a lot of premium apos on the defensive - and I'm a refractor fan.

Olly

[nightfisher]

29 minutes ago, ollypenrice said:

The TEC 140, second hand, is not entirely nuts on price and is about as good as it gets unless you are a Cloudy Nights Fundamentalist bent on holy war. But a slow Newtonian has to be a good idea, too. They are entirely out of fashion but fashion is fashion. (Think platform soles.) A 200mm F8  Newt with curved spider vanes could put a lot of premium apos on the defensive - and I'm a refractor fan.

Olly

Have to agree with Olly re a 200 f8, if it was optimised with curved vanes and small secondary it would be rather good

[spaceboy]

Thanks for all the input and advice guys. I can't find a thing on the net regards collimating a Mak-newt so that's on the back burner for the time being. I almost purchased an Orion optics 8" f/8 scope off ebay some time ago. I think it went for £100 or £150 in the end. The only trouble was it was all good mirrors wise but the scope itself was a DIY skeleton scope. I guess I should have for the mirrors but the thought of messing around sorting some sort of OTA, caps, mounting etc put me off. I will see if I can find the details as I'm sure I put something about it on SGL at the time.

Would having a small secondary mean it is more suited to planets though ?? Part of the reason behind this thread is because I still want to be able to pick out those large clusters and DSO's but that the stars are just better. A mak-newt would allow this wouldn't it ? or do they also have small secondary's ??

[Highburymark]

2 hours ago, Stu said:

Good advice already Nick. If it were me, I would probably go for one of the two suggested already ie an Orion Optics f8 8" with 1/10th wave optics and curved vane spider, or an MN190.

The 8" would be a bit of a handful on an EQ mount, so I reckon dob mounted on an EQ platform would be best. Perhaps an AZEQ6 in Az mode would cope?

The MN190 is a heavy beast from what I've heard, plus 'needs' a focuser upgrade from standard (ok, benefits from) and I've read of collimation challenges but I'm sure it gives fabulous views.

Both these scopes are on my 'would like to own at some stage' list

http://scopeviews.co.uk/OrionOptics200Dob.htm

Stu, 

Didn't/don't you have an Edge HD? Just wondering how you rated that for star sharpness - on axis as well as at margins?

[spaceboy]

http://www.cloudynights.com/page/articles/cat/user-reviews/telescopes/maksutov-newtonians/intes-micro-mn-68-r1042 M-N back on

[Bodkin]

10 minutes ago, spaceboy said:

Thanks for all the input and advice guys. I can't find a thing on the net regards collimating a Mak-newt so that's on the back burner for the time being. I almost purchased an Orion optics 8" f/8 scope off ebay some time ago. I think it went for £100 or £150 in the end. The only trouble was it was all good mirrors wise but the scope itself was a DIY skeleton scope. I guess I should have for the mirrors but the thought of messing around sorting some sort of OTA, caps, mounting etc put me off. I will see if I can find the details as I'm sure I put something about it on SGL at the time.

Would having a small secondary mean it is more suited to planets though ?? Part of the reason behind this thread is because I still want to be able to pick out those large clusters and DSO's but that the stars are just better. A mak-newt would allow this wouldn't it ? or do they also have small secondary's ??

Collimating my Mak Newt is easier than my standard newtonian and it tends to stay in good collimation unless treated very roughly.  No problem with DSOs because the f-ratio is not so high that you cannot get a 7mm exit pupil with standard eyepieces. The small secondary is not well suited to photography of course.

[John]

1 minute ago, Bodkin said:

Collimating my Mak Newt is easier than my standard newtonian and it tends to stay in good collimation unless treated very roughly.  No problem with DSOs because the f-ratio is not so high that you cannot get a 7mm exit pupil with standard eyepieces. The small secondary is not well suited to photography of course.

 

Thats what I found with my Intes 6" F/5.9. The central obstruction was 19% of the primary but the deep sky views were still very good. I spent a lovely night with my friend Mark (at Beaufort) a few years ago at the SGL star party "trading" the views of faint galaxies between his 150mm F/5 newtonian and my 6" MN and the scopes were well matched. I found even my 31mm Nagler give great views with the MN.

 

 

[Scooot]

The view through my 16" dob with a 6" aperture mask using a paracorr was very refractor like. I don't think I'd buy a big dob for that purpose though.  

Its f4.5 without the mask and about f14 with.

[Chris]

53 minutes ago, Highburymark said:

Stu, 

Didn't/don't you have an Edge HD? Just wondering how you rated that for star sharpness - on axis as well as at margins?

Hi, I'm not Stu but I did own an 8" Edge HD for a year, and prior to that I had the C8 XLT so I can compare them both.

The Edge HD was a bit sharper on axis and considerably sharper off axis, and I used ES100 degree eyepieces with both scopes so off axis performance was a definate consideration.

The C8 is a good compact light bucket, but the Edge was a definate step up in image quality. Then again I've only ever owned one C8 xlt so maybe it wasn't the best example? I've heard they can vary a bit from scope to scope.

I've just picked up a C6 which came with a goto mount I was after. I'm looking forward to pitting it against my CN-6 Newt to see wich I think is best.

[spaceboy]

I think so far the MN190 ticks most of the boxes. I will have to hold out for a good used example as £900+ isn't happening any time soon. I'm currently doing a bit of DIY dew heatering so I should be all sorted regards any dew problems there. The aperture is a little shy of the 8" I was hoping for but the focal length and the improved edge performance should still offer me the fov to fit most of my favourite DSO's in.

Thanks again to everyone for your input

[nightfisher]

A while back i spotted an 8" F7 dob for sale at a pretty good price with oldham optics mirrors, i was very tempted

[bomberbaz]

I can very much ewmpathise with your rationale for wanting to go this way, I love my dob for dso hunting but I to get turned off by the stars blob of fire view especially when looking at doubles. 

Fyi I decided the answer to this from my point of view was a ED100 and a az mount. The mount is now in place but I am making an ext pole as it sits too low. 

I did consider a sct but that brought its own problems with it these being mainly the focal length being excessive and pushing me into looking for extra ep's, the Ed100 makes use of my existing glass. 

[timwetherell]

Having once owned an 8" f9 Apo, I'd have to say they are great scopes but.. and there are quite a few buts! They are ENORMOUS. You'd need a massive observatory and a mount from a WWI battleship's gun to hold it steady! They cost a fortune - in my younger richer days it seemed more worth it but in relatively impoverished retirement it would be very hard to justify that much capital tied up in one scope. In the UK it would be virtually uninsurable especially if you kept it in an outbuilding. And in my admittedly limited experience of observing here, the UK seeing isn't generally up to delivering the maximum performance from such a beast.  A 5 or 6" apo would give you 95% of the performance with a lot less grief. Indeed a good Mak with a 4" f5 apo finder may be a best of all worlds on 10% of the budget