Help me pick a new Refractor! ~600mm at ~f/5.6 reduced or native - Forums

Hi everybody,
I‘m in the market for a new refractor. I want to get deeper into galaxy imaging and my current 80mm f/7 ED Doublet is a little limiting in terms of image scale and resolution, even paired with the 183MC Pro.
I really don‘t want to get a Newtonian (I know a 130PDS would be the cheapest way to get 650mm at f/5 but I don‘t like spikes at all and the constant need for collimination is offputting).

I use a CEM25P which runs guided reliably with my 5.5-6kg Payload at RMS 0.5-0.6“ total all night long. I mean it‘s half the specified weight so I‘d expect that.
My image train, AAP and cables come out at ~2-2.5kg on top of the scope, I need to weight it but I think it‘s closer to 2kg as I got a color cam.

Soo…I want a refractor. And I‘m unsure. I want to be in between 0.75-0.85 Image scale at the end. Not sure if Doublet again or Triplet.

I‘m limited by my budget (~1500€ prefered but if I wait a month longer I could go up to ~2000€ max but thats a stretch and at that price point I want a forever scope, which means a triplet) and by my mount obviously.
I figured I could go up to 7-8kg total and still be fine, but that‘s the most I‘d do. So the scope should be 6kg or lighter.

I looked at the following options:
AT115ED f/7 or the similar TS Optics 115mm f/7 Triplet - reasonable priced, pretty close to the resolution I‘d get with an 130PDS reduced and a triplet although a budget one. It‘s probably pushing the mount, so I‘m not sure.

ZS103 or a similar wellmade FPL53/Lanthanum Doublet from TS Optics, 4.5kg total, probably a safe bet in terms of how my mount would handle it, affordable, but it‘s image scale is 0.87“, and it‘s a doublet.

Another Option would be the Sharpstar 94EDPH, and get a Field Flattener which doesn‘t reduce the image scale to run with it. 517mm focal lenght, so the image scale is not what I really want but safe in terms of mount capacity.

The Esprit 100 is pushing it financially and it‘s also crazy heavy, but also in the specified range.

I mean my forever scope for galaxy imaging with the 183MC Pro would be the new WO FLT120, but that one is over 6kg, and probably belongs on a CEM40. It‘s also expensive. But it‘s basically my dreamscope.

If all of the above options (minus the Esprit 100 because it‘s over my budget honestly at 2200€) are just bad compromises in terms of image quality and a not-so-safe bet on a CEM25P (I mean I see people take images with a 6“ f/5 on it and be fine, also a few rare cases of an 8“ f/4 or I even saw a Deep Sky imaging setup with an RC8!!) in terms of mount capacity (my mount runs pretty well for a CEM25P but still…) - I‘d rather sell my CEM25P and get a CEM40, but I kinda want to postpone this whole get a new mount thing because I live in the fourth floor without an elevator, our basement is moldy, and my motivation to carry the equipment downstairs to drive to my imaging places is correlating to the weight of my equipment 😅

I‘m really hoping for a buying guide because honestly, I‘m overwhelmed by the sheer amount of refractors around the ~4“ mark.

Thanks and Clear Skies,

Mine

Hi Mine,

If your goal is an imaging scale of about 0.7"pp you should go with an 8" aperture scope. Even if this leads to a smaller image scale below 0.7" you can still bin your sensor to improve SNR and keep a suitable resolution.

Regarding the scopes you mention: I do own the TS115mm f/7. On mine the quality of the triplet is very good. The issue I had was the flattener, which you definitely need. You need to calculate another 300 Euros for the flattener. From my own experience, the TSFLAT2 is not really suitable for this scope and you
would have to go for the 2.5" which will produce the necessary image quality.

Personally, I'd say switching from an 80mm to a 100 or even 115mm scope for galaxy imaging isn't a sufficient leap forward. For the galaxies, I've been using an 8" f/10 SCT (reduced and unreduced) and use a RC8 at the moment. I admit that I haven't been trying the APO for galaxy imaging.

Cheers,
Björn

Hi Björn,
thanks for your answer and for sharing your experiences with this scope! I'm aware of the extra cost for a flattener/reducer in this case - I'd probably use the WO Flat6AIII with the ZS103 or the similar TS Doublet, because it's apparently working for it according to WO, but for a 115mm scope I'd need a seperate one, I figured so much, that's why I prefer to stay closer to the 1500€ if possible. I saw that you got great results with it, although on a CEM40. I'm contemplating for a while already to upgrade the CEM25P to a CEM40, but even if I sell the CEM25P for 700€, I'll still have another 1500€ roughly in my upgrade path. But I could do 8" scopes then. What's keeping me from this step is besides money and weight the fact that I'm hesistant to go reflector because of the tricky collimination in RCs, the mirror flops and slow speed with SCs and the overbearing spikes in all Newtonians.
I like refractors, they are easy to use, collimination stable, usually have amazing focusers and paired with a fitting flattener/reducer, they just work out of the box. But yes, bigger apartures are not possible then. I figured I could do ~0.8" Image scale with a 4-4.5" refractor and paired with small pixels - I mean aren't we all limited by seeing anyways? Of course bigger aparture is better, but the theoretical resolution of an 8" scope isn't possible under my average seeing. I figured people take these scopes because they offer fast imaging ratios and long focal lenghts at reasonable prices (f/4 and f/5 is nice and the selling point for Newtonians imho).

I mean I can't be the only one who had this thought that considering, we are all seeing limited anyways, you could pair a reasonable sized refractor with small pixels to up the image scale? My current Dawes Limit is 1.45 with the 80mm scope but I image at 1.1 currently, so I'm also under the dawes limit and my images look nice enough?

In case I'd go Newtonian (if there's really no other option), I'd probably buy a high quality 6" f/4 and be done with it, tbh - at least theoretically, this seems a fit in terms of resolution, pixel scale with my camera and it's fast. 0.83" image scale, 0.77" Dawes limit, and a fast optics - if it wouldn't be for the downsides. Weightwise, that's doable on my mount, but those are so finicky to colliminate and I'm worried about a steel tube option not keeping collimination over the imaging session. And the spikes…well…

Mine

edit: Basically it seems like I have the following options: Go all in and upgrade my mount to a CEM40, get a RC8, 8" f/4 or similar scope, I could probably toss a 4.5" refractor on this one easily as well.

or keep my mount and go the safe route with a 4" refractor which probably has not enough aparture for galaxy imaging (I'm looking mostly at the ones that are sized like 8'-10'x8'-10' or bigger, like M51, M63, M64 and the likes, not the the tiny ones like M58 etc.) on my CEM25P or a 6" reflector which seems like a compromise…

In case I'd go Newtonian (if there's really no other option), I'd probably buy a high quality 6" f/4 and be done with it, tbh. That's doable on my mount, but those are so finicky to colliminate and I'm worried about a steel tube option not keeping collimination over the imaging session. And the spikes...well...

I'd agree with Björn on the need of much larger aperture to go galaxy hunting. This not about resolving power per se but because larger aperture always win in the end, as you gather more light for the same time lapse. And you shouldn't believe of all the scare stories about Newtonians losing collimation on the go. A well made one, such as those from TS, do not do that and keep collimation really well (disclosure:I have one). Coupled with a good coma corrector they allow even for some slack in your collimation abilities. Spikes, while I don't like them so much, I can live with, but that is ultimately your call.

Hi Mine,

Hi again, have not had time to answer on FB yet, but here you can see the 8kg of gear i have on my CEM25P

Guiding wise I am able to get below .5 RMS on a regular basis but balance is extremely tricky if i get it wrong (which happens i get .9) with very good seeing i can even get as low as .3 Cant really give any advice on which Scope to get, myself I am going replace my CEM25P first with a CEM70 and only than invest in a heavier and longer FL scope. For the longer FL I am always also running into the fact that I most likely would have to replace my camera, filters, filterwheel etc.

Also dont forget to factor in the cost and weight of whatever flattener/reducer would need to be part of the setup

andrea tasselli:
In case I'd go Newtonian (if there's really no other option), I'd probably buy a high quality 6" f/4 and be done with it, tbh. That's doable on my mount, but those are so finicky to colliminate and I'm worried about a steel tube option not keeping collimination over the imaging session. And the spikes...well...

I'd agree with Björn on the need of much larger aperture to go galaxy hunting. This not about resolving power per se but because larger aperture always win in the end, as you gather more light for the same time lapse. And you shouldn't believe of all the scare stories about Newtonians losing collimation on the go. A well made one, such as those from TS, do not do that and keep collimation really well (disclosure:I have one). Coupled with a good coma corrector they allow even for some slack in your collimation abilities. Spikes, while I don't like them so much, I can live with, but that is ultimately your call.

Hi, would a 6" Aparture do nice enough for the galaxies that are in size around M51, M64, M94 and similar sized NGC objects? Like I thought about this one if I toss the idea with a bigger refractor aside: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5881_TS-Optics-UNC-150-mm-f-4-Newton-Teleskop-mit-Carbontubus.html

It has a carbon tube and seems to be wellmade. If I go Newtonian, I'd rather take one that is as high in quality as possible and not some cheap 300-400€ tube which comes out as a DIY-project (blackening, getting another focuser, etc). Image scale with this one would be 0.83", and resolving power is 0.77".
8" would require a new mount, thats for sure...While a bigger mount is in it in the long run, I don't want to go that step now because I'm pretty sure I'm not running my mount at the limit right now, a little headroom for a 4" refractor or a 6" reflector should be there.

Sean van Drogen:
Hi Mine,

Hi again, have not had time to answer on FB yet, but here you can see the 8kg of gear i have on my CEM25P

Guiding wise I am able to get below .5 RMS on a regular basis but balance is extremely tricky if i get it wrong (which happens i get .9) with very good seeing i can even get as low as .3 Cant really give any advice on which Scope to get, myself I am going replace my CEM25P first with a CEM70 and only than invest in a heavier and longer FL scope. For the longer FL I am always also running into the fact that I most likely would have to replace my camera, filters, filterwheel etc.

Also dont forget to factor in the cost and weight of whatever flattener/reducer would need to be part of the setup

Hi Sean, thanks for your answer, this is really interesting. Maybe I'm underestimating my current load? I got scope weight with rings and both dovetails around 3.7kg, Flattener ~0.6kg, then comes the Camera at 0.4kg, plus Filterdrawer, OAG and 120mm mini - probably another 0.4kg. I got also an EAF (300 gr according to you) and an AAP plus TP Link (~ 500 gr). That's without cables. I'm probably over 6kg, but I need to weight it to see. Didn't expect my setup to be this heavy, but you kinda gave me a reality check - that's a lot of stuff for a small scope

If I'm closer to 6.5 kg probably now, I could add another 1.5kg pure scope weight at max.
4" Refractor or 6" short newton seems the maximum my mount would do. I save weight capacity because I don't image with a mono cam and I use an OAG, but still...

Tbh I think about upgrading to the CEM40, even if my CEM25P runs like a dream - the 0.5-0.6" rms total is with dithering inbetween, if I take long subs and the dithering error doesn't get calculated into it, I'm down to 0.4... so it does its job but I'm so hesistant to tossing more stuff on it at the risk of screwing my performance. A bigger mount would solve my worries - but also create a huge hole in my finances...

Hi, would a 6" Aparture do nice enough for the galaxies that are in size around M51, M64, M94 and similar sized NGC objects? Like I thought about this one if I toss the idea with a bigger refractor aside: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5881_TS-Optics-UNC-150-mm-f-4-Newton-Teleskop-mit-Carbontubus.html

It has a carbon tube and seems to be wellmade. If I go Newtonian, I'd rather take one that is as high in quality as possible and not some cheap 300-400€ tube which comes out as a DIY-project (blackening, getting another focuser, etc). Image scale with this one would be 0.83", and resolving power is 0.77".
8" would require a new mount, thats for sure...While a bigger mount is in it in the long run, I don't want to go that step now because I'm pretty sure I'm not running my mount at the limit right now, a little headroom for a 4" refractor or a 6" reflector should be there.

Yep, that's the same as mine, only mine is steel tube. Very well made. Carbon tube will buy you no need to refocus if temperature drops for more then few degrees. They seem also somewhat dew-resistant, based on my tests. At that image scale you'd do nicely although probably you'll need either longer times or down-sampling to get to a decent SNR for the fainter subjects. The Messier objects you mentioned should be all within your grasp, depending on the sky you image from.

Sean van Drogen:
Hi Mine,

Hi again, have not had time to answer on FB yet, but here you can see the 8kg of gear i have on my CEM25P

Guiding wise I am able to get below .5 RMS on a regular basis but balance is extremely tricky if i get it wrong (which happens i get .9) with very good seeing i can even get as low as .3 Cant really give any advice on which Scope to get, myself I am going replace my CEM25P first with a CEM70 and only than invest in a heavier and longer FL scope. For the longer FL I am always also running into the fact that I most likely would have to replace my camera, filters, filterwheel etc.

Also dont forget to factor in the cost and weight of whatever flattener/reducer would need to be part of the setup

Hi Sean, thanks for your answer, this is really interesting. Maybe I'm underestimating my current load? I got scope weight with rings and both dovetails around 3.7kg, Flattener ~0.6kg, then comes the Camera at 0.4kg, plus Filterdrawer, OAG and 120mm mini - probably another 0.4kg. I got also an EAF (300 gr according to you) and an AAP plus TP Link (~ 500 gr). That's without cables. I'm probably over 6kg, but I need to weight it to see. Didn't expect my setup to be this heavy, but you kinda gave me a reality check - that's a lot of stuff for a small scope

If I'm closer to 6.5 kg probably now, I could add another 1.5kg pure scope weight at max.
4" Refractor or 6" short newton seems the maximum my mount would do. I save weight capacity because I don't image with a mono cam and I use an OAG, but still...

Tbh I think about upgrading to the CEM40, even if my CEM25P runs like a dream - the 0.5-0.6" rms total is with dithering inbetween, if I take long subs and the dithering error doesn't get calculated into it, I'm down to 0.4... so it does its job but I'm so hesistant to tossing more stuff on it at the risk of screwing my performance. A bigger mount would solve my worries - but also create a huge hole in my finances...

Am in the same scenario here and am opting for the financial hole to switch to the CEM70 around 3k to spend on this. But i only have to take it as far as my roofterrace so the added weight is not really an issue for me. For next year a new scope in the 700mm FL range so i can keep the rest of the gear, but i am scared of all the collimation that comes with newtons and RC's but finances wise they fit better than a long FL refractor.

Have you considered a C5 with a reducer ? It has a low weight and should be fine with a CEM25.
It's not a refractor but, in my opinon has the best weight / aperture proportion.

Stefano Ciapetti:
Have you considered a C5 with a reducer ? It has a low weight and should be fine with a CEM25.
It's not a refractor but, in my opinon has the best weight / aperture proportion.

Hi Stefano,
no, I don‘t want to image at f/6.3. It‘s really slow even reduced, and as I have very few clear nights, I‘d rather have a faster scope. The C5/C6 would be a nice planetary scope for my mount though! For DSO Imaging I want to keep it at f/5.6 and under. As 4-5kg OTA weight seems the doable maximum on my mount, I‘m now looking mainly at 4“ refractors or maybe a 6“ f/4 Newtonian, it‘s fast, but has a few downsides I‘m not sure yet.
Honestly - I‘d love a RC6 or C6 sometime - but they are so slow, even with their reducer and I can‘t justify the cost rn for any of them, as I want a main scope that‘s fast enough to do medium sized galaxy imaging besides the few huge ones (M33, M31, M81…).
I imaged at f/7 for a while and now I‘m at f/5.6, and I never, ever go back to anything slower than that

the amount of depth I get in an average night is amazing with f/5.6, and for f/7 - well tbh I should have taken two nights for each object back then.

@andrea tasselli : So you use the TS Newton 6“ f/4? How hard are they to colliminate? How often do they need recollimination? I looked at pictures with the UNC Newtons & a quality coma corrector and in this case, the spikes look a lot less pronounced than with some other cheap Newtonians. Also they seem to be blackened so the reflection will be less bothersome.
I figured the carbon tube would also save me a little extra weight and the focuser seems nicer on the UNC carbon tube.

@Sean van Drogen The CEM70 is amazing. Like honestly, if I had a permanent pier I‘d say screw it, save a few months extra and go all in. But yeah, the weight - in your case it doesn‘t seem a problem though.
I feel you - I‘m also hesistant for buying a reflector - collimination and the spikes are bothering me.
However there is no such thing as free lunch - a perfect, nice big aparture refractor like the FLT120 or even bigger is breaking my bank. Can‘t justify 3000€+ for a scope rn.

So you use the TS Newton 6“ f/4? How hard are they to colliminate? How often do they need recollimination? I looked at pictures with the UNC Newtons & a quality coma corrector and in this case, the spikes look a lot less pronounced than with some other cheap Newtonians. Also they seem to be blackened so the reflection will be less bothersome.
I figured the carbon tube would also save me a little extra weight and the focuser seems nicer on the UNC carbon tube.

Fairly simple once you got the right tools: Laser collimator, cheshire EP or autocollimation EP. I don't know how long as I haven't used that long to have evidence on the long term stability of collimation. Suffice to say however, that after 3 weeks of taking it off and on the mount to test it seems fairly stable (I check in autocollimation which is very sensitive to even small movements) once the rear knobs are properly tightened. I'd venture to say a fairly long time for a permanent set-up. Yes, the UNC version adds few nicer bits, such a quartz primary, nicer focuser, shorter tube and thumb screws for secondary collimation (I don't know how often you'd need to touch them though...).

So far I think out of everything mentioned the 6" Newtonian is the best bet. A quick search on Astrobin shows some really nice pictures taken with the scope!

Don't fear the collimation! It's not that bad and once you get used to it it maybe takes a few minutes max. This is coming from an RC user, and trust me when I say compared to that, a good old fashioned Newtonian is child's play compared to an RC.

Also, don't be afraid of longer focal lengths. I think you'll find that it will be hard to find telescopes that can get the image scale you want with a f ratio lower than 5, especially if you ever switch from the 183MC. I think if you can keep it at or below f/7 you'll be in a good place. Dealing with slower telescopes is just the trade off once you start getting into this kind of detail work.

If it's galaxy imaging you want, I wouldn't go for a 4" refractor, regardless of the advantages it provides. Besides the few largest galaxies like M31, M33, and M81, a small refractor is just disappointing in its light-gathering ability and resolution. 4" refractors are optimal for imaging larger, extended objects like nebulae, but not the best option for galaxies under 10 arcminutes size, IMHO.

I own both an Esprit 100ED and a C11 EdgeHD. I will echo the sentiment of those posters above who said to go for larger aperture, whether it would be a Newt, RC, SCT, etc. I prefer to use my C11 EdgeHD for imaging any galaxy smaller than M33, even with the well-known limitations of long focal length imaging.

I’m a big newt supporter so aperture is in my blood. While refractors definitely have there advantages as you mention once you get working with even a smaller 6” f4 you will immediately see the difference in detail/structure in your images!

I do have a small 80mm WO TMB that I’m using for wide field images but my main imaging scope on my mount is my 10” f5.

Defraction spikes, well can’t argue with personal tastes. Personally I love them otherwise I wouldn’t be using newts. A couple tips from me would be when collimating as mentioned above, use a laser collimator but if you really want tight stars go the extra step and collimate with your camera in place! You can collimate all you want with a laser but in the end what the eye see’s (or in this case the camera) is GOD. I’m in a permanent setup in my observatory so I get the tweaking collimation your talking about. I only collimate maybe 2-3 a year unless I accidentally bang the OTA hard while moving around the observatory.
As far as collimation goes, once you get used to it. You will be fine and you will find ways to transport it to help eliminate the bouncing.
Use some old pillows or blankets underneath the scope to act as a cushion.

This is just my opinion based on my personal experiences.

I’m currently working on a new to me carbon fiber ES 6” f4.8 mak-newt just to see what it will do but am still waiting for some things before I get to test it.

Whatever your decision, in the end its you that has to be happy/comfortable with the purchase.

Best of luck and post your pix’s!

Dale

@andrea tasselli Thanks, that‘s encouraging! I heard a lot of horror stories that those fast Newts are really difficult to colliminate - even some that they lost collimination? I have an EAF, which I‘ll use, so I refocus often anyways - maybe they lost focus and didn‘t realise it? Also if I go Newt I go all in - a premium one it is then, as I read a lot about people switching things up, blackening everything etc.

@SemiPro That‘s good to hear. Yes, you all seem to agree that a 6“ Newton would be the best, aperture is nice. And it‘s not an uncommon combination, especially the f/4 one as those are shorter.
I‘d need a good coma corrector then though.
Regarding longer focal lenghts: I know - at least with the 183MC I get sub 1“ with reasonable focal lengths - but the weight and cost of some of those setups are not really doable for me. I plan to get a 183MM or maybe even a 294MM in the future, the latter one can do tiny pixels or big pixels which is nice. But everything bigger than 8“ is kinda pushing me away, because I don‘t really know if I want to carry a scope heavier than 10kg. Like at all… Some time I‘ll for sure get a bigger mount and then probably a bigger scope - I‘ll see how big. I‘d rather do tiny pixels and 120-180 seconds max for broadband (low full well of 183mc pro) and reasonable sized scope than huge scope and bigger pixels - it is probably better, but it comes at a cost. An 8“ SC or RC would be nice at some time - but I still consider myself a beginner and that‘s a far stretch.

@rhedden Thanks for your input! Seems like it‘s clear, a small Newtonian is probably better than a 4“ refractor for that kind of work. I‘d really like to see some comparisions though, that‘s so interesting - the same small-ish galaxy taken with similar or same image scale but different apartures.

@Dale Penkala thanks for your long and thorough answer! It‘s really a trade off - sharp views and ease of use from a refractor vs lots of light gathering ability at fast speeds for reasonable money.
Thanks for your tips regarding collimination as well - I‘ll keep that in mind should I pull the trigger on the f/4. Payday is end of this month - so I‘ll keep you updated how I decided. Right now I‘m strongly leaning towards a quality f/4 6“ - I‘d need a ton of extra stuff though (coma corrector, collimination tools, dewcap, etc) while a scope similar to the ZS103 would mean I could even use my FF with it.

Your Mak-Newt sounds interesting - I‘ve only ever saw them in 8“ though.

I‘ll sleep a few more days about it, do some more research etc.

Thanks a lot y‘all, at least the refractor bigger than 4“ is now off the table.

I was hoping to shoot NGC 7331 with my C11 this fall to do a direct comparison with the result I got from my 4" refractor in August. The problem is that I want to use the same camera on the C11, but I don't have the hardware to connect it just yet.

A lot of people will argue that the extra aperture won't help resolve more detail because the resolution is often limited by local seeing conditions. It makes sense up to a point, but there's another factor at work: larger aperture generally produces smaller stars at the same image scale, resulting in a more pleasing image. If anyone wants to contradict me, then show me a comparison between a 50-60 mm APO and a 20-24" scope of any design that proves your point.

A lot of people will argue that the extra aperture won't help resolve more detail because the resolution is often limited by local seeing conditions

A lot of people would be wrong, then...

andrea tasselli:
A lot of people will argue that the extra aperture won't help resolve more detail because the resolution is often limited by local seeing conditions

A lot of people would be wrong, then...

I‘m really wondering when the marginal benefit decreases in terms of aperture and average seeing of 2-3“ which describes my imaging location and lots of others pretty well.
Like of course a 150mm scope beats a 60mm scope with the same image scale even if you are seeing limited - but what about a 200mm vs a 300mm scope? is more aperture really better then, going by the same image scale?
I read conflicting stuff about it and I think it‘s an interesting debate.

I‘m really wondering when the marginal benefit decreases in terms of aperture and average seeing of 2-3“ which describes my imaging location and lots of others pretty well.
Like of course a 150mm scope beats a 60mm scope with the same image scale even if you are seeing limited - but what about a 200mm vs a 300mm scope? is more aperture really better then, going by the same image scale?
I read conflicting stuff about it and I think it‘s an interesting debate.

If you hold the image scale constant, the increasing aperture will collect more photons in the same time and it goes square with diameter. An increase of 50% in diameter will collect 125% more photons.

EDIT: a rough number is 100mm aperture is the break even between diffraction and seeing limited (for common seeing values like 2"). Of course this isn't exact but more a rule of thumb.

It isn't just a matter of collecting more photons in the same amount of time (although this is a pretty BIG one reason to go for it). It is also that the bigger aperture has a smaller Airy disk (assuming diffraction holds sway) and "potentially" the image can be deconvoluted to reveal more detail (or reveal the same detail with more contrast). IOW, a bigger aperture has more resolving power than a smaller one. Try it with tight doubles, it makes for some interseting observations!

Hi Mine,

i started with a Newton and also was not sure because of collimation. But as I did it the first time, it was much easier than I expected remembering the comments of so many users. But I would suggest a laser collimator, too. They are not that expensive and the adjustment process itself is really simple.

Today, I mainly use my TS 8" f/4 Newton. Star spikes are of course a matter of taste, but even Hubble images shows them quite heavy. They are only visible on the brightest stars. But the advantage of having that f/4 aperture is really great and I realize the difference even when I use my TS Flatfield APO with an aperture of f/5.

I think, the 8" is too heavy for your mount. But the 6" may be a good choice and your 183MC will be a good imaging cam for that (personally I use a 183MM). But you need a coma corrector. I own the ES HR Coma Corrector, which is quite expensive but works very well for me. I don't have experiences with other ones.

The TS Newton you picked will be a good choice. I own the 8" f/4 and the 10" f/5 both with a steel tube. The advenced version will work at least as good as my versions. They are much lighter than the steel tube versions. Maybe you should add a Dew shield to your wish list. It will potect the secondary mirror. The TS ones are light and very stable.

I hope this will help…

CS

Christian

I also wanted to comment about the quality of the 6” f4 ota’s as well. Don’t get the cheaper ones. If budget can afford I’d second @andrea tasselli on the CF tube. Not only from a looks stand point but from strength and help with temp stability. Plus I really like the looks of the CF tubes but thats just my personal taste there.

You said that you never seen a 6” mak-newt so for what its worth here is a pix of it on an AVX mount that I had it on for testing. This was a ES/David Levy collaboration so I have wanted to give one a try.

Dale

Hi Mine,

I have a big newton (250 mm) and a dob (300 mm). The 250 mm arrived alredy collimated in 2014 and never touched. The dobson I have collimated a couple of times in 8 years. Very easy to do. Don't worry about Newtons, they are very nice and fast instruments. I have used (and I still own) a wonderful Vixen ED114 F 5.6 refractor. Almost 20 years old. It is natively at F 5.6 (but needs a new field flattener - original one was created for film phtography) but can be reduced at 4.4. I have taken many images with that. But the weight, including all accessories, with a DSLR and without guide scope is around 7.5 Kg. I think too much for the Ioptorn 25. If I were you I would go for a small Newton.

Cs
Stefano

Dale Penkala:
I also wanted to comment about the quality of the 6” f4 ota’s as well. Don’t get the cheaper ones. If budget can afford I’d second @andrea tasselli on the CF tube. Not only from a looks stand point but from strength and help with temp stability. Plus I really like the looks of the CF tubes but thats just my personal taste there.

You said that you never seen a 6” mak-newt so for what its worth here is a pix of it on an AVX mount that I had it on for testing. This was a ES/David Levy collaboration so I have wanted to give one a try.

Dale

The Explore Scientific MN-152 Maksutov-Newton here seemed to be a great solution. So I thought some time ago and bought one myself. I hope that Dale is happy with his scope.

Personally I am not happy with my copy. It seems that I have a really bad one. The images I took with the scope had really bad artefacts on bright stars. There are some examples in my gallery here. It seems, that this problem comes from the corrector lens in front of the scope. I did a lot of research and was not able to fix it. I realized, that it seems to be a common problem. I regret the investment. But there are other users (like Dale?) that are really happy with it. It is really sad, because the specs were pretty amazing.

CS

Christian