To RC or Newtonian: That is the question.

Topic starter

Sep 1, 2023

After 2.5 years owning the same telescope(s)/mount combo, I have now saved up enough to purchase new mount and telescope which I would plan to use for a much longer-term. As well as doing my own AP, I also have a small (retirement) business opening my observatory to visitors, who participate in AP/astronomy sessions.

I current own a GSO RC8 and TS Hypergraph8. Both of which are used with a full frame sensor [ASI6200]. I love both, but both have their drawbacks. As a fast Netwonian, the Hypergraph is challenging to collimate, and the location of the camera is in an awkward position. The RC is much easier to use, but it is slow at f/8. [Given that I can bin - I think to think of slow and fast more in terms of narrow- and wide-field]

For public viewing, I would like something that could give me recognisable data on targets in a relatively short time, but also at a decent focal length if I ever wanted to the image the solar system.

Given my budget [about USD 5000 each for telescope and mount], should I go with a RC or Newtonian design? [I plan to replace my EQ6-R Pro with a CQ350.]

I have seen TS offer purpose-built 10inch astrographs (with correction/flattening over a full-frames sensor) in both RC (f6.4) and Netwtowian (f4.6) design. The Newtonian is 10% less expensive, but I wouldn't want to make the choice simply on cost if image quality/useability was to suffer.

Initially I thought RC would be the way to go, but lately i am not so sure. There appears to be a lot more images with Newts on AB.

So, I am appealing to the wisdom of crowds [aka my Astrobin friends] to give me some guidance here.

Great telescopes though they undoubtedly are, I have dismissed RASA [too short focal length], Celestron Edge [too long], Planewave [too expensive] and anything above 250mm in diameter [too big for the observatory and too expensive with full frame correction/reduction].

Many thanks

Brian

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Pistachio_Enjoyer

Sep 1, 2023

Depends on what focal length you want to image at. I own and use an RC 10 Truss-Tube, which images at a focal length of 2 meters (without the reducer, just the 1x flattener). If that is too much for your taste, consider the newt instead, preferably the f/4 version which has a 1 meter focal length. The CQ350 mount would be able to handle either one without trouble I'd imagine (no personal experience here as I use an EQ8). The newt would be easy to collimate, though you'd have to check on it more often I'd imagine, while the opposite is true for the RC.

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Rafał Szwejkowski

IOTD Staff

Sep 1, 2023

To me the camera position on Newtons is just a mental block, and also their length/size/balancing past 8" . Physically I feel more comfortable with RCs. I'm also a big fan of small objects and for such RC gives you a better scale.

On the other hand I enjoy other's work with Newtonians very much. So in the end I'd ask myself: do I want to photograph something more like Stephan's Quintet or do I want to have an option to shoot some wide nebulae like the Shark or Rosette? Newton will give you the latter option (bit more versatile), RC will excel at the former.

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Oscar

Sep 1, 2023 · Edited: Sep 1, 2023

I agree with Rafal, you'll get the smaller objects like galaxies better with an RC. Things like diffuse or dark nebula will mostly be better with newts.

vercastro

Sep 1, 2023 · Edited: Sep 1, 2023

Do you want easy/fast but more maintenance? Newt.

Do you want focal length and potential collimation rabbit holes but low maintenance? RC.

A note on RCs. The Truss version are vastly better mechanically than the tube versions. This makes collimation a lot easier. You can get reducers for them that push them down to low f/5 ish.

And how about another option? Check out the Sharpstar SCA260. It's more premium than the GSO based RCs, faster, and comes native with a corrector. But it's not nearly as expensive as CDK.

Another thing, it's really hard to get a telescope that does both DSO and planetary well. You end up making compromises if you try. It's better to prioritize one.

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Pistachio_Enjoyer

Sep 1, 2023

Do you want easy/fast but more maintenance? Newt.

Do you want focal length and potential collimation rabbit holes but low maintenance? RC.

A note on RCs. The Truss version are vastly better mechanically than the tube versions. This makes collimation a lot easier. You can get reducers for them that push them down to low f/5 ish.

And how about another option? Check out the Sharpstar SCA260. It's more premium than the GSO based RCs, faster, and comes native with a corrector. But it's not nearly as expensive as CDK.

Another thing, it's really hard to get a telescope that does both DSO and planetary well. You end up making compromises if you try. It's better to prioritize one.

Only real mechanical difference I know of is that the truss-tube models have a built-in tilt plate and have the focuser decoupled from the primary mirror, while the closed-tube models do not. I'm also not sure that the .67x reducer you're alluding to (only one that can get near f/5) would work with a full-frame camera. There are specific .8x reducers however for the truss-tube rc scopes.

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vercastro

Sep 1, 2023

Only real mechanical difference I know of is that the truss-tube models have a built-in tilt plate and have the focuser decoupled from the primary mirror, while the closed-tube models do not. I'm also not sure that the .67x reducer you're alluding to (only one that can get near f/5) would work with a full-frame camera. There are specific .8x reducers however for the truss-tube rc scopes.

Starizona ApexED would be what you'd want. Although they do only rate to APS-C. It might still be acceptable beyond they depending on your personal standards.

Björn Arnold

Sep 1, 2023

I‘m not sure why people are obsessed with reducers. If your camera allows for sufficient FOV, just go without reducer.

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Pistachio_Enjoyer

Sep 1, 2023

I‘m not sure why people are obsessed with reducers. If your camera allows for sufficient FOV, just go without reducer.

Variety, I suppose. Might get a .8x reducer for my scope in the future.

Ruediger

Sep 1, 2023 · Edited: Sep 1, 2023

I‘m not sure why people are obsessed with reducers. If your camera allows for sufficient FOV, just go without reducer.

Hello Björn,
I share your opinion. A reducer is only the last resort if I have the wrong telescope for the desired target. A reducer is an additionnel optical component, which always reduces the image quality. It should be avoided whenever possible. Actually it converts your scope into something it is not designed for and you degrade its performance.

CS
Rüdiger

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Björn Arnold

Sep 1, 2023

Variety, I suppose. Might get a .8x reducer for my scope in the future.

But for what purpose? It makes sense if you need to vary FOV but if resolution is the issue, binning is the way to go.
Otherwise, adding a reducer adds only additional variables to be controlled instead of actually solving an issue. Especially for a well corrected RC.

Pistachio_Enjoyer

Sep 1, 2023 · Edited: Sep 1, 2023

But for what purpose? It makes sense if you need to vary FOV but if resolution is the issue, binning is the way to go.
Otherwise, adding a reducer adds only additional variables to be controlled instead of actually solving an issue. Especially for a well corrected RC.

As you mentioned, mainly FOV. It would make sense for a few targets, say for instance M33 which would fit very well with a full frame sensor using a .8x corrector/reducer.

Michael Ring

Sep 1, 2023

For me there would be 2 choices:

10“ newt from telescopes Express because it is fast and well built to hold collimating even when transporting it. I own a 8“ version that I bought used and was very happy with it until I found a used Lacerta 10“ Newt which I just got properly working and I am deeply in love with this new toy since the day I own it. The 10“ give this little extra in resolution. However, I am not sure if they allow you to use full frame cameras, I thing I read that there is a vignetting issue but I may be wrong and for 10“ you are fine…

The other choice would be the Edge HD 9.25, if possible together with hyperstar.

You can use it for Planets, Deep Sky with Reducer @f7 and with the Hyperstar you have 525mm at F2.2, so it collects photons very fast. For public viewing the option to use a Barlow for visual of planets is also nice. Switching from long focallength to Hyperstar is easy, last time I switched to long focallength I did not even need to work on collimation. It also overall holds collimation very well and I move it quite a lot.

Hyperstar with a full frame will not be that good because the camera is a little big but it could be worth a try.

Michael

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Antonio Parisi

Sep 1, 2023 · Edited: Sep 1, 2023

How about a Quattro 250 ST, it is not a Takahashi cca-250 but there are very nice pictures around and collimation is not a pain.

Focal Length 1000mm
F/Ratio f/4
Highest Practical Power508x
Finder Scope8x50
Focuser Diameter2" (50.8mm) Dual-Speed 10:1 Linear Power Focuser
Tube Weight15.1 kg

there is also a more practical 200st half the weight almost.

regards,
Antonio

SemiPro

IOTD Staff

Sep 1, 2023

Brian Boyle:
For public viewing, I would like something that could give me recognisable data on targets in a relatively short time, but also at a decent focal length if I ever wanted to the image the solar system.

You might be asking too much from one scope. The Newtonian would be great for public viewing, but the RC will be great for focal length. Although a Newtonian that big will still give you 1100mm+ of focal length (unless I screwed up the math) which can do some real solid work with small targets.

Mike Sample

Sep 1, 2023

I‘m not sure why people are obsessed with reducers.

Reducers address two issues. 1) is the framing your region of interest, and 2) is OTA speed.

I use them frequently. Achieving a wide FOV without changing optical tubes may be easier on the back and not require mosaic to capture the region.

The scope speed is very important for me. The faster scope permits shorter exposure times. That provides more image detail for a given imaging time.

Clear skies, Mike

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Björn Arnold

Sep 1, 2023

Mike Sample:
Reducers address two issues. 1) is the framing your region of interest, and 2) is OTA speed.

I use them frequently. Achieving a wide FOV without changing optical tubes may be easier on the back and not require mosaic to capture the region.

The scope speed is very important for me. The faster scope permits shorter exposure times. That provides more image detail for a given imaging time.

Clear skies, Mike

For FOV, that’s an option, as I mentioned earlier but not for speed.
If you’re 1x1 binning is already ideally sampling, getting faster - no matter how - will reduce resolution. As for the typical case, where long FLs lead to oversampling, binning is much easier, doesn’t involve additional glass, avoids fiddling with correct back focal distance to reducer, avoids adding optics that have risk of deteriorating image quality (the RC will likely be well corrected if of decent quality), less vignetting.

CS, Björn

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Ruediger

Sep 1, 2023 · Edited: Sep 1, 2023

Mike Sample:
I‘m not sure why people are obsessed with reducers.

Reducers address two issues. 1) is the framing your region of interest, and 2) is OTA speed.

I use them frequently. Achieving a wide FOV without changing optical tubes may be easier on the back and not require mosaic to capture the region.

The scope speed is very important for me. The faster scope permits shorter exposure times. That provides more image detail for a given imaging time.

Clear skies, Mike

Well, this is a quite common and repeated misunderstanding. A telescope does not get „faster“. You only collect the same photons of the object on fewer pixels - at the cost of resolution - as Björn also stated.
As a result you suffer from distortion and stronger vignetting. I often see as a consequence, that images taken with a reducer (without need, only it is „faster“) being cropped due to trouble with gradients - esp. when working with full frame.

Telescopes get only faster, when they are slipping of the mount, getting dropped from above or transported…. 🤣

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Mike Sample

Sep 1, 2023

Brian Boyle:
For public viewing,

Looking at the Hypergraph product description, I think your complaints around "the location of the camera is in an awkward position" is when you are doing visual. Would live stacking and stretch be a reasonable consideration when doing public viewing on DSO targets. I would buy a One Shot Color (OSC) camera rather than a new OTA, and find the software tools to live stack and stretch. Displaying the image on a big computer monitor would enable multi-people simultaneously viewing.

Your imaging projects might beg for a new OTA, but I look at the targets which are difficult with my current equipment when shopping for an OTA. Then I buy for that target class. You currently don't have a focal length in the 2 meter range, nor much less than 340 mm. Those a not likely the same OTA.

Clear Skies, Mike

Björn Arnold

Sep 1, 2023

@Brian Boyle, what do you mean with public viewing in detail? Do you want to point your camera at a specific target and show people an object through live stacking?

Björn

Mike Sample

Sep 1, 2023

Björn@Brian Boyle, what do you mean with public viewing in detail? Do you want to point your camera at a specific target and show people an object through live stacking?

Björn

That is my thought. Does that sound reasonable to you? The target would need to be low magnitude and a size that 320 mm focal length would offer enough magnification.

Mike

Brian Boyle

Topic starter

Sep 2, 2023

Really helpful responses. The public viewing is imaging via live stacking…
Agree with comments on reducers - it is really a field-of-view issue - but for an RC with a FF sensor you do need correction for the curved field. So there is glass there anyway.
It is also helpful to see people so evenly split on the issue (at the moment the poll is 50:50). I had expected to see a heavy majority in favour of the Newt - particularly given the popularity of this design on AB.
This reassures me that an RC is not a fringe choice, and there are been a couple of suggestions for scopes that I had not been aware of.
Thank you.
Brian

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Brian Boyle

Topic starter

Sep 2, 2023

Also interesting comments on the ease of use. I have found collimation with an RC to be relativly straightforward [using a Takahashi and the 1ary baffle unscrewed). In contrast my Newt Hypergraph is an absolute beast to collimate. This might just be me of course - and the difference in native focal length. Also the RC appears to hold collimation better, but again this could be a collimation issue [or that I am not as fussy as I should be].

Really I am looking for a "set and forget" collimation that can be done during daytime [with check on defocussed star in twilight] perhaps once a month during full moon, for a telescope permanently mounted on a pier. My gut feel tells me that an RC is more up to this task, but happy for others to tell me they have the same experience with their Newts.

BTW, the Skywatcher Quattros look good, but I think the 2inch focusser will limit the field to a APS-C sized sensor. TS do a specialised f/4 - f4.6 with the coma corrector - and 3" focussed which appear to have a corrected image circule which fits an FF sensor.

Matthew Proulx

Sep 2, 2023

I would go with RC every time. I have owned an 8" quatto, a GSO 10" F4 truss and a 12" ONTC F4 and they were all shoddy design, yes even the ONTC was plagued with the typical newtonian mirror slop due to cell design. I will never own a newtonian again unless I was to build it myself, noone can change my mind on that. I also have owned several RC8, an RC10 and an RC12 and still currently use the RCs. Never had a single bad one. The 12" doesn't even need a flattener with an APS-C. They just work out of the box. Collimation is easy when you've played with them like I have.

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Brian Boyle

Topic starter

Sep 2, 2023

Matthew Proulx:
I would go with RC every time. I have owned an 8" quatto, a GSO 10" F4 truss and a 12" ONTC F4 and they were all shoddy design, yes even the ONTC was plagued with the typical newtonian mirror slop due to cell design. I will never own a newtonian again unless I was to build it myself, noone can change my mind on that. I also have owned several RC8, an RC10 and an RC12 and still currently use the RCs. Never had a single bad one. The 12" doesn't even need a flattener with an APS-C. They just work out of the box. Collimation is easy when you've played with them like I have.

Hi Matthew,

That is great feedback. I hadn't imagined that there would be this stark a contrast, but your experience is really helpful.

I am only sorry you had to go through the Newtonian trials and tribulations.

CS Brian

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Which telescope would you recommend?