Ritchey Chretien, 8” or 10”?

I am thinking to get a RC scope as a complement to my 12cm refractor as an astrograph for smaller objects. But I cannot decide on 8” or 10”.

I have considered FOV, mirror cool-down time, cost, and all. These are not the key factors.

What I cannot choose from is aperture (resolution), and weight that I need to lift.

Obviously 10” is larger in aperture. If it weighted as much as 8”, it is a no-brainer choice. But it weighs twice as much as a 8”. And I do not have a dome or a shed, nor do I have the space for that in the backyard, not in the foreseeable future. Should I wait until I move? No.

My backyard is lower than the house, meaning that I have to walk down a flight of 10 or more stair cases to it. I cannot imagine that I move 18KG weight (scope, guide scope, camera and all) every time I need to do imaging. I used to use a Losmandy G11 mount that weighted 15KG one piece and I was inclined not to lift it unless I had to. Then I got a G11 that can be separated to RA and DEC, and I love it because each axis weights much less. I am not old. But I am not getting any younger tomorrow. Lifting weight is not my strength.

Very occasionally, I would go to a dark sky site for imaging. That also needs me to lift all the equipments.

On the other hand, keeping optics and camera under a 365 cover seems not to be a popular choice that many people like to do.

So I am leaning to a 8”. But I do not want to settle down on it. 10” may be a scope that I will settle down on and never need to upgrade. And 10” is about the maximum weight that my Losmandy G11 can handle.

That is all the rambling. Thank you for reading. I welcome any inputs, thoughts, ideas.

I think you answered your own question with the weight and bulk concerns. Get the 8" for now and if conditions change, sell it and buy a 10" in the future.

I have a 10RC and a C11EdgeHD. I love both OTA's but if I had to only have one I would choose the Celestron. F10 plus F7 with reducer and HyperStar F2 imaging and with a nice barlow do some respectable planetary imaging all in one OTA. I have seen great images with many of the GSO style RC's in 8" and larger apertures. I myself will be in the market for a 14"+ RC/CDK sized OTA in the near future only because I am moving to better skies that can feed the larger optics. In the end, an 8" RC will deliver, a 10"RC will deliver, and 8"/9.25" Celestron will deliver as well. My steel tube 10RC is heavy, the websites say the Carbon tube truss ota's are of similar weight but, of course, are open tube…

Good luck on your choice.

CS Tim

I would just leave the mount outside year round, that would eliminate a lot of the setup and you won't have to polar align for every session. As to choosing an 8 or 10 OTA, yes, weight is a concern for both you and the mount but I would look at it more in terms of focal length. How good a fit is 1600mm verses 2000mm for your pixel scale and objects you want to image? Is your guiding and seeing up to the task? I guess I should also say are your collimation skills up to the task of an RC? I'm sure you've read the same horror stories that I have here on the bin. I have the impression that an RC can be a bear to get perfectly adjusted. It's not nearly as simple as a Newtonian and a lot of people have trouble with even that.

I had an 8" GSO RC for over a decade. Good scope, but you would most certainly want a moonlite or FT on it, not the stock GSO focuser for imaging. The problem with the 6 and 8 is that the focuser/camera hangs off the primary, so its prone to some issues. Not sure if the 10 has the same design. Some of the higher end 10'+ RCs have a better design for carrying the weight.

One issue is to consider how to keep dew off the secondary - didn't happen a lot, but when it did it was a pain. I had a dew heater attached, but then it made the diffraction spikes ugly on one vein.

My other major gripe with it was for long-exposure times on DSO, it was very prone to internal reflections under my Bortle 4-6 skies I tend to image in. I've had a much easier time with a 152 TMB Refractor, and zero of the above issues now. More expensive, and heavier, with a bigger moment arm, so less portable and harder on the mount, but otherwise it was by far the best imaging choice I ever made.

Hi
It seems like your situation is very similar to mine, so in short, I bought an 8” RC Ioptron. I use it for galaxies and planetary nebulae. I am using the Apex reducer and a moonlit focuser since the stock focuser is not good. For wide field I have the RASA 8.

I use my gear in my light polluted backyard or I travel to darker places. So I need something that it is not too heavy and easy to transport.

I first bought a 10” RC steel tube and the full rig was a bit more than 50 lbs, so over time, I used less and less. Cooling time was longer so it was a problem for one night AP.
I sold it and bought the 8”RC. To collimate I use the OCal and it seems to make collimation easy.

I have a 127mm refractor which I like, but it is difficult to transport due to the length and you need extension in your mount so it does not hit the leg and mostly if you use a filter wheel

I have a dew heather for the secondary, but I found ou that a dew shield is enough.

Another option could be the 8” Celestron EDGE which is a bit more expensive and the reducer costs much more too.

I have both, but I recommand a RC10 , truss version if you can because it has a desolidarised focuser from the primary that is not true with all tube version (6,8,10 and 12).

Truss is Easier to colimate (focuser tilt ring decoupled from primary miror and you have direct access to the baffle so it is easy to remove (it is necessary to colimate)) and the pictures are far more detailled than with a RC8.

Now with a RC10 (or 8) you need to consider the following :
- a decent tool to do the colimation
- add a decent focuser to replace the stock one
- a tilt ring for a RC8 (or other tube version)
- motorize the focuser
- add a focal reducer , at minima a CCD47 or CCDt67 , the best is a reducer flatener as the Riccardi or Ts-optics
Once you add this you have added almost half the price the RC with miscellaneous equipment.

- RC10 is 15kg alone, with optical train the total weigt of the OTA is 18 to 21kg.

-Regarding the collimation: it is not so complicated to acheive, but it requires some method to follow in order not to finish with a totally uncollimated scope.

The RC design is one I strongly champion. I had an RC8 for 3 years, but upgraded to a RC12 - which is permanently mounted in my observatory. This is my workhorse telescope and I am pretty happy with the images I get off it - all (good or bad) posted here on AB.

The stability of collimation and ease of access to instrumentation can't be beaten.

A few things to note with RCs

The field is not flat. Noticable for APSC sensor and much worse for full frame. At its native f-ratio, you will also likely need a reducer, and there are some very good 0.8x reducer/flatteners out there., Strongly recommend you buy one.

The secondary can dew up. And there are a few purpose built dew heaters for PCs out there.

The primary mirror baffle is too short and stray light can caused real issues. Despite GSO claiming this is fixed in the latest models, my own experience with a 2024 model demonstrates that it is not. 3D-baffle extenders can be purchased.

8-inch or 10-inch? My 12-inch truss RC is surprisingly easy to lift. I wouldn't want to do it every night but it is possible. The RC8 I owned was very light, so I suspect that you wouldn't have too much of a problem with an RC10. Compared to the mount you would need, I suspect it is a breeze.

If you are really into the hobby, I would always recommend to go as big as you can afford.

Have fun!

Brian

It depends in my opinion. Out of the box (and bought new) maybe the EdgeHD might be a good option because you can more or less start with it right of the bat.

The GSO focuser of the RC8/10 sucks and for serious photography you will have to switch it for something better. With a new focuser you will need a tilter plate. TS offers one for the M117 flange but it is low quality and catches stray light like crazy. I had to tape my Tilter all around to fix this.

I had a steel tube RC10 and later switched to a custom made carbon RC10 with a starlight instruments focuser. I did not know until then that Starlight Instruments offers a tiltable and rotatable M117 Adapter for the 2,5 inch focuser. In my eyes this is the perfect match for the RC10. If you need bigger threads than M63, I would take an Esatto or Peg. Astro Prodigy.

Collimation is fine, with a collimation laser (that itself can be collimated, too) and a backlit cheshire or similiar you can get 90% done in the day and finish off at the star in the evening. I tried the OCAL, but never got it right with it so I sold it.

If you like to fiddle/upgrade your stuff -> RC10
If not, you may be better off with the EdgeHD.

If you are thinking about buying used, then I would definetly go for the RC10. In my country they seem to sell low, so both my RC10s were very cheap.

The secondary can dew up. And there are a few purpose built dew heaters for PCs out there.

Oh yes, I learned that the hard way. But I can recommend the DeepSkyDad Dew Heater band for the Newton/RCs. You can hide the heater behind the secondary and the cables are thin enough to be hidden by the spider vanes. And the customer support is great, too (Two dew heaters were dead on arrival).

Regards

As some mentioned but not as the point it actually is: 10” truss tube construction is better with its decoupled focuser, open design but -specially for your use scenario- muuuuch easier to carry as it is so much easier to grab.

8-11 kg in a solid tube won’t be much easier to carry than a 15-18kg truss tube you can actually grab perfectly with both hands as it has handles.

the normal 8-10-etc (no truss tube)… carrying method is somewhat similar to carry a big fat baby.

I was dreaming about RC in the past but it was a dream because of the price of RC, and in fact my most dream limit about it was 8", that just all changed immediately once i saw a tempo quick offer of 10" RC truss tube, i didn't have a mount for it, not a high end model, maybe needs accessories and changing focuser too, all what i did is just click the order and VIOLA, it is with me, what happened after that just a history, i never took out that scope yet from the shipping box, but the quick look and i am fallen in love, beautiful design truss RC, in fact i was able to carry the box alone, yes, it is heavy, but not a DEAD heavy, and i can carry it with the truss bars if i want or added a carry handle but that will add slight weight, but i NEVER regret the purchase, and that RC offer is gone maybe forever, and i never look about having 8" because it is less weight, i always upgrade, never downgrade, so going with 10" from beginning and the truss design in particular was the best decision i made, now in future i can buy a mount that can carry 10" RC and more and never look back, i can wait all my life to use, other buy to use it now immediately so they decide in hurry and change later in future, good for them, and good for me i wasn't like them.

Just to add, the weight of the scope as it is is about 35 LB, and i won't add too much accessories so i could be around 42-45LB at best, so in future i will buy a mount that can at least handle 60LB, going with 50LB capacity mount isn't a future proof and long lasting, 80LB payload mount is even better if i can afford it, but the scope of 35LB isn't a big deal really, and 10" is a nice sweet spot aperture as well.

Brian Boyle:
The secondary can dew up. And there are a few purpose built dew heaters for PCs out there.

Personnally I use piece of sport carpet to extend the tube. I have never experimented dew with that even when I have 95% humidity in the air winter and early spring time. So no need of a complex expensive heater.

below my RC10 tube version with the extension (it is black inside face ). At the end of nigth the metal tube and external carpet are all wett but nothing on the mirrors. Best solution against dew in my opinion.

Olivier Constans:
Brian Boyle:
The secondary can dew up. And there are a few purpose built dew heaters for PCs out there.

Personnally I use piece of sport carpet to extend the tube. I have never experimented dew with that even when I have 95% humidity in the air winter and early spring time. So no need of a complex expensive heater.

below my RC10 tube version with the extension (it is black inside face ). At the end of nigth the metal tube and external carpet are all wett but nothing on the mirrors. Best solution against dew in my opinion.

How to do that with an open truss design scope?

I did use an Astrozap dew shield on my RC10s which did not help in the slightest unfortunately, still dewed up (pretty fast actually). And my scope acted as a sail which was a dealbreaker for me as an mobile astrophotographer. Once I went the heater route I never went back.

My whole setup can be covered in ice/dew but my mirrors don't care. For the primary I use a heater band on the focuser which transmits the heat via the primary mirror cell. And yes my primary suffered from dew also, especially in zenith.

I attached some images of how my secondary mirror is set up. It holds with one cable tie and some fabric tape (reducing stray light). I would not call this complex.

A C 9.25 Edge is the way to go in my opinion. I had several 8"-10" cats, one 10" RC along with several very nice refractors over the years. My new C9.25 Edge HD outperforms them all.

Tareq Abdulla:
Olivier Constans:
Brian Boyle:
The secondary can dew up. And there are a few purpose built dew heaters for PCs out there.

Personnally I use piece of sport carpet to extend the tube. I have never experimented dew with that even when I have 95% humidity in the air winter and early spring time. So no need of a complex expensive heater.

below my RC10 tube version with the extension (it is black inside face ). At the end of nigth the metal tube and external carpet are all wett but nothing on the mirrors. Best solution against dew in my opinion.

How to do that with an open truss design scope?

This is the same, I will take a picture end this week , I don't have one at that moment. The difference is the one of the tube was closed and attached to form a tube , the one of the RC10 can be opened . I have small area not totally closed but it works well, new dew. I use some scratch ribon (velcro) I bougth on amazon so it can be done at the correct size.

On the other hand, keeping optics and camera under a 365 cover seems not to be a popular choice that many people like to do.

@ariesram

This is what I do now since almost 3 years. I remove the camera when not imaging several days in a row, but rest of the setup stays outside. Your back may like you having a look at this post on my strategy to keep everything in condition under (two) covers:
https://www.astrobin.com/forum/c/astrophotography/equipment/long-term-outdoor-cover-storage-thoughts-after-18-months/

Clear skies

Patrice

Hi,
i was having a similar dilemma couple yrs ago.

i started with 8” newton on EQ5 for about a year and
then i had a chance to upgrade to 10” newton.
i was considering 50% brightness.

i went for that. i had to upgrade to eq6 but i don’t regret at all.

After those yrs of using I’ll tell you:
1) 50%+ brightness is good
2) be careful it is significantly heavier. i wouldn’t go for that if i would be physically small or when being old. it’s really heavy.

vlad

Olivier Constans:
Tareq Abdulla:
Olivier Constans:
Brian Boyle:
The secondary can dew up. And there are a few purpose built dew heaters for PCs out there.

Personnally I use piece of sport carpet to extend the tube. I have never experimented dew with that even when I have 95% humidity in the air winter and early spring time. So no need of a complex expensive heater.

below my RC10 tube version with the extension (it is black inside face ). At the end of nigth the metal tube and external carpet are all wett but nothing on the mirrors. Best solution against dew in my opinion.

How to do that with an open truss design scope?

This is the same, I will take a picture end this week , I don't have one at that moment. The difference is the one of the tube was closed and attached to form a tube , the one of the RC10 can be opened . I have small area not totally closed but it works well, new dew. I use some scratch ribon (velcro) I bougth on amazon so it can be done at the correct size.

This is how is made my anti dew extension that works also for the RC10 truss. I have never got any dew on the secondary with this. I can easily adapt to the tube or truss with the way I have done it.

Would I be better off choosing

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