Ritchey Chretien Questions

[Sarek]

I'm thoroughly enjoying my astrophptography journey so far and I'm starting to narrow down where my main interests lie going forward. I've been very happy with a lot of what I've been able to achieve with my current imaging scope (SW Evostar 72ED) but I would like to reach a bit deeper for those further away galaxies. To that end I've been looking at a Ritchey Chretien scope.  I've landed here on the basis that they are not too heavy for my HEQ5 Pro mount and won't take up too much space in the house as I like to always keep my set up fully assembled.

So my research has turned up a few questions which I'd be grateful for some advice on:

- Is it preferable to mount a guiding scope on top on the scope to help achieve dec balance or is there anoher solution if its mounted on the side using a finder shoe?

-  How important is a tilting adaptor? 

- Do I need a different bahtinov mask - can't find much on this but did find some refernces to a tri-bahtinov?

- How do people counter dew on these scopes? would a dew shield be of value?

- What do people think is the easiest way to collimate this type of scope? Ideally I'd want ti do it in daylight.

I've currently been looking at a StellaLyra 6" f/9 M-CRF and would be interested to hear opinions form those who have experience of that model or similar.

Thanks

 

[Paul M]

I recently bought a StellaLyra RC10.

My EQ6 Pro mount seems to be coping OK.

I was using a standard SkyWatcher finder for guiding but ive recently bought a second hand Borg 60ED for guiding. That'll be going on the top dovetail bar when I get round to it.

Here is my work in progress thread which also shows my collimation and dew control.

 

[Adreneline]

52 minutes ago, Sarek said:

Is it preferable to mount a guiding scope on top on the scope to help achieve dec balance or is there anoher solution if its mounted on the side using a finder shoe?

I mounted mine (SW-50ED) on the top and even then it was only just possible to balance the DEC with the supplied bottom rail. In the end I added an additional bottom rail (see image below).

54 minutes ago, Sarek said:

How important is a tilting adaptor? 

I upgraded the focus unit to a BDS which has a tilt compensation system built-in, not that I had to use it. The fitted focus unit was really not up to the task.

55 minutes ago, Sarek said:

Do I need a different bahtinov mask - can't find much on this but did find some refernces to a tri-bahtinov?

I found the spider worked just as well as a BM - especially combined with the autofocus in NINA/ASIair.

56 minutes ago, Sarek said:

How do people counter dew on these scopes? would a dew shield be of value?

I didn't have any problems but I am aware some folk use a shield.

56 minutes ago, Sarek said:

What do people think is the easiest way to collimate this type of scope?

I used an inexpensive laser collimator to get in the ball park and then refined it with a star test outside; it is fiddly but I got a really good result with a bit of perseverance.

58 minutes ago, Sarek said:

I've currently been looking at a StellaLyra 6"

Exactly the model I used to own. I sold it last year purely because I'm losing my grip! The old hands are not what they used to be. I got some great results in the time I owned it so it was a reluctant but necessary sale - before I dropped it  

Here's my setup just before I sold it. NOTE!! The counterweight hanging below the lower bar is just a coincidence - it is my CEM25 standing behind the AZEQ6. You can see the 'gold' extension bar I fitted below the RC lower vixen bar to help balance the OTA assembly. The third 'orange' bar is permanently attached to the AZEQ6 saddle clamp and has an ADM clamp attached for mounting the OTA.

HTH with your deliberations.

[Sarek]

Thank you Adreneline. That's incredibly helpful. 

I like the way you've mounted the ASI Air.  What is the white box next to it?

[Paul M]

23 minutes ago, Adreneline said:

The fitted focus unit was really not up to the task.

I'm easily pleased, honestly, so the box standard focuser on my RC10 will likely do for me. But I had trouble installing the reducer/flattener that was a recommended item with FLO. Had to spend more to get an unusual reducer that FLO identifiedand sourced. Apparently most RC owners upgrade the focuser so don't need that adapter! 

Perhaps I'll rethink the focuser if I ever get the impression that it's holding back my imaging! 

 

[Adreneline]

1 minute ago, Sarek said:

I like the way you've mounted the ASI Air.  What is the white box next to it?

It is a TP link wifi range extender which worked very well, however, in the end I opted for a hard-wired system - much more reliable.

Can I also point out the little mini-clamp at the front end of the 'gold' vixen bar. This was to provide extra reassurance when mounting the OTA - it prevented the whole lot from sliding out of the ADM clamp whilst I got things tightened up. I use this arrangement on both my RedCat and my Samyang - better safe than sorry!

[Adreneline]

2 minutes ago, Paul M said:

Perhaps I'll rethink the focuser if I ever get the impression that it's holding back my imaging! 

I made the mistake of looking at one of my lights in ASTAP and the tilt was crazy - by 'tilt' read 'droop'. With the BDS installed the 'droop' was virtually eliminated. Too much information is a dangerous thing - to the wallet   

[Paul M]

1 minute ago, Adreneline said:

I made the mistake of looking at one of my lights in ASTAP

I'm a big ASTAP fanboi and have looked at a few of my subs for tilt and flatness. Not been too bad. Certainly not my biggest issue at this juncture!

I need way more time under the stars with this scope to get to grips with it. Unfortunately, we're still under the drizzly, grey overcast of the cloudiest High pressure system in human history, pre-history and the Universe in general. 😢

So far I'm very pleased with my new toy. I'm going to remove the reducer for a while and go back to native f8 to track down a few small, insanely faint objects. The peripheral field won't be worrying me too much.

I think I'd have been as well using your collimation method. Laser to center the secondary and do the primary under the stars.

[Adreneline]

58 minutes ago, Paul M said:

I think I'd have been as well using your collimation method. Laser to center the secondary and do the primary under the stars.

I was happy with this - I know it's not perfect but for a £375 scope it wasn't too bad - taken without the flattener/reducer, L from an ASI1600MM and colour from a Canon 6D.

@Sarek - why do you need a BM when you've got spikes like this - it the focus is off you get tramlines instead of single lines.

 

[pipnina]

One factor to consider is that (as I understand) all of the affordable 6" and 8" RC scopes are rebrands of the GSO RC line. This means they all have a small flaw in the primary baffle (you can print or buy a print to pop over the baffle tube to fix it, but unless you do, flat calibration isn't as good.)

Another is cost. At the end of the day you're pitting these scopes against others in their price range.  The only type of scope I can think of that is cost competitive with the 6 & 8 inch RCs is a newtonian. But as you say despite being cheaper for more aperture, they are heavier and take up more storage space! Other compact options like those from celestron could work but do cost a lot more.

Then there's the collimation, which seemingly can be quite complicated on an RC as the focuser needs to point at the center of the secondary, but the secondary then needs to be tilted to bounce the laser back to the source in the focuser. This can apparently create a little dance that can take some doing. I forget the final step for getting the primary lined up but I recall it being easier than getting the secondary and focuser to behave!

Another factor is that RC scopes get better with size, their illumination and corrected diamater get larger with a bigger primary, and they can even go down to f6 above a certain size instead of the common f8 or even f9 for small ones. I think (?) the RC6 struggles to provide a well illuminated and corrected view for APS-C

Sadly I don't have direct experience, but as I understand this is some of the more prudent info when considering one.

[Sarek]

40 minutes ago, pipnina said:

One factor to consider is that (as I understand) all of the affordable 6" and 8" RC scopes are rebrands of the GSO RC line. This means they all have a small flaw in the primary baffle (you can print or buy a print to pop over the baffle tube to fix it, but unless you do, flat calibration isn't as good.)

Another is cost. At the end of the day you're pitting these scopes against others in their price range.  The only type of scope I can think of that is cost competitive with the 6 & 8 inch RCs is a newtonian. But as you say despite being cheaper for more aperture, they are heavier and take up more storage space! Other compact options like those from celestron could work but do cost a lot more.

Then there's the collimation, which seemingly can be quite complicated on an RC as the focuser needs to point at the center of the secondary, but the secondary then needs to be tilted to bounce the laser back to the source in the focuser. This can apparently create a little dance that can take some doing. I forget the final step for getting the primary lined up but I recall it being easier than getting the secondary and focuser to behave!

Another factor is that RC scopes get better with size, their illumination and corrected diamater get larger with a bigger primary, and they can even go down to f6 above a certain size instead of the common f8 or even f9 for small ones. I think (?) the RC6 struggles to provide a well illuminated and corrected view for APS-C

Sadly I don't have direct experience, but as I understand this is some of the more prudent info when considering one.

Thank you. Some good points to consider there.

I'm definitely going to research collimation thoroughly before making a decision. 

The model I'm looking at is f9. Initially I'll be using this with a Canon 700D but will probably upgrade to a ASI 533 at some point soon.

[Sarek]

1 hour ago, Adreneline said:

why do you need a BM when you've got spikes like this - it the focus is off you get tramlines instead of single lines.

Fair point! Showing my ignorance of this type of scope 🙂

[Adreneline]

2 hours ago, Sarek said:

The model I'm looking at is f9. Initially I'll be using this with a Canon 700D but will probably upgrade to a ASI 533 at some point soon.

2 hours ago, pipnina said:

I think (?) the RC6 struggles to provide a well illuminated and corrected view for APS-C

Just to add one thing - this is a single 120s frame taken with an unmodified Canon 6D (full frame) using the 6" RC at 1370 mm with no calibration frames - all I have done is apply a screen stretch and then a screen capture.

... and yet people claim you cannot use a full-frame sensor with a 6" RC - well I have done and it looks pretty good to me in terms of frame illumination / lack of vignetting.

I also used the RC with a mirrorless Canon M6 MkII (APS-C) sensor :

... this is a single uncalibrated frame - 120s - a simple screen stretch in PI as with the 6D - 1370 mm.

HTH

Adrian

 

Edited March 2, 2023 by Adreneline
Correction to f.l. of 1370 mm

[Clarkey]

Just to add to the comments / advice above. I have the RC8 version and for the money, it is excellent in my opinion. I actually purchased a 115mm triplet with a view to replacing the RC8, but I couldn't bring myself to do it. I am planning to put it on my HEQ5 with an OAG. Should just about be within the weight limit. I did replace the stock focuser with a BDS as it was not great and slipped slightly.

With regards to the flats problem - I have never had an issue. I think the later models have a slightly longer baffle tube. As for dew, I do use a dew shield and I have a secondary heater. I'm not sure if they are actually needed as I have used them from day 1.

Edit: Forgot to add - I think the flat field on the RC6 is smaller that the larger models. Although the illumination might be ok, you might want a flattener.

Edited March 2, 2023 by Clarkey

[Sarek]

31 minutes ago, Adreneline said:

.. and yet people claim you cannot use a full-frame sensor with a 6" RC - well I have done and it looks pretty good to me in terms of frame illumination / lack of vignetting.

I also used the RC with a mirrorless Canon M6 MkII (APS-C) sensor :

Those look good to me too. Reassuring - thank you

[Sarek]

8 minutes ago, Clarkey said:

Just to add to the comments / advice above. I have the RC8 version and for the money, it is excellent in my opinion. I actually purchased a 115mm triplet with a view to replacing the RC8, but I couldn't bring myself to do it. I am planning to put it on my HEQ5 with an OAG. Should just about be within the weight limit. I did replace the stock focuser with a BDS as it was not great and slipped slightly.

With regards to the flats problem - I have never had an issue. I think the later models have a slightly longer baffle tube. As for dew, I do use a dew shield and I have a secondary heater. I'm not sure if they are actually needed as I have used them from day 1.

Is the focuser you refer to? https://www.altairastro.com/diamond-steeltrack-2-focuser-bds-sc-for-schd-teleskopes-30mm-focus-travel--incl-adapter-for-7516-p.asp

[Adreneline]

38 minutes ago, Sarek said:

Is the focuser you refer to? https://www.altairastro.com/diamond-steeltrack-2-focuser-bds-sc-for-schd-teleskopes-30mm-focus-travel--incl-adapter-for-7516-p.asp

I ordered this one:

https://www.firstlightoptics.com/baader-diamond-steeltrack-focusers/baader-steeltrack-diamond-rt-for-refractors.html

with this:

https://www.firstlightoptics.com/baader-diamond-steeltrack-focusers/baader-steeltrack-diamond-rt-adapter-m90x1-for-refractors-gso-rc-scopes.html

Adrian

Edited March 2, 2023 by Adreneline

[Sarek]

28 minutes ago, Adreneline said:

I ordered this one:

https://www.firstlightoptics.com/baader-diamond-steeltrack-focusers/baader-steeltrack-diamond-rt-for-refractors.html

with this:

https://www.firstlightoptics.com/baader-diamond-steeltrack-focusers/baader-steeltrack-diamond-rt-adapter-m90x1-for-refractors-gso-rc-scopes.html

Adrian

Really helpful  - thank you!

I don't suppose you remember where you got your dew shield and secondary heater from?

 

[pipnina]

1 hour ago, Adreneline said:

Just to add one thing - this is a single 120s frame taken with an unmodified Canon 6D (full frame) using the 6" RC at 1370 mm with no calibration frames - all I have done is apply a screen stretch and then a screen capture.

 

... and yet people claim you cannot use a full-frame sensor with a 6" RC - well I have done and it looks pretty good to me in terms of frame illumination / lack of vignetting.

I also used the RC with a mirrorless Canon M6 MkII (APS-C) sensor :

 

... this is a single uncalibrated frame - 120s - a simple screen stretch in PI as with the 6D - 1370 mm.

HTH

Adrian

 

That definitely busts the myth I heard then!

Maybe the myth applies when these scopes are used with the 0.67x reducer/flattener...

 

This thread is making me want one of these now ha.

[Adreneline]

12 minutes ago, Sarek said:

Really helpful  - thank you!

I don't suppose you remember where you got your dew shield and secondary heater from?

 

I can honestly say I didn't have a problem with dew so I didn't use either - sorry, can't help with that one.  

[Clarkey]

23 hours ago, Sarek said:

I don't suppose you remember where you got your dew shield and secondary heater from?

The dew shield is a standard 8" Astro Essentials one. The secondary heater is one I made from a row of resistors which wraps round the secondary holder. Seems to work quite well, albeit a bit DIY.

[Sarek]

On 02/03/2023 at 19:14, pipnina said:

 

Then there's the collimation, which seemingly can be quite complicated on an RC as the focuser needs to point at the center of the secondary, but the secondary then needs to be tilted to bounce the laser back to the source in the focuser. This can apparently create a little dance that can take some doing. I forget the final step for getting the primary lined up but I recall it being easier than getting the secondary and focuser to behave!

 

Collimination is the one thing that's holding me back now. as I've had no experience of it before. I've now seen quite a few  different approaches - or least different tools being used.  I was thinking to start with a decent Cheshire, a tilt ring and basic laser.  I won't ask how difficult people think it is because I guess that's a bit subjective and varies with experience levels!

 

[ollypenrice]

In my view it's a mistake to think about the telescope in isolation from the camera. Ten or twelve years ago I felt that a 1 metre FL fell into a no man's land between a galaxy and a nebula imager.  Since then, though, pixels have become smaller and a 1 metre FL will now give you an image scale and resolution which will probably reach the limits of what your seeing will allow. Indeed, we took this recently at a FL of just 400mm. You'd want more for a dedicated galaxy scope but this shows how the need for long focal length has diminished.

https://ollypenrice.smugmug.com/Other/Galaxies/i-Sbc5zmk/A

With a metre I took this, and that's with pixels which were quite large by modern standards.

https://ollypenrice.smugmug.com/Other/Galaxies/i-d5BBZQp/A

What we don't know is your camera, but what we do know is that an image scale of around 1.3 to 1.5"pp  is likely to be optimal. That means that there may be an easier option than the very difficult RC. When sorted, they are good. They can, however, defeat some owners.

Olly

 

Edited March 4, 2023 by ollypenrice
False click

[Paul M]

Olly's points above got me thinking why I chose an RC.

I already had a 10" Newt but I'd always had a hankering for an axial optical train. In the fast 10"Newt the secondary never seemed to colimate just right. Being of a rough nature, it was still near enough for me 🙃 And it is a beast to handle.

When the StellaLyra Cassegrains came along I fell in love with the idea of imaging at f12. How I'd zoom in on the Universe...

But as Olly points out its way more complex than that!

So doing more research pointed me at the RC's and then seeing Es Reid give them a big thumbs up on some YouTube channel, I was hooked. My ASI071 camera just about falls within usability. Near to over sampling, or actually oversampling.

So although I did research imagescale and pixel size. I was undoubtedly led by my ❤️,  as always!

But anyway, it's a thing of beauty and I enjoy just using it. Still very early days. Only had 3 outings with it and got more changes to make. I do think that RC collimation is unnecessarily seen as a dark art. I think Newts are just as quirky.

Not being a pixel peeper does help but if I'm honest, I know there are better combinationsthan mine for imaging 🙈

[Sarek]

I'd be interested to hear what people think about this collimation guide for an RC. It seems to me the most straightforward and simple solution I've come across so far:

https://www.ancientphotonsastro.com/post/bench-collimating-a-gso-rc8