Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

StellaLyra Classical Cassegrain & Ritchey-Chrétien Telescopes


Recommended Posts

11 hours ago, globular said:

Vlaiv, if you redo the maths with manufacturers 200mm and 60mm with the claimed 7.34" stepped down and solve for the mirror distance you get 406.9mm.
This is pretty close to Johninderby's approx. measurement of 410.
So doesn't this uphold, rather than discredit, the reviews stepdown claim?

Problem is that even small variations change things significantly. John measured primary to be 204mm and that is more in line with 8" = 203.2mm.

I think we would need full specs to be able to do the math - otherwise it will always be few mm here and few mm there that change the picture.

I wonder if we could devise a test that can be easily carried by someone that would solve this.

I know how I would test it, but it requires a bit of gear that most people interested in this scope don't have - camera and artificial star (can be done on a real star but artificial will give better results I think). One needs just to create bunch of aperture masks out of cardboard in 1mm steps and shoot single constant source of light and measure how much light was collected.

At some point, there will be change in intensity between different aperture masks and that will tell us how much primary is stopped down by secondary.

  • Like 1
Link to post
Share on other sites
  • Replies 328
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

You can now buy Classical Cassegrain & Ritchey-Chrétien telescopes at FLO 🙂  StellaLyra Classical Cassegrain & Ritchey-Chrétien telescopes Manufactured by Guan Sheng Optical in Taiwa

Lyra meet Mira. 😁

Just pulled the trigger on a Stellalyra 6” f12 CC. Ooops!   Now to decide which scope must go to make space for it? 🤔

Posted Images

What I would like to know is how accurate the figure is on the mirrors as this will ultimately restrict the image quality when the seeing is good.  

It did also occur to me to ask if the secondary was center spotted to simplify collimation. If it was it would make a clear usp for them over similar clones in addition to FLO's customer service.

Regards Andrew 

Link to post
Share on other sites

This is all very exciting John. I am really looking forward to the unboxing and first light. Looking at the 6CC I assume that the Crayford focuser can be rotated. Plus a favour for when you view Mars - I would be interested in your comparison to your 80mm f/10 StellarMira.

  • Like 2
Link to post
Share on other sites
37 minutes ago, andrew s said:

What I would like to know is how accurate the figure is on the mirrors as this will ultimately restrict the image quality when the seeing is good.  

It did also occur to me to ask if the secondary was center spotted to simplify collimation. If it was it would make a clear usp for them over similar clones in addition to FLO's customer service.

Regards Andrew 

Yes the secondary mirror is centre spotted. 

The mirrors are excellent. Compared to a Skymax 180 the image holds up better at high magnification so very high magnification is usable in good seeing.

C2D57983-368A-45B2-9878-C870FE49014A.jpeg

Edited by johninderby
  • Thanks 2
Link to post
Share on other sites
15 hours ago, John said:

I'm feeling rather awkward now that a review that I posted because I thought it might help a prospective purchaser has resulted in a rather technical discussion in this thread that FLO started announcing these new scopes.

Perhaps a mod might snip out some of this and stick it into the scopes discussion section which might be a more apt place for it ?

Apologies to FLO.

No problem and no need for a snip 🙂 

Reviews on other forums are interesting but we are more interested in new reviews of StellaLyra telescopes. Reviews posted by owners here at SGL. Sales are good so I don't think it will be long. 

At FLO our understanding of these designs comes largely from Ian King. Ian is a colleague but prior to him joining FLO he sold (through his website, Ian King Imaging) these designs for around a decade so has plenty of knowledge and experience. 

Steve 

  • Like 2
  • Thanks 1
Link to post
Share on other sites
4 hours ago, andrew s said:

What I would like to know is how accurate the figure is on the mirrors as this will ultimately restrict the image quality when the seeing is good.  

It did also occur to me to ask if the secondary was center spotted to simplify collimation. If it was it would make a clear usp for them over similar clones in addition to FLO's customer service.

Regards Andrew 

I often wonder how accurate the centre spots are, especially as they're often such a key part of collimation. For a big newtonian primary it must be quite difficult to establish precisely where it is (the true optical centre, not the centre of the "slab"). For a small secondary, as long as you're prepared to remove it, it should be fairly easy to find on a hobby-sized lathe.

Edited by Captain Magenta
Link to post
Share on other sites
19 minutes ago, Captain Magenta said:

I often wonder how accurate the centre spots are, especially as they're often such a key part of collimation. For a big newtonian primary it must be quite difficult to establish precisely where it is (the true optical centre, not the centre of the "slab"). For a small secondary, as long as you're prepared to remove it, it should be fairly easy to find on a hobby-sized lathe.

Interesting @Captain Magenta. For an imaging Newtonian you only have one element with an unique optical axis as the secondary and focuser don't a unique optical axis only mechanical ones .  They may however tilt or de-center the image and possible lead to vignetting. Adding an eyepiece adds a second optical axis. So I suspect unless the error is large it probably only makes a second order error. (How any people check the focuser travels along the optic axis?)

For a Cassigrain both mirrors have unique optic axis and they are very sensitive to misalignment. Worse still the primary has a whole so no chance of spotting its center!

Dipite the waffle I don't have any figures!

Regards Andrew 

 

  • Like 1
Link to post
Share on other sites

First impressions and a few pics now I've unboxed the Stella Lyra 8" RC, mounted it, checked collimation etc 

Fit and finish appears generally very good, It's a very solid well finished scope and feels more premium than the price suggests. The only minor faults are a single bolt missing from the finder shoe (missing in action somewhere other than the packaging) and a fleck of paint? on the secondary which wont effect anything (This didn't cost Tak Mewlon money!). I love the piano black and the Stella Lyra logo not only on the OTA but on the dovetail and focuser too, nice touch! The focuser is pretty good considering the price point, there are no rough spots and it's fully rotatable, but you obviously get smoother if you spend more on a third party higher end unit. 

One concern was not being able to switch the Losmandy and Vixen rails around to fit mounts with only a Vixen saddle, but thankfully the screw positions are the same top and bottom of the OTA so it was an easy job to switch them around. Come to think of it, the spec of paint on the secondary could have been the result of me doing this!? The rails are on par with ADM quality which was a nice surprise! The Orion GSO version comes with two finder shoes whereas the Stella Lyra comes with one. The Orion may well be a tad bit more expensive though.  

The primary mirror looks mint and super reflective, and the external paint job looks good. Baffling excellent, it's very dark in there! The back focus extension rings are very nicely machined with lovely threads. I checked collimation using my Cheshire and self centring adaptor and both the primary and secondary were quite far out which isn't surprising considering the distance the optics have travelled. I made some adjustments and the collimation screws appear to be spring loaded, smooth and accurate. Making adjustments was intuitive and I soon got the secondary and primary lined up according to the Cheshire. I needed to over correct the primary to make up for a bit of malalignment caused by the focuser I'm guessing? so I may need a third party tilt plate? of course I need to properly star test before deciding on further action there.

The dust cap is quite tight and can be tricky to get on and off, but I prefer that to too loose. The 2" to 1.25" adaptor on the focuser has a brass compression ring so it doesn't mar accessories, max points for that one, I really don't like pointy scratchy set screws. 

I couldn't see any paper work with the scope but pretty much everything you need to know is online anyway so happy to save a fraction of a tree lol The secondary obstruction isn't as big as I had imagined or worried about, so it might even be ok for a spot of visual once I've got the collimation spot on. 

That's it for now. I of course recorded a video whilst I was doing all this so that will follow. Here's some pics :) (I Know, I know, I'm under mounting it for DSO imaging but we'll see how that goes)

 

IMG_20201013_131250104.jpg

IMG_20201013_131326623.jpg

IMG_20201013_131337838.jpg

Edited by Lockie
  • Like 6
  • Thanks 1
Link to post
Share on other sites
5 minutes ago, Lockie said:

The only minor faults are a single bolt missing from the finder shoe

Nice write up Chris!  I only had one bolt and (what looked like) a grub screw on my StellaLyra RC 6" so not sure if that's a standard thing.

Edited by geeklee
  • Like 1
Link to post
Share on other sites
1 minute ago, geeklee said:

Nice write up Chris!  I only had one bolt and a grub screw on my StellaLyra RC 6" so not sure if that's a standard thing.

Thanks, and that's interesting! There is a second threaded hole for a second screw but I'm sure one will work just fine. Maybe that's how it's meant to be :)

  • Like 1
Link to post
Share on other sites
30 minutes ago, Lockie said:

I of course recorded a video whilst I was doing all this so that will follow.

I've wine and snacks at the ready Chris 🙂

Looks a lovely scope. Enjoy!

Edited by JeremyS
  • Haha 2
Link to post
Share on other sites
4 minutes ago, sputniksteve said:

Okay, so for the novices among us (me), what's the difference between a CC and a RC?

CC is really for visual observing, particularily of the moon and planets and the StellaLyras are f/12.

RCs are for imaging and are faster (shorter focal length). and are f/8 or f/9.

Edited by johninderby
  • Like 1
Link to post
Share on other sites
2 minutes ago, sputniksteve said:

Okay, so for the novices among us (me), what's the difference between a CC and a RC?

RC is also corrected for coma and has only astigmatism left. It has large corrected field with very small amount of curvature. It is good scientific instrument (most professional scopes are RCs) and good for imaging.

Not as good for visual because central obstruction is usually much larger. It has two hyperbolic mirrors.

In this particular case it is F/8 scope suited to DSO imaging.

CC in this case is F/12 and central obstruction is smaller - good for visual and imaging of planets.

  • Like 2
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.