10 Inch TS Optics Ritchey-Chretien Review and 2nd Light on M51

[Catanonia]

Firstly I would like to thank all that helped me with the collimation of the 10inch RC. Especially @vlaiv who is a fountain of knowledge.

The scope arrived from TS Optics and as expected, it needed collimation. The focuser tube was out (surprising) and the mirrors needed collimation too (not surprising as happens in shipping)

My learning process was very steep as never owned a RC before. The OCAL electronic collimator is good and helps get the focuser / primary and secondary close in the warmth of your house. But it only got it close and not perfect.

My first light was good, but it was obviously my stars were not good and collimation was indeed out.

Last night, I taught myself (with help from others, thanks) the defacto bright star collimation and eventually nailed it..... Yippeeee !!!!

So below is my 2nd light of M51 that I took last night. I am on the limit of CCD suitability with the scope and camera, but my guiding was very good averaging 0.5 in PHD2 so I risked 1x bin subs mainly to see any imperfections in collimation.

Amazing that M51 fills 1/2 of the sub frame at 1:1 zoom.

Click the M51 pic and zoom in  It is HUGE !!!!

• 138x 2min subs at 1x bin (about 4.5 hours)
• TS Optics (GSO) 10 inch RC open truss
• ZWO 2600 MC Pro and no filters
• EQ8-R Mount
• WO66 guide with ZWO 120mm guide camera  (PHD2 averaged 0.5)
• ZWO ASI Air Pro
• Bortle 6 skies and 83% moon

2000mm is probably too much for my Bortle 6 skies / imaging resolving power. Next is to experiment with the 0.67 reducer as I think this will be the default for me.

So my initial impressions are

• Awesome service from TS Germany as always
• Get the reducer from TS to give you options for 2000mm @F8 or 1340mm @ F5.3 - I have only tried at native F8 so far.
• It has a very flat field out of the box when properly collimated. 
• Open truss picks up dust easily, get a hand blower if this concerns you.
• Scope needed collimation on all 3 of focuser, primary and secondary so be ready for that
• It is heavy, 15.3 KG for the scope, about 22kg with all the kit on. It is fun lifting it up to the EQ8-R for mounting. I would say a EQ8 class of mount is a must as a EQ6 class would really struggle.
• I didn't need the cloth shroud as the baffle tube to the primary works well. Even last night under a 83% moon and I had no issues with light leaks.
• Taking flats is an issue, I used the teeshirt during the day method with the cloth shroud to stop the teeshirt falling into the open truss. I still need to refine this more.
• There is no ZWO EAF bracket for the GSO focuser, I had to 3d print a shim.
• Putting the primary mirror cover in / out is a PITA, ensure you have the secondary one on 1st to avoid scratches
• Due to extreme 2000mm, I hardly got any Elon trails (depends on target) - Nice
• It is impressive to see M51 fill half the image sub and not have to zoom in massive amounts 
• It is great to be galaxy imaging again as my Rasa8 is just not cut out for this type of work. RC for summer / RASA for winter

Again thanks all that helped with my new scope and the stupid questions I had

 

 

Edited March 15, 2022 by Catanonia

[Neil27]

Great write up, and now a proud RC owner …. 😉👍🔭

[powerlord]

great result. I think what you've got there is the spider shadow rather than the 'airy rings' yer meant to look for though. But it's probably good enough - others can comment, I can't having never done the airy rings thing.

result pretty similar to what I got with my 12" newt (1500):

 

I don't know how you process, but I've found startools gets me better results with galaxies than anything else I've tried. might be worth a go as I'm sure there must be a lot more data in that massive frame to eek out.

stu

[Catanonia]

8 minutes ago, powerlord said:

I don't know how you process, but I've found startools gets me better results with galaxies than anything else I've tried. might be worth a go as I'm sure there must be a lot more data in that massive frame to eek out.

stu

Thanks Stu, much appreciated. Not sure on the collimation airy either as was the 1st time for me too. Will do some more reading, but the collimation was a marked improvement upon the 1st attempt.

Will check Startools a I only use PixInsight at the moment

Edited March 15, 2022 by Catanonia

[vlaiv]

That collimation needs a bit of tweaking to get it fully right.

These are top left stars:

Not very round.

These are center stars - much better:

While RC has rather flat field - it is not fully flat and best thing to do is focus on stars that are about 3/4 away from the center (2/3 to 3/4). If you get these to be as small as possible, stars in other parts will be also good (provided you have collimation ok).

Bottom left corner shows some defocus (that is primary tilted):

And of course that top right star has double spikes.

With focal length this big - you really need to learn to bin your data in processing stage.

Take your stack, while still linear and do integer resample to 1/3 of the size in PI (if that is what you are using) - that is bin 3x3.

[powerlord]

free trial available - and unlike pi trial you don't need to prove to the gestapo that you are genuine user.

stu

[Catanonia]

3 hours ago, powerlord said:

free trial available - and unlike pi trial you don't need to prove to the gestapo that you are genuine user.

stu

Trying it now, nice concept, but hard to work out. Will keep playing, but can see how easy images can be taken out of it.

Ok played a little more, StarTools is quite clever. My quick playing and it seems star tools gives an unnatural feel to the images with too much sharpening, local shadow enhancements and a reliance a lot on wavelets. Perhaps it is just me and my obvious lack of skill in Startools. I will keep it downloaded and play more with it on other images

In PixInsight, a little Wavelet action without much testing gave this, I feel a more natural image.

Edited March 15, 2022 by Catanonia

[Catanonia]

3 hours ago, vlaiv said:

That collimation needs a bit of tweaking to get it fully right.

and more

At times Vlaiv I hate and love you   Still a little improvement to be had.

• Yes, forgot, bin in software to increase SNR
• Not sure if I can focus on a single star with ASI Air Pro and ASI EAF as it auto detects a star.
• Will experiment a little more with the collimation. Although for Galaxy hunting, I will no doubt be cropping the centre portion of the image.
• If I add a 0.67 reducer, will I have to re-collimate (assuming a good straight / quality reducer and correct spacing) or will the native collimation hold true for the reducer as well ?

Thanks for your patience.

Edited March 15, 2022 by Catanonia

[vlaiv]

56 minutes ago, Catanonia said:

If I add a 0.67 reducer, will I have to re-collimate (assuming a good straight / quality reducer and correct spacing) or will the native collimation hold true for the reducer as well ?

If collimation is good - it will stay good when you add reducer. If not - then it will look worse. This is because reducer "squeezes" in more physical focal plain onto sensor surface and further away from center you are - issues are more noticeable (even if collimated perfectly - edge of field aberrations will get worse with reducer).

Do bear in mind that you already have APS-C sized sensor. Using 0.67 reducer is like putting 42mm diagonal sensor onto the scope. Do you really expect field to be good all the way to 42mm?

According to TS - scope offers correction only up to APS-C sized sensor - so in reality up to 27-28mm diameter.

What you'll end up doing with reducer - is simply cropping away anything pass those 27-28mm and what is the point in using the reducer when you'll end up using the same field anyway?

You'll say - but I'll have "faster" system, and I'll say - speed of the system is resolution at aperture. With both reducer and without, you'll need to fix your working resolution with binning as you will be oversampling, and you'll have same usable FOV. You'll end up with same resolution, same FOV and same speed.

In that case - I see no point in using reducer. It makes sense to use it only if you use smaller sized camera (like 4/3" or 1") to utilize more of the FOV.

Dedicated flattener / reducer is another matter.

Something like this:

https://www.teleskop-express.de/shop/product_info.php/info/p11145_TS-Optics-RC-0-8x-Corrector-Reducer-for-Ritchey-Chretien---big-sensors---M68-connection.html

although not cheap, will allow you to use even full frame sensors, and most certainly APS-C sized one.

 

Edited March 15, 2022 by vlaiv
typo say/stay ...

[Catanonia]

4 minutes ago, vlaiv said:

Loads of stuff

 

Mind blown, will have to re-read this many times, but I think I get your reasoning. Watch this space and thanxs

[powerlord]

11 hours ago, Catanonia said:

Trying it now, nice concept, but hard to work out. Will keep playing, but can see how easy images can be taken out of it.

Ok played a little more, StarTools is quite clever. My quick playing and it seems star tools gives an unnatural feel to the images with too much sharpening, local shadow enhancements and a reliance a lot on wavelets. Perhaps it is just me and my obvious lack of skill in Startools. I will keep it downloaded and play more with it on other images

In PixInsight, a little Wavelet action without much testing gave this, I feel a more natural image.

 

aye- very quick walkthrough - just go through buttons top to bottom, left to right. oh - and make sure you are using latest beta.

unless i say otherwise, everything is default:

autodev

crop

wipe

autodev. and now, select box just covering m51. experiment till you get as above visible

contrast

HDR. this bit is important, [removed word] up the bottom left sliders a bit at a time until you have pulled back all the detail from the core

sharp

svdecon - left top two sliders here - move each up a wee bit at a time while highlighting a box around m51. keep moving up till it breaks up then back off a bit

I usually find around 20/20 good

color. play with this a bit

shrink. as you wish

usually at this point I save it out. and use topaz for denoise and sharpening.

And I agree re: look, things can easily get a bit 'startoolsy' looking. Whether you think mine does above or not, dunno, but that's why i tend to drop out before denoise, and bring it into affinity photo for a bunch more work - starnet, yada yada

Edited March 16, 2022 by powerlord

[powerlord]

10 hours ago, Catanonia said:

At times Vlaiv I hate and love you   Still a little improvement to be had.

• Yes, forgot, bin in software to increase SNR
• Not sure if I can focus on a single star with ASI Air Pro and ASI EAF as it auto detects a star.
• Will experiment a little more with the collimation. Although for Galaxy hunting, I will no doubt be cropping the centre portion of the image.
• If I add a 0.67 reducer, will I have to re-collimate (assuming a good straight / quality reducer and correct spacing) or will the native collimation hold true for the reducer as well ?

Thanks for your patience.

asiair manual focus - just click on a star in focus mode. it will put a box around it. click the + and it will take you into the measurement screen where you can manually adjust eaf to minimise size.

[ollypenrice]

11 hours ago, Catanonia said:

At times Vlaiv I hate and love you   Still a little improvement to be had.

I know how you feel but we have to love him!!!

🤣lly

[Catanonia]

1 hour ago, powerlord said:

asiair manual focus - just click on a star in focus mode. it will put a box around it. click the + and it will take you into the measurement screen where you can manually adjust eaf to minimise size.

Ah, thanxs, that I did not know

[tomato]

1 hour ago, ollypenrice said:

I know how you feel but we have to love him!!!

🤣lly

I inwardly groan when Vlaiv starts a post with “Take a look at your stars”…. But hey, he is spot on (literally) every time.☺️

[Tomatobro]

I wish I had not read this post......I have just started with a 10 inch RC.....will take a look at my stars🤨

[Catanonia]

46 minutes ago, Tomatobro said:

I wish I had not read this post......I have just started with a 10 inch RC.....will take a look at my stars🤨

It is worth the effort. A steep learning slope for me, but well worth it.

I have almost got good collimation, but as Vlaiv has shown, there is still a little way to go.

I will play a little more tonight, but being this close is good enough for me

[vlaiv]

20 minutes ago, Catanonia said:

I will play a little more tonight, but being this close is good enough for me

In order to judge collimation of secondary - place star in center of the FOV and defocus - but do it only slightly.

With very large defocus like in your image - you won't be able to spot the small difference in thickness of the sides of the doughnut.

I found one of my old images of defocused star - it was not for collimation but rather for telescope testing so I had to defocus it just right amount:

This is still too much defocus.

You want very small defocus shown in the image above and image of defocused star should look something like this:

You should clearly see outer edge and few rings. In your image above - there are plenty of rings and they have fused in solid surface - much like 30 wave defocus image on the diagram.

My image is about 15 or so waves - so resembles 14 wave image on diagram - note that diagram is image of newtonian so secondary is much smaller - but we don't care about that but rings - in my image you can see some rings separation - same as in 14 wave example - you want to go down to just 5-6 waves.

Do be careful - seeing will start to play havoc on these scales - more you defocus, less seeing effects will be seen on defocused star profile - but here (as shown on diagram - outer edge is not perfect circle and will be dancing a lot)

Also notice that diagram - 30 wave defocus looks round and concentric - but look at 5/7 waves - it is obvious that things are not concentric anymore - bottom side of doughnut is thinner than top side (actually caused by thermals in this image).

This is all corrected by adjusting secondary - while star is in the center.

You adjust primary by making sure that focused star stays focused in each of 4 corners. Here you can use FWHM / HFR tools to obtain same number after you slew scope so that test star hits each corner.

Do couple of rounds - adjust secondary - adjust primary, primary, secondary,...

as when you adjust one - other needs additional tweak as well.

[powerlord]

Just to be clear Vlaiv, you are talking about doing all this visually/optically yes ? with eyepiece, etc. Not digitally via a camera ? That is what puts me off doing all this tbh - as I'm really all geared up for imaging only.

[vlaiv]

Just now, powerlord said:

Just to be clear Vlaiv, you are talking about doing all this visually/optically yes ? with eyepiece, etc. Not digitally via a camera ? That is what puts me off doing all this tbh - as I'm really all geared up for imaging only.

I actually did mine with camera as I find it much easier.

Just take your imaging camera - not guide camera so you can move collimation star to far corners of the sensor (guide camera has small sensor and you won't get good collimation that way as measurements won't be as sensitive).

I started by looking / reading thru this tutorial:

https://deepspaceplace.com/gso8rccollimate.php

and things simplify down to what I've written above:

1. Secondary - star in center, concentric defocus

2. Primary - stars in corners - all equally good in focus

Tutorial itself calls for bahtinov mask - but I never liked it and preferred FWHM measurements instead.

[powerlord]

hmm. ok good to know. I mighy try this tomorrow night, when it looks like being clear.

[Catanonia]

@vlaiv  

So getting getting

• Central hole centred is via secondary mirror adjustments
• Stars in 3/4 of corners (because I am APC) aligned is primary mirror adjustments

As a rough rule of thumb , flipping between the adjustments of secondary and primary.

Edited March 16, 2022 by Catanonia

[vlaiv]

7 minutes ago, Catanonia said:

Stars in 3/4 of corners (because I am APC) aligned is primary mirror adjustments

Stars in corners as far as you can place them (like 50px from each side), just make sure you place them in more or less the same position in each of the corners.

3/4 is when you are imaging and you want to achieve good focus all over the frame. You then focus on single star that is about 3/4 away from the center. If your autofocus routine examines all the stars in the sub - you don't need to bother, it will find best focus position so it minimizes star sizes all over the place, but if you focus on a single star - then don't choose one in the center of the sub but rather ~ 3/4 out (or 2/3 - no need to be very precise about it).

11 minutes ago, Catanonia said:

Central hole centred is via secondary mirror adjustments

Yes, but make sure you have doughnut centered in your frame - like dead center.

On a separate note, since you have focuser tilt to adjust as well, and above procedure does not address that - here is what I would do.

You adjust tilt of focuser as a first step prior to collimation of the rest of the scope - you'll need some sort of laser that is collimated itself - that you can put in your focuser. Procedure is simple - laser spot should hit dead center of secondary mirror and remain there as you rotate laser while in focuser (like rotating eyepiece that is placed in focuser).

If dot moves when you rotate laser - laser is not square to focuser so you need to fix that - otherwise - if it's hitting center of the secondary - you are done.

[Catanonia]

22 minutes ago, vlaiv said:

Stars in corners as far as you can place them (like 50px from each side), just make sure you place them in more or less the same position in each of the corners.

3/4 is when you are imaging and you want to achieve good focus all over the frame. You then focus on single star that is about 3/4 away from the center. If your autofocus routine examines all the stars in the sub - you don't need to bother, it will find best focus position so it minimizes star sizes all over the place, but if you focus on a single star - then don't choose one in the center of the sub but rather ~ 3/4 out (or 2/3 - no need to be very precise about it).

Yes, but make sure you have doughnut centered in your frame - like dead center.

On a separate note, since you have focuser tilt to adjust as well, and above procedure does not address that - here is what I would do.

You adjust tilt of focuser as a first step prior to collimation of the rest of the scope - you'll need some sort of laser that is collimated itself - that you can put in your focuser. Procedure is simple - laser spot should hit dead center of secondary mirror and remain there as you rotate laser while in focuser (like rotating eyepiece that is placed in focuser).

If dot moves when you rotate laser - laser is not square to focuser so you need to fix that - otherwise - if it's hitting center of the secondary - you are done.

thanks, focuser tilt was the 1st thing I sorted out and pretty sure I have that boxed off.

Will play a little more tonight to see if I can refine the collimation before my imaging session.

Thanks

[Catanonia]

Cracked it