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Thin rotator (M68 or M54) for ZWO train (OAG-L, EFW, camera)

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#1 Linwood

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Posted 05 August 2021 - 11:56 AM

I'm hoping the new ZWO OAG can replace my Celestron OAG, for various reasons.

 

The Celestron is inherently also a manual rotator.  The ZWO OAG appears not to be.

 

Correct? 

 

It comes packaged with a 48mm tilt (why the tiny one on the large OAG I have no idea), but none of the OAG tilt adapters appear to provide for rotation.

 

From it I would have the EFW and ASI6200MM camera, neither of which can rotate. 

So I think I need to put a rotation device in between the OTA and OAG.  

 

Note that something like the Pegasus Falcon may (I can't really tell) not work because of the guide camera and its mount being thicker than the OAG, so the flat surface on the Falcon will hit it, I think.

 

Any ideas?  What are people doing for rotation when all the components (OAG, EFW, camera) are screw threads? 

 

Linwood

 

PS. I was originally thinking the CTU would work, but in checking I see no sign it does rotation.


Edited by Linwood, 05 August 2021 - 11:59 AM.


#2 aroughroad

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Posted 05 August 2021 - 01:05 PM

I'm hoping the new ZWO OAG can replace my Celestron OAG, for various reasons.

 

The Celestron is inherently also a manual rotator.  The ZWO OAG appears not to be.

 

Correct? 

 

It comes packaged with a 48mm tilt (why the tiny one on the large OAG I have no idea), but none of the OAG tilt adapters appear to provide for rotation.

 

From it I would have the EFW and ASI6200MM camera, neither of which can rotate. 

So I think I need to put a rotation device in between the OTA and OAG.  

 

Note that something like the Pegasus Falcon may (I can't really tell) not work because of the guide camera and its mount being thicker than the OAG, so the flat surface on the Falcon will hit it, I think.

 

Any ideas?  What are people doing for rotation when all the components (OAG, EFW, camera) are screw threads? 

 

Linwood

 

PS. I was originally thinking the CTU would work, but in checking I see no sign it does rotation.

Which scope / flattener are you using?  I am also trying to solve this problem and have had a hell of a time trying to figure it out.  I have a feather touch 3.5" focuser, which I am able to rotate manually if I loosen the collar.  But I am not crazy about this solution, as it might risk collimation issues (although William Optics tells me it won't be a problem at all) and I'm not sure where I could mark out the degrees to measure how much I'm rotating. 

 

The folks at optec have told me I will be able to attach one of their rotators between my focuser and my flattener (therefore not affecting backfocus) provided i have sufficient drawtube space available on my focuser when i am at infinity focus.  unfortunately i won't be able to check whether i will have enough drawtube space until i order all the parts of my train and set them up!  keeping my fingers crossed there as that would be my preferred solution. 

 

The other option would be to rotate my flattener (william optics 68iii), which rotates but would require me to change my backfocus by ~1mm to do so.  Not ideal.

 

Let me know if you find any other solutions!



#3 Linwood

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Posted 05 August 2021 - 01:14 PM

Right now I have this set up: 

 

ASI6200MM -> ZWO EFW -> Custom adapter -> Celestron OAG ->   (think of this as a whole assembly)

 

(assembly) -> Custom adapter -> C11 Edge HD

(assembly) -> Custom adapter -> Large field adapter -> NP101IS

 

In the latter case the custom adapter is the absolute thinnest that Precise Parts could make.

 

The advantage of this setup is I can just unscrew the three OAG set screws and move the camera, OAG and EFW between scopes.  However, when I did this, I had the adapters made without any room for adjustment, assuming the backfocus was a precise number.  So I can't adjust anything, and with the COAG in there I cannot make the refractor backfocus any shorter, everything is as small as will fit.

 

My thinking is to replace the COAG with something thinner, and in doing so put in M54 threads so I can put in and remote spacers to adjust thickness.

 

But the COAG has a built in rotator.  So I think what I will have to end up with is this: 

 

ASI6200MM -> ZWO EFW -> ZWO OAG-L (M54) ->  (New assembly) 

 

(new assembly) -> Rotator -> new Custom adapter -> C11 Edge HD

(new assembly) -> new Custom adapter -> Large field adapter -> NP101IS

 

In this setup I would have to use the rotator only one the C11, and the scopes built in rotator for the refractor as it has no space for another rotator.  Maybe.  

 

That means separating the camera side assembly at the OAG, which I guess is OK.  But it would be nice to have the rotator the same on both, I just don't think I have room unless I find a thin one.



#4 Linwood

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Posted 05 August 2021 - 03:47 PM

Some friends on Discord pointed me here: 

 

https://agenaastro.c...er-m-caa63.html

 

or maybe: 

 

https://agenaastro.c...hread-r-06.html

 

The Blue Fireball is the thinnest.  I just worry... ok, shoot me because this is silly in some ways... it is quite affordable.  Will it be precise enough to rotate without sag carrying an OAG, Camera and FW?



#5 Linwood

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Posted 05 August 2021 - 04:24 PM

I did the math, I can use it in this way only if I use the refractor's own rotator, and add a rotator to the C11.

 

But it brings up another question: 

 

With the COAG I have a dovetail, so removing and re-attaching it feels like it will be fine for a long time.

 

The M54 threads are both short and pretty tiny. And aluminum so soft.  Do you think they will hold up (or conversely for whatever you screw into them) over the long haul, if I take it off and on each night? 



#6 Peter in Reno

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Posted 05 August 2021 - 04:47 PM

For a camera with full frame size sensor, do you really need a rotator especially for C-11? Why not give it a try without a rotator? 

 

Peter



#7 Linwood

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Posted 05 August 2021 - 04:59 PM

For a camera with full frame size sensor, do you really need a rotator especially for C-11? Why not give it a try without a rotator? 

Well... Maybe.  It's a fair question.  I went back and looked at the (very few) things I have shot.  M81 if it was cross ways would be very tight, and given imprecisions on the edge on multi-night plus wanting to include fine detail, I would not want to have gotten it on the narrow side.  Same with M106 though maybe not as bad.  Horsehead -- I did several nights in portrait mode and liked it, might have been ok landscape, but at some random angle... I think I would lose some interesting stuff around it.  But a lot like clusters it is moot.

 

So at least as a working point I think yes.  Plus I have tons of space on the C11.  I guess there I could put it between some spacers and use the Falcon or something similar.

 

I guess at this point if I know I can't do the refractor, I just need to find a good rotator, doesn't have to be thin.



#8 Peter in Reno

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Posted 05 August 2021 - 05:20 PM

M81 FOV with ASI6200MM or QHY600M sensor, C-11 EdgeHD at f/10. It looks like it easily fits. Click on image for better details.

 

M81_FOV_C-11_F10.jpg

 

Peter



#9 Peter in Reno

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Posted 05 August 2021 - 05:21 PM

M106 FOV with ASI6200MM or QHY600M sensor, C-11 EdgeHD at f/10. It looks like it easily fits. Click on image for better details.

 

M106_FOV_C-11_F10.jpg

 

I agree HorseHead Nebula might be pretty tight.

 

Peter


Edited by Peter in Reno, 05 August 2021 - 05:24 PM.


#10 Peter in Reno

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Posted 05 August 2021 - 05:29 PM

HorseHead FOV with ASI6200MM or QHY600M sensor, C-11 EdgeHD at f/10. It looks like very tight fit. Click on image for better details.

 

HorseHead_FOV_C-11_F10.jpg

 

Peter



#11 Peter in Reno

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Posted 05 August 2021 - 05:32 PM

HorseHead FOV using f/7 reducer. Better fit but cuts off flame nebula. Might be better to get electronic or automatic rotator but the back focus may be too thick.

 

HorseHead_FOV_C-11_F7.jpg

 

Peter


Edited by Peter in Reno, 05 August 2021 - 05:36 PM.


#12 Linwood

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Posted 05 August 2021 - 05:37 PM

Yeah, I had the same view in stellarium.  A lot depends on how much of the halo detail you end up picking up.   I've been working on M31 for example (at 540mm), and it extends maybe half the width of the main spiral out.  I'm not sure why everyone crops it so tight.

 

For M81, I went back to a shot I had, and looked at how wide I thought I needed to crop to include the fine detail off the ends.  It's something like this: 

 

M81.jpg

 

That's wider than the narrow direction (14900 vs 12276 -- this was a drizzle output, it got downsampled). 

 

Now... is that halo interesting, does anyone notice it.  Probably not. 

 

For M106 I remember now, I wanted to include some of the other spirals nearby, so I needed a specific rotation to get the, in.   Again, needed?  Interesting?  But I liked it at the time, and being able to rotate seemed handy.  Not sure I'm ready to give that up.  I mean, if it's a mosaic or just going outside to spin something 30 degrees, one's a lot easier than the other -- well, if you have a rotator.

 

i-QZDj5zr-XL.jpg



#13 Peter in Reno

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Posted 05 August 2021 - 05:40 PM

Are you using an automation software that will help you manually rotate your imaging train to your liking? I know Voyager has full capability but not sure about NINA. It would be very difficult to manually rotate the imaging train to your liking without software support.

 

Peter



#14 Linwood

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Posted 05 August 2021 - 05:42 PM

If you got my horsehead note, ignore -- I didn't see the inner box at first.

 

But all this is an argument as though it is a big deal.  If I'm going to redo my imaging train to include a new OAG, I think I want to maintain a rotator in the mix. It's far from the most costly component, and I just need to find a nice rigid one. 

 

You are arguing strongly against, but it seems more a matter of mild convenience than a significant issue?



#15 Linwood

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Posted 05 August 2021 - 05:43 PM

Are you using an automation software that will help you manually rotate your imaging train to your liking? I know Voyager has full capability but not sure about NINA. It would be very difficult to manually rotate the imaging train to your liking without software support.

 

Peter

Yes, NINA has it, Voyage does not so far as I know (last I checked it said "just take repeated images, plate solve, and manually compare the angle to what you want).  NINA is very nice, it just stops and prompts you "Rotate camera 30 degrees right".  If you miss you get "Rotate it 6 degrees left" to whatever level of precision you want -- each time you say OK it plate solves again.  Takes moments (I take my cell phone out to hit "ok") to get the right rotation.



#16 Peter in Reno

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Posted 05 August 2021 - 05:47 PM

If you got my horsehead note, ignore -- I didn't see the inner box at first.

 

But all this is an argument as though it is a big deal.  If I'm going to redo my imaging train to include a new OAG, I think I want to maintain a rotator in the mix. It's far from the most costly component, and I just need to find a nice rigid one. 

 

You are arguing strongly against, but it seems more a matter of mild convenience than a significant issue?

I am not against it, just wondering what's your experience using rotator? I've tried it long before using automatic rotator was easily available and affordable but I was not successful.

 

 

Yes, NINA has it, Voyage does not so far as I know (last I checked it said "just take repeated images, plate solve, and manually compare the angle to what you want).  NINA is very nice, it just stops and prompts you "Rotate camera 30 degrees right".  If you miss you get "Rotate it 6 degrees left" to whatever level of precision you want -- each time you say OK it plate solves again.  Takes moments (I take my cell phone out to hit "ok") to get the right rotation.

That's great to hear. I'm sure NINA will make your life much easier.

 

Peter



#17 Linwood

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Posted 05 August 2021 - 05:53 PM

I am not against it, just wondering what's your experience using rotator? I've tried it long before using automatic rotator was easily available and affordable but I was not successful.

Oh, I did try it with TSX for a bit.  It was a royal pain, it would give me a PA but it was pierside dependent, so despite it being a 50/50 chance which way to turn, at least 80% of the time I went the wrong way the first try. 

 

But it's incredibly easy and fast with NINA -- at least with the Celestron OAG where you just loosen a couple screws, turn, tighten -- hardest part is the last degree or two just because fingers are not calibrated. 

 

Which automated rotator are you using? 



#18 Peter in Reno

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Posted 05 August 2021 - 05:56 PM

Which automated rotator are you using? 

Never owned one.

 

Optec Inc. is probably the earliest automated rotator for the amateur market but now there are several automated rotators available from several different brands at lower cost than Optec.

 

Peter
 


Edited by Peter in Reno, 05 August 2021 - 05:57 PM.


#19 Peter in Reno

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Posted 05 August 2021 - 06:00 PM

This is one of the latest automated rotator with 18mm back focus:

 

https://optcorp.com/...-falcon-rotator

 

Peter



#20 Linwood

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Posted 05 August 2021 - 06:05 PM

Yeah, I mentioned it above.  The issue is it's not really 18mm since it cannot go up against (most, all?) OAG's as they have either focusers or cameras or both that stick out wider than the width of the OAG.  So I'd have to put a (maybe 10mm?) spacer between OAG and Falcon.  That kind of makes it 28mm.

 

But... unlike when I started this thread, if I do not need to put it on my NP101is (because I can't -- I only have about 5-6mm) then optical length is not really an issue, plenty of backfocus .


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#21 Peter in Reno

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Posted 05 August 2021 - 06:19 PM

What are people doing for rotation when all the components (OAG, EFW, camera) are screw threads? 

 

Linwood

I've become a huge fan of using dovetail connections. My QHY600M camera uses dovetail connections. I ordered Optec Sagitta OAG which also uses dovetail connections at both sides of OAG but consumes 32mm back focus and has a huge 3" or 76mm clear aperture. Dovetail connections allows rotation of imaging train and it's strong enough to support heavy imaging train. 

 

My A-P QuadTCC also has dovetail connections and it's extremely strong and very straight (not tilted).

 

Peter


Edited by Peter in Reno, 05 August 2021 - 06:26 PM.


#22 Linwood

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Posted 05 August 2021 - 07:45 PM

Yeah, I looked at that one, but besides being a bit pricy by the time you get an adapter it's pretty thick.  That's a downside of the dovetails, they take space. 

 

For what it is worth, the reason I'm trying to keep the OAG very thin is so the part I move to the refractor, the camera + EFW + OAG, is VERY easy to get working there, since the guide camera stays in focus (because the guide and main camera are rigidly attached).  So you spend zero time re-focusing your guide scope, like you might if you had different guide scopes or cameras for the two OTA's.   It saves a fair amount of time since focusing the guide camera is rather tedious since it's manual, and at least for me I'm staring at a cell phone and moving it by hand, stare some more, etc.  No auto-focus. 

And yes, I know I could buy auto-focus also, but... this works pretty well.  And with more than about 24mm I can't move it back and forth (the 29 COAG moves but I have no room for adjusting spacers, which i want to add). 



#23 PincoPallo

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Posted 06 August 2021 - 02:04 AM

Yes, NINA has it, Voyage does not so far as I know (last I checked it said "just take repeated images, plate solve, and manually compare the angle to what you want).  NINA is very nice, it just stops and prompts you "Rotate camera 30 degrees right".  If you miss you get "Rotate it 6 degrees left" to whatever level of precision you want -- each time you say OK it plate solves again.  Takes moments (I take my cell phone out to hit "ok") to get the right rotation.

Voyager ...

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#24 Linwood

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Posted 06 August 2021 - 08:29 AM

Hey, that looks terrific.  Originally the response to requests for it was "is not necessary".  Looks like he came around; I had not looked since he changed his mind.  Here's what I saw late last year, and you can see in March this year it was re-considered.

 

https://forum.starke...capability/1403

 

Voyager and Nina are both rapidly evolving platforms.



#25 davidparks

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Posted 06 August 2021 - 09:57 AM

The folks at optec have told me I will be able to attach one of their rotators between my focuser and my flattener (therefore not affecting backfocus) provided i have sufficient drawtube space available on my focuser when i am at infinity focus.  unfortunately i won't be able to check whether i will have enough drawtube space until i order all the parts of my train and set them up!  keeping my fingers crossed there as that would be my preferred solution. 

 

The Optec folks are correct, I was able to slide their Pyxsis right into the draw tube on my WO Z73, followed by Flattener, OAG (or spacer), EFW (or spacer), and Zwo Cam.

 

The Pegasus Rotator is pretty thin at 18mm and the Primeluce Arco looks very interesting (but doesn't ever seem to be available).

 

The nice thing about these Rotators is that you can orient them in any position, so that their motors don't collide with OAG's or whatnot.  They don't need an absolute rotational home position within your image train.  Ascom compatible software like NINA etc simply uses the relative position between platesolves.  Even shooting the same target multiple nights if you have the rotator in a different orientation it still just works automagically.

 

I no longer have either my Optec Rotator or WO Z73, having gone exclusively ASIAIR Pro, so I'm hoping ZWO comes out with a Rotator some day waytogo.gif




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