Lodestar 2 and OAG

[RayD]

21 minutes ago, Rodd said:

Will using the lodestar 2 with a scope be easy?  Or will there be compatibility issues.  Maybe a camera scope combo would be better--like the vario guider from Gaacder--or something similar--comes all set up

No it is about making sure your pixel scales match, so your guide scope just needs to match your camera and your main imaging scale.  Use this tool to see what will work best for you.

[Rodd]

I know my various pixel scales--there are 6 different ones--2 for each refractor.  How closely does the guidescope/camera pixel scale have to be to the imaging scope/camera pixel scale?

[RayD]

7 minutes ago, Rodd said:

I know my various pixel scales--there are 6 different ones--2 for each refractor.  How closely does the guidescope/camera pixel scale have to be to the imaging scope/camera pixel scale?

I think a rough guide is targeting a ratio of 1:5 or lower (I think some say 4 and some 6, so in between these is probably nearer to reality).  Obviously with OAG you could technically be 1:1.  Many will guide successfully higher, but I think if you can achieve around this then it will be pretty good.  I have heard another thing mentioned of the fl of the guide scope being 1/3 of the main scope, but I'm not sure how accurate that would be as the pixel size of the camera would have an effect.

I don't think it needs to be exact, and of course the biggest thing to get right is eliminating flexure.  I image with my Esprit at about 2.5 "/p and guide at 7.5 "/p and this works great being a ratio of 1:2.5.  This is with a 225mm fl (Altair 60mm) guide scope and Lodestar X2.

I'm sure there are others with more expert experience of guiding who could advise in more detail, but I can't emphasise eliminating flexure enough.

[Rodd]

I guess an ultera-mini guidescope would not be as good as a 60mm scope.  Some of the minis are only 3-4 inches long.  weight and flexure would be at a minimum.

Edited March 17, 2018 by Rodd

[RayD]

1 minute ago, Rodd said:

I guess an ultera-mini guidescope would not be as good as a 60mm scope.  Some of the minis are only 3-4 inches long.  weight and flexure would be at a minimum.

Not at 1000mm focal length, no.  I would have thought a good bet for you would be something like an ST80, or something else 60mm +?  I have 2 of the Altair 60mm guide scopes and they have been great, but I know a lot of people use the ST80 with great success at longer focal lengths.

There's some info here which is a bit of a guide, but I think you could do a lot worse than looking at a 60 to 80mm scope.  

[LightBucket]

I have guided my SCT at 1500mm focal length with an 80mm guidescope, no problem....I have never used an OAG..

[Rodd]

3 minutes ago, LightBucket said:

I have guided my SCT at 1500mm focal length with an 80mm guidescope, no problem....I have never used an OAG..

My C11Edge with reducer is 1,960mm--I think that's pushing it.  But I can use my self guiding STT-8300 fro that scope (providing I get the filter wheel to stop jamming).   I already have the Lodestar 2--providing it I not broken.  It is very sensitive.  I would love to be able to get by with a tiny guidescope

[RayD]

Just now, LightBucket said:

I have guided my SCT at 1500mm focal length with an 80mm guidescope, no problem....I have never used an OAG..

Oh yes it can definitely be done; that's why I refer to things as a guide.  You just need to have a really good mounting and be brave enough to try it.  I'm sure most imagers would recommend OAG at this type of fl, me included, but that's not to say it is essential by any means.

[RayD]

1 minute ago, Rodd said:

My C11Edge with reducer is 1,960mm--I think that's pushing it.  But I can use my self guiding STT-8300 fro that scope (providing I get the filter wheel to stop jamming).   I already have the Lodestar 2--providing it I not broken.  It is very sensitive.  I would love to be able to get by with a tiny guidescope

As long as you can stick around the 1:5 ratio, and the aperture is big enough to get a star (shouldn't be an issue with the X2 as it is very sensitive) then there are a lot of options out there.  What about the new Skywatcher Evoguide (50mm).  Veeeery nice.

[Rodd]

Just now, RayD said:

As long as you can stick around the 1:5 ratio, and the aperture is big enough to get a star (shouldn't be an issue with the X2 as it is very sensitive) then there are a lot of options out there.  What about the new Skywatcher Evoguide (50mm).  Veeeery nice.

I am not up on guide scopes--never used one.  Just beginning my perusal.  I know Baader Planetarium has the Vario Finder--and a Baader scope mage for Astro Physics--61mm F4 250mm focal length.  That would be 1:4 with 1,000mm focal length.  For 700mm it would be less than 1:3.  For 318 (the FSQ at F3) it would be almost 1:1

[RayD]

1 minute ago, Rodd said:

I am not up on guide scopes--never used one.  Just beginning my perusal.  I know Baader Planetarium has the Vario Finder--and a Baader scope mage for Astro Physics--61mm F4 250mm focal length.  That would be 1:4 with 1,000mm focal length.  For 700mm it would be less than 1:3.  For 318 (the FSQ at F3) it would be almost 1:1

I would think something like that would be ideal.  My 60mm is 225 fl and it works great.  Never had an issue with getting stars and the Lodestar focuses with no issues.  It is possible that you could need a short extension, but it would only be a standard eyepiece type one.

If you image at a longer fl then you can just look at a bigger guide scope.  As is the case with @LightBucket, the 80mm seems to be a good choice, but at your noted fl you probably wouldn't need to go that big, particularly with the X2.

[Rodd]

1 minute ago, RayD said:

I would think something like that would be ideal.  My 60mm is 225 fl and it works great.  Never had an issue with getting stars and the Lodestar focuses with no issues.  It is possible that you could need a short extension, but it would only be a standard eyepiece type one.

If you image at a longer fl then you can just look at a bigger guide scope.  As is the case with @LightBucket, the 80mm seems to be a good choice, but at your noted fl you probably wouldn't need to go that big, particularly with the X2.

Yes- the absolute maximum I would go is 1,000mm.  Probably 700mm.  But it still gets me that the OAG is a flub.  Allot of thought, time, waiting, and money went into the F3 considerations.  He should have just said a guidescope would be 100x easier.  

[RayD]

1 minute ago, Rodd said:

Yes- the absolute maximum I would go is 1,000mm.  Probably 700mm.  But it still gets me that the OAG is a flub.  Allot of thought, time, waiting, and money went into the F3 considerations.  He should have just said a guidescope would be 100x easier.  

Oh crikey a guide scope is definitely easier.  I don't think anyone would suggest going with OAG unless you need to.  The only reason I have them is because it all worked out easy, but they can be a mare to get right if you are mixing and matching.  The main benefit of a OAG is to remove flexure, and this is accentuated at longer focal lengths.  At your focal lengths, providing you have a good secure fixing, then this should not be an issue.

[Rodd]

6 minutes ago, RayD said:

Oh crikey a guide scope is definitely easier.  I don't think anyone would suggest going with OAG unless you need to.  The only reason I have them is because it all worked out easy, but they can be a mare to get right if you are mixing and matching.  The main benefit of a OAG is to remove flexure, and this is accentuated at longer focal lengths.  At your focal lengths, providing you have a good secure fixing, then this should not be an issue.

I guess the issue was that if I can't fix my STT-8300 with its self guiding filter wheel (awesome guiding by the way.  I start to complain when my rms errors are greater than .2 pixels (about .2 arcsex/pix with the TOA 130) then I would be stuck with the ASI 1600 as my only camera--so I would have to use it with the C11Edge, hence the OAG.

[RayD]

2 minutes ago, Rodd said:

I guess the issue was that if I can't fix my STT-8300 with its self guiding filter wheel (awesome guiding by the way.  I start to complain when my rms errors are greater than .2 pixels (about .2 arcsex/pix with the TOA 130) then I would be stuck with the ASI 1600 as my only camera--so I would have to use it with the C11Edge, hence the OAG.

Ok I see.  For me personally, if you are imaging with your C11, I would use OAG for sure.  As noted above, it isn't impossible to image/guide without one, but to coin a phrase, "it ain't 'arf hard".

[RayD]

Just by coincidence, this was just posted on another thread.

https://stargazerslounge.com/topic/311042-guidescope-mount/?do=findComment&comment=3404750

 

 

[Fellside]

Rodd

This may be a sound a bit silly but you should be able to wind the scopes main focuser in and out slowly and get the lodestar into focus. Is the OAG fitted the correct way round. Is it looking towards the CCD. I may have missed it but which OAG are you using?

Graham

[Jkulin]

Hi Rodd, Just a small comment, currently I use a Lodestar 2 with my RC F8 which is 1625mm and I use an ST80 guidescope, absolutely no problem guiding with it, however I am switching over to a Moravian OAG and to go with my Esprit 80 & 100, only as an experiment when my new G2-8300 arrives, total backfocus of the Camera, OAG and FW is 55mm which is perfect for my Esprits+FF.

NB. Just to add to minimise flexure I use a Skywatcher Guide Mount, that lock everything up brilliantly.

Edited March 17, 2018 by Jkulin

[Yawning Angel]

I’m running the ZWO asi1600 with both their OAG and Filter wheel, asi120mc guiding. It all stacked up correctly, although it’s a close thing on inward focus travel! For my own sake, I documented the setup, so maybe this could help. Note the back focus of the 120mc is 12.5mm

 

[RayD]

Nice work well done.  This confirms what I said earlier, which is spacers are needed between the OAG and the FW otherwise it can never work.  Does the OAG come with a shallow profile T2 to C mount adaptor as the Lodestar is C mount, not T2 like the ASI?

[Merlin66]

Not my images, (from a previous SGL thread) but you can see how the OAG can be tested during the day......

[Merlin66]

Alex,

A perfect addition to this discussion!!

All we need now is for Rodd to submit an image of his set-up for comparison.

 

[Yawning Angel]

The OAG comes with a 5mm T2 spacer, then T2 to 1.25” adapter for a nosepiece. My mistake when building it up was to include the nosepiece adapter, it adds far too much. Looks like it needs a T2 to C adapter where I’m using the 5mm T2, unless the Lodestar has something hidden for T2? 

One with the nosepiece (too long) one without (just right)

Edited March 17, 2018 by Yawning Angel
Submitted too early

[RayD]

Good job, looks neat.

I think Rodd would need to have measure up with the Lodestar as they are C mount with no T2 option.  It's 12.5mm from the end of the well, so anything added is simply added.  I had the same issue using mine on my SX and Atik OAG's.  The only possible help is if the turret is very thin, like on the SX, and it then slides up inside the camera chamber right up to the lens window, which can resolve the issue.

I'm not sure his supplier has given him the right spacers. I did ask earlier whether there are spacers for between the OAG and FW but he doesn't seem to think so.  I can't see how it can work any other way due to the short 6.5mm back focus on the ASI 1600.

Your image is a great visual representation now as the CN post I linked to earlier seemed to indicate that the only reason the guy installed the internal spacer was to align the sensors, but that didn't make sense.

 

[Yawning Angel]

This should do the job, and for only 4mm TS-Optics ultra low profile T-2 to C-mount adaptor length only 4mm, T2-CS