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Walking on the Moon

Quick one about guide scopes.


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I'm using a SW ED80, eq5, 450D, all running through an Asiair Pro.  I bought a Zwo 120mm as a guide cam but despite months of trying every trick I could find on this and other forums, I cannot get it to focus with my Skywatcher finderscope. 

So with Christmas coming up I have decided to get a new guide scope, the Zwo mini guide scope sprang immediately to mind but while looking at the details on the FLO site I remembered the SW50 Ed. 

The Zwo is f4 with a 30mm objective 

The SW is f4.8 with a 50mm objective but 100 quid more. 

I am new to guiding and don't know what I'm looking for in a guide scope. I have no Idea what these numbers mean regarding guiding.  Not sure if the extra 100 quid is worth it. 

The long term plan is to upgrade the EQ5 to an EQ6R and the 450D to a dedicated astrocam. I don't know if this makes any difference. 

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For getting focus with SW 9x50 finder scope, try removing the front lens & locking ring, then screw just the front lens back on (no locking ring). This should give you the extra movement you need to obtain focus. ;) 

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The camera should work with the SW finderscopes though they usually have a need for an adapter depending on whether they are the right-angle or straight through.

With the right-angle you will need a C extension to make up the missing backspace. The straight through need the adapter screwed in quite far.

Both of course are adjusted using the locking screw/turn objective to focus. Can be done during the day to get a rough focus and twaeked on a star when clouds permit.

 

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Thanks all for the suggestions, I have tried all of these and cannot get focus.  I will be getting a new guide scope.  As I am new to the dark art of guiding I am not sure of how to match a guide scope to a camera, what difference focal length and size of the objective make when paired with a specific camera. 

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I'm no expert but I tend to work on the rough rule of thumb FL of guidescope around a third or more compared to FL of imaging which works for me. In reality the image scales of both should match closely. The F4 30mm does the job, but once I changed to the Altair 50mm with helical focuser guiding was immediately improved slightly, more stars were visible, and focusing the camera is very easy, it's just a bit heavier which affects light mount setups.

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The 9x50 finder makes a fantastic guidescope, what adapter have you as some require more inward travel, some outward depending on where the sensor is placed at the back.. try focusing during the day, it will be different at night but at least you're be closer

I'd say save your money for something else

Ed80 and 9x50 guidescope... Perfect..

Focal length is 180mm from memory btw

 

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7 hours ago, SmokeyJoe said:

Not sure if the extra 100 quid is worth it.

I use the SW ED 50 as a guide scope and it works really well.  I also use it as a very wide field imager as the glass in it is very good (too good tbh for just using as a guide scope).  However, to use it as an imager you’ll probably also need a guide scope 🙄.  I have the Flo Astro Essentials Mini Guidscope which is the same spec as the ZWO and just as good.  The only other bit you’d need is a mounting bracket as per attached pic.  A93C4827-9F53-442E-8DED-1185455DE11A.thumb.png.228677dfc458d6148ce6c93545baea8b.pngI use the ZWO 120 as guide cam too btw.  

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9 hours ago, SmokeyJoe said:

I'm using a SW ED80, eq5, 450D, all running through an Asiair Pro.  I bought a Zwo 120mm as a guide cam but despite months of trying every trick I could find on this and other forums, I cannot get it to focus with my Skywatcher finderscope. 

So with Christmas coming up I have decided to get a new guide scope, the Zwo mini guide scope sprang immediately to mind but while looking at the details on the FLO site I remembered the SW50 Ed. 

The Zwo is f4 with a 30mm objective 

The SW is f4.8 with a 50mm objective but 100 quid more. 

I am new to guiding and don't know what I'm looking for in a guide scope. I have no Idea what these numbers mean regarding guiding.  Not sure if the extra 100 quid is worth it. 

The long term plan is to upgrade the EQ5 to an EQ6R and the 450D to a dedicated astrocam. I don't know if this makes any difference. 

 

My plan is to use the 9x50 as a guider too - managed to find an M12 webcam adaptor and have achieved pretty good focus with my trusty Philips SPC900 webcam. However, I’m struggling to find a way to connect a modded handset to PHD2 so will likely use the bigger brother of the ASI120mm, the ASI120mc-s (I already have the T thread adapter), and multipurpose it as a better planetary cam - probably retiring the webcam to its original purpose!

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5 hours ago, SmokeyJoe said:

Thanks all for the suggestions, I have tried all of these and cannot get focus.  I will be getting a new guide scope.  As I am new to the dark art of guiding I am not sure of how to match a guide scope to a camera, what difference focal length and size of the objective make when paired with a specific camera. 

Show us a pcture of your finderscope, adapter and camera. The SW finderscope is a mainstay for some so your problem may be a simple fix.

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Yes a picture would help enormously to diagnose the problem.  I have used both the standard 9x50 SkyWatcher finder scope with adapter as a guide scope and the SkyWatcher ED50 as a guide scope. So it’s all doable. 

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I use the ZWO 30mm F4 and ASI120mm set up and it works just fine.  A bit of a faff getting focus first time (did it in daylight on a distant tree and jiggled the cam in-out of the tube and then locked it off) but once set it's never needed adjusting.  Guides my 90mm reduced FL (432mm) set up ok at 1s guide exposures.  Hope you get sorted.

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On 25/10/2022 at 12:28, SmokeyJoe said:

I bought a Zwo 120mm as a guide cam but despite months of trying every trick I could find on this and other forums, I cannot get it to focus with my Skywatcher finderscope. 

I have this combo. It's exactly 246mm from the front of the scope to the rear of the camera. Don't think you can alter the distance from the front to the lens, so if you can get this total lenght with bits and pieces you have laying around, your good to go! And, of course, any optics in the rear must out. Only tube, front lens and camera.

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I see you're receiving a lot of posts about making your existing guider work - I can't advise there, but if you decide to go down the route of purchasing another one, I'd say the SW50 is overkill unless you're also planning on using it as a widefield imager as it's a decent doublet in its own right (I say this as an owner of said scope, which is now only used exclusively for guiding).

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Thanks all for you helpful posts.  My guide/finder was supplied with my Sw200p Newtonian.  I am currently trying to use it with a SW ED80 refractor I assume that the finder scope supplied with these scopes is the same but could be wrong. 

I am set on buying a new guide scope,  as I say I am new to guiding (but not to AP) and would like to eliminate as many possible problems as possible. 

I read something in the past about an ideal ratio of something to something between the guidescope/guide camera assembly and the main scope/main camera.  Can find the post now, I suppose I could have been dreaming. 

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Just popping in to give a +1 for the Evoguide 50ED. I use it mounted on my Skywatcher 80ED and EQ6-R. Just the other night I'd got everything setup to give the ASIAIR Plus its first run and it was guiding as low as 0.36". I took my first proper  image with the 50ED using the field flattener - its a very respectable wide(r) field scope. You can guide it with your 80ED once you adjust the settings. I decided on this as you essentially get two scopes in one. Oh, and it looks beautiful in green against the red 😍

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1 hour ago, SmokeyJoe said:

I read something in the past about an ideal ratio of something to something between the guidescope/guide camera assembly and the main scope/main camera.  Can find the post now, I suppose I could have been dreaming. 

Is this thread of any use:

 

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You don’t say what imaging camera you are using. There are several things to bear in mind. First, is rule of thumb not to have your guiding pixel scale more than 4 or 5 times your imaging pixel scale. Pixel or imaging scale is 206 x (pixel size of the  guide or imaging camera sensor divided by focal length of the guide or imaging scope). It is measured in arc seconds per pixel. Second, the guiding imaging scale needs to relate  sensibly to your seeing conditions, as you are trying to measure the centroid of the guide star. Rule of thumb here is for the guiding scale to be half to a third of your seeing (again in arc seconds per pixel) to avoid bloated or blocky guide stars. Third, I have a 30mm f4 guidescope and use it with a Samyang 135mm setup as it is convenient and decent pairing for widefield.  My main scope is a 71mm refractor with 420mm focal length coupled with a zwo asi183 camera. I use the 120mm zwo mini as guide camera for both setups. I obtained much better results with a  zwo 60mm / 280mm focal length guide scope, which was picked up preowned for around £50. The 50mm & 60mm guide scopes come up quite often. PHD2 calibration is also much faster and less prone to error messages, plus the focussing is easier as well as the larger guide scopes tend to have more user friendly focusers. Suggest running the numbers - probably 50/60mm is what you need. Then check out the preowned ads before parting with £130. 

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