Lodestar 2 and OAG

[Rodd]

I am using teh ASI 1600 with an OAG and the lodestar 2.  The ASI 1600 comes to perfect focus, but the lodestar 2 cannot be focused.  There is no way to focus it--moving the prism in or out does nothing for focus--it just positions the prism further into the light cone from a horizontal perspective.  I tried a flush mounted connector between the OAG and filter wheel and a 21mm spaced connector--there was no observable difference in the sub taken.  The sub taken with Lodestar 2 looks like a white circle that fills most of the FOV--but its not round--its looks like its chopped in half.  It looks like this for any position of the prism that penetrates the light cone.  Not sure what to do--vendor is stumped, not many answers at Starlight Xpress.  Its a common set up but no one seems to know much about it.  Dead in water until its solved.  Any Ideas?

 

Rodd

[Merlin66]

I assume your set-up is OAG>filter wheel>ASI 1600..... Roughly what's the distance from the centre of the OAG to the imaging plane?  55,60mm??

Does the Lodestar "usually" work OK? ie when imaging on it's own?

If everything else checks out I'd work backwards - ignore the imaging camera for the moment and get the lodestar to focus.... then move the Lodestar in/out the OAG until it's close to your measure 55-60(?) and retest the Lodestar focus when it works OK, then look at the imaging focus .... one small adjustment to the imaging camera, one small adjustment to the Lodestar - repeat until success.

 

[Rodd]

5 minutes ago, Merlin66 said:

I assume your set-up is OAG>filter wheel>ASI 1600..... Roughly what's the distance from the centre of the OAG to the imaging plane?  55,60mm??

Does the Lodestar "usually" work OK? ie when imaging on it's own?

If everything else checks out I'd work backwards - ignore the imaging camera for the moment and get the lodestar to focus.... then move the Lodestar in/out the OAG until it's close to your measure 55-60(?) and retest the Lodestar focus when it works OK, then look at the imaging focus .... one small adjustment to the imaging camera, one small adjustment to the Lodestar - repeat until success.

 

The 1600 focuses perfectly.  I was told to focus the 1600 first then the lodestar.  But there is no way to focus the lodestar.  The prism arm is only about an inch ong an it needs to stick into the Lodestar receptacle at least 1/4 inch and then into the OAG.  Moving the prism in and out does not effect focus.  Nothing I do effects focus.  I moved the telescope focus in a full 4' then out the maximum amount and the image taken by the lodestar does not change.  

I got the lodestar for this set up--haven't used it before.  But it connects and exposes so it should be fine. 

[Merlin66]

I understand...

That's why I suggested focusing the Lodestar (using the telescope focusser) first - just to confirm 100% it's seeing the light beam and can indeed focus on your system.

 

Then review the imaging camera to see how far you have to move the telescope focusser to bring it into focus - the difference is what you need to address with the Lodestar positioning.

 

[Rodd]

1 minute ago, Merlin66 said:

I understand...

That's why I suggested focusing the Lodestar (using the telescope focusser) first - just to confirm 100% it's seeing the light beam and can indeed focus on your system.

 

Then review the imaging camera to see how far you have to move the telescope focusser to bring it into focus - the difference is what you need to address with the Lodestar positioning.

 

I tried that--I cranked the focuser for the scope all the way in and all the way out and the lodestar did not change very much.  I know the prism was in the light cone because I moved it out until it wasn't and the image changed dramatically--got all snowy.  Before there was a white blob in middle.

[Merlin66]

Hmmmm

If the focus travel is longer than the backfocus of your OAG>Fliterwheel>ASI 1600 then you should have found a Lodestar focus - somewhere.

Have you tried the Lodestar on another telescope to verify the settings - exposure etc.

I use the Lodestar (under PHD2 - Latest Ascom driver) to guide my spectroscope using a "similar" oag set-up on a C11 at f10.........

[Rodd]

3 minutes ago, Merlin66 said:

Hmmmm

If the focus travel is longer than the backfocus of your OAG>Fliterwheel>ASI 1600 then you should have found a Lodestar focus - somewhere.

Have you tried the Lodestar on another telescope to verify the settings - exposure etc.

I use the Lodestar (under PHD2 - Latest Ascom driver) to guide my spectroscope using a "similar" oag set-up on a C11 at f10.........

I just got the lodestar to use with the 1600 and OAG.  I think the OAG is terrible design--there is no way to focus the lodestar except with the mainscope.  The lodestar trns on, connects to maxim and snaps subs--doesn't seem like there is much to check--it works.  But it doesn't at the same time.

[Merlin66]

If you can get an acceptable image from the Lodestar  using the main telescope focusser then other than verifying the distance - see my previous message - I don't know what to suggest.

 

[Rodd]

4 minutes ago, Merlin66 said:

If you can get an acceptable image from the Lodestar  using the main telescope focusser then other than verifying the distance - see my previous message - I don't know what to suggest.

 

I can't.  That's the problem....no one, including the technicians at OPT can help.

[Merlin66]

https://astronomy-imaging-camera.com/products/accessories/zwo-oag/

If the EFW is 20mm and the backfocus on the camera is 17.5 (assuming a T to T adaptor) this would infer a 37.5mm distance 

It could be that you need a spacer between the OAG and the filter wheel (or one between the filter wheel and the OAG) to bring this up to around 50-55mm to produce a focus at the guide camera.

Sounds like the guide focus could be too close to the top of the OAG body to allow the Lodestar to go inward. The lodestar needs 12.5mm plus adaptor

[Tim]

Ken is spot on Rodd, (as always ), the OAG chip must be physically brought up to the same focal plane as the ASI 1600 chip.

I use mine with a whole range of different telescopes and cameras that happen to be on review. To attach the OAG to the filter wheel, I have an Atik, I use a Baader adjustable locking clamp. The distance of the OAG can be altered by positioning it in the clamp.

On the odd occasion I need extra inward positioning to focus, I add a spacer in front of the imaging camera. But usually extra outward positioning is needed so I add a 1.25" nosepiece to the Lodestar.

Perhaps post a pic of your rig and we can advise where and what you need to change.

The only time it gets tricky is with field flatteners or reducers that have a critical back focus, sometimes a custom adapter is the only answer, but I have used my OAG's with every focal length from 70mm - 5500mm, there is always a way. 

Tim

[Tim]

An adapter similar to this one is what I meant,

https://www.firstlightoptics.com/adapters/baader-clicklock-2-125-adapter-2956214.html

[LightBucket]

I assumed the only way to focus the OAG is to move the Lodestar closer or further away from prism....so if no adjustment on OAG to move Lodestar then you will need spacers..or an adjustable spacer..

[RayD]

Tim and Ken are spot on.  The Lodestar can be a bit awkward to focus with an OAG, especially with the ASI1600, which from memory only has something like 6.5mm sensor distance.  I did a simple YouTube video here showing how I overcame this with the Atik 16200 and Atik OAG, but with the ASI it is very tight.

Edited March 17, 2018 by RayD

[Rodd]

6 hours ago, Merlin66 said:

https://astronomy-imaging-camera.com/products/accessories/zwo-oag/

If the EFW is 20mm and the backfocus on the camera is 17.5 (assuming a T to T adaptor) this would infer a 37.5mm distance 

It could be that you need a spacer between the OAG and the filter wheel (or one between the filter wheel and the OAG) to bring this up to around 50-55mm to produce a focus at the guide camera.

Sounds like the guide focus could be too close to the top of the OAG body to allow the Lodestar to go inward. The lodestar needs 12.5mm plus adaptor

 

3 hours ago, Tim said:

Ken is spot on Rodd, (as always ), the OAG chip must be physically brought up to the same focal plane as the ASI 1600 chip.

I use mine with a whole range of different telescopes and cameras that happen to be on review. To attach the OAG to the filter wheel, I have an Atik, I use a Baader adjustable locking clamp. The distance of the OAG can be altered by positioning it in the clamp.

On the odd occasion I need extra inward positioning to focus, I add a spacer in front of the imaging camera. But usually extra outward positioning is needed so I add a 1.25" nosepiece to the Lodestar.

Perhaps post a pic of your rig and we can advise where and what you need to change.

The only time it gets tricky is with field flatteners or reducers that have a critical back focus, sometimes a custom adapter is the only answer, but I have used my OAG's with every focal length from 70mm - 5500mm, there is always a way. 

Tim

 

1 hour ago, LightBucket said:

I assumed the only way to focus the OAG is to move the Lodestar closer or further away from prism....so if no adjustment on OAG to move Lodestar then you will need spacers..or an adjustable spacer..

 

18 minutes ago, RayD said:

Tim and Ken are spot on.  The Lodestar can be a bit awkward to focus with an OAG, especially with the ASI1600, which from memory only has something like 6.5mm sensor distance.  I did a simple YouTube video here showing how I overcame this with the Atik 16200 and Atik OAG, but with the ASI it is very tight.

OK--I have tried a spacer between the OAG and filter wheel--the OAG came with 2--neither helps.  I have tried this setup with the telescope focuser all the way in and all the way out (and points between)--there appears no change in the subs generated by the Lodestar.  If I move the loadster away from the OAG (out--like if I put a nose piece on) it gets worse.  It has to move closer not farther.  I have spoken with OPT (a major telescope/camera store in the US--considered among the best).  They calculate backfocuses and such--they are aware of all my setups because I put together my rigs with their help.  Before I star buying spacers and extension tubes, there has to be way to know what, exactly, I need.  The scope, camera, OAG and guider are all commonly used.  There are no custom or homemade parts, or odd configurations.

Rodd

[RayD]

3 minutes ago, Rodd said:

 

 

 

OK--I have tried a spacer between the OAG and filter wheel--the OAG came with 2--neither helps.  I have tried this setup with the telescope focuser all the way in and all the way out (and points between)--there appears no change in the subs generated by the Lodestar.  If I move the loadster away from the OAG (out--like if I put a nose piece on) it gets worse.  It has to move closer not farther.  I have spoken with OPT (a major telescope/camera store in the US--considered among the best).  They calculate backfocuses and such--they are aware of all my setups because I put together my rigs with their help.  Before I star buying spacers and extension tubes, there has to be way to know what, exactly, I need.  The scope, camera, OAG and guider are all commonly used.  There are no custom or homemade parts, or odd configurations.

Rodd

You could try by eliminating an issue with the OAG prism by installing the Lodestar directly in a 1 1/4 eyepiece holder in your focuser to make sure you can indeed get focus, and it will then let you calculate a rough distance.  It's a basic starting point but may stop you chasing around in circles.

Edited March 17, 2018 by RayD

[Rodd]

6 hours ago, Merlin66 said:

https://astronomy-imaging-camera.com/products/accessories/zwo-oag/

If the EFW is 20mm and the backfocus on the camera is 17.5 (assuming a T to T adaptor) this would infer a 37.5mm distance 

It could be that you need a spacer between the OAG and the filter wheel (or one between the filter wheel and the OAG) to bring this up to around 50-55mm to produce a focus at the guide camera.

Sounds like the guide focus could be too close to the top of the OAG body to allow the Lodestar to go inward. The lodestar needs 12.5mm plus adaptor

The lodestar can't go inward--in fact the lodestar cant move at all--it sits in its receptacle and is held with a locking screw.  The receptacle sits atop the prism arm.  The prism arm can only be adjusted a few mm in or out.  No position seem to do much.

[Rodd]

5 minutes ago, RayD said:

You could try by eliminating an issue with the OAG prism by installing the Lodestar directly in a 1 1/4 eyepiece holder in your focuser to make sure you can indeed get focus, and it will then let you calculate a rough distance.  It's a basic starting point but may stop you chasing around in circles.

Visual and imaging setups are very different.  I never change from one to the other because one may need a 2" extension and the other does not--it changes everything--balance, then alignment.  That is what is so annoying with the C11EDge--the FOV is so small that sometimes to find a planet or focus star I have to use an eyepiece and hunt--what a pain.  If I switch to a eyepiece holder, all the connections change.  I forgot to say I am using a .7x reducer with the TOA 130.  

Rodd

Edited March 17, 2018 by Rodd

[RayD]

1 minute ago, Rodd said:

The lodestar can't go inward--in fact the lodestar cant move at all--it sits in its receptacle and is held with a locking screw.  The receptacle sits atop the prism arm.  The prism arm can only be adjusted a few mm in or out.  No position seem to do much.

As I noted Rodd, you may not be able to use a Lodestar with the ASI1600 and OAG in its standard configuration as the ASI has a particularly short back focus distance.  I think the ZWO OAG is really designed for use with the ZWO cameras, the 120MM usually, which I believe also has a 6.5mm back focus.  The Lodestar has 12.5mm, so you simply may not be able to get it close enough.  With the SX OAG I got mine to work as the turret goes inside the camera chamber, but I don't think this is possible with the ZWO one.

[RayD]

2 minutes ago, Rodd said:

Visual and imaging setups are very different.  I never change from one to the other because one may need a 2" extension and the other does not--it changes everything--balance, then alignment.  That is what is so annoying with the C11EDge--the FOV is so small that sometimes to find a planet or focus star I have to use an eyepiece and hunt--what a pain.  If I switch to a eyepiece holder, all the connections change.  I forgot to say I am using a .7x reducer with the TOA 130.  

Rodd

Yes I appreciate they are different, I was just trying to obtain a focal point for your Lodestar to see if it can move in close enough when mounted to the OAG.  I would say not due to the very short back focus on the ASI1600.

[RayD]

You may need to swap the Lodestar for a ASI120MM or similar, or a camera where you can take the C mount connection off to push the sensor closer to the prism.

Edited March 17, 2018 by RayD

[Rodd]

1 minute ago, RayD said:

As I noted Rodd, you may not be able to use a Lodestar with the ASI1600 and OAG in its standard configuration as the ASI has a particularly short back focus distance.  I think the ZWO OAG is really designed for use with the ZWO cameras, the 120MM usually, which I believe also has a 6.5mm back focus.  The Lodestar has 12.5mm, so you simply may not be able to get it close enough.  With the SX OAG I got mine to work as the turret goes inside the camera chamber, but I don't think this is possible with the ZWO one.

But others use it like this--see my thread regarding Maxim DL and the Lodestar under software.  He had no problems (can't recall his name).  If the lodestar can't be used with the camera--someone at OPT should know this.  You may be right, but that would be surprising to me.  I had allot of different people at OPT involved with this purchase because I have 4 scopes and I want to use it on all of the.   (yeah...right!)

Rodd

[Rodd]

Just now, RayD said:

You may need to swap the Lodestar for a ASI120MM or similar, or a camera where you can take the C mount connection off to push the sensor closer to the prism.

I tried it with an ASI 174--which is supposed to work and I got the same results

[RayD]

Just now, Rodd said:

I tried it with an ASI 174--which is supposed to work and I got the same results

Well then that says to me it's a faulty OAG with a misaligned or damaged prism. 

[Rodd]

1 minute ago, RayD said:

Well then that says to me it's a faulty OAG with a misaligned or damaged prism. 

Maybe....I would bet against it though.  Its brand new, and looks ok....pretty simple thing).  Besides, Broken or "wrong" parts are not usually the cause of my troubles (which are at times numerous).  For example, I have sent my SBIG camera back 3 times because the filter wheel jams.  It has always been diagnosed in perfect health (another long and sickening story--hence the ASI 1600).

Rodd