From oag to guidescope

[Robindonne]

Oke very helpfull thx.  So to make my setups complete and good...

my newtonian is now equipped with my oag and dslr.   Need to look for a better guide camera and a comacorrector to make te whole setup complete.  

i bought another sct-oag/360 rotator(secondhand but cheap and unused/sealed) for the occasional use of my c8. Bought is because it came for sale and the mentioned refocussing of the oag-guidecam when swapping an oag between scopes.  
This setup also gets the better guidecam to make it complete also.

whats left are two old ed refractors.  Kind of planned to use as guiders when not used as mainscopes, but the oag’s are the guiders from now on.  

So my final question ( for now😬) would be: how to guide the refractors?   Also the oag (what some mentioned an overkill) or for this maybe a small guidescope?
Both zenithstars and both need extenders to get in focus. I would prefer spending another 80,- on a thick oag then on a simple 2” extender.

my budget is not made of 6 figures but spending money on the right stuff (instead of the earlier mentioned “asi120-paper-weight) is always justified.   
 

-better guidecam like the asi290 mono?

-f4 aplanatic coma corrector

-small guidescope for the refractors or also oag?

its rainy and cloudy here in the best soccer/f1 country, so plenty of time to look for missing items. 

 

[uhb1966]

The Dalek Obs??? Cool!

[uhb1966]

4 minutes ago, Robindonne said:

Oke very helpfull thx.  So to make my setups complete and good...

my newtonian is now equipped with my oag and dslr.   Need to look for a better guide camera and a comacorrector to make te whole setup complete.  

i bought another sct-oag/360 rotator(secondhand but cheap and unused/sealed) for the occasional use of my c8. Bought is because it came for sale and the mentioned refocussing of the oag-guidecam when swapping an oag between scopes.  
This setup also gets the better guidecam to make it complete also.

whats left are two old ed refractors.  Kind of planned to use as guiders when not used as mainscopes, but the oag’s are the guiders from now on.  

So my final question ( for now😬) would be: how to guide the refractors?   Also the oag (what some mentioned an overkill) or for this maybe a small guidescope?
Both zenithstars and both need extenders to get in focus. I would prefer spending another 80,- on a thick oag then on a simple 2” extender.

my budget is not made of 6 figures but spending money on the right stuff (instead of the earlier mentioned “asi120-paper-weight) is always justified.   
 

-better guidecam like the asi290 mono?

-f4 aplanatic coma corrector

-small guidescope for the refractors or also oag?

its rainy and cloudy here in the best soccer/f1 country, so plenty of time to look for missing items. 

 

+1 for the coma corrector! IMHO absolutely needed for good pics. Tip: they dont put the infos on "distance of coma corrector to cam" for nothing, as i learned the hard way - even if you're like 3mm off, you see it in the pics :/  

[Robindonne]

16 minutes ago, uhb1966 said:

+1 for the coma corrector! IMHO absolutely needed for good pics. Tip: they dont put the infos on "distance of coma corrector to cam" for nothing, as i learned the hard way - even if you're like 3mm off, you see it in the pics :/  

Do you think i get in trouble when between the cc and dslr is 16 mm space used by the oag?Or does the required backfocus of 55 mm mean that between the cc and dslr sensor 55 mm is required?  When thats the case i need to extend more.   Strange because i had to move the focuser almost completely in to get focus(no coma corrector)

Edited June 4, 2020 by Robindonne

[wimvb]

34 minutes ago, Robindonne said:

Do you think i get in trouble when between the cc and dslr is 16 mm space used by the oag?

Yes. 45 mm is inside the dslr. 10 mm is the t-ring adapter between the cc and dslr. There are some coma correctors that allow/need more than the standard 55mm distance. But I believe, these are more expensive.

59 minutes ago, Robindonne said:

how to guide the refractors?

If you have a working oag solution, you can use it on basically any telescope. But imo, you'll get tired of swapping guiders around. Once you find a stable, functioning configuration, you probably don't want to disturb it. But take that hurdle in due course. 

[alacant]

46 minutes ago, Robindonne said:

i get in trouble when between the cc and dslr is 16 mm space used by the oag?

Hi

Yes. You don't have enough distance. The gpu requires 55mm, so you have only 10mm for the oag. 16mm will take you too far. 

Why not get one specifically designed for DSLRs? Apart from the economics, this one just works. 

HTH

Edited June 4, 2020 by alacant

[alacant]

9 minutes ago, wimvb said:

10 minutes ago, wimvb said:

I believe, these are more expensive.

 

Hi

The GSO is less expensive and gives you 75mm to play with.

[Robindonne]

4 hours ago, alacant said:

Hi

Yes. You don't have enough distance. The gpu requires 55mm, so you have only 10mm for the oag. 16mm will take you too far. 

Why not get one specifically designed for DSLRs? Apart from the economics, this one just works. 

HTH

Wow.  To solve one problem you receive another one for free.  Oke.  The 45 is swallowed by the dslr that gives me 10 mm left for oag and ring.  Thats tight.   Then im glad im still free to choose the gso cc.   Im really curious to the problems that will bring😅

[Robindonne]

4 hours ago, alacant said:

Hi

The GSO is less expensive and gives you 75mm to play with.

Very much thx.   This is the one that will be on its way to Nl soon

[Robindonne]

The gso is not available at flo nor in the netherlands.  The germans offer one that looks the same.  Also the 75 mm. But is it any good?   

[wimvb]

9 hours ago, Robindonne said:

The gso is not available at flo nor in the netherlands.  The germans offer one that looks the same.  Also the 75 mm. But is it any good?   

Very  likely rebranded from the gso factory

Edited June 5, 2020 by wimvb

[alacant]

9 hours ago, Robindonne said:

This is the one that will be on its way to Nl soon

¡CAUTION!

I wouldn't recommend it.

The focus position is 35mm further out from normal focus making it very wobbly. Even with a solid 2.5" hexafoc, it was difficult to hold a dslr correctly and balance is made much more difficult as the turning moment at that distance from the tube is excessive. Not workable for us at least, but of course YMMV.

It's available here.

Edited June 5, 2020 by alacant

[wimvb]

Have a look here

https://www.astrofotoblog.eu/?p=856#more-856

cc review, only one with a distance larger than 55 mm

[Robindonne]

Oh okay.   Wanted to ask why it is this much cheaper then the most alternatives. Mine is a quattro8 f4.   And even though i dont have any experience with these issues, i dont want to rebuy another one later due to my fear of more astro paperweights.   But basically the aplanatic from skywatcher (the one thats reviewed very very good for the Quattro’s), and many other 55 mm backfocus needed cc’s, leaves only room for 10-12 mm between the oag and camera housing.  Thats very tiny.   It means buying a third thin oag😑.   Probably better go safe for a skywatcher cc with an asi camera and use my existing oag.

Edited June 5, 2020 by Robindonne

[wimvb]

8 hours ago, Robindonne said:

Probably better go safe for a skywatcher cc with an asi camera and use my existing oag.

Probably. Eventually you may want to try mono imaging or get a cooled camera anyway. If you have the funds, then why not now?

[uhb1966]

I'm using the baader mpcc. Not bad. Works very well with Canon EOS. With my QHY8, i needed to get a bit creative. Can send pics if needed. Best, U.

Edited June 5, 2020 by uhb1966

[SimM]

On 02/06/2020 at 23:03, wimvb said:

3. More aperture means more light on the guide cam, so easier to find a star, and better signal to noise ratio.

Is that 100% true e.g. any scope that's F/7 or F/10 etc. has the same speed? So a 8" SCT with a Reducer at F/7 is more/equal sensitive as some 50mm guide scopes at F/7-ish?

I must admit I thought an OAG on a SCT would have no trouble compared to a small finder (with it's tiny comparative objective area) - but maybe I didn't think it through enough.

Simon 

[alacant]

12 minutes ago, SimM said:

Is that 100% true

Hi

Over the same period of time, an 8" f7 telescope collects the same amount of light as an 8" f10.  The f7 has the advantage that the oag will see more of the sky and so it's more likely to be able to find a suitable guide star.

A 2" f4 guide telescope collects far less light compared to either of the 8" telescopes but it sees far more of the sky; it has far more stars from which to choose.

Cheers

Edited June 5, 2020 by alacant

[Robindonne]

20 hours ago, uhb1966 said:

I'm using the baader mpcc. Not bad. Works very well with Canon EOS. With my QHY8, i needed to get a bit creative. Can send pics if needed. Best, U.

Ok while this post is almost finished.  One last ???    What does mpcc stand for?

[Robindonne]

20 hours ago, uhb1966 said:

I'm using the baader mpcc. Not bad. Works very well with Canon EOS. With my QHY8, i needed to get a bit creative. Can send pics if needed. Best, U.

Oh thanks for offering pics.  But im really not in the position to judge them😬.  Maybe in a year or more.  But for this moment im still in a learning phase

[Starflyer]

If you plan to use the camera and OAG combination on a refractor as well as your newt then get the very thin (10mm) OAG.  This combo will have to work on both scopes and most flattener / reducers for fracs need 55mm backfocus.

Once you have a working set up with 55mm backfocus you can simply swap the coma corrector for the flattener / reducer to use the camera on a different scope.

To complicate matters the SW coma corrector uses a 48mm thread, I'd go with the Baader MPCC, which uses a standard T thread, but check the flattener / reducer for your frac uses a T thread.

Complicated I know, but worth getting it right and only spending the money once.

[SimM]

On 07/06/2020 at 20:40, Starflyer said:

If you plan to use the camera and OAG combination on a refractor as well as your newt then get the very thin (10mm) OAG.

A 10mm thin OAG is just the OAG throat with an adjustable prism and possibly a focuser. That's good, because you can add t- adapters et.c each side to get the required setup and BF.

I'm finding it hard to get a decent spec. on any of the available (and not to specialist/expensive) OAGs.

They don't seem to do a good job at detailing the available movement of the prisms and what the BF behind the prism is.

By only concentrating on the total BF for a camera e.g. when using a DSLR, they neglect to say important details about the range of adjustments on the OAG for the prism.

Since the BF is common to both cameras, it needs more information about the prism adjustments to allow selection and operation of the OAG.

As an example, if you don't know the range of prism height adjustment available, then you can't be sure that the prism can be moved into and out of the way of the main sensor, especially when the available depth of the guide camera has to be considered before adding extension tubes between the OAG and the camera, which will effect how much the prism interferes with the main sensor.

Simon

[Robindonne]

I bought a 16 mm oag, a flattener, and again an even thicker oag before i asked questions on this forum.  I realize now that  it wasn’t the smartest move.   Didn’t even know the importance of the correct backfocus.  So im back to the drawingboard!   Although not really experienced with this oag issue, i do think moving the prism in and out the path of the main sensor doesn’t get the guidecam in focus.  In my case its the t-mount for the guidecam that has to be adjusted closer Or further from the prism.  The prism just stays in place.   I needed 1 mm extra to get the guidecam in focus so just used a small washer between the guidecam t-thread connection 

Edited June 9, 2020 by Robindonne

[Robindonne]

On 07/06/2020 at 21:40, Starflyer said:

Once you have a working set up with 55mm backfocus you can simply swap the coma corrector for the flattener / reducer to use the camera on a different scope.

That was indeed my initial plan.  To build one camera/guidecam/oag assembly to swap between scopes.  Again warned by members here and again have to admit they were right.  I think it is going to be a seperate oag for the newtonian.  
I bought the oags secondhand and didnt pay more then 100,- for the two, so no bigg losses till now. Both TS, a 16 mm and a thicker rotatable one that’s on my c8 and stays there i hope(while typing starting to think of the backfocus of that f/6.3 reducer on the c8🙄).  

If it was more standard i would definitely build a swappable camera/guider set.  But with the different connections needed between the correctors i probably end up having at least two configurations.  
 

 

edit: the backfocus seems to be 105 mm so i’m safe for the c8/reducer/ultra thick oag/dslr config🙏🏼

Edited June 9, 2020 by Robindonne

[Robindonne]

On 07/06/2020 at 21:40, Starflyer said:

Complicated I know, but worth getting it right and only spending the money once.

Can you give me some advice from where i have to start measuring the 105 mm backfocus in this setup?

 

Edit.  I did find some info on measuring and from what point to start.  Although it seems not very logical to start measuring from the end of the sc thread (it is like 10 mm behind the glass of the reducer??). I had a 10 mm extension ring somewhere laying to keep some paper in place but it suddenly had a purpose for reaching that 105 mm backfocus.  The total package from the glass of the reducer is now around the 105 mm: 66 mm (extensionring, oag, T-mount) and 45 mm inside the dslr.
I couldn’t use the whole thread on the reducer, only 6 mm. 

Edited June 9, 2020 by Robindonne