Recommended guiding for 250pds

[EchoTango]

Hi. First time poster. 
What would be a recommended guiding scope or OAG and camera for a 250PDS Newtonian? 
 

EDIT: Can a moderator move this to the Beginner forum please?

Edited April 5, 2023 by EchoTango
Wrong sub-forum

[ONIKKINEN]

Hello and welcome to SGL,
For a newtonian i will recommend an OAG over a guide scope any day of the week because the primary mirror itself can move a little bit during the night and the tube itself could slightly deform under gravity in different positions. If guiding with a guidescope, the guider is unaware of these movements and you can have bad looking frames while guiding reports everything is ok. OAG guiding fixes this since whatever movement happens anywhere between the OAG and the primary mirror will affect guiding also and be corrected.

For OAGs you have some choices, but most of these are convenience and sensor size related. Cheapest ones have 8x8 prisms and no guide camera focuser, more expensive ones have slightly larger prisms and integrated focusers for the guidecam. I have an Askar OAG in my 8'' newtonian which i have found to be very nice.
As for a guidecam, just a simple ASI120MM will do the trick almost all of the time. If you plan to place narrowband filters before the OAG (such as at the end of the comacorrector) then a 220MM will be a better choice.

[RolandKol]

It is always a trade off,

Depends what you want to achive....

If you want to increase the guiding perfomance, - AOG will do it, but Only Slighlty, - the main guiding factor is the Mount.

If you have not yet bought guiderscope and not sure which way to go to save money, - guider scopes are cheaper and easier to set up as you will be made to dance around AOG at the start for sure.

My personal experience: 
I did not like AOG on my small 130PDS + ASI1600MM as the prism casted a slight shadow on the chip, also I had some issues with polar alligment using Nina and/or SharpCap, - it was quite long time ago, so maybe updates have sorted PA issues out.

My rig is extremly Front Heavy (130PDS is quite small), - I just always need something  heavy at the bottom to offset it and the guider scope + cam was a good match.

These problems were quite managable, as I could do PA with guider scope I had (plus it worked in darker nights using AOG anyway), plus I could spend more time placing AOG prism in a correct distance to reduce the shadow,

However,

I was Not able to get a Correct ASI1600 SPACING! it was 1 or 0.5mm I missed and I just could not get rid of comma, it drove me mad, so I went back to the classical guiding. 

However (again),

I still think  AOG is the best way to go anyway and will try it again, as :
1) Easier balancing + less cables as you will not need dew heater for the guidercam, plus both cameras are in one place, cabling becomes easier (my guidercam was connected to the main cam with a short USB cable).

2) Slightly better guiding (I have not noticed any extreme guiding "profits").

3) The main advantage (in my opinion),  -  easier to go for the "Double Rig" with Newtonian, -  as you will be able to place a smaller rig on the top, - for example something with Samyang 135 which also works as counter-balance for the Front Heavy Rig (in your case it will be quite different as 250PDS is much larger)

Edited April 5, 2023 by RolandKol

[Craig a]

+1 for off axis guiding, I tried for months and months with a separate guidescope on my 10 inch Quattro, differential flexure was my problem, I got a zwo OAG and guiding was much much better 

[mikeyj1]

I started guiding on my 250pds with the SW finder and a guider adapter, this arrangement commonly called the 'finder guider' with a QHY5ii colour camera.  it worked well, and was easy to set up.  I've also changed to an OAG now and a 250 Quattro, with mixed results.  I agree with @RolandKol that the OAG is more difficult to set up, for not much improvement in guiding performance.  It also affects the back focus, so the Baader Quick lock that I  was using doesnt fit in the image train any more, which has led to a bit of Tilt in the images i think.  

In summary, the finder guider and big pixel colour QHY worked very well, is cheap to start and easier to set up.  I would start this way again if I had to do it over.

Mike

[powerlord]

I second that. All 3 of my setups use SW finders with my own 3d printed designed adapters - I use them no matter what I'm shooting with - from an 8mm samyang, through to 250mm redcat, through the newts all the way up to the 300pds and the C9.25. They work a treat. I also designed and printed basic ring mounts for them to clamp them tightly so I don't need to use adjustable finder style brackets. So they are pretty robust - just stuff em on, wrap a 5v usb dew heater round them, and job done. It also means that all my asiairs share the same guiiding setup.

[Paul M]

As above, I used the box standard 50mm spotter that came with my 250PDS and the 120mm mini guidescope. I did buy the proprietary adapter from FLO so the camera just screws on and is focused by the movable front element of the spotter.

Absolutely no problem. 

I have just upgraded my main scope to a RC10, so decided the longer focal length might need a longer f/l guidescope, so I upgraded that to a 60mm x 350mm Borg ED. But that is overkill with the 250 PDS. Nothing wrong with it either but the 50mm spotter is fine.

I've always avoided OAG's as my set up is not permanently set up and I have enough on my plate to get things going without going down that rabbit hole!🤪

Edited April 7, 2023 by Paul M

[michael8554]

"I've always avoided OAG's as my set up is not permanently set up and I have enough on my plate to get things going without going down that rabbit hole!🤪"

If you store the OAG with both cameras mounted, then it becomes a plug-and-play item, no setup required.

And the 1200mm FL of the 250PDS  is crying out for an OAG, but I appreciate the "sideways" configuration might cause other problems.

Michael

[EchoTango]

Thank you all for you Feedback. It is highly appreciated. 

[Paul M]

2 hours ago, michael8554 said:

If you store the OAG with both cameras mounted, then it becomes a plug-and-play item, no setup required.

I do, I do!

I only move the optical train if I've got good reason.

The faff is in the setting up of an OAG. And as I say. By the time I'm up and running, and the routine problems solved, the last thing I then want it to do is complicate things voluntarily!

Another advantage of having a guidescope on a dovetail clamp on top of the scope is that I can use it for fine balancing of the OTA also. Just slide it up or down as required and job done!