Skywatcher heritage 130p helical microfocuser

[pointofthis]

I recently bought a skywatcher heritage 130p, and was planning on getting a helical microfocuser for it (https://agenaastro.com/baader-1-25-t2-eyepiece-holder-helical-microfocuser.html), my questions is, can a helical microfocuser work with the helical focuser already on the skywatcher heritage 130p, or would I need to mod it?

[Louis D]

May I ask why?  The focuser on it is already basically a helical microfocuser.  Adding anything above it would probably prevent you from reaching focus.  I've not read of anyone trying to replace the original focuser with another helical microfocuser.  There is this thread documenting adding a 2" Crayford focuser to one:

 

Edited December 13, 2022 by Louis D

[vlaiv]

Hi and welcome to SGL.

If you want to replace stock focuser with Baader one - you'll probably have to do some modding.

As far as I can tell - stock focuser does not have T2 thread on it, so there is no easy way to attach Baader one.

Best course of action is to try to replace it. Adding another focuser on top of stock one will cause issues with reaching focus, as already pointed out by Louis above.

Can stock focuser be removed? From images online, it seems to be single piece with top assembly that holds secondary? That might cause problem when trying to replace it as only way would be to cut it off.

[happy-kat]

Some have found wrapping PTFE tape around the focuser will take up any movement there might be, I've also seen photo of one wrapped with insulating tape to make for a very snug fit. I haven't found it essential to do on the heritage 130p I use so haven't got round to trying.

[Vulisha]

Fancy trick with heritage is that you can retract a tube a bit and then there is no focus you cannot reach, just watch for colimation 

Edited December 13, 2022 by Vulisha

[vlaiv]

1 minute ago, Vulisha said:

Fancy trick with heritage is that you can retract a tube a bit and then there is no focus you cannot reach

I would worry about retracting each column by slightly different amount - that would cause tilt / misalignment which would result in poor colimation, but maybe there is nothing to worry about if top assembly is very stiff and does not allow for different amount of retraction?

[Vulisha]

You just need that pinhole colimation/camera film  cap and adjust it, it is good enough. My heritage has some aberations so it cannot achieve perfect picture anyhow

Edited December 14, 2022 by Vulisha

[Louis D]

4 hours ago, Vulisha said:

My heritage has some aberrations so it cannot achieve perfect picture anyhow

I'm curious what they are.  Certainly there's uncorrected coma since 1.25" CCs are hard to come by.  Are there others?

I had thought about getting a Heritage 150, but decided I'd miss 2" eyepieces and CCs too much, so I recently picked up a used 6" f/5 GSO Newtonian with the dual speed focuser.  I have been impressed with the quality of the mirrors.  Our weather has been terrible, so it's been difficult to critically evaluate it, but so far it exceeds my expectations for about $300.

[Vulisha]

It is spherical aberation together with coma, mirror was not polished perfectly. Well it is space conscious telescope, but I bought 127 mak now, perfect optical performance. 

[Louis D]

1 hour ago, Vulisha said:

It is spherical aberration together with coma, mirror was not polished perfectly.

Thanks for the info.  I wonder what its wavefront error measurement is.

If the weather ever clears up here, I'll try to do a careful star test on the GSO 6".

[happy-kat]

can you have spherical aberration on a parabolic mirror?

[CraigT82]

24 minutes ago, happy-kat said:

can you have spherical aberration on a parabolic mirror?

Absolutely, if the parabola isn’t actually a parabola due to poor figuring 

[cajen2]

I have to say, after collimation, that my Heritage 150p shows no aberrations at all. I've never needed to try shortening the light path but I'd imagine this wouldn't throw off collimation much, as the two trusses are stoutly supported.