VectorQuantity

43 minutes ago, teoria_del_big_bang said:

Okay as I have only had the Sesto Sensos (well also I had a belt driven DSD very early on) then I have to accept what you say.
To be honest I never thought of the collar of the focusser not being concentric, I only thought the issue would be is if the fine focusser spindle was bent, which is easily done, I think I just assumed that within a few tens of microns they must be concentric, but yes if not then I guess it could be an issue with that type of attachment.
I guess I have been lucky then as mine must have been pretty much concentric (stock focusser on Esprit 100ED, Baader steeltrack on my RC6 and a stock focusser on my WO72) as I certainly have not had any wobble.

Also same really regarding the number of pulses you can afford to loose without seeing any visual determinable difference in focus of the image. Now hands up I have not yet used the RC6 in anger as this is still very new to me, but the 100ED you can achieve good focus in NINA , or EKOS, and then go 10 or 20 steps either side of that before you could see any real change to the actual focus, but as you say the focal length of the scope would affect this.

So I accept there could be issues with this mounting method.

Steve

If it's of any help to anyone the approximate cricial focus zone (depth) for different F numbers for blue (470nm) which is the most sensitive is along the lines of: (the ratios should be correct even if absolute values don't tie up with your calcs)

F2, 4, 6, 8, 10 ,12

9, 36 ,82, 146, 229, 330 microns

This is just to give an idea of sensitivity to F number, in practice you'd want to place focus within the CFZ up to 10 times better than these figures.

6 minutes ago, teoria_del_big_bang said:

I have two Sesto Senso focusers for my two rigs and very happy with them (hence why I bought the 2nd one.

The first one was the version 1 and that came with a solid coupling (well several couplings to fit various focusers) and yes that does have to be aligned pretty accurately but I really did not find that difficult.
The second one I got is the V2 (so I guess the version you would get if buying new) and that has flexible couplings to allow for some mis-alignment. So they are flexible to allow for this mis-alignment but in a rotary direction have no flex and so are very accurate.

Personally I like the way they fit to the collar of the focusser where you removed the focusser knob and find it a real neat solution with no flex at all between the stepper motor and the focusser fine tune spindle so super accurate.

I think focusers that are on a right angle bracket can suffer from some flex and those using a timing belt can suffer backlash and flex. BUT, after saying that my thoughts are that so long as you attach the motor to the fine tuning know or spindle then a few lost pulses of the stepper due to flex or backlash should really have no noticeable affect of the final focus as seen in the resulting images. If the motor is driving the rough focuser knob then it might be more prevalent.
So it you are doing the first scenario I guess any of these auto focusers would be just as good as the other.

Steve

 

I've had a Sesto senso (V1) with flexible couplings fitted to three different WO scopes. The connection method to the outside of the focuser collar is a nice idea but assumes the focuser collar is concentric with the focuser shaft. On two of my WO's it was not concentrice and despite all attempts at alignment you could actually see the Sesto senso 'wobble' as it's stepper rotated. Luckily these scopes had relatively long focal lengths and a non-critical focus zone.

To just compare the EAF/Senso/WhateverFocuser by itself is difficult maybe impossible, leaving out the attachment method and step size other significant variables are the focus software and scope focal length (focus criticality) both of which have large effects on the focus outcome.

Having used both EAF and Sesto senso (and Moonlite) on multiple scopes.

ZWO EAF works well, as long as one of the ZWO choice of mounting plates fits your scope, or you adapt a ZWO supplied one. Backlash seems good, accuracy seems good, undecided about load handling.

Sesto senso 'can' be fine but suffers from it's mounting method. The attachment point being the outside of the focuser train which is not necessarily concentric with the focuser shaft. If the focuser shaft and focuser 'outer' are not concentric the Sesto senso will 'wobble'. Backlash seems to appear if 'wobble' is present, otherwise accuracy seems good, load handling seems good.

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