Thanks Nigel and Peter, max travel is probably the culprit as you say, but based on experience of other autofocus programmes, I was expecting EKOS to determine a limit of increasing size itself to decide whether to focus in or out, to auto v-curve the action.

Is there a description of the algorithms employed in the various measurement options so I can see how the main variables the user inputs will affect the operation of the system?

All the best

Mark

Yes, the Litecrawler has extremely fine steps, for long focal length scopes. While I don’t manually focus at all, it has a dial to adjust the step size increment so you can move the focuser quickly if needed.

I’m a little confused at to what you referring to when you say “degrees”. I am not using the normal C11 focuser. The Litecrawler sits in the optical train and has its own focuser and rotator.

Here's some help that shows the relationship between the initial step size, max step size, and max travel. The goal is to get a nice curve. I can get a good curve with just 3 steps outward and inward. I have used more but it didn't improve anything.

You need to know how many steps YOUR focuser needs to go from an ideal HFR (smallest value obtainable) to 2 times that number.
This is first done by moving the focuser in small amounts and manually capturing images and noting the HFR values. Once you know how many focuser steps you need to double the HFR - the rest is easy.



This is how I set mine up, There may be other ways or methods - but this technique works VERY well for my setup. Obviously your actual values will be different, but the technique should work.

By degrees I was meaning how much you rotated the knob on the telescope. I was thinking you were using the standard focuser knob on you C11 like I do on my C6 but it looks like I’m mistaken.

Thx for the tips Peter, I'm sure people will find this very helpful.

I'm wondering if the 2x HFR "rule" that you use to setup focus would be more generally applicable to SCTs. If so, I can update the focus documentation. It would be interesting to hear your comments Nigel as you and Peter almost bookend the size range of generally available SCTs.

(Small point but just FYI, Linear and Linear 1 Pass don't use Max Step Size).

No I don’t use the built-in mirror focus. It leaves the mirror unstable and allows mirror flop. Also, it causes image shift while focusing. I’m at such a long focal length that neither effects are acceptable to me. The Moonlite Litecrawler allows me to keep my mirror locked down tight. In addition to focus it also gives me automatic rotation, perfect for remote control use.

Thanks John, I had a feeling I wasn't seeing any changes with the Max Step Size. It wasn't greyed out, so I wasn't sure.
I think my 2X rule is for long focal length scopes - such as an SCT with an OAG. I am imaging at either 0.8 or 0.4 arc seconds per pixel, and so small changes in HFR are noticeable.

Hi John

do linear and linear 1 use the max travel ?

I’ve noticed max step size being greyed out at times but not took much notice of it, but max travel seems to be available all the time.


Regards

Nigel

The Max Step Size should be greyed out but isn't on initial load for some reason. If you change the algorithm to something other than Linear/Linear 1 Pass and then back to Linear/Linear 1 Pass it is greyed out. Guess I need to fix that!

Max Travel is used by Linear and Linear 1 Pass. The idea is to provide some protection for focusers that don't know the max / min position. I think now most focusers have their own protection and if asked to move outside the min/max range wouldn't do it. I would recommend setting it above the normal range that the focuser would travel during a focus run. The algorithm will attempt to recover if you impede the range of movement it wants to use but there's no real benefit to this... just set the step size and number of steps appropriately and let the algorithm do its thing.

Hi John,

Can you clarify for me what tools in the focus module best cope with diffraction annuli as the focus is automatically moved in and out of optimum HRF for a scope with central obscuration - in my case an 8” RC?

Reading the evolving discussion between yourself, Peter and Nigel, and looking at the online documentation, I’m not entirely sure whether there is a mechanism in each algorithm to determine the outer diameter of an annulus (donut)? What I am finding with an obviously course focusing iOptron electronic focuser is that EKOS passes a point where it stops measuring the enclosed energy of the donut and limits itself to part of the donut (or indeed determines if can no longer detect a star).

I’m really just looking for guidance on what are the critical variables per implemented algorithm that are most appropriate for obscured catadioptrics?

Many thanks

Mark

Hi Mark,

Peter etal have more experience of this than me as I’ve only just got a focuser so you might want to take what I say with a pinch of salt….

The way I see it you need to move far enough from focus to get hfr’s that produce a V. Peters said how he does it and from his graph he gets a nice V. Me with my simpler equipment I’ve yet to get a proper V but I am developing an understanding of how this works now so maybe I will come up with an initial steps setting etc which works.
However I suspect that to get enough of a change in hfr I will stray into donut territory which leads to problems. Now I believe to handle those I need to pick/tweak the appropriate SEP settings. To do that I’m aiming to take some images that are out of focus to see what helps count the whole donut rather than just little bits. I’ve tried reading the ‘do not panic’ guide to SEP but obviously that’s for phd level people so I’m going to have to do some poking until I get an idea…unless of course someone else has already worked it out.


Regards

Nigel