EdgeHD 8 and Lakeside Focuser issues

[souls33k3r]

Hi All, 

Last night I thought I should bring out my EdgeHD 8" scope and try out my Lakeside focuser and also get all the spacing correct since now I'm using and OAG. 

Spacing came down to 105.6mm which I measured it with caliper. Installed the lakeside focuser bracket which had a bit of an issue aligning the second L bracket which connect to the OTA so filed the aluminium. Once done, I took the setup out and when started to do focus run I noticed that the lakeside focuser shaft was sandwiched between the two L brackets moved slightly in the middle and all started to work. But that was all that worked for me. 

I then brought my scope close enough to focus (The numbers of steps the focuser was moved from 0 - focus was around 112,000), reserved the motor on Pegasus UPB and marked the new position to 0 (because for some reason lakeside max steps that it auto focuses is around 65536?). Any way, using SGP and HFR values and Lum filter, I was focused at around 2.4 - 3 HFR (The values jumped with each frame even when the focuser position was not changed and I don't know maybe it was the seeing). Then using @RayD video I calculated the steps it took to have the HFR values between x3 - x5 and the steps it took was nearly 1500. Calculated the steps size for SGP and away I went. I entered the backslash compensation to values of 100 - 800.

Now the issues. 

1) Every time I was close enough to focus (the HFR values being low) I took an image and my stars looked blown out. Even when I was moving the focuser position to 500 steps the HFR values would not change. 

2) I was able to focus disregarding the HFR values to make the stars look smaller by manually focusing to a higher number. 

3) When running the auto focus run, some times I would get a straight horizontally but at times when the auto focus run would be successful, I would get a lower value of HFR on the green line but then the last two subs would make the value go higher. Even if the higher number was acceptable, the "Auto focus is complete) value would be around 2x higher than what it showed on the green focus line. 

Also not sure what the first 3-4 points are, how these are getting introduced? 

4) I'm not sure where this 1197 value of the focuser is coming from? I did something at the beginning of the session but did not pay much attention to it but the 1197 value was around 532, again not sure where this value is coming from? 

5) Attached is a 30s sub, I think I know collimation is my first issue but also would an out of collimate scope show out of focused stars and also have an impact on focus run? 

elephant lum.fit

Sorry about the lengthy post but I wanted to list them all and see if I can get some assistance on the points. 

Please mention the point number when answering so that I can document everything. 

Cheers

 

[symmetal]

The first 4 points being horizontal means the backlash compensation value used is not enough or things are not tighted up in the focuser. The stepper is rotating but the scope focus tube ( or mirror if connected directly to Edge HD focus control) is not yet moving until the gear backlash is taken up. This also explains why your final focus position is incorrect as the final move is in the opposite direction to get back to the centre position and so backlash is being taken up rather than the focuser tube actually moving. The excessive backlash is possibly the grub screws on the lakeside shaft adapter not being aligned on the flats of the shaft. Not sure how your two brackets are fitted. A picture may help. 

The lakeside probably uses a 16 bit value to store the focuser position, hence the limits being 0 - 65535 steps. Your setup having 112,000 steps means you cant have full travel with the lakeside but that shouldn't be a problem if you set it in the range you normally use it.

Alan

Edited April 6, 2020 by symmetal

[souls33k3r]

57 minutes ago, symmetal said:

The first 4 points being horizontal means the backlash compensation value used is not enough or things are not tighted up in the focuser. The stepper is rotating but the scope focus tube ( or mirror if connected directly to Edge HD focus control) is not yet moving until the gear backlash is taken up. This also explains why your final focus position is incorrect as the final move is in the opposite direction to get back to the centre position and so backlash is being taken up rather than the focuser tube actually moving. The excessive backlash is possibly the grub screws on the lakeside shaft adapter not being aligned on the flats of the shaft. Not sure how your two brackets are fitted. A picture may help. 

The lakeside probably uses a 16 bit value to store the focuser position, hence the limits being 0 - 65535 steps. Your setup having 112,000 steps means you cant have full travel with the lakeside but that shouldn't be a problem if you set it in the range you normally use it.

Alan

Cheers for the very value input Alan. 

I used 800 as the backlash value but it still did not help. I know @PhotoGav has the same setup apart from the fact that he is not using the reducer while I am and I'm pretty sure he mentioned the backlash value he has used was super low.

I think I will have to find a way to figure out the backlash then.

I will take off the focuser and re-attach it because I did do that while in the dark but I was certain that the flat end of the focuser was properly aligned and tight. I did also make sure that the focuser was moving with every command so not sure where this all mignt be coming from now. Time for a rethink. 

Here are a few pictures showing how the focuser is attached to the back and the focuser which might help explain the setup slightly better

The gap between the focuser pin and shaft. 

Screws that hold the focuser L bracket and L bracket attached to the scope

L bracket attached to the scope stock focuser

The two L brackets 

[Davey-T]

Never had much success try to autofocus my SCT on the stock focuser knob, too much backlash ie mirror movement, works a whole lot better after locking the mirror focusing with some sort of motorised final focuser, I know you're dying to spend more money 😂

Also tricky working out backlash and step size on a moving mirror setup.

Dave

[Stuart1971]

Yes, I think you would be much better with a motorised Crayford focuser on the back of your SCT, as has been said, with the mirror shift it will never work, I tried it a few years back, and someone gave me this advice, I took it and never looked back..... 👍😀

[souls33k3r]

Oh here we go again. I think I should stop coming here because you lot make me keep spending money  which focuser do you recommend that isn't silly price? 

I don't know if it's the motor or not but this is how it sounds, listen carefully (volume up please and close to your ear) There's a grinding noise at the end of the focus run. 

 

[symmetal]

1 hour ago, souls33k3r said:

Cheers for the very value input Alan. 

I used 800 as the backlash value but it still did not help. I know @PhotoGav has the same setup apart from the fact that he is not using the reducer while I am and I'm pretty sure he mentioned the backlash value he has used was super low.

I think I will have to find a way to figure out the backlash then.

I will take off the focuser and re-attach it because I did do that while in the dark but I was certain that the flat end of the focuser was properly aligned and tight. I did also make sure that the focuser was moving with every command so not sure where this all mignt be coming from now. Time for a rethink. 

Thanks for the pictures. It makes more sense now. 😀 As Dave and Stuart have said it looks like trying to move the mirror directly with the autofocuser is more trouble than its worth, and using a separate focus tube on the rear of the scope with the autofocuser is the way to go.

You can check whether you have sufficient backlash compensation by checking the focuser knob moves slightly 'inward' after having completed a focus out command, (assuming you have selected the 'IN' direction in the SGP focuser setup). This means the compensation has taken out all the backlash and your first autofocus V curve segment should then not be flatter than the rest. Setting the backlash compensation too high is not a problem. It just means the focuser moves a greater total distance when focusing out so takes more time.

Alan

[symmetal]

The 'grinding' noise may be the mirror weight and mechanism pushing back against the autofocuser once the stepper has stopped moving. The residual torque of the stepper once de-energized may not be enough to hold it in place. As the lakeside motors are heavily geared down this should not normally be a problem but I don't know how much force the mirror mechanism is exerting. Just a thought. 🙂

Spending more money is the best cure. 😁

Alan

[Davey-T]

On special offer ATM or go mad and get the R&P version.

Dave

https://www.telescopehouse.com/accessories/revelation-2-sct-crayford-1-11-dual-speed-focuser.html

Edited April 6, 2020 by Davey-T

[Davey-T]

Have you tried having the camera looping and using the Lakeside utilities to play around with step sizes ? you can set step size, backlash and move it a number of steps while observing the on screen image.

Dave

Edited April 6, 2020 by Davey-T

[souls33k3r]

Ok I just had 2 different thoughts. 

1) Because I use the Pegasus UPB, when I had to go from 0 - infinity, I noticed I had to go in reserve so change the directions on UPB and it was fine. In SGP, for backlash, I was using the IN option rather than OUT. Could that be another thing I need to look at? Thoughts? 

2) I'd love to solve this issue with a Crayford / R&P focuser but having just spent a good sum on something else, I do not like the sound of spending more money on Moonlite CHL focuser which is for EdgeHD scopes but that too needs collimating from time to time so how about the celestron focuser? Could this be a solution? 

https://www.firstlightoptics.com/astronomy-cables-leads-accessories/celestron-focus-motor-for-sct-and-edgehd.html

Not sure how it would be any different to having Lakeside? 

[Stuart1971]

6 minutes ago, souls33k3r said:

Ok I just had 2 different thoughts. 

1) Because I use the Pegasus UPB, when I had to go from 0 - infinity, I noticed I had to go in reserve so change the directions on UPB and it was fine. In SGP, for backlash, I was using the IN option rather than OUT. Could that be another thing I need to look at? Thoughts? 

2) I'd love to solve this issue with a Crayford / R&P focuser but having just spent a good sum on something else, I do not like the sound of spending more money on Moonlite CHL focuser which is for EdgeHD scopes but that too needs collimating from time to time so how about the celestron focuser? Could this be a solution? 

https://www.firstlightoptics.com/astronomy-cables-leads-accessories/celestron-focus-motor-for-sct-and-edgehd.html

Not sure how it would be any different to having Lakeside? 

Why do you have to change direction on UPB...? Are the “in”and “out” the wrong way round as that was supposed to be fixed....?

[symmetal]

16 minutes ago, souls33k3r said:

https://www.firstlightoptics.com/astronomy-cables-leads-accessories/celestron-focus-motor-for-sct-and-edgehd.html

Not sure how it would be any different to having Lakeside? 

This uses a DC motor rather than a stepper motor so accurate positioning would be more difficult. It has an Ascom driver but I don't know if SGP will work with it or if SGP just works with stepper based focusers. Hopefully someone can say how well they perform.

Alan

[souls33k3r]

23 minutes ago, Stuart1971 said:

Why do you have to change direction on UPB...? Are the “in”and “out” the wrong way round as that was supposed to be fixed....?

No they're not but for this scope it was so had to reverse it. 

 

10 minutes ago, symmetal said:

This uses a DC motor rather than a stepper motor so accurate positioning would be more difficult. It has an Ascom driver but I don't know if SGP will work with it or if SGP just works with stepper based focusers. Hopefully someone can say how well they perform.

Alan

Ah, bummer. Did not see that but because there was a massive hype behind this a few months ago, I thought I should throw this in the mix. 

[symmetal]

On 06/04/2020 at 19:04, souls33k3r said:

Ah, bummer. Did not see that but because there was a massive hype behind this a few months ago, I thought I should throw this in the mix. 

Actually, in the specification it states it uses a DC servo motor which implies feedback via optical encoders or similar, in order to give more precise control of angular position, which is what you need. Nothing in the description mentions this, which I thought would be a good selling point, so am not sure what actual system it uses. The reviews state that people are happy with it and that it works well for automated focusing, so it may be worth a try. Hopefully someone here uses one and can give a more informed answer. 

Alan

[souls33k3r]

12 minutes ago, symmetal said:

Actually, in the specification it states it uses a DC servo motor which implies feedback via optical encoders or similar, in order to give more precise control of angular position, which is what you need. Nothing in the description mentions this, which I thought would be a good selling point, so am not sure what actual system it uses. The reviews state that people are happy with it and that it works well for automated focusing, so it may be worth a try. Hopefully someone here uses one and can give a more informed answer. 

Alan

Happy to try it if I'm not paying for it but then happy to pay for it if it works out well. Let me do a little digging around the forums and see what people's experience has been with it. Should not be discounting anything at this point. 

[eshy76]

On 06/04/2020 at 18:52, symmetal said:

This uses a DC motor rather than a stepper motor so accurate positioning would be more difficult. It has an Ascom driver but I don't know if SGP will work with it or if SGP just works with stepper based focusers. Hopefully someone can say how well they perform.

Alan

I have one of these - easy to install and calibration simple. Frustratingly I've yet to produce a finished image yet with this setup due to calibration issues, but I can say that my capture software (Voyager, SharpCap and NINA) have worked perfectly with the autofocuser. I used SharpCap to find first focus and since then the other capture software gets on with it.

Voyager, in particular, autofocuses intensively when producing it's V-curves at speed...the last night I imaged, Voyager must have autofocused 20 times as I specified, each time churning out a V-curve within a minute and the FWHMs were in the 1.8-2.4 arc second range on an Edge 8 aimed at M81.

For imaging, I think it is a great solution.

What's grinding my gears about it is that as I don't have a Celestron mount, I don't think it can be used for visual, unless I control the focuser with a computer or tablet...if anyone has worked out a way to hook up some sort of simple controller either directly to the focuser or via PC, I'm all ears!

[m.tweedy]

I use a Lakeside on my Refractor and it is fully configurable re step sizes ETC and it focuses great for me. The only time i had issues with the v (mines more like a U) is then the grub screw came loose and the motor was turning but not the focuser. Having had a C11 that had very minor mirror flop (now sold to a good home) I installed a Crayford focuser and attached a motor on it for all of the reasons mentioned above. I am currently looking to do the same with my vintage 1979 C8 that it intend to use for Galaxies.

I am sure you can buy pre used SCT crayfords for very reasonable prices and attach the focuser to that.

[souls33k3r]

Sorry I haven't been able to update this thread. Documented everything on the link here

So for now, I'm going to pass on any external focusers for now. Have spent too much on this hobby in the last year already.