Auto Focus (Lakeside, JMI etc...)?

[kirkster501]

11 hours ago, sloz1664 said:

What another TEC140 

I wish.....!  At £5800 nigh on I doubt it Steve   Spent a fortuen this year on the TEC140 and a MESU - £11000 worth.  And rubbish skies for weeks - as is the norm for winter in recent years.

[kirkster501]

11 hours ago, gnomus said:

Could be.  My guess was a TEC 180.

Now that would be nice.  And rather expensive....!

How do you guys do flats when using motorised focus?  Your falts are meant to be done at the same focus point to ensure the bunnies and vignetting is all the same size...

[sloz1664]

Hi Steve,

I do all my flats by filter. If using SGPro you define a filter list and you have to set a focus point for each filter. I used the frame & focus routine to get "near to focus" then used the focus routine to get true focus and inputted the value into my filter list. One important step you will have to evaluate when you attach your auto focuser is the "step size" . This is the relation between how many steps the auto focuser motor has turned to the actual distance the telescope has moved. There is a section in the SGPro manual on how to achieve this. Read & re-read this, it's important you get this right. Exiting times ahead

 

Steve 

[kirkster501]

Before  the focuser arrives I have been doing some reading up and I have read there are settings for the "step size"?  Could anyone let me know what they are for the Lakeside or does it depend on the scope/camera combination?

[sloz1664]

 

4 minutes ago, kirkster501 said:

Before  the focuser arrives I have been doing some reading up and I have read there are settings for the "step size"?  Could anyone let me know what they are for the Lakeside or does it depend on the scope/camera combination?

Hi Steve,

It is scope / camera dependant.

 

Steve

[Davey-T]

4 minutes ago, kirkster501 said:

Before  the focuser arrives I have been doing some reading up and I have read there are settings for the "step size"?  Could anyone let me know what they are for the Lakeside or does it depend on the scope/camera combination?

If you have digital calipers you can drive the focuser out 1000 steps and divide the measurement by 1000 to get the step size, some software claims to use auto to calculate it but it never worked for me.

Dave

[kirkster501]

51 minutes ago, Davey-T said:

If you have digital calipers you can drive the focuser out 1000 steps and divide the measurement by 1000 to get the step size, some software claims to use auto to calculate it but it never worked for me.

Dave

Hi Dave, What do you mean "drive the focuser out 1000 steps?"

With my TEC focuser the actual focus point for all filters is right at the end of the focuser.  So I'd do these "steps" there?

[Davey-T]

Just now, kirkster501 said:

Hi Dave, What do you mean "drive the focuser out 1000 steps?"

With my TEC focuser the actual focus point for all filters is right at the end of the focuser.  So I'd do these "steps" there?

Ignoring where the actual focus point is, if you drive the focuser nearly fully in with the Lakeside Utility app that comes with the focuser then measure the space between the fixed and moving parts of the focuser, make a note of it then drive the focuser out 1000 steps and remeasure the gap, then divide this measurement by 1000 you get the step size to enter in the focussing software.

Make sure you use all metric measurements

Hope that makes sense 

Dave

[Helen]

7 minutes ago, kirkster501 said:

Hi Dave, What do you mean "drive the focuser out 1000 steps?"

With my TEC focuser the actual focus point for all filters is right at the end of the focuser.  So I'd do these "steps" there?

You may also need an extension tube then...  The auofocus needs to measure either side of focus to be able to interpolate the best focus point.  I had a similar problem, but as mine was lack of in-focus it was rather more difficult to get around!

Helen

[Davey-T]

16 minutes ago, Helen said:

You may also need an extension tube then...  The auofocus needs to measure either side of focus to be able to interpolate the best focus point.  I had a similar problem, but as mine was lack of in-focus it was rather more difficult to get around!

Helen

Good point, you need wriggle room each side of actual focus.

Dave

[kirkster501]

I do indeed have a 2" extension tube.  TEC 140 requires this with my camera to achieve focus.  Even then (with the extension), focus is achieved when the focuser is nearly entirely racked out minus a cm or so

[Davey-T]

A 1000 steps takes about 10mm on my Star71 , I've got it set to travel 0 to 2000 steps 0 is just before it runs out of inward travel and focus is achieved around 1370 steps.

All this is set up to suit your configuration when first commissioning the Lakeside.

Depending how good the focuser is it may be better to rack the focuser in and add more extension, don't know why no one makes a longer 2" extension tube like the 1.25 ones.

Guess you could always saw a bit of the tube 

Dave

[gnomus]

Steve

I tried the caliper method but I found it easier to use the other method described in the SGP instructions.  In essence, get good focus using your stepper motor and a Bahtinov mask.  Then take the mask off and take a 5 second (or so) exposure.  Get SGP to calculate the HFR.  Note the stepper motor position.  Then move the focuser out a number of steps and repeat.  Keep going until you get an HFR that is 3-5 times the 'in-focus' measurement.  Note the stepper motor position.  Calculate the difference in stepper motor position.  Divide by 4.  That is it.  At least for a 9 step routine (which is what I suggest).

[kirkster501]

1 hour ago, gnomus said:

Steve

I tried the caliper method but I found it easier to use the other method described in the SGP instructions.  In essence, get good focus using your stepper motor and a Bahtinov mask.  Then take the mask off and take a 5 second (or so) exposure.  Get SGP to calculate the HFR.  Note the stepper motor position.  Then move the focuser out a number of steps and repeat.  Keep going until you get an HFR that is 3-5 times the 'in-focus' measurement.  Note the stepper motor position.  Calculate the difference in stepper motor position.  Divide by 4.  That is it.  At least for a 9 step routine (which is what I suggest).

Thanks Steve.  I'll check it out and RTFM....

 

[gnomus]

18 hours ago, kirkster501 said:

..... RTFM....

 

AFL

[kirkster501]

On 07/02/2017 at 09:25, swag72 said:

Another Lakeside user here.... and I use SGP for focus. It's already been described how it works with V curves so I won't dwell on that! I set mine to a refocus at every 1 degree temp change.

Also one thing worth noting is that the Lakeside and SGP play nicely working in dual as well...... With two instances of SGP open, then the Lakesides always opens in the same com port so you always know that the right Lakeside is connected to the right scope...... That's been very useful.

So presumably Sara you have two Lakesides with two control boxes as well?  iI was thinking of doing that so I have one permanently on my TEC and the other on my FSQ and I have no need to then re-calibrate.

[gnomus]

I think the calibration data is 'stored' in the control box, so even if you weren't planning on using both scopes at the same time, you would need to recalibrate every time you switched.  I think the novelty of calibration would very quickly wear off.

[swag72]

10 hours ago, kirkster501 said:

So presumably Sara you have two Lakesides with two control boxes as well?  iI was thinking of doing that so I have one permanently on my TEC and the other on my FSQ and I have no need to then re-calibrate.

Yes I do have two boxes, one for each stepper

[kirkster501]

That's what I thought guys, thanks for confirming.  If it's worth doing then it's worth doing properly.

I will get AF going with the easier-to-focus TEC 140 first.

[Davey-T]

You can run two Lakesides at once with the 2 X driver not sure how it works but I'm about to find out 

Dave

Don't know about 3 though 

 

[kirkster501]

4 hours ago, Davey-T said:

You can run two Lakesides at once with the 2 X driver not sure how it works but I'm about to find out 

Dave

Don't know about 3 though 

 

Any problems then just buy another cheap laptop off of ebay - small beer in costs compared to this astronomy lark.  You can run SGP on three machines for the one license.

[gnomus]

No problem.  You download different drivers for the Lakesides - Lakeside 1 and Lakeside 2.

[Davey-T]

40 minutes ago, gnomus said:

No problem.  You download different drivers for the Lakesides - Lakeside 1 and Lakeside 2.

And 3 ?

42 minutes ago, kirkster501 said:

Any problems then just buy another cheap laptop off of ebay - small beer in costs compared to this astronomy lark.  You can run SGP on three machines for the one license.

Now you want me to buy SGP, when will all this spending end ? 

Dave

[RayD]

10 minutes ago, Davey-T said:

Now you want me to buy SGP, when will all this spending end ? 

Never.........Mwah ha ha ha ha ha ?