SGPro Focus settings with Lakeside Focuser

[Uplooker]

Ok, so I have rechecked my sensor to back flange of the focal reducer. It was 110.58mm, it is now at 111.0mm I checked it with a set of digital vernier calipers.

To clarify some details, I am using a TS Flattener 2, as shown on the link

https://www.teleskop-express.de/shop/product_info.php/info/p1010_TS-Optics-PHOTOLINE-APO-Flattener-Corrector-for-Refractror-Telescopes.html

The link  has the spacing as being 111mm for a 700 fl scope. I am using an APM 107/700.

The other distance that is relevant is the distance from the front face of the camera (QHY9) to the sensor. The online manuals quote this as being 15mm, but I have a vague recollection of reading somewhere that someone actually measured theirs as being 16mm.

To arrive at my 111mm spacing I have also included 1mm for the filters in the SX wheel.

I appreciate that FF spacing can be fickle but would not have thought that having my spacing at 110.58mm would be causing the issues I am having. I am more than happy to be proved wrong ?

That said, I am coming round, more and more, to thinking sensor tilt may be the culprit- that's maybe a bit more difficult to solve ?

Roll on a clear night so I may check it.

[symmetal]

Hi Ian,

I wouldn't have thought 0.5mm spacing error would have a great effect. On mine I did test runs from +/- 2mm in 0.5mm steps from the specified distance to check the optimum spacing and at 2mm out the image was visually still usable, just slightly elongated stars at the corners. CCD Inspector also indicated defocused stars at the centre though. I have the William Optics Flattener-IV which allows you to move the lens elements inside the tube so it's easy to adjust.

Did you get my pm to you about CCD Inspector?

Alan

[RayD]

If the spacing noted by TS is 111mm for that particular FF, and you are using filters of 3mm (@1/3 for your 1mm allowance) then I would have thought you need to set your physical spacing at 112mm to allow for the filters, so will need to add a 1mm delrin?  

[Uplooker]

51 minutes ago, symmetal said:

 

Did you get my pm to you about CCD Inspector?

Alan

Yes, I did. Sorry thought I had replied.

 

15 minutes ago, RayD said:

If the spacing noted by TS is 111mm for that particular FF, and you are using filters of 3mm (@1/3 for your 1mm allowance) then I would have thought you need to set your physical spacing at 112mm to allow for the filters, so will need to add a 1mm delrin?  

Mmmh, will have to have a think on that.

Adjusting the spacing isn't too difficult as I have one of these:-

https://www.altairastro.com/m48-17-29mm-variable-spacer-set-3-part.html

[RayD]

Just now, Uplooker said:

Yes, I did. Sorry thought I had replied.

 

Mmmh, will have to have a think on that.

Adjusting the spacing isn't too difficult as I have one of these:-

https://www.altairastro.com/m48-17-29mm-variable-spacer-set-3-part.html

That's ideal.  I personally would start at the 112mm and then tweak from there as sensors are often +- 0.5mm, so it can just be a bit of trial and error.

[symmetal]

As Ray says you need to add 1/3 the thickness of your filters to the flattener/ccd distance stated. I should have read your post more carefully. For a lengthy discussion on the subject read this thread. 

Do Filters Add To Back Focus

Alan

[Uplooker]

Ooovve, there was some discourse in that thread.

Right, I am going to increase the distance 1mm to take it to 112mm.

If 112mm is the correct distance it would mean that previously I was 1.42mm off the optimum FF to sensor spacing, which may well have been causing my problems.

 

[Uplooker]

Small update having read that thread again. Apparently the Baader umounted 36mm filters are 2mm thick, so I have set the distance to 111.6mm.

I may have a chance to try things this evening, fingers crossed.

[Uplooker]

Well, it seems that my FF to sensor spacing was at fault!

This evening/ last night I was able to get a lovely clean image with my Bahtinov mask. I am now able to understand exactly where the focus point. I was even able to run Autofocus - to a point is. I need to play around with a few settings to smooth things out.

I am now a lot clearer on where I need to go. I suspect that tonight will be the last opportunity until next weekend.

Thank you to everyone who gave me invaluable advice.

I will continue to provide updates to this thread.

All I need to do now is figure out the rest of SGPro ?

[symmetal]

Glad to hear you've managed to get it working after all your perseverance.  It looks like your FF spacing is much more critical than mine.

Alan

[RayD]

Great stuff, love a happy ending 

I only mentioned the extra 1mm as I have Baader, so they are 0.6mm, and it made a huge difference for me.  In fact, when using CCD Inspector to fine tune, just a home made 0.3mm spacer was very noticeable.

I think once auto-focus is working properly you really start to appreciate just how good SG Pro actually is.  Last night I watched the auto meridian flip again and it just never fails to amaze me how well it works.

[Uplooker]

Thanks Alan & Ray.

Although my spacing was only out by 1.02mm I am still amazed at the impact it was having on the image. I am also amazed by how much it has changed the focus point. With the earlier setup I thought I was in focus at 453 steps, with the correct spacing the focus point is at 402 steps!

I may need to tweak things slightly one I have analysed my images.

Thank you all again.

[Uplooker]

Well, what can I say. Firstly, a big thank you to everyone who replied with help and suggestion. Secondly, I got a lovely "V" curve???????

conditions were not and have not been ideal. I have been out whenever there was the slightest chance of a clear spell, mostly it was cloudy.

The problem apart from FF spacing was that I was using a step size that was waaay too large - 20 steps. I have actually ended up with a step size of 4!

I still have a bit of playing to do with regards to my other filters but I got there in the end with lots of help from you guys.

Thank you once again, your help has been invaluable ?

[symmetal]

Excellent result Ian!  

A step size of 4 is all you need. Wouldn't have guessed that. Your gearing must be quite a bit different to mine. It's very satisfying when it all eventually works together. 

Alan