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Motorized Focuser recommendation for a William Optics FLT 132mm APO

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#1 pcos

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Posted 21 August 2019 - 07:50 PM

Hi Folks. 

 

New member here. 

 

I am interested in getting a  motorized focuser that is know to fit a William Optics FLT 132 APO refractor - I am looking for something that would be suitable for automated focus operations when using Sequence Generator Pro....

 

I looked at a lot of systems but few seem to confirm that they are compatible with this scope. 

 

Thanks in advance for your help!

 

Pcos



#2 Benni123456

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Posted 22 August 2019 - 10:29 AM

i know that the sesto senso focuser from prima luce is compatible with many focusers. It comes with a large set of adapters and is very strong and precise.

 

https://www.primaluc...sing-motor.html

 

i do not know why it should not be compatible. one mounts it by removing the precision wheel. Then one has the axis of the focuser and for this the motor comes various adapters. 

 

I guess to be sure ask the manufacturers themselves. But the refractor looks like it should fit.


Edited by Benni123456, 22 August 2019 - 10:31 AM.


#3 pcos

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Posted 22 August 2019 - 02:31 PM

Thanks for that Vostok 1!  I have sent them a message to get their input.

 

I have also contacted Pegasus Astro around their Focus Cube 2.  They asked for a photo of the back of my focuser and they have indicated that their universal bracket should work on my scope. 

 

So right now I am looking at Sesto Senso, the Pegasus Focus Cube 2, and the EAF from SWO.  They all look like possibilities.

 

Any I am missing that I should look at as well?

 

Any significant puts or takes on the three I have listed?

 

I could always go Moonlite and get the Nightcrawler.  Only $2900. Gulp,  Maybe down the road but now?  No.... 

 

Thanks,

Pat



#4 Benni123456

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Posted 22 August 2019 - 05:17 PM

i can only say that the sesto senso is very precise.

 

And it would, if not locked, still allow to focus the telescope manually. It is very strong, more precise than my software can spot any focus differences, with recent indi drivers it also works on linux, and windows so i have no problems with it. It may need a firmware upgrade to work with windows 10. the recent firmware is on the homepage of the manufacturer.



#5 pcos

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Posted 22 August 2019 - 05:55 PM

That's actually a very interesting point - its kind of nice to still have manual focus if you wanted it!

 

I have heard back from everyone now except the primalucelab guys... so the decision is getting closer....

 

Thanks,

Pcos



#6 DaveHume

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Posted 02 September 2019 - 09:27 PM

Have you contacted Moonlite?  I also have a FLT132 and am considering the purchase of a focuser next year.  I met with Moonlite at NEAF this year and they confirmed they have focusers that would be suitable for the 132.  Eager to see what you come up with...


Edited by DaveHume, 02 September 2019 - 09:29 PM.


#7 pcos

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Posted 03 September 2019 - 03:27 PM

I did look at Moonlite.  I absolutely loved the NightCrawler, at would fit, but the price was just too high for me. 

 

Another issue I ran into was availability.  Most were out of stock right now except for the Pegasus Focus cube 2.  They responded to my email very promptly and showed how their universal bracket would fit on my focuser.   

 

I ordered it and installed it in about 15 minutes when it arrived.  The screws and washers they provided helped, but they were too long.  It would have been nice had they included some spacers or least some versions of the screws that were not so long.  I improvised a couple of spacers and it went on pretty well. 

 

I have tested it one night, but that night was cut short with clouds and I did not have a chance to get it going on SGP.  Pegasus provides a document that explains how to set up the focuser on SGP so I hope that goes smoothly.   Seems to work well - very quiet.  Very smooth. I also ordered the hand controller so when I want to do visual without the computer I can still focus. 

 

Once I get auto-focus on SGP going, I will report back on how it all worked out.  But so far, so good!


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#8 txo

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Posted 10 September 2019 - 09:01 AM

I did look at Moonlite.  I absolutely loved the NightCrawler, at would fit, but the price was just too high for me. 

 

Another issue I ran into was availability.  Most were out of stock right now except for the Pegasus Focus cube 2.  They responded to my email very promptly and showed how their universal bracket would fit on my focuser.   

 

I ordered it and installed it in about 15 minutes when it arrived.  The screws and washers they provided helped, but they were too long.  It would have been nice had they included some spacers or least some versions of the screws that were not so long.  I improvised a couple of spacers and it went on pretty well. 

 

I have tested it one night, but that night was cut short with clouds and I did not have a chance to get it going on SGP.  Pegasus provides a document that explains how to set up the focuser on SGP so I hope that goes smoothly.   Seems to work well - very quiet.  Very smooth. I also ordered the hand controller so when I want to do visual without the computer I can still focus. 

 

Once I get auto-focus on SGP going, I will report back on how it all worked out.  But so far, so good!

Could you please post the photo of installed focuscube please? Do you have 2019 FLT132 model? I think they changed their focuser this year.

 

t.



#9 pcos

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Posted 10 September 2019 - 07:34 PM

Could you please post the photo of installed focuscube please? Do you have 2019 FLT132 model? I think they changed their focuser this year.

 

t.

I just bought the WO FLT 132 a few weeks back from Highpoint.  I assume it is a new model but do not know for fact when it was built. 

 

Another note on the application here.  I was having trouble get SGP to do auto focus with it and I discovered the problem is that the sleeve that couples the stepper motor to the focuser was slipping.  I used the focus lock screw to attach the bracket and the spacing here made it a little tricky to get coupler to slide over the ends of the shafts in each side such that the set screws could get a good grip. I played with it and got a decent setup with a really positive lock on both shafts.   I found the included bolts to not be too helpful as they were too long for my use here.  If I screwed them all the way into the focus lock hole - I ended up with a - you guesses it - locked focuser!  So I went to the hardware store and got a shorter M4 0.7 pitch screw and used that.   Here are a couple of (crappy) photos - I hope this is helpful to you. 

 

 

 

 

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Edited by pcos, 10 September 2019 - 07:49 PM.

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#10 txo

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Posted 11 September 2019 - 02:07 PM

Thank you, that is the new one. It doesn't have "engraved" logo on the focuser.

 

According to this manual, there are dedicated focuser motor screws. https://williamoptic...Z126-Manual.pdf

 

I don't know why they don't have flt 132 manual.



#11 pcos

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Posted 11 September 2019 - 06:44 PM

Thank you, that is the new one. It doesn't have "engraved" logo on the focuser.

 

According to this manual, there are dedicated focuser motor screws. https://williamoptic...Z126-Manual.pdf

 

I don't know why they don't have flt 132 manual.

Well - that's a much better manual than the one that came with mine (i.e. NO manual!).

 

It's not clear to me that the same holes are there on this focuser - which it too bad - I could have used them!

 

ON a follow-up note, after I made sure of the proper coupler positioning and that the shafts were well locked in, I tried setting up SGP again to do autofocus.  Worked like a champ!  Very pleased with it.

 

In case anyone else is considering the focus cube, I also ordered the manual focus controller for it.  It plugs in where the temperature probe plugs in - you can't use both at the same time.  Without it, the arrangement is fine for imaging work.  But if I ever wanted to use this scope visually - the computer controlled focusing would be hugely awkward.  The controller is really nice to use. Turn the knob one way and you get coarse focus steps in. Go the other, and you get coarse focus steps going out.  Click on the knob and it toggles to fine focus Steps.   The controller can work at the same time as the app - unless you disable it from the app. 

 

For the price - its seems to be a reasonable setup.  Having said this, the Moonlite Nightcrawler - with its ability to handle rotation as well as focus - is amazing and I would love to get that one day.... ;-)



#12 noisejammer

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Posted 11 September 2019 - 09:09 PM

OP, you haven't really told us enough to make a solid recommendation. In particular, we need to know whether you're using the WO field flattener (this is necessary for large sensors) or a reducer.

 

I have a few Moonlites including a CFL on my FLT scope. Ron makes good focusers and this is more than adequate for a light load (say K8300 chip + filter wheel.) They're to small to accommodate the large flattener.

 

If you have a large imaging load, Starlight Instruments makes some excellent - albeit a bit expensive - focusers. You might consider their 3545 model with this adapter and a couple of end caps from this range. In case it's of interest, you could use the Tak 72mm end cap which would allow you to use the TO 130R reducer. On the other hand, the 92mm WO end cap makes the focuser accept native WO fittings. I have both of these available to my 6" instrument.

 

Automating focus is relatively easy with the solutions offered by either of these manufacturers.



#13 rgsalinger

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Posted 11 September 2019 - 10:49 PM

Moved topic here to get a better response.

Rgrds-Ross



#14 pcos

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Posted 12 September 2019 - 07:30 AM

OP, you haven't really told us enough to make a solid recommendation. In particular, we need to know whether you're using the WO field flattener (this is necessary for large sensors) or a reducer.

 

I have a few Moonlites including a CFL on my FLT scope. Ron makes good focusers and this is more than adequate for a light load (say K8300 chip + filter wheel.) They're to small to accommodate the large flattener.

 

If you have a large imaging load, Starlight Instruments makes some excellent - albeit a bit expensive - focusers. You might consider their 3545 model with this adapter and a couple of end caps from this range. In case it's of interest, you could use the Tak 72mm end cap which would allow you to use the TO 130R reducer. On the other hand, the 92mm WO end cap makes the focuser accept native WO fittings. I have both of these available to my 6" instrument.

 

Automating focus is relatively easy with the solutions offered by either of these manufacturers.

I am using a ZWO ASI294MC Pro camera with a Hotech Field flattener.   The load is not very large and the field in not very wide - in fact it is unclear to me how much value I am getting from the flattener.  I have attached a photo so you can see the image train.  Pegasus Astro claims the focuscube 2 has a really strong motor which can handle loads up to almost 9 lbs. 

 

Like I said - the main reason I bought this one was 1) availability  2) specs sounded promising  3) cost was reasonable  4) I could easily return it if it did not work out. Is it the best solution?  Probably not.  Is it working for me? - so far so good - once I cured some initial mounting issues. 

 

Pcos

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#15 noisejammer

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Posted 13 September 2019 - 11:37 PM

Ok, so I'd ask myself whether I _need_ to autofocus this early in my imaging career. You may find that a Bahtinov mask provides you with all the precision you need.

 

On whether you need the field flattener - most refractors' field has a radius of about 1/3 of the focal length (not true for Petzvals and some exotics, but it's a fair approximation for the WO FLT series. So, let's guess the field has a radius of 7*132/3 = 308mm.

 

Field flatness starts to become an issue when the star bloat caused by field curvature exceeds the bloat caused by other factors like the atmosphere - let's say around 2 arcsec for a first pass.

 

There are 4.8 microradians in an arcsec so a 2 arcsec spot at the focal plane will subtend about  9.6 *10-6 * 7*132 (mm) ~= 9 microns.

 

So if the cone caused by the field curvature exceeds 9 microns, you need to pay attention to it. Because it's an f/7 scope, this translates to 7*9 = 63 microns However, if you focus optimally, you can probably tolerate 100 microns error before field curvature produces an observable blur.

 

To estimate the angle that this corresponds to, we can use the relationship

r cos(theta) = r - 100 um or cos(theta) = 1 - (100um/r). For small angles,

cos(theta)~=1-0.5*theta2

 

Recall that we've calculated the radius of curvature to be 308mm so we can write

0.1/308 = 0.5*theta2 >>>> theta = 0.025 radians = 1.46 degrees.

 

Since this is half the field, we have that a field diagonal of about 2.9 degrees can be focussed well enough on a 5" f/7 scope for a field flattener to be unnecessary. (That's about a 46mm diagonal, or roughly the size of a 36x24 ccd.)

 

All you need to know is that to achieve 2 arcsec resolution, you should focus accurately about 2/3 out to the edge.


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#16 Delta608

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Posted 14 September 2019 - 07:28 AM

   You should check your math, I got 1.44567 degrees...GAWD Im only kidding...You lost me at "There are 4.8 microradians in an arcsec so a 2 arcsec spot at the focal plane will subtend about  9.6 *10-6 * 7*132 (mm) ~= 9 microns." Im still struggling with Amp Hours !!!




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