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Focuser - Electric or Feathertouch

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#1 ben2112

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Posted 06 March 2013 - 06:46 AM

Well, even though I haven't been able to get out to use the scope with the NI5 I received. I did notice while playing around with it that focusing is going to be a bear due to shakes and vibrations. I knew that when I bought it. I was going to do a DIY electric focuser but the servos I want are on back order at every reliable hobby site on the net. :mad: I have an order in at my local hobby store but they are on backorder as well. :flame: SO!! I have decided to scrap the DIY and just buy one. I was looking at the JMI electric focuser and the Feathertouch focuser.

I like the JMI as I wouldn't have to touch the scope at all, but I like how I can super fine tune the focus with the Feathertouch.

Any input would be very appreciated and helpful.

#2 Arctic_Eddie

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Posted 06 March 2013 - 07:26 AM

The secret to smooth focusing is to not touch the scope. I saw that when I started using my DIY stepper focuser.

The JMI focuser is overpriced in my opinion. However, if you're adept at mechanical things then take a look at an Orion electric focuser which is intended for refractors. A different bracket might make it work nicely on your scope.

Also, take a look at Jameco and MPJA.com. Both companies have numerous low voltage DC gear motors for a reasonable price.

#3 ben2112

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Posted 06 March 2013 - 07:39 AM

How heavy are stepper motors? That is why I liked the idea of using a servo. I know they are lightweight.

#4 Peter9

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Posted 06 March 2013 - 07:43 AM

I would advise you go with the electric focus for, as Eddie has said, you don't have to touch the scope.
As for fine focusing, I have the Celestron motofocuser (now discontinued) which has variable speed control, so I can focus as fine as I wish to. I assume the JMI has speed control too.

Regards. Peter.

#5 Arctic_Eddie

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Posted 06 March 2013 - 08:02 AM

The stepper motor I use came from Adafruit. It was selected for it's high angular resolution. It's probably 5-10 times heavier than a DIY continuous rotation servo.

http://www.adafruit.com/products/324

If you use a variable speed motor as the focuser then look for a controller that acts like a bi-directional variable speed device with a center zero position. If you use a DIY servo then get a cheap servo tester. This type of servo has a very sensitive neutral position so you'll need to cut power immediately on reaching focus.

#6 ben2112

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Posted 06 March 2013 - 08:26 AM

OH!! So that is why you use stepper motors. For the accuracy of stopping the motor. Better control. I was wondering why because stepper motors are usually used for torque and holding of something heavy, etc.. That is good to know. :bow:

#7 Arctic_Eddie

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Posted 06 March 2013 - 11:00 AM

A rotary shaft encoder and a stepper act like a closed loop servo control system providing the motor has enough torque to overcome the load resistance. This is no problem with the focus knob on the SE scopes. When you turn the encoder knob, the motor responds directly as if there was a mechanical connection between the two items. On my system, there is an electrical 8.33:1 reduction ratio. This allows very fine adjustment of focus. The down side is that it's a rather involved project. However, but works remarkably well.

http://www.cloudynig...hp?item_id=2784

#8 jerwin

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Posted 06 March 2013 - 12:49 PM

scopestuff has whats called a fine focus knob that slides over your normal knob. A buddy in my astronomy club has one of those, it's decent for getting him better focusing, and at $23, he said it was worth a shot.

I've had the JMI motofocus and it gave me 0 vibrations so it was very nice, but I think I paid $179 for it. Ouch...

Have a feathertouch on my lunt and a moonlite on my dob. I personally think the feathertouch is better between the 2


Jim

#9 WarmWeatherGuy

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Posted 06 March 2013 - 02:34 PM

A focusing motor will allow you to turn the focus knob without vibration but you will still not know when you have perfect focus. For that you can use a Bahtinov mask. This video explains.

How to focus a wobbly telescope.

#10 Thanatos78621

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Posted 06 March 2013 - 04:16 PM

Ben:

I'd go with the feathertouch. If you decide you need hands off focusing, Starlight offers a digital motorized controller. Its not cheap but it does work with the feathertouch.

#11 budman1961

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Posted 07 March 2013 - 01:33 PM

+1 for electronic focus, whether is via servo/stepper or DC motor. The stepper system makes precise focus repeatable (absolute), which is handy for imaging. The DC solution is less $$, but isnt as repeatable as the stepper setup. Rigel Systems has several options for either system.

If you use a PC in your setup, I recommend their USB-n-focus adapter, which will allow you to focus from your PC....great when its very cold out!

I have used the Moonlite focuser with great success. The owner Ron Newman answers the phone. They have no resellers, so no middleman markup. They design, machine, anodize, sell and most importantly support their setups. I give them an A+++++

I hope this helps!

Andy

#12 cpl43uk

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Posted 20 March 2013 - 06:24 PM

I have tried both motorised focuser and currently have a feathertouch. Both in my opinion are over priced vs cost of the scope itself but I guess that is because they are not mass manufactured. The electric focusser was fine but I found the setup added to the 'bulk' around the scope (too much clutter, wires, boxes etc). The feathertouch is easier to use in that regard but still suffers from jitter when used. I am not convinced the price is worth it vs the clothes peg alternatives!!! The batinov might be an alternative but I always use my dewcap and its less easy to use in his configuration.

#13 WarmWeatherGuy

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Posted 20 March 2013 - 08:17 PM

The batinov might be an alternative but I always use my dewcap and its less easy to use in his configuration.


If you get the Farpoint mask you can just rest it on your dew shield. Be sure to get the type that have the adjustable rubber grommets which are not available for the C11.

#14 ben2112

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Posted 21 March 2013 - 12:19 PM

The local hobby store just called me saying my servos just came in. Going to go pick them up and work on my DIY electric focuser next weekend while I am on vacation. I am hoping to have it working so I can use it to get pics of Saturn. :D :cool:

#15 ben2112

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Posted 01 April 2013 - 09:31 PM

I finally got it finished. I got a chance to test it tonight. It works pretty good. Just need to find an o ring that is big enough. The rubberband works ok, but it stretches some.

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#16 ben2112

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Posted 20 May 2013 - 06:13 PM

I finally found an o-ring that will work. Fastenal sells it by the foot. :D So I got 3ft. of 3/16in.. Works great. But I cursed myself. Since I made it, it's been cloudy and rainy and it doesn't look like it's going to clear up any time soon..

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