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Focuser - which type


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#1 gfamily

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Posted 16 November 2013 - 04:30 PM

I'm thinking of getting a focuser for my new LS8. However it looks as though the Meade Zero Shift Focuser fits into the eyepiece holder, so it wouldn't let me mount a DSLR using the T mount, is that right?

As a result, it looks as though I'll get a JMI Focuser instead, as that works by directly moving the mirror. Makes more sense to me. What have other people used?

#2 gunfighter48

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Posted 17 November 2013 - 07:07 PM

I don't know about the T mount, not into AP. But the reason I bought the Meade Zero Shift Focuser was Because it DIDN"T move the mirror. There's almost no vibration with the Meade focuser. One of the cronic problems with SCTs is mirror shift esspecially with AP. I use the scopes focus knob bot get a decent focus and then use the Zero Shift focuser to do the fine focus. I don't have to touch the scopes focus knob unless I'm making a big change in the eyepiece type. I've not noticed any mirror shift once I get the course focus set, no matter which way the tube is pointed in declination. So the JMI Focuser might work fine for the T mount.

#3 gfamily

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Posted 20 November 2013 - 02:27 PM

Further investigations shows that the T mount can be fitted to the Meade focuser, so it's still an option. But it's a lot more expensive, so I'll probably still go with the JMI. Compromises, compromises!

#4 G3oak

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Posted 22 November 2013 - 02:12 PM

Can I have some help on this topic?
I purchased Meade's zero image focuser, installed it as shown, but can't see how this works. The instructions talk of unlocking the mirror, but it looks like a LX option, not an LS option. This is for my LS 6.
Help!

#5 gspie

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Posted 22 November 2013 - 02:46 PM

Zero-Image Focuser plugs into the Focuser port of your mount base (if you have one). If you don't have a Focuser port, and the focuser didn't come with a control box, then it probably isn't suited for that scope. If there is a focuser port, then focusing is controlled via the hand paddle. I have an LX-850, so I'm sure the hand paddle is quite different, so I can't say which buttons.
LX850 with 10" ACF OTA and Takahashi FS 60C OTA -- SBIG STT-8300M CCD with FW8G-STT Self Guiding Filter Wheel and SBIG AO-8 Adaptive Optics -- Camera Control and Image Calibration with Maxim DL/CCD Pro, Image processing with PixInsight, and final composition with Photoshop CS5

http://home.comcast....ie/astroweb.htm

#6 G3oak

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Posted 22 November 2013 - 03:50 PM

Gspie,

Thanks for the quick reply. I finally installed it and it does plug into the scope controlled by the Autostar. I tried it indoors and the focusing must really be "fine" because the difference is not very noticeable when I get it to focus. How subtle is this system?

#7 gspie

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Posted 22 November 2013 - 04:42 PM

The way it is supposed to be used is:
Use the manual focuser to get a good rough focus.
Now use the micro focuser to get precise focus.


LX850 with 10" ACF OTA and Takahashi FS 60C OTA -- SBIG STT-8300M CCD with FW8G-STT Self Guiding Filter Wheel and SBIG AO-8 Adaptive Optics -- Camera Control and Image Calibration with Maxim DL/CCD Pro, Image processing with PixInsight, and final composition with Photoshop CS5

http://home.comcast....ie/astroweb.htm

#8 gspie

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Posted 22 November 2013 - 04:48 PM

The micro-focuser is best used IMHO for Astrophotography where precise focus is a must. But can still be used for visual.
LX850 with 10" ACF OTA and Takahashi FS 60C OTA -- SBIG STT-8300M CCD with FW8G-STT Self Guiding Filter Wheel and SBIG AO-8 Adaptive Optics -- Camera Control and Image Calibration with Maxim DL/CCD Pro, Image processing with PixInsight, and final composition with Photoshop CS5

http://home.comcast....ie/astroweb.htm

#9 G3oak

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Posted 23 November 2013 - 07:35 AM

Hi again gspie,
Took the scope out last night and did not see any difference. This morning I pulled it out of the scope while still plugged in and saw no parts on this focuser moving when pushing the focus buttons. Hear the motor running but nothing else. Am I supposed to loosen something? Maybe I'm missing something because the focuser just sits on the back of the scope?

#10 gspie

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Posted 23 November 2013 - 09:41 AM

You're supposed to use the focuser controls to place the focus ring half-way in before using to focus (so you have play in both directions). It sounds like you aren't getting any movement in either direction. Does the inner sleeve of the focuser move in-and-out when you pull lightly on it? If so, then it may be defective -- I had one like that and had it replaced. When you have it plugged in, you should hear the motor, and there will be a slight motion (it is quite slow -- hard to notice). If you look at the place where the tightening screws (that hold the eyepiece) while 'focusing' you should be able to see the inner sleeve move slightly. If not, then I would call Meade support and report it. The focuser itself will always look like it is just sitting at the back of the scope -- it is only the inner sleeve connected to the eye-piece holder that moves, and ever so slightly.
LX850 with 10" ACF OTA and Takahashi FS 60C OTA -- SBIG STT-8300M CCD with FW8G-STT Self Guiding Filter Wheel and SBIG AO-8 Adaptive Optics -- Camera Control and Image Calibration with Maxim DL/CCD Pro, Image processing with PixInsight, and final composition with Photoshop CS5

http://home.comcast....ie/astroweb.htm

#11 G3oak

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Posted 23 November 2013 - 10:48 AM

Gspie,

You are right. It does move after all, even if ever so slightly. Please help the newbie understand the concept. I have a 2" diagonal so it's moving that back and forth. And then?




#12 gspie

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Posted 23 November 2013 - 06:36 PM

Yes. That's why you do the focus manually, then use the micro-focuser to nail-it! As I said, the manual focusing is pretty good for visual observing, and easier if you have more than one person at the eye piece (they can tweak it for themselves easily). The zero-image shift micro focuser is for more demanding applications -- specifically astro-photography where being just a little out of focus is a major issue. The micro focuser can also be controlled by some of the software that imagers use so that auto-focusing software can manipulate it too; and yes, in your cane the 2"diagonal is moving verrrryyyy slowly.
LX850 with 10" ACF OTA and Takahashi FS 60C OTA -- SBIG STT-8300M CCD with FW8G-STT Self Guiding Filter Wheel and SBIG AO-8 Adaptive Optics -- Camera Control and Image Calibration with Maxim DL/CCD Pro, Image processing with PixInsight, and final composition with Photoshop CS5

http://home.comcast....ie/astroweb.htm




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