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Craigslist CPC 800 - what to look out for?

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#1 DrBoring

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Posted 11 April 2013 - 07:53 AM

I did a good bit of research and determined that I wanted to get a telescope in the CPC series. Since this will be my first scope, I wanted to purchase a used model. I found a used CPC 800 on craigslist in my area and negotiated a good deal.

The scope is about 6 years old, though in photos it appears very similar to the current model. I called celestron and found out that 1. The starbright coatings have been used for many years, so it would still have that, and 2. you need to check the controller firmware version. The seller looked and it is version: hc 4.03 mc 5.07 5.07

We have settled on a price, and I am going to meet up to inspect its condition and see that the motorized components work. Do you have any advice for things I should check before accepting the exchange?

I understand that the 4.xx version is good - so no problem?

I would appreciate any additional advice you might have!

#2 MikeBOKC

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Posted 11 April 2013 - 08:04 AM

I would very definitely view it at night and go through at least one alignment to test that function and some sample go tos. I wuold also make sure the scope moves freely in both axes with the clutches loosened and of course eyeball the corrector plate for any scratches or damage. Lastly run the focus in and out some to make sure it is functioning well.

#3 DrBoring

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Posted 11 April 2013 - 08:07 AM

Thank you for the advice! How would I loosen the clutches to move the scope manually?

#4 Footbag

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Posted 11 April 2013 - 09:13 AM

You'll know where the clutches are when you are standing in front of it. There is one knob on the arm and one in the center of the base.

#5 MikeBOKC

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Posted 11 April 2013 - 11:18 AM

Just a suggestion -- go online and find the CPC owner manual and either print it out or make notes on its operation so you know what to look for when you see the scope in person, specifically the alignment procedure.

#6 Steve Daniel

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Posted 11 April 2013 - 11:39 AM

Check that the power connector provides a good connection. If wiggling the cable connected to the connector causes a reset or any visible change in the handset, you'd need to deal with that by replacing the connector. The stock connectors are notoriously not great.

With the scope on, wiggle the hand controller cable where it plugs into the scope base, as well as the other end where it goes into the hand controller. Make sure the display lighting doesn't fluctuate or change during this test... this is a common failure point.

Check all parts on the tripod, especially at the hinge point between spreader bars and tripod legs for cracks. These seem to be a weak point on this tripod.

While observing, look for lots of mirror movement when focusing. Not that you could do much about it, but it might be a negotiating leverage point. Some of these scopes have a lot more than others.

Check for good thread conditions where the visual back screws on, and on the visual back. These parts are aluminum and could have gotten cross-threaded in the past.

Check for proper clutch operation. You shouldn't have to tighten the clutches very much at all to lock in place.

Check for any fog/haze buildup inside the corrector or on the primary mirror. These are addressable, but not trivially.

#7 DrBoring

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Posted 14 April 2013 - 05:33 PM

Thanks so much for your helpful advice. I took a full day trip there and back, and the guy wasn't really helpful about demonstrating it. There was an apparent snafu about aligning it during the daytime and using the controller to slew. He told it worked fine a few months ago, so I still bought it and I am beginning to learn a few hard lessons ...

I ought to be able to select sky align, wait for it to stop saying 'GPS linking', then press 'enter' to continue, then the top line reads 'center object 1' - bottom line 'press enter when ready'. I press enter, and both clutches are tight. Top line is 'align object 1'. Bottom line reads 'use direction button to center object. Press align when finished.'

Here, if I press left or right, the lower line text scrolls. If I press up, it goes to 'initializing'. 'Cpc ready'. It's right back to where I started !?!?

This can't be right. Does it seem like the problem is me or the scope?

#8 MikeBOKC

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Posted 14 April 2013 - 07:41 PM

Here is the alignment procedure I have found to work best with the CPC:

-- Before I even power up I loosen clutches and put Polaris in the field of view, then tighten them and switch on.

-- Press enter to begin allgnment, then select auto two star align, which is just as good as sky align and quicker.

-- Wait until GPS completely links. The HC tells me this when it asks me to select first alignment star. I scroll the list to Polaris and hit enter.

-- The HC should then tell you to center the object in your finderscope and press enter. Then it will tell you to center it in the eyepiece and press align. It is best to set slew rate to 5 or slower for these maneuvers, and to use the up and right directional buttons for the final movements.

-- Now the scope will ask you to choose the second alignment star by scrolling a list. This time of year I choose Sirius. After scrolling to it hit enter and the scope should slew on its own to that target or pretty close to it. Do the same finderscope-EBNTER-eyepiece=ALIGN there and you should get a message saying "alignment successful" and you are off and running.

Remember to let the GPS completely synch at the beginning. Just because it may show the correct time does not mean it has downloaded everything it needs. You will know when it is ready when the star list pops up.

If you continued to get "initializing" messages at any point in this process you definitely have an issue.

#9 DrBoring

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Posted 14 April 2013 - 08:20 PM

Thanks Mike, I did like you said to a "T" and no dice.

This did work to auto slew to sirus on a fake alignment (cloudy night) but only slewed in one axis from Polaris - probably not right. I have yet to make it slew left or right with the motor.

I did solar system alignment to moon and as soon as it accepted alignment - back to the startup menu and ready for alignment ...

I think I got a lemon. The controller wont stop going back to the startup.

I do get initializing anytime i try and use the direction arrows to slew for the second star on manual 2-star alignment.

The guy was nice, and maybe he will trade back

Thanks again Mike

#10 sanlopez

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Posted 14 April 2013 - 09:31 PM

Do not despair... the software in the hand-controller and the telescope's motor are user-upgradeable. Look for detailed info here or at the Nexstar's resource site, where you can also download and print the user's manual

#11 herrointment

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Posted 14 April 2013 - 10:18 PM

Have you tried a factory reset on the hand controller? That or a re-flash of the hand controller has solved many a mystery.

#12 DrBoring

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Posted 14 April 2013 - 10:38 PM

I think I found it: they gave me the wrong power adapter. I used the cigarette lighter adapter and it worked great! I'm so relieved!

Thanks again for all your help and advice!

#13 MikeBOKC

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Posted 15 April 2013 - 07:42 AM

Yes inadequate power can surely mess with the CPC's operation. Glad you got it up and running. First target? Jupiter or wait later in the evening for Saturn?

#14 Steve Daniel

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Posted 15 April 2013 - 09:00 AM

woohoo, glad to hear you got it figured out. Now the fun begins!

#15 DrBoring

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Posted 15 April 2013 - 11:19 AM

I got a peek at Jupiter - though it wasn't what I expected. I suspect is has a lot to do with the eyepieces. I started with a 40mm eyepiece - the whole moon fit in my field of view! I also got the celestron eyepiece kit in the deal, so I went to 22mm (I think) and added the 2x barlow. It still wasn't much more than a small beige-ish dot. With a little more time I can check out all the other eye pieces. I suspect I need to use the smaller eyepieces. Any recommendations for eyepiece size to view Jupiter & Saturn?

It was late for a work-night when I figured out the fix. I did check out the moon and was blown away! Wow! I can't wait for another night!

#16 MikeBOKC

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Posted 15 April 2013 - 01:08 PM

Keep in mind that Jupiter, with all its intricate detail, is also very sensitive to poor seeing, meaning it can go from a very neat object to a featureless blob when the air is cruddy and turbulent. Saturn is less so. It also takes a while for SCTs, because their tubes are closed, to reach ambient temperature, which can cause thermal currents inside the tube itself for an hour or more after you take it outside. Lots of owners plan to set up well before dark to allow cooling.

As a general rule, when viewing planets in particular and most objects in general in a larger SCT, an eyepiece around ir under 10mm is probably too much magnification unless seeing is really good; you start losing detail and going all blobby with too much power.

One thing the CPCs have that is really neat, especially for a beginner, is the tour function. It will take you in sequence to 50 or more great targets on any given night, and you can then punch the identify key and learn about them.

#17 DrBoring

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Posted 23 April 2013 - 08:05 AM

I finally got a bit of time to work with the scope last night. I had an excellent view of the moon. From my view, two of the edges had significant sections of craters. I started playing around with my eyepieces and getting comfortable with the equipment. It was really cool to get up close on the craters.

I started looking at Saturn, and it appeared like a blob so I used the goto to check out a few other items. I did the tour feature, like Mike suggested. It worked just fine, but it became apparent that my scope was not collimated correctly.

I severely unfocused on a bright object and the dark circle was no where near the center. So I did my first collimation. Then I went back to Saturn. I saw the rings! It was super cool. I stayed on Saturn for the rest of the evening and worked on seeing what setup gave the best viewing results.

It seemed like my celestron barlow from the 1.25 kit only made viewing worse. This evening I am going to examine it and see if it needs cleaning. I compared my 9mm with 2x barlow vs my 4mm all alone and the 4mm was significantly better. I'm going to try and upload a pic from my iPhone with the 4mm EP. This looks exactly like what I saw. I would like anyone's opinion of this because I have no comparision to know if this view is coming in as good as it should.

I'm using a CPC 800 with Celestron eye pieces from the 1.25" EP kit. All of it is used. I found out that the previous owner had all the collimation screws a few turns from a snug tight, so I did a few lefty-loosey turns ... I think this is only supposed to be done if the screws get fully tightened. This is just to say that my scope and EP have an unknown history, and I'm interested in learning anything that I can do to tune up my optics!

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#18 MikeBOKC

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Posted 23 April 2013 - 12:31 PM

That 4mm eyepiece in the CPC800 puts you over 500 power, which is very rarely useful, especially on a planetary target. A good rule of thumb is that the maximum magnification for any scope should be no more than about 50x per inch of aperture, and more commonly 30-35. Try Saturn with an eyepiece in the 10-25mm range and I think you'll see a lot more detail.

#19 Schaden

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Posted 17 May 2013 - 12:11 PM

Most nights in my 8" F10, I use an 11mm as my Saturn and Jupiter ep. 180x mag looks good when cleardarksky predicts the seeing will be average or better, ie the nights I will go out to observe. If you wanted to be conservative, maybe get a 13mm. I think you could use that for planets most nights unless the seeing was pretty bad.






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