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CPC800 Alignment and GoTo

Spudd

By Spudd
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Spudd

Spudd

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I recently purchased a CPC800. First night was great achieved alignment and goto was very precise. Since then, the alignment is achieved but goto is all over the place except on the named star identified. Any advice would be welcome.

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johnh

johnh

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Welcome Spudd, not used the CPC but you need 2 stars for good alignment in one hemisphere and 3 for excellent all sky alignment and if you setup every night you need to realign each time unless you have an obervatory.

JohnH.

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brantuk

brantuk

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Hi Spud and welcome to the group ;)

Check the date and time first - make sure the date is in correct format and daylight saving is set appropriately. Also make sure you are in EQ North mode (I see you're in Canada), or Alt/Az mode if you're not using a wedge.

Once you confirmed those are ok then make sure there's no magnetic interference around - the gps can sometimes be sensitive to overhead cables/sub stations etc.

Run off battery if you can rather than mains initially, and remove all dew heater systems. Mine sometimes reacts strangely to various combinations of those.

Do come back to me if you try all thos ideas and it's still being funny with you.

Cheers :mad:

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brianb

brianb

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Usually when the goto on CPCs misbehaves it's because there is a problem with the power. The plug at the scope end often doesn't fit very well, if it's loose then the scope will do odd things. You can try very gently bending the inner pole in the mount to improve the contact, but securing the top end of the cable to the fork arm is strongly reccomended in any case. (I use electrical tape ... not pretty but hey, it's a working tool, not an art object!)

The other thing to watch with CPCs is the tube balance. They have a tendency to be bottom heavy anyway, and sometimes if you're using a heavy 2" diagonal and eyepiece, or camera, the altitude clutch will slip ... the answer here is to balance the tube with a counterweight at the "top" end rather than simply cinching the alt clutch up extra hard, if you do that then you can get little jumps in the drive due to flexure and backlash in the drive train.

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Johnboy

Johnboy

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The other thing to watch with CPCs is the tube balance. They have a tendency to be bottom heavy anyway, and sometimes if you're using a heavy 2" diagonal and eyepiece, or camera, the altitude clutch will slip ... the answer here is to balance the tube with a counterweight at the "top" end rather than simply cinching the alt clutch up extra hard, if you do that then you can get little jumps in the drive due to flexure and backlash in the drive train.

Hi folks,

Interesting thread. I have just bought a CPC 1100 and will be adding a 2"diagonal so I can use my 2" eyepiece. Are there any paricular counterweights that you recommend? Also, which do you consider best for anti dewing - a shield, a heater or a combo of both.

Also will any diagonal / 2" eyepiece clear the space between the fork arms at the bottom (when viewing near the zenith.)

Thanks for your help.

Regards,

John

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brianb

brianb

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Are there any paricular counterweights that you recommend?

I have a hook attached to the lower side of the corrector plate end of the tube & simply clip on a counterweight made from iron scrap. Ugly but cheap and very effective.

Also, which do you consider best for anti dewing - a shield, a heater or a combo of both.

You really need both with an SCT in typical British dewing conditions. The dew shield buys you a couple of hours but it's fogging over by the time the main mirror has cooled enough to get you good sharp images. I use heater tapes on diagonal & eyepiece too.

Also will any diagonal / 2" eyepiece clear the space between the fork arms at the bottom (when viewing near the zenith.)

"Any", well I can't answer for everything on the market, but the CPC has generous fork clearance compared with most others. I have a "large SCT" 2" visual back and a William Optics 2" diagonal on my CPC1100 and there is about 1.5" clearance. If you hang a Crayford on the back of the thing you will almost certainly foul the mount.

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Johnboy

Johnboy

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I have a hook attached to the lower side of the corrector plate end of the tube & simply clip on a counterweight made from iron scrap. Ugly but cheap and very effective.

You really need both with an SCT in typical British dewing conditions. The dew shield buys you a couple of hours but it's fogging over by the time the main mirror has cooled enough to get you good sharp images. I use heater tapes on diagonal & eyepiece too.

"Any", well I can't answer for everything on the market, but the CPC has generous fork clearance compared with most others. I have a "large SCT" 2" visual back and a William Optics 2" diagonal on my CPC1100 and there is about 1.5" clearance. If you hang a Crayford on the back of the thing you will almost certainly foul the mount.

Cheers brianb. Very helpful. Looks like I'll be doing a few upgrades over the next few weeks!;)

Thanks again,

John

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Spudd

Spudd

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Thanks, Brianb, I will try two things mentioned here - power: make sure my tank is full, examine the fitting, and tape over the plug (hey, it is isn't an art object!) and selection of alignment stars: make them as wide as possible and on both sides of the meridian.

I'll let you know the results.

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brianb

brianb

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selection of alignment stars: make them as wide as possible and on both sides of the meridian.

Three stars in a stright line is bad. Try to make a nice big triangle ... Polaris is good as it doesn't move ... last time I used by scope the alignment stars were Altair, Arcturus and Polaris. The time before that, Hamal, Vega and Polaris ... it was later in the night when it cleared up.

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Johnboy

Johnboy

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Hi folks,

I've been looking at this 2" diagonal: http://www.firstlightoptics.com/proddetail.php?prod=WOcfDielectric

and this one: http://www.harrisontelescopes.co.uk/acatalog/Revelation_Quartz_Dielectric_Diagonal_SCT.html

I know the William Optics one has a very good reputation, but is it worth paying the extra £35 for it against the Revelation? Does anyone know if I'll see any difference between the two or am I paying for the William Optics name?

Thanks in advance for your help.

John

edit. Mistakenly posted here - Reposted in Equipment Help

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Martin-Devon

Martin-Devon

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Hello Spudd, I've had a CPC800 now for 6 months, and it has been superb. I always use the 3-star alignment over the other shorter methods, and I think this helps. Normally all of the GoTO points I request are bang in the middle of the EP. The only exception was when I used 3 stars that were fairly close together - when I went outside of these to find something, then on occassions it was at one right towards the edge of the view. Normally though, with 3 well separated stars it has been impecabble.

Welcome to SGL though...

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