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SN design and Paracorr?

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#1 Astrolupa

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Posted 14 July 2005 - 12:59 PM

Hi! I'd like to hear the experts :grin: on this matter. Will a coma corrector like Televue's Paracorr work in a SN optics design? What would be the probable outcome?

Thanks!

Nelson Viegas

#2 Don W

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Posted 14 July 2005 - 02:34 PM

The SN design uses a spherical mirror which has no coma. The Paracorr corrects for coma. Therefore it has no purpose in a SN scope.

#3 Starman1

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Posted 14 July 2005 - 07:01 PM

Hi! I'd like to hear the experts :grin: on this matter. Will a coma corrector like Televue's Paracorr work in a SN optics design? What would be the probable outcome?

Thanks!

Nelson Viegas

The corrector plate in a Schmidt-Newtonian corrects spherical aberration, and flattens the field. There should be no reason to use a Paracorr in that scope. The result would be a less-flat focal plane, and coma added! The Paracorr is for f/3.5-f/6 paraboloidal mirrors in simple newtonians.

#4 Guest_**DONOTDELETE**_*

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Posted 15 July 2005 - 01:58 AM

The Tele Vue 2.5X Powermate has reduced any residual aberrations in my SN8 scope. I use it almost all the time for visual observation. I think what it does is allow the EP's to work where they are optimized, f/10 instead of f/4.

#5 Astrolupa

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Posted 15 July 2005 - 05:15 AM

Thanks for all the answers! I think Meade states that a 10"SN has half the coma of a "normal" newtonian. The reason for all this is that I used a Nagler 31mm in a XT10 classic newtonian and in a 10"SN. In the XT10 the field was corrected over the entire fov. In the 10"SN, some coma was noticable, and trying to focus the whole field results in a kind of "okayish" focusing. Maybe there's some over-correcting effect because of this eyepiece construction?

Best regards,
Nelson Viegas

#6 Guest_**DONOTDELETE**_*

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Posted 16 July 2005 - 11:43 AM

Nelson, if you have a Meade SN, then you NEED a Tele Vue Powermate to change between visual observation and astrophotography. The difference is not subtle. Don't listen to those who haven't tried it in a Meade SN and give armchair observing advice based on other OTA's. I have both and I know. I just got my Stellarvue F50 finder scope. It is awesome for the price. It doubles as a spotting scope because of the erect image right angle finder with helical focuser and 1.25" EP holder. Drops right in the Meade finder rings.

Besides getting the mount working up to full potential, you must address these issues: 1) Powermate (if visual is your bag), 2) Finder (if you use one for more than initial star alignment), 3) Dew Heaters (That Schmidt plate dews up at the drop of a hat. Try Dew-Not heater strips with Thousand Oaks controller for less $$$ and lower energy drain over Kendrick and Astrozap. www.dew-not.com Astronomics sells the Thousand Oaks heater controller. It has unique features and is very lightweight.), 4) Carrying case for mount (that declination plastic cover is VERY prone to breaking, and mine has already been replaced by Meade under warranty). A strong cardboard box lined in foam is OK at first, but I bought the JMI case., 5) Better focuser. The best thing is a JMI NGF-55 Crayford. Those that want bang-for-buck will probably end up with a Borg helical like I did. $60 to $100. 6) Heater power supply. I made my own from a Radio Shack 13.8VDC 3A switching power supply and their SLA batteries that are on sale now, and an auto cigarette plug accessory power outlet, plus an in-line germanium power rectifier diode to prevent the power supply from draining the charged batteries in storage and a 25W 8 ohm series power resistor for charging protection (it drops the voltage to around 13.5V at a 25mA trickle charge). You can bypass the resistor with a switch for faster charging after a night of deep drain use. You can mount the whole shebang in a rugged waterproof military ammo can ($5) and rig it up to where it serves as a UPS when you use it at home. It float charges the batteries at 13.5VDC when you use it as a UPS. You always run off the battery for no ripple from the switching PS. There is enough room left in the ammo can for carrying your heat controller, accessory red light (you can build from red diodes and a rheostat and a max current limiting resistor), insulation for battery, bug repellent, etc. More versatile than a Power Tank and funky cool.

Could say more, but no time today for that.


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