PEC

[Bryndalf]

Periodic Error Correction...what, how ??

I have a HEQ5 Pro and Im still learning all the set up that goes along with this. Im also starting to read up on astrophotography and as part of that it has been mentioned that PEC is a good thing for long exposures, however the section in the HEQ manual is way beyond me

I can now get a good polar alignment, but what do i do from there??

[weega]

a good alignement is the first step to obtain great pictures:

without a good alignement you can guide as well as you want, but There will be field rotation, look here:

orion's sword [1] :: spada_ori.jpg :: Fotopic.Net

on the right it's ok, on the left the stars are blurred.

Once you have aligned very well your mount, the next step is the guide.

With the PEC the mount records all the corrections you do during one rotation of the worm gear. In the next rotation, the mount knows theese corrections and does them automatically. So all you have to do are the corrections caused by the irregularities of the worm-wheel.

The simplest way to obtain a perfect polar alignement (afther the use of a polar scope) is the Bigourdan's method:

<<You aim a star on the celestial equator at the meridian, in a reticulated ocular. And you follow it with the motor running. If it is necessary to elevate the nose of telescope to keep the star on the recticle line, that means that you must move the north of the platform toward east., and vice versa. When the star follows accurately, you aim at another star on the equator, but relatively low in the west. If you must elevate the nose of scope to maintain the star on the line, you must elevate the north end of the platform, and vice versa. After two or three passages progressively refined, you are sure that the platform axis is aimed to celestial pole.>>

from Celestial Alignment

I suggest you do do the alignment with the highest-power eyepiece you have.

ciao

dan

[Merlin66]

The RA axis drive on your mounting is a worm and wheel driven by the stepper motor through a series of gears. It takes 8 mins for the worm drive to make one complete revolution. This is also known as the period or the cycle time of the worm. By setting up the PEC, (which only works for the RA axis) and running it over the full period (i.e 8 mins) any correction you make (using the RA direction buttons on the handcontroller) to keep a star in the centre of the field, are recorded by the motor controller and then "played back" the next time the motor runs. This means that 90% of the corrections you would normally make are already done for you - pretty smart!

PEC can certainly improve the tracking performance of any EQ mount.

Ken

[ollypenrice]

PEC does improve accuracy greatly but sometimes, when you read the manufacturers' blurb, there is an implication that this will provide real photographic tracking accuracy. It won't, on anything but the exotically costly mounts. However, on your mount you should get a couple of minutes and enough to get started in imaging.

The next step is an autoguider, a parallel camera-telescope which sends correction in real time to the mount. When these are used most imagers disable the PEC.

Olly

[Bryndalf]

Thanks for the replys, I thought that i had to do some calculations and set it, nice to see its auto.

Now why couldnt skywatchers manual have explained it the way you guys did

[lukebl]

The simplest way to obtain a perfect polar alignement (afther the use of a polar scope) is the Bigourdan's method

...which we know as Drift alignment. Good tutorial here