Eq5 Periodic Error

[pjphilli]

Hi
I have an EQ5 mount with the simple paddle arrangement extended to the parallel port of my PC in ST4 fashion for guiding. There is no PEC.

I am using PHD guiding and the arrangement works fine for guiding my Meade 80mm f6 but too much RA ovaling when I use this as the guide scope and try
to image with my 150mm Mak f13. I suspect I have stretched the EQ5 beyond reasonable limits. The 150 Mak use is just acceptable when focal reduced to f6 with about 30% of images which are rejected prior to stacking.

Last night I measured the periodic error of the 10 minute worm cycle and found that the overall drift was about 60 arc seconds but for a lot of the time the short term (eg 1 minute) drift was within about 8 arc seconds total.
Guiding with PHD improves this somewhat but it can't correct for a few of the steep PE transitions in each 10min worm cycle.

I would be interested of others experience in using the EQ5 mount for guiding and whether it is possible to introduce PEC. Cheers Peter

[Ian Robinson]

That's not very flash. I guess you get what you pay for, I expected these el-cheapo EQ5's to be cheap and nasty , but that is worse than I thought they'd be. No wonder they don't advertise their periodic error or give any guarantees on this.

I think all GEM and fork mounts should come with a guaranteed maximum PE with and without PEC enabled.

[pjphilli]

Hi Ian
Yes I agree but I have yet to see any guarantee's in this respect. To be fair, the EQ5 is quite a good mount for the price and I suppose it was really intended for eyepiece viewing where it does a good job. CCD imaging is another ball game altogether. The solution is to buy another mount - but which mount as I don't think I have ever seen PE specs in mount sales blurb. Perhaps those such as Takahashi may supply these but this would be a bit out of my price league - besides I can still get a lot of pleasure out of the EQ5 - so long as I do not expect too much of it and be prepared to discard quite a few images before stacking!
Cheers Peter