My first post on CN, so please forgive any formatting issues. I recently became the proud owner of an iOptron CEM120 EC2. Given the many positive comments and supporting quantitative data posted here at CN, and my desire to image planetary nebula in the highest resolution my seeing will permit, I decided to bite the bullet and go with the dual-encoder version. I purchased it from a well-known store in Europe, and after a short delay due to back-ordering it arrived here within a few days of receiving the shipping notice. On opening the shipping box I was surprised to see that the DEC axis was unlocked and the DEC worm in the engaged position. Here's an image of the opened box minutes after arrival:
With the mount still in the box I carefully felt the RA gear switch and axil lock (on the underside of the mount) and noticed that they too were set to axis unlocked, worm engaged. This was confirmed when I carefully removed the mount from the box. Perhaps I am mistaken but if my understanding is correct, the axes need to be locked and the worms free when moving and transporting the mount; the worms are prone to damage in the "worms locked, axes unlocked" state. I can imagine there may have been quite a bit of torque applied directly to the worms while carrying the mount to the box and placing it into the box, given its considerable weight and lack of carrying handles like the EQ8 has. I immediately emailed the store the above findings to "cover my behind". I had asked the store to check the mount prior to shipping, so I assume the store simply forgot to return the switches/locks to their correct "safe for transport" positions.
Time passes while I wait for a clear night to test the mount. What follows below are my observations over two days of testing. I am fairly new to astronomy and astrophotography so my inexperience may be leading me to the wrong conclusions, but I am concerned as to what I am seeing; being quite different to those experiences and data that other members have posted. I may simply have a software setting incorrect, or old firmware (my mount has version 180810).
- My equipment is the CEM120 EC2 with a Celestron Edge HD 1100 + ZWO OAG + ASI 1600MM pro.
- Using iOptron Commander V6.1 and PhD2 via USB to control the mount.
- Guide speed 0.6x (also tried 0.5x)
- No wind
- Using an OAG
- Cabling is tight, as is the optical train. Cable management is a dream on this mount.
- The RA has a periodic "tick tick tick" during fast slews.
What I am seeing that I am a little concerned about is:
- a repetitive, predictable sawtooth guide trace in RA when RA guiding is enabled (see below). Even low values of RA aggression like 10% cause this. These periodic oscillations can be as much as 4 arc-sec peak to peak, and certainly don't help in minimising my RMS guiding error. However I think I remember seeing others with this mount post similar concerns so perhaps my mount is "normal" in this respect? In any case I hope there is a method or software setting to reduce them.
- frequent sudden excursions in DEC, but only when guiding (see below). These ruin any chance of imaging at high resolution and result in the loss of many subs.
I tested the mount using a second completely independent scope and imaging train (TS Photoline 130 F7 refractor) to confirm that the source of the problem is probably either the mount hardware or mount/software/firmware bugs. The DEC instability does not occur as often using the refractor, perhaps because it is lighter and/or has a much shorter focal length (720mm vs 2800mm). Both scopes were 3D balanced on the mount.
Perhaps I don't understand how the DEC encoder is supposed to work, but it would appear to me it is not attempting to correct these excursions; it appears to be PhD doing all the heavy-lifting. I guess it is possible that the DEC encoder is causing the excursions?
Here are my settings in Commander:
Example PhD2 guide logs can be download here if you wish to take a look:
So colleagues, what would be your best guess as to what is happening and why? Are there any further tests I should undertake to isolate the cause of these problems? Under EU law I believe I have 14 days from receipt to return the mount "no questions asked", but thanks to terrible weather 11 days have already passed, so I need to make a decision soon. If I do return it it will be for a replacement; I'm not giving up on this mount just yet. I have my fingers crossed that this is simply a software/firmware incompatibility/bug, not to mention operator error
More to follow.