high frequency Ra movment

[Szymon Kierzenkowski]

my Dec is pretty much fine but Ra jumps around 2''-3'' between every single exposure. it can't be seeing since it would affect both axis. i my images are coming out with lie 0.5 roundness i't really annoying and can't do any proper astrophotography unless i fix it.

EQ5 pro guided with SV015C on a skywatcher 30mm guider(120mm fl)

periodic error is also a problem but im guiding with predictive pec and after e few cycles it calms down

i don't know if it may be it but im on the edge of the payload capacity of my mount

 im sending over a guide log, 3h45min guiding session was on m33 and 1h54min was on orion neb if that helps in anything

[Brian Valente]

Hi Szymon

can you share a few pictures of your setup from different angles including your guidescope setup?

I'm not sure I agree with your assessment. It looks like you have significant issues on both axes.

Looking at your 3h45min run, your Dec is actually higher than RA. 

On the second shorter 1h45m run it's not that much different, although RA is a touch higher.

Your min moves are a higher in dec, but even with a backlash compensation of 2 seconds, it's taking dozens of guide pulses before the axis responds:

So on your Dec, i'd say there's a lot of mechanical backlash that you need to address. you didn't have any opposite side of pier guiding, so i can't comment if it's impacted by balance.

It would help to upgrade to the latest release and follow your calibration (via the calibration assistant) with a guiding assistant run. It will help measure backlash there

On RA, the primary PE is really  high, nearly 100" peak to peak. PPEC can help some (and you have the right period length, although I would disable auto adjust period) but the amount is just too large.

 You will need mount-based PE to help here (or possibly some mechanical adjustments as well)

On top of all that, it looks to me like your axes have some bleed between them, note the dec has a similar sinusoidal pattern that matches RA

it's possible the magnitude of your PE is influencing this, but it may also be your guiding setup is rotating slightly and may be contributing to this (and why I asked for some pictures).

Brian

--
You received this message because you are subscribed to the Google Groups "Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to open-phd-guidi...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/57e70f49-7914-4b76-9991-20cfb1313772n%40googlegroups.com.

--

Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Szymon Kierzenkowski]

thank you for the quick response sadly my rig has been in my room taken apart since my last clear night on the 22nd but i can make pictures of the guidecam assembly without putting the whole thing back together. the slowly rotating guidescope is possible i will figure something out to make it rigid. just in case. 

backlash on dec has meen an issue for me in the past and i coudn't find any solutions so i custom made a Dec belt mod for my mount, the saw shaped Dec moves are basically gone since that upgrade but the guiding assistant still says "dec backlash mesurment failed, backlash to high' or something like that. 

about PE, i didn't think is was possible to fix it physically i will disable the automatic period adjustment like you said.

in the sent image you can see im using a finder scope holder, the finder/guider is taped around so it fits tightly in there to not move around during the night but the camera at the end of it is a little loose and can rotate tho to prevent that i have this and few other cables fit under the dovetail with a piece of hard foam, there is enough friction that the cable betwen dovetail and the camera never moves no matter what happens on the other side. maybe the camera rotates due to gravity alone tho i'd be supprised as the cable holding it in place is really stiff esepecially now in the cold.

[Brian Valente]

Szymon

I think you pretty much summarized the problem areas for you to focus on:

- Dec backlash - your 'fix' solved your prior  problem, but introduced a new one which is excessive backlash. You will probably need to tune the belt drive to reduce backlash

- RA - High PE can come from worm runout, mechanical misalignment, etc. - however the easiest fix may be if your mount has PE correction feature. See if you can do that

- re: guidescope setup, as you said, this is far from ideal. Hopefully you can find something that does not require finger screws or tape as the solution. Remember we are talking differences less than the width of a human hair. 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/3e3f3e6f-6001-4f5d-a02d-0382f938a78fn%40googlegroups.com.

[Szymon Kierzenkowski]

i will try and work on all that and check the results on my next clear night