Attempts at 10m exposures and guiding issues!

[Notty]

Hi all.  I've been trying to get my photography rig set up and working with an SW200PDS on an HEQ5 with an ST80 guide.  I originally had issues with weight and balance, but I can balance it now albeit with a third counterweight.

I had a go the the other night, trying various targets at different lengths to see how it worked out, and it has thrown out a load of issues I wondered if anyone could assist with?

The first issue I have is with Phd very frequent "star lost" occurrences.  I am using a QHY5l-iic cam which I know is a usable cam on this mount.  I have a heath robinson assembly of 1.25"-2"-1.25" extension tubes to get focus, but even with the recommended 2 sec exposure I can normally only see one or at absolute most 2 guidestars.  Is this normal?  

I tried a few 10 min exposures, and have observed some strange effects.  I took 3 x 10m subs on M31 below.  The first shows these streaks; do you think these are meteor showers or something else?

The second has these strange shaped squiggles.... am I looking at periods where the guidestar has been lost?  THe seemingly equal intensity of the light in the trails suggests to me that the movement was constant over the 10minutes?

The last one shows neither effect but a slight trailing.  Is this because I'm pushing it with this much all up weight on the HEQ5?

To note though, 5 minute subs look fine generally, though I haven't done too much processing.

Secondly, I had a look at the pretty Peaides, and did a bit of messing around in PS after stacking a few, but looking at the shapes of the stars and the halo around them, there is a slice missing off each of them at the same 10 o clock position.  Is this my collimation off do you think?  Incidentally, if anyone has a 200pds I'm desperately trying to find out the spider vane offsets position, as I took it apart when I got it to try and learn to collimate it from first principles (yes I know very daft) and I have no idea if I've put it together right.

I'd love to hear your opinions on any of these observations.  

Many thanks

Andy

[Leveye]

You have something inside the tube like possibly screwheads or whatnot possibly getting in the image and causing those gaps.You want the spider centered perfect i feel it's off here slightly. Check that first. Also it looks as if you had some dew fogging up the mirrors. Might be time for a fan and a heater.

[toxic]

the large gap in your stars to the right is your focus tube going into the ota in the last picture.the second is definitely tracking to do with the weight and or possible wind.

to save on weight i would take of the st80 and use the finder as a guide scope and you will get way more stars to choose from. i use the 200 pds with the finder as a guide cam but with a different mount i may be wrong i never own'd a heq5 but i think your pushing it a bit with the weight on the heq5 i had similar problems when i had that setup on my celestron cg5 tg .

[D4N]

The first image looks like the scope slewed quite quickly as those streaks are on everything even the galactic core of M31. Or perhaps you just stopped tracking, that can happen if the mount reaches the meridian.

Second one could be down to backlash, have you set up the anti backlash? Or it could just be something g wrong in the guiding.

Third ones not bad, just slight trailing.

I think 10min might be too long for Pleiades, you will struggle to control those stars in processing.

TSED70Q, iOptron Smart EQ pro, ASI-120MM, Finepix S5 pro.

[Notty]

Thanks for all the tips everyone it's very helpful.

Leveye, with regard to these screws or whatnot, I'm a bit stuck here are you saying something "alien" to the scope is in the tube, or that it's a side effect of the vanes not being centred?

I have a heating band though I only turned it on a tiny bit as it wasn't cold, though it was very wet air I should have cranked it up more. Question though, firstly I was understanding that reflectors didn't suffer from dew all that much due to their design, ie the tube being a massive dewshield over the primary, and the secondary facing down the tube helped shield it. I had my band wrapped around the base of the tube I.e around the primary. How do we all heat our secondary, if at all?

Regarding backlash, I'm using Stellarium/Phd via EQMOD- are there specific backlash calibrations I need to do inside EQMOD? The other question I had was on guiding should I force a re calibration each time I change target?

Toxic, I'm not sure what you mean about my focus tube goin into the main tube causing a gap in the picture? If I've focused properly, which I more or less had with my bahtinov, then I've got no control over this surely? Could you elaborate a bit please?

I'm going to try converting my finder to a guider, as I just feel I've got too much structure and weight on top of my little HEQ5.

Many thanks again everyone.

Andy

[Owmuchonomy]

The first one: the mount was slewing to position during the exposure

The second one: the mount has suffered a sudden 'jump' often associated with backlash being taken up, wind, balance or just a physical jolt. Could be one or a combination of all these. Could even be trapped cables.

The third one looks good, so I conclude the mount has settled down

Lost stars for me means dew, thin cloud or too short a guide exposure. I'm lucky in that I have a Lodestar so I can pick up stars even when it's cloudy!

The Pleiades needs seconds of exposure rather than minutes in my experience.

[g0ibi]

Hi Andy, I've got an MN190 (200 tube) on an HEQ5 with 3 weights and a finder/guider + Canon 1000d and can just achieve balance but it is almost on the limit! You should re calibrate if you move targets and try using 3-4 secs  on the guide scope, it helped me a lot!

Cheers

Ron

[D4N]

Backlash is the mechanical play in the gears of your mount. It really messes up guiding.

To check for backlash use the controls to move the mount in all the directions whilst looking at a star (or anything else really). If there is either a delay or a jerky movement then your anti backlash needs adjusting. There should be a setting for it on the handset.

I think toxic was referring to a problem you can get on Newtonian scopes where because you have the focuser tube racked all the way in to achieve prime focus it could be obstructing the light path. Just look down the scope while you are focused to check.

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[Notty]

Thanks all. I've been looking into this backlash issue, but am I right in that the Phd calibration routine actually detects backlash as part of its routine, then adjusts tracking accordingly, ie do I need to take any other action to compensate outside of Phd?

[D4N]

The mount should have an anti backlash feature that will rewind the motor slightly after a move, PHD isn't able to do this.

The other way to do it is to adjust the mount so that guiding is always in one direction then e gears remain meshed together.

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[Christopher Davenport]

One more thought for you, other than backlash, which affects Dec more really, my EQ5Pro has a 7min worm drive cycle. i.e the drive takes 7min to do a rotation.

If I put my balance east side heavy to keep my worm drive engaged through the cycle and and I misalign Polar align to be DEC heavy, then I can push subs further than 7min.

But honestly it is a bit of a phaff, so I stick to subs below 7mins.

BTW, +1 on using a finder guider to save on weight and reduce the wind sail effect. 

[Notty]

Thanks all.  So thinking about how my mount tracks when I'm looking at the happy screen say when I'm zapping to and fro when doing a solar mosaic, I now realise that large pause before movement in one axis in one direction is this "Backlash" of which we speak.  To be honest my Phd graphs look pretty revolting in both axes so maybe I'd better check my PA again, but having used the natty little EQMOD PA alignment process I'd hoped I'd got it nailed.

The "East heavy" thing, that is shifting the weights in the RA axis, not the scope to and fro in the DEC am I right?

Just unwrapped my FinderGuider adapter from Modern Astronomy to convert my 9x50 finder!  Thanks for that tip as well.  Should I see more or less guidestars through that than the ST80 do you think?

[DaveS]

Yes, just adjust your counterweights to keep the east side heavy. I'm getting fairly reliable 10 min subs even though my PHD graphs look like the Himalayas, but there again I'm putting much less load on my HEQ5. I'd say a 200 PDS is pushing it a little on a HEQ5.