Tracking Issues

[happy-kat]

My baby Virtuos mount can track but I have only managed this twice with it. I am not suspecting it's an alignment thing as I have a synscan v3 handset to use with it and used the synscaninit app to make sure I entered the right details in. Whislt the tracking is no doubt generally OK for visiual I am inteneding to push the mount to within the limitqtoins of field rotatiion with a camera slapped on it.

I did a bit more digging last night to work out what is going on. Took the first image with the mount so called tracking and the second image with the mount turned off and static. Both are 20 seconds long with a 50mm vintage lens. Both images are a crop. The static image is showing as expected star trails left to right and Orion was still climbing. The tracking image is indicating (to me) that the mount is tracking in azimuth but is not tracking altitude.

I know from previous use that the mount does track (that was the 85mm lens and tracking was good) in both axis so I have to look at variables.

Lenses, there is great weight variance between the kit lens, 85mm and vintage lenses in both weight and length of lens.

The other observation is that the two times that tracking has worked the camera was pointing south, the first time was just by default Virtuoso mount alignment (and a resonably high elevation) and using AA batteries and the second time using synscan alignment and a power battery cell. So the only consistent observation is pointing South, but that does not make great sense when I thought for AltAz use the better directions to point to are lower altitudes and east or west.

The clutches were suffiently engaged as the mount would move the camera up and down altitude so I assumed that there was no slipping. The camera was lens heavy but this would only show when near horizontal. I am using the skywatcher camera L bracket attachment.

Thoughts, might see about getting a dovetail bar and fitting the camera to that as that would hold the altitude weight close to the mount head.

Location situations either front or back graden are only either S/W/N or N/E/S however the latter is inflicted with 4 street lamps (only clear direction is E across houses/trees) and the latter with street lamp and hedge/buildings all views are restricted.

I will carry on and all stones are not yet upturned.

Driven

Static

[mikeyj1]

I think you may have hit the nail already, with the weight issue.  if its not balanced, could be that the weight is overpowering the steppers and they are actually going backward (downward in Dec).  As you dont have any horizontal movement, looks like the RA is working ok?

just a guess,

Mike

[Peter Drew]

I agree that it is most likely weight induced slippage. I don't think you would get such trailing even undriven with a 50mm lens during a 20 second exposure.

[happy-kat]

Thank you both.

They are close crops of the original and the static trail is more or less the same length as the altitude trail but is the amount of movement an equal comparison of altitude to azimuth, my head is saying that the amount of movement should be less in altitude then azimuth and therefore the mount is potentially extra slipping altitude. Edit: I'll rubbish my own thought it's rubbish it would be the same.

Current camera mount. So I need to see about changing the L bracket to a dovetail bar direct in the head or adding a T peice to the existing camera position, need to balance the camera front to back.

[happy-kat]

Whilst it's cloudy I am reading again the synscan mamual and the chestnut to remember for this mount ALtAz:

Rules for choosing alignment stars:

• It is recommended that the altitude of the two alignment stars are between 15 and 60 degrees and the deviation of altitude is between 10 and 30 degrees.

• The azimuth deviation of the two alignment stars can be between 45 and 135 degrees, it is best to be close to 90 degrees.

This willl suit me just fine with my limited viewing options.

[happy-kat]

Dovetail bar on order hopefully this will make all the difference.

[happy-kat]

Dovetail arrived and have raided my fitment box from the barndoor build and have a tripod 1 1/4 screw which fits through the provided threaded holes on the bar. Just got to raid the bike box next for some rubber to pack out the fitment to the camera quick release plate.

[happy-kat]

Quick release plate fitted with a bit of inner tube for packing. Next need to try balancing the camera starting with the 50mm lens.

[happy-kat]

A dry run proved not there yet... The weight of the camera and lens was too much for the clamp, I can't turn it to fully tighten because the adjustment handle is too large and fouls the bar. So made a wooden chuck that stops the quick release clamp from moving. It is positioned on the two end bolts and I'll fix a bolt and nut right through just got to rummage in the garage for that. There is a tiny bit of play still but in practice I don't think this will matter.

[happy-kat]

Yey the bar worked. Used my 135mm lens and got good stars facing SE 30 seconds, so could expect more facing E or W, but I think if facing west I'll need to mount bar other way round to make camera front heavy from what is now tail heavy that I used tonight. 

[happy-kat]

This is a single 30 second image resized 50% NGC2244 and saved as png just to show that the Virtuoso mount is now tracking great, it was all about gettting the balance and weight distribution right. For observing the original tracking was fine, I just wanted to see if I could improve it.

ISO 800 vintage 135mm lens 1100d 30 seconds f2.8 or f3 I forgot to check this morning when I put the gear away. I would have gone for longer subs but I couldn't get DSLR timelapse to work right I have had a recent update and I need to day time fiddle to get that right.