MikeV wrote:

ausastronomer wrote:Hi Mike,

Notwithstanding that your altitude bearings are eccentric, have you done the red laser test to ensure that the altitude encoder is centred, as best as can be centred, on the altitude axis of rotation? I found this helped pointing accuracy enormously in the pre TPAS days. It also helps post TPAS as there are less errors to be corrected by TPAS.

If you haven't done it I can walk you through it.

Hi John! Rosalie says Hi! too. Hope you are well. We are traveling to NZ this spring (I'm taking the travel scope that's the subject of these posts). We haven't yet visited all the places you recommended for our last trip!

Thanks for the kind offer to help. I don't know the red laser test, but it looks like Gary posted a how-to guide so I'll take a look at that.

I discovered this problem because I could see that the ALT-encoder was moving as I moved the scope in altitude. I set out with paper and protracter to find the "right spot" but discovered there wasn't one right spot. But, as you say, there is probably a "best" spot.

Many thanks,
Mike

Hi Mike,

Say hi to Rosalie !!

Sue and I will be in New Zealand ourselves for the first 2 weeks of December. We sail on Celebrity Solstice on 20/11 for 12 Nights out of Sydney and depart the ship in Auckland on 2/12. Sue's parents will drive up from Napier to Auckland in their Motor Home and meet us off the ship in Auckland. We will then spend 2 weeks travelling in the North Island with them, before flying home about 14/12. We won't do too much travelling around as her parents are getting on, we don't have that much time on this trip and the 4 of us have all done countless trips around NZ previously. We will revisit some favourites like Taupo and Rotorua and maybe head up to the Bay of Islands for a few days. I never get tired of revisiting places like Wai-O-Tapu https://www.waiotapu.co.nz/ and Huka Falls http://www.hukafalls.com/ which are within about 50km of each other on the highway between Rotorua and Taupo


Firstly, if you can't adjust the altitude encoder position in both axes you don't have any options that don't involve a lot of work on the mount. On a scope like an Obsession (which is what is pictured in Scott's powerpoint) it is very easy. Scott's powerpoint is very detailed and actually makes the process sound a lot more complicated than what it is.

Let me explain it simplistically:-

I prefer to do this at night in a position where I have an exterior light, with the switch in a handy position. You turn the light off when moving the scope through its altitude range, which makes it easy to see the movement of the laser dot and then turn it on to make the adjustments under good light. I use my normal red dot laser collimator. I set the laser up about 2 or 3 metres from the scope, which makes it easy to move around the scope without kicking the laser rig over and having to start again. You want to set the laser up so that the laser axis is "very roughly" in line with the altitude encoder axis. It doesn't need to be that accurate, as you are working off the point, not the plane. You also however, don't want the laser firing from a 45 degree angle, as the red dot will elongate to an ellipse. I usually set the laser on a milk crate or chair or something around that height and then a small cushion with a heavy book on the top. I then "wedge" the laser between the book and the cushion. The cushion allows you to "wiggle" the laser and make slight adjustments to where it points to get it hitting the dead centre of the encoder axis shaft, but able to retain its position when it is set.

I then loosen the adjustment screws and nut slighty on the encoder bracket so that the encoder remains in place without moving, but you can move the encoder yourself, to make the adjustments as required. This saves tightening and undoing the screws and nut 400 times, while you play with it. Move the scope through it's full altitude range and you will see the laser dot move as the scope moves through its full range. A little trial and error will soon show you where you need to move the encoder to make appropriate corrections. Keep going with trial and error until the laser dot remains fixed on the centre of the encoder shaft as the scope is moved through its full altitude range. It usually takes me about 10 to 15 minutes only from start to finish to get the altitude encoder spot on. I do this as a matter of course every time I remove the altitude encoder on any of my scopes. It helps pointing accuracy a lot, particularly for those that don't do a TPAS run before an observing session.

Cheers

Hi Mike,

Notwithstanding that your altitude bearings are eccentric, have you done the red laser test to ensure that the altitude encoder is centred, as best as can be centred, on the altitude axis of rotation? I found this helped pointing accuracy enormously in the pre TPAS days. It also helps post TPAS as there are less errors to be corrected by TPAS.

If you haven't done it I can walk you through it.

Well done on setting this up so quickly Gary!!

I think this forum software will prove to be more user friendly and versatile, than the older style Yahoo Message Boards.