It is now the end of January and finally the skies clear! However a full moon makes the sky much too bright for deep sky photography. So it is a good opportunity to calibrate the scope and check the links to the pc software. The primary objective of this session is to see how well I can get the Meade LPI (Lunar and Planetary Imager) to act as a guide camera. This is no easy feat. Polar alignement is the first task. To do this the tripod needs to be as level as possible, this being done with a spirit level. Secondly the OTA (Optical Tube Assembly) is rotated 90 Degrees and the Pole star viewed through the Polar scope embeded in the body of the mount. Technically the Pole star is not dead centre and it's position is slightly off centre depending on time of day and day of year. Close to centre is best I get so far. Then switch on the motor and perform the easy align on two stars.
The Scope is now set up (about 30-45 minutes) and a GOTO my target set. Tonight it is Alnitak (Zeta Orionis) which is a double star and interesting to see what an image will show. I replace the 25mm lens with Off Axis guider and DSLR camera. I connect to camera and run DSLR Focus to get best focus of a star in the field of view.
With Focus set I place a 25-30mm lens into the off-axis guider, locate the brightest star in field of view and centre is best I can. This will mean the DSLR camera field of view willl move slightly. I remove the lens and replace with an illuminated cross-haired reticle lens. With this I centre the guide star exactly into the centre of the off axis-guider. The illuminated reticle lens is replaced by the LPI at a depth I know to be aproximately at focus point. Focusing the LPI can be done using sophisticated packages but for guiding absolute accuracy is not required. I fire up the Meade LPI Envisage Software and start to get images from the LPI. I might have to set 2 seconds or so to start with. Focusing is then a case of moving the LPI up and down in the guide tube.
ok, with the LPI focusesd I can switch to tracking by drawing a box around the brightest (usually only) star in the image. The software will do some calibration by moving the scope in x-y axis and measuring the effects. It then starts to track the target star and one can watch it happily for hours.
So back to the DSLR camera and a quick double check to see it is still on the object, Alnitak. I am using MaxDSLR from Cyanogen for imaging. I double check the focus using this software and perform a test 1 minute exposure. The result is good so I raise my ambitions. I set the software to perform 10 x 5 minutes images plus a 5 minute Dark.
To be honest I was pleasantly surprised by the results. 5 out of the ten images were first class. Well I think so! Above you can see the resultant image of stacking these which is binned 3x3. And here is a portion of a single frame at 100% zoom. Notice how round the star are.
I am also pleased that it splits the double star very impressively. If I get some more clear nights this week I am tempted to focus again on this target as there is plenty of nebulosity in this area which I wonder if my camera can catch?
Hi John,
My polar allignment is somewhat problematic as I am southern hemisphere based however I am reading up on few tricks to try and improve this.
I have just purchased an OAG for my 8" Newtonian and an LPI to guide. A lot is said in different sites by people who don't own a LPI or OAG that it just isn't possible.
The indications that I am getting from folks like yourself that do have them is that it's a t least worth a try.
My imaging camera is a DSI Meade but I aim to upgrade down the track once I've honed a few of the techniques.
thanks for your writeup
mike
Hi Mike,
My guiding has gone all pear shaped recently. The gears in my LXD55 mount have decided to work at their own pace! Rather than a hypertune I will be looking to replace it shortly for something that can be more reliable for tracking. Possibly a Skywatcher EQ6 Pro.
I am experimenting now with a Starlight Xpress MX7C (from ebay). Rather than use this via the OAG I have attached an M42 (Pentax) lens (also from ebay) directly to it and piggybacking on the main scope.
Not much time for observations at the moment as I am retiring from work in the next month or so. This should give me much more time to persue my hobby.
Where abouts in teh Souther Hemisphere are you?
hope you get more clear skies than we do in the UK!
John