M42 with round stars at last.

At last after 2 years of trying to get round stars, this is a stack of 47 images unguided. The "seeing" was poor and the wind was a bit gusty so I pulled out about 10% of the images. My Polar setup was really good so I just did a 2 star align and let the scope guide itself.

The problem in the past was a sticky gearbox in the base of the Etx making the stars jump into a line on the final image. I simply tightened the bearings and lubricated the gears before adjusting the gearbox position and it now runs really smoothly.
To check how smooth it was moving I engaged PHD guiding and ran the graph below. I think the scope has been sticky from new as the graph always jumped very erratically before alarming out.

This has shown me that its the quality  and smoothness of the mount is very important if round stars are needed.

Betelgeuse 06/02/2012

So windy last night that long exposures were not possible without long stars so this was a 10 second exposure. The image is cropped in but I just liked the look of this giant sun. Clasified as a Red Supergiant its about 640 light years away.

My DIY Dew Heaters for just a few £'s

I thought I would share my Dew Heater design as it was so easy and cheap to make.
Without the battery these heaters cost me less than £10.

Dew heaters can be expensive and often need expensive controllers to adjust the temperature output of each heater. The idea is to heat the corrector plate end of the telescope just enough to replace the heat lost to space thus stopping dew from forming on the lens. Much like the dew on your car windscreen collects overnight.

My aim was to design a simple and cheap 12 volt system without the fancy heat controllers.This would save me using a 240 volt hair dryer with is obvious dangers outside in the damp night conditions.

I worked out from research on the net that I needed somewhere between 0.5 watts and 1.5 watts of heat on my finder scope and between 1 watt and 2.75 watts on my 105mm dia Meade etx.

If you look at the diagram this can be achieved by wiring both dew heaters together across a 12 volt battery (mines an old car battery). To adjust the heat output I simply use a direct connection across the battery for maximum heat or add either one or two 10 ohm resistors in line next to the battery as shown in the diagram below. SIMPLE.

The wiring is looped back around the heater band so that it can be easily attached.
The parts list shows roughly what I needed.

The resistors are really cheap. They come in bags of 20 and you only need 11 x 4.7 ohm resistors
and 13 x 10 ohm resistors for the whole job.
Just solder the resistors together exactly like the diagram and stick them on the inside of the foam using duck tape. Connect them to the battery car with speaker wire and watch out for any short circuits.
A cheap foam camping matt was used as the band to carry the resistors. It would make loads of bands.

I use self adhesive Velcro on each end to easily attach and detach the heater bands.

Last night I used the heaters connected to a car battery continuously for 5 hours at between +3 and -2 degrees with no dew on my lenses. I did not see any reduction in image quality due to the heat.

Please note that I am not an electrician and if you choose to copy this design you do so at your own risk .If wired incorrectly the resistors or wiring could overheat.

M42 Last night poor seeing?

Poor seeing in the upper atmosphere and -2 degrees made it a difficult night with the scope. I only managed 6 images worth saving and stacked them to produce this image. I spent most of the time indoors shooting tethered to the unmodified DSLR camera.
6 x 30secs subs.
3 darks
3 lights
2 bias.
Analysing the reject subs for "jerky star trails" on my etx made me strip the RA drive today. I have found the base was tight to turn and the gear train sticking.