Lidl "Computer Telescope" forum

Anyone got access to optics testing gear?

I was wondering if it is better to use the regular eyepiece slot and the flip morror or the prism?

ie does more light get reflected off the mirror than would be passed through the prism and is the prism really just for terrestrial use?

Cheers,
~Al

Major problem!!
Last night I placed the threaded dew cap onto my etx and now it wont come off, its on too tight! I'm afraid to force it too much incase I do any damage, and with the scope this way it wont fit into the caryy bag. :oops:
Any suggestions for getting it back off?

You do not need to polar allign the scope or place it on a wedge for this!

Great stuff! I have a Toucam Pro II which I can hook up for planetary imaging. Might just get Saturn if we get lucky with the weather. I have ordered the piggyback mount for my Nikons. How long an exposure will I get with, say, a 50mm lens before I see field rotation in the image?

Hi again folks,
Just a quick update on my 'problem'. As AlbertW pointed out, it is indeed a hex nut. It took a while for the penny to drop, as the nut itself is so damn small I found it hard to make out if it WAS a nut, or the remains of a screw.
So after spending 10 minutes on the ground outside with a flash-light in hand searching for a non-existant screw, I sat down with the focus knob and finally figured out that it is indeed a hex-nut. The hex shape was quite difficult to make out because of it's size, plus some white substance on the screw itself.
I checked through my inventory of allen-keys but couldn't find a key to match the size. I used a kitchen implement to tighten the knob back on the shaft temporarily, but will search out the correct tool for the job this weekend.
Thanks to everyone for the help and advice. SilverBarrel, cheers for the link. I also got my ETX in Shannon. We were indeed lucky !
Especially with everyone sprinting to get one as soon as the doors were opened! Just like a clearance sale in Brown Thomas

Cheers!
K.

Anthony,

Part of the answer is dependent on the altitude of your object of interest. The higher the object is, the longer you can expose before field rotation sets in. Of course, if there is a choice, it is best to wait for the object to reach its maximum altitude for the evening and shoot around then.

I am going by shear memory but I recall something like 52 seconds for 60-deg altitude without any star trails being visible on film ... and something like 20 seconds near the horizon.

Michael Covington's book has a detailed description and formula for computing the maximum exposure as a function of the lens focal length and altitude.

Anthony.

Anthony,
I am going by shear memory but I recall something like 52 seconds for 60-deg altitude without any star trails being visible on film ... and something like 20 seconds near the horizon.

That's pretty damn short. I was hoping for a bit longer. That's the same length of time for exposing just on a normal tripod without piggybacking. Presumably if I had the telescope in equatorial mode I'd get piggyback exposures as long as I wanted - say 10 minutes, 20 minutes, half hour??