Fri/Sat 12/13th March. Fingers crossed.
If anyone wants to bring a couple of bags of premix, you're welcome to construct your own 'spot' with alignment marks etc.
I am going to try to make it to the March gathering - haven't been able to get there since November. I have been making slow progress at home getting my drift alignment right - but I think I've cracked it.
My wishlist of things to do that weekend would be:
1. wouldn't mind doing some tracked/unguided shots with my Canon through the 8" newt to see how it goes. The camera is an old 10D - way to much noise / hot pixels as I found out with the widefield shots I took in November. Will need to get a T-ring and adapter though beforehand....
2. Would like to try using Alignmaster. I haven't been able to do it at home as the star pairs it asks for are all but impossible from my place in Brissy - trees mostly
3. Would very much like to do some plain old observation. I have been putting so much time into learning about the mount / scope etc that I haven't had much time to actually look at anything...
Peter - I've been reading about some people who have trouble getting focus after adding the t-rings / adapters etc. How do I know in advance if this is going to be an issue?
Peter - I've been reading about some people who have trouble getting focus after adding the t-rings / adapters etc. How do I know in advance if this is going to be an issue?
Adam
Get the scope to focus visually on something bright - the moon would do. Lock it in place. Remove the eyepiece. Hold a sheet of paper over the end of the scope and move it until the image of the moon is in focus on the paper. That's the focal point of your scope. The imaging chip of your DSLR needs to be at that same point. The T-Rings are about 12-13 mm thick and the distance from camera front to its chip is about 20mm - give or take. So, on your Canon 10D, I'd say you would need to have about 35mm of travel inwards on your focuser to accommodate the camera. Have a look at the focuser and see how much of the silver inner tube is showing above the body of the focuser. That's where your inward travel will come from.
thanks peter - I'll try that. Would it be any easier in the daytime to use the camera instead of a piece of paper, and try to determine the focal point through the camera's viewfinder? Or is it too hard to find something terrestrial at optical infinity??
thanks peter - I'll try that. Would it be any easier in the daytime to use the camera instead of a piece of paper, and try to determine the focal point through the camera's viewfinder? Or is it too hard to find something terrestrial at optical infinity??
Doesn't matter. Focus is focus. Whatever works for you.
P.
I hope it clears up for March. I wouldn't mind bringing up the water heater for a run up there. Finally got rings for the stellarvue. That's stripped about 5 kilos off the weight
Get the scope to focus visually on something bright - the moon would do. Lock it in place. Remove the eyepiece. Hold a sheet of paper over the end of the scope and move it until the image of the moon is in focus on the paper. That's the focal point of your scope. The imaging chip of your DSLR needs to be at that same point. The T-Rings are about 12-13 mm thick and the distance from camera front to its chip is about 20mm - give or take. So, on your Canon 10D, I'd say you would need to have about 35mm of travel inwards on your focuser to accommodate the camera. Have a look at the focuser and see how much of the silver inner tube is showing above the body of the focuser. That's where your inward travel will come from.
Peter
All sound advice - thats the easiest way to do it... I only have one correction here.. the distance between any Canon EOS DSLR mounting ring and the sensor is 44mm + your T-ring (12-13mm) = 56~57mm from sensor to the end of your focuser drawtube...
As a general rule, Newtonians rarely come to focus without some form of modification..
Robin - That light bucket of yours will be a serious force to be reckoned with out at dark skies!
the distance between any Canon EOS DSLR mounting ring and the sensor is 44mm
when I first read that i thought 'they can't all be 44mm' - then I realised that Duh! - they all use the same lenses, so they have to have the same distance from the flange to the focal plane....
all the same 44mm seems like a long way - I wouldn't have thought the camera was even that deep!
So what to do about the focussing arrangement?? I don't really want to get into moving the primary up the tube....
1 - a low profile focuser.
2 - longer collimation bolts/springs in the primary to lift it a little bit.
3 - a combination of 1 and 2
4 - cut 10~30mm off the end of the tube and move the mirror/mirror cell up the tube .
44mm sounds like a long way, I agree, but that is the optical backfocus distance of an EOS Digital SLR.. no ifs whats or buts about it.
If you look at the top of your camera there is a small circle with a line across it. This is location of the focal plane. You will be surprised just how far back in the camera it is - but if you measure from the front of the lens mount to where that focal plane marker is it will be 44mm. (I know these marks exist on Nikon cameras - they are 46.5mm back I think)
If you look at the top of your camera there is a small circle with a line across it.
You know what - I have had this camera for 6 years, and I have never noticed that there! BUt sure enough, and 44mm too. You learn something every day...
Bravo David - the Nikon lens back focus distance is 46.5mm..
Its funny, both these measurements seem too far to be true, however you should see the measurements for a Hassleblad setup, or other medium format setups 645's and 6x7's etc... up to 107mm between lens mount and focal point!
That's why you can't put a Canon lens on a Nikon Body, but you can put a Nikon lens onto a Canon Body with an adaptor (although none of the electronics will work!) - think about it...
Yep - there are going to be issues getting focus with my newt/Canon DSLR....
I found focus by putting the camera flange against the 2" Ep holder and looking through the cameras viewfinder. Turns out that there is only 4mm of inward travel left on the focuser - and that is without any T-ring or adapter.
I am going to look at the available low-profile focusers, and see whether they will be any better.
. 
