Thanks again Dave for the useful reply.
Quote:
Originally Posted by naskies
The OAG lets you adjust the focus distance by a small amount, which you tweak with a focusing mask on a bright star.
As for figuring out the focus distance, get your 6D attached to the OAG first. Once you've done that, use a pair of callipers/ruler and measure the distance from the centre of the pick-off mirror to where the camera sits flush to the EOS bayonet and add 44 mm (EOS mount to chip distance). Next, measure out that same distance from the OAG mirror and up the guider mount - this will show you what distance (possibly spacers) you'll need.
I'd recommend attaching the DSLR, OAG, and focus all as close to each other as possible - if you add in long distances such as with the TRUE 2 adapter, you'll substantially increase the moment arm on the stock focuser. It's better to use the beefy extension rings on the telescope side of the focuser to minimise your focuser-to-camera distance.
Good luck!
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I've resigned myself to going the path you suggest, because deep-down I realise it makes the most sense.
I was just trying to avoid it to re-use what I already had.
I'll put the True 2 adapter aside and just use it for non guided shooting, e.g. the moon.
So, I think for the Camera to OAG, I need the bit you suggested:
EOS to M48, plus the other bit I mentioned:
M48 Adapter. That should allow the maximum amount of useable light through.
As I'll be doing a Teleskop Express order for the above, I'll probably get the T2 to M48 adapter you linked - I've sent off a question about it to confirm it's the correct bit required. Given the formula you specify, I'm almost 100% certain I'm going to need a spacer on the guide camera side. I've also asked for the width details of the EOS bayonet so I can attempt to calculate the spacer required.
Given the data on the OAG from TS's website:
-- Distance from prism center to sideward T2 terminal: 26mm ... 38mm
-- Distance from prism center to OAG front side: 6.7mm
-- Distance from prism center to camera terminal: 4.5mm
X = EOS bayonet width.
Y = Guide Camera adapter width (T2 to M48).
Then, using your formula, the camera side is 44 + X + 4.5, so X + 48.5.
The spacer is then = X + 48.5 - (26<->38) - Y; X-Y + (22.5<->10.5).
Although it's near impossible to tell from the photos, I suspect X and Y are going to be very similar values, only a few mm apart. Assuming everything so far is right and I've done the calculations correctly, something like this
17mm spacer or
20 mm spacer will be needed - but I can hold off until I get the TS items in hand before ordering the spacer.
The next piece is the connection from the OAG to the focuser. Assuming I keep my current stock focuser, I think I need one of these:
https://www.teleskop-express.de/shop...mm-Laenge.html? If that's not quite correct, it's still going to be something that adapts from the threaded system on the camera side to the tube of the focuser. This to me does not seem ideal.
So, I've been looking into focusers now such that I can join the OAG to the focuser via a threaded system, no ring/tubes. The MoonLite 68mm system looks interesting (especially with all the extra toys to motorise/control it
). I'll do some searching around to see if anyone has hooked up a similar system for the RC10...