Canon 350D prime focus on Celestron C8-N

[trevboyd]

Hi all

I just received a new C8-N from my lovely wife for my birthday and thought I'd have a bash at prime focus imaging last night. This might become a long post, so please bear with me!

I also have a SkyWatcher 120mm refractor, which came with a t-adaptor (I think that's the right name - it screws into the t-ring for the camera and then slots into the focusser). I've been using this successfully on my refractor. It appears to have an outer diameter of 2" (fits nicely in draw tube). The inner diameter is exactly the right size to fit the barrel from an eyepiece in (so slightly larger than 1.25"). This is shown in the pic below (attached to the t-ring on the right - old pic)

I have a 1.25" Neodymium LP filter, which I've found works well for imaging. I've screwed it into the end of an eyepiece barrel and fitted that into the t-adaptor. The t-adaptor has a little silver screww to hold it in place - no visible in the pic. This seems to work well, although it does introduce some vignetting since the light path is only 1.25" wide.

My C8-N comes with its own t-adaptor. Basically, you unscrew the eyepiece holder and that reveals a t-thread that the t-ring screws directly onto. This works brilliantly, and the Canon came to focus no problem.

The only problem with this is that there is no way to insert my filter into the light path. The new t-adaptor has a slightly larger diameter hole in it that is too big for an eyepiece barrel, and no screw to hold it in place anyway. I don't have a pic of it - meant to take one this morning. The Celestron t-adaptor looks like it has threads for a 2" filter in the end, but I haven't measured them to check the diameter.

I tried simply fitting my old t-adaptor directly into the draw tube of the C8, but the tube is slightly too wide for it. The C8-N also comes with a 2" eyepiece adaptor that fits into the draw tube. This is about 1.5" long. My old adaptor fits directly into the end of this, so I thought this would be the solution. However, with the 2" eyepiece adaptor in place, the camera won't come to focus - not enough inward travel to quite work - I would guess its maybe 10mm too far. I've seen other people on SGL mention that their SLR won't come to focus on a newt, and others suggesting that they move the mirror etc. I don't want to do anything that drastic! Sounds scary.

I think if I had a new eyepiece adaptor that was shorter, it would probably work and allow me to continue to use my old t-adaptor. Or alternatively, I could get a 2" filter and hope that fits into the Celestron adaptor. That would of course have the advantage of introducing slightly less vignetting in my images.

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  [li]Does anyone else have a similar setup, and what do you do?[/li]
  [li]Does anyone know of a low profile 2" eyepiece adaptor that might allow mine to come to focus?[/li]
  

Sorry for the long post, but thanks for getting this far!

TIA

Trev

[daz]

Trev

On top of the focuser, does the plate that holds the 1.25" and 2" adapter unscrew?

If so, there is a replacement available for this that allows the DSLR to be inserted and come to focus. I used to have one, but I cannot for the life of me tell you what its called.

SGL member anthony now has it and may be able to see if there are any identifying marks on it.

Other than that, its a low-profile focuser for you my lad!!

[trevboyd]

Hi Daz - thanks for replying!

On top of the focuser, does the plate that holds the 1.25" and 2" adapter unscrew?

If so, there is a replacement available for this that allows the DSLR to be inserted and come to focus. I used to have one, but I cannot for the life of me tell you what its called.

SGL member anthony now has it and may be able to see if there are any identifying marks on it.

Yep, the top bit does unscrew (as far as I remember - need to check tonight). I assume the replacement bit is basically like the t-adaptor I have, but a bit wider so it fits in the hole? I'll PM anthony and ask him.

Other than that, its a low-profile focuser for you my lad!!

Or just a low profile version of the 2" eyepiece adaptor that came with the scope? No need to replace the whole focuser, presumably?

Thanks!

Trev