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Missing something????

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Have been out tonight, really to play with my camera more than anything, but decided to try attaching it to my scope (114mm newt) to see what I could get.

I have a Canon EOS 500n, which I T-Mounted to the focusser with a short adaptor (is there a technical name for this??).

I could not focus, so I switched to a longer adaptor. Still no good, so used both, and then finally a 40mm with both adaptors and still I could not focus.

I wanted a wide-field shot, hence the 40mm, but just couldn't get it.

Have I missed something, or do I need a really long adaptor :?:


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My guess is, you're too far behind focus, rather than in front of focus. Newts tend to not have enough back focus to achieve it with a camera.

Most people call the configuration "prime focus", when it's actually Newtonian focus, but quibbles are just that. If there's an eyepiece in between the scope and the camera, it's called "eyepiece projection" and is the method I use mostly to shoot the Sun.

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Yeah, I figured that I could not pull the focusser back far enough to get the focus, but wasn't aware of the limitation of newts. Ah well, I'll see what I can get with the normal lenses and wait for my SC1 mod to my Toucam.


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I've just found this while starting to use the Toucam with my 150mm f5 Explorer. Luckly it has a SLR direct connect thread, the adaptor I bought came with SLR thread, so I unscrew the eyepiece holder from the focuser & screw on the ToUcam. This proves to be fine... no worries with focus. If I leave the eyepiece holder screwed into the focuser.. I can't focus.

So I agree with Astroman, the newtonian seems to have a 'behind focus' problem. :)

Hope that makes sense?.... does your 114 new offer direct connection for SLR?.


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Hi Rob

Just been and looked at the focusser and yes, I can unscrew the eyepiece holder. So this should mean I can attach the SLR adaptor directly to the focusser......

OK, will play with this and see what happens.

Thanks matey :)


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Most Newts now come with a low profile focuser - this helps a little but there are a few other things that you can do.

Gaz mentioned removing the lense of a barlow and using the remaining partas an extension tube, try ignorning the extension tube part and using the lens screwed in in front of the camera - this has the disadvantage of increasing the F/Ratio of the setup which increases exposure time lowers the FOV BUT has the advantage of moving the focus point outwards away from the focuser. If you using the a 1.25" barlow then you may well end up with some vignetting.

As you focus inwards/outwards you should see the out of focus stars becomming either smaller or larger. This will tell you which way you need to go and also roughly how far you need to go to get the stars in focus. You may find that you can get pretty close without any modification.

I found that once I bought my new crayford focuser the 300D wouldn't reach focus - I was about 3mm away from the focus point with the focuser fully "In", so I had no choice but to move the main mirror up the tube by about 4mm. I was lucky, I managed to do that with the collimation screws...

So there are a few things that you can do.

1. Buy a low profile focuser (if you haven't already got one)

2. Use a barlow (lens part only) which will move the focus point out.

3. Move the primary mirror up the scope - if it's more than a few mm then other things need to be considered before doing it.

4. You could get something like a coma corrector from TS in germany - I found out the other day that this corrector helps by moving the focus position out and sharpens the stars :)


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OK, I played with the focusser last night and nope - it ain't an SLR connection :)

So, I will wait for my new scope (the Skywatcher 200) and try again, as that does support direct SLR.

Thanks for all your input guys, as soon as I have this figured out and an image to post, I will do!!


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