Help!! 200pds!

[pringlepowell]

Anyone think of a reason why my skywatcher 200pds, coupled to my Sony Nex 3 camera with a tailor made t-minus adapter still appears to be too far from the secondary mirror to focus properly? All I get, even with the focuser in fully is a view of the primary mirror!

[TheThing]

I always get this round the wrong way, but I'm sure it is not enough in focus. You either need a lower profile focusser or move the primary towards the secondary.

TheThing

[Cornelius Varley]

Did you watch the video ?. The NEX 3 appears to be a system compact camera which have much slimmer bodies than DSLRs so I can't think why you are unable to get the sensor close enough to the the focal plain. Can you post a picture showing the setup ?

Peter

[Cornelius Varley]

I always get this round the wrong way, but I'm sure it is not enough in focus. You either need a lower profile focusser or move the primary towards the secondary.

TheThing

The DS versions of the Skywatcher Explorers are designed to allow a camera to come into focus (they shortened the tube effectively moving the primary closer to the secondary)

Peter

[pringlepowell]

Hi

I bought a t-minus mount from the U.S which is made specifically for the Nex 3. The sensor is right in close to the end of the focusing tube as shown in the video, but still all I see is the primary mirror in the screen. I've written to the manufacturer of the mount who suggested using a Barlow lens, but it seems annoying to be paying £60 for a 2 inch barlow if there's another solution. Given the DS is designed for astrophotography I'm a little suprised.

[Cornelius Varley]

Does the t adapter look like this one http://www.telescopeadapters.com/ which appears to have a built in 2" nosepiece.

Peter

[pringlepowell]

It's this one - so it fits the e-mount, plus goes all the way into the focus tube of the DS.

[Cornelius Varley]

From my understanding of the description the barrel is a 2" nosepiece which would fit into a normal 2" focuser eyepiece holder. The Skywatcher focuser is designed to allow a normal t adapter to be screwed directly to the flange part of the eyepiece adapter (the flange has a t thread to allow this). This allows the camera to be positioned close enough to the primary mirror to allow it to reach focus. If you try to use a nosepiece and your t adapter the camera will be too far away from the focal plane. The type of t adapter you need is one of these http://www.amazon.co.uk/Kiwifotos-Lens-Mount-Adapter-microscopes/dp/B0043X8Z20/ref=sr_1_1?ie=UTF8&qid=1345706121&sr=8-1. This type is designed to attach a t threaded camera lens to your camera and keep the correct distance between the sensor and the rear or the camera lens, which is what you are tyring to achieve.

Peter

[pringlepowell]

Interesting. I did look at one of these but it looked too big. The one I bought goes so far into the barrel these is nothing visible left except the ridged part (grip). Given it's only £11 I think I'll try it instead of investing in another Barlow.

Thanks, I'll let you know the results.

[Cornelius Varley]

Let me know how you get on.

Peter

[pringlepowell]

Right. The above item finally arrived and unless I'm very stupid, it does not fit into the focuser barrel. The diameter is too big, so another adapter to go on eBay I'm afraid.

[RikM]

Canon EOS backfocus distance is about 44mm, the Nex-3 looks to be about 18mm so I would have thought you'd be too close rather than too far out still. Does the 200PDS come with a 2" EP adaptor? Try adding that as an extension between the focuser and your camera nosepiece and see if that makes it better or worse.

[pringlepowell]

I'll give it a go. The manufacturer of the custom piece says a barlow might be the way forward, which suggests the sensor is too far away! I also thought that might be why all I see is a silouette of the secondary mirror. This is what I see:

If I focus in as far as I can go this becomes a very small dot.