Focusing using a flip mirror.

[MarvinZ]

Progress is slow on my road to Video Astronomy. I have a Phil Dyer camera and have now purchased a flip mirror. The weather and work mean I have had little time to try the setup out. The other night I was able to get out for a very short time before the clouds came to assist me in my setup (they mean well), I found that when I had my eyepiece in focus the camera was not all that far out, but when I got the camera in focus I was not able to get the eyepiece back in focus as it wanted the adjuster on the diagonal turning in and there was no adjustment left.

This is the set up

Celestron Nexstar 127 SLT

Skywatcher 1.25" Flip Mirror System (http://www.rothervalleyoptics.co.uk/skywatcher-125-flip-mirror-system.html)

On Top of Flip Mirror the eyepiece

At rear of flip mirror adaptor to accept cameras with 1.25" nosepieces then Phill Dyer Camera.(The camera body is up against the adapter)

Any advice on weather this setup is correct or not and how to achieve focus on both eyepiece and camera would be appreciated.

Thanks

[Oddsocks]

When the camera is in focus but the eyepiece is out of focus, and moving the eyepiece towards the body of the flip mirror brings it almost to focus but not quite reaching focus then you need a spacer on the camera mount side to take the camera chip further away from the flip mirror body.

(And, of course, the reverse may be true: When the camera is in focus but the eyepiece is out of focus, and moving the eyepiece away from the body of the flip mirror brings it almost to focus but not quite reaching focus then you need a spacer on the body of the eyepiece  to take the eyepiece further away from the flip mirror body)

I had a quick look on the Phil Dyer website but as you didn't specify your camera I couldn't tell if the camera you have is a C-mount or a T2 but either way you will need to fit a spacer ring of some sort between the body of the camera and the camera nosepiece or between the camera nosepiece and the body of the flip mirror.

If you are only talking about a few mm extra distance needed then one option is to fit a par-focalising ring around the nose piece of the camera, this is just a washer cut to fit around the nosepiece to act as a spacer between the camera and the flip mirror, it works by preventing the camera nosepiece sliding in all the way to the body of the flip mirror, effectively moving the camera chip a few mm further back.

A popular method of making par-focalising rings was to cut a slice out of the body of an old plastic 35mm film canister to make the thickness of ring required and then splitting the ring so that it slips over the camera nosepiece, but any material that can be cut easily will do, even waxed cardboard or plastic from a fruit juice container can be cut to size and shape with a pair of scissors and simply stack a few together to make up the required thickness.

If you wanted, 365 Astronomy have a ready made option but a piece of cut up plastic tube or cardboard works just as well and costs nothing:

http://www.365astronomy.com/Parfocal-Rings-for-1.25-inch-Eyepieces-Set-of-4.html

If you do use a par-focalising ring on the camera nosepiece you just need to make sure you don't bring the nosepiece so far out of the body of the flip mirror that the clamp screw no longer grips the camera securely.

One other option, though a bit hit-and-miss is to leave the camera where it is and use a lower power eyepiece in combination with a low power Barlow lens, this has the effect of moving the focus point for the eyepiece further out from the body of the flip mirror, it is not often though that the exact combination of Barlow and eyepiece can be found that has just the right amount of focal point shift to still be in range of the flip mirror focus adjuster.

William

[Lonestar70]

Hi Peter,

The setup you describe sounds correct as far as the location of the eyepiece and the camera on the flip miror unit is concerned.

Determine which item requires the focuser closest to fully inward and focus that item using the scopes focuser... then lock the focuser.

The other item then needs to be made Parfocal with the first one and this will mean that the second item needs to be withrawn from the flip mirror unit a little at a time until it is focused... if the distance is not more than a few millimeters then a parfocalising ring can be fitted to the 11/4" nosepiece barrel to ensure that it always is inserted the correct amount.

If the distance required is more than a few millimeters then a short adaptor tube will need to be fitted in order that you have sufficient barrel length left to lock the item in place.

Parfocalising rings and short adaptor tubes can be obtained from FLO or most other good astro retailers.

It is much the same process that is required when setting up a camera and an off-axis guider... both items need to be parfocal.

I hope this helps.

Best regards and good luck.

Sandy.

[shirva]

use a 6mm eye piece in your scope and try and focus on furthest away object you can find,,then try the camera for focus..mark your focusser tube with a pencil as a ref..i don't believe a flip is going to work sorry.

[MarvinZ]

Thanks for the input will try things out as mentioned as soon as I get the chance (long weekend off this weekend so maybe a chance for some clear sky) I have it in my head that William and Sandy may have the solution I am looking for, fingers crossed.

 

Thanks

p.s the camera is the PD COLOUR VIDEO CAMERA http://www.astrophoto.co.uk/cameras.htm

[johnno]

Peter, your flip mirror is similar to mine and I had to use a parfocal ring also as suggested above .