unable to focus 6"se

[red dwalf]

Hi everyone,

can anyone help me with my focus problem ? last night i tried to image Jupiter with my Celestron 6" se 1500 focal length and using a Philips 900nc webcam and a 2 x barlow lens but was unable to get a focused view, tried it without the barlow and the same thing, just a blur, seemed to be to much magnification, i don`t understand what i`m doing wrong as i thought that more focal length using the barlow was needed to get better images and the webcam should be around the same as a 6 mm eyepiece, 3 when barlowed, tired it on the Moon and the same thing, could not get a focused view, any help please.

Rob

[brianb]

Seeing .... you need exceptionally steady air to be able to focus Jupiter at 3 metres focal length. I find it's best to focus on one of the satellites, making it as small as possible, though last night Callisto's shadow helped a lot.

Also check the collimation. SCTs do need to be accurately collimated in order to get decent images of small low contrast detail such as Jupiter abounds in.

To assist focusing with a webcam, turn the gain full up, reduce the gamma to about 50% (this increases the contrast) & adjust exposure - then re-adjust gain, gamma & exposure to suit after completing focusing.

[red dwalf]

thanks Brian,

tried to do a daylight collmination yesterday but i do not think that i`m anyway near, this was my first time trying with the SCT and i`m not used to it.

[Psychobilly]

Try using the Camera in daylight ..

Was the camera and/or barlow straight in the back of the SCT or in a diagonal... I would normally expect an SCT to have enough focus travel to allow you to use the camera directly in the SCT viewing port or in a diagonal - I know I can use either setup with my CPC800... worth a try...

Like all these things get them up and running in daylight as its saves frustration under what have been rare clear skies this summer...

Peter...

[red dwalf]

I tried putting the webcam stright into the back of the scope and tried the diagonal, but no luck, I thought that the more you increase the focal length the better the image, is this wrong ? and can anyone help with other ways of coillminating an SCT scope other than daylight from the front.

much help needed thanks

Rob

[Psychobilly]

Hmmm...

When you tried last night did you ever get to a point where the diameter of the object decrease to a minimum and then expanded again... in other words you went through a "focal" point... even is the scope was out of collimation you should have seen the Variation in the size of the image object...

Whats it doing on daylight terrestrial targets..?

You might also need to think about a UV/IR cut filter at some point in the future...

I find the easiest way to collimate an SCT is to use Metaguide and an Artificial Star...

Peter..

[red dwalf]

Thanks Peter,

I have bought a uv/ir filter 2 days ago for this very purpose and was looking forward to getting something to image and was so disheartened when I got nothing,

I have not used the webcam on daylight targets as of yet but will try, I have used it normally with and eyepiece and it wasn`t a bad view but I thought it might be a little blured but put it down to heat thermals,

also when trying to focus last night I did think that I went through a focal point, especially when I tried it on the Moon, but was very blured and no detail at all, all very disheartening at the moment as I was really looking forward to getting somewhere.

cheers Rob

[Merlin66]

Use say a 10mm eyepiece to focus on something during the day; without touching the focuser, remove the eyepiece and insert the webcam... slide it in and out until you get good focus, then mark the nosepiece with a pencil line against the focuser.

When you focus the same eyepiece at night, you should be able to remove it and re-insert the webacm to the mark and be very close to focus.

Hope this helps.

[Psychobilly]

Once you have the pencil mark you can also put a couple of wrap of insulating tape above the line to make it easier to put the cam in in the dark... or if you have some old 35mm film canisters hanging around you can make a ring from them...

Peter...

[brianb]

Once you have the pencil mark you can also put a couple of wrap of insulating tape above the line to make it easier to put the cam in in the dark... or if you have some old 35mm film canisters hanging around you can make a ring from them...

.... or even invest in a set of parfocalising rings!

[Psychobilly]

Indeed but the tape you can do straight away whilst waiting for the rings to turn up....