Imaging and the Coronado

[mickw]

I've been playing with the Coronado visually on the 2 clear days I've had time - brilliant

For over 2 hours now I've been trying to focus a DBK camera with it.

Is there a method to get focus with a camera on the Coronado ?

[Mike]

Are you putting the camera directly into the eyepiece?

[MarkS]

Mick,

Can you use a white sheet instead of the camera - the projected image will show you where the focal plane is.  If the cannot get camera CCD in the same palne then you won't achieve focus.  (Remember to adjust focus knob as well!)

Mark

[Mac]

If you focus the coronardo whilst you are looking through it, the focal plane is about 1cm above the eyepiece
as this is where your eye is. (obvious)

you are using this as eyepiece projection. i.e the eyepiece is projecting the image into your eye.

you need to get the front of your lens to that same point (give or take)

If you remove the eyepiece the the focal plane will be somewhere totally different.

when i used my small canon with it, i had a ring that fitted around the eyepiece and allowed the camer to be adjusted to fit

Mac.

[mickw]

No eyepiece, straight into the diagonal which I assume has the etalon thing in it.

OK thanks for all that, I'll have to give it a try again tomorrow - clouds and tall buildings stop play

[Mike]

Use an extension tube if you have one.

[RobertM]

From memory you will need about 2-3" of extension tube if not imaging afocally with an eyepiece.

Robert

[Fay]

Should you be using a diagonal?

Are you using IC capture prog that came with the camera?

[mickw]

I have an extension tube somewhere, time to go a hunting

Fay I think I need the diagonal because it looks like there is a filter built in and I wouldn't like to burn a hole in the back of my head.

Tomorrow is another day

[MarkS]

If you focus the coronardo whilst you are looking through it, the focal plane is about 1cm above the eyepiece
as this is where your eye is. (obvious)

I'm not quite sure what you mean by the above.  With the eyepiece in, there is no focal plane above the eyepiece since no real image is being formed by the eyepiece.  The true focal plane is possibly somewhere within the eyepiece tube itself (coinciding with the focal lengh of the eyepiece), so the image appears at infinity, for the observer.  

For instance, look at the final diagram on this page http://www.antonine-education.co.uk/Physics_A2/options/Module_5A/Topic_1/topic_1_lenses_and__refracting_t.htm

To perform imaging, you must ensure that the CCD is positioned at the focal plane.  As far as I can see, an extension tube will make it even less likely to achieve focus.

Mark

[mickw]

Today, we try again

Fay the blocking filter is mounted in the diagonal so got no option really (I think)

Mac and Mark, I understand the logic and know that the focal plane (length) will be constant.
So if you get focus with a 20mm eyepiece, you would need to wind the focuser out for a 5mm eyepiece and in for a 30mm eyepiece to move the optics back to the focal plane.
So if the optics of a 5mm eyepiece are in the same position as the ccd of a camera, you should be able to focus using the eyepiece then simply replace it with the camera.

Isn't maths fun 

[MarkS]

So if you get focus with a 20mm eyepiece, you would need to wind the focuser out for a 5mm eyepiece and in for a 30mm eyepiece to move the optics back to the focal plane.

In principle yes (though you would wind in for a 5mm eyepiece and out for a 30mm).  In practice though, manufacturers tend to make the eyepiece itself shorter or longer according to its focal length so very little (if any) focuser adjustment is required when swapping eyepieces.

[Rocket Pooch]

Mick,

I used that scope when I had a DMK (and I used my web cam with it).  All I did was to put the camera with IR filter on the nose piece into the diagonal and the reduce the exposure quite a bit, or leave it on auto exposure, the focus on the edge of the sun, its really obvious where your about there.  Then you can fiddle with the exposure and the tuner to get a good image.

Chris

[mickw]

Thanks Chris, I think I've got it sussed now.

I was originally moving the draw tube a bit, then trying to focus, then repeating it loads of times until I got fed up.  I should have done the obvious and rough focus with the draw tube then use the focuser 

Managed to get 3 short sequences between the clouds but I think they were under/overexposed - prominences partly buried in a red halo with spots and granulation a bit washed out.

I'm getting there but need less clouds 

Next time I get a chance I'm also going to try the Canon.