Should I get a 5x Barlow for imaging?

[Stonius (Markus)]

Okay, so I'm a big fan of seeing things with my own eyes, but that doesn't stop me from attempting to capture some brighter objects with my 8" f/6 dob (see below for my latest attempt).

I'm told that one needs a tracking scope to get the really stunning images seen in these forums. Fair enough. What I'm not sure is why you can't just capture the same total number of frames with a non-tracking scope, as the object drifts through the field of view?

Is it because;

1) EP projection has issues with focal plane curvature and other optical problems because *suprise* eyepieces are made for eyes, not cameras. Even so, shouldn't I be able to negate 80% of those issues by only using frames where the planet is near the centre of the field, even if it requires joining several passes together?

2) Even with a 5x Barlow, Jupiter is still only ever going to be 28 pixels edge to edge in my 5DMkii. Maybe 'proper people' have scopes with higher f/ ratios? Or smaller sensor sizes?

3) Is it that the movement of the object through the frame is enough to create motion blur on each frame that obliterates all the finer details.

If the problem is the first or second issue, I can buy a 5x barlow and see how I go, but I won't use it for visual observing, so it would be a waste of money if it won't make any difference.

If the problem is the motion blur, maybe one day I'll have a more sensitive camera, but at least I'll know that there's not much I can improve on till that day.

So, would a Barlow help?

[raymo]

You have one huge problem if you are using your listed 8" f/6 scope.
It has a focal length of 1200mm ; using a 5x barlow it becomes 6000mm
[f/30]. With a system that photographically slow you'd probably be forced
to use a very high ISO setting, which would result in very noisy images.
It's much easier to use a cheap webcam with a 2x barlow, which will
give a decent size image. Take about 1500-2000 frames, and stack them in Registax[freeware].
raymo

[Merlin66 (Ken)]

The rule of thumb for planetary/lunar/solar imaging is that the optimum focal ratio would be x5 the size of the camera pixel (In micron) I.e. For a 5 micron pixel camera, f25 would be the target.

[Stonius (Markus)]

Originally Posted by raymo

It's much easier to use a cheap webcam with a 2x barlow, which will
give a decent size image. Take about 1500-2000 frames, and stack them in Registax

So does the webcam work where the 5D doesn't because the webcam sensor (and I assume the individual pixels) are smaller?

Sounds like the cheapie webcam might be the way to go so I can satisfy my desire to have a bit of a play with astrophotography, without jumping in at the deep end.

...aaaand queue the endless tabs of more research being done. Thanks for the suggestions.

Markus

[raymo]

I've no idea what size the 5Ds sensor is, but I suspect that you are right.
A $15 webcam will produce stunning images once you are familiar with Registax.
raymo

[Stonius (Markus)]

Apparently it's 6.4uM. But the sensor as a whole is full frame - 24 x 36mm. Webcams have much smaller sensors, I think so the pictures produced there will be correspondingly larger, I suppose.

Edit; Ugh, I phrased that really poorly. A smaller sensor placed at the focal plane will capture a smaller portion of the image formed there, thus the captured image would look larger.

[Anth10 (Anthony M)]

Alternatively you could use a camera adaptor with a reasonable quality compact camera and use the optical zoom to enlargen the image. I did when i used to run my 10'newt on a dob mount. I found I could get 15-20sec passes of jupiter through the field of view. I would then use pipp to stitch say three movie grabs to create a decent data set. This certainly works. I ran a 7.5mm tak eyepiece for 170 Mag for this image I took some time ago.

[raymo]

That's quite nice Anth, but a webcam will produce sharper more detailed results than that.
raymo

[Anth10 (Anthony M)]

Fair call Raymo, less fiddly too.