Eyepiece projection problems

Hi

I've found out so much since joining this forum about all aspects of amateur astronomy but I'm having a few problems with eyepiece projection photography.

I have a Fuji Finepix S5500 digital camera, which has a 10x optical zoom lens that doesn't come off the camera. It has a 55mm threaded adapter ring in front. I have purchased a eyepiece adapter from Scopes and Skies that allows me to fit the camera to the scope.

When it is fitted, it is like looking down a drainpipe there is that much vignetting. I have slackened the screw on the adapter and pushed the lens as close to the eyepiece as possible which reduces vignetting. But I sometimes get a dark spot in the centre of the image which I assume is either the secondary mirror holder or the colimnation spot in the centre of the primary mirror.

Plus I find it really hard to get a decent focus with this set up.
I'm a complete newbie where is comes to F stops etc with photography so am having to start from scratch and finding it heavy going.

The front of the lens says:
1:2.8-3.1 10x Optical Zoom f=5.7-57mm

what effect will this lens have upon say an image of the moon through my 25mm eyepiece as I dont really understand this part of it all

I took some images of the moon recently and mostly they were ok, but not great and I think they were more luck than judgement. Anyone have this camera or has any advice?

Also, this camera has a video mode which are avi's, can I use this camera for planets, DSO's and with registax

thanks

Hi CJ,
You've just encountered the main reason why very few use this method with their telescopes.
One way of reducing this problem it is increase your optical zoom to the max, the side effect of this is a narrower field of view.
Use as low a power an eyepiece as you can find.
The reason for this problem is that eyepiece lenses are design for the size of the lens in your eye, when you use what is effectively a much bigger lens in your camera, the eyepiece fails to give a fully illuminated field of view.

There are very specialised eyepieces you can get for this, the only ones I know of are from scopetronics (which seem to be still in business).
www.scopetronics.com/dslradapters.htm
They are expensive and are really designed for DSLR cameras but can be made to work with a camcorder.
Have fun.

Also, this camera has a video mode which are avi's, can I use this camera for planets, DSO's and with registax

thanks

Only if you can clearly see the disk of the planet in the AVI, a tiny faint spec wont give you any detail.
I doubt its sensitive enough to see DSOs.

That's a common problem with afocal coupling - your wide range zoom lens will be a retrofocus design which doesn't couple properly to an eyepiece as the effective position of the front of the lens is in fact within the body of the lens so you can't get close enough. The best lenses for this kind of coupling are small lenses of short (3x) or even no zoom. They are of a simpler design and couple to eyepieces more effectively - even the better phone cameras can do a decent job!

Now I'm confused, are you using an eyepiece doing this or not.

Paul, I have been able to get decent moon shots by holding the camera plus its lens up to a 26mm eyepiece (afocal)

I would have thought that a short focal length eyepiece with give such a small amount of eye relief, would not a longer focal length eyepiece be easier.

I think were getting confused with terminology here.
afocal = scope + eyepiece + camera lens + camera body
eyepiece projection = scope + eyepiece + camera body
prime focus = scope + camera body (just to be complete about it).


Have a look at this link for eyepiece projection
www.stargazing.net/Astroman/Craters.html

and this for afocal
www.dur.ac.uk/nigel.metcalfe/astro/afocal.html

Hi

I guess this is the problem with being a newbie, not understanding all the terminology and getting it mixed up. I'd never heard of afocal photography, but I guess that's what I'm trying to achieve. i.e Telescope + eyepiece + lens/camera

I have some new eyepieces coming this week so will try with those and the new moon in the next week or so. I have another digital camera 2megapixel that has no zoom, I might try that too.

Another question, with regard to prime focus or webcam photography, how do you get such detail and image size if no eyepiece is used, even when a barlow is attached, surely that is only 2x magnification? I've held my webcam up to the 2x barlow and all it sees are the secondary mirror arms plus a series of rings, 'scuse me for being thick!

cheers