Eyepiece projection equipment recommendation

[PESKYWAABBIT]

Hi guys, we at Athenaeum Astronomy Association are running our 3rd public star party in Nowton park at the end of march and I've been thinking it may be worth getting my 8" refelctor hooked up to a webcam. 

I would like to try eyepiece projection(for the first time) as we can showcase what we can see on a nearby laptop for the younger ones.

The only issue I need a recommendation from someone who has done this before. I have been given by a nice fella a Logitech webcam with a 1.25" nose piece. I do have one eyepiece projection kit but I found that my 1.25" eyepieces are too wide in the body and so don't slip down the tube. So I need recommendations if possible from you guys as to what to get in short notice. I hope that makes sense, cheers.

 

[michael8554]

Unless you're after huge magnification, I would try various power Barlows, unless Barlows give you focus range problems on the reflector.

Michael

[vlaiv]

Not sure if that is going to be the best combination - 8" F/5 scope, webcam and eyepiece.

Webcam has very small sensor and small pixels. So you would need long FL eyepiece and also place web cam close to field lens. Here is calculator to help you out:

http://www.wilmslowastro.com/software/formulae.htm#EPP

Something like 32mm plossl placed 40-50mm away from field lens seems like a good idea, but be aware, you might have trouble reaching focus this way. If you use shorter FL eyepiece and/or place webcam sensor further away from field lens - you will get magnification factor bigger than 1 - and you certainly don't want to do that with such a small sensor and small pixels - it will have same effect as using barlow and prime focus - so things will be really "zoomed in".

Maybe better idea would be to use afocal approach if you can find webcam that can be manually focused at infinity.

Other option is to get x0.5 reducer and use that and webcam at prime focus.

 

 

[Louis D]

16 hours ago, vlaiv said:

Maybe better idea would be to use afocal approach if you can find webcam that can be manually focused at infinity.

For what the OP is trying to do, afocal projection is the way to go.  Most eyepieces aside from the Pentax XP range don't project a flat image plane, so the edges will be blurry.  A small imaging sensor might negate some of that, but then you're viewing a massively cropped image.

Even a phone in live view would show the view through the eyepiece using its camera pointed into the eyepiece eye lens.  Adjusting gain is the main issue to overcome.  It will want to make the black background 18% gray, blowing out the stars/planets/etc.  There are multiple phone brackets designed to hold the phone in alignment with the eyepiece.