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Old Jun 5, 2008, 7:01 AM   #1
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Hi folks,

My background:

I'm the proud owner of the most gadgety P&S camera Canon makes; The TX-1. It's a little 7 MP pocket camera with a super 10x optical zoom lens.
I'm a gadgeteer myself, and I've been messing around coupling cheap digital cameras to cheap (and often home made) telescopes and microscopes for about 7 years now.
I finally bought a decent scope to mate my decent P&S camera to. I bought a used (but in great condition) Baucsh & Lomb "Discoverer". I thought it might be of better quality than the new Discoverer model now made by Bushnell, though I found nothing on the web that compared the two. I figured at the very least, it couldn't be worse.

It's great. Just as advertised. Sort of.
It goes from 15x-60x, which makes sighting and then honing in on the subject super easy. The objective is 60mm, so at high zoom, it's pretty dark, but I'll work with it.
I put my 80mm Canon C-8 1.4 tele-converter on the end, raising the zoom to 24x-84x.

But there is terrible blue fringing while looking at high contrast (backlit) subjects. REALLY terrible. (With or without the Canon tele-converter)
Is this true "chromatic aberration"? My web-research tells me that this is the normal result of light refracted by glass and the air between the lenses alternately.

My questions:
  • Is what I'm experiencing "chromatic aberration"?[/*]
  • Is there a filter for this, and if so, what is it called? (An hour worth of searching on Ebay was unhelpful.)[/*]
  • The Canon C-8 tele-converter I have attached has an objective lens size of 80mm, and a rear lens size of 60mm, which is the same size as the telescope objective lens. Will this make a difference in NOT lowering the effective aperture of the overall combination, or is the coupling of any two lens systems always doomed to a lowered brightness?[/*]
Thank you-thank you!
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Old Jun 12, 2008, 6:26 AM   #2
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120 views and no answer?:?
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Old Jun 19, 2008, 10:58 PM   #3
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Sorry you are having problems with digiscoping.

About the scope:
No, you should not have blue fringing from the scope, it is multi-coated. Be sure the lenses are clean and there is no internal fog. If you clean lenses use good technique and camera type lens cleaner. Never use a Micro-fiber cloth for anything but shining your shoes. It is said that cleaning should be infrequent. You do a bit of damage each time a lens is cleaned. So, keep them clean. Do you see the blue fringing when you look through the scope without the camera? I guess the eye piece of the scope is attached and cannot be removed, so you have no option there.

I my recent post about Digiscoping I said my scope lens has a worth of about $75, but I did not mention that I only paid $10 for it at Surplus Shed. It is not coated and has some age marks from the 1970s, but it works quite well.

Very little of the light that goes into a scope ends up as part of the image. It bounces off the sides and this tends to create fog. Try adding a large black poster board shield with a rubber band. Wrap around the end of the scope and let it stick out about 6 inches. It should help a lot and you can replace it with a black metal one.

You would have some advantages with a fabricated scope, such as adding light baffles all over the place, selecting an eyepiece known to be good for digiscoping, such as the Orion 20mm Expanse, and perhaps most important, using a 2 inch focuser.


The Camera:
The TX-1 is an unknown (to me) for digiscoping. I checked the sample image on Steve's Reviews and it has fair sharpness.

So, that is about all I can think of now. Get back to me if you like. Gene9


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