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Posts Made By: Alex McConahay

October 26, 2006 03:46 PM Forum: Telescope Making

Mirror blank made from laminated glass?

Posted By Alex McConahay
Have you looked up BVC (Black Vitrified Ceramic??????)--which sounds like what you are proposing.

Alex

October 26, 2006 03:46 PM Forum: Telescope Making

Mirror blank made from laminated glass?

Posted By Alex McConahay
Have you looked up BVC (Black Vitrified Ceramic??????)--which sounds like what you are proposing.

Alex

October 27, 2006 07:30 PM Forum: Mounts

8 Inch Reflector on a tracking mount?

Posted By Alex McConahay
There's a thread on some Forum around here where Rob is asking whether he can mount a 12.5 inch newt on a GEM. Find it and follow. SOme of the same issues will come up. The most important is that the mirror cell design must be able to accommodate the movement of the mount. If you are talking German Equatorial, than some mirror cell designs would be unacceptable.

It sounds like you have a tube with no mount at all, not even a Dob. If so, you might want to build yourself a rocker box and bearings, and just use it as a non-tracking scipe while you figure out a tracking platform for it.

Any GEM you get would have to be pretty hefty. Not only is an eight inch newt tube heavier than most of these were designed to handle, but it is also larger, thus creating more wind load and such.

By the way, I use a 10 inch Newt on my GEm regularly, so there is no reason it cannot be done. You just have to engineer everything right.

Good luck.

Alex

October 29, 2006 02:01 PM Forum: Landscape Photography

Sunrise from Borrego Springs CA

Posted By Alex McConahay
Jerry,

You were at Nightfall when you took this? Were you at the Palm Canyon or in the state park?

Alex

October 29, 2006 06:15 PM Forum: Equipment Talk

Recommendations for a good-cheap upgrade

Posted By Alex McConahay
Mike,

The goto model in and of itself offers no great advantage in beginning astrophotography over a scope which has a handpaddle that can adjust tracking in RA and Dec. (In advanced astrophotography there are advantages to goto.) The essential things would be to have a good equatorial wedge, a sturdy tripod, and a handpaddle that can track. Add a guidescope or off axis guider, a camera bracket or adapter, and you are ready to begin.

However, there is a lot more to astrophotography than just the bare essentials. To take quality deep space astrophotographs you will eventually need a very high quality mount. And you will find that starting with a small refractor and digital slr is a lot easier than with an SCT, with its high magnification, weight, and so forth.

My advice, get a piggyback bracket and start with what you have. See what you get.

Alex

October 31, 2006 10:33 PM Forum: Digital SLR AstroPhotography

Canon 20D Backfocus?

Posted By Alex McConahay
The 20D is an EOS camera. It uses EOS lenses, just as a film EOS uses. Therefore it is exactly the same backfocus as the film EOS cameras.

When you say how much "backfocus" does one need, are you asking how far from the lens mount to the ccd chip?

Alex

November 8, 2006 04:39 PM Forum: TeleVue

Used Pronto

Posted By Alex McConahay
It somewhat depends on how good a price you pay for the Pronto. Once upon a time, the Pronto was the best you could get for the dollar. However, since then, a whole lot of people have started putting out APO refractors that beat the Pronto in performance and price. You may want to look into these.

Alex

November 9, 2006 03:29 PM Forum: Beginning Astronomy?

RA/Dec to alt/az & catalogs

Posted By Alex McConahay
Mark,

regarding cnverting the RA/DEC coordinates to ALT/AZ--

Instead of converting, why not just use a planetarium program like the Sky or Cartes Du Ciel to tell you where an object is. I mean, if you are carting around a computer to help you with conversions, you might as well have a planetarium program in it.

Alex

November 14, 2006 02:30 PM Forum: CCD Imaging and Processing/Deep Sky

Need Some "Steering"

Posted By Alex McConahay
five minutes at ISO 800 is my standard at a dark sky site. Then I collect as many of those as I reasonably can. At least twelve of them.

However, M42 presents a peculiar challenge. You need to have some short exposures (as short as thirty seconds) to get good exposure on the core. But thirty seconds will get you little on the outer fringes. So, you layer that short exposure in with the longer exposures to get the whole thing.

In general, take a picture at whatever setting. Then look at the histogram in the back of the camera. Unless you are trying to get lots of color in the stars, make sure that the long extension of the histogram gets to the right edge of the graph. Try also to have the big hump at the bottom at about one quarter of the way up (from the left) the graph, with just a little gap at the bottom (left) of the graph.

Alex

November 14, 2006 09:17 PM Forum: Equipment Talk

Anyone know how use a meade LPI as an autoguider w

Posted By Alex McConahay
Try the folks at Shoestring Astronomy. Ask them.

Alex

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