Posts Made By: Alex McConahay

You should not loosen all three screws and adjust by hand.

You should slightly loosen one screw as you tighten (slightly) the other two.

All screws should remain fairly tight through the whole process.

This will give very precise adjustments.

Alex

Considering how many of us use Kellners for reticle eyepeices, I am not surprised.

What we use reticle eyepeices is not viewing, but finding and guiding. The object of interest is, by definition, in the center of the field, where nearly all eyepieces will give a pretty sharp image. So, I don't see much need for quality to the edges.

I suppose it would be nicer to have the extra field of view, but not worth the Televue prices.

Alex


Alex

Nobody has mentioned yet--the thermal stability of the material. It does not change much when the temperature changes.

Alex

Google DSLR Focus and look at their website.
And then try Images Plus by Mike Unsold.

It is good software. There are others even more powerful, but more expensive.

Alex

For about $300-400 you could probably find an LXD-55 goto. (Actually, you could get by with some of the department store goto's.--Just take the telescope off and mount your camera instead.)

Make a bracket to hold your camera, and off you go.

And how on earth does one use an electrical tripod for birding?

Alex

I have not looked into it yet, but I would suggest skipping Hawaii. Any place you are on the mainland, you can be somewhere else 300 miles away, in a completely different weather pattern, within five hours. In Hawaii this may or may not be true.

Otherwise--you are welcome to try southern California. It is often clear here that time of the year. And if you have never seen Mt. Wilson and Palomar, you should add this to your list.

Alex

Karl,

Here's my answer, and I am willing to be corrected by others:

A "Full Frame" digital chip means it is as big as a 35 mm piece of film (36x24 mm or so). The 20D is not that big (22.5 x 15). SO, the 20 D only senses the middle area of what the lens is putting out.

However, DSLR sellers have decided to turn this into some kind of an advantage--Your "100 mm lens now acts as if it were a 160 mm lens." In fact what is happening is that the camera is throwing away all the light that comes in from the lens but is beyond the central portion where the chip resides.

With the 5D's FULL frame sensor, does that mean that at any given magnification the image recorded by the sensor will be wider field ( 1:1 vs 1.5 or 1.6:1 on non full frame DSLRs ).. or will it be the same field with just more resolution?

The shortest answer is--take a 35mm negative or slide, and cut out the central 22.5x15 mm. That is the picture you now have. Throw the rest away. If you print out that central portion you have left--at the same magnification as you printed the original, and it will be smaller. Blow it up to the same size as you printed your whole frame, and it will be an enlargement of the central portion--with the rest thrown away. (Yes, then your full frame is getting a wider field.)

The problem is with your question--there is no such thing as "for any given magnification." Let us instead say--for any given focal length. We need to make this distinction because the final magnification is determined by how you view the image. If you take an image that is 43m across the diagonal (the diagonal of a 35 mm negative)on an 8x12 piece of paper you will get one magnification. But if you take only the central 27 mm cross section and use that to fill the whole 8x12 piece of paper, then you will get a bigger magnification (by that famous factor of 1.6).

But--and this is the important factor--you have not changed the native "magnification" of the focal length. You have just thrown out some light that was on either side of the chip, and spread what you got in the center over the whole piece of paper.

So--has the resolution gone up? That depends on the size of the pixels. If the two chips have the same size pixels, and you are using the same length lens, then the number of arc seconds you spread over each pixel will remain the same. And that is what determines resolution. (But note that if you plan to make a "print" of the image, you will not have as many pixels to work with if you have kept the pixel size the same.)

But in order to make the chip larger, you must either increase the number of pixels or the size of each pixel (or both!). If you have increased the number of pixels (and kept the size the same), the resolution remains the same. If you have kept the number of pixels the same, and merely increased the size of them, then your native resolution has actually decreased. You are getting more arc seconds onto each pixel.

How's this for an answer.

And as for vignetting, etc. Since that generally shows up around the edges of the frame, it is largely ignored by the smaller 20D chip--it is in the area that the chip cannot see. So it is not as big a problem. But that does not mean it is non-existent.

Alex

Why would Iran invade Iraq?

It would not be an invasion if there were merely sending some (maybe 500,000) peacekeeping police at the request of the newly elected Shiite government.

I hear religion runs deep there.

Alex

Yes, everything must now be seen as either "with me" or "against me." And "against" must be ridiculed and demeaned.

Do you remember once upon time, at least before Newt, when politics was "half a loaf"? One had to be a diplomat, and work at things, and listen some to the other guy, and learn how to compromise to get most of what one wanted.

Whatever happened to those days?

Alex

>>What's the basic difference between using a CCD camera versus a digital camera such as the Canon EOS 20Da?

The CCD has cooling, and probably a better chip in the first place. Therefore, it has a higher top end. However, it is usually black and white, whereas Canon is single shot color. On the other hand, you have a lot more control over the color in a CCD, probably. In short--A Canon will get a very good picture, but a CCD will get even better.

Of course, the DSLR has a much easier learning curve, so you will be getting that picture sooner than with a dedicated CCD.

>>Overall, if I spend that much for a camera, I'd like to use it for other things as well. Does the CCD take better shots because of the cooling? Or, are there other differences?

Yes, the cooling is a big deal, but there are other differences, also. Resolution is probably better in a CCD. The other differences are too technical, here.

>>Also, why are most shots taken with refractors? Is the high f/ number better? I would have thought reflectors are better because of their higher light gathering capabilities. Are refractors easier to focus?

Ther is no inherent reason you cannot take astro images with a reflector, and depending on how well it is made, collimated, etc, it can get pictures as good or better. But you can probably get smaller stars with a refractor, and small stars are what you are after. You can probably mount a small refractor much more easily than a large reflector, also.

Alex