Meade LX50 Manual de Instruções descarregar pdf (Página 6)

[This message was in answer to questions about the brand of coma corrector and comments concerning the

common occurrence of rolled edge at both inner and outer portions of the main mirror.]

I don't know what brand the coma corrector was, but will find out. I suspected exactly what you referred

to -- the coma corrector may have had a small amount of spherical aberration itself that just happened to be

equal to and opposite from that in my scope. That was the "happy coincidence" possibility I mentioned in my

message.

I had the scope out again for a couple of hours tonight. The seeing was just a bit better than last weekend.

I am convinced that the scope has a small amount of under-correction, but it doesn't seem to be much. I did

get a chance to try a Ronchi grating and null test tonight. The null test showed a very smooth figure with little

roughness. As you observed, I also saw a bit of roll-off at the inner and outer edges (presumably the mirror.)

The null also showed a subtle deviation from flatness. While I couldn't tell in the null if it was over or under

correction, the star test shows it to be under correction. There was no sign of any zoning at all. The Ronchi

bands (using a 133/inch grating) showed a slight bowing again pointing to an under correction. Overall, the

optics seem to be quite good. I am also pleased with the performance of the scope on doubles. It's going to

be pretty cold here this weekend (at least central Texas standards), but I hope to try the scope out on Jupiter

and Saturn Saturday morning.

I also did a little investigation of the drive electronics last night. I found that it is indeed safe to use an

external power source while there are batteries loaded into the internal pack of the LX50. (I was worried

about accidentally charging non-rechargable batteries by connecting and external source.) I haven't

completely reverse engineered the design, but discovered that the two power sources are not wired directly

together. I found that when the external power plug has something plugged into it, the internal batteries are

isolated from the drive system. This is good news in the ease of use category and shows that some good

thought went into the engineering of the drive system.

[Subj] #264712-Meade LX50 7" First Look

[This message is in response to a comment that one reason the coma corrector may have helped the spherical

aberration is that it forced a new focus point for the scope. Since these telescopes focus by moving the

primary mirror, spherical aberration is a function of focal plane position. Indeed, the residual spherical

aberration is better with a camera extension tube installed.]

Thanks for the explanations. You may have hit on exactly the explanation as to why the coma corrector

improved the images. I guess it is possible that the addition of the corrector forced the primary focus

movement to a point that was very near the optimum spacing. I had not considered that possibility. I had

completely forgotten that the system will have a "sweet spot" in the focusing movement of the primary. This

gives me yet another experiment to try. On my next outing, I will try the star test again by moving the eyepiece

in and out at several fixed "focus positions" of the primary. This should prove interesting.

There indeed a "sweet spot" in the focus travel. While it could be detected in the star test, it was not

obvious during general observations. My conclusion is that for most purposes, it is not worth worrying about.

John D. Upton

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