Here is what my mirror looks like, just out of the package. I carefully lay it out on the tissue it was wrapped in, sitting atop a nice, comfy cushion. I don't want this thing to get scratched up before I even use it. I currently am keeping it in the packaging it arrived in for safety.
When I took that picture I forgot that when you focus on a mirror you will get one of two things; either the mirror itself in focus and the reflection blurred, or vice versa. So I took another one with part of the window frame being reflected in the mirror.
As sharp as the image appears, my camera is not that great, and does not do justice to the clarity and sharpness of reflection this mirror provides.
When I said above that the mirror is 1.1" that refers to the measurement on the narrow axis. Since the secondary mirror is placed at a 45 degree angle from the primary, the optical field is distorted - i.e. it appears shorter on one axis than on another. The elliptical shape addresses both the issue of foreshortening, and that of providing as much field of view with as little obstruction to the primary as possible.
I'm sure we all get it - you tilt the mirror and the shape appears to change. Still, I'm a very visual-minded person, so I like to use images to illustrate my point.
The mirror as it appears directly front-on:
The mirror as it appears when tilted:
That second view is roughly the same angle as that it will be placed at in the telescope, and, as you can see, the area of vision appears round rather than elliptical.
Notice also that the edge is angled. This is to maintain a good thickness of the mirror glass (important for keeping a sharp image - glass is subject to warping rather more easily than one might expect) while permitting for more visibility around the mirror. I'm holding it upside down to show the angled edge, but in reality it would be positioned the other way, so you see only a very small edge.
That's it for now. As I progress so will the blog. I don't have a "deadline" for this project, so I don't have a time line for it. However, as I learn more I will post more.
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UPDATE
To answer the question posted by Albatross (and for anyone else who has wondered - like me, for instance), this is how you clean your mirrors:
Mirror Cleaning
The short story is, avoid cleaning them as much as possible. Dust will not inhibit viewing. If a mirror actually needs cleaning, the link above gives a great description of how to do so safely.
Take your time. Slow an' easy. I enjoy the way you go for detail. Can you get a close up of the 'angle'? I can't really see it. Now I'd really like to see a picture of the back 'a it too. How is this thingy fastened onto the spokes to connect it to the tube? I hope you got a good price, or was it costly? Your project just gained quite some concreteness. Hey, it became very real.
ReplyDeleteAlb
What a barrage of questions I managed there. But, I have another one. How does one dust off the mirror? I mean one has to be extremely careful of the surface, I guess? Ain't that so? What kind of care is recommended?
ReplyDeleteI can definately get some more detailed pics of the mirror. I had intended to do that actually, but ran out of time. As to your question of how it's attached to the spider... good one. I haven't gotten that far yet. LOL Once I learn that I'll share it hear for sure. The cost was not bad. The mirror itself was about $10 USD (add a bit more for shipping, and the Canadian exchange and you're looking at more than $25, but I still consider that reasonable). I assume one can clean the mirror with a very soft cloth, like those used for glasses, but I will also look into this. I fact, I will not clean it at all until I find out for sure the best way. Methinks I will go to the forum source I posted a link to earlier here and ask a few questions.
ReplyDeleteThanks again.