Talk:Telescope Making

Today I laid out the 'bones' of the book on Telescope Making. My focus for the book is to impart the basic techniques to build a Newtonian reflector. I have a target audience in mind of people who might like to try this hobby but are frightened by the complexity and the cost. Throughout the book I will be documenting my building of a scope using scrounged parts and commonly available materials. The primary mirror is a Pyrex pie pan, used to make pies, and purchased for 99 cents at a second hand store.

A possible shelving for the book could be in Do It Yourself, or maybe in the Wikijunior section. I do plan on focusing the writing towards young adults, maybe between the Cub Scout range and the teen looking for a science project.

I would like to invite anyone with experience, maybe some pictures of a project, to contribute.

I think a question section could be good too, so invite those also.

--Vorblesnak 18:12, 3 November 2006 (UTC)vorblesnak

I got the basics of the Refracting Telescope page typed in. I am thinking at the end of the reflecting project I should do a section on making and repairing refracting telescopes. Many folks may be interested in buying that cheap Tasco at Goodwill for $10 and fiddling with it.

I have a heading on the second page of, "Contents". I don't know if that will stand or not. I am leaving it right now so that I can keep track of the book sequence; add or remove as is necessary.

I am still up in the air on final format. One long sequence OR! a nested web page design. I see arguments and discussions for both.

--Vorblesnak 18:22, 4 November 2006 (UTC)

Bit more done. I got down to Optical design. I need to find out some stuff from someone. How to do the links properly. Importing and embedding images.

--69.59.200.230 21:01, 5 November 2006 (UTC)

I am working on some of the illustrations and diagrams I want to use for the book. Much of the text for the section on Optics, located in the design section, hinge on these illustrations. Hence, slow going right now. I should be able to finish the optics section in a doay or two. Long weekend ahead.

Lord what a task. I am still not even sure it is right. I got the basics of the optics page up, pics and all. I need to find out how to list the scope werks as the author.

--Vorblesnak 21:18, 11 November 2006 (UTC)

Finished the section on the design of the optics. On to the hands on section. I will need to get materials and keep an accurate cost list. --Vorblesnak 05:11, 16 November 2006 (UTC)

Adding   { { PD-self } }   to a page will insert the open license. Remove the spaces after you paste it narnal!

--Vorblesnak 00:05, 18 November 2006 (UTC)

After 4 months of grinding and messing with glass I am finally ready to write the next chapter or so. Posted today, I have tried to stay within the editing constraints setup by the admin.

--Vorblesnak 21:10, 17 March 2007 (UTC)

Added some links to the page, did some editing of the verbage. Tried to gather my thoughts. I believe I will do the tube and focuser pages next, then come back to the optics.

--Vorblesnak 01:31, 24 March 2007 (UTC)

Some interest from the world at last. An editor wants to take a crack at making the book more readable. I will post some of the other chapters and see if we can't put this tome to bed. Mirror grinding next ..

Vorblesnak (talk) 06:26, 30 August 2009 (UTC)

Dave C has taken up the challenge of editing. I hope to move our discussions here so that anyone can share and learn form the experience. First edits went into the page. What follows is an email from Dave and my reply ..

> Today I went over the intro of the book. It's still mostly yours and I > hope it still "sounds like you." I felt the need of defining the basic > term focal length, which you used without defining, and had to cobble > up a couple of diagrams to add to your "sagitta" diagram.

We need to discuss audience and process. I wrote the book for 10 to 12 year olds and I wrote it as an introductory text. It really leaves a great deal unsaid. It is a hands on text. But as you have noticed there are some things that need to be expanded on. I thought about that and decided in the spirit of the web I would link to other pages that brought the detail focus to those loose ends. At the end of each section is a little piece called ... Links to new terms and topics for this page: This is the repository for those detail pages. I have been using Wikipedia for many of those links but other sources exist.

I see what you are saying about loose ends and undefined terms but I am not sure I want those in the text. I see the text as a hands on, wind in your hair, flying along scope making treatise. If you need more detail the links are there, follow them. If you just want to make a scope do what the book says and you will. The first image actually covers the elements of mirror design, including focal length, but I like the color in your images. I think the text could be reworked with hyperlinks so the links to "bird scopes" is in the text and at the end in the new terms.

I also think the style may be too loose, to much verbiage. Trying to strike a balance between verbose and laconic I think I come across as trite, too folksy. I want to hold their interest but not scare them off with the physics.

What do you think?

We should take this to discussion on the book's web page.

David Davis Toledo, OR 97391

> Thanks,

> Dave C. Vorblesnak (talk) 15:47, 1 September 2009 (UTC)

OK, I cut the paragraph on f-number as interesting but irrelevant, and I made the diagrams uniform size and centered.

(I would like to put a frame around them but I can't find a combination of diagram keywords that both sets the size at 400px and puts the frame. Any use of the |frame| keyword seems to ignore the |400px| keyword and goes to full width. I don't want to downsize and re-upload the images either... but I digress.)

Now, I get & sympathize with wanting a "hands on, wind in your hair, flying along treatise" but you have to realize, you aren't going to be there to back it up. Maybe if you were giving a hands-on scope class you could get by with a few xerox sheets plus your own dynamic teaching style :-) But this is the internet, you gotta picture some kid in Bangladesh or Sasketchawan trying to follow it. What is not in the book, will not be available. Yeah we want to do links, but I think every technical term you use, needs to be defined at least informally.

When I asked about the "bird" versus "planet" versus "galaxy" scope I was thinking you were getting ready to explain how well-lit targets (birds, mountains) can get by with a smaller mirror but need a shorter focal length (your point about seeing feather detail only), while dimmer targets (galaxies) need a bigger mirror and a longer F, with planets and the moon in between. But I guess that also would "interesting but irrelevant"??? Given that you are going for a pie dish mirror, mirror size is pre-set. But focal length is still open to choice.

I'm thinking of moving your reflecting-sphere discussion up to this more theoretical section ahead of "Thinking About Your Telescope" -- comment? fernly|Talk 16:38, 2 September 2009 (UTC)

Scratch that -- dumb idea. fernly|Talk 16:51, 2 September 2009 (UTC)

Too many "mounts" -- mount the mirrors in a mirror mounting but the scope is held by a scope mount... I'm going to try to reduce the number of use of mount/mounting to avoid ambiguity. Are you OK with speaking of a "bracket" to hold the mirror(s) and confine "mount" to the frame that holds the tube? fernly|Talk 17:03, 2 September 2009 (UTC)

Also I would like to use "magnification" instead of "bigger image" even tho it is a longer word. Reason is, "bigger" confuses me! To me, a "bigger" image is a WIDER field of view (you see more, more==bigger). But a long-focal-length image actually shows you a SMALLER piece of the sky (the bird feather detail again). But it would be just as confusing to say it's "smaller" hence, more magnified. Or think of another word... fernly|Talk 17:09, 2 September 2009 (UTC)

David, can you explain this sentence to me? "The [short focal length] image is a bit smaller but that is rarely an issue when looking through the eyepiece." It seems to raise a problem and leave it hanging. Can I delete it? fernly|Talk 17:25, 2 September 2009 (UTC)

In the Sagitta calculation, you first had "say you want a three foot telescope" but later you actually work out a 48-inch focal length, so I am changing the first example to 4 feet. fernly|Talk 18:31, 2 September 2009 (UTC)

Finally (for today) I'm looking ahead and seeing a lot of dense prose in the "making" section, with no images. We Need Photos!!! Surely you've taken some pictures of mirror making? I don't want only to rely on external links. If you don't already have suitable pics, I hope you can arrange to make some soon. Run a class or recruit a single kid and do it and take pics??? Cheers fernly|Talk 18:52, 2 September 2009 (UTC)

Fernly said .. "Yeah we want to do links, but I think every technical term you use, needs to be defined at least informally."

When you are right, you are right. I agree completely. But looking at other countries, do they even have pie plates? We should probably think about that and explore possible substitutes. Further down you make the point ..

"Given that you are going for a pie dish mirror, mirror size is pre-set. But focal length is still open to choice." This bears on a couple of points in the book. I was going to have them use the existing curve with no modification. Adjusting focal length was not going to be part of the process. However, if they are using the bottom of a jug or some other short focus curve then we need to examine adjusting the focal length.

Vorblesnak (talk) 19:56, 2 September 2009 (UTC)

Fernly wrote: "Too many "mounts" -- mount the mirrors in a mirror mounting but the scope is held by a scope mount... I'm going to try to reduce the number of use of mount/mounting to avoid ambiguity. Are you OK with speaking of a "bracket" to hold the mirror(s) and confine "mount" to the frame that holds the tube?"

Mirrors are held in cells. The cells are mounted in tubes using brackets. The telescope tube is mounted in a bearing assembly that allows it to be moved and pointed. There is just alot of mounting in telescope making! That does not mean we cannot tinker with the lexicon. Thesaurus time .. MOUNT .. affix, frame .. Synonyms: emplace, exhibit, fit, install, place, position, prepare, produce, put in place, put on, set up, show, stage hmmmmmmmm

Mirrors are held in cells. The cells are put in place in a telescope tube or truss assembly and held in position with brackets. The entire telescope tube is put on a mount that allows it to be easily pointed in any direction. How about that, work with that.

Vorblesnak (talk) 20:50, 2 September 2009 (UTC)

Fernly wrote: "Also I would like to use "magnification" instead of "bigger image" even tho it is a longer word. Reason is, "bigger" confuses me! To me, a "bigger" image is a WIDER field of view (you see more, more==bigger). But a long-focal-length image actually shows you a SMALLER piece of the sky (the bird feather detail again). But it would be just as confusing to say it's "smaller" hence, more magnified. Or think of another word..."

If I understand where you are in the book we are talking optics. The main difference between two mirrors of the same diameter but different focal lengths is the physical size of the image. It isn't magnification. The Airy Disk, the actual focused image, is larger and deeper on a long focal length than it is on a short focal length. A longer focal length means you have more data to work with so you can magnify the image a bit more, you could be a bit sloppy on your figuring and not affect the image. Conversely you must figure a short fl mirror very precisely because it will affect the image. Of course there is more to it than that but your larger field of view is the apparent field of view. The true angular field of view may not be that different between the two scopes. The apparent field of view is set by the eyepiece. So should we talk about that in the book? Airy's equations aren't that complex. Or maybe just use this http://en.wikipedia.org/wiki/Airy_disk

Vorblesnak (talk) 20:50, 2 September 2009 (UTC)

Fernly wrote: "Also I would like to use "magnification"... Ok, now I see it, in the section on Technical Terms. I belabored the physics above so you can look there for arguments. It is not really about magnification but your sentence does read smoother. And beginners do use the two terms interchangeably. I'd let it stand. If the book catches on there may be discussions about it but it is nice clean copy and I like it.

Vorblesnak (talk) 21:07, 2 September 2009 (UTC)

I posted the section on grinding. It is un-checked, un-edited but it is rewritten. I need to find the piece on polishing and figuring rewrite it and post it. I will do that in the next day or so. Both pieces need some illustrations and those I cannot find. I may have to redo them. Bear with me, I'll get them there.

Vorblesnak (talk) 05:32, 3 September 2009 (UTC)

I really wish you had not embedded so much text in your images. First off, Da Rules say there should be an alt= in every image to explain it and that's too much text to copy into the alt=. But also, text in a .png can't be edited or moved around. So, would you consider re-doing those diagrams to remove the text from them? Or I can do it. The words that apply directly to the image then go into the image caption, and the rest gets integrated into the preceding and following paragraph.

I have pulled this link out of the section I just edited, as the word is not referenced there. I'll put it back in after wherever it actually shows up, if it does.

Further on photos -- I don't know if you ever thought about using them, but they would be really, really useful. Worth >>1000 words to explain what a "tool" is, how grinding is done. Just get somebody, preferably someone of an age to be in the target audience, out to your garage actually doing this, and take a digital camera and shoot a bunch of pics. Cheers, fernly|Talk 19:46, 3 September 2009 (UTC)

Photos do not print well, line drawing do, hence my predilection for line drawings. Sorry the images irritate, I try to make them stand on their own. I take it from your last posting the labels with arrows would be allowed but not the explanatory text. I will remove it.

69.59.200.230 (talk) 17:27, 4 September 2009 (UTC)

Oh yeah, callouts with arrows, excellent.

As to photos: color pics may be a problem, if somebody just looks at a wiki page and clicks the print button on the browser. But wikibooks supports "printer-friendly" editions (see the Chess book on the home page) which is actually PDF. We can make color pics look great in a PDF, we have it incorporate the 300dpi version, not some little 512-pixel-wide, 72dpi thumbnail in the online version. That aside, I have more than once used photoshop to take a color pic and make it into a higher-contrast b&w so that the key features stand out, even printed newspaper-style. That's the middle ground between photos and diagrams. Neither you nor me are illustrators who can make a nice drawing showing hands doing grinding. Maybe your network includes a technical illustrator? If not, pictures. fernly|Talk 21:24, 4 September 2009 (UTC)

Vignetting is found in the text associated with the drawing on sizing the tube.

69.59.200.230 (talk) 17:30, 4 September 2009 (UTC)

Aha! that's why I couldn't find it with a search (another reason not to put text in a png!).

I've made some significant changes in the "Mirror Materials" section. First off I found the US Mint page on coin dimensions, and they are metric, so I had to recast the whole sagitta-depth thing in millimeters. Also the pyrex dish I got from our kitchen is a nominal 10-inch, its bottom is exactly 8-inch. So I think the reader is about equally likely to find a nominal 9-inch (7-inch bottom) or 10-inch (8-inch bottom) so I wrote to accomodate that possibility.

When I "ran the numbers" as directed on my dish I got a 56-inch focal length, based on its measured depth (just short of a nickel, or 1.9mm)

However, now when I hold my dish at a shallow angle to the light I can see the bottom is not a smooth curve. It's more like this:

--\____...____/--

There's a steepish curve in the outer 1-inch and then a shallower, almost flat curve across the bottom. The "..." is the raised lettering. So chances are by the time the curve is smooth, it will be deeper than 1.9mm hence a shorter F than 56 inches. Comment?

fernly|Talk 21:24, 4 September 2009 (UTC)

OK, keep in mind the section was written as a general guideline to help folks find materials. The coins may be in mm sizes but I took a pair of calipers to a hand full of change. The idea was to give them some basic tools to use to make decisions. You may have a couple of coins in your pocket and they can be used in this way to approximately guess at the sagitta.

Yes, you will see some irregularities in the pressed shape of the plate bottom. And if you remember I cautioned against using a plate with a big hump in the middle. Look for one with a more homogeneous curve. But those flaws are why on a regular pie plate you end up with about a 7.5 inch mirror, +/- a 1/4 inch or so. As the grind progresses the area inside the foot, that raised rim, is what gets worked. Right there you lose 1/4 to 1/2 inch of diameter. And as you scrub the writing out and remove the casting artifacts from the glass the curve is deepened. It also depends on the tool used. A cast tool of close diameter will yield a deeper curve. An over sized tool will flatten the curve. A ring will act more like a same diameter.

Keep the verbiage casual and simple. You get too deep into splitting hairs about coin size and you will confuse them or scare them off.

Vorblesnak (talk) 17:01, 5 September 2009 (UTC)

So I cleaned up the three images in the area of secondary mirror sizing. I remembered I had added the text to the images because I wanted the text adjacent to the image, to the right or the left of the image, and could not get the XML to do that. There must be a command for that. The appropriate text is now above or below the image. Hope fully you know how to get the text where I would like it.

Vorblesnak (talk) 18:02, 5 September 2009 (UTC)

OK I used two-cell tables to put the text beside the 3 images. I'm not totally happy with how it looks but it isn't bad. Oh, and shall we do the ROC drawing earlier same way? Thanks for making that change, and thanks for the pictures you sent. fernly|Talk 19:35, 7 September 2009 (UTC)

"We cannot use tempered glass as it shatters when ground" aghhhh! We must tell people a reliable way to identify such glass! Otherwise it would be like saying "go pick mushrooms to eat, and oh by the way don't pick any death caps..." Is the rather cryptic sentence about polarized glasses the method of identifying tempered glass?

I sense an experience has occurred. Care to share?

No, you cannot use tempered glass .. yes the cryptic sentence about polarized sun glasses does refer to that. Polarized sunglasses will reveal a dark areas or zones or spots in tempered glass, or glass with strain entrained in the glass. Get a pair and go look at the side windows of your car. You will see a pattern of dark spots in the glass. That is strain, that is bad. Don't grind that.

The classic method of identifying tempered glass is to use two polarizing lenses, one one each side of the glass. Light shines through the back lens, through the glass and is viewed through the front lens. Tempering is revealed as the front lens is rotated. It shows up as a series of dark zones.

Now the interesting thing is, pie plates use to be fine annealed pyrex, hence my choice to push those for mirror blanks. However I have discovered pyrex is now just a marketing term and the bakeware is probably not made by Corning and is probably not true pyrex, though it may be a hardened borosilicate. So the caveat about tempered glass should be at the start of the finding your mirror section not buried in the other parts section. I originally felt safe about pie plates, now I am not certain. Old scratched up pie plates are very probably pyrex and can be handled without concern. New stuff?? Lokk for strain.

Here is a link to a good page on strain ... http://www.public.asu.edu/~aomdw/GSI/Glass_Strain.html

Here is a topical page on tempered glass ... http://www.cuttingedgesandcarving.com/forums/index.php?showtopic=4492&pid=36710&mode=threaded&start=

Vorblesnak (talk) 01:33, 8 September 2009 (UTC)

I moved the tempered-glass discussion up in the glass-finding section and gave it a heading. I think the experience of seeing spots in a car window thru polaroid shades is common enough it should be understandable.

I edited the tool-making section. I moved some things around for more logical order; you had the grinding surface preceding the casting/shaping of the base, and I thought making the base should come first. I added some more cautions on breaking up a pie plate for glass (I could just see some enthusiastic 12-year-old with a hammer and no eye protection..)

The paragraph about your friend with the bubbling pitch lap seems a bit of a digression, consider deleting it or saving it for some later section ("troubleshooting"?). Also I didn't understand the remark in it, the cure for a wet tool was to soak it? Seemed counter-intuitive...

I installed one of your pictures. When I look at them closely they were not really in sharp focus. I sharpened the one as much as I could in photoshop, but if you should happen to be standing around the shop with a digicam in your hand you might have another go at it. Also, I didn't have much info for the caption. What's the casting material of the one on the right and the big one in the back? Plaster? What's that big one for, it looks like 15-inch or bigger, wow. 21:35, 8 September 2009 (UTC)

Good work on the tempered glass and the warning about breaking up the pie plate ..

"The paragraph about your friend with the bubbling pitch lap seems a bit ..." Not enough development of the argument for it to make sense. The classic cast tool was called a tile tool. The original idea was to lay tiles on the glass and cast dental plaster for the body of the tool. The dental plaster wraps around the tiles and binds them. The problem with these tools is they are thirsty. They absorb water from the grinding wet and dry out the process, at least until you slake their thirst. The common fix is to soak the tool before using it. This works fine if you are grinding, a very wet process. However all that stored moisture causes the pitch to fall off when you cast the lap on the tool for polishing. Some folks combat this by using a different backer for the pitch lap. I said screw that. I cast the backer and then glue glass on for a grinding surface. No water absorbtion and the pitch sticks to a fully dry tool.

re: the pictures. I am not a photographer, but I know one and I am on his schedule. The picture was to show finished laps, one under construction and materials. The casting material is rapid setting grout. IT is ready to use in one hour. You can cast the backer from anything that will pour and harden, I don't like plaster. Dental plaster is OK. Concrete works fine, The big tool is for the mirror that is under it. A 22 inch 7 segment tessellated blank. That is a proof for a 2 meter project this winter.

Vorblesnak (talk) 02:53, 9 September 2009 (UTC)

OK I have edited all the available text to my satisfaction at least. I am going to be travelling for a few weeks but will check in periodically when I have a good wi-fi connection and some time to kill. Meantime you can be writing! Filling in the sections that currently have a heading only.

I would like to say how much I am enjoying this book as I read it closely. It is chock-full of solid practical advice, as you intend. I think when it is filled out it will be an impressive resource and will inspire lots of telescope making.

THINGS TO THINK HARD ABOUT:

One, what really to do with links. There is not a consistent method of placing links. Take John Dobson. I stuck in a link to his Wikipedia page at the end of the first section where you quote him. But he's quoted several other places. The reader might remember there was a link but would have a hard time finding it. So I repeated it along with links to Bartels and Oiton whom you refer to, after the intro to grinding.

On the one hand, my instinct is to do inline links, just make a hyperlink out of anything like Dobson, or the U.S. Mint -- as you would do in a web page. But that apparently is not the wikibooks style. OR-- put all the links in one single =Links= topic at the end, and liberally use "(see Links)" throughout the text. Right now there are little blobs of links at the ends of topics which is kind of the worst of both worlds.

TWO, the outline! Now that all the headings are ==wiki-style== they show up in the TOC, which is rather impressively long. No doubt the book should be split into chapters but I'm not sure we are ready. The problem that keeps bugging me, tho I have no solution yet, is that logically speaking, almost everything is a sub-topic of "Project 1: The Newtonian Reflector." Only the last main topic, "The Telescope Mount," is really generic to almost any kind of amateur scope. Much of the mirror-making part is also generic, I suppose. But all the secondary-mounting part is Newtonian.

I guess the main issue here is, do you intend to write a "Project 2: The some-other-kind-of-scope"? (and BTW, I put in a vote here for a Schiefspiegler if you do) Because if so, then you need to think about how to pull out the mirror-making text that would be generic. Then we can have an intro, a generic chapter on mirror-making, a generic chapter on scope mounts, and a specific chapter on each "Project".

THREE, missing, even as empty headings: (1) how to grind a flat mirror (2) how to silver a mirror. Insert those headings where you think they should go.

Cheers, DC fernly|Talk 22:09, 9 September 2009 (UTC)

A quick perusal later I find just a couple of simple errors that I will touch up. Nice job on the edit. I will write. Lets see if I can button this up by Christmas.

A schief? Hmmm. I spoke to a man the other day that learned from Oscar Knab. I wonder if I can find him.

Vorblesnak (talk) 17:01, 12 September 2009 (UTC)

Dave, I sent you two chapters for editing. Not sure if you got them. Should I just post them here?

Vorblesnak (talk)

Refracting and catadioptric telescopes
Should there be a section about making refractors, or about making catadioptric telescopes (those with both lenses and mirrors)? --Whoop whoop pull up Bitching Betty 19:45, 12 March 2011 (UTC)


 * Refractors and catadioptrics seems like reasonable topics to cover (or plan to cover). The question is how best to expand the outline for them.  At the moment, apparently all the content after the first section is "Project 1".  --Pi zero (discuss • contribs) 03:05, 13 March 2011 (UTC)

Copyvio
Hello, I am vorblesnak. You may contact me a  I am not sure what the alleged copy write violation is since I built this page and most of the content from scratch. Perhaps someone could contact me at the above email and let me know what the issue is.


 * I have no reason to doubt that you may be vorblesnak, but you should use your registered account to address the issue.
 * The issue is about the copyright notice you added (see bottom of diff). It prevents the use of the content for commercial uses this restriction is not compatible with Wikibook's licenses.
 * I will try to contact you via email. --Panic (discuss • contribs) 02:54, 2 May 2012 (UTC)

Question re Cc Violation
I, user id fernly, am Dave Cortesi who edited/rewrote much of this text in consultation with the original author. Just checking in to the book for the first time in a long time, and was dismayed to see the big (c) violation notice. I am not aware of any (c) material in it. Please say specifically what you "believe" to constitute a copyright violation. If I can't justify it I'll delete it.


 * You can remove the notice after the issue regarding this copyright restriction is lifted "Permission is granted to reproduce and distribute these files for non-profit, personal use." as it is incompatible with Wikibooks copyright license. I couldn't contact the poster in the above thread to resolve the issue, if you have better information please share here and feel free to act of it. --Panic (discuss • contribs) 06:40, 7 October 2013 (UTC)