Anyone here ventured in making their own telescope by hand? Especially the optical side with grinding their own mirrors from blanks; finding the best tubes; mounts; and rigging a good camera system to it for remote viewing?

Because good class astro-photography level telescopes cost a mint (well over 20k) for 24" size, I'm asking. Can find mirror blanks for under 1k, pre-formed over 1k, and thinking despite the time and precision required, it's the only way to get a great scope without mortagaging your grandchildren.

Furthermore, are the new fangled CCD cameras have better resolution than the old gas hyped method, too?

Trying to reach a happy medium of affordability+quality.

Unless you have super seeing at your location there's little gain in going to such a large scope. Today's CCD's have resolution far beyond the seeing unless you live atop Kitt Peak so someplace similar. Take a look at Iceman's animation of Jupiter in the photo section to see what a 12" scope can do in today's digital world. Unless you are planning some rather extensive scientific projects such as spectra of very faint AGN or something similar there's no need for anything much larger. I can easily reach beyond 20th magnitude with my 14" LX200R with half second of arc pixel size. Though since my seeing is usually far worse I go with 1" pixels most of the time. I'd need some perfect setting to use the full resolution mode.

To get much field of view with a large scope you need very large and expensive CCD's as well since their image scale is so big. They'd set you back at least another $10,000. Then there's the filters. You need big expensive ones with a large scope. That's another couple grand if you go narrow band as well as LRGB. Then the filter wheel for those filters. It keeps mounting up, the scope is only the event horizon of the black hole your money can disappear into.

I figured I got a range of about 1000 to one on hypered 2415 but get a range of over 30000 to one with the CCD meaning I can go deep and yet not over expose the bright regions of most objects, something very difficult to do with 2415. To get the faint outer halo on some galaxies I'd way overexpose the core. That's no longer a problem with CCD and its much wider range. For instance this is a link to a shot of mine of M81 and the dwarf galaxy Holmberg IX in the same frame. In days of film there was no way to get Holmberg IX without completely over exposing M81 into a bright blob. Yet it is quite easy with a CCD and 14" scope.
http://www.usenet-replayer.com/cgi/c...567447.10.jpeg
As to resolution how about Leo 1 resolved to the core along with several of its carbon stars identified, 3 quasars down to mag 19.49 (bottom right) and 5 asteroids. This link is to a reduced image due to band with limits. The full size one shows a lot more resolution.
http://www.bautforum.com/attachments...5b2x5rid67.jpg
Best I ever did with 2415 was a blob with a few dozen stars across its face and lots of glare from Regulas. Digital processing allows you to take that glare right out of the shot as if it was never there.

Several years ago I auctioned off my chemical darkroom. No more stained itchy fingers. Even if 2415 was still around I'd never go back.

I know one fellow who built his own 18" classical Cassigrain but it is on an AP1200 mount. He only built the scope part.
http://www.narrowbandimaging.com/mar...egrain_hex.htm

Rick

I'm afraid that ATMing a 24" in order to save money is a moot point since you most likely won't be able to afford the mount and drive that would be required for a 24" astrograph anyway.

Those are great images, Rick, by the way.

Dave Mitsky

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I'd make them, if need be -- casting, machining -- no problem. Noticed CCD cameras can be handmade, too.

Ghettoed telescope...hehehe.

Thing is I have the time and energy, but not the money. So the only solution is build the thing by hand or go without (and I'm tired of even the 8" telescopes costing too much).

The only reason I'm shooting for a 24" is to get good images of deep-sky objects. Want my own collection of superb photos.

Yeah, but the 8"+ telescopes are tooooo expensive for me, and it's either cash upfront or use credit (which I want to avoid). Reckon I can buy in piecemeal, and assemble the parts when all are finally bought (or made).

Don't know if it's an analog vs. digital issue, but although your photos are clear with nice contrast, the stars look smudged. Know CCD video stacking can improve image quality for more luminous objects (like the moon and other planets), but can the same be said with deep-sky objects (or is the surface brightness too faint for video to pick up)? Really out of the loop with CCDs for astro-photography. :/

You will need to build an observatory also. I can't see a 24" Newtonian (I assume) being very portable. Even building scope, mount, camera, and observatory, it seems to me that you are still going to spend a lot of money.

Before you target 24" try building something smaller...just to confirm that you understand the process and whatever test equipment you have to make is made and functional.....plus saving the 24" blank from 'newbie' issues. On what I've read a lot of the outcome depends on your patience, the test equipment and the interpretation....physically pushing glass on grit is just that....

I've used www.atmsite.org....

The fuzz around the stars is due to the wider dynamic range of the CCD. Film just doesn't have the range to see it. It is due to seeing moving the star around. Sometimes seeing moves it well away from where it belongs but this all averages out so you get this halo effect. It is also caused when seeing takes a star completely out of focus for a split second. Something that happens all too often in my location. The motion is too fast and too faint to register on film (film has an inertia of some sort not found in CCDs). Put my scope on Kitt Peak and they'd go away. They are less of a problem in smaller scopes as well as they are less bothered by seeing! Big scopes are in good locations so you don't see them on those shots. Deconvolution and other techniques can greatly reduce them. They though cause artifacts if used too heavily handed so I usually avoid them. Also there are fast response guiding units available that can move the whole field of view every fraction of a second to compensate for this problem but again they are expensive and get really expensive with the larger light cone of a large scope!

Deep sky CCD images are usually stacked as well. There is a slight increase in resolution if you use dithering but it is very slight, mostly due to a slight noise reduction since the same pixel doesn't get the same piece of the image over and over thus evening out defects flat fielding and darks don't remove. Planetary shots freeze seeing. The object, say Mars, is moving around on the CCD from one shot to another due to seeing and has various degrees of sharpness, even across its face. By selective stacking of hundreds of images (Software picks or you can) and with auto alignment this motion is removed and you get a clear shot. But these are made over no more than a minute or two using at most 1/10" shots. Deep sky you are using long exposures (I usually use 10 minute frames though the two I listed are using 5 minute ones). During that time seeing has moved and blurred everything as much as it is going to so little can be gained from stacking. There are no selected ones to use. All are equally ruined by seeing. Hence the need to go to Kitt Peak or someplace similar for sharp images. They won't be one iota sharper in the 24" than in the 8" due to your seeing. You'll just have more light for a spectragraph or other scientific instrumentation. You won't go much deeper either (oh maybe a third of a magnitude to a half depending on your sky conditions) and since local seeing is usually 2" in the best of locations even an 8" can do that with ease and so so optics! Plus, if you are building your camera you can get by with a CCD chip that will cost you several thousands of dollars less as well as save lots of bucks on the filters. Good photos is technique and location NOT telescope size, that just allows you to get the image a bit quicker if you have the proper image compressors (lots of bucks for a 24").

So why stack at all with a CCD? Really there's only one reason with a non blooming chip and that's to reduce wasted time. Things go wrong. A plane goes through the image, a cloud blocks the guide star and the guider takes your scope on a cross sky trip, a bright satellite nails you, etc. By taking a lot of sub frames you just lose a few minutes of time, not hours. Also the more sensitive chips are what are called non anti blooming gate chips. They are about 25% more sensitive as their pixel isn't partially blocked by the anti blooming gate. If a star saturates the sensor you get a nasty streak of light (bloom) that runs across the image. So with those chips SOMETIMES it is possible to use short exposures to prevent the bloom and still get plenty of signal. But for going faint this doesn't work well. Each time you read out the data from the chip you get noise. If the object is faint the difference in signal level from the object and the readout noise is very low and you get little to no gain as you stack short exposures. Since readout noise is constant and random it builds with the square root of the number of readouts while the signal builds in a linear fashion. So if you have a signal well above the noise by stacking more and more you do reduce the noise. But one single shot 60 minutes shot has less noise than 12 5 minute ones. You do need some more time when using stacking than when using one long shot. Still, since it seems in an hour I usually get one nasty satellite through the image or a bad cosmic ray hit, I still get images quicker stacking than by using one long shot.

But if you have a 200" scope you can get enough signal to noise ratio to use 1/10th second shots and stack those as planetary photographers do and get images that beat Hubble! It's a complex procedure.

If you have never done this type of photography and it doesn't sound like it from your post, you have no chance at all starting big, the hurdles you face are far too large. Start small and work up. Over my 7 decades in this hobby I've watched as several have tried and all failed.

One club member is now up to a 36" and about $100,000 spent, he started at 16", and he is yet to get a decent image. Each failure leads to more money spent on bigger toys. He's made someone's retirement fund a success but his photos are worthless. He can't figure out why I can do better with a 6" f/4 scope I paid $100 for 40 years ago than he can with his super duper $100,000 set up with a 36" using top line everything. But he's still greening up the astro community so some good is coming from his failure I suppose.

Rick

Will do. Have to test the equipment anyway, and like my experience with sanding and polishing jewelry (let alone a CPU and HSF), it IS a trial and error method!

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Thanks, Rick, for a v-e-r-y informative post. Sure helped with explaining why the stars showed smudged. Was thinking it was movement, as it's so subtle, but it's more than that. Fascinating.

Trying to get the ideas in place for this endeavor. Have to go cheap, simply because there's not enough money to persue this hobby (oh, life and it's requirements!), but cheap doesn't mean little quality. I'm trying to also avoid commercial telescopes because there's so many sold with lower quality parts. I don't buy off-the-shelf computers, and software I tweak for personal use, so this telescope will have to have that special touch, too. To me, it's not as enjoyable unless you put time and effort in your equipment, you'll also respect it much more. It'll be something to pass down the family.

BTW, would you have any recommendations on books to read on both telescope making and astro-photography (especially for someone of the "old skool")? Gone are the days when Sky and Telescope were talking about what manual camera to buy, or what hyper kit will suit your shutterbuggness. The first "automatic" Canon AE-1 was the last real camera I bought, even!

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I built my last scope in 1954 so books I don't know about.
I got into CCD imaging several years ago when Willman Bell's Handbook of image processing was the book. Since then many have been written. I don't have any idea which is best. I do most of my processing with Photoshop though IRIS is a free program that some use for processing. All the top imagers though (far better than me and often using far smaller scopes too) also do most processing with Photoshop. Whether GIMP could do it I don't know. Needs to handle 32 bit FITS files. Even Photoshop doesn't but plug-ins are available (FITS Liberator is free) to do the job. Most of what I learned was from postings on various groups dedicated to this art and web pages of top imagers.

I don't use AIM4Win which comes with the book. The book isn't about the software though it does use some screen shots to illustrate its various topics that are independent of the software.

Rick

1954! YIKES!!

Appreciate the technical help, Rick. It's this knowledge that sure helps tracking down the info needed. It's a maze! What type of glass; what polishing compounds; what type of polishing equipment; then all the way to mounts; and enclosures; and finally to the fun part, imaging.

Can't wait!! Hurry up, Christmas!!

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Pyrex.jeweler's rouge or equivalentyour grinding blank (tool) with a pitch lap formed on topFor that size Newtonian scope, fork equatorialshed with sliding roof is cheapestThe people to talk to have already spoken.

Thompson's book is still available. For someone starting out it's ideal.

Concerning the mount, I take it you have or have access to, a short-run foundry and large CNC machining center?

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I don't think you realize that "glass pushing" is going to take far longer than you expect! Even a 6" mirror can take weeks or months to figure and the time goes up exponentially with diameter. Expect to spend the best part of several years grinding and polishing!

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Jean Texerau's book is also available, I think. And the venerable Amateur Telescope Making (3 vols.).

Ground my last mirror in 1969. Maybe someday...

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Sis is a jeweller and can cast and fashion anything with metal (has the tools for the most finest precision work), including knowledge of rigging up a foundry for the task (she wants the telescope as bad as me). It's something right up her alley. Don't believe CNC is needed for the task, but even if it was, there's a millwright shop down the street (where we can get metal stock -- including the telescope tube and other hardware).

Getting the pieces and all isn't the hard part, assembly will be, as sis wants a special deck for it, and it has to be motorized for remote viewing (that will tax our electrical engineering skills...especially sis and her love for frying components! DC...DC...DC please!).

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Maybe I'm not aware of the current trends in jewelry, but an equatorial fork mount for a 24" Newtonian is going to involve some really large, massive components.You'll be lucky to have a functional mount with just CNC. It is of prime importance that the bearing journals be precisely machined such that, for instance, the axis of the declination axis is at a right angle to the right ascension axis within a few thousands of an inch (could express this with GD&T, but that's another subject). Even more importantly the center of rotation of the right ascension fork bearings has to coincide (best explained by position tolerancing, used to be concentricity (now mainly used as a symmetry control), then coaxiality) with the geometric center of the right ascension shaft's surface of rotation for its entire engaged length. Plus if there's a large bearing surface at the bottom of the fork, it too must be closely related to these centers of rotation.

If not, no matter how much time you spend aligning the mount in its permanent location, it will mistrack. The only correction here is computer control, which means $$$.

Then you're creating bearing bores. For proper fit, machining doesn't "cut" it, especially in a casting. A common solution is tool steel inserts. A plus here is the CoTE will usually closely match the CoTE of the bearing and shaft material. Once machined to where they're within the ball park, a series of fine grinding (and possibly polishing) operations are required. Some CNCs have tool holder adapters for this, some don't. Plus if it's a large CNC, the accuracy and precision of the tool holder may have a negative effect on the results. Thus another machine would be called for, probably a jig grinder.

Then there are the shafts. And the base. And the brakes. And the mirror mount, which is a whole textbook in itself. And the sensor locations for CCT and astrophotography.

Don't forget about size. A 24" mirror means an even larger diameter tube, which means the space between the forks will be more than that. And that's just the width dimension. You also need to compute stock thickness and reinforcing ribbing for supporting the scope without unacceptable vibration or sag.

Plus there are many other factors, all of which come under the heading of "engineering", be it quality, design, or manufacturing.

Is this your first equatorial mount? Don't underestimate the task. As well as starting with a smaller mirror, I'd recommend starting with a good old alt/az Dob mounting. Ever collimate a large Newtonian? Have fun!Best of luck with that last part while keeping the cost down!

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I'm not sure that you fully understand just how difficult a task constructing an astrophotography capable mount and drive for a 24" OTA will be.

Dave Mitsky

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Film astrophotography is pretty much a dying art for a number of reasons. However, you may want to pick up a copy of Michael Covington's Astrophotography for the Amateur.

http://www.covingtoninnovations.com/astro/index.html

Ron Wodaski's The New CCD Astronomy is a good treatise on CCD imaging.

http://www.newastro.com/newastro/order.asp

Another ATMing book that hasn't been mentioned is The Dobsonian Telescope: A Practical Manual for Building Large Aperture Telescopes by David Kriege and Richard Berry

http://www.willbell.com/tm/dobtel.htm

Working a camera from the focuser of a 24" Newtonian won't be much fun. Large Cassegrains, especially Ritchey-Chretien Cassegrains, have major advantages for astroimaging.

Dave Mitsky

__________________
Chance favors the prepared mind.
De gustibus non est disputandum.
Never attribute to malice that which can be adequately explained by stupidity.

...don't forget the finder-scope...for a 24" its going to be a 'scope' in its own right....maybe try building that first...