Anonymous
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Welcome one and all, and let'er rip.
Joe Donahue
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Anonymous
Unregistered
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Hi Joe,
Thanks for this area.
I'm more involved in designing of various products than actually marketing or manufacturing. I work for 2 companies. One is for aircraft displays and military Night Vision. The other is involved in industrial, medical, and astronomical optics.
There are a number of items and processess that I designed so long ago that I would have to be trained to use them.
I here to inform on some of the coating processess that is often regarded as a black art by some.
One thing, though, I'm opinionated at times. I tend not to hold any particular brand of telescope at any great level of esteem. I do realize that some the expensive and more exotic telescopes are excellent. At the same time I feel that many of the more common Chinese Telescopes and SCTs hold their own, very well, against these more 'elite' scopes. Some easy modifications can bring these affordable telescopes to a high level of performance at little cost and effort.
Al M
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rboe
Numbfinger
Reged: 03/16/02
Posts: 39739
Loc: Phx, AZ
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I believe your process is called Molecular Beam Epitaxy. Is Chemical Vapor Deposition ever used in your industry? I seem to remember a third method but I don't recall the process. But the latter is used in fabbing computer chips so I don't know if it's useful in filter making.
My attempt to get the ball rolling! Nice little home you got here.
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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Stacy
Carpal Tunnel
Reged: 09/15/02
Posts: 2076
Loc: The Great Northwest
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Right on! Al's a moderator with his own forum!  I’ll look forward to your helpful solutions and ideas. (When I’m not bugging you at the shop.) 
Thanks Admins for recognizing Al’s unique and valuable contribution to Cloudy Nights and the astronomical community as a whole. 
Regards,
Stacy
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NS11-GPS-XLT, XT-8, 120ST, AEX-10X50
www.darksky.org
Human history becomes more and more a race between education and catastrophe.
- HG Wells
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Anonymous
Unregistered
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Well said, Stacy. Let 'er rip, Al
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Anonymous
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Thanks to All,
Remeber to keep me straight! If I err, correct me.
Hey Ron. The equipment used to make computer chips can be quite the same as the optical stuff. One thing is that the level of cleanliness for the chips is much more stringent. Those are the guys with the white outfits and and white booties and the like.
I may start and describe different materials used in coatings along with different systems involved.
Al M
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rboe
Numbfinger
Reged: 03/16/02
Posts: 39739
Loc: Phx, AZ
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The big boys tend to use a proprietary coating process or recipe then tack a brand name on it. Do you have an in house recipe that you would use on a corrector plate to approach or surpass what the famous brands have?
And what do you mean you don't use white booties! 
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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Anonymous
Unregistered
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Hi Ron,
CVD is occasionally used, though appears to have a lower optical grade but is less expensive.
AR coating formulas are more generic than manufacturers let out. All this hoopla between Celestron and Meade is just silly advertising. Both coatings are just fine. The multilayer AR coats are usually 2 or 3 layers, but can have more. I have done a number of multi-layer ARs for military and friends, but not for myself. The trick is to find suitable materials with the needed indexes(indices?) of refraction. There are dozens of materials that can be used.
One of the first single layer AR coats was Cryolite(Na3AlF6). Its more effective than MgF2 but is very delicate and doesn't tolerate handling. Its only used in very well sealed situations. CaF2 is about as good as MgF2, but is also more delicate. Thorium Fluoride is a fine coating, but radioactive. Its not the coating that's the problem since the material amaount is so small. Its just that when we clean the machine, you don't want to breathe the radioactive dust.
Different vapor deposition systems have different strengths. The E-beam system can be very smooth and capable of evaporating anything. The one problem is decomposition of certain material. As an example, when an E-beam strikes TiO2, it will diassociate some of the titanium and oxygen. Most of these molecules will recombine, but not all. The optical properties will be inconsistent at times. This can be corrected by adding minute amounts of oxygen at the source. I don't like to do that.
The sputter system doesn't disassociate materials. It uses a powerful RF aimed the source material to evaporate.
Materials behave differently when evaporated. Most metals melt into a quivering puddle while evaporating. Silver puts out a pleasant green glow from it ionized atoms.
Most materials sublime(solid to vapor). This includes SiO2, Chromium, TiO2. MgF2 shows some melting at first, but actually sublimes too.
One must be careful not to look through the viewport at some material because of extreme light emissions. Al2O3 and ZrO2 are so bright that eye damage can occur. SiO2 is also very bright, but somewhat less.
I'll continue on with clarification later. Hope I'm not boring anyone.
Al M
Edited by AlM (12/17/03 08:29 AM)
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miniventures
Something Else
Reged: 09/13/03
Posts: 11064
Loc: Powell Butte, Central Oregon
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Al, this isn't boring, it's fascinating! It's just . . . I wish to hell I knew what you are talking about  I have an MA degree in English so I guess I won't be adding much to this conversation (except to correct your writing process ) LarryC
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LarryC
Volunteer
http://www.sunrivernaturecenter.org
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Anonymous
Unregistered
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Hi,
This is Stacy's AR5 focuser after the image-shift was removed and larger knobs installed.
Al M
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miniventures
Something Else
Reged: 09/13/03
Posts: 11064
Loc: Powell Butte, Central Oregon
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Oh, you put on those cheesy knobs on that you just knocked together the other day, eh? Gosh they look great!
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LarryC
Volunteer
http://www.sunrivernaturecenter.org
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Anonymous
Unregistered
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Hi,
Cheesy Knobs? .... OK they are cheesy. They are, however easy to make. I just put a lot of holes in them ... wow!
The real story are those aluminum blocks. They support the setscrews and the teflon blocks beneath.
This focuser is good ... now. Meade could have them made better. The Synta focusers are better.
Al M
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Stacy
Carpal Tunnel
Reged: 09/15/02
Posts: 2076
Loc: The Great Northwest
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Now that's a manly looking affair! And no shift!!! Can’t wait to get my grubby paws on that thing. You guys should have seen the teeter-totter effect Meade had going with their single point adjustment. I looked at the design previously and figured there wasn’t anything that could be done with it except replace it.
Thanks a million Al! 
I’d kill for a clear night. Focuser fixed, re-coated mirror, filters to try! How ‘bout a giant fan to blow away these clouds? 
Regards,
Stacy
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NS11-GPS-XLT, XT-8, 120ST, AEX-10X50
www.darksky.org
Human history becomes more and more a race between education and catastrophe.
- HG Wells
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Anonymous
Unregistered
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Al do you have any plans for a finer rack and worm gear for these focusers?
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Anonymous
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Hi Schultze,
There's a point no return here. The larger knobs afford a finer focus in themselves. Burgess has an add-on fine focus knob that will become available at low price.
To add fine R&P raises the effort and cost at which point one would just buy a JMI or WO Crayford.
The Crayford focuser is actually easier to make than the R&P.
Al M
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Anonymous
Unregistered
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You're all very welcome.
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Anonymous
Unregistered
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Hi,
Joe did a PM to me concerning Modulation Transfer Function(MTF).
This sounds really fancy and complicated especially the way the pros handle. I get confused reading some of their hi-faluting papers.
We can see some of this function in our telescopes. Generally, unobstructed scopes(refractors), have better planetary contrast than the obstructed telescopes(Newtonians, SCTs, etc.)
When very fine resolution is considered(double stars), the tables are reversed.
When a perfect telescope is pointed at a star you will get a diffraction pattern. There will be the Airy disk(a tiny disk), which will have 84% of the light and the rest of the light is transferred to the diffraction rings.
The obstruction of a telescope will transfer some of the light energy from the Airy disk to the diffraction rings. This has an effect of shrinking the Airy disk and improving double star resolution. Of course, these scopes have to be optically very good. With the Newtonian, there are spikes produced from the spider supports that may interfere with the binary resolution. Just rotating the tube a little can solve this.
SCTs and Maks don't have the spiders, so that spikes aren't an issue. Maks usually have a, somewhat, better optical quality than the SCTs, because their correctors are easier to figure accurately. This doesn't mean that the SCTs don't achieve excellent quality, because many do.
A while ago, at a star party, I had my 5" achro next to a 5" Tak APO. I had selected a double star with a seperation of 1". Both scope performed identically.
Someone had a 12" Meade SCT nearby. I usually thought that those scope were too sloppy to do a good job on doubles.
I was wrong, that 12" had a beautiful diffraction pattern and that same double was resolved so well and both refractors went away with their tails between their legs.
Al M
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Anonymous
Unregistered
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For more on MTF, try this site:
http://www.licha.de/AstroWeb/articles_fullsize.php3?iHowTo=20
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rboe
Numbfinger
Reged: 03/16/02
Posts: 39739
Loc: Phx, AZ
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Al;
Mirror arrived this afternoon with high thin clouds around the skys. Hope to install and give a quick look see tonight. Very surprised to see the box pointed rightside up when it arrived!
Now if I can home in one piece...
Ron
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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Stacy
Carpal Tunnel
Reged: 09/15/02
Posts: 2076
Loc: The Great Northwest
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Quote:
Very surprised to see the box pointed rightside up when it arrived!
Must have been a new guy!
I'm off to the University to see Al's presentation, should be interesting if I can follow along ... Good luck with your mirror Ron.
Regards,
Stacy
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NS11-GPS-XLT, XT-8, 120ST, AEX-10X50
www.darksky.org
Human history becomes more and more a race between education and catastrophe.
- HG Wells
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