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tim53
Pooh-Bah
Reged: 12/17/04
Posts: 1454
Loc: Highland Park, CA
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Quote:
I owned both a B&L 4000 (like this one) and a Meade 4" Cass. The B&L did indeed have a Schmidt corrector, whereas I *suspect* the Meade used a simple plane parallel window, as it employed a corrector lens very close to the secondary mirror. Note that light would pass through this lens twice. I didn't like it in use, as the B&L delivered a *much* sharper image.
I don't know of any Meade 4" Cass that used a corrector lens in front of the secondary mirror. The only 4" Meade I'm familiar with that predates the ETX Maks is an SCT (like the one I bought last friday: Meade 2045LX3 which uses a full-aperture corrector at the front of the OTA with the secondary attached.
That particular Meade is actually pretty good, somewhat better than the OTA I bought in 1986 (and still have).
-Tim.
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"We`re just waiting looking skyward as the days come down.
Someone promised there`d be answers, if we stayed around."
-Orchestral Maneuvers in the Dark, "The Romance of the Telescope"
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1283
Loc: Ottawa, Ontario, Canada
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Tim,
Thar she blows! That's the one I'm talking about. Can you remove the stuff from the back end and then peer up into the primary baffle? Look *very* carefully for additional reflections from the coated surfaces of a lens mounted almost against the secondary. If the newer scope doesn't have such a lens, check the older (purchased in 1986) unit.
I desperately want to know if my memory is on or off on this. Thanks!
By the way, a word in the title of that thread, "...carrion..." made me howl. You know that carrion is dead meat, right?  Yes, I know you meant "carry on."
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
My Gallery
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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Strix2
member
Reged: 06/25/09
Posts: 41
Loc: southern Chile (Osorno)
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Glenn,
thanks again for your most enlighting advice. So the fuzzy halo IS the spherical aberration!!!!! Well, this scope is plenty of that...better, plagued of.... My hope was that the halo was an artifact due to vignetting, being the secondary somewhat nearby the primary's baffle, but as you pointed, and of course it makes sense, focusing takes care of that. When comparing the views that my concoctions and factory-made gear brings me, the views through this scope are simple horrible!!!! But you give me a new experimental avenue: setting some sort of corrector INSIDE the secondary tube!!!! For my bouts on swapping optics I was using an old barlow tube, although I was thinking to set the best combination before the prism diagonal, inside the primary's baffle tube. Right now, it seems that repairing this little scope will be a rather difficult task, which of course I’m eager to accept. As my late Dad used to say, “only death could stop us” (he was a military engineer  ). Best regards and thanks for your sound lectures,
Strix
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http://www.cloudynights.com/item.php?item_id=1117
PARAPHERNALIA:
a) Homemade stuff: 3" f/12 reflector; 4.5" f/12 reflector; 80mm f/11 refractor; 80mm f/5 refractor; 83mm f/12 refractor Astrix-Jaegers; 8" f/4 astrograph (on work).
b) Factory-made: Unitron 102mm f/15 refractor; Zeiss Jenoptem 10x50 binos; Jenoptik 10x30 binos; B&L Criterion 4000 SCT (on repair).
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tim53
Pooh-Bah
Reged: 12/17/04
Posts: 1454
Loc: Highland Park, CA
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Glenn:
Well, I'll be dipped!!! I went downstairs with my iPhone fully expecting to say 'AHA!' at you, but you're right! I didn't take apart the LX3, just the 2045 spotter from 1986. Partly because I didn't want to mess with the collimation on the LX3, but partly because years ago I cut the secondary baffle out of the spotter to reduce the obstruction (but my holographic laser collimator confirmed recently that stray light is making it into the primary baffle, so I need to put an aperture stop in there - or put back a secondary baffle!).
There is indeed a correcting lens in front of the secondary. Actually, the lens is a doublet, and the sky end of it is aluminized. So, the "full-aperture corrector" could indeed be a simple optical window, though I don't have any ready way to check that.
Here's a pic of the corrector assembly sitting on a cart in my shop (yeah, the stains under it are coffee spills!, but they're not in contact with the optics). I've unscrewed the sleeve that holds the lens elements in place. The focus isn't quite good enough to show that the secondary is a cemented doublet, but it is.
Depending on the shapes of the various optical elements (likely spheres), this is most likely a Klevtsov Cassegrain, not a Schmidt Cassegrain!
Strix: Does your secondary look like this? If so, you might be able to actually get yours to work without the "corrector" if you can place the secondary accurately where it was designed to go.
-Tim.
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"We`re just waiting looking skyward as the days come down.
Someone promised there`d be answers, if we stayed around."
-Orchestral Maneuvers in the Dark, "The Romance of the Telescope"
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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I did not know that the Meade 2044 / 2045 came with such a type of corrector lens.
However, this does not necessarily mean that the "Schmidt" plate is just flat glass.
e.g. the Russian MTO 100/1000 Maksutovs also have both a corrector lens AND the Maksutov plate in front. With the russian optics, the lens is not placed directly behind the secondary mirror, but at the rear end of the tube. The corrector lens is there to flatten the field for photography PLUS the Maksutov plate is there to minimise the spherical abberation.
It could be that the Meade 2045 uses a similar setup with both a true Schmidt plate AND the field-flatting lens.... ? I really would love to have a 2044 / 2045, it's one of the dreams of my childhood but they are absolutely rare in Europe because no one could really afford them when new.... (those who could would have paid just a little bit more to get a 8" SCT ....).
Is it possible to check whether the Meade 2045 has a true Schmidt plate? It should be curved like this:
http://upload.wikimedia.org/wikipedia/en/thumb/7/7c/Schmidt-Cassegrain-Telescope.png/800px-Schmidt-Cassegrain-Telescope.png
...but I don't know if it's easy to see this kind of curvature with the eyes on a 2045 front plate, even when looking from the front into my Meade 2080 it really looks more like flat glass 
here comes a new idea for you Strix:
http://en.wikipedia.org/wiki/Klevtsov-Cassegrain_telescope
Klevtsov-Cassegrain telescope
these use a spheric main and secondary mirror (I assume - just as your broken B&L 4000 has !!) and one (!) little corrector lens behind the secondary.
The corrector lens itself is more or less the same shape as a Maksutov plate. These look very different from Schmidt plates. Now probably you could source some kind of such a little corrector lens and experiment with this....?
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Celestron C90 Astro
Meade 2080 LX3
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2926
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Hmm maybe an Argunov? The Klevtsov has a positive meniscus.
-drl
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Strix2
member
Reged: 06/25/09
Posts: 41
Loc: southern Chile (Osorno)
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Thomas, Tim, Glenn and Danny,
thanks you all for the suggestions and sound information. I've seen this add before:
http://www.surplusshed.com/pages/item/l3923.html
SS has been my main and reliable source for optics all these years. Although the info is scanty, it seems that permits to make some rough calculations. OOOhhh, this is getting pretty interesting 
Best regards,
Strix
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http://www.cloudynights.com/item.php?item_id=1117
PARAPHERNALIA:
a) Homemade stuff: 3" f/12 reflector; 4.5" f/12 reflector; 80mm f/11 refractor; 80mm f/5 refractor; 83mm f/12 refractor Astrix-Jaegers; 8" f/4 astrograph (on work).
b) Factory-made: Unitron 102mm f/15 refractor; Zeiss Jenoptem 10x50 binos; Jenoptik 10x30 binos; B&L Criterion 4000 SCT (on repair).
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Joe Lalumia
Post Laureate
Reged: 01/24/07
Posts: 3611
Loc: Rockwall, Texas, USA
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Look at what's on Craigslist!
However call before you buy-- check out the seller:
http://dallas.craigslist.org/ndf/spo/1447865593.html
Might be OK to risk $175 to get all the backup parts you will ever need.
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LX90 8" LNT, SV Nighthawk & TelePOD, SV 80/9D & M4 mount, ETX 90, Orion XT10i, 20x80 binoculars, SV-BV3s-- www.texasastro.org
"Great minds discuss ideas;Average minds discuss events;Small minds discuss people." Unknown
Edited by Joe Lalumia (11/06/09 09:40 AM)
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tim53
Pooh-Bah
Reged: 12/17/04
Posts: 1454
Loc: Highland Park, CA
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Strix:
Uncle Rod prompted me to look again at the two 2045's I have. I still haven't taken the LX3 apart, and will be out of town for the next week so won't have the chance to do so, but:
My 2045 Spotting scope differs from the 2045 LX3 in that it doesn't say "Schmidt Cassegrain" on the ring around the corrector lens up front, it says "Mirror Lens". So, while they look virtually identical on the outside, they may not be configured the same optically.
Joe: I think that's the best option for Strix and his B&L. I think there are a couple of these on astromat at any given time, and I seem to see them on ebay semi-regularly, too.
-Tim.
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"We`re just waiting looking skyward as the days come down.
Someone promised there`d be answers, if we stayed around."
-Orchestral Maneuvers in the Dark, "The Romance of the Telescope"
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tim53
Pooh-Bah
Reged: 12/17/04
Posts: 1454
Loc: Highland Park, CA
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I'm taking my lx3 with me so I decided to take a look inside. It is definitely an sct, but the 2045 spotter is definitely not
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"We`re just waiting looking skyward as the days come down.
Someone promised there`d be answers, if we stayed around."
-Orchestral Maneuvers in the Dark, "The Romance of the Telescope"
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Strix2
member
Reged: 06/25/09
Posts: 41
Loc: southern Chile (Osorno)
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Joe and Tim,
thanks a lot for your efforts and kind advice. Although $ 175 will almost a bargain for two B&L SCT, I fear that the price I'll pay here (Chile) will be almost twofold. In the interim I'll go cheap (means experimenting...). Thanks a lot, you are much more than kind.
Strix
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http://www.cloudynights.com/item.php?item_id=1117
PARAPHERNALIA:
a) Homemade stuff: 3" f/12 reflector; 4.5" f/12 reflector; 80mm f/11 refractor; 80mm f/5 refractor; 83mm f/12 refractor Astrix-Jaegers; 8" f/4 astrograph (on work).
b) Factory-made: Unitron 102mm f/15 refractor; Zeiss Jenoptem 10x50 binos; Jenoptik 10x30 binos; B&L Criterion 4000 SCT (on repair).
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1283
Loc: Ottawa, Ontario, Canada
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Ascertaining whether it's a plain plate or Schmidt corrector is easy.
When installed in a scope, carefully observe the two reflected images of an object, one each from the front and rear surface of the glass. Stare at the two images and bob your head about like an Owl. If the space separating the two changes at all, it's a Schmidt.
If you have the 'corrector' removed, then tilt the glass at an angle and move it about while carefully observing through it the scene beyond. A Schmidt corrector, while optically weak, should reveal a slightly distorted and changing view.
--------------------
Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
My Gallery
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2926
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Glen, yes I did this and got a null result. Good suggestion.
-drl
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2926
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Quote:
Look at what's on Craigslist!
However call before you buy-- check out the seller:
http://dallas.craigslist.org/ndf/spo/1447865593.html
Might be OK to risk $175 to get all the backup parts you will ever need.
The report on Excelsis is that some of these were very fine optically, while others, particularly the spotting scope with the gold band, were not. I'm dealing with the latter, so that could be due to the optical window. In its role as a spotting scope, the user would likely have a small entrance pupil and be stopping down the system during daytime use. With a 25mm eyepiece it would have a 2mm exit pupil, as say the eye's 1.5mm or 1mm in full daylight, so it may be adequate during the day. I have a drill press lined up so once I've got the spider installed I'll be able to see and take pictures of the diffraction patterns.
-drl
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