memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hello everyone,
I am new to this forum. I recently bought a Celestron C90 Astro and am very happy to have finally found one locally (here in Germany, nearby Cologne) to replace my Meade ETX90.
Now a few questions have come up about my new toy.
1. How can I drive the telescope on batteries? I have the European version that has a 220 V 50 Hz synchro motor. Did Celestron (or any other maker) ever make battery controls or something like that? Today, no one seems to care any more because modern motors are always low voltage DC.
2. Probably there is a replacement DC motor available from Celestron for later C90 units? This would of course also work. I would not mind changing the motor as long as nothing inside the mount needs to be permanently changed. However, the original motor is just sooo nice, it is totally silent and works just a charm on AC mains so I'd rather have some kind of external battery pack/control that just drives the old motor.
3. I would like to get an eyepiece with the maximum FOV that the C90 permits. Right now, I have a 20 mm SWA eyepiece that is rated with a FOV of 66 degrees. Together with a 1 1/4 diagonal. (So far, I do not have a "proper" connection so I used my camera adaptor to fix the 1 1/4 equipment.) With 1000 mm focal length this should give 50x and thus, 66/50 = 1.32 deg. But I can see that the edge of the FOV in the eyepiece is slight blacked-out so I assume that the C90 is just not capable of giving such a "big" FOV. The maximum seems to be rather 1.25 deg. or so. Can anyone confirm this?
4. Focusing is not so easy because the whole front barrel of the C90 needs to be turned. I have seen that special focusers are sold e.g. to be mounted on the back of a C8 or other SCT but I think they are somewhat big and bulky, is there anything very small or "short" that could probably be fitted as an external focuser, at least for fine focussing?
So many questions.... any input would be appreciated!
CS,
Thomas
PS. below is my first attempt to take a picture of the good old moon. It was hard to focus as my DSLR does not have live view.... but I still like it. With the ETX, I had trouble using the camera at all because the scope mount would not handle it properly....
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Celestron C90 Astro
Meade 2080 LX3
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rmollise
Post Laureate
Reged: 07/06/07
Posts: 4573
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Quote:
Hello everyone,
I am new to this forum. I recently bought a Celestron C90 Astro and am very happy to have finally found one locally (here in Germany, nearby Cologne) to replace my Meade ETX90.
Now a few questions have come up about my new toy.
1. The easiest way to power the scope away from mains current is with a 12volt battery and an inverter. I know this doesn't make for a very portable solution, but the only other alternative is to replace the whole drive system with something of your own devising. A smaller 12v battery and a small inverter in a plastic battery box would be workable.
2. As above, there is no off-the-shelf DC motor replacement.
3. The little guy has a small baffle tube and is not really suited to wide-field viewing.
4. I suppose it's possible you could attach a Crayford focuser to the C90 via a LAR, but I would be skeptical about the scope having enough back focus to accomodate one.
The C90 is a great scope for what it is...enjoy it that way; "IT IS WHAT IT IS."
NICE Moon pic!
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Uncle Rod
Rod's New Book:
Choosing and Using a New CAT
Available now!
Edited by rmollise (08/20/08 08:04 AM)
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Jay_Bird
scholastic sledgehammer
Reged: 01/04/06
Posts: 959
Loc: Nevada 36N 115W
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Hi Thomas
Uncle Rod is a tough icon/expert act to follow...
I've been using a garage sale C90 orange tube spotter version.
3. You're right - this scope has a small rear baffle. I have used 30mm Plossl with no complaints, for about the same FOV.
3 & 4. With a 'large adapter ring' or LAR and a 2-inch SCT diagonal, even though the view is vignetted at the edges, a 32mm or 40mm 2-inch eyepiece fits in the Double Cluster, or Andromeda and companions, so this scope can pushed a little more outside it's envelope, not ideal but more fun when it is the only scope that I take on a trip.
The really large 2-inch diagonal moves the front tube a few turns closer to the back of the scope at infinity focus. My example seems to have less woear on the focusing threads in that part of the focus travel, so the big diagonal helped a little with focusing. The size of the 2-inch diagonal and a 2-inch eyepiece on this scope looks a bit comical.
Since the C90 still has several turns of focus travel left 'beyond infinity' even with a large 2-inch diagonal, that makes me think a helical focuser would fit in the 2-inch diagonal for fine focusing, or that a simple/short SCT add-on focuser might fit, I will experiment if I find one cheap.
I try to keep in mind that it would be easy to spend more on such accessories than the scope itself cost before I get too carried away.
Nice moon photo! FYI the C90 also makes a nice, very close focusing daytime spotting scope with an erect-image diagonal.
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'these things stand like stone - kindness in another's troubles, courage in your own' Gordon
C-8, Nighthawk, C-90; Binoculars 6-11x21-80mm; Paragon p-mount
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dougspeterson
Pooh-Bah
Reged: 09/01/04
Posts: 1041
Loc: Murrieta, CA
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Watch out for vignetting with a 2" diagonal, I already learned that the F6.3 compressor for the bigger SCTs stops down the aperture. You can check for this by focusing a high powered eyepiece, then look thru the front end and see if the tiny exit pupil disappears off axis before your line of site moves off the edge of the corrector.
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18" Dob
12" SCT
8" TMB F6 + Chromacor
6" F6 APM/LZOS Fluorite triplet, 32", 32lbs
2ea. 6mm singlets, one blind
"--Granted, that's a worse case scenario. The destruction might in fact be ... limited to our own galaxy."
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Protheus
Vaguely offended
Reged: 09/01/07
Posts: 5080
Loc: Illinois, US
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Hey Thomas,
The C90 is a cool little telescope. I have an older Meade that is similar to it. I'm curious about why you wanted to replace one 90mm Mak (the ETX90) with another? 
Chris
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"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hello together,
wow - thanks for the fast replies ! This is a great help for me !
1. I have found another thread at Cloudy Nights where it is stated that the LAR from Meade (that they sell for ETX) would not fit the C90. Is that true? Having both the ETX90 and the C90 here at the moment, I find that I can mount e.g. the Meade photo adaptor and the 45deg. Amici prism without problems onto the C90. So what could be the reason that the Meade LAR would not fit? The advantage would be that I could just order it new, while sourcing an original Celestron LAR is probably rather complicated.
2. When searching for diagonals, I found this:
1 1/4" diagonal with SCT thread and micro focuser
This is a diagonal made by German dealer Baader Planetarium. (sorry German link only, I try to explain what the website says:) While at 119 Euro it surely seems a bit pricey (but with all scope stuff, 1 Euro buys you the same as 1 USD in the USA ...), it does look rather nice to me (and probably I can find one used or as a bargain sale). On the front, it has a direct screw connection to SCT, so that the diagonal would not move so far away from the scope body. On the eyepiece side, that diagonal comes with a built in "micro focuser", probably this would make it easier to fine-focus. It is advertised at 96% transmission (I believe this is a quality feature?) and 32 mm optical width so probably already a bit more than one would need for the C90.
So I am now looking for that LAR ring and then probably get this nice diagonal and should then be ready to go? Or are there other diagonals that would work? My standard 1 1/4" diagonal would, even when I get the LAR, still require some additional adaptor....
3. I think I will keep my 20 mm 1 1/4" eyepiece for the time being, as it already gives me more or less the maximum possible FOV and nice views, and add some nice eyepiece around 10-12 mm for a bit more magnification like for open clusters and the like, or for the planets when the seeing is bad. The original Kellner 18 mm .96" eyepiece is also really nicer than I thought. But in direct comparison there is just much more FOV with my 20mm and I do like that more. What brands of eyepieces do you use on your C90?
4. Did anyone of you ever dare to mount the C90 on a (heavy) photo tripod? I have a Manfrotto tripod and head that are rated for 5 kgs. For the C90, I would have to make some kind of base to attach it). This would mean that I won't have to carry a second tripod for the scope on trips with me.
Comparing the C90 with the ETX90, I must say that although it comes with a lot of little questions (while the Meade is readily useable out of the box), and although the optics seem very similar, I do already much much more enjoy the Celestron C90 !! and I can surely see what Uncle Rob means with.... enjoy it the way it is.
CS,
Thomas
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Celestron C90 Astro
Meade 2080 LX3
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BRisley
sage
Reged: 09/04/06
Posts: 345
Loc: SW Florida
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I have heard that the LAR for the ETX would fit. I think that the newer C-90s are different but the older orange tube have the right threads. If you can fit other ETX items on it, I suspect the LAR would fit too.
They are definitely nice little scopes, I used mine for daytime telephoto work with an OM-1 for years. With ASA 800, I could often do 1000/sec shots in bright daylight, so motion wasn't a problem. I even did radio controlled planes in flight, they filled the frame and looked like real planes!
Brian
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3 C-8's (2 OT 72/80 and SPC-8)
8" f5 Dob
Meade 4450 on EQ-2
Meade 4501 on EQ-2
Tasco 4.5" on EQ-2
Tasco Starguide 60GT
C-90/Cometron Sky Scanner 80 mounted tandem in a C-8 Fork
Cometron CO-62
Meade 11x80 Bino
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hi everyone,
now I've updated my little C90 with a "hybrid" diagonal that I found locally, it is a GSO mirror diagonal that has a 24.5 connector on the telescope side. Also got a beautiful 12 mm Pentax XF eyepiece as a late birthday present. Now it's cloudy, I'd really like to check out the moon and Jupiter with the new eyepiece.
Question: I notice when attaching the diagonal to the scope, that the scope barrel where the diagonal goes in, is somewhat odd. It's not really a tight 24.5 mm fit, but rather the diagonal has somea little "play" in it. Also it is not a really smooth surface inside (see pic).
Now I wonder if there is any kind of an adapter or the like missing? This is how the scope looks at the end (see attached file). Is that okay or should there be any additional parts where the eyepiece/diagonal goes in?
CS,
Thomas
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Celestron C90 Astro
Meade 2080 LX3
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Don W
Postmaster
Reged: 05/19/03
Posts: 14621
Loc: Wisconsin, USA
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You need an LAR (Large Accessory Ring) that screws on the threads shown in your image. That allows you to use a 1.25" diagonal on your C90. Your unit seems to have been altered with a thumb screw in the side of the threaded area. This is not normal and not the way the scope was designed. The opening does not meet any standard eyepiece or diagonal size. You are supposed to have some sort of diagonal holder that screws to the threads shown.
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Don Wyman
Obsession 18" f/4.5 #1166
W/Argo Navis DSC and Torus Primary
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hi Don,
... thanks! The LAR would help me with 1.25" equipment. I already found a special diagonal that would directly fit onto a LAR, but for now I thought I'd first give the GSO diagonal a try because it was way cheaper...
But how were original 0.95" eyepieces and diagonal attached to the scope? There must be some kind of original Celestron attachment piece, then?
CS,
Thomas
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Celestron C90 Astro
Meade 2080 LX3
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woodsman
Pooh-Bah
Reged: 03/12/08
Posts: 1072
Loc: Colorado Springs, CO
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Quote:
Your unit seems to have been altered with a thumb screw in the side of the threaded area. This is not normal and not the way the scope was designed.
This is EXACTLY how the unit was designed. I have an old c90 astro telescope, and that is how the diagonal inserts into the scope. I have 3 manuals and each one shows that configuration, so I am not sure who told you that wasn't 'normal'. It is how the scope came from factory. Richard
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artisticwoods
C-14 Orange Tube, C-8, C-5, C-90 Astro Model, C8 Schmidt Camera 8" f1.5, C5.5 Schmidt Camera f1.65, SPI 42mm f/19 Refractor, Sears 90mm f/15.56 Ref, Sears 80mm f/15 Ref, Swift 77mm f/13 Model 831, Scope 60mm f/11.7, Sears 50mm f/12
Unitron Model 140 75mm/1200mm, Unitron model 128 60mm/900mm
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Jay_Bird
scholastic sledgehammer
Reged: 01/04/06
Posts: 959
Loc: Nevada 36N 115W
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You beat me to it -- that looks just like my old orange tube C-90, too. The fine machined grooves inside the rear opening are anti-glare, and the big setscrew holds in 0.965 accessories. I have the old diagonal, 2.5x Barlow and 18mm Kellner supplied with the C-90 and they fit smoothly.
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'these things stand like stone - kindness in another's troubles, courage in your own' Gordon
C-8, Nighthawk, C-90; Binoculars 6-11x21-80mm; Paragon p-mount
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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... now I checked the original diagonal and my new hybrid one ... seems that the new one in reality has a very slightly *smaller* diameter. I put a stripe of adhesive tape around it, now it's a tighter fit. But it's probably not a permanent solution... (see attached pic)
Just out of curiosity, I believe the C90 was also sold by Celestron as a 1 1/4" variant? How did they do that? Was there just some kind of adapter added, or were there any alterations to the scope itself? If so, does anyone know further details about that adaptor?
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Celestron C90 Astro
Meade 2080 LX3
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Don W
Postmaster
Reged: 05/19/03
Posts: 14621
Loc: Wisconsin, USA
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Ah yes, I stand corrected. I had a C90 Astro as my first scope. The first thing I did was to get the LAR and switch to 1.25" eyepieces. Forgive my memory, it was 28 years ago.
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Don Wyman
Obsession 18" f/4.5 #1166
W/Argo Navis DSC and Torus Primary
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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My first impressions with various eyepieces, we were watching the Moon and Jupiter with the C90 and a C8, out of the balcony.
18mm original eyepiece seems surprisingly good. I had some kind of ghost image when viewing Jupiter and moving my eye a bit. I dunno if that's normal. Also had a short look at the Pleiades which were standing directly next to the Moon.
20mm Skywatcher Ultrawide eyepiece - not any better than the original 18mm. Of course, it give a wider FOV but the extreme corners were slightly shadowed and it is not that easy to look into. I prefered the "viewing experience" of the original eyepiece.
35 mm Baader eudiascopic eyepiece - surprisingly good. It has about 50 deg FOV. The edge is shadowed but I would say at least 45 deg are clearly visible. It was able to show the whole Pleiades at once.
26 mm Celestron Plössl (late 80s) - was not bad but very "nervous" to look into.
We also tried a 9 mm and a 6 mm Vixen Ortho but I found both eyepieces are already pushing it a bit, also it becomes hard to focus. That's why I decided to get a 12 mm ep instead, more easily handled by the scope, the focuser and the mount.
I also got a 25 mm original eyepiece (0.96"). The seller also had a 40 mm 0.96 Celestron but that's really not nice, there was probably 25 deg FOV or so.
So I guess the optimum is to use the 25 and 18 original eyepieces, the 12 mm Pentax as a "luxury" planet&moon eyepiece, and to find something wider than 25 mm. The Celestron 26 Plössl was not so very convincing, the 35 Baader was better but it's a very heavy eyepiece and I'd like to find some eyepiece that does not show any shadowing in the corner. Probably an old 30 mm or 40 mm Kellner or Ortho, if they were ever made. I got the impression that the 25 mm Kellner 0.96 is easier to the eyes than a Plössl, also I can't make use of the wider FOV of the fancier eyepieces anyway... so thats why I'm thinking Kellner now...? Any suggestions?
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Jay_Bird
scholastic sledgehammer
Reged: 01/04/06
Posts: 959
Loc: Nevada 36N 115W
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Since you seem to like the 35mm eudiascopic aside from some vignetting at edges of view, you could try a 30mm or 32mm Plossl, or the 30mm eudiascopic/Ultima/Parks Gold/Ultrascopic. I find the 30mm Ultima comfortable with the C90 for day and night use at about 33x and 1.5° field of view (about 52° apparent field of view).
HOWEVER - in the vein of Uncle Rod's "enjoy it for what it is" thought - is the vignetting with the 35 really difficult to ignore? You've already tried a pretty wide range of EPs with this scope...
I use either the LAR or a screw-on 45-degree correct image 1.25-inch diagonal. I don't notice vignetting with a 30mm eudiascopic-type eyepiece, and since the 30mm and 35mm are so similar I wonder if you are more sensitive to this and I am less so.
While I do notice vignetting with the silly extreme of 32mm or 40mm 2-inch eyepieces, I overlook that for the 2° FOV they provide...
You might see slightly less vignetting with an LAR (maybe enough for you to like the 35mm after all) since the LAR will do away with the slight added vignetting from the .965" barrel of the hybrid diagonal.
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'these things stand like stone - kindness in another's troubles, courage in your own' Gordon
C-8, Nighthawk, C-90; Binoculars 6-11x21-80mm; Paragon p-mount
Edited by Jay_Bird (08/28/08 02:53 PM)
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Protheus
Vaguely offended
Reged: 09/01/07
Posts: 5080
Loc: Illinois, US
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Quote:
I can't make use of the wider FOV of the fancier eyepieces anyway... so thats why I'm thinking Kellner now...?
Why do you say that?
Chris
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"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hi Chris,
I say that because with the 20 Wideangle or 35 Baader I get vignetting at the edge of the FOV. The old Celestron 26 Plössl just barely shows the vignetting.
The rear baffle (that goes through the main mirror) has a plate on front of it with a circular aperture of probably 15 mm or so? I believe this is set in to block any light coming through the front lens to directly enter the eyepiece. But this also limits the available FOV, as far as I can tell.
So I think it's probably best to just stay within this limitations.
CS,
Thomas
PS. pic shows the aperture opening of the baffle. The baffle itself has more or less 24.5mm inner diameter, but due to the aperture that is installed at the front, it is limited to probably 15 mm or so. Sometimes I wonder if one could make this opening a bit wider, or if that already would harm overall image quality .... or if it just would be visible in daylight viewing (I'm not using the scope at daylight anyway)
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Celestron C90 Astro
Meade 2080 LX3
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Protheus
Vaguely offended
Reged: 09/01/07
Posts: 5080
Loc: Illinois, US
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Quote:
I say that because with the 20 Wideangle or 35 Baader I get vignetting at the edge of the FOV. The old Celestron 26 Plössl just barely shows the vignetting.
Ahh, ok. I haven't tried something quite that wide in my own similar scope for comparison, but you might give a focal reducer a try, with a somewhat higher magnification eyepiece. Could work. I have a .5x, and my 90mm Mak responds really well to it.
Chris
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"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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....somewhere, I found a short reference to someone who did apparently really change the rear baffle, in that case to enable the C90 to take full 35mm pictures without shading in the corners.
I wonder if it would harm the scopes other qualities to do this "surgery" - or if a rear baffle with a bigger opening would only mean that contrast in daylight goes down (which does not bother me) ?
@ Chris - if I just throw in a .5x focal reducer, that would not improve the maximum field of view? I think I would again see the black corners with the wider eyepieces....
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Celestron C90 Astro
Meade 2080 LX3
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Protheus
Vaguely offended
Reged: 09/01/07
Posts: 5080
Loc: Illinois, US
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Quote:
@ Chris - if I just throw in a .5x focal reducer, that would not improve the maximum field of view? I think I would again see the black corners with the wider eyepieces....
It wouldn't (couldn't) do much, but I suspect it might do something. If you had one, it would be worth a try. If you don't (and don't want one), I'm not sure I can really recommend just running out and buying one with the hope that it will fix this particular problem...
Chris
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"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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no, I haven't got a reducer on hand... sadly.
Judging on what I've seen through the various eyepieces, I think I'll either get a good 25 mm Plössl or a Baader eudiascopic eyepiece (the Baader is supposedly identical to the Celestron Ultima ED) with 25 or 30 mm for low magnification.
In the meantime, I've designed a platform that mounts under the C90 Astro base so I can attach it with my Manfrotto tripod. It will be machined in CNC from 8 mm (1/3") aluminum. The grey area in the drawing is where the scope will go, the holes are either to save weight or to put 1 1/4" eyepieces in.
I hope it will turn out well
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Celestron C90 Astro
Meade 2080 LX3
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Protheus
Vaguely offended
Reged: 09/01/07
Posts: 5080
Loc: Illinois, US
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Good luck with it. The dovetail adapter I had to cook up for my similar Meade (which has a single 1/4" 20 camera-tripod style attachment point) was not nearly so complicated, and I was able to just get some parts from the hardware store for it. This should be cool.
Chris
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"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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I admit I got a bit away with it when I designed this adapter .... but the guy who does the CNC work said it would be good this way
I just sold my Meade ETX, the buyer will collect it tomorrow locally. Also a little 76 mm Newton that I once got from a friend will go these days.
Could be just the right time to start thinking for the next scope to complement the C90 Astro ... 
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Celestron C90 Astro
Meade 2080 LX3
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hi everyone,
now I got a Televue Plössl 25 mm ep. The trouble is, even with this moderate eyepiece (approx. 50deg apparent fov) the scope exhibits vignetting at the edge. The rest of the image is superb but the vignetting somehow just disturbs the viewing experience.
25 mm means approx. 40x magnification, with 50deg this is a true fov of about 1.25deg which really shouldn't be too much for this type of scope?
Did anyone ever successfully solve this?
Second question: The front tube of the scope is secured with three allen screws. What size are they? 1/16" ? I am asking because I have to mail order inch-sized allen tools over here, as we have everything with metric measures, and I don't waht to order any tool that wouldn't fit.
Thanks,
Thomas
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Celestron C90 Astro
Meade 2080 LX3
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hi everyone,
it's been a year after that last post and I just want to update this thread because in the last days, I've fallen in love with the C90 again
I find myself enjoying it much more in its "original" form, that is with an old quality 0.96" star diagonal and the old eyepieces, than with the 1 1/4" newer eyepieces that I thought so much of in this thread.
The 1 1/4" eyepieces are still there and accompany my newer toy that I bought in the meantime (Meade 2080). Probably having a second, much bigger and somewhat more "state-of-the-art" scope also made me see the C90 with clearer eyes, as what it is:
It is a little vintage telescope that works best with its vintage eyepieces. For whatever reason there might be (I did not take the scope ever apart to find out), the view through the original Celestron 40 mm 0.96" eyepiece (30 deg apparent fov - approx. 1.2 deg true fow) is absolutely perfect right to the edge, while all my trials with those 1 1/4" eyepieces that should give the same true fow turned out to be somewhat compromised at the very edge of the image. So be it...!
The small apparent fov of the longer eyepieces is just something that adds this certain "classic" atmosphere to any viewing experience with the C90 - while I found it even somewhat boring to use newer 1 1/4" eyepieces with it! It's a bit like having a classic car with a tuned engine and modern seats and at some day to realise that you've somehow spoiled the purity of the original.... (of course no pun intended to people who modify their scopes and their cars - its just that for me and the C90, this didn't work out !)
Probably that sounds strange and no one can understand what I mean! But probably it just shows I should think of another quirky old little telescope to accompany the C90. Now if these Zeiss Telementors would not be that freaking expensive....
regards,
Thomas
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mwedel
super member
Reged: 12/16/07
Posts: 183
Loc: Claremont, CA
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Cool! I think it's awesome that you're loving the scope and that you rehabilitated the thread.
I've always been curious about the C90 and I'm pleased to say that I've got one coming in the mail, thanks to CNC. The new scope curse has already struck--last night our club had a moon party and got totally clouded out. I hope that's all the weather gods have to throw at me, but I've been doing this long enough to be cautious!
I have come to terms with the fact that I am a nut for small Maks. I've owned four between 70mm and 105mm. My favorite of the lot, and probably my favorite telescope of all time, is my Orion Apex 90. I got it to serve as a grab-n-go and travel scope, and it does, but it also fills a larger and even more important role: it's my no excuses telescope. It is so small and so trivially easy to set up and gives such good views that I don't stop and think about whether I should take it along on a trip or whether I should haul it out to look at the moon on a nice evening. I just do. No excuses!
I have bigger scopes and use them, too. They just don't have the same indefinable appeal. Sounds like you feel something similar for your C90.
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Orion XT6 "Shaft"
Little Maks: Orion Apex 90, Celestron orange tube C90, Synta MC90
Edmund Astroscan "Baby Red"
76mm ongoing ATM experiment
Celestron UpClose 10x50
Celestron SkyMaster 15x70
10 Minute Astronomy
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Erik Bakker
professor emeritus
Reged: 08/10/06
Posts: 532
Loc: Haren, The Netherlands, Europe
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Quote:
Watch out for vignetting with a 2" diagonal, I already learned that the F6.3 compressor for the bigger SCTs stops down the aperture. You can check for this by focusing a high powered eyepiece, then look thru the front end and see if the tiny exit pupil disappears off axis before your line of site moves off the edge of the corrector.
Agreed. The C90 cannot possibly illumimate a 2" ocular. Stick to 1 1/4' and try what suits your needs best: something around 25mm or 32mm, both of which may show some vignetting depending on the particular design of the eyepiece. In most cases, a Plossl or Ortho will work best.
CS,
Erik
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Visual astronomer, main instruments:
Fully mounted Questar 7 P-BB
Celestron C 102F f/8.8 fluorite
Vixen FL 70S f/8 fluorite
Celestron C 55F f/8 fluorite
Sets of Zeiss, TeleVue and Brandon eyepieces
Zeiss 7x50 Marine B/GA
Zeiss TM german equatorial
Gitzo 224 with Manfrotto 501 fluid head
Unitron alt-az mount
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Quote:
Agreed. The C90 cannot possibly illumimate a 2" ocular. Stick to 1 1/4' and try what suits your needs best: something around 25mm or 32mm, both of which may show some vignetting depending on the particular design of the eyepiece. In most cases, a Plossl or Ortho will work best.
Hi Erik,
yes 2" is not possible at all with the C90. (BTW, the russian MTO 10/1000 Maksutovs work fairly well with some 2" eyepieces, there are even some commercial 2" adapters available. The MTO also can be used with a full-size 35mm camera while the C90 will not cover the corners of the 35mm frame.)
My C90 would not 100% illuminate even the TeleVue 25 mm Plössl. And although it's not exactly a "big" eyepiece, even this and the 1 1/4" diagonal already spoil the counterbalance of this small scope.
As I said, I have stopped using any 1 1/4" eyepieces with it anyway and now enjoy it much more with the original 0.96s
CS
Thomas
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Celestron C90 Astro
Meade 2080 LX3
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hello,
Quote:
I have come to terms with the fact that I am a nut for small Maks. I've owned four between 70mm and 105mm. My favorite of the lot, and probably my favorite telescope of all time, is my Orion Apex 90. I got it to serve as a grab-n-go and travel scope, and it does, but it also fills a larger and even more important role: it's my no excuses telescope. It is so small and so trivially easy to set up and gives such good views that I don't stop and think about whether I should take it along on a trip or whether I should haul it out to look at the moon on a nice evening. I just do. No excuses!
I have bigger scopes and use them, too. They just don't have the same indefinable appeal. Sounds like you feel something similar for your C90.
yes, you sum up everything that I like of my C90. It was a youth's dream anyway. Back in the 80s all these scopes were totally out of reach for me, at the time I had a small (also nice, of course) 60/800 Vixen refractor. I also always liked the Meade 2044 when it came out - but later I learned that the optics have a rather mixed reputation, anyway the C90 is even smaller and more classic in design and operation. I LOVE that C90 fork mount, its a beautiful design and offers very smooth operation, there is really nothing I find to complain about after one year ownershop.
The whole scope just feels like it is a quality scale model of a real big classic observatory. It takes you back to the 70s or even 60s in apperance and operation. This is totally different to the Meade ETX90 that I owned previously. The ETX hat rather better optics (but does that really matter? I'm not using it above 80x or so anyway...) and the ETX worked also much better with 1 1/4" eyepieces as it was designed for that in the first place. But the feel of the whole assembly was - to me - not "quality" at all. I might end up buying another ETX90 when I find a computerised version for a real bargain price at some time - the ETX is then such a different experience to the C90, and in my opinion it is a future 1990s classic in it's own right, that I might give it a second try.
What I now like so much about the old little eyepieces, is their quality feel: It's not the "wow, this is the best you can ever have, cost no object at all" quality of a Nagler. But it's more a "we know it's small, it has limited technical data, but still we want to make it high quality" approach that shines through with these old eyepieces.
Now I have the original (i.e. Vixen or Celestron) 25 mm, 20 mm, 18 mm eyepieces, after some time I now also sourced the 40 mm Celestron, I will then need the 30 and 12 mm, probably the 9 mm as well, to have a complete collection. The even higher magnifications I personally find not so important with this scope. Also, classic feelings aside, the eye relief with say a 6 mm ortho is really not so nice for me. We have a 6 mm and 9 mm Vixen ortho (1 1/4") and I really dislike using the 6 mm, no matter how classic it might be while the 9 mm is still somewhat okay.
The photo attached shows both my 90s, back when I still owned the ETX.
CS
Thomas
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mwedel
super member
Reged: 12/16/07
Posts: 183
Loc: Claremont, CA
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Nice photo!
My C90 arrived today, and I got in a little driveway birding with it this afternoon, and then the moon, Jupiter, and Pleiades this evening. It's a lovely little scope. I see what you mean about the old-fashioned feel of the thing. It's small but dense, almost all metal. Optics are great. Charm is unquantifiable.
My Apex 90 will now have a run for its money as my grab-n-go and travel scope. The C90 beats it in two important areas: it's even smaller (and I don't have to explain the appeal of that, right? ), and at f/11 it has a slightly larger field of view than the f/13.9 Apex. Doesn't sound like much, but I can get all of the Pleiades together in the C90, which I've never managed with the Apex.
So glad I finally got one!
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Orion XT6 "Shaft"
Little Maks: Orion Apex 90, Celestron orange tube C90, Synta MC90
Edmund Astroscan "Baby Red"
76mm ongoing ATM experiment
Celestron UpClose 10x50
Celestron SkyMaster 15x70
10 Minute Astronomy
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Congratulations to your new toy and great to hear that you already had the initial first looks through it! But, as you said, having a scope SO portable there is no excuse at all to NOT using it
Sometimes I even use the C90 from my bedside table, when the moon is visible through the window. I personally find it even aesthetically nice in that place but not everyone would agree to this, I fear
What kind of eyepieces did yours come with, especially which one is the one where the whole pleiades would fit in?
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Celestron C90 Astro
Meade 2080 LX3
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mwedel
super member
Reged: 12/16/07
Posts: 183
Loc: Claremont, CA
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Quote:
What kind of eyepieces did yours come with, especially which one is the one where the whole pleiades would fit in?
Mine came with a mirror star diagonal and 30mm and 18mm Kellners. I'm pretty sure they were part of the original kit, because all three fit in a box with a styrofoam insert. The whole rig came in a nice foam-lined hardcase...gone are the days when something like that was included gratis!
With the 30mm EP I can just barely get all of the Pleiades in. I like both of the little eyepieces, they are a bit dated by today's standards but like you said, the quality is evident. Time to hunt down some more focal lengths, methinks.
I like the idea of a telescope on the bedside table. With the whole mini-observatory vibe the C90 gives off, I'm sure it looks great. Unfortunately all I can see out my bedroom window is trees. But trees have birds and squirrels, and I'm having fun with the C90 as a daytime spotter, too. Not from the bed, though!
As you might have guessed from my comments above, I have been on a quest to find the smallest, most portable telescope with good optics and mechanics. I like long f/l scopes and I've always been drawn to Maks. I started out with an Orion 102mm, then got the 90mm (as Ed Ting wrote, "because it was there") and decided I liked it better. In exchange for giving up 10% of the aperture I also got rid of 10% of the length and close to 20% of the weight.
For a long time the Apex 90 has been my optimum. I tried a Celestron C70 spotting scope, but the views were too dim and the mechanics were rough (other samples may be better). I tried a Synta MC90, a weird little f/5 Mak also sold by Omcon and Orion, but the views were soft. The C90 was about the only thing smaller (well, shorter, anyway) than the Apex 90 that I hadn't tried.
One of my fellow club members has a fully equipped Questar 3.5 that he brings to public outreach events. It's a sweet scope for sure, but going head-to-head against the Apex 90 I didn't see any differences. Saying so might bring down fire and brimstone from Questar devotees  , and I happily admit that other samples of both scopes might have yielded different results. The point is that optically I don't feel like I am giving anything up with the Apex 90. I'll be curious to compare things over the long haul, but so far the C90 seems the equal of the Apex. The shorter f/l gives a wider field but doesn't seem to affect image quality, which I guess makes sense: f/11 is still pretty darn long.
Nice to chat with someone who shares my obsession!
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Orion XT6 "Shaft"
Little Maks: Orion Apex 90, Celestron orange tube C90, Synta MC90
Edmund Astroscan "Baby Red"
76mm ongoing ATM experiment
Celestron UpClose 10x50
Celestron SkyMaster 15x70
10 Minute Astronomy
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1269
Loc: Ottawa, Ontario, Canada
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How to minimize vignetting, and other concerns.
Install the available adapter collar which allows to use 1-1/4" accessories. If a 0.965" diagonal is used (commonly inserted directly into the baffle tube), the even sub-24.5mm diameter barrel only further restricts the available field.
The adapter ring also places the now-larger diagonal *farther* back behind the baffle opening. This further de-focuses this small opening, thus making the resulting vignetting less sharp and concomitantly less obtrusive.
About the approx. 15mm diameter plastic baffle on the innermost end of the baffle tube. It is there to block non-image forming light which would otherwise directly fall on the image surface. Even so, if you remove any accessories and look into the rear baffle opening at an extreme angle, you may see a small sliver of light passing directly through the front corrector. This light can actually reach the corners of a 35mm film frame. But in normal use, where the diagonal and eyepiece field stop diameters are more restricted, this is not a problem. That plastic part is there only because the C90 doesn't use a *tapered* baffle tube as is found on high-end Mak-cass 'scopes--it's a cheap 'n easy alternative.
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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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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Hello Glenn,
thanks for your information. This is very valuable for me.
Probably I will, at some point, also collect a glossy black C90 as they were sold in the later 80s which as far as I know came standard with 1 1/4" eyepieces? And then try again the 1 1/4" eyepieces.
regards
Thomas
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Celestron C90 Astro
Meade 2080 LX3
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memento
member
Reged: 08/19/08
Posts: 27
Loc: 51N 7E
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Quote:
Mine came with a mirror star diagonal and 30mm and 18mm Kellners. I'm pretty sure they were part of the original kit, because all three fit in a box with a styrofoam insert. The whole rig came in a nice foam-lined hardcase...gone are the days when something like that was included gratis!
now you mention it: My C90 also came with a black hardcase. I don't know for sure that it's original.
I am now offered a pair of 18 mm 0.96" Vixen orthoscopic eyepieces. (The Celestron 18 mm that came with my scope is a Kellner.)
As I now could have *two* identical 18 mm Orthos, I'm wondering how the C90 would do with a binoviewer....... ?
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Celestron C90 Astro
Meade 2080 LX3
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DiffractionRings
newbie
Reged: 08/06/09
Posts: 2
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Another C90 appreciater here(rummage sale find). This one is black, all metal except big rubber focusing ring. I think it has a .965" to 1.25" mirror diagonal, and came with a Olympus stereo microscope eyepiece 10x that does surprisingly well, someone said it would be a 25mm equivalent ('tho it had a "23" engraved on it, along with the 10x) so mag. would be about 40x.
I didn't notice vignetting, but don't know how to identify it in a telescope (I am familiar with it in photography).
So, I want it as a birding spotting scope and very informal astronomy scope - two young and interested daughters (mags of about 35 and 60 or so, 2 different eyepieces), so can the experts here suggest what other eyepieces I should consider? I only have $35.00 into it, but its in very good shape, so used market, and a good match to the older C90 with the 1000mm f11 focal length?
Should I really try to track down the large aperture adapter collar, a true 1.25" mirror diagonal to replace the hybrid diagonal, to avoid vignetting? Thanks!
Bruce
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RLTYS
Carpal Tunnel
Reged: 12/18/04
Posts: 2156
Loc: New York (Long Island)
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DiffractionRings
Welcome to the Cloudy Nights Classic Telescope Forum. I'm sure you'll get the info you need here.
Rich (RLTYS)
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10" F4.8 Refl.
4" F5 Refr. (Genesis)
3" F4 Celestron FirstScope
50mm F12 Refr. (Tasco #6TE-5)
12x63 and 10x50 Binoculars.
"I want to do more then just look."
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albert1
Pooh-Bah
Reged: 01/01/07
Posts: 1369
Loc: Northern New Jersey
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C-90 on the juice. Just couldn't enjoy the helical focuser so I added a SCT focuser and now I'm getting much more use out of this little guy. I almost had to bottom-out the helical focus ring but was happily surprised it comes to focus on all EP's I've used. It's nice to see other folks are still enjoying this vintage "built like a tank" scope.
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Albert
1 Great 'ole Newt
4 Good 'ole Newts
2 Great 'ole Cats
1 Lousy 'ole Newt
One of these days I'll try a Refractor better than my 90mm finderscope
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Jeff Lee
professor emeritus
Reged: 09/17/06
Posts: 509
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I've got a 1996 starbright, rubber coated C90. When used with the LAR (large accessory ring) and a high quality diagonal, and good EP's it's a great little scope. Built like a tank, but it does take some cool down time. .
I use a fairly large CF tripod and a Ball Head rated at 22 pounds. Added a red dot finder and upgrade to a 6 x 30 LER finder, and it's been to lots of places. Cool little scope. bought mine new as a spotter/birder/astro scope.
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Jeff Lee
C90,C5,C8, 10 x 50's
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astroman3113
newbie
Reged: 08/05/09
Posts: 3
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hi. i have the 1000 mm f.l. (older) c90, but the rubber armored one. i have it on an older celestron photo tripod and this works nicely, esp. with the red dot finder. i did contact precise parts (saw an ad in the back of sky and tel) to make an adapter for a 1.25 in diagonal. it screws onto the back. i suppose i could have done something that costs less than this custom part if i had been reading sites like this one. anyway, the astrotech dielectric diagonal works well with the scope. it seems that 80-100x is the max useable power before the image softens. it's just so darned easy to grab and set up, i tend to bring it out even when using my c8 or 60mm refractor. and for trips, it's a no brainer, with such a small carrying case. overall, a great scope!
dennis r.
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