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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: 4565
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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: 958
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: 5067
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: 14620
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: 958
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: 14620
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: 958
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: 5067
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
--------------------
"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: 5067
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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