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Something for nothing: Celestron C90

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#2276 digsetcrush

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Posted 01 February 2019 - 10:29 AM

Ok, I just received C90 Mak 2 nights ago, used it both nights, reasonably clear in NJ.  First night, I could barely see the 4 stars of the trapezium of M42.  Last night, did see 4 stars with 18mm, 14.5mm EPs, but it was not as clear as I thought it would be?  I had it on a CG3 mount with dew shield.  Cool down for about 45mins.  What is wrong?  My expectations too high?  reading this thread did raise them a bit.



#2277 Jim1804

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Posted 01 February 2019 - 10:48 AM

Ok, I just received C90 Mak 2 nights ago, used it both nights, reasonably clear in NJ. First night, I could barely see the 4 stars of the trapezium of M42. Last night, did see 4 stars with 18mm, 14.5mm EPs, but it was not as clear as I thought it would be? I had it on a CG3 mount with dew shield. Cool down for about 45mins. What is wrong? My expectations too high? reading this thread did raise them a bit.


That seems strange - the Trapezium is clear for me. Have you checked collimation? Mine arrived slightly off from the factory. I’ll check which EPs I’m using this weekend and let you know.

#2278 Jaimo!

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Posted 01 February 2019 - 12:08 PM

Ok, I just received C90 Mak 2 nights ago, used it both nights, reasonably clear in NJ.  First night, I could barely see the 4 stars of the trapezium of M42.  Last night, did see 4 stars with 18mm, 14.5mm EPs, but it was not as clear as I thought it would be?  I had it on a CG3 mount with dew shield.  Cool down for about 45mins.  What is wrong?  My expectations too high?  reading this thread did raise them a bit.

As windy as it has been in NJ the last two nights with the Polar Vortex, I would not be surprised if it was a "seeing" issue.  45 minutes should have been sufficient for thermal equilibrium, again with the Polar Vortex, the change in temperature is almost 65°F...  it may take a little longer.  I'm in NJ, I'll try and get mine out this evening and see it I can catch the E and F.

 

Jaimo!

 

Edit:  digsetcrush, you are one dedicated amateur astronomer!  I noticed that it has been clear the last few nights, but it was WAAAAAAAAAY too cold for me.


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#2279 Sarkikos

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Posted 01 February 2019 - 05:03 PM

E and F might be pushing it for the C90, depending on the seeing and light pollution, of course.  

 

When the temps get much below freezing, I'm almost thankful if the sky is cloudy.  lol.gif

 

Mike


Edited by Sarkikos, 01 February 2019 - 05:03 PM.

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#2280 digsetcrush

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Posted 01 February 2019 - 06:28 PM

As windy as it has been in NJ the last two nights with the Polar Vortex, I would not be surprised if it was a "seeing" issue.  45 minutes should have been sufficient for thermal equilibrium, again with the Polar Vortex, the change in temperature is almost 65°F...  it may take a little longer.  I'm in NJ, I'll try and get mine out this evening and see it I can catch the E and F.

 

Jaimo!

 

Edit:  digsetcrush, you are one dedicated amateur astronomer!  I noticed that it has been clear the last few nights, but it was WAAAAAAAAAY too cold for me.

good points.  yes it was cold, but new scope inspired me.  and thanks jim1804, i will check on collimation.



#2281 Jaimo!

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Posted 01 February 2019 - 06:45 PM

Mike you may be right, according to this article, E and F are 11th magnitude and may require a 6" instrument.  The C90's good, but it does not defy physics.

 

I'm still going to try...

 

Jaimo!



#2282 Jim1804

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Posted 01 February 2019 - 06:51 PM

good points. yes it was cold, but new scope inspired me. and thanks jim1804, i will check on collimation.


It’s cloudy here tonight, but looking clear tomorrow. I’ll check it out then - but last week even my kids could see it clearly, although I don’t remember which EP.

#2283 Jaimo!

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Posted 01 February 2019 - 08:11 PM

OK...  I stand corrected.  Took out the C90 (3.5") and the MK-67 (6") and tried to get the E and F, both scopes had an 8-24mm zoom, Baader Mk IV in the C90 and Celestron in the MK-67 from my back yard in light polluted NJ.  The C90 could only support about 120x until the image dimmed and no gain from magnification, while the MK-67 could pull well over 150x and occasionally up to 200x.  But the C90 gave no hint of the E and F while the MK-67 they came in and out of view as the seeing in the upper atmosphere changed.  I guess the article was right and the C90 is a great little scope, with the emphasis on little.

 

C90 vs MK-67 - small.jpg

 

Jaimo!


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#2284 Jim1804

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Posted 02 February 2019 - 12:14 AM

OK... I stand corrected. Took out the C90 (3.5") and the MK-67 (6") and tried to get the E and F, both scopes had an 8-24mm zoom, Baader Mk IV in the C90 and Celestron in the MK-67 from my back yard in light polluted NJ. The C90 could only support about 120x until the image dimmed and no gain from magnification, while the MK-67 could pull well over 150x and occasionally up to 200x. But the C90 gave no hint of the E and F while the MK-67 they came in and out of view as the seeing in the upper atmosphere changed. I guess the article was right and the C90 is a great little scope, with the emphasis on little.

C90 vs MK-67 - small.jpg

Jaimo!

Nice setup, Jaimo!

#2285 andycknight

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Posted 02 February 2019 - 04:04 AM

Jaimo!, on 01 Feb 2019 - 11:45 PM, said:

Mike you may be right, according to this article, E and F are 11th magnitude and may require a 6" instrument.  The C90's good, but it does not defy physics.

 

I'm still going to try...

 

Jaimo!

 Interesting article, thanks for the link.

 

...But (when I get a really good clear night) I can now see another C90 challenge! grin.gif

 

The article suggests a 3 inch is required to "easily see" the main 4 components, but my old dodgy 60mm department store telescope would clearly show all 4. Even my tiny 62mm F8 cat (500mm f8 mirror lens) with it's huge central obstruction and rather poor optics, also splits them.

 

So like you, I'm now wondering if the C90 can glimpse E and F. I know my C5 reveals both of them reasonably easy. Their magnitudes are certainly bright enough for the little C90, but obviously the challenge lies in the surrounding nebulae and nearby brighter components killing the contrast.

 

Interesting that you note 120x was about the limit on the failed attempt. I have gone much higher when conditions are very good. Using adverted vision to pick up faint stars - I've even used 250x before (a 5mm Ortho) with success.

 

Regards

 

Andy.


Edited by andycknight, 02 February 2019 - 04:06 AM.

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#2286 Sarkikos

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Posted 02 February 2019 - 09:05 AM

You can push the magnification as far as the focal lengths of the telescope and eyepiece will let you.  And even then, you can always throw on a Barlow.  But will the telescope reveal any more detail in the image, show dimmer objects or allow you to split doubles any easier?  There is such a thing as empty magnification.

 

50x per inch is a good power for planets.  You can push it to 100x per inch for double stars.   So for the C90 that's about 175x and 350x, respectively.

 

Mike


Edited by Sarkikos, 02 February 2019 - 09:07 AM.

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#2287 Binojunky

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Posted 02 February 2019 - 01:17 PM

Seeing make a huge difference with the C90, my sample bought last summer bottoms out at around 175-200x depending on the conditions, D.


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#2288 andycknight

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Posted 02 February 2019 - 05:18 PM

Hi, I Just spent an enjoyable hour an a half looking at the trap in M42, with the little C90.

 

I also wanted to try out some of the 0.965" Eyepieces I've recently purchased, so it seemed an excellent opportunity to have a go at spotting E and F (note the Or5 and K9 where not recently purchased).

 

gallery_135796_6581_6619.jpg

 

I started with the Antares 25mm Plossl (50x). M42 Filled the 50 degree FOV, with the wings and fish mouth plainly visible with direct vision. Using adverted vision all kinds of knots and twists could be seen. Stars were nice pinpoints (when the seeing co-operated) to the edge of the FOV. The 4 main components of the trap were easy to see and split. However occasionally "B" would disappear from view. One minor negative with this eyepiece is when a bright star is placed just outside the FOV, you get a little white line at the very edge of the view pointing towards it. But move the star slightly further in or out and the stray light is gone.

 

Moving up to the 12.5mm Ortho (100x) gave a much better view of the trap and surrounding nebula. The FOV was narrower at around 40 degrees, but as expected stars were pin sharp to the very edge. Seeing was an issue now with the tiny first diffraction ring only seen about 25% of the time. Despite spending around 15 mins E and F were not seen. The eyepiece showed no ghosting and it did not matter where you place an object in the FOV, with the image remaining just as sharp in the moments of good seeing.

 

I then tried the little "36x" Eyepiece, which I believe to be a Unitron ~9mm Ortho or Kellner from one of their spotting scopes. On the C90 it gives about 140x. This also has a ~40 deg FOV. When seeing co-operated (which was now quite rare!) it showed a very nice clean and sharp airy disk and first ring, again regardless of where the star was placed in the FOV. Like the 12.5mm there was no ghosting on bright stars. The "B" component was still occasionally disappearing, but during two fleeting moments of good seeing I do believe I saw a point of light where the 'E' component should be. laugh.gif

 

Attempting to confirm, I tried a Vixen 5mm Ortho (not a recent purchase, but a very good eyepiece). However tonight the 250x view was total mush. It was very difficult to focus and clearly way too much magnification. Dropping back to my trusty old 9mm Circle T Kellner (140x) told me the seeing was now quite bad, but about 15 mins later it improved and I spent about another half hour looking for E and F using the K9. I did see a couple more glimpses of E, but not even the slightest hint of F.

 

So I think I spotted E (but I really require a few more sightings to confirm this), but definitely not F. However given a better night F might be possible in the little C90. I'll certainly try again, but this is one of those challenges that requires very steady seeing and transparency which can be quite rare. frown.gif

 

But on a more positive note - I do like the new 0.965" Eyepieces!

 

Regards

 

Andy.


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#2289 Jim1804

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Posted 02 February 2019 - 06:31 PM

Just took mine out - still not completely dark. The Trap is clear and widely split in a 25mm Plossl. I’d suspect seeing, collimation, or both on your scope. It sounds like it’s capable of much better performance than you’re getting.

#2290 digsetcrush

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Posted 02 February 2019 - 07:23 PM

I tried once more last night and it was clearer, from 20mm on down to 9mm, although 9mm lacked some clarity.  I'm a happier camper now. Thanks!  This c90 is a keeper.  Another satisfied customer!


Edited by digsetcrush, 02 February 2019 - 07:29 PM.

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#2291 Jim1804

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Posted 02 February 2019 - 10:01 PM

I tried once more last night and it was clearer, from 20mm on down to 9mm, although 9mm lacked some clarity. I'm a happier camper now. Thanks! This c90 is a keeper. Another satisfied customer!


Glad to hear it! Welcome to the Club!

#2292 Messierthanwhat

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Posted 06 February 2019 - 10:12 PM

I joined the ranks of C90 Mak owners about ten days ago. Except for about a half-hour of partly clear sky that allowed me to collimate on a nice star, we've had cloud cover ever since. But I've been using it for terrestrial views of some distant towers with a 10mm Plossl, and the view at 125X is sharper than I expected. I've also used it with my DSLR. I've flocked the primary baffle, and can hardly wait to see how this little gem might work for lunar/planetary imaging.

 

One mostly academic question: I see that Celestron sells a device labelled as the "Celestron T-Adaptor C90."  Here is one on ebay. I'm not much of an accessory buyer (I lose them tongue2.gif ), but I'm really puzzled by this item. What purpose is it supposed to serve? The visual back of my C90 is T-threaded, as described in the manual I downloaded, and I've already used those threads to attach my T-ring and Canon camera and shoot images of targets 8 miles away. Was there perhaps a time when the 1.25" visual back wasn't T-threaded?


Edited by Messierthanwhat, 06 February 2019 - 10:12 PM.

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#2293 jrbarnett

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Posted 08 February 2019 - 07:50 PM

Ok, I just received C90 Mak 2 nights ago, used it both nights, reasonably clear in NJ.  First night, I could barely see the 4 stars of the trapezium of M42.  Last night, did see 4 stars with 18mm, 14.5mm EPs, but it was not as clear as I thought it would be?  I had it on a CG3 mount with dew shield.  Cool down for about 45mins.  What is wrong?  My expectations too high?  reading this thread did raise them a bit.

The C90 is a bit of a puzzle.

 

While you have 90mm (3.5") of resolving power, your light gathering due to losses in transmission, imperfect reflectivity and vignetting, are equivalent to a ~70mm refractor.

 

If you were used to using a 90mm refractor, your impression of the C90 would be "wow look how much dimmer stars are in the C90 than the refractor at the same magnification".  If you were used to using a 70mm refractor, your impression of the C90 would be "wow, I can split that tight double star more easily at 100x in this scope than 100x in my 70mm refractor but the stars are no brighter".

 

What you describe - seeing all 4 Trapezium stars distinctly at 86x in the C90 during average or better seeing - sounds about right.  Maybe a little "under-performing" the theoretical potential but not far off the mark.  My hunch is that you're not cooled enough.  Unless you store the scope in an unheated garage, you are probably bringing it from a cozy house interior to a very frigid winter exterior.  The scope is hefty.  It's a brick of metal and glass.  Overcoming a big temperature delta is going to take quite awhile.  While it's cooling the shape of the meniscus, primary mirror and length of the OTA are all in motion.  That can affect performance to the degree you describe.

 

Best,

 

Jim  


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#2294 jrbarnett

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Posted 08 February 2019 - 08:00 PM

We're fast approaching *that* time of year again.

 

What time of year is that you ask?

 

Why the Messier Marathon time of year of course.  This year the best weekend for the attempt will be the last weekend in March.

 

For those who don't know, a Messier Marathon is an observing session from dusk to dawn during a New Moon period where, due to the placement of Messier objects relative to one another, it is possible to observe all or at least most of them in a single night.  The Messier Marathon is the brainchild of Don Machholz, the greatest living comet hunter.  Like Don, Charles Messier was a comet hunter too.

 

Messier observed from urban Paris near the end of the 1700s and beginning of the 1800s.  He used a variety of telescopes but his most used instruments were 90mm refractors.  Lenses in his day were not great in figure accuracy or polish, and they were uncoated.  Some of his refractors were "slow" and yielded high magnifications with their fixed eyepieces, though some were "fast" and delivered lower magnification and wider fields of view.

 

Due to the optical technology constraints of Messier's day a Modern C90 probably performs similarly to and perhaps a bit better than any of Messier's 90mm slow achromats.  Observing Messiers through the C90 gives you a fairly "authentic" view comparable to the view Messier saw when he first observed each object.

 

Whether you decide to try a Messier Marathon or not, it's fun to think about this historical authenticity of view shared by you and the object's original discoverer.  Yet another fun aspect of the venerable C90.

 

Best,

 

Jim


Edited by jrbarnett, 08 February 2019 - 08:01 PM.

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#2295 jrbarnett

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Posted 08 February 2019 - 08:13 PM

OK...  I stand corrected.  Took out the C90 (3.5") and the MK-67 (6") and tried to get the E and F, both scopes had an 8-24mm zoom, Baader Mk IV in the C90 and Celestron in the MK-67 from my back yard in light polluted NJ.  The C90 could only support about 120x until the image dimmed and no gain from magnification, while the MK-67 could pull well over 150x and occasionally up to 200x.  But the C90 gave no hint of the E and F while the MK-67 they came in and out of view as the seeing in the upper atmosphere changed.  I guess the article was right and the C90 is a great little scope, with the emphasis on little.

 

attachicon.gif C90 vs MK-67 - small.jpg

 

Jaimo!

I have a relatively easy time with E and F in a 95mm f/16 achromat, but not in the C90.

 

A couple of factors are in play I suspect.  The biggest is that in my experience all significantly obstructed scopes (i.e., scopes with linear COs of >25%) suffer more than unobstructed scopes of the same aperture in poor seeing.  The second is that it takes much longer for my C90 to reach equlibrium in winter when I mainly observe M42 than it does for my 95mm doublet.  The C90 really sharpens up once it is completely equalized with ambient and there are no tube/baffle currents.

 

I find E and F in the 95mm achromat to become definite at around 100x for reference.

 

Best,

 

Jim  


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#2296 Sarkikos

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Posted 11 February 2019 - 07:07 AM

Completing the Messier Marathon is pretty much impossible unless you live below a certain latitude.  My observing sites are all at about 39 N.  My best number for the Marathon was 101 ... but that was for the MMM:  the Memory Messier Marathon.  I found the Messiers from memory. 

 

I could not see nine of the Messiers.  I did not see M74 in the evening.  The morning objects I missed were M70, M55, M75, M15, M2, M72, M73, M30.  I remembered their locations and was looking right at where they were supposed to be.  But they were lost in the bright skies of dusk and dawn. 

 

Maybe if the horizons were lower or the dark site were darker or my aperture were larger (I was observing with a 10" Dob), I could have seen those last nine.  But I doubt it.  I'll never try the Messiers Marathon again unless I can get to a lower latitude.

 

Mike


Edited by Sarkikos, 11 February 2019 - 10:58 AM.


#2297 Jaimo!

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Posted 11 February 2019 - 10:21 AM

I guess Charles Messier could not complete the MMM either, as Paris is 48°N.

 

Mikle, if you were more south, do you think you could complete it with a C90?  A 10" dob does not count...  at least not in this thread.

 

Jaimo!



#2298 Sarkikos

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Posted 11 February 2019 - 10:57 AM

Messier had to observe them throughout the year.  He just couldn't do it all in one night!  :grin:

 

Sure, at a lower latitude, with low horizons and a dark enough sky, the Messier Marathon could be completed by a C90.

 

Mike



#2299 Adun

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Posted 11 February 2019 - 04:45 PM

Messier had to observe them throughout the year.  He just couldn't do it all in one night!  grin.gif

 

Sure, at a lower latitude, with low horizons and a dark enough sky, the Messier Marathon could be completed by a C90.

 

 

C90: check

Low latitude: check

low horizons: tongue2.gif

Dark enough sky: bawling.gif  



#2300 Jaimo!

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Posted 11 February 2019 - 04:47 PM

C90: check

Low latitude: check

low horizons: tongue2.gif

Dark enough sky: bawling.gif  

You need a gas filter.

 

J


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