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Something for nothing: Celestron C90

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2432 replies to this topic

#226 khendrix2

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Posted 07 February 2014 - 10:05 AM

No matter how dark it is here you are, you have to remember that the moon is in bright sunlight. Expose as if you are taking photos during daylight hours.

#227 hardwarezone

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Posted 22 February 2014 - 01:28 PM

The c90 has a $30 price hike in this month.

#228 Sarkikos

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Posted 22 February 2014 - 03:11 PM

Strike while the iron is hot ... and the scope is cheap.

Mike

#229 ChristianG

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Posted 22 February 2014 - 07:47 PM

Has anyone tried to take some snap shots of the moon or Jupiter through the C90? Or is the f/11 and 1200mm focal length make it too slow?


With a Pentax k-x, i.e. 1.53X smaller than 36 mm sensor, or about 23.5 mm wide. Single frame snap shot 1/100th second at ISO 800, no processing except for resizing and compressing. There is evidence of shake from mirror motion unfortunately...

The C90 is great, if the inside of the primary baffle is flocked. I used 200 grit sandpaper painted flat black--improvement in contrast was spectacular! There are a few C90 contrast threads in the ATM/DIY forum section about this, but the search function sucks...

--Christian

Attached Thumbnails

  • 6391123-FlyMeToTheMoonSmall.jpg


#230 t.r.

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Posted 24 February 2014 - 08:42 AM

Well, I finally got out with the C90/Orion 70MF combination last night. I do have some pics to post later. I have the finder loaded with a 25mm ELux eyepiece and the cheapo Celestron 90 diagonal that comes with scopes these days. Wow, pretty sharp optics. I easily found Jupiter with a lot of sky surrounding it, 4.7 degree fov.Wow, what alot of curvature! As to be expected I guess in such a short/fast finder. The unit is not user friendly to eyepiece swaps due to the helical requiring a set screw to "lockin" the point of focus, but others mentioned using plumbers pipe tape on the threads of the helical to tighten it up and hold the weight of diagonal, eyepiece and focus position. I did pop in my ES 14mm 82* while sliding the diagonal in/out for focus and the curvature cleaned up nicely, the finder took the magnification well and made for a better albeit, narrower view of 4.2 degrees. I will probably settle on my Meade 20mm SWA for a 14x 4.9 degree fov. I'll try more mag later with the TV 3-6 zoom just to see how it does on planets. The greater aperture especially for a finder was immediately realized and apreciated and I think the two will indeed compliment each other. But this is a heavier rig than just the C90 alone with its tiny finder, needing two counterweights on the EQ2, but dampening was still at a second or less. It is nice to look through this size finder and actually see DSO's in the fov before going to the main scope...cool! :cool:

#231 ChristianG

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Posted 24 February 2014 - 02:08 PM

I use a red-dot finder. Orion makes a red/green version now, at the dimmest setting it's ok. Since I use my C90 for planets, Moon and other bright objects, that finder is good enough!

--Christian

#232 hardwarezone

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Posted 27 April 2014 - 08:18 AM

My attempt at the baffle mod without sandpaper


Adhesive-backed Nylon Flock Sheet 0.6mm thickness
I've cut it to 50mm width for rolling
Posted Image

The adhesive have a tendency to gum together, easily removed with just finger effort.
Posted Image

Pushed into the scope to determine final length before trimming
Posted Image

Here it is almost ready, made a foam ring cutout to prevent it from sliding into the scope.
I have added epoxy glue to the foam ring after this photo.
Posted Image

Daytime testing , eyepiece direct to visualback , serious vignetting.
With star diagonal it looks good, no visible vignetting , contrast is good on power and cellular towers but not trees.

Night time testing, visible vignetting like a thin crescent at the bottom edge , top and sides of visible field are fine.
Moon is not out so I could not test the contrast improvement.

Likely my flock is too soft causing imperfect circle and cutting into precious lightpath.
Will cut away the front sticky tape ring as I spotted it causing a minor bump due to overlaping flock.

#233 RefracNick

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Posted 29 April 2014 - 08:49 AM

Just placed my order for a C90! $199 w/ backpack and accessories, no tripod. I have a few GSO plossls and was wondering if I should upgrade to some Tele Vue plossls or maybe even a couple Naglers. Can anyone advise on what types of eyepieces work well with this scope?

Thanks!

#234 oliverschurer

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Posted 29 April 2014 - 09:05 AM

I mainly use a Celestron 8-24mm zoom on this scope - works well for me.

#235 gustavo_sanchez

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Posted 29 April 2014 - 09:12 AM

I mainly use Vixen NPL Plossls with my C90, and they work Great.

#236 Usquebae

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Posted 29 April 2014 - 10:29 AM

For DSO viewing I generally bring out 3 EPs with the C90: 24/68, 18/82, and 11/82. An 8-24 zoom will of course hit all those focal lengths and probably approach optimum for planets at 8mm, while the 32mm plossl that comes with the scope will max-out TFOV and be perfect as a finder EP. A 2x Barlow on the zoom could be useful on Moon. And the C90's focal ratio will be forgiving on inexpensive EPs, so Naglers probably aren't necessary, but they will definitely work well with that scope.

For ultra-light, cheap, wide-field EPs that work nicely in slow scopes, check out Russell Optics konigs. He's also got an 8-16mm zoom that weighs under 5 oz. Another nice inexpensive EP line would be the 66 degree EWAs from Agena, which are available in 6, 9, 15, & 20mm.

Have fun! :jump:

#237 stevenf

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Posted 29 April 2014 - 07:47 PM

Just placed my order for a C90! $199 w/ backpack and accessories, no tripod. I have a few GSO plossls and was wondering if I should upgrade to some Tele Vue plossls or maybe even a couple Naglers. Can anyone advise on what types of eyepieces work well with this scope?

Thanks!


These small maks do very well with cheaper eyepieces. I don't think you need to break the bank for fancy ones. My favorites are 25, 15, and 10mm with a barlow.

#238 azure1961p

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Posted 29 April 2014 - 08:26 PM

My attempt at the baffle mod without sandpaper


Adhesive-backed Nylon Flock Sheet 0.6mm thickness
I've cut it to 50mm width for rolling
Posted Image

The adhesive have a tendency to gum together, easily removed with just finger effort.
Posted Image

Pushed into the scope to determine final length before trimming
Posted Image

Here it is almost ready, made a foam ring cutout to prevent it from sliding into the scope.
I have added epoxy glue to the foam ring after this photo.
Posted Image

Daytime testing , eyepiece direct to visualback , serious vignetting.
With star diagonal it looks good, no visible vignetting , contrast is good on power and cellular towers but not trees.

Night time testing, visible vignetting like a thin crescent at the bottom edge , top and sides of visible field are fine.
Moon is not out so I could not test the contrast improvement.

Likely my flock is too soft causing imperfect circle and cutting into precious lightpath.
Will cut away the front sticky tape ring as I spotted it causing a minor bump due to overlaping flock.


I'm looking forward to your update. Nice report and thanks for relaying your experiences.

Pete

#239 n1toga

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Posted 30 April 2014 - 07:10 AM

Hi all,

Im having a problem with a brigh halo surrounding the moon and planets. What is this all about?


Rahul

#240 Sarkikos

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Posted 30 April 2014 - 09:13 AM

^
|
|

Look up.

Also, look here:

C90 Contrast Issue

If you are a stickler for details - or a glutton for punishment? :thinking: - peruse this thread:

MCT Secondary Baffle Mod

:grin:
Mike

#241 n1toga

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Posted 02 May 2014 - 12:04 AM

Thanks
Tried the painted sandpaper mod. Definate contrast improvement in daytime terrestrial photos. Some corner vignetting in pics but not visually. Night time hard to tell the difference but I think that there is some improvemet.

Still, the bright halo persists. Another problem cropped up. With a fully De-focused star, when I move the the image to the top half of the fov the defraction pattern gets sliced off/ squished at the top. The same cannot be said when the image is moved towards the bottom of the fov. this is regardless of the sand paper. I also rotated the meade zoom eyepiece in the diagonal to rule out eyepiece issue.

Any comments if this is normal?

Rahul

#242 n1toga

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Posted 02 May 2014 - 07:09 AM

Well just flocked the inside of the of the ota with the remaining flat black sand paper. Initial day pight tests look promising. Better than with just the baffel mod. Hopefully the halo effect on bright objects is cured. Wont know till tonight.

Rahul

#243 ChristianG

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Posted 02 May 2014 - 03:13 PM

With a fully De-focused star, when I move the the image to the top half of the fov the defraction pattern gets sliced off/ squished at the top. The same cannot be said when the image is moved towards the bottom of the fov. this is regardless of the sand paper. I also rotated the meade zoom eyepiece in the diagonal to rule out eyepiece issue.


Hi Rahul.

What kind of diagonal are you using? Cheap prism diagonals can be a problem.

Also, is your telescope perfectly collimated? I found--with the Orion Apex 90 cousin--that even when the mirror cell is shifted laterally with respect to the rest of the tube, it is possible to achieve 'ok' collimation but the defocused pattern can looked clipped. One has to make sure that the primary mirror is centered properly before attempting to collimate by tilting with the screws.

As for contrast, on mine I did:
--painted sandpaper inside primary baffle,
--sticky flocking material inside the conical plastic secondary baffle,
--flocking material inside main tube,
--light/dew shield 12" long.

Contrast is now very good, as good as my Broad Band coatings Questar. Here's what it looks like now. Cheers!

--Christian

Attached Thumbnails

  • 6502679-C90.JPG


#244 n1toga

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Posted 03 May 2014 - 03:28 AM

Thanks christian,

Ur mod is a lot more impressive than my humble effort.

Last night was all clouded over. As for the diagonal it an Agena Astro 30 dollar unit, better than the oem unit. Will try the Di-electric unit if the clouds relent.

Rahul

#245 hardwarezone

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Posted 04 May 2014 - 02:00 AM

Update on my C90 mod from last week (previous page)
Cut off the 2 sticky tape, vignetting still exist at the bottom of AFOV.
The halo is gone though ....
Jupiter and Saturn looks "normal" to me.
Could be my el cheapo $5 plastic mirror diagonal.

#246 t.r.

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Posted 04 May 2014 - 06:07 AM

Here is a pic of the Orion 70mm Multi-Finder with the C90 on an EQ-2 mount...I posted a first light report a page ago. The MF provides a near 5 degree fov at 11x for a wide complimentary view to the C90, with the advantage of a lot of light gathering over the supplied finder or 8x50's for the same price. It is pretty cool to actually "SEE" dso's in the finder before going to the main scope to zoom in. The only negative is its helical focusing which works best using just one eyepiece and not swapping out, which was my original intent.

Attached Thumbnails

  • 6505350-c9070.jpg


#247 Sarkikos

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Posted 04 May 2014 - 09:37 AM

t.r.,

What eyepiece do you have in the 70 MF? Looks like maybe some flavor of Meade 4k? Yes, this is not a scope set up for switching eyepieces. You could put a zoom in it, but then the relatively narrow AFOV at lowest power would defeat the purpose of a rich field scope.

Alas, I have the early version 70 MF that did not have a detent screw installed. I've used plumper's tape to take up the slack. But I've noticed that this needs to be replaced about every six months or the diagonal begins to move on its own. I'm still looking for a permanent solution to this problem. I don't see me installing a set screw.

Mike

#248 KarlL

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Posted 04 May 2014 - 02:34 PM

TR -

What mount do you have the C90 on in the photo?

Regards,

Karl

#249 t.r.

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Posted 04 May 2014 - 02:38 PM

It is from a Jason 313 Discoverer...it would be called an EQ-2/CG-3. The eyepiece is an extremely light weight 25mm ELux supplied with my C-6. With the plastic light weight diagonal, it makes a for a light setup on the C90.

#250 KarlL

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Posted 04 May 2014 - 04:38 PM

TR -

How's stability overall? I'm currently using a VersaGo II with great success. However, I'd like to try tracking without spending too much.

Regards,

Karl


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