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Equipment Discussions >> Cats & Casses

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WadeH237
Pooh-Bah


Reged: 02/24/07

Loc: Snohomish, WA
Re: C14,versus a 10" apo... What will you do? new [Re: Erik Bakker]
      #5744663 - 03/20/13 08:30 AM

The view in the eyepiece is the combination of many factors.

APO refractors between 4" and 6" seem to be a sweet spot in that they don't really have anything that the user needs to do to make them perform. They cool quickly and are permanently collimated. Plus, they present phenomenal wide field views and have amazing contrast. There is truly something special about looking through them.

But over 6", they quickly start to get big and heavy. A couple of weeks ago, Roland Christen posted an interesting discussion on the largest practical size for APO refractors using current design technology. In particular, he said that for a 10" APO triplet, it was impossible to get visual colors to come to the same focus, while also correcting for spherical aberration. This discussion was in the context of why a 10" Mak-Cass was putting up better views side-by-side than a 10" APO at a particular star party.

In larger sizes, reflecting telescopes are really the way to go. Even a mass produced SCT can put up stunning views when it's at temperature equilibrium and properly collimated. At a star party last year, I was observing through my C14 early in the night. When I was ready to walk the telescope field, I left it pointed at M13 with a 31mm Nagler. The next day, a camper near me said that while I was gone, a short line formed at my C14. Some of the people looking through it made comments that it put up the best view of that object at the event - even better than the large dobs on the field.

But back to the question at hand, if I were looking for a telescope to use every day, I'd take the C14. If I were looking for a seriously cool scope to bring out to a star party, I would take the 10" APO. The question would be a lot harder if I were forced to choose between a C14 and something like an AP-130 or AP-175.


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mgwhittle
Pooh-Bah
*****

Reged: 08/24/11

Loc: Chattanooga, TN
Re: C14,versus a 10" apo... What will you do? new [Re: WadeH237]
      #5748440 - 03/21/13 08:15 PM

Having a 175mm triplet with no prior experience with APOs this size I was surprised at the length of time required for it to cool down for best performance. Going from 70 indoors to 50-55 outdoors with falling temperatures this winter has required cool down times exceeding an hour, closer to two hours some nights. My unvented C11 easily beats it on cool down times by a factor of 2. In addition, anything larger and I would need help getting it up on the mount.

Having said that, once up in the rings and cooled down......WHOA! The purity of the image is outstanding. Yeah, I'll take a 10 inch APO.


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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: C14,versus a 10" apo... What will you do? new [Re: azure1961p]
      #5748629 - 03/21/13 10:08 PM

10" unobstructed FTW!

But I'd want both. I'd center punch the C-14. Well, six or seven of them, and use them for counterweights for the 10-incher.



- Jim


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stevew
Now I've done it


Reged: 03/03/06

Loc: British Columbia Canada
Re: C14,versus a 10" apo... What will you do? new [Re: azure1961p]
      #5748656 - 03/21/13 10:17 PM

Quote:

Hypothetically: you are an observer of deepsky galaxies and such as much as mars and the moon. Even more amazingly you are given a choice (oh hell it s free) of a ten inch apo or c14 - which would you pick?


Pete



"Hypothetically" If I could have a scope butler to set up, tear down, mop my brow, and hand me eyepieces whenever I call out "Jeeves,..9mm Nagler!!"
then I'd take the 10 inch apochromat.
If I had to hump it around and set it up myself, the C14.

Steve


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DJCalma
member


Reged: 01/17/13

Loc: Northern California
Re: C14,versus a 10" apo... What will you do? new [Re: jrbarnett]
      #5748667 - 03/21/13 10:21 PM

I'd take a 7" apo over a C14, does that count? Never been a fan of those short, stubby looking things aside from small Maks. Although, to be fair I've never seen the views through an Edge HD.

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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: C14,versus a 10" apo... What will you do? new [Re: DJCalma]
      #5748749 - 03/21/13 11:27 PM

Now that you mention it, a hundred or so people a year who opt for a lowly 5.5" TEC 140 over a C14 OTA, the latter being cheaper than the 5.5" TEC, make a similar choice to the one you describe.

- Jim


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johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: C14,versus a 10" apo... What will you do? new [Re: jrbarnett]
      #5748834 - 03/22/13 12:02 AM

I know this is the Cat forum but it is surprising to me as well as noted before, many would opt for the 30% obstructed commercial mirror over a handmade work of art with no obstruction, no diffraction, perfect images. Of course the mounting issue is not at all practiclal in fact almost... insur-mountable.



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Mark Costello
Carpal Tunnel
*****

Reged: 03/08/05

Loc: Matthews, NC, USA
Re: C14,versus a 10" apo... What will you do? new [Re: johnnyha]
      #5749268 - 03/22/13 09:26 AM

Quote:

I know this is the Cat forum but it is surprising to me as well as noted before, many would opt for the 30% obstructed commercial mirror over a handmade work of art with no obstruction, no diffraction, perfect images. Of course the mounting issue is not at all practiclal in fact almost... insur-mountable.






One reason might be because that the cat would be a good bit more maneagable than the large refractor. Personally, I'd take a 8" SCT or Dob over an 8" refractor, no matter how good it was - any day, hands down, not look back....


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mikertx
sage
*****

Reged: 09/29/05

Loc: Austin, TX
Re: C14,versus a 10" apo... What will you do? new [Re: johnnyha]
      #5749615 - 03/22/13 12:47 PM

I think you bring up an interesting point. You can view a telescope as a cherished work of art or as a tool for accomplishing a task. Both views are completely valid. I can't bring myself to sell my TEC140 even though I don't use it much because IMO it's a work of art. For most of what I am doing these days (spectroscopy, photometry) my C11 is a much better choice.

Mike

Quote:

I know this is the Cat forum but it is surprising to me as well as noted before, many would opt for the 30% obstructed commercial mirror over a handmade work of art with no obstruction, no diffraction, perfect images. Of course the mounting issue is not at all practiclal in fact almost... insur-mountable.






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cavefrog
Carpal Tunnel
*****

Reged: 11/11/08

Loc: loozyanna
Re: C14,versus a 10" apo... What will you do? new [Re: David Pavlich]
      #5750722 - 03/22/13 09:37 PM

Quote:

First, you're comparing an off-the-shelf SC to a hand built refractor. This is a common comparison, one I could never understand.

Now, let's get Mike Lockwood to make us a hand figured primary and secondary mirror to the very best of his ability...maybe Mike's best mirrors ever! And we'll also get Mike to figure the corrector as closely matched to these mirrors as his prolific skills will allow.

Now, let's make sure that the OTA has active cooling. And let's make sure that the tolerances of the mirror riding on the baffle tube is incredibly tight, to the point that the lube is specially formulated so that it can be very slippery but the amount of lube is only a few microns. And the focusing mechanism is extremely rigid to limit image shift to virtually nothing.

Ok...now we would have a fair comparison in optics, mechanics and price.

David




+1... NOW your talking comparison!!!

Theo


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azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: C14,versus a 10" apo... What will you do? new [Re: David Pavlich]
      #5750894 - 03/22/13 10:58 PM

Quote:

First, you're comparing an off-the-shelf SC to a hand built refractor. This is a common comparison, one I could never understand.






Hi David,

The comparison to a stock C14 was intentional as an optimized one to your spec (which Is a nice spec) doesn't really speak for the instrument on its own out of the - real world - box (as most people would use it). It is that the instrument is nt a custom product and is readily available at a fantastic price that makes it the contender it is. I didn't see the c14 as a mass market whipping post but rather the possibility in this hypothetical that off the shelf it is better for a variety of objects. It'd be gangbusters to be sure with all those custom fabricated optics but the achievement here is in the success of the instrument with out it.

Pete


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Darren Drake
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
Re: C14,versus a 10" apo... What will you do? new [Re: azure1961p]
      #5750944 - 03/22/13 11:35 PM

Lets not forget what Damean Peach uses to image the moon and planets....

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Fomalhaut
scholastic sledgehammer


Reged: 08/16/08

Loc: Switzerland
Re: C14,versus a 10" apo... What will you do? new [Re: DJCalma]
      #5751248 - 03/23/13 06:54 AM

Quote:

I'd take a 7" apo over a C14, does that count? Never been a fan of those short, stubby looking things aside from small Maks. Although, to be fair I've never seen the views through an Edge HD.




I had owned and frequently used two different C8s (an orange good one, and later on a "so,so" black Powerstar one) for over 20 years.
Meanwhile, for the last twenty years, I've had (amongst other scopes) two good 4-inch apos (at first the Vixen Fl-102 and after that a perfect Tak FCT-100). Instead of a C8 I now have a Mewlon-180 delivering at least the same performance as the better of my past C8s, and I'm using it on fainter galaxies, GCs and PNs.
So I believe to have "the best of both worlds" within my weight-class (terrace, no permanent mount plus problems with my disks).

If I had to decide for just one scope, the one which would stay would be the 4-inch apo. - It may show less than the 7-inch-DK on the objects mentioned above, but what it shows is (comparatively independent from seeing conditions) of outstanding contrast and beauty! Through the SCs or MCs or Casses I have always felt like looking at kind of nice pictures, while the Apo seems to show me "the real thing". This may sound magic, but nevertheless in my case is the case ...
Thus, my decades of observing with apochromatic refractors (AND reflectors) somehow must have spoilt me irreversibly .
OTOH, I'm still happy to own both!

Conclusion: When now thinking of scaling up both of the above scopes by the same factor of 2 there results exactly a proportional pair of a hypothetical 14-inch DK/SC versus an 8-inch Fluorite triplet refractor... => Personally, I'd prefer that one.

Chris


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ValeryD
Vendor (Aries)
*****

Reged: 11/26/05

Loc: Kherson, Ukraine.
Re: C14,versus a 10" apo... What will you do? new [Re: WadeH237]
      #5755506 - 03/25/13 04:48 AM

Quote:

A couple of weeks ago, Roland Christen posted an interesting discussion on the largest practical size for APO refractors using current design technology. In particular, he said that for a 10" APO triplet, it was impossible to get visual colors to come to the same focus, while also correcting for spherical aberration. This discussion was in the context of why a 10" Mak-Cass was putting up better views side-by-side than a 10" APO at a particular star party.






Can you, please, give a direct link to this discussion where Roland said such things?


Thanks.

Valery.


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De Lorme
professor emeritus
*****

Reged: 12/30/08

Re: C14,versus a 10" apo... What will you do? new [Re: Erik Bakker]
      #5755516 - 03/25/13 05:02 AM

Apo for sure. Find some way to mount it. De Lorme

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Illinois
Carpal Tunnel


Reged: 12/18/06

Loc: near Dixon, Illinois USA
Re: C14,versus a 10" apo... What will you do? new [Re: De Lorme]
      #5755589 - 03/25/13 07:16 AM

I remember that Astronomic selling 254mm (10") F9 OTA for $39,999....just tube!!!!! If I can afford it and I wouldnt buy it. Meade 16" SCT!

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Classic8
professor emeritus


Reged: 04/12/06

Loc: Naperville, IL, USA
Re: C14,versus a 10" apo... What will you do? new [Re: Illinois]
      #5755875 - 03/25/13 10:49 AM

Quote:

I remember that Astronomic selling 254mm (10") F9 OTA for $39,999....just tube!!!!! If I can afford it and I wouldnt buy it. Meade 16" SCT!




That would look impressive set up in the living room.


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WadeH237
Pooh-Bah


Reged: 02/24/07

Loc: Snohomish, WA
Re: C14,versus a 10" apo... What will you do? new [Re: ValeryD]
      #5756232 - 03/25/13 01:58 PM

Quote:

Can you, please, give a direct link to this discussion where Roland said such things?


Thanks.

Valery.




It was in a conversation on the AP-UG forum. Here is the direct link to his quote (which I paraphrased).

-Wade


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AlienRatDog
Carpal Tunnel
*****

Reged: 07/15/05

Loc: Ann Arbor
Re: C14,versus a 10" apo... What will you do? new [Re: PatHolland]
      #5756273 - 03/25/13 02:15 PM

Quote:

If I bought a 10" APO, I would need to take out a loan for my divorce attorney. My APO and I would most likely have to get an apartment somewhere - but at least we'd be together.




FYI there are A LOT more women than 10" APOs out there...just sayin'...


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Paul G
Post Laureate
*****

Reged: 05/08/03

Loc: Freedonia
Re: C14,versus a 10" apo... What will you do? new [Re: AlienRatDog]
      #5756793 - 03/25/13 06:41 PM

Quote:

Quote:

If I bought a 10" APO, I would need to take out a loan for my divorce attorney. My APO and I would most likely have to get an apartment somewhere - but at least we'd be together.




FYI there are A LOT more women than 10" APOs out there...just sayin'...






Go Blue, beat Kansas!


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