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New scope for the Mars opposition.

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#1 ArneN

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Posted 22 June 2020 - 05:38 PM

What will be the benefit of chosing a 152mm ED frac over a 10 inch Classical Cass?

Prices are about the same.

 

Arne


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#2 siriusandthepup

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Posted 22 June 2020 - 05:51 PM

If the seeing is marginal, then the 6" might provide more consistent viewing.

 

Good seeing - the 10" Cass smokes the 6" performance wise.

 

Where do you live? How are your seeing conditions?

 

Any reason that you don't want a 12" Newt?


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#3 ArneN

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Posted 22 June 2020 - 05:59 PM

I live in Norway, under a Bortle 5 sky. A CC will give me a long FL in a short tube, a Newt will be way to long.

 

Arne



#4 Echolight

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Posted 22 June 2020 - 06:12 PM

Less maintenance and setup on the refractor. And wider field of view makes finding stuff in the eyepiece easier.

No central obstruction.

Refractors have the crispest, purest views.


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#5 Bomber Bob

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Posted 22 June 2020 - 06:58 PM

The 152 ED is MUCH easier to collimate -- and will stay collimated between sessions.  It will also adjust to temperature differences & changes during the session much better & faster than the 10" CC.


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#6 siriusandthepup

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Posted 22 June 2020 - 07:02 PM

I agree with the guys, a 152ED is likely your best option. It will be a lot less trouble to keep collimated and will cool down faster than the CC.

 

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#7 coopman

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Posted 22 June 2020 - 08:02 PM

If you're thinking about the GSO 10" CC, it isn't even an effective 10" of aperture.



#8 Echolight

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Posted 22 June 2020 - 08:22 PM

That GSO also weighs about 50 kilos!


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#9 ArneN

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Posted 23 June 2020 - 01:00 AM

Weight is about 16 kilos! Cool down is not a problem with either scopes, They will be permanentely mounted in my obsy.

 

 

Arne


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#10 eros312

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Posted 23 June 2020 - 10:37 PM

I know this is the refractor forum, but I'd choose the 10" CC. Much greater resolution and light gathering. And the tube is almost half the length of the refractor so it should be more stable on your mount. Plus, you have a permanent setup. 


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#11 BillP

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Posted 23 June 2020 - 11:19 PM

The 10" can resolve to 0.45 arcsec.  The 152 to 0.76 arcsec.  Hmmm...wonder why so many amateurs seem to have consistent sub-arcsec seeing when the professional observatories have such a hard time finding that idea.gif

 

Perhaps you should approach it from the exit pupil perspective.  Once you get below a .65mm exit pupil or so the view is dim enough that lowest contrast features often vanish from view.

 

0.65mm EP in 152 = 234x

 

0.65mm EP in 254 = 391x

 

So choose the magnification you would like and the aperture you will need falls into place.  Of course, can your seeing often support 391x?  If not then realize you might need so filtration to cut down the brightness because a too bright planetary view masks features as well.


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#12 Jared

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Posted 24 June 2020 - 12:53 AM

From Oslo (not sure where you are in Norway), at this opposition Mars will only be about 35 degrees in altitude as it crosses the Meridian.  If your seeing conditions are not above average, you are unlikely to be able to run very high powers.  I think I would lean towards the refractor. My 10” and larger scopes always struggled to put up good planetary views if the seeing was poor, and with Mars that low I’d be worried about that.

 

If your seeing is particularly good, even a top quality refractor would have a hard time putting up views as detailed as a scope with 4” of extra aperture.  I’d lean towards the 10” for a location with particularly good seeing.


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#13 Daniel Mounsey

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Posted 24 June 2020 - 02:41 AM

What will be the benefit of chosing a 152mm ED frac over a 10 inch Classical Cass?

Prices are about the same.

 

Arne

Good luck finding a good 10” classical cass. Secondaries are near impossible to make. Way better options on the market. 


Edited by Daniel Mounsey, 24 June 2020 - 02:43 AM.

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#14 ArneN

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Posted 24 June 2020 - 06:27 AM

Because of reduced eyesight  ( diabetes ) I will probably use a camera / lucky imaging.

 

Arne



#15 Cbaxter

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Posted 24 June 2020 - 06:54 AM

I love and prefer refractors, but from my experience the larger apature 100% of the time wins on almost everything, especially planets. Others will disagree and reference maths, seeing, or obstruction, and contrast, but from the light polluted skies of Seattle to the darkest skies I've ever experienced, in the middle of the Afghanistan desert, a 10 inch dobsonian or 8 inch SCT always provided the better more detailed view of absolutely everything vs a 102mm and 152mm ED refractor, especially planets. No side-by-side has ever convinced me otherwise, regardless of the seeing or anything else. I've read and heard all of the various arguments and formulas that attempt to show that a smaller unobstructed apature will out perform a larger obstructed apature in this or that conditions, but I continually visually find the larger apature wins every single time. Also, a 6" refractor is an absolute beast to mount and handle. Of you've never personally worked with a large refractor, I highly encourage you to do so before you decide to purchase one specifically for Mars this year. They are beasts! And not necessarily in a good way.

Edit* if you intend to do lucky imaging rather than visual then you absolutely should be considering an SCT or the like reflector. A 6 inch refractor will be a LOT to handle and mount for something like lucky imaging. Not to mention that the 6 inch refractor will have a much shorter focal length than even an 8 SCT, and from experience the refractor may have issues getting into focus with a planetary camera and barlow. A barlow will be almost a necessity for Mars in just about any refractor.

Regards.

Edited by Cbaxter, 24 June 2020 - 07:00 AM.

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#16 Echolight

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Posted 24 June 2020 - 09:19 AM

My 6 inch f8 achro is more stable on an AVX mount than my C8 on the Nexstar mount. Both have similar 2 inch steel leg tripods.

 

And to me, the view is better through the C6R than the common C8. No cool down and no dew. No collimating.

 

But the C6R is big. Although substantially lighter than a 10 inch classical cassegrain.

 

I would imagine that the view from a 9.25 SCT equipped with 2 inch accessories would be a good next step up over a 6 inch refractor. As would any 10 inch scope. But in this range, only the a 10 inch dob would rival the affordability of the C6R on an AVX. 


Edited by Echolight, 24 June 2020 - 09:21 AM.

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#17 Daniel Mounsey

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Posted 24 June 2020 - 10:32 AM

I love and prefer refractors, but from my experience the larger apature 100% of the time wins on almost everything, especially planets. 

Regards.

 

I've never quite understood this philosophy. Maybe you could enlighten me. smile.gif


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#18 bobhen

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Posted 24 June 2020 - 10:42 AM

Because of reduced eyesight  ( diabetes ) I will probably use a camera / lucky imaging.

 

Arne

Living in Norway, and if you are just imaging the planets, consider a Celestron C-9.25 or C-11. At your location and for your needs, I doubt better optics will serve you any better. If you do want better optics, consider a Takahashi Mewlon 250.

 

Bob 


Edited by bobhen, 24 June 2020 - 10:43 AM.

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#19 BillP

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Posted 24 June 2020 - 11:03 AM

I love and prefer refractors, but from my experience the larger apature 100% of the time wins on almost everything, especially planets. Others will disagree and reference maths, seeing, or obstruction, and contrast, but from the light polluted skies of Seattle to the darkest skies I've ever experienced, in the middle of the Afghanistan desert, a 10 inch dobsonian or 8 inch SCT always provided the better more detailed view of absolutely everything vs a 102mm and 152mm ED refractor, especially planets. No side-by-side has ever convinced me otherwise, regardless of the seeing or anything else. I've read and heard all of the various arguments and formulas that attempt to show that a smaller unobstructed apature will out perform a larger obstructed apature in this or that conditions, but I continually visually find the larger apature wins every single time. Also, a 6" refractor is an absolute beast to mount and handle. Of you've never personally worked with a large refractor, I highly encourage you to do so before you decide to purchase one specifically for Mars this year. They are beasts! And not necessarily in a good way.

 

Wow.  My experience is completely different.  Not saying your experience is not what you had.  But it is not how it plays out for me.  I have used my 10" Dob side-by-side with my Apos for a decade and yes the 10" gets more details for planets, but at an operational cost.  With the 10" one looks for those "moments of best clarity of the view" as the instrument tries to deal with the seeing and its own thermal quirks.  With the refractors the characterization of the views are just the opposite as the views are for the most part always completely rock steady long term.  Plus, in reality, having done so many side-by-sides, quickly realized that for the most part, the seeing controls the details -- and no way everyone out there has sub-arcsecond seeing most of the time.  So when you do enough observation sampling, you quickly realize the more detailed views from the larger aperture are less often than you think.  If one just goes out to observe a few times a month then statistically easy to hit a stretch of better seeing evenings skewing ones perspective.  And I do have a 6" f/8 Apo and it is not a beast by any means,  And when you mount them on simple alt-az mounts the entire thing is no more cumbersome than my 10" Dob to move around.  And finally, while larger aperture has its place where it outperforms, like on faint fuzzies, a 10" that limits you to less than 2 degrees TFOV will mean you are missing a lot of nice open clusters and larger interesting vistas.  And when the seeing is limiting magnifications, can also force you to have to move to filtration to reduce the brightness of the planet as too bright obscures features.  So my experience is that the act of observing a planet has a lot more going on then simply level of details.  I personally find the entire process more effective and more rewarding with a smaller refractor than with a larger mirrored instrument.  That's my experience.  So folks should understand both your experience and my experience as it is not a slam dunk in either direction.  Where it falls for them will be something that they have to figure out in the field as it can swing either way.
 


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#20 Bomber Bob

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Posted 24 June 2020 - 11:04 AM

If not then realize you might need so filtration to cut down the brightness because a too bright planetary view masks features as well.

 

This wasn't a factor for me in all those years with an 80mm F15 refractor -- except for maybe Mars at a very close opposition.  Then, I got my first 6" scope, and saw the light -- too much of it...

 

OP, I'm a CC Fan from way back -- drew up plans for my own 40+ years ago.  I'm currently restoring my antique Tinsley 6" F20 Cass for the 3 Planet Season.  And, I finally have a trans-portable EQ mount (pedestal with big casters) that can carry a 10" CC.  If you can deal with the scope, mount, & such to where you're observing with it more than maintaining it, go with the 10" Cass...

 

I love my 2017 APM 152ED, and I'll be using it on 7 / 10 or better seeing nights at 300x (Jupiter) & 400x (Mars / Saturn).  But, my vintage Meade 8" F6 Newt is much easier to set up.  I may have to push the power up on it if the planetary disks are too bright.

 

Where it falls for them will be something that they have to figure out in the field as it can swing either way.

 

That's why I like having Options:  

 

APM ED 152 S076 (Meade SF Restore).jpg Meade 826 Restore S01 - Lumicon 125 HF.jpg Tinsley - Progress Check S02 (Assembled).jpg

 

** Is this the 10" CC you're considering:  https://agenaastro.c...truss-tube.html


Edited by Bomber Bob, 24 June 2020 - 11:18 AM.

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#21 Hesiod

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Posted 24 June 2020 - 11:11 AM

If the telescope is meant for lucky imaging, I'd opt for the larger aperture.

If are striving for the best optical accuracy, probably a good Newtonian could be the answer, or a Mak-Newt from Intes.


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#22 JP-Astro

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Posted 24 June 2020 - 11:40 AM

The 10" can resolve to 0.45 arcsec.  The 152 to 0.76 arcsec.  Hmmm...wonder why so many amateurs seem to have consistent sub-arcsec seeing when the professional observatories have such a hard time finding that idea.gif

 

Perhaps you should approach it from the exit pupil perspective.  Once you get below a .65mm exit pupil or so the view is dim enough that lowest contrast features often vanish from view.

 

0.65mm EP in 152 = 234x

 

0.65mm EP in 254 = 391x

 

So choose the magnification you would like and the aperture you will need falls into place.  Of course, can your seeing often support 391x?  If not then realize you might need so filtration to cut down the brightness because a too bright planetary view masks features as well.

 

Sorry for my interference but Bill just suggested a formula that is almost inline with my perception of the "acceptable image brightness" in respect to the aperture size. I never estimate the exit pupil size, I use the aperture size as a guide.

 

I normally use the following relationship for my astro scopes:

- D x 1.5 = ~Max useful magnification, where D is of course the aperture size. For me the higher power for a given aperture begins to give me too dim a picture for my liking regardless of the telescope type.

 

So when using my 120 mm ED I get 120 x 1.5 = 180x (I can still push up to 200x but any further and I don't like the picture any longer). Unacceptable for me.

For 152 mm ED that would be  152 x 1.5 =~ 225x (pretty close to Bill's 234x)

 

Now, how do good people on this forum manage to run a scope at triple and even higher the aperture power? What do they see? Dim blurry smudges?

For instance I often see claims that someone runs his 120ED at 300x and even 500x. I don't get it.



#23 BillP

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Posted 24 June 2020 - 12:28 PM

OP, I'm a CC Fan from way back -- drew up plans for my own 40+ years ago.  I'm currently restoring my antique Tinsley 6" F20 Cass for the 3 Planet Season.

That Tinsley is just beautiful!!


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#24 BillP

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Posted 24 June 2020 - 12:31 PM

Sorry for my interference but Bill just suggested a formula that is almost inline with my perception of the "acceptable image brightness" in respect to the aperture size. I never estimate the exit pupil size, I use the aperture size as a guide.

 

I normally use the following relationship for my astro scopes:

- D x 1.5 = ~Max useful magnification, where D is of course the aperture size. For me the higher power for a given aperture begins to give me too dim a picture for my liking regardless of the telescope type.

 

So when using my 120 mm ED I get 120 x 1.5 = 180x (I can still push up to 200x but any further and I don't like the picture any longer). Unacceptable for me.

For 152 mm ED that would be  152 x 1.5 =~ 225x (pretty close to Bill's 234x)

 

Now, how do good people on this forum manage to run a scope at triple and even higher the aperture power? What do they see? Dim blurry smudges?

For instance I often see claims that someone runs his 120ED at 300x and even 500x. I don't get it.

Wow.  Lot easier to calculate in your head your way.  waytogo.gif


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#25 Bomber Bob

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Posted 24 June 2020 - 12:40 PM

That Tinsley is just beautiful!!

Thanks Bill!  The OTA will be going from that weird blue + green + silver to cranberry satin in the near future...




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