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#1 HowardK

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Posted 02 January 2013 - 04:09 PM

Maybe the wrong forum but there are a lot of knowledgeable people here so.....

I have 2 great scopes...

TEC 140mm APO ....f/7... F/l 980mm
PLANEWAVE 12.5" CDK with a 42% obstruction....f/8....f/l 2541mm

I put a X2.5 Barlow in the APO to equal the 2 focal lengths

I observe in poor seeing...3-4 on the Pickering scale.

Which scope when viewing/imaging Jupiter with a planetary webcam would you guys say gave the best resolution?

Bear in mind...the Planewave has its 42% obstruction and is very well collimated and my poor seeing conditions.

Very interested in all answers

Howard

#2 skybsd

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Posted 02 January 2013 - 04:20 PM

Hello,
Hmmmm., You're asking "people on the Internet" to comment on how YOUR two scopes may perform under YOUR skies, and YOUR seeing conditions? :scratchhead:

Don't mean to be awkward, but seems to me that the simplest approach here is for YOU to take YOUR two scopes outside.., and see for yourself, really..,

Have you given that a try?

Regards,

skybsd

#3 HowardK

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Posted 02 January 2013 - 04:28 PM

Yes...i have...

What is best for planetary detail, contrast....

A great 5.5" APO...or....
A great 12.5" , 42% obstructed CDK in poor seeing conditions?

Howard

#4 skybsd

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Posted 02 January 2013 - 04:43 PM

Yes...i have...


So..., what were your_own results?

I mean.., you are the one that's got the two scopes..., at your location with your observing conditions.., therefore your own experience of how your equipment performs in your environment is paramount here.

Best..,

Regards,

skybsd

#5 Tank

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Posted 02 January 2013 - 04:43 PM

I pretty sure the TEC 140 takes it in poor seeing and then in great seeing the 12.5" should take it.
Done these comparos many times with all kinda of scopes!

#6 M13 Observer

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Posted 02 January 2013 - 05:08 PM

With a webcam, the CDK will win. Much brighter image = quicker webcam operation = faster timeslicing = seeing frozen better = sharper and more contrasty images for software to stack and manipulate. With the APO and a 2.5x Barlow, the light getting through is significantly decreased therefor the webcam has to extend exposures = mushier images, compensate with huge gain = poorer contrast = overall poorer soft low contrast images to start with = poor end results after stacking and manipulating.

That is my guess but what do I know. You are supposed to tell us which one worked out better.

#7 BarrySimon615

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Posted 02 January 2013 - 05:48 PM

Your question should have been one to ask when you had one or the other of your two telescopes and you were looking for a rationale to buy the second one and maybe replace the first one. Like skybsd, I think you are better served doing a head to head for yourself and drawing your own conclusions.

Barry Simon

#8 BKBrown

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Posted 02 January 2013 - 06:23 PM

With a webcam, the CDK will win. Much brighter image = quicker webcam operation = faster timeslicing = seeing frozen better = sharper and more contrasty images for software to stack and manipulate. With the APO and a 2.5x Barlow, the light getting through is significantly decreased therefor the webcam has to extend exposures = mushier images, compensate with huge gain = poorer contrast = overall poorer soft low contrast images to start with = poor end results after stacking and manipulating.

That is my guess but what do I know. You are supposed to tell us which one worked out better.


Honestly, I think it is a bad guess. The CDK image will be brighter and show better contrast, color saturation, and resolution...but the TEC 140 image will be equally sharp and detailed, with excellent color saturation for its size. Notice the similarities between these two images; both were shot with the same camera at 60 fps under very similar seeing conditions. In poor or fair conditions I prefer imaging with my small refractors, they can typically shoot at near max resolution while the C11 Edge (an excellent sample in this case) leaves much of its capability on the floor. On steady nights this situation is totally reversed and the C11 wins. Assuming the CDK is perfectly collimated and used in good to excellent seeing conditions it should blow the TEC away with the detail and color it can show. Otherwise, my experience says the TEC will likely have the advantage in more ho-hum conditions. Just sayin'...

Clear Skies,
Brian

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#9 M13 Observer

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Posted 02 January 2013 - 07:06 PM

With a webcam, the CDK will win. Much brighter image = quicker webcam operation = faster timeslicing = seeing frozen better = sharper and more contrasty images for software to stack and manipulate. With the APO and a 2.5x Barlow, the light getting through is significantly decreased therefor the webcam has to extend exposures = mushier images, compensate with huge gain = poorer contrast = overall poorer soft low contrast images to start with = poor end results after stacking and manipulating.

That is my guess but what do I know. You are supposed to tell us which one worked out better.


Honestly, I think it is a bad guess. The CDK image will be brighter and show better contrast, color saturation, and resolution...but the TEC 140 image will be equally sharp and detailed, with excellent color saturation for its size. Notice the similarities between these two images; both were shot with the same camera at 60 fps under very similar seeing conditions. In poor or fair conditions I prefer imaging with my small refractors, they can typically shoot at near max resolution while the C11 Edge (an excellent sample in this case) leaves much of its capability on the floor. On steady nights this situation is totally reversed and the C11 wins. Assuming the CDK is perfectly collimated and used in good to excellent seeing conditions it should blow the TEC away with the detail and color it can show. Otherwise, my experience says the TEC will likely have the advantage in more ho-hum conditions. Just sayin'...

Clear Skies,
Brian


Agreed if you are using the scopes at the same focal ratio. The original post was not describing such a situation, it was at the same focal LENGTH. Just saying . . .

#10 HowardK

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Posted 02 January 2013 - 07:16 PM

I pretty sure the TEC 140 takes it in poor seeing and then in great seeing the 12.5" should take it.
Done these comparos many times with all kinda of scopes!


it appears you are correct.
resolution and contrast after stacking is much better with the smaller refractor.

I believe that the large CDK cannot see thru the turbulent air.

Have you come to the same conclusion in your own sise by side tests, Tank...do tell more...

#11 HowardK

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Posted 02 January 2013 - 07:20 PM

Brian

thanku for the reply.

more detail to be seen on Jupiter with the bigger scope as per your images...

how would u rate the seeing conditions when u captured these?

Howard

#12 Tank

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Posted 02 January 2013 - 07:53 PM

I pretty sure the TEC 140 takes it in poor seeing and then in great seeing the 12.5" should take it.
Done these comparos many times with all kinda of scopes!


it appears you are correct.
resolution and contrast after stacking is much better with the smaller refractor.

I believe that the large CDK cannot see thru the turbulent air.

Have you come to the same conclusion in your own sise by side tests, Tank...do tell more...


I have done these test visually not with the Camera and in poor seeing the smaller scope tends to keep the image cleaner and doesnt distort as much as in the larger scopes.
Also CO (central obstruction) seems to play a role too. A cental obstruction scope vs a unobstructed scope similiar in apeture accounting the CO i found the unostructed seems to give a cleaner view in poor seeing but i couldnt conclude if that was just better optics in the unobstructed or the CO affect the image alot in poor seeing. In great seeing the unobstructed gave a bit better image also but not by much. THis was comparing a 102 ED APO vs a 127 MAK. My buddy Mike can give you more findings and his interpretation.

In average to great seeing the larger apeture scope are equal and start to pull away from the smaller scope for planetary viewing.

#13 BKBrown

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Posted 02 January 2013 - 07:53 PM

Brian

thanku for the reply.

more detail to be seen on Jupiter with the bigger scope as per your images...

how would u rate the seeing conditions when u captured these?

Howard


You're welcome Howard. Conditions were 6-7/10 during both sessions, pretty good for where I live in northern Virginia. And this result is exactly what you would expect for these scopes under the conditions. Sure the C11 will show more (it better!) under decent skies, but in poorer seeing I tend to prefer smaller refractors...and I have had a lot of luck with them. That said, if I had only one to choose from I would probably go for the aperture for those nights when they get to strut their stuff. Fortunately, I don't have to choose :grin: Hope this helped!

Clear Skies,
Brian

#14 dscarpa

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Posted 02 January 2013 - 08:39 PM

My C-9.25's CO isn't that much smaller than your Planetwave's. My cat kills for lunar-planetary with good and above seeing but my WO ZS-110 walks all over it with fair or less. David

#15 HowardK

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Posted 02 January 2013 - 08:44 PM

Thanku David

Very interesting to know that in poor seeing big scopes are pretty poor performers on planets

#16 jrbarnett

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Posted 03 January 2013 - 11:01 AM

The Planewave. No question. The large CO is pretty much irrelevant due to the huge mismatch in aperture and resulting contrast transfer advantage of the larger instrument, however...

While "by the numbers" and pretty graphs and such that often accompany them in "*BLEEP*-aperture rules" posts, the higher quality (in ultimate wavefront terms - a 42% CO scope cannot be diffraction limited at the eyepiece even with *perfect* optics), smaller, unobstructed scope has an effect on "how" those details captured by the scope are rendered. While you will certainly be able to see smaller scale detail in the Planewave, what you will see will be gauzy, hazy, mushy and soft by comparison to the TEC, which will be, in contrast, crisp, sharp, etched and tight. It comes down to what you prefer aesthetically - a larger number of fuzzier festoons or a smaller number of sharply defined ones.

:grin:

Regards,

Jim

#17 HowardK

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Posted 03 January 2013 - 11:45 AM

Jim

You sure know what you are talking about

Your description fits well with my observations
The TEC is sharp where the P Wave is mushy...but there is smaller detail there in the mush, somewhere.

Like the word etched...that is what the TEC shows compared to the big boy..in my poor seeing anyways

#18 ckwastro

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Posted 03 January 2013 - 11:47 AM

I'm strictly a visual observer and cannot speak to imaging, however I find similar results with my Stowaway vs my larger scopes when seeing is fair to poor.

During these times, the target detail in the 92mm Stowaway will stay fairly clear, however the image as a whole will bounce around the field of view. In my Mewlon, and my old 10" and 14.5" Newtonians, the image as a whole does not bounce around, however the target detail is smeared out, except for those fleeting moments when the atmosphere calms.






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