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Long focus Newtonian Vs refractor

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#51 Jon Isaacs

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Posted 29 March 2013 - 07:32 PM

I think the contrast important on DSO too. Then how about long focus Newtonian VS short focus Newtonian on DSO?


Not as apparent if apparent at all. Its a different level of resolution in seeing contrast when viewing skotopic versus photopic as on Jupiter for example. I highly doubt you'd ever see the difference on M51 or M33 - buiuttt - in terms of resolving stellar galactic nuclei it might work in your favor.

Open clusters and globular clusters are another matter. The small CO puts more light into the spurious disk do the rings are fainter which boosts contrast of dimmer stars. Its subtle but when you are at the limits there is no doubt a 20% CO. will show fainter cleaner stars than a 38% CO.
The less you spread out faint light in diffraction patterns the higher the apparent contrast against the night sky.

Pete


:waytogo:

Contrast is important when viewing DSOs but a larger CO results in a fine scale loss of contrast, not overall contrast and at the low light levels, the eye cannot resolve those fine scale contrasts..

Jon

#52 Jeff Morgan

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Posted 29 March 2013 - 09:28 PM

As much as I like fiddling with my big Dob's, sometimes it's refreshing to set up a larger APO without needing to tweak anything. Just mount it and you're good to go. I like the variety in setup and use between these two types of telescope. At 63, it keeps my brain working.


I play in both leagues and can sympathize with you - to a point. Hauling out the 150+ pounds of equatorial mount and tripod (or pier) such a 7" refractor requires is most definitely not refreshing.

At least on the Dobsonian side of the field those big loads can be managed with wheelbarrow handles and don't have to be lifted to shoulder level, or higher.

#53 Peter Natscher

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Posted 29 March 2013 - 11:15 PM

Fortunately, I'm strong and energetic enough to spend the 15 minutes setting up the 50 lb. transportable pier, 35 lb. equatorial mount, three 18 lb counter weights, and a 43 lb. OTA. The pieces sit in my garage all day at near outside temperature and are hand-carried out onto my driveway 20 ft. distance. But once set up, there's no recollimating or equilibration time needed on this refractor system -- I can start observing right away at sunset or twilight. If I roll out my larger Dob, I have to recollimate and wait for cool down, about 30 minutes, and this doesn't settle until way after twilight as the air temp. keeps dropping and upsetting to primary mirror that's close to the pavement. Dob's need a cooler grassy field to sit on to escape this constant ground heat problem. Running Dob mirror fan's just blows more warmer ground air onto the primary extending the time to cool down. The APO sits way above the warmer air influence from the ground (at 6.5 ft. up) and escapes this eternal Dob problem. So, observing at home off of my driveway is more enjoyable using my refractor than my larger Dob. The Dob gets used away from home at darker sites. At home, the APO beats the larger Dob for immediate planetary-quality observing time!


As much as I like fiddling with my big Dob's, sometimes it's refreshing to set up a larger APO without needing to tweak anything. Just mount it and you're good to go. I like the variety in setup and use between these two types of telescope. At 63, it keeps my brain working.


I play in both leagues and can sympathize with you - to a point. Hauling out the 150+ pounds of equatorial mount and tripod (or pier) such a 7" refractor requires is most definitely not refreshing.

At least on the Dobsonian side of the field those big loads can be managed with wheelbarrow handles and don't have to be lifted to shoulder level, or higher.



#54 Peter Natscher

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Posted 29 March 2013 - 11:42 PM

Yeah, but I won't need to fiddle with it at every observing op and it's dependably consistent in performance. Very maintenance free. A Dob will require mirror recoating or eventual replacement, too.

As much as I like fiddling with my big Dob's, sometimes it's refreshing to set up a larger APO without needing to tweak anything.



Indeed. But no scope is 100% immune to collimation and the need to fiddle. When that 175mm A-P refractor needs attention, it needs to go back east where Roland can fiddle with it. :)

Jon



#55 azure1961p

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Posted 29 March 2013 - 11:45 PM

Nice dob Pete. I love the minimalist base the altitude bearings rest on - has this conceptual art feel about it.

Pete

#56 CollinofAlabama

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Posted 30 March 2013 - 01:57 AM

God! I shudder to think what a 6" apo costs! I don't even own a Synta 120mm ED largely because of the cost, and those are a bargain compared even to 4" TeleVue equipment. 6"? ¬°Ay Caramba! Besides, I've seen for myself about 6 years ago a brand new Meade LB 8" throw up a better view of Saturn than an Orion 120mm ED scope.

Anyone who wants excellent views of anything, get an 8" F/6 dob. Best deal going for visual astronomy. Reasonably stable collimation, should cool down relatively fast (compared to 10" + mirrors) and will show WAY more than anybody's sub $2.5k refractor. Of course, if money's no object, perhaps taxes are too low on the wealthy :smirk:

#57 jpcannavo

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Posted 30 March 2013 - 05:10 AM

Yeah, but I won't need to fiddle with it at every observing op and it's dependably consistent in performance. Very maintenance free. A Dob will require mirror recoating or eventual replacement, too.

As much as I like fiddling with my big Dob's, sometimes it's refreshing to set up a larger APO without needing to tweak anything.



Indeed. But no scope is 100% immune to collimation and the need to fiddle. When that 175mm A-P refractor needs attention, it needs to go back east where Roland can fiddle with it. :)

Jon


Sometimes (but not always) I see the whole refractor vs. reflector debate as really being about differences in disposition. Excuse the sloppy analogy to cars (of which I know little) but the Dob strikes me as being more like the tricked out hot rod, with the Apo being like the hit the road out of the factory BMW. Both may ultimately be comparable performers, but they capture very different sensibilities. The former is more of an ongoing work in progress, appealing more to the inveterate hands-on tinkerer, while the latter to the no fuss or muss, lets-get-going-and-perform type. Now surely this an idealized and over simplified generalization - and there are often elements of both orientations in many of us - but I do think it captures something.

#58 buddyjesus

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Posted 30 March 2013 - 05:27 AM

Long focus Newtonian Vs refractor

don't think you can go wrong either way. or both ways. or a cassegrain. or binos. They all are tools and have a place.

I am admittedly a refractor guy, but for how/what I observe, not having an apo doesn't really interfere. After I get a couple more cheap bits for the refractor, I plan on saving up for a Z12. They should complement each other well.

#59 Peter Natscher

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Posted 30 March 2013 - 10:52 AM

The way you might enjoy differences between your longer-focus Newtonian, larger Dob, or APO really depends on what location you're observing from.

Yeah, but I won't need to fiddle with it at every observing op and it's dependably consistent in performance. Very maintenance free. A Dob will require mirror recoating or eventual replacement, too.

As much as I like fiddling with my big Dob's, sometimes it's refreshing to set up a larger APO without needing to tweak anything.



Indeed. But no scope is 100% immune to collimation and the need to fiddle. When that 175mm A-P refractor needs attention, it needs to go back east where Roland can fiddle with it. :)

Jon


Sometimes (but not always) I see the whole refractor vs. reflector debate as really being about differences in disposition. Excuse the sloppy analogy to cars (of which I know little) but the Dob strikes me as being more like the tricked out hot rod, with the Apo being like the hit the road out of the factory BMW. Both may ultimately be comparable performers, but they capture very different sensibilities. The former is more of an ongoing work in progress, appealing more to the inveterate hands-on tinkerer, while the latter to the no fuss or muss, lets-get-going-and-perform type. Now surely this an idealized and over simplified generalization - and there are often elements of both orientations in many of us - but I do think it captures something.



#60 GeneT

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Posted 30 March 2013 - 11:38 PM

An F9 mirror has the potential to perform well. However, my F5, 12.5 inch Portaball also gives excellent planetary views. A Zambuto mirror will serve you well!






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