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Fast or slow? Light or heavy?

GordonCopestake

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MartinB

MartinB

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Gordon, I can see that living in a light polluted area means you want to concentrate on planets but astonomy based around visual observation of planets must be pretty limited. When imaging planets the loss of contrast with an SCT isn't an issue. Also using good imaging filters such as astronomik HA or CLS filters can do a fantastic job on LP allowing imaging of DSOs. I agree that major planets don't look as appealing as smaller fracs visually but resolution is aperture dependant - give me an 8" SCT over a 4" frac for planetary imaging any day. They are so portable and convenient and fantastic imaging scopes.

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GordonCopestake

GordonCopestake

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Thanks for the link Gaz, i'll have a play

Martin: I have looked through my 8" SCT and i have looked through my 4" APO. I know which i prefer visually, the 4" APO. I dont do that much imaging, so the visual performance is critical to me. I would like to keep the contrast of the APO view but have the resolution of the 8" SCT. The way to do that is with an 8" APO..... or a newt with a central obstruction of 20% or less.

I completly agree about the portability and convenience. However nobody has designed a small form factor with high contrast OTA yet, and given the short length of the tube needed i doubt they will. The only option i can think of that achieves this apart from the refractor is the off axis newt. But they are not comercially available and therefore are costly. For £500 i can get a 8" newt with 1/6th wave mirror, a 20% central obstruction, a curved spider and a hernia.

Theres not much else available in this price range that will offer such good performance visually with this much aperture. If there is please let me know!

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russ

russ

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give me an 8" SCT over a 4" frac for planetary imaging any day

Martin has a point, all the best imagers use an SCT, although none use the 8" mind. Celestron seem to rule as well. And their C9.25 is pretty special as it uses an f2.5 primary mirror whereas the other SCT's use an f2. Also the Celestron OTA's are lighter than their Meade counterparts. But one thing is for sure, from an imaging standpoint the SCT's are brill.

Would also agree with Martin that a bit of LP is no reason to give up on the Deepsky. I had mag 2 (M45 and the whole of Lyra except Vega were invisible) skies from my old house but still managed to get by with filters.

Russ

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GordonCopestake

GordonCopestake

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Actually thats not that bad an idea Steve, as it's a lot lighter and has a 16% CO! Could be a winner...

I appreciate that in imaging aperture rules everything. However visually contrast is key. As i said im very keen on SCT's as they are small and convienient. However they are just not contrasty enough for me. (Is that a real word?)

With imaging and long exposure deep sky is accessable (I took an image of M57 only the other day) however to be honest, im not really "into" imaging at this point. If i want to see a picture of a galaxy on my screen there are images from the hubble that far outstrip anything i could produce. I appreciate that it's a whole new argument, but for me seeing it with my own 2 eyes is key. In my light pollution visual observing of DSO's is just not realistic.

Saying that the idea of a dob apeals to me in that i can drag it easily to a dark site and it will take about 30 seconds to setup. Although i'll miss the tracking and GOTO which is why i want a tube i can mount on my CG5 as well.

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GordonCopestake

GordonCopestake

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Earlier today I ran a tape measure out to 1600mm to see just how big it would be and was shocked i must say. Although saying that i believe the OTA weights that Orion Optics have supplied are incorrect. I think the 6" f11 is only 4.5kg and not the 7kg they have told me. I believe the 7kg includes the dob base.

Even so, as you mention Gaz, the torque is excessive.

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GazOC

GazOC

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Nope, but when I used to have my 127mm 9.4 (1200mm) on an EQ5 the main problem was the wobble caused by the distance that the lens cell was away from the centre of the mount rather than the weight of the scope.

I'm don't know if it would fail, I just said it would be substantial. :D

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OXO

OXO

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Had a 10" SCT on a EQ5 that wasnt too bad with an extra counter weight, on the Heq5 it is just about right with again another counter balanced weight.

Resolution is the key IMHO for Planetry imaging and the 8" 10" scts do a good job of it.. 8" f8 reflector would be awsome but tube lengths would be a problem i think esp as the tripod legs dont go so high..

James

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GordonCopestake

GordonCopestake

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As gaz says the moment arm is the problem and stability and, at extremes, usability are the issue. If the OTA moves too much it is useless. The weight isn't the issue, just the play in the "twist" of the saddle. Unfortunatly the CG5 is particularly Rubbish in this.

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The Warthog

The Warthog

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One other thing about a longer tube is that if you are using a tripod, the bottom of the tube is more likely to bump into the tripod legs when you are trying to view objects overhead. This was an issue with my older scope, about 1m long, while my newer scope, about 25cm shorter, doesn't bump into the tripod. If I were using a longer scope again, I would be tempted to use a pier mount.

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Guest MoJo

Guest MoJo

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Hmmm MN 68??

for all of the reasons given??

Dunno, trying to work it out for myself too!!

MoJo :D

I do like the MN68, as it only has a 15% CO, however it's only 6" aperture, over 10kg heavy and costs £1000...

....Ahem

http://web26.h137151.serverkompetenz.net/html/

taken from the buy and sell section of this website......Euro 1295........

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Guest MoJo

Guest MoJo

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Opps, sorry guys

a. got euro/£ rate wrong ( :))

b. Yeah, it is long and heavier, don't think I'd like that clubbing me round the head if you hit the wrong button on a goto and it took off........... :tearyeyed:

the search goes on................

MoJo.

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iancandler

iancandler

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I wouldnt want to try and do it all with one scope..

The eyepiece issue you mentioned I havent found to be that much of a problem and My beast is F4.5 I think ( off the top off my head) and Im using mainly Antares W70 eye pieces in the msaller sizes (14mm - 5.7mm) I havent had any problems there.

Maybe it would be owrth considering two scopes? a faster 8" dob for the DSO stuff and a 6" long focal length reflector for the planetary .. Both could probably be picked up from either uk astro ads or e bay and fall within your budget. I think you would be able to even get the 8" dob new if you went for the revelation and it does have pretty good optics and the 2" crayford focuser going for it. Then hunt out a secondhand orion 6" OTA or simular to put on your mount.

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