Damn why is bigger aperature so tempting...

[BenBroad]

I've got a 6" Celestron NGT and been able to get it working fine just once... with all the poor weather in South Yorkshire.

I just had the bright idea of selling it and getting a 12" truss Dobsinian, now of course I havent given it much of a testing yet but the idea of doubling the aperature is so damn tempting... Maybe its best to think about it next year.

[legion48]

Doubling the aperture isn't going to fix the weather, I'm afraid.

If there's one thing I've learnt with this hobby, it's never to buy during a period of bad weather. It's usually a "boredom" buy and will be regretted sooner or later.

[Viking]

Ben,

Going from 6 to 12 isn't just doubling, its four times greater.

Aperture fever setting in. Bad sign for the old bank balance!!!

John

[almach]

Ben,

Going from 6 to 12 isn't just doubling, its four times greater.

Aperture fever setting in. Bad sign for the old bank balance!!!

John

Assuming that is to do with the sqaure of the aperture i.e. (12x12) = 4 (6x6). i'm assuming that 8" is 1.8 times better than 6" and 10" is 2.8 times better than 6"? I was thinking of increasing as well and was wondering were to go from 6".

Also, how does focal length factor into that? I am into double stars and understand that a longer focal length is better for that. So is 6" with a long focal length better than a 10" with a shorter focal length?

Hope that makes sense.

[adamsp123]

Hi, I would be a bit careful of just looking at the numbers versus what your eye will see, for example my 120ED (4.7") v my 10" SNT = 4 times the light gathering in theory, but my eyes "see" about 2x only. I think it is like sound levels in decibel,s where 3dB is doubling the sound pressure level but it takes 10dB for the ear to sense 2x the sound level, ie it is not a simple linear function.

Some of the "lack" of difference beween my 2 main scopes is the Refractor v Reflector argument, the refractor gives a crisper view with more contrast aiding the eye to "see" fainter objects more easily.

If I could keep only one, I would keep the Refractor! but the 2 compliment each other nicely.....until I get a massive Dob!!!

Pete

[kniclander]

Also, how does focal length factor into that? I am into double stars and understand that a longer focal length is better for that. So is 6" with a long focal length better than a 10" with a shorter focal length?

Hope that makes sense.

I have spent an hour or so tonight looking at doubles. My 10" newt is way better than my 6" newt for doubles because it shows up colour so much better (and of course the resolution is in theory better but I don't notice that so much).

[proflight2000]

I think one of the main aspects as well is that just staying put brings out so much. I am the same, I want to move around to everything and never stop to ponder. The it was mentioned to me to just find a good spot, say the seven sisters, and just keep looking, allow the eyes to really grasp what it there then you start to see things that you'd miss by scooting off. So try that with the 6 inch, you'll be quite suprised.

[adamsp123]

I think one of the main aspects as well is that just staying put brings out so much. I am the same, I want to move around to everything and never stop to ponder. The it was mentioned to me to just find a good spot, say the seven sisters, and just keep looking, allow the eyes to really grasp what it there then you start to see things that you'd miss by scooting off. So try that with the 6 inch, you'll be quite suprised.

Agree absolutely with this I tend to want to flit but if I OBSERVE I see more and more detail.

Your other question on focal length, I suspect it is the magnification you get from an eyepiece ie a 10mm EP in a 1000mm focal length tube will give 100x mag in a 500mm it would give 50x mag so for splitting doubles, easily obtained magnification with the EP must be a help.

[philsail1]

Doubling the aperture isn't going to fix the weather, I'm afraid.

If there's one thing I've learnt with this hobby, it's never to buy during a period of bad weather. It's usually a "boredom" buy and will be regretted sooner or later.

Good sound advice "Legion48"

philsail1

[acey]

Yes, this is the best advice. Upgrade the aperture once you've done all you can with your existing scope.

In terms of what more you can see, a 100% increase of aperture will bring in approximately 1.5 extra magnitude of visibility. But exactly how faint you can see depends on how dark your sky is. In my back garden the limiting magnitude is 4.5 - I drive to a place where it's 6. That difference is equivalent to doubling the aperture of my scope. So again, before upgrading aperture, think about upgrading your sky.

The extra resolving power of larger aperture is limited by the turbulence of the atmosphere: the air will very rarely be still enough for a 12-inch to resolve more detail than a 6-inch would. The reason for increasing aperture is so as to get a better view of faint deep-sky objects.

I recently upgraded from an 8-inch to a 12-inch, which gives me more than double the light-gathering (144/64 = 2.25) and a magnitude gain of 0.9 [5log(12/8)=0.88]. This is enough for a visible "wow" factor, any less of an aperture increase might not be. In general I wouldn't want to upgrade by less than 50% of aperture, otherwise I wouldn't get enough wow per bulk. If I ever make another step up it will be to an 18". But I don't ever expect to run out of things to see with the 12".

Andrew

[almach]

Yes, this is the best advice. Upgrade the aperture once you've done all you can with your existing scope.

As cool as it would be to get a shiny new scope, that is a very good point. I have barely scratched the surface of what i want to see and could see with my current scope. Besides, my dishwasher was pronounced dead yesterday and my missus seems to think that is a higher priority

[BenBroad]

Thanks for all the advice, I certainly agree I should give my current scope a proper testing. And really get used to it, but maybe consider keeping the mount and upgrading the OTA at some point.