Help with a new dob

[Bryan h]

I've just brought a revelation 12" dob and used it for the 1st yesterday and was looking at Jupiter but it looked the same as through my 127 mak,I wasn't expecting Hubble type views but considering there's a 7 " difference In aperture size I thought i would see a difference.

Having said that I've only had the mak for 10 months and still learning and I have no experience with a large dob, It could be down to the seeing conditions but I need tips and advice on getting the best out of it.

How long does it take for the mirror cool down and how much would that effect the views?

Collimating worries me and I can't tell if the mirrors a aligned even with the Cheshire eyepiece

[GuillermoBarrancos]

The 127 mak has a very long focal length (F11,81), while Your 12" dob has a very short focal length (F5).

So magnification wise you will not see much difference between the 12inch dob and the 127 Mak with the same eyepiece.

Tho, With good colimation and decent seeing conditions you should see more details in Your 12inch dob.

Your 12inch dobsonion is a huge light bucket that excels at deepsky targets. It will blow away your 127 Mak. No contest.

[ronin]

At a guess the newtonian will be about f/4.8, this gives it a focal length of 1450-1500mm, basically the same as the Mak.

So with the same eyepieces you will get almost an identical magnification.

So in terms of size expect no difference.

The newtonian will collect more light so the object should be brighter, but in terms of size/magnification I would expect a similar result.

[Moonshane]

on average the Mak and dob will give similar views of Jupiter, although the disc will be a lot brighter at the same magnification in the dob. on nights of good seeing the detail will be substantially higher in the dob but you might have to wait for steadier spells. with my 12" f4 the views are only slightly better than my 6" f11 but when they are better the detail is jaw dropping. in fairness it is in both

on faint objects the 12" will be a lot better than the mak as aperture wins.

[LukeSkywatcher]

I think the fundamental mistake people make is in thinking bigger aperture = larger image. This isnt the case. Larger aperture = more light from a given object,which in turn = finer detail.

If you want a larger image with any EP, you need a barlow lens or similar. Great!!!!!!!!!!!! but you run the risk of the detail being darker and more blurred. Not always, but it happens.

Of course none of this matters if the atmospheric "seeing" and "Transparency" conditions are rubbish. 

On a really bad night you may even struggle to see good detail on the Moon.

[ChrisSJ]

I believe the others have hit the nail on the head.

For me personally, 12" Dob verses 127 Mak, no contest, the 12" would be my preference all day long. However, for AP, then I'd take the Mak.

12" mirror cool down isn't that important for DSO, I start seeing straight away, but for planets it depends on conditions. Good rule of thumb, 30 - 45 minutes should be sufficient.

If you can get to a dark site with both scopes, I believe the 12" will give you better satisfaction. That doesn't sound quite right.

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[swamp thing]

I think the fundamental mistake people make is in thinking bigger aperture = larger image. This isnt the case. Larger aperture = more light from a given object,which in turn = finer detail..

What Paul is saying (I think) is don't expect to see a much larger image of a planet just by looking at the size of the aperture.

The fundamental reason for increasing aperture as far as planets go is to increase resolution. This is often compromised by atmospheric seeing.

The fundamental reason for increasing aperture for deep sky observing IS to increase image scale. When observing faint objects we can't make them appear any brighter. What aperture does is make them bigger so our eyes can see them better.

Any extended object like a galaxy reaches its maximum surface brightness when the exit pupil is the same as our dilated pupil. Once this point is reached we cannot make it brighter. What we can do is to increase image scale at this max exit pupil size by increasing aperture.

What does this mean. Well, when observing our little faint galaxy through a 4" scope we select our minimum power eyepiece to make it as bright as we can. The trouble is its tiny. When we observe the same galaxy with the same exit pupil through an 8" scope. It's no brighter but what it is, is twice the size. This allows our eyes to pick out more detail. The bigger the scope the more we increase the image scale without losing surface brightness.

Hope that makes some sense

[jabeoo1]

If you can get to a dark site with both scopes, I believe the 12" will give you better satisfaction. That doesn't sound quite right.

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chrisSJ this made me laugh lots.  Thanks.

James

[Bryan h]

cheers everyone that has cleared up a few things for me...I think I had made some classic mistakes in terms of expectations,now to get out there and gain experience.

[Astro Imp]

cheers everyone that has cleared up a few things for me...I think I had made some classic mistakes in terms of expectations,now to get out there and gain experience.

This hobby is all about experience and patience.