Big dobs, are they a pain when viewing higher magnifications?

[Jimtheslim]

I am oh-so-close to ordering a Skywatcher Skyliner 250p dobsonian. I would still like to observe planets at as higher magnification as possible (who wouldn't?!). I'm just wondering if this is likely to be a pain, given that you need to keep 'nudging' the scope and it's not like an eq where you can just feather the RA fine control. Does the constant nudging mean you can't let your eyes rest and start focusing on the details? I am talking about magnifications of 150x and above when seeing allows. On my current refractor a target such as Jupiter is very fast across the eyepiece, but giving the RA control a little wind every 20 seconds or so is not big deal. Is it likely to be a nightmare with a large dob? Anyone have much experience with this? The more I think about it, the more the goto systems seem attractive.

[estwing]

a tracking platform will help....goto also....100* eyepieces help...driving a big dob soon becomes easy...

[brantuk]

The larger the aperture the more light you gather and the deeper you can peer into space. With large dobs this usually means you are looking at dso's way out beyond the planets and using lower magnifications than you would use to see planetary detail.

It can take a nebula or galaxy for example several mins to cross the field of a low power wide field eyepiece in a big dob. It would only require a very small nudge to track it back to the other side again. I remember how surprisingly easy it was first time I nudged a big dob. You'd have no problem with a dob - it may even seem easier than manual tracking a planet close up in RA on a small scope.

[Jimtheslim]

21 minutes ago, brantuk said:

The larger the aperture the more light you gather and the deeper you can peer into space. With large dobs this usually means you are looking at dso's way out beyond the planets and using lower magnifications than you would use to see planetary detail.

It can take a nebula or galaxy for example several mins to cross the field of a low power wide field eyepiece in a big dob. It would only require a very small nudge to track it back to the other side again. I remember how surprisingly easy it was first time I nudged a big dob. You'd have no problem with a dob - it may even seem easier than manual tracking a planet close up in RA on a small scope.

Thanks, the more I have read about DSO's the more I now want to observe them, hence the desire to go for a big reflector to replace/go alongside my 90mm frac. If I had to sell this to buy the dob I would still like to look at the planets when I get the chance. I just didn't want to spend money on a scope that would mean this would be a lot of hassle.

[brantuk]

You'll still be able to view planets with a dob - my 12" used to give great views when I had one - but it did have alt/az tracking motors so I could regularly use up to 180x mag or so. It just means you use less magnification to track manually at a speed your comfy with on a non tracking dob. The nudging though is smooth and easy if you've set up the scope well.

[John]

I've used my 12" dob at 300x often and have used 400x and even 500x on occasions. The mount on mine is very smooth which helps and I use wide angle eyepieces which also helps with tracking but I've not found any particular issues.

One of the things I have noticed about the dob mount design is that it holds a big scope really steady even at those very high magnifications. Vibrations dampen down real quick. For my 12" F/5.3 scope tube, which is nearly 6 feet long, I'd need to have a huge and really sturdy equatorial to achieve the same. Apart from the cost, the fast setup time and relative portability of my 12" scope would evaporate with such a mount - it would become an observatory instrument which is not what I need.

 

[faulksy]

as john says, easy to acheive around 3 - 400x mag and its very easy if your dob moves smoothly like the 00. if you look at planets with your 90mm you had better sit down if you look through a good dob

[niallk]

Hi, fwiw I've had great views with my 250px - and I typically look at Jupiter and Saturn at 200x with 50° plossls in a binoveiwer.  I've seen beautiful details like the GRS, barges, festoons, fine banding structure on Jupiter; the Cassini division and subtle shading on Saturn and the darker polar region where the hexagon is; polar caps and the Syrtis Major on Mars.

While I do have a tracking platform, I find that I rarely use it tbh - I like to keep the setup fuss to a minimum most of the time. It does take a little patience to get the knack, but soon you'll be compensating for any overshoot without thinking.  While I haven't really done any, there are many suggestions out there to make the motions a little smoother.  As Estwing says, wider afov EPs plus the platform does really help too!  One thing I find is sitting down really helps on planets - I find my body is just more stable as I track and concentrate on the view.  Ever watch people sway as they stand still in a crowd?!

I'd say go for it - the 250px is a very capable scope - quick and easy to throw outside, and cools down (without fans) in 30-40mins for the best views of planets, or good to go straight away for low power DSOs. I find mine holds collimation exceptionally well.

Best of luck,

-Niall

[Jimtheslim]

38 minutes ago, niallk said:

Hi, fwiw I've had great views with my 250px - and I typically look at Jupiter and Saturn at 200x with 50° plossls in a binoveiwer.  I've seen beautiful details like the GRS, barges, festoons, fine banding structure on Jupiter; the Cassini division and subtle shading on Saturn and the darker polar region where the hexagon is; polar caps and the Syrtis Major on Mars.

While I do have a tracking platform, I find that I rarely use it tbh - I like to keep the setup fuss to a minimum most of the time. It does take a little patience to get the knack, but soon you'll be compensating for any overshoot without thinking.  While I haven't really done any, there are many suggestions out there to make the motions a little smoother.  As Estwing says, wider afov EPs plus the platform does really help too!  One thing I find is sitting down really helps on planets - I find my body is just more stable as I track and concentrate on the view.  Ever watch people sway as they stand still in a crowd?!

I'd say go for it - the 250px is a very capable scope - quick and easy to throw outside, and cools down (without fans) in 30-40mins for the best views of planets, or good to go straight away for low power DSOs. I find mine holds collimation exceptionally well.

Best of luck,

-Niall

Thanks, I guess it was this kind of reassurance I was looking for. I just wondered if there was a point at which large dobs become almost impossible to spend time looking at targets without a mechanical drive like a goto. I guess not. My in-laws live at a dark sky site just a few miles away and it's here that I would want to drive and set up with minimum fuss to really start looking for some DSO's. My garden is still pretty dark, but LP to the Eastern Horizon and the sun setting to the West means I have a fairly narrow band of good sky above, hence I will probably still spend a lot of time at home observing planets.

7 hours ago, faulksy said:

as john says, easy to acheive around 3 - 400x mag and its very easy if your dob moves smoothly like the 00. if you look at planets with your 90mm you had better sit down if you look through a good dob

 I have a little camping stool which I use to sit and study planets with my frac. I hear a used, adjustable drumming stool is the way forward with a large dob.

[Brasspoodle]

Nudging can also be something of an advantage on faint DSOs. The movement of an object in your eyepiece helps your eye notice the object (we pick out a moving object better than we do a static one). I've only ever wished for tracking with Orthoscopics at high power but at 300x with a 70° view Jupiter was (for me) enjoyably observable even with the fast drift time. 

[Moonshane]

Seeing will dictate magnification so on planets (in the UK) you will rarely use more than 200x and still get a good stable image. Assuming a 6mm eyepiece with a 60 degree field it would take an object 72 seconds to cross the field. You then just nudge it back to the right hand side of field and watch for another 72 seconds. Assuming an 8mm eyepiece at 150x (a more usual magnification) you'd get 96 seconds with the same apparent field. It soon becomes second nature. 

[niallk]

43 minutes ago, Jimtheslim said:

I just wondered if there was a point at which large dobs become almost impossible to spend time looking at targets without a mechanical drive like a goto. I guess not.

I've a 15" Obsession, and it's movements are exquisite. I was viewing Jupiter at 380x in an 82° Nagler last week, and manual tracking is a joy - smoothly move a fraction of the fov in any direction with zero 'backlash/overshoot. You point and it it stays pointed where you place it

[swamp thing]

Dobs gain stability as they get bigger. 

The bigger the Dob the easier they are to use.

[faulksy]

1 hour ago, Jimtheslim said:

Thanks, I guess it was this kind of reassurance I was looking for. I just wondered if there was a point at which large dobs become almost impossible to spend time looking at targets without a mechanical drive like a goto. I guess not. My in-laws live at a dark sky site just a few miles away and it's here that I would want to drive and set up with minimum fuss to really start looking for some DSO's. My garden is still pretty dark, but LP to the Eastern Horizon and the sun setting to the West means I have a fairly narrow band of good sky above, hence I will probably still spend a lot of time at home observing planets.

 I have a little camping stool which I use to sit and study planets with my frac. I hear a used, adjustable drumming stool is the way forward with a large dob.

what i ment by that was you will fall over when you loose your breath with the sight through the dob