Little question

[Amit]

I want to know whether 150P skyliner dob will fetch me views of moon,planets, doubles, star clusters,nebulae, galaxies and all DSO stuff. The focal length is 1200 mm. So if I use a .5x focal reducer will the views be affected by any way. Will my slow scope become fast by using a focal reducer?

[Amit]

And also if i use less power EPS like 30-40 mm EPS will i be able to get wide field views??

[brantuk]

You may be thinking of the 150PL which is 1200mm and f-8. The 150P is 750mm fl and is f-5 so you wouldn't need a reducer. To get an idea of the views and camera image you can put the details into Ccdcalc or 12DString which are free to download

[Amit]

I am thinking of dobsonian 6" 153/1200. I have seen in the simulator but i dont know what the actual views might be. I want to use it both for DSOs and lunar and planetary

[swamp thing]

Hi

May I ask, why do you wish to reduce the focal length?

Regards Steve

[Amit]

In order to have wide field views and see DSOs. I found various sites stating short focal length is good for DSOs and wide field views of milky way and long focal lengths are good for planetary and lunar

[Parus major]

You may be thinking of the 150PL which is 1200mm and f-8. The 150P is 750mm fl and is f-5 so you wouldn't need a reducer. To get an idea of the views and camera image you can put the details into Ccdcalc or 12DString which are free to download

The Skyliner 150P is the same as the Explorer 150PL and are both F8.

Here's a few pictures taken, granted on EQ mounts, of what the scales are.... http://stargazerslounge.com/discussions-scopes-whole-setups/171668-skywatcher-150pl-owners-tips-mods-2.html Bare in mind that camera's see things differently to your eye but it shows the sorts of things to expect.

[swamp thing]

In order to have wide field views and see DSOs. I found various sites stating short focal length is good for DSOs and wide field views of milky way and long focal lengths are good for planetary and lunar

This is indeed true what you have read.

However the 6" Dob you have has a wide enough view to get nearly all DSO,s within.

The only objects that won't fit within the field are the giant ones that have low surface brightness. These are the ones that rich field telescope (RFT) or fast small scope can show best. But how well a RFT can show them is directly linked to how dark the sky it's being used from is. If your sky isn't ink black the RFT will not show the object.

Unless your sky is very dark I doubt that a focal reducer would be of any benefit.

Regards Steve

[Amit]

@Swamp thing

You ve had experience with dob mounts. Are objects easy to find and keep a track of ? This is my first scope so i dont want to go wrong anywhere, and i live in a light polluted city so I agree with you. In your opinion, what would you choose 150 dob or 150 on EQ mount?

[swamp thing]

I used to use powered EQ mounts. But have now switched to Dobs.

Personally I find EQ mounts very tedious to set up every observing session, and if using a newt on one, the eyepiece position frequently becomes very uncomfortable requiring constant faff about sessions with the tube.

Dobs are much more comfortable to observe with. Just stick it on the ground pull up a chair then sit down in comfort and observe.

If you are buying a scope to house in an observatory then a powered EQ is handy but out in the field IMO, they are a regular PITA.

Obviously if you wish to try your hand at imaging then an EQ mount will be required at some point.

Regards Steve

[Amit]

Well if i get 150P dob i can later switch to eq mount if if find interest in AP. Right now all i want to do is visual use and dobs are appealing to me quite a lot. And one last thing in skywatcher the tube would be of metal and the mount of wood right? bcoz i read in turn left at orion that some dob tubes are cardboard covered with plastic.

[brantuk]

The SW dobs have wooden bases and metal tubes - at least I've never seen a cardboard one. You also have a choice of solid tube or truss tube

[Parus major]

Well if i get 150P dob i can later switch to eq mount if if find interest in AP. Right now all i want to do is visual use and dobs are appealing to me quite a lot. And one last thing in skywatcher the tube would be of metal and the mount of wood right? bcoz i read in turn left at orion that some dob tubes are cardboard covered with plastic.

All you need is a mount and a pair of tuberings, if you buy a skywatcher mount the dovetail bar is in the box with it.

[Ags]

You may find it difficult to achieve focus with a focal reducer and a newtonian.

[swamp thing]

The SW dobs have wooden bases and metal tubes - at least I've never seen a cardboard one. You also have a choice of solid tube or truss tube

For my homemade 10" Dob I used concrete forming cardboard tubing. It works very well as its a good insulator unlike ally or steel tube.

It has lasted very well indeed as its a lot harder wearing than it sounds.

Regards Steve

[brantuk]

I wouldn't mind seeing that Steve - I quite admire folks who can make a working instrument the Blue Peter way lol. Would you be at Kelling at all this year?

[swamp thing]

I wouldn't mind seeing that Steve - I quite admire folks who can make a working instrument the Blue Peter way lol. Would you be at Kelling at all this year?

Not sure yet buddy. My work is kinda all over the pace at the moment. Very difficult to know what I'm doing week to week. So alas I'm not making any plans yet.

I've had to shelve plans for SGL7 this year that is an event I would really liked to have attended.

Regards Steve

[Amit]

Even though focal length is 1200 and focal reducer may be out of question but is it that the field of view is primarily dependent on eyepieces and not on the focal length? What if I use a 40mm or low power EP on the dob, would i get the same wide field views that a fast scope would show?

[Amit]

Ok let me ask this another way. At a given magnification, does the field of view stay the same for both fast (f/5) and medium (f/8) ratios? Say at 30x

[brantuk]

I think you need to read a few tutorials wich explain the consepts you are asking about. I'm not sure what you are trying to achieve but this tutorial is a good start and it explains some of the stuff you're asking about:

http://stargazerslounge.com/primers-tutorials/63184-primer-understanding-choosing-eyepieces.html

It's very good and I often revisit this page myself. Hope it helps

[todd8137]

Dobs are much more comfortable to observe with. Just stick it on the ground pull up a chair then sit down in comfort and observe.

i could not agree more