E.P to purchase for the Skywatcher 150P Dob.

[Andy-T]

Hi Guys

I have recently purchased the 150, what a fantastic scope! I have managed to locate a few objects that i targeted such as Albeiro, the double cluster and Andromeda.

The sky was not great when looking at Andromeda (why is that the case when you just buy a telescope?) so the view was little more than a greyish blur.

I have the supplied 10 and 25 mm E.P and  a 3 X Barlow lens (this was a cheap £8.00 one off Amazon).

What would you recommend i purchase to get the most out of my scope when looking at planets, nebulas and galaxies? 

The 3 x Barlow is fine with the 25 mm E.P but with the 10 it is badly out of focus. Should i buy a 2 or 2.5 x barlow or a higher quality E.P maybe 6mm to get the best results?

As always, thanks in advance!

Andy

[emadmoussa]

Nice to hear you like your scope. And of course, thanks for all the clouds! Well, I got a new scope recently ...so we're both responsible for the clouds

Anyway, for eyepieces there are a lot of opinions out there on what is ideal and what it is not. However, it seems there's an agreement on the quality of certain eyepieces.

I remember those supplied eyepieces. They're not very bad, but they could be so much betters. With my first scope I replaced the stock eyepieces with a bunch of Plossls. In all honesty, they did show a bit of difference in image clarity and contrast. Also like you say, these stock eyepiece don't barlow very well while the Plossls were fine with both the stock Sky-watcher barlow and the better quality GSO 2.5x barlow. However, I tend not to use barlows simply because I've got a range of eyepieces that make up to that.

So, if you want to keep the spending low, go for a 15mm Plossl, perhaps a 8 or 9mm and 25mm. You can always barlow the 15mm and you'll still get a decent magnification and resolution on planets, provided the barlow is at least of an acceptable quality.

Bear in mind that eyepieces below 8mm (be it 5mm or 2.5mm) tend to have a very small eye hole which I personally found  incredibly annoying.

If you have few bucks to spend, I'd suggest you get yourself a nice wide-field eyepeice. With your scope a 5mm Baader Hyperion will give excellent views on planets without compromising much of the field of view. In other word, with wide field eyepieces you'll see a bigger chunk of the sky at a time. Usually a regular Plossl will give you a 45-50 degree FOV on average, while the Hyperion on the other hand will give you 68 degrees. Some eyepieces stretch it to 82-degree or even 100-degree (like the case with Explore Scientific latest models). Most of my eyepieces are wide field, and use one or 2 Plossls on rare occasions when I want to align the finder scope or quick test of optics. But for proper sessions especially if you're observing deep sky objects, the wide-field eyepieces are worth every penny.

One last suggestion - of course if you have the cash  you can go for a Baader Hyperion Clickstop Zoom eypeiece. It retails at about £180. It gives 5 levels of magnification yet maintain a decent field of view. You have 8mm *68-degree'', 12mm, 16mm, 20mm and 24mm (the lower power has notoriously a Plossle like field of view), Personally, I found the Baader zoom to produce a similar image quality to that of the fixed length eyepieces of the same make (Baader Hyperion), but the only difference is that from 16mm to 24mm you lose few degrees in field of view. Having said that, I have mine almost welded to my 102mm refractor and pretty happy with it. However, optical quality aside, when it comes to convenience and hassle free observing, the Hyperion Zoom is the way to go. Nothing beats not having to swap between eyepieces when it's freezing out there

Good luck!

[Astro Imp]

I don't know how recently you have had your scope but the skies have not been great the last few times I have managed to get out. 

The 150P Dob has a focal length of 1200mm so with a 10mm EP and a 3X Barlow you are getting 360X mag, this is far too much. As you have found using the Barlow with the 25mm gives a nice image, that is only 148X mag., which is much more reasonable. 

You mention a 6mm EP, this will give a mag of 200X which is usually about the maximum we can employ with the skies we have in the UK.

Remember it is not all about high big you can make the target but how clear.

For a good introduction to the subject of EPs have a read of Warthog's post:- http://stargazerslounge.com/topic/43171-eyepieces-the-very-least-you-need/

HTH and good luck

[hippie]

You cant go wrong with the 1.25" 25mm BST Explorer EP From  Skies unlimited,  They do 18mm,15mm,12mm,8mm,5mm, lens also For £49 each , They are great lenses I use them with my 10" Dob and would recommend them as they are half the price of Meade our Orion lenses,  You will find Alan extremely helpful also if you have any questions, you can find him on ebay item no 161049463833 with all lenses in stock,  

[Qualia]

What would you recommend i purchase to get the most out of my scope when looking at planets, nebulas and galaxies? 

My journal has a number of observations on exit pupil. Exit Pupil = EP's focal length / telescope’s f/ratio which concludes:

• 6mm - 4mm - nice wide field, handy for star hopping, really nice for star fields and large open clusters
• 4mm to 3mm - nice contrast, good on star-fields.
• 2.5mm to 1.5mm - nice for most DSOs and general planetary viewing.
• 1.6mm to 1mm - nice contrast and resolution on planets, Moon and globs.
• 1mm to 0.5mm – possible finer detail on planets tweaked, Moon work, tight doubles split.
• 0.4mm – not any occasion to justify an assessment.

In practical, everyday terms, on most evenings I'm not pushing 200x. I may - on occasion - use 250x for the Moon, Jupiter, Saturn, but not every evening. I have never observed over 250x+ on anything. I’m not saying it isn’t possible; it’s just that I haven’t had cause to do so.

From this pattern, a number of observations can be made:

I feel one only needs one decent long focal length EP, something around the 50x. And that small focal lengths are not going to be used that much.

However, the range of possibility between 2.5mm to 1.5mm exit pupil is huge. What looks relatively tiny in terms of exit pupil is in fact a wide range of magnification dependent on the given object being observed, the atmospheric conditions, one’s state of mind, level of fatigue and even one’s age. That tiny 1mm covers most DSOs and a good general level of planetary viewing.

As you appreciate, then, there isn't really an ideal focal length to view galaxies, nebulae and planets. But I can offer a kind of working idea:

If you take your  telescope's aperture and divided it by 2 , you end up with 100. If  you look at that in terms of magnification you would require a 12mm EP. So, one EP could be around 12mm to 10mm and this would be quite a workhorse which would get a fair deal of use. Personally, if the forcal length is 1200mm I'd go for the 10mm.

From this, I figure little steps could be made on a 1.3 or 1.4 ratio.

So, for example, from the hypothetical 120x mag, or 10mm workhorse EP, I'd divide the mag or multiply EP's focal length by 1.3 and 1.4. So, I end up with 96x to 89x, or an EP of around 13mm to 14mm, or an exit pupil of between 2.6mm to 2.8mm.

So now we've got just 3 EPs: 50x, 90x, 125x.

With a 2x Barlow, that gives a useful range of magnifications: 50x, 90x, 100x, 125x, 180x, and 250x (weather and atmospheric conditions permitting). Sure, there is room for improvement, a lot of room, you might fancy 150x for Jupiter, for example, it's a rare night one can use 250x on Saturn, but you get an idea of what is possible with just 2 EPs.

I'm not sure if this helps, but I feel the numbers offered do help getting a general gist of what is possible and some kind of map to work around.

[ronin]

Not sure if said already but Andromeda will generally be a greyish blur. Do not expect the same as the many processed images you see. It is also big, you need a 3 degree view to get it all, which means something like 20x, or a bit less. Basically a wide low powered eyepiece.

[Andy-T]

Brilliant, thanks to all for taking the time to give clear information, certainly helps those new to the hobby like i am. Saw jupiter for the first time last night. Clearly see the moons with my 3 X Barlow and 25mm E.P in, was awesome!