150p end cap

[Wikiastro]

Hi. I was wondering what the purpose of the small removable portion of the end cap on my scope is (SW 150p) The large disc has two small raised circles on, one of which is removable. This leaves a hole in the end cap about 1/4 of the way in from the edge. Can't fathom it. Any idea please?

[Floater]

It's for cutting down on glare from, for example, the full moon - like tomorrow night :-)

Leave the large cap on and take off the small cap and store it on the 'small raised circle' before looking through the eyepiece.

[Alien 13]

Its to allow the scope to be used with a much larger F ratio can be handy sometimes for luna but great for solar viewing with a suitable solar filter fitted securely over the small hole.

Alan

[rwilkey]

Hi, this small cap when removed stops down the aperture, say for example if you are looking at something really bright, one usually removes it and places it on the fixed cap so it doesn't get lost.  To be honest few people use this facility.  But what it is good for is observing the Sun, by using the correct solar film - Baader Astrosolar film, by sticking it firmly across the back of the hole and viewing off-axis, avoiding the spider and secondary mirror.  Baader Solar film ND.5 here: http://www.firstlightoptics.com/solar-filters/baader-astrosolar-safety-film-nd-50.html  Always ensure you do not use the finder when viewing the Sun, keep the lenses covered with their endcaps.

[Floater]

Just to fill in another detail:

Your 150P normally gives an f ratio of 8; using only the 'small hole' gives f30.

[Uplooker]

Just to fill in another detail:

Your 150P normally gives an f ratio of 8; using only the 'small hole' gives f30.

The 150P has an f ratio of 5, the 150PL is I think f/8.

Ian

[Wikiastro]

Brilliant. Always get a prompt and detailed answer on SGL. thanks folks.

[Wikiastro]

I suppose that covering the hole is cheaper than covering the whole aperture with solar film.

[Floater]

Hi, Ian. My SW Skyliner 150P has a focal length of 1200. I'm pretty sure that means f8 but happy to be corrected. :-)

There seem to be so many models that it can get confusing, so please come back on that, if I'm wrong.

EDIT: Just checked FLO website and the Skyliner 150P is specced as primary 153mm and focal ratio of 7.84.

[Stu_]

The Dob 150p is a f8, the newt comes in 2 flavours 150p is f5 & the 150pl is f8

[Floater]

There we are!

As I wrote: so many models ... Have changed my sig!

[Wikiastro]

Just to clarify mine is the 150p newt on an eq3. 750mm fl so f/5.

[John]

When equatorially mounted the F/8 variant is known as the Explorer 150PL while the F/5 version is the Explorer 150P. The dobsonian versions are all F/8 but slightly confusingly the scope is known as the Skyliner 150P - no "L" suffix is used despite the longer focal length.

[Stu_]

From experience removing the cap makes the exit pupil too small, but does help.

When lunar observing I use a 9mm x-cel lx on my 150p newt, as it frames the moon nicely & a moon filter is better, as it still gives you the full resolving power of the scope.

[Floater]

I feel I ought to apologise if I caused any confusion. My intentions were honourable and I was so excited at coming across the first semi-technical question I thought I could help with!

Anyhow, no harm done I hope. Plus I've learned even more ...

And, from my desktop machine, rather than my usual iPad, I can follow the time-hallowed SGL ritual and put a face on things -

(My conscience was bothering me.)

[John]

Don't worry Gordon, It's not your fault that Skywatcher have confusing scope nomenclature !

[Uplooker]

Hi, Ian. My SW Skyliner 150P has a focal length of 1200. I'm pretty sure that means f8 but happy to be corrected. :-)

There seem to be so many models that it can get confusing, so please come back on that, if I'm wrong.

EDIT: Just checked FLO website and the Skyliner 150P is specced as primary 153mm and focal ratio of 7.84.

I feel I ought to apologise if I caused any confusion. My intentions were honourable and I was so excited at coming across the first semi-technical question I thought I could help with!

Anyhow, no harm done I hope. Plus I've learned even more ...

And, from my desktop machine, rather than my usual iPad, I can follow the time-hallowed SGL ritual and put a face on things -

(My conscience was bothering me.)

Hi Gordon,

You have no reason to apologise, I almost feel I should be apologising if you do. It seems we have both been confounded / thrown a curve ball by Skywatcher. I had no idea that the 150P dobsonian was a different f ration to the equatorial 150P. Seems we have both lived and learnt.

Ian

[FunkyKoval35]

I think using end cap with this small hole is not good idea... You have to remember that cutting aperture = lower resolving power! And this is why there is something like moon/solar filter in every astronomical shop