using 1.25" 40mm eyepiece - doesn't "fit"

[rogueElement]

I am a complete beginner; I received a telescope today as a present (Skywatcher Skyhawk 1145p) and included from the supplier was a gift pack which included a Celestron 40mm eyepiece (I have already established from reading articles/posts that the benefits of such are dubious but...)

Whereas the supplied, Skywatcher eyepieces fit perfectly and I can use the focus wheels, the 40mm eyepiece only just slots in and on attempting to focus nearer objects, it is pushed out; I have to hold it in place

Is the Celestron 1.25" eyepiece just not compatible with the Skywatcher telescope or is there something else I need to do to use this particular eyepiece?

Confused and befuddled...

Edited April 21, 2020 by rogueElement
incorrect size

[Mr niall]

Can you post a picture of the eyepiece / your focusser please?

What do you mean when you say: "the benefits of such are dubious"? 40mm eyepieces are absolutely brilliant, but often much maligned sadly. When you say 1.5" eyepiece - do you mean 1.25"? I will assume you do. The problem with 40mm eyepieces is that the field stop of a 1.25" eyepiece means that generally speaking a 30mm Plossl or a 25mm wide angle eyepiece will give you the widest view that your scope can accommodate - so you don't really gain any extra FOV by using a 40 over a 30 in most cases. However where they do excel is on very long focal length scopes such as Maksutov's, Shmidts and long focal length refractors - where their larger exit pupil is a real advantage over smaller eyepieces in some circumstances. I use one in my 90mm refractor most nights.

You need to do two things really:

•  compare the barrel diameter to the other eyepieces that came with your scope - if they are the same then it will fit fine BUT...
• Also check the focal length of your scope. I think they did an older version of the Skyhawk that had a built in barlow (a small lens physically fitted to the bottom of the focusser). If yours really is a 1145P then it wont have that but probably worth checking. Your scope should be around 500mm I think, with the Barlow's ones being about 900mm. Although I'd still be surprised if that were he culprit even if it were one of those.
•  Dont bother trying to focus on anything closer than about 50 feet away. Telescopes aren't designed for that, many wont come into focus much closer than that.

Having said that if you do have the standard 500mm one then a 40mm eyepiece wont be the perfect choice for widefield viewing due to the large exit pupil, but still one I would hang on to. 40mm have their place! All 1.25" eyepieces will fit in all 1.25" focussers (general rule, there are subtleties regarding focusser travel etc but don't worry about it).

Edited April 21, 2020 by Mr niall

[John]

When you say nearer objects, how near do you mean ?

The focal plane (the point at which the eyepiece reaches focus) is often different with 40mm eyepieces in the 1.25 inch fitting.

 

[rogueElement]

thanks for the swift response! I came back here to edit the 1.5 to 1.25 to find you'd already responded!

I appreciate there's no point focussing on close objects but there is nothing distant for me to try the scope on in daylight...under current lockdown, I can only see surrounding houses and just wanted to get it setup in readiness for tonight.

The barrel diameter is the same, so 1.25" but then the top is wider and only just fits into the scope...I assume my issue is that there is very little travel fitted directly like this.

Interesting that you mention the barlow lens...one of these came with the Skywatcher and taking it out I realise that it is in an adaptor of sorts (can be unscrewed) and I can the use that on the 40mm eyepiece too...so problem solved.

Apologies for denigrating the 40mm eyepiece...you're right though, people don't seem to be fond of them :-S

 

I have to say that the telescope came with much literature on the SynScan system but only one generic leaflet on telescope set-up - I'm surprised there was nothing specific to this model.

[John]

If you try it on the stars you might find that the problem goes away. The eyepiece will reach focus further inwards on a target that is effectively at infinity rather than a much closer target. The 40mm may well not reach focus at just the same place as your other eyepieces though, it's worth being aware of that.

The usual criticism of 40mm eyepieces is that they cant show any more sky than a 32mm in the 1.25 inch focal length, which is true. So the view down them can seem a little like looking into a tunnel. Owners of long focal length scopes find them useful tools though.

 

[Mr niall]

6 minutes ago, rogueElement said:

Apologies for denigrating the 40mm eyepiece...you're right though, people don't seem to be fond of them :-S

Sorry I wasn't trying to criticise I was just saying that the 40mm eyepiece - like you've realised - does seem to attract a lot of negative opinion. But its not really an "all rounder" and does have it's place. Sadly they do not really excel in shorter focal length scopes like yours. But they are a useful eyepiece in their way. I really enjoy using them.

[rogueElement]

4 minutes ago, John said:

If you try it on the stars you might find that the problem goes away. The eyepiece will reach focus further inwards on a target that is effectively at infinity rather than a much closer target. The 40mm may well not reach focus at just the same place as your other eyepieces though, it's worth being aware of that.

The usual criticism of 40mm eyepieces is that they cant show any more sky than a 32mm in the 1.25 inch focal length, which is true. So the view down them can seem a little like looking into a tunnel. Owners of long focal length scopes find them useful tools though.

 

it's not just that I couldn't focus it, I could if I held the eyepiece in place by hand; the eyepiece only fitted into the scope if the focuser was fully retracted, if I did then try to use the focus controls the eyepiece was "ejected", hence I held it in my hand. Using the part I found on the barlow lens, I was able to secure the eyepiece in place. I'm trying to upload pics from my phone to mac to explain but having difficulty....there's a common element here, I know.

[Ruud]

I think the thumb screw (or the ring that it is attached to) that fixes the eyepiece in place blocks it when you try to insert the eyepiece. Which is why the eyepiece doesn't sink in deep enough and falls out too.

 

 

 

Edited April 21, 2020 by Ruud

[rogueElement]

37 minutes ago, Ruud said:

I think the thumb screw (or the ring that it is attached to) that fixes the eyepiece in place blocks it when you try to insert the eyepiece. Which is why the eyepiece doesn't sink in deep enough and falls out too.

 

 

 

There isn't one??

Anyway, here are the photo's:

1) (8219) eyepiece inserted into focuser

2) (8220) try to focus and out it pops

3) (8221) adaptor supplied with barlow lens inserted into focuser and 40mm eyepiece into that..problem solved...unless there was something else I could have done?

[DaveL59]

looks to me like there's a part missing off the end of the focuser tube?

Mine's an older SW130 newt so perhaps a little different but it has a ring that screws onto the focuser draw-tube that is a smaller diameter inner 1.25-in for the EP to fit properly and also has screws to secure the EP as per pics. Your drawtube however seems short of a threaded section which seems odd to me. Would explain why the EP is sitting at an odd angle also on your pics.

 

Edited April 21, 2020 by DaveL59

[Ruud]

🤔 Makes sense, if the missing ring would hold this black part in place everything would be fixed.

 

EDIT

In Dave's pictures the focuser drawtube is threaded at the top, but yours isn't. Maybe the black part (the eyepiece holder) is supposed to be held in the draw tube by friction or glue? 

Edited April 21, 2020 by Ruud

[DaveL59]

Didn't find a manual for this scope but did find this youtube vid:

 

looking at that and around 8mins, I see the focuser looks quite like the one on my SW130 and quite different to yours before you fitted the "barlow". Can you show what parts you have "left over" for your scope after you've assembled it all? If that section is broken off the inner drawtube then you'll struggle to be able to use the scope at all as the eyepieces will never sit square and give a distorted image if any at all.

 

[John]

As said above, the eyepiece fitting is missing from the end of what is known as the drawtube - the chrome part that goes in and out when you focus.

There should be a thread on the end of the chrome tube to take the eyepiece fitting but I don't see one. Maybe it is an internal thread ?

It actually looks like the drawtube (chrome) is in backwards in the photo.

[rogueElement]

Brilliant, got it, found it, thank you all. Thanks too for the correct nomenclature - why did the telescope not come with a basic diagram indicating the component parts - I appreciate there aren't many but it helps to call them by the right name eg draw tube.

It was my fault entirely, I'd removed the eyepiece fitting in error, not appreciating that it had a cap on the end; I thought it was all one piece and therefore needed removing in order to insert eyepieces.

great, I'm all set, it's been a very clear sunny day today, hoping for clear skies tonight.

Thanks again!