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Scope and EP help.


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Ok so its a clear sky and I'm all setup with my 300P ready to have a good look around.

I have just tried using my Rigel 32mm SWA, and the two Skywatcher EP's that came with the scope, 25mm and 10mm plossls.

I cannot get any of them to focus, if I pull the EP's out of the focuser draw tube I can get them to focus but they would barely be in the tube and not in it enough to be able to tighten up the screws.

Is this normal? Or do I need an extension tube?

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I don't think it is normal. The supplied eyepieces at least should come to focus - the Rigel might have a different focus position but should not need to hang out of the drawtube. What were you trying to focus on ?.

The focus region of an F/5 scope is quite shallow so it's possible that you went right through it - it's a pretty fine business focussing a short focal ratio scope.

John

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Hi John,

I tried to have a look at the Pleiades. I'm pretty new to this but I normally wind the focus all the way in and then slowly bring it onto focus by winding it out. I get a nice circle which gets smaller as I wind it out but it never reaches focus, if I then undo the EP and then slowly pull it out the circle gets smaller until it reaches focus.

I know what your saying as when I use my smaller Newt I can take the object either side of focussed but with my 300P its as if the draw tube just dosnt have enough travel.

I will go and try again but I'm pretty sure somethings up.

Cheers,

Simon.

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Just went out and tried it again. Same thing happening. I collimated the scope this afternoon before dark, can the position of the mirror i.e. distance between primary and secondary have any effect on focussing?

If the focal point for an f5 is shallow I dont see how that might be an answer as the EP is almost out of the tube before focus can be achieved.

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Was it able to reach focus before you collimated?

If it worked OK until you collimated it, I would say you need to re collimate but move the primary mirror further up the tube via the collimation knobs.

Normally if you cannot focus there are just two options, move the primary up or buy a shallower Focuser.

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Simon, I am guessing that you have bought one of the first batch of Explorer 300p that had tubes cut to the wrong length. Have a chat with your supplier, it will need to be modified or replaced (assuming you weren't made aware of the problem when you bought it).

HTH

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Hi Doc,

Unfortunatley tonight has been the first night that I've been able to use the scope since I got it Monday just gone.

If the EP needs to be further away from the secondary then wouldnt a shallower focuser just add to the problem?

I will see how much further up the tube I can move the mirror, and see if that has any bearing on it.

If all else fails there is always the unenviable task of making a call to the supplier....

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Simon, I am guessing that you have bought one of the first batch of Explorer 300p that had tubes cut to the wrong length. Have a chat with your supplier, it will need to be modified or replaced (assuming you weren't made aware of the problem when you bought it).

HTH

Hi Steve,

I had no idea that there was any kind of problem. Would it be ok if I sent you a PM?

Cheers,

Simon.

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Simon, I am guessing that you have bought one of the first batch of Explorer 300p that had tubes cut to the wrong length. Have a chat with your supplier, it will need to be modified or replaced (assuming you weren't made aware of the problem when you bought it).

HTH

Wow :icon_eek: - thats a fairly serious fault !.

John

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The length of a Newtonian's tube is not necessarily the same as its focal length, though it will be similar. I am not at work so I cannot quickly measure the OTA's length but if somebody else can and posts the measurement here you will soon know whether there is something amiss.

Also, if you bought the telescope at a discounted price and you do discover that the tube is too short by only a few millimetres then you might consider keeping it and buying a focus extension tube.

HTH

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In case the seller doesn't solve this, I can sell you a 2" extension tube at a cheaper price.

It's new. I bought it so I could attach 2" filters to it and then change both 2" and 1.25" EPs freely while keeping the filter in.

It arrived 2 weeks ago and, has I tested, I found out it added too much length and I couldn't bring any of my EPs to focus on it. It's been stored since.

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Thanks for the offer Pvaz, I will let you know how I get on with the seller Monday.

John, I've been made aware tonight that that is something that could be done to allow focus of a dslr but this scope was bought from a shop in a "as new" condition.

I'll see what they say Monday.

Cheers everyone for all your help, first light turned into first fright for a while there but with all your help and insight its made the evening a whole lot more bearable, and at least I got to see the Pleiades through my binos.

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well from top to tail its measuring in at 1465mm...

We don't have an Explorer 300p in stock atm but I asked Skywatcher's importers to measure one for me, they came back with 1420mm, which makes yours 45mm longer than normal.

Why am I not surprised, two emails and a few phone calls all unanswered.

This is a very buy time of year for astro retailers, they might answer tomorrow.
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Just to follow up I've spoken to the supplier, who is quite busy at the moment so more patience on my part required. No one is quite sure whats happening but the fact that an extension tube will sort it out makes for a simple solution.

I'm now waiting for a call back to let me know that they can issue me with whatever is needed to get the scope up and running. Something about checking with the owner first, so fingers crossed they'll sort something out for me. I've been assured and it would nice to get your opinions that using an extension tube wont hinder viewing in any way. They also mentioned that it will help when attatching my dslr to the scope. So thumbs up if they sort it out.

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Maybe you should consider yourself lucky that this modification has been done. An extension tube will not degrade your observing one bit and you will not need to change to a low profile focuser or bring the mirror up or hack a slice off the tube to get a DSLR to the focus point.

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