some advice please, newbie in distress

[jonstrike]

Good morning ladies and gents, I was recently given a Soligor MT750 6"E newt with a 25mm plossl, a 2x adapter and a 4mm lens. I'm having trouble resolving the focus on images I'm seeing through the eyepiece.

At first I couldn't get an image of the moon-and yes, I had taken the cover off :-) . it was pretty dirty so i disassembled the scope entirely, cleaned it and reassembled. I then got a laser collimator, and was able to get an image. The trouble is that it is literally at the end of the eyepiece adjusters extension using the 25 mm lens and 4mm needs more length to resolve it.

I have improved things slightly by playing with the primary mirror, after cleaning I made it sit tight on the clips at the end of the barrel. This morning I moved the primary outwards on the adjusters so it sat flush at the end of the barrel. This improved things slightly but if I keep going the primary assembly will be poking out of the bottom of the barrel. I would love to know what's going on. I'm a total newb and if I sound like I know what I'm talking about its only from trawling lots of guides and sheer perserverence.

[jonstrike]

Forgotten my manners this morning, thanks in advance!.

[michael.h.f.wilkinson]

You could use a simple extension tube to place the EP further out. BTW, if the 4mm EP has "SR-4" markings, I would advise replacing it. At F/5 the magnification of a 4mm is not really over the top, but the SR design is not good.

[ronl]

Have a read of this http://stargazerslounge.com/topic/83359-fitting-a-crayford-to-my-soligor-mt-7506e/ sounds like

the focuser is not very good, you might need this modification on your scope, but if an extension

tube does the job, you should be ok.   

[jonstrike]

Thanks an extension tube sounds like a good idea, it seems silly that even a 25mm lens would be almost too much though. I'm sure there must be a physical configuration problem within the scope that is causing the issue. Could it be related to the secondary mirror?I also removed and cleaned that too.

I'll check the 4mm, I was given a 1" refractor scope too so I'm just waiting for an adapter to be delivered so I can use the lenses that came with that.

[jonstrike]

Thanks ronl, I'm at work ATM so will give that a read tonight.

[michael.h.f.wilkinson]

Thanks an extension tube sounds like a good idea, it seems silly that even a 25mm lens would be almost too much though. I'm sure there must be a physical configuration problem within the scope that is causing the issue. Could it be related to the secondary mirror?I also removed and cleaned that too.

I'll check the 4mm, I was given a 1" refractor scope too so I'm just waiting for an adapter to be delivered so I can use the lenses that came with that.

Some Newtonians are configured like that to allow photography. Having the focal plane well outside the tube is essential. They should supply extension tubes with the scope in that case, I would say.

[jonstrike]

Aha, that may be the case here. I was given the scope so there nay be parts missing. I'm sure an extension would work as since I moved the primary backwards I've been able to get a clear image but remain frustrated as it feels like I need an extra inch or two of adjustment for the 4mm. Thanks!

[RichM63]

The odd thing is that it is normally inwards rather than outwards adjustment that requires an extension, thus adding an extension moves the EP further out giving more available inward travel.

This line is confusing;

The trouble is that it is literally at the end of the eyepiece adjusters extension using the 25 mm lens and 4mm needs more length to resolve it.

You mention 2x Adapter, if this has a lens element it is most likely a Barlow lens and is best kept in your pocket for now. A simple extension tube will not have any lenses and behave as outlined above.

If you are trying to use a 2x Barlow lens with a 4mm EP in a 6" f5 telescope, forget it, the theory is good, but the seeing conditions will never allow you to use it. (Moon on a very very rare night perhaps.)

Try without the 2x 'adapter', if you still can't hit focus, try unscrewing the lens bit of the Barlow and use the empty tube as an extension.

In all instances, start by sorting focusing problems with the 25mm EP.