Help please thank you

[Tonino]

Hello Guys,

Don't know if you might be able to help me with this one.

I have acquired a very old 'Vixen Saturn P102L f/15, 1500mm telescope refractor' you know 102mm objective lens, it dates back to Dec 1983, I acquired it from a seller advertising on the Astro Buy and Sell site.

My questions are this, I can't actually achieve focus? With the Star Diagonals I use I can't focus freely and properly except for one, a rather cheap and basic one which reaches focus but only right to the very end of the focuser 'inwards' direction I might add, with just a mere mm or two to spare!

My trusty, posh, and pricey Sky Watcher Dialectric 1.25'' inch one won't work and focus, it's blurry towards the end as it comes to an abrupt end of the 'inward' focuser travel!

I have tried a barlowx2 first in the end of the focuser (Because diagonal, then barlow after does not work, I tried it already!?), then the diagonal, and then the eyepiece that works! But rather dim in view looking at stars etc., and looks like some kind of shadow dancing/vignetting I suppose around the sides and corners of the eyepiece?

I think it's to do with the v long focal length of this telescope, and any accessory that is too big or too long in design will not work and focus, it only works really properly if I do not use any diagonals, and just simply put the eyepieces straight onto the end of the focuser! But then I get a v stiff and contorted neck, and I'm on the ground trying to look through my telescope if you see what I mean

Is there anything on the market like some specific Star Diagonal that might work for this particular very long refractor? Or particular accessory that I need to put at the end of the focuser for me to get my telescope focusing? I'ts about five and a half foot long!

I await your reply, thank you.

P.S. I also attach a couple of pics for your perusal.

Kind regards,

Tonino
 

[Roy Challen]

Hi Tonino,

 

You have answered your question yourself - you don't have enough in-focus. It doesn't have anything to do with the focal length as such.

The answer is to find a diagonal with a very short light path (the Takahashi prism diagonal is one, the Tal mirror diagonal is another), but even that might not be enough. If that's the case you'll either have to try a shorter focuser/low profile focuser or you'll have to have the telescope tube shortened.

The Japanese are known for observing without a diagonal - eyepiece straight into the focuser.

HTH

[Tonino]

OK Roy, thanks for your help, nothing to do with focal length as such? I guess yeah I did in part answer some of the questions myself, still a bit new and learning about all this specific and technical Astronomical telescope subject matter etc. I'll see what I can do with your ideas, see if they work, and maybe try, one or two of my own other experiments etc., if I'm to look through it without a diagonal I think I may have to attach an extension pillar (I do have a 16'' Sky Watcher one attached to my Vixen Porta 2 mount, don't know if it will fit the CG4?) for this telescope because it's so long, and to attach to it to a Celestron CG4 XLT Mount, and tripod because it's a bit short and I''ll be on the ground doing neck, back, and kneeling on the floor acrobatics!

Thanks for your help Roy, and have a nice day.

Tonino

 

[spaceboy]

I'm thinking this may have originally been used with 0.965" eyepieces and it has been adapted to 1.25" ep's which is where your loosing the inward focus. Does there appear to be any modification to the draw tube??

[Tonino]

Hello spaceboy,

Thanks for your reply and help, uuuummmmmh to be honest with you I don't believe so, I was initially suspicious of that fact when I acquired it, I did use .96 eyepieces with adaptor for 1.25'' etc., and it works if rather small FOV, and a bit dimmy, I have googled this scope, and seen it on Cloudy Nights, and it looks like the pics I have seen anyway appear to have 1.25'' diagonal and eyepieces. I did attach a couple of pics beforehand in my previous email of the focuser end, don't know if you saw them? Thank you spaceboy for your help, and I shall continue with my quest!

Kind regards,

Tonino

 

 

[spaceboy]

It was the pictures in your previous post that made me think thre may have been some kind of modification but if you have already eliminated this possibility then I'm out of ideas. I'm sure someone will be along with the solution to your dilemma soon enough,

[Peter Drew]

I think the problem may be the unpainted looking aluminium adaptor that the diagonal is attached to, I'm sure it's a non standard part. The Vixen refractors used a special fit diagonal that screwed into the drawtube which would have provided more in focus than you already have.

[Tonino]

OK Spaceboy, thank you for your reply and help etc.

And Peter yes to be honest I did notice that there seems to be a thread inside at the end of the...., as you say 'unpainted looking aluminium adaptor that the diagonal is attached to', so one might assume that it should screw off? I've tried this but it doesn't screw off? It's well stuck! I don't want to use plyers or anything, I could damage it!

Anyway, where would I find such a thing as 'a special fit diagonal that screwed into the drawtube'? I can't seem to find anything like that online.

Thanks,

Tonino

[Peter Drew]

Try Opticron in Luton, they are the Vixen importers, they may be able to help you.

[Tonino]

Oh yes, thanks Peter, I did actually try them last week but the guy who is the expert on these particular issues is on holiday at the moment, so First Light Optics have told me anyway, I also contacted them for advice. I sent an email to Opticron, Luton, so I shall wait for his reply when he's back. The guy who deals with this specific enquiry is also called Pete.

Again thanks for your help Peter.

 

[Tonino]

OK guys, I was now able to screw off the end of the diagonal/eyepiece holder at the end of my focuser drawtube , it was quite firmly stuck in there, it took some doing in unscrewing it! If I can perhaps find one that is a bit shorter in length maybe by about 3 quarter to 1 inch on the market, online etc., so that I can then go in further inward into my focuser to...., well get proper focus, that would be great, can't actually see anything as such online, when one Googles something you get too much information and pics etc! I attach a couple of pics I just took for your perusal of the holder I screwed off my focuser drawtube. If anyone knows where I can get a shorter one, a 1.25 inch fit for the diagnol at the front, then at the back as you can see from the pics there are screwing in threads either side to attach into the drawtube, that would be great also, thanks.

[spaceboy]

What is the ID of the draw tube ? Could you cut down the adapter you have and re-tap the fixing screws or does a diagonal not fit in to the draw tube with the adapter threaded in place ?

[Tonino]

I've measured the ID of the Draw Tube to which is 40mm. I did think about cutting down the adapter, and 're-tapping the fixing screws' as you say but I think that is a little beyond my skills, I'm alright with normal house DIY and maintenance, such as painting, decorating, gardening etc., but this would be a little too technical for me to do. Although I suppose I could give it a go! New skill and all that! I could send it to a skilled Machinist to be done properly. No the diagonal won't fit without the adapter threaded in place. I am searching the internet/online, see if there is a shorter length one so as to reach that inward focus more freely. Though thanks for your help and suggestions Spaceboy.

[almcl]

Not sure if tnis is a possibility, but could the OTA be shortened, where the focusser joins it?  Other examples of the tube I've seen have the focusser secured by bolts.  cutting a short length off the tube (a plumber's pipe cutter should be able to make a neat, square job) and then reattaching the fcusser should give all the inward trave needed?

[Tonino]

Yes I have thought about this being one of the options, I suppose really I don't want to spoil it being such a lovely classic old telescope, I am seeing if I can get a shorter diagonal/eyepiece holder at the end of the focuser so that I can reach more freely the inward focus aspect, or perhaps just have the holder machined off by a few mm's. But thank you for your helpful suggestion.