Celestron travel scope 70 - can't focus anything without the 45 degree correct image prism

[cupu]

Hello to all,

I have recently bought a celestron travelscope 70 telescope and after replacing the mount I've started to actually be able to find things on the night sky. First up was saturn from my apartment window in a very light polluted environment; I could discern the planet from the rings and so my heart rate went up significantly

I have the 45 degree image correct prism connected to the scope and then I connect one of my eyepieces to that; I've read that every optical element you add will lower the quality of the image so I've thought about removing the prism since I don't care about seeing anything "the right way" up; however, without the prism (even in day time while trying to view something that's 100 meters away) I can't focus at all and everything is a blurry mess ( I can't see any details at all, just a white smudge wherever I point the telescope). I've tried to insert the eyepiece fully into the telescope, part way and so on, fiddled with the focus knobs but nothing seems to work.

Is it not supposed to work without the prism?

Thank you for taking the time to read!

Stefan

[Steve Ward]

Welcome to the forum Stefan ,

If you remove the 45 degree "right way up" prism you need to fit the 90 degree "wrong way up" diagonal in it's place in order to achieve focus.

This will not remove a piece of glass from the system though so I would just use the prism and enjoy the views ... 

OK , Cancel that ... after reading the relevant manual I see that your 'scope only comes with the prism.

[valleyman]

Without the Diagnal fitted you will not have the focal range to obtain Focus. If you want to view straight through then you will need to have an extension tube.

if you have a Barlow try that in front of the EP to get focus.

[cupu]

Steve, valleyman thank you for the replies!

I've just tried with a 2x barlow lens and I still can't focus. I suppose the extension tube doesn't have any optics (being just a tube) so maybe I'll keep an eye out the next time I can spend some money on this. Until then, I guess, I'll just use the prism as I've only seen one thing so far (and already I'm complaining ). Maybe good (or bad) seeing will dwarf watever benefit I could get from not using the prism.

Thanks again!

[philj]

As above you need a prism or diagonal to reach focus. If you are restricted to viewing from a window makes sure the window is open, windiw glass no matter how clean is not optically perfect and will degrade your view.

[cupu]

Thank you phil. Yes, when looking at Saturn I've opened the window, but when just trying to focus on the building nearby, I keep it closed.

[Steve Ward]

You'll want to get a diagonal rather than an extension tube , an extension will prove itself useless once you start pointing the 'scope at things higher in the sky.

You really want to avoid viewing from inside the house even with the window open , the warm air rushing from inside to out will destroy any chance of a clear and steady view ... think about the heat-haze you see rising off the tarmac on a hot summer's day ... same turbulence will surround you viewing from inside out.

[DRT]

Stefan,

Before you spend any money on this wait a few days until the Moon is back in the night sky. It is easy to find and easy to focus on. If you cannot achieve focus on the Moon with the kit you have then you will have confirmed you have a problem.

There is a good chance that your out of focus view of Saturn was more to do with the seeing conditions and the positioning of your telescope at the window than it is to do with the equipment.

If you want to try a mirror diagonal instead of the prism you can pick one up on AstroBoot for as little as £5.

[happy-kat]

Not sure if astroboot ship to romania

[DRT]

Oops! Didn't notice the OP's location. Sorry.

[cupu]

@Steve

What you're saying make sense; on the first clear night I'm going to take the telescope into a nearby park and have another go. Unfortunately I've lost some of the mobility due to the new mount but I had to take it out anyway so it's ok.

@DRT & happy-kat

Good advice! Don't worry, there are plenty of shops that will ship now that I know what I'm looking for.

Thank you all.

[LukeSkywatcher]

I'm not sure why you need to buy anything. The erect prism that came with the scope is all you need (along with an eyepiece). If it isnt working then you should return it to the place where you bought it. 

[DRT]

Good point, Paul. If this turns out to be a faulty scope or prism it should be returned.

[LukeSkywatcher]

It may be helpful to check the screws that hold the focuser in place. If these are loose, the focus wheels will not grip and you wont get focus.

The screws are marked in red.

What eyepiece are you using?. 

[jimbo747]

I can achieve focus with my DSLR just attached on my travelscope 70 with plenty of focal travel left, so would have thought a 24mm or so ep would focus too.

[IckleImp]

As far as I am aware you cannot use the Travelscope without either an erecting prism for star diagonal. I tried it myself and could not achieve focus.

[jimbo747]

If the sun comes out I'll let you know!

[cupu]

And again more thanks is due , thank you guys!

I'm afraid I may have not correctly worded my problem. I can focus just fine with the prism connected and any eyepiece connected to it in turn. I foolishly expected to be able to see something when connecting an eye piece directly to the telescope (no prism). I understand now that that's not possible so I won't bother with it anymore. I'll just use the prism I have, it seems to work ok!

Cheers,

Stefan

[LukeSkywatcher]

Problem solved. I know what you were trying to do as the scope is a refractor. Older refractor scopes like Prinz come with a fixed eyepiece on the scope which only gives you one magnification (like binoculars do). For the travelscope or many other refractors which are modern, you need the diagonal or erect prism to be able to focus.

[DRT]

An extension tube (around 70-80mm I think?) will allow you to do what you want to do but your image will be upside down and flipped right to left

[LukeSkywatcher]

If the sun comes out I'll let you know!

I hope you are practising safe solar. 

[LukeSkywatcher]

Stefan, here is one of the older refractor scopes i mentioned. Its a Prinz. Notice the fixed magnification eyepiece on the scope. I'm not sure but maybe back then it was possible to buy different eyepieces to attach to the scope. I had a scope similar to this one when i was about 8 yrs old. 

Thanks to L8-NITE, whose image i have posted.