Haze or problem with scope?

[chicharrero]

Hello everyone

Just been taking my Swift 831 for a spin. The objective is dirty and when I've got a bit more time on my hands I'm intending to dismantle it and give it a good clean (as well as other bits of restoration on the tripod and mount).

Anyway, I'm getting a sort of hazy halo around Jupiter, about 1.5 times the size of the planet when in focus. The haze gets bigger as I focus in and smaller as I focus out. When in focus I can easily see two main dark cloud bands and perhaps more. The four Galilean satellites are clear enough. This is with a 15mm Celestron Omni Plossl, so about 67x.

I'm a bit concerned about the haze. Could this be a problem with the objective? Is this the likely effect of the dirt and fungus that I haven't cleaned up yet? There is some hazy cloud in the sky. Could it just be that?

[brantuk]

It is quite clear tonight in my area but transparency is around 60%. If you also have some high level hazy cloud it could easily cause the effect you describe. A thin film of dust on the mirror doesn't usually detract from the views. Depends how many nights you've spent out under the stars - the more you do the easier it becomes how to judge the "seeing". But I wouldn't blame the scope at this point.

[chicharrero]

Phew. Thank you. I was hoping that might be the case.

[Bruce Leeroy]

8 hours ago, chicharrero said:

I'm getting a sort of hazy halo 

If you have a moon filter try using it on Jupiter to reduce the haze. It can improve contrast too.

[Peter Drew]

There is a further possibility, as the telescope has probably been "round the block" a few times by now, maybe a previous owner had removed the objective, separated the optical components and then reassembled them incorrectly. The curves on the biconvex front element are similar at a glance but have slightly different focal lengths. Assembled incorrectly, the telescope will still work but it will mean that some light will remain unfocussed. Worth checking when/if you remove the objective for cleaning, in general the flatter curve of the biconvex is the outer one.   

[chicharrero]

1 hour ago, Peter Drew said:

There is a further possibility, as the telescope has probably been "round the block" a few times by now, maybe a previous owner had removed the objective, separated the optical components and then reassembled them incorrectly. The curves on the biconvex front element are similar at a glance but have slightly different focal lengths. Assembled incorrectly, the telescope will still work but it will mean that some light will remain unfocussed. Worth checking when/if you remove the objective for cleaning, in general the flatter curve of the biconvex is the outer one.   

It's very likely that the objective has been taken apart before. The focuser has certainly been removed and replaced awkwardly with cross threading (which I have fixed). I will take a look at the elements. Thank you for the suggestion.

[BellP]

2 hours ago, chicharrero said:

It's very likely that the objective has been taken apart before. The focuser has certainly been removed and replaced awkwardly with cross threading (which I have fixed). I will take a look at the elements. Thank you for the suggestion.

When you say you fixed the cross threading, what did you do?

[Dave In Vermont]

'Cross-Threading' usually means it wasn't straight-on the threads and was screwed-down with force just to make something hold. It's a sign that whoever worked on the (whatever it is) shouldn't be anywhere near the (whatever it is) again!

That they lack even the most basic of mechanical-aptitude.

Hope this defines it for you!

Dave

 

Meet Our Mechanics For Your Telescope! I Hope You Brought Your Cheque-Book!

[chicharrero]

2 hours ago, BellP said:

When you say you fixed the cross threading, what did you do?

It was screwed on at an angle, such that I assume the collimation would have been out. One side was at least a millimetre off compared to the other. I eventually had to resort to a vice and brute force to loosen it! Luckily the thread appears not to have been damaged and I was able to screw the focuser back on correctly.

[JOC]

3 hours ago, chicharrero said:

I eventually had to resort to a vice and brute force to loosen it!

Poor telescope - I'm sure it will reward you for your loving care in due course.

[BeerMe]

7 hours ago, Dave In Vermont said:

'Cross-Threading' usually means it wasn't straight-on the threads and was screwed-down with force just to make something hold. It's a sign that whoever worked on the (whatever it is) shouldn't be anywhere near the (whatever it is) again!

That they lack even the most basic of mechanical-aptitude.

Hope this defines it for you!

Dave

 

Meet Our Mechanics For Your Telescope! I Hope You Brought Your Cheque-Book!

He wasn't enquiring about a definition, just the solution. 

:-)

[chicharrero]

13 hours ago, Peter Drew said:

There is a further possibility, as the telescope has probably been "round the block" a few times by now, maybe a previous owner had removed the objective, separated the optical components and then reassembled them incorrectly. The curves on the biconvex front element are similar at a glance but have slightly different focal lengths. Assembled incorrectly, the telescope will still work but it will mean that some light will remain unfocussed. Worth checking when/if you remove the objective for cleaning, in general the flatter curve of the biconvex is the outer one.   

Perfect diagnosis! I took the objective apart and, yes, the front element was back to front. Welcome back, Swift 831!

[BeerMe]

2 minutes ago, chicharrero said:

Perfect diagnosis! I took the objective apart and, yes, the front element was back to front. Welcome back, Swift 831!

Ooft.  Wow!  

This place never ceases to amaze!  Glad you've found the solution (assuming that's fixed this particular problem?) and hats off to Peter for a pretty obscure diagnosis :-)

[chicharrero]

10 minutes ago, BeerMe said:

Ooft.  Wow!  

This place never ceases to amaze!  Glad you've found the solution (assuming that's fixed this particular problem?) and hats off to Peter for a pretty obscure diagnosis :-)

Yes, this problem is fixed! Just had a look at Jupiter. Far crisper than before with lots more detail visible. Also looked at some double stars and M13. I think this is going to be a great scope. Apart from cosmetics, I just need to fix the focuser rack and pinion - which is missing some teeth! I've been using the back end of a Celestron Travelscope gaffer taped to the Swift tube. Well, it works!

[Dave In Vermont]

Ah Ha! Moment found!

Congratulations!

Dave

[brantuk]

I was way out but glad you got it sorted. Been looking at the Swift today and it's a very nice looking little scope. Congrats from me too.

[BellP]

Yes, well done, glad it's fixed, I would never have thought of an element of the objective being out like that. And yes, correct I was enquiring about the solution.Thanks .