Star Diagonals.

[LukeSkywatcher]

This is more of a "whats up with that?", rather than seeking help.

Today i had my first peek through my Bresser ar 102 xs. I was only checking things out and looking at the house across the road. I was using the star diagonal supplied. As you would expect from diags, the view was flipped on the X and Y plain (upside down and mirror image). However, the view was also rotated by (IIRC) 45 degrees (clockwise or anti.........i cant remember).

I dont care because i use an erecting prism for all my observing. Ive just never seen a view through a refrac which was rotated by 45 degrees (as well as flipped on X or Y....or both).

Im happy to report that CA in the scope was absolute minimal. It was a slight yellow tinge in the 12-2 o clock position and really not very noticable.

[25585]

What make & model of diagonal - I have a WO erecting prism one. 

A semi-apo filter might cut down some more CA, glad it's good

[johninderby]

Here’s a poor pic taken through the same scope using an Omegon 90 degree prism. As you can see indeed minimal CA. Replaced my old WO prisim with the Omegon and what an improvement. No need for a semi-apo filter.

https://www.astroshop.eu/amici-prisms-90d/omegon-1-25-amici-prism-90d/p,14172?utm_medium=cpc&utm_term=14172&utm_campaign=1806&utm_source=froogle&gclid=CjwKCAjw9qfZBRA5EiwAiq0AbXZknawLfkHgbTr4cvZSSZmaB4izKN7vwkgkV5NTm5fklK8c0I9kmRoCHCIQAvD_BwE&utm_content=

 

[Stu]

3 hours ago, LukeSkywatcher said:

This is more of a "whats up with that?", rather than seeking help.

Today i had my first peek through my Bresser ar 102 xs. I was only checking things out and looking at the house across the road. I was using the star diagonal supplied. As you would expect from diags, the view was flipped on the X and Y plain (upside down and mirror image). However, the view was also rotated by (IIRC) 45 degrees (clockwise or anti.........i cant remember).

I dont care because i use an erecting prism for all my observing. Ive just never seen a view through a refrac which was rotated by 45 degrees (as well as flipped on X or Y....or both).

Im happy to report that CA in the scope was absolute minimal. It was a slight yellow tinge in the 12-2 o clock position and really not very noticable.

A diagonal in a refractor should give a view which is left right reversed but the right way up.

If you have the diagonal rotated though it will xhange that orientation.  Did you have it at 45 degrees by any chance?

[LukeSkywatcher]

22 hours ago, Stu said:

A diagonal in a refractor should give a view which is left right reversed but the right way up.

If you have the diagonal rotated though it will xhange that orientation.  Did you have it at 45 degrees by any chance?

Yep. I had it rotated. I checked again but with diag in different positions and the view rotates accordingly. Havent checked my erect prism yet. 

[NGC 1502]

 

The rotated view is normal.  This caused confusion recently at my club with a new member who was using a 90mm refractor on loan. 

We explained to him that if he rotated the diagonal to bring the eyepiece to a convenient angle, then the view will rotate accordingly. Gets confusing when starhopping, but nudge the scope towards Polaris, new stars will enter the field of view on the north side, and of course south is on the other side. If the scope has a drive, turn it off, new stars will enter the field of view on the east side, west is on opposite side.

Ed.

[LukeSkywatcher]

On 20/06/2018 at 22:02, Stu said:

 

[LukeSkywatcher]

All is right with the universe again. Just got my erect prism out and I can see normally again. Diags are strange things. Shan't be trying that again. 

[25585]

Does your Bresser have a rotateable focuser?

[johninderby]

It has a great 2.5” rotatable rack & pinion focuser and comes with extension pieces for the drawtube.  I fitted the optional 1:10 fine focuser knob.?

 

[LukeSkywatcher]

5 hours ago, 25585 said:

Does your Bresser have a rotateable focuser?

It does.

[LukeSkywatcher]

4 hours ago, johninderby said:

It has a great 2.5” rotatable rack & pinion focuser and comes with extension pieces for the drawtube.  I fitted the optional 1:10 fine focuser knob.?

 

Those 2 black rings, i thought were for attaching a DSLR. I do like the R&P focuser. Silky smooth. Also the Alt-Az (not the flexi Slo-Mo controls) are sweet.

The numbers on the draw tube, what do they mean?.

Ive searched for the full user manual online and its no better than the booklet i got.

Sad to report that my Celestron erect prism shows a hell of lot more CA than the star diag supplied. It does however put the EP at a more comfortable angle.

 

[johninderby]

Yes the rings are for more put focus as when using a DSLR etc.The numbers are just the mm of travel. Usefull more for imaging. 

The Celestron prisim is shall we say cheap and cheerful and is the cause of all that CA. Unfortunately only cured by buying a better prism.

[RiponJas]

Just bought my own bresser frac and found the first time use of a diagonal rather odd after looking through a dob for the past month or so.. 

But soon adapted it, just need to buy a better diagonal as the supplied one seems a bit plasticky and cheap. 

[johninderby]

The accessories Bresser supplies with their fracs are a bit rubbish except for the eyepiece which is actually fairly decent and usable. Wish they would sell them without accessories or supply decent ones but that would put up the price. 

[RiponJas]

The diagonal does seem a bit rubbish so just purchased an Altair Astro one, hopefully should improve things a tad. 

I agree on the EP supplied though, it's a 26mm super plossl and it's leagues above the skywatcher ones that came with my dob.. 

[RiponJas]

The Altair Astro diagonal turned up today, really is a nice looking piece of kit, looking forward to trying it out now. Really is quite big in comparison to the supplied bresser toy!