Prism diagonal reflections

[DeanCJ]

Hi everyone, I will try and keep this as short as possible, so here goes.

 My wife and I have three telescopes, a ST 102, a 127Mak, and a 8”SCT, but only two diagonals, a Skywatcher 99% dialectric, and the standard Skywatcher kit supplied, both 1 1/4”. 
We are now looking to buy a new diagonal for the 8se and having read many reports and reviews, such as BillP’s over on CN, we have decided on a prism diagonal such as a Takahashi, or Baader T2. 
In the meantime we have been loaned a well used, unbranded non amici prism. I must say Jupiter’s cloud bands do seem to be better than the dialectric diagonal, slightly more contrast with a richer colour, not massive but subtle. Now here’s the problem, horrendous reflections from my eye, and of my eye, in the 15 to 30mm range. We use Vixen eyepieces, Slv and Npl, so I tried a couple of Skywatcher super plossls and exactly the same, change back to a mirror diagonal and no reflections. My wife particularly finds this a problem. We have replicated this maybe a dozen times and can only assume that the diagonal is the cause, perhaps poor or no coatings at all ??

My question is this, before we spend our money, is this a common issue with prism diagonals?

any advice would be very much appreciated.

Dean.

 

[johninderby]

Not with a proper prism diagonal. Should be no refections. I’ve never noticed any with my Baader prism.

Not a fan of the Tak prism. Not as well made as you would expect from a Tak product. The Baader prism is extremely well made and so adaptable as you can change the eyepiece holder or nosepiece to suit your needs.

Is the unbranded prism one of thecheap plastic bodied ones?

[DeanCJ]

Hi, sorry I’ve been slow to reply, I have just spent a good hour setting up for the GRS transit and right on time it’s clouded over !! but yes it is a cheap plastic body type, and unbranded. It’s a shame as it does provide good views on targets that are not so bright. I have been looking at the Baader T2/32 as the price seems very good especially for the kit package, the Zeiss Prism is a touch out of my price range and I can’t remember when I last saw a used one for sale, although there is always the wanted section but I’m not sure if I can post there yet. 
Thanks for your quick reply much appreciated.

 

[John]

I have the Baader Zeiss T2 prism diagonal which I use with my Tak FC100. The Tak is F/9 and the prism works excellently with that but I'm not sure that they are as suitable for faster refractors ?

 

[johninderby]

Most people have trouble telling the difference performance wise betwwen the T2/32 and the Zeiss prism in most scopes.  Finding stock of the T2/32 prism is the hard part right now. Looks like it will be October before they come back into stock.

Have bought a few bits from this place. Good service and price.

https://www.microglobe.co.uk/baader-prism-diagonal-t-2-90-degree-32mm-set-p-14278.html

They do have the Zeiss version bit as you mentioned ££££

https://www.microglobe.co.uk/baader-t-2-star-diagonal-prism-with-malefemale-t-2-thread-p-12365.html

 

 

 

Edited September 9, 2020 by johninderby

[DeanCJ]

21 minutes ago, John said:

I have the Baader Zeiss T2 prism diagonal which I use with my Tak FC100. The Tak is F/9 and the prism works excellently with that but I'm not sure that they are as suitable for faster refractors ?

 

Hi John,

thanks for your reply, that’s exactly what I have read, so we would use it only with the 8se as it is f10 I assume this should be fine, and it gives the best planetary views of the three scopes we have.

[DeanCJ]

25 minutes ago, johninderby said:

Most people have trouble telling the difference performance wise betwwen the T2/32 and the Zeiss prism in most scopes.  Finding stock of the T2/32 prism is the hard part right now. Looks like it will be October before they come back into stock.

Have bought a few bits from this place. Good service and price.

https://www.microglobe.co.uk/baader-prism-diagonal-t-2-90-degree-32mm-set-p-14278.html

They do have the Zeiss version bit as you mentioned ££££

https://www.microglobe.co.uk/baader-t-2-star-diagonal-prism-with-malefemale-t-2-thread-p-12365.html

 

 

 

You’re right, stock does seem to be very thin on the ground. The annoying thing is that I could have bought one at the beginning of the lockdown, but although I am a key worker I was unsure of my income and my future health so I held off, as it turns out my income was cut for a while so with hindsight I should have bought one when I had the chance. I mainly looked at the T2/32 as we have no plans to use 2” eyepieces so 32mm vs 34mm and the lower price makes it a very attractive buy.

[Cosmic Geoff]

I don't know the story of your C8 SE but they come with a decent Celestron prism diagonal, #94115A.  I have not noted any odd reflections caused by this diagonal.  I bought a Circle T prism diagonal for my 127mm Mak and have not noticed any issues with that either.

[DeanCJ]

1 hour ago, Cosmic Geoff said:

I don't know the story of your C8 SE but they come with a decent Celestron prism diagonal, #94115A.  I have not noted any odd reflections caused by this diagonal.  I bought a Circle T prism diagonal for my 127mm Mak and have not noticed any issues with that either.

We bought the Se as an Ota only with a 1.25 visual back, glad you mentioned the Mak though as I haven’t tried it with this yet.

[DeanCJ]

Thanks again everyone for your replies. As you all seem to be happy with your prisms, I am now convinced that the prism my son has given me is the cause. To be honest prism looks old and well used, it was in a large box of spares and accessories that came with a Dobsonian he bought a while back, everything was like new except the diagonal.

Once again thanks all.