Diagonals

[F15Rules]

Fascinating thread  .

I know the diagonal this vs the diagonal that debate is a longstanding one, and in many ways very subjective: I'd just offer the following points in case helpful to anyone:

• I agree that in many situations it is impossible to visually see much difference between diagonals. (I exclude here the cheapo nasty jobs supplied as standard with a lot of chinese scopes)..but decent branded (and many unbranded) modern diagonals, whether mirror or prism, (most are mirrors) are on the whole very good quality. I personally think that any claim for a 1/12 wave vs 1/10 wave is spurious marketing hype.
• I've used most diagonal brands at one time or another. Until recently I was using an Opticron 2" one from FLO (they have sold out now I think) which was great and cost around £60 or so: versus a WO dielectric I could detect zero difference in image quality. I recently bought this one as a back up and it is an utter bargain from Astro Boot at £29 plus £1.50 carriage in their sale! ...http://www.astroboot.co.uk/images/astroboot/dynamic/800w-532h/diagonal.jpg - well made, solid, great mirror and to my eyes as good as any diagonal I've used!
• The only reason I personally would invest in a high end mirror diagonal eg Tele Vue Everbrite is the following -and in fact I have just done this recently - ie the use of binoviewers or heavy 2" eyepieces:most diagonals use a simple thread-in nosepiece..when loaded with a binoviewer and two eyepieces the weight can and does cause the nosepiece to begin to unscrew itself, leading to the danger of eyepieces falling out of the binoviewer if they are not fully secured. Similarly, if viewing cyclops style but using a heavy 2" ep, the same thing can happen. For this reason alone, the use of a diagonal with no separate nosepiece is worth serious consideration. I myself am only aware of the Tele Vue units being made from a single block of aluminium - but others may be aware of different brands too?
• I have used several older prism type diagonals and found them to be excellent. Also durable, with no coatings to wear off as with mirrors. I'd endorse AndyH's comments about the Tak 1.25" diagonal - a really excellent unit for around £70 for the 1.25" version (but well over £300 for the 2"  !).
• I have also used a Baader Zeiss 2" prism and bitterly regretted letting it go: in my Intes M603 mak it was superb. Not sure if the nospiece issue could still arise though, as I wasn't using bv's or heavy 2" eps then.. in general I really like Baader gear, very well made, very flexible in permutations of use, and overall, very reasonably priced.

HTH,

Dave

[AndyH]

 Good post, Dave !

Regarding nosepieces unscrewing - Thread-locking fluid is your friend   . Various strengths available(http://en.wikipedia.org/wiki/Thread-locking_fluid). I've used it on a couple of my diagonals, to great effect. Not expensive.

[YKSE]

Yes, great experience Dave, thanks for sharing with us.

[trazor]

In case anyone is wondering what is being talked about on this thread, here are a couple of links to threads that started the prism discussion......

All started here, by BillP(Bill Paolini) http://www.cloudynights.com/topic/443262-eyepiece-performance-using-a-prism-diagonal/

Then continued to this 18 page thread http://www.cloudynights.com/topic/448635-mirror-dielectric-prism-performance-comparison/

Rather long discussions. If you want to skim, it may be an idea to first flip through the pages to Bill's posts, especially the ones where he jots down his notes after a session, trying out various combinations of prisms/eyepieces and scopes. As always with BillP's posts, a fascinating read.

Andy.

Here is the link to the final report from the 18 page thread.

http://www.cloudynights.com/page/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877

[jetstream]

 Good post, Dave !

Regarding nosepieces unscrewing - Thread-locking fluid is your friend   . Various strengths available(http://en.wikipedia.org/wiki/Thread-locking_fluid). I've used it on a couple of my diagonals, to great effect. Not expensive.

Hi Andy I use Loctite myself and I think a word of caution is needed. The Red is considered permanent here and my experience is that it is permanent or torches are required to break the bond. Blue is a good, strong agent, and bolts, nuts can be unthreaded with a wrench with effort. The weakest purple might be OK to use on the nosepiece, with caution. Even a non drying sealing compound might "gum" the threads up enough to help out. I guess it depends on whether the items need to be disassembled again or not- trying to take a nosepiece off after Red/Blue thread locker is used may cause some real damage IMHO. Great idea though to use something on the threads.

[AndyH]

I used Loktite 270(from memory) on mine. That's classed as a green. Just as well I wanted it to be permament as no stinking torque will be shifting that nosepiece.

But yes you are 100% right in bringing this up. Good shout.  eg: if you're using a diagonal that has various uses, like a T2 type with various nosepieces etc, or perhaps you have one that uses both a straight nose AND an SCT adapter and use both on the diagonal from time to time, tread carefully.

[alan potts]

Mark,

Yes it should be in eyepieces but I didn't move it and now, well it's here. Because of the amount that have joined in I am worried I will do something wrong and loose the content. So here goes lets try my super powers.

Edit,

Woopie it works.

Alan.

[GavStar]

I've just received my Baader T2 zeiss prism diagonals and there are few different pieces to them!

[Mark in Macc]

Wow Gavin, you really have splashed the cash. Nice pair, ooh err missus. Interestingly, the way your Clicklock is connected is different to mine. I'll try to post an image tomorrow. My Clicklock sits much closer to the diagonal body and that's why I use a spacer on the nosepiece to stop it getting in the way of my visual back, which is also a Clicklock. You might be ok with that configuration. Have you tried it yet to see how it fits?

[GavStar]

Mark, yes it fits fine onto my visual back. However you have given me an idea - I'm not happy with the 2 inch adapter currently on my main scope so will give your idea of also getting the Baader click lock for the visual back to give a solid connection that doesn't have a risk of rotation.

Look forward to seeing your photos.

Thanks

[alan potts]

Gavster,

I can see you order one of each size and I would be interested in getting the larger one.  Can you tell me what you ordered and from where to get that and does it all come together?

Alan

[Mark in Macc]

The diagonal bodies that Gavin has purchased are identical. The difference is the fittings. That's the beauty of the T2 system, very flexible.

[Mark in Macc]

Mark, yes it fits fine onto my visual back. However you have given me an idea - I'm not happy with the 2 inch adapter currently on my main scope so will give your idea of also getting the Baader click lock for the visual back to give a solid connection that doesn't have a risk of rotation.

Look forward to seeing your photos.

Thanks

A ClickLock as a visual back on a SCT is a delight. The best gadget I every bought. What OTA will you be using the diagonal with the 2" fittings with?

[Tinker1947]

Here is the solution i put together, changing anything was just a click and job done....

[alan potts]

Mark,

The idea of the prism diagonal was just for a little extra edge on the tight doubles and planetary detail.

I would use it in all my scopes that take a diagonal. So it would be 2 inch fittingss ( that was what threw me on the two diagonals the smaller fitting) 

I like Tinkers setup but I have a Moonlite on the back of my SC and if I went down that road the Moonlite would be redundant, it's the one that takes the reducers as well.

Alan

[Mark in Macc]

Hi Alan, just be aware of the fact that the T2 version does not have a full 2" aperture. The prism isn't big enough. It is stopped at approximately 35mm. It can accept 2" fittings though. Mine will be used with binoviewers, so that isn't a problem for me. Only one of my eyepieces has a field stop larger than this (ES 82deg 30mm) and I will use my 2" dielectric diagonal for that. If you need the full 2", you will need to bite the bullet and choose that option.

[alan potts]

That is very usefull information Mark, I would use it with my 41mm Panoptic and 31mm Nagler so it will be the wallet draining Zeiss, it's only 329 Euros which compared with some of the things with that name on is cheap, I have a hunting scope upstairs which my wife is dealing with and that is 2200 euro and then you need a gun.

Alan

[jetstream]

Alan, looking into my Zeiss prism I see nothing. Its very strange, its like the glass disappears- the polish, glass type and coatings are amazing to the eye, amazing as "nothing" can be!

My 2" has SCT threads in the body for easy SCT connection and there is a "ring" available to facilitate turning the diag and locking in place. The connection is also shorter than other systems, which may be desirable, focal length considered.

[John]

Must use the same glass / coatings that Tele Vue use. The huge field lens on the Nagler 31 just seems to "disappear" when you look at it. All too easy to forget it's there and poke it with a finger !

[jetstream]

Yes, Televue uses great glass types and know their coatings well. Its awesome that we have the opportunity to buy such good stuff. I think Baader discontinued the 2" Zeiss prism diag and are announcing an improved version (according to their website)- it would be great to get a report on this new version.

[GavStar]

Mark, I'm going to use this diagonal with my tak fc100df - the existing adapter for the visual back is not great in my opinion using 2 screws to hold the diagonal so the click lock should be much better. I ordered the baader click lock for tak refractors - thanks for the tip.

Alan, like you I'm using these on planets and double stars which will hopefully give better views than my mirror diagonals - we shall see!

I went for the smaller diagonal a) because it was cheaper I had read that being smaller less ca was introduced by the prism and if I want really wide field I can go back to the 2 inch mirror.

So details of the pieces

1) 1.25 t2 prism diagonal

http://www.teleskop-express.de/shop/product_info.php/info/p609_Baader---Zeiss-90--diagonal-prism---T2-thread-on-both-sides.html

2) 2 inch adapter for visual back

http://www.teleskop-express.de/shop/product_info.php/info/p481_Baader-Adapter-2--auf-T2--fuer-2--Steckhuelse---Fokaladapter.html

3) baader 2 inch click lock sct thread

http://www.firstlightoptics.com/adaptors/baader-click-lock-2-for-celestron-meade-sct.html

4) 2 inch to 1.25 inch click lock adapter

http://www.firstlightoptics.com/adaptors/baader-clicklock-2-125-adapter-2956214.html

5) t2 to sct adapter to allow 2in sct thread click lock to attach to male t2

http://www.365astronomy.com/Baader-Expanding-Ring-2-male-T-2-female.html

Hope this helps

Gavin

[John]

This is a fascinating thread but it does create another potential area of substantial expentiture for the keen planetary / binary star observer 

Up until comparatively recently the perceived wisdom was that it was worth upgrading the stock diagonal to a decent mirror one such as the Revelation, William Optics, Opticron etc. For those that regularly used heavy eyepieces the Tele Vue Everbrights had the appeal of being machined from a single block although optically the lower cost ones mentioned seemed (to me at least) to compete on equal terms with the more expensive mirror types.

Now though we are offered the option of finding £300+ for a Zeiss or equivilent diagonal if we want the last word in light scatter control.

I'm not complaining, just observing how things can change relatively quickly on the equipment side of things. I'm just as bad on eyepieces   

Mind you, I guess the "serious" (whatever that means) binary / planetary observer will be happy using standard field eyepieces so some funds can be diverted from the wide field budget to the scatter removal fund

[Mark in Macc]

When are you planning to buy one John?

[Dude_with_the_tube]

just need to know where to look John

I bought my 2" Baader Zeiss prism for close to 190 quid or 249 euros brand new,it was on offer from one of the Polish astro shops,also got the click lock adapter from them as the original prism uses that tall compression ring thing with 2 thumb screws.As someone mentioned,when you look through it,you cant see the glass,it is like there is nothing there.Compared the 2" Zeiss to 2" WO dielectric and on DSo`s there was no noticeable difference,but on planetary and stars Zeiss was sharper,better controlled,however,i tend to think it is only partly  of the quality of the glass used,it is also of the shorter light pass in the prism.If you remember,Japanese astronomers dont use any diagonals on they refractors and it has been mentioned a few times in different forums that you do get a better image with straight through views as with any diagonal/prism.

I bought mine as i intend to binoview (well thats the idea ) and for binos prism is the way forward.I did try  both WO and Zeiss with binos and WO deffinetly where not usable there.Image was very dimm,basically the optical pass was way too long in WO diagonal,Zeiss on another hand was much brighter and everything popped out as it should be.I would say that despite "Zeiss " price tag they are worth every penny.You will love it

[John]

I think my problem is that I've never paid more than £100 for a diagonal, even the TV Everbright which I got as a good used deal. I have figures in my mind for certain pieces of kit and some times find if hard to re-calibrate those

Funnily enough I did try my ED120 Japanese-style a couple of nights ago and found the image got worse rather than better. When I put the Istar Dielectric diagonal back in the star images were somewhat better defined to my eyes

One thing I can't understand is, if the decent diagonals such as the WO and the others have 99% reflectivity and 1/10th wave PV mirrors, how do they seem dim compared to the Zeiss ?. We are not supposed to notice a difference of even 10% in brightness, let alone just 1%, plus some scatter I suppose

Mind you, the seeing has been decidely "odd" just lately, thanks to the Jetstream, so I'll need to keep my options open