Diagonal Recommendations?

[Alkaid]

Hi all,

Looking to purchase a good diagonal for use with my TAL100RS.  As I purchased the scope 2nd hand, the original TAL diagonal was not included in the sale (fair enough).

I have a budget of around £100 and would even be willing to spend more, if the justification is good.  This diagonal will be a 'lifetime' purchase,  will be used predominantly for lunar and planetary observing, and used with larger telescopes in the future.   It must be figured well, and not induce much (any?!) light scatter, due to the rather critical optics needed for planetary use.  I now know that for planetary use, the choice of diagonal is as important as the eyepiece.

As my eyepieces are 1.25", I'm not sure I would need a 2" model.

Any planetary observers who might wish to comment on their diagonal of choice?

Many thanks

[John]

If minimising light scatter is critical to you then you should consider the Zeiss prism diagonals. Have a look at the report linked to in this thread:

http://stargazerslounge.com/topic/211695-diagonals-prism-vs-dielectric-vs-aluminum-vs-silver/

Prepare your wallet to spend more than the scope has cost !

Personally I use Istar and Tele Vue Everbright mirror diagonals with my ED102 and ED120 refractors. You can get a pretty decent diagonal for less than £100 if you are not going to chase the absolute ultimate in planetary performance.

You can of course use 1.25" eyepieces with a 2" diagonal, assuming your TAL will accept 2" accessories.

[alan potts]

I too use Televue Ever-bright diagonals and they are expensive but in my opinion worth it. I have just bought a Williams Optic and it's very good but I can see differences between them. Even the WO are pricey but this for me would be a step up in bulid quality over the entry level offerings. I used to have a Meade 5000, this too was very good.

Also bear in mind with Televues you do not get a reducer, they know how to inflict pain on fussy people like me.

Alan 

[Alkaid]

Thanks John, yes I read reports of the prism models outperforming their mirrored cousins, (particularly the Baader model with Zeiss prism) very interesting indeed.

How would you personally rate your Everbrite as a percentage of improvement over a stock diagonal?  30% better??    I'd be interested in learning what you remember when you first used that diagonal - was it a definite improvement for you?

[Dude_with_the_tube]

i am using Zeiss 2" prism with baader click lock on one end.Costly,but as you say,it is a life time investment

And yes,i found prisms better then normal diagonals.

[damnut]

The Opticron dielectric diags are excllent,  FLO had them for about 10secs at £69  :-- http://www.firstlightoptics.com/diagonals/opticron-dielectric-diagonal.html

1.25" insert clamping bands and solid!

[F15Rules]

I've owned a few Tal 100RS's (nice scopes) and I seem to recall that some 2" diagonals didn't come to focus in the Tal using 2" eyepieces (I think 1.25" eyepieces should be ok though). My personal favourites are the original 1.25" Tal diagonal (which although not having compression rings are built like a tank with a great mirror), and the Tele Vue Everbrite whether in 1.25" or 2" variants. Light scatter on both seems very well controlled to my eyes.

I do also like prism diagonals but I personally don't think you see much difference in scopes of less than F12 or slower. 

We are very lucky though that most brands of diagonals these days apart from the stock cheapies supplied with new Skywatchers etc are actually pretty good  .

Dave

[russ.will]

Get a decent Quartz Diaelectric like the GSO/Altair Astro and don't worry about it. The multiple Meade/Williams Optics/Skywatcher clones are also very good and even better if you make sure they are collimated.

There is this assumption that all (like refractors) diagonal arrive in serviceable condition, but it's not true. I've seen with my own eyes the staggering difference a professional collimation each element of the optical chain (objective-focuser-diagonal) can make and it's not small. The differences between the types of competently constructed diagonals, by comparison, is.

That's my 2p and other may well disagree, but what ever diagonal I buy in the future, it will have a pro applied to it. £40 unbelievably well spent - that's my view.

Russell

[Sirius Starwatcher]

For want it's worth I am using a WO 2 inch Dielectric and I am delighted with it. really clean and crisp views, good quality engineering, and it looks good.

[Joves]

Get a decent Quartz Diaelectric like the GSO/Altair Astro and don't worry about it. The multiple Meade/Williams Optics/Skywatcher clones are also very good and even better if you make sure they are collimated.

There is this assumption that all (like refractors) diagonal arrive in serviceable condition, but it's not true. I've seen with my own eyes the staggering difference a professional collimation each element of the optical chain (objective-focuser-diagonal) can make and it's not small. The differences between the types of competently constructed diagonals, by comparison, is.

That's my 2p and other may well disagree, but what ever diagonal I buy in the future, it will have a pro applied to it. £40 unbelievably well spent - that's my view.

Russell

That's interesting, Russell. Are Televue Everbrites even collimatable? Being a single slab of metal, I'd not even considered the fact they may go out of collimation.

[Alkaid]

Get a decent Quartz Diaelectric like the GSO/Altair Astro and don't worry about it. The multiple Meade/Williams Optics/Skywatcher clones are also very good and even better if you make sure they are collimated.

There is this assumption that all (like refractors) diagonal arrive in serviceable condition, but it's not true. I've seen with my own eyes the staggering difference a professional collimation each element of the optical chain (objective-focuser-diagonal) can make and it's not small. The differences between the types of competently constructed diagonals, by comparison, is.

That's my 2p and other may well disagree, but what ever diagonal I buy in the future, it will have a pro applied to it. £40 unbelievably well spent - that's my view.

Russell

Thanks Russell,

Just out of interest, who did you approach for that service?  Sounds good.

[adamw]

I recently bought a baader zeiss prism model no BA2456095 from TS in germany and it is rather good. I could see a definate improvement over my 2" dialectric mirror diagonal on jupiter.  Good saving on uk prices too partly due to the exchange rate. I got the diagonal, T2 1.25" clicklock ep holder, T2 2" focal adaptor and a 15mm T2 extension tube for £250 delivered by UPS. You might need the extension tube to reach focus depending on the amount of back focus you have. I needed it with my vixen SLV 5mm + 6mm ep's.

[Odd Thomas]

Judging by the number of replies this is a popular subject.

I am primarily interested in lunar and planetary observation and use a 2" Baader Zeiss prism on my 6" f15 frac. I've tried other diagonals but non can compare with it. It costs more than your stated budget but in my view, its worth the extra. It all comes down to personal choice and budget. A 2" is a much more substantial piece of kit if you wish progress to hanging cameras, binoviewers etc off it.

[russ.will]

That's interesting, Russell. Are Televue Everbrites even collimatable? Being a single slab of metal, I'd not even considered the fact they may go out of collimation.

They're not a single piece of metal, otherwise you'd never get the mirror in! The nose-piece, body and draw tube are monolithic, but the mirror is inserted on a plate that forms the back of the diagonal and is held in place by four counter-sunk screws.

I would imagine that it is perfectly possible to make a diagonal like this extremely well collimated from the factory (review linked to above seems to bear this out) simply through sheer machining tolerances and such a method has Televue written all over it. The WO/ES/Meade items have a removable plate that covers the mirror holder which is collimatable by four screws - one at each corner. Definitely lower tolerance manufacture, but a method by which the errors can be adjusted out and they did need adjusting out!

So, given that most of these diagonals have quartz dialectric 99% mirrors of a nominal 1/10th wave quality, would you see the difference between a TV and a well adjusted Meade/etc? I think you would be very, very hard pushed, especially if it was done as a blind test. Would I be more confident in the TV's performance after a knock? Definitely and for some that would quite reasonably be good enough reason to have one.

That review makes me want a Zeiss prism more though.

Russell

[russ.will]

Thanks Russell,

Just out of interest, who did you approach for that service?  Sounds good.

SC Telescopes.

Russell

[Piero]

I use the revelation dielectric quartz 1.25" and is pretty good to my eyes at least. 

I would prefer if it has a single body for robustness, like the TV everbrite, but the latter costs 3 times more than the revelation and I don't think it is much more performant optically. 

[Alkaid]

Thanks all. 

Anyone know what the difference is between the Baader Zeiss T2:

http://www.widescreen-centre.co.uk/Products/BAADER_T-2_STAR_DIAGONAL_.html

and this Baader model...which is about half the price but still called 'T2'

http://www.widescreen-centre.co.uk/Products/Baader_PRISM_DIAGONAL_T-2_.html

Does the latter just have a non - Zeiss branded prism?

[YKSE]

I think the Zeiss one has 35mm free aperture, and the other has only 32mm, so different prism size inside.

Better description on these diagonals here:

http://www.teleskop-express.de/shop/index.php/language/en/manufacturers_id/5/filter_id/9/astro/Baader.html

[Alkaid]

I see, thanks. The cheaper one has slightly less reflectivity at 96%....not sure that would make much difference for planetary (where contrast is perhaps more important).

[jetstream]

My stock Skywatcher is a very good diagonal, much better than a more expensive one I have. For planetary and star work the Baader Zeiss prism works very well, I have the 2" but some say the T2 Zeiss version offers even less scatter if this is possible. Not sure where the prism in the non Zeiss Baader comes from, but is most likely a VG performer. BillP's review offers insight into diagonal performance. 

[De Lorme]

Hi, I'm De Lorme;  Here is a great review on diagonals by Bill Paolini:  http://www.cloudynights.com/page/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877. 

Clear Skies, De Lorme

[Piero]

I use the revelation dielectric quartz 1.25" and is pretty good to my eyes at least. 

I would prefer if it has a single body for robustness, like the TV everbrite, but the latter costs 3 times more than the revelation and I don't think it is much more performant optically. 

Update to my own post! ( what a shame! )

In less of 1 month from my previous post, as I reported in another thread, the screw + screw hole of the diagonal mentioned above broke. The screw simply got stuck inside as the threaded hole collapsed.. Now, I believe this was a single case, due to the many positive reports that these diagonals have on this forum and others from many members. However, I find myself uncomfortable with the fact that a screw breaks after less than 6 months from the purchase.

I am still thinking what to do.. Moonshane very kindly offered his help to repair the hole and replace the screw. I am sure this can be repaired, but the idea that other parts of this diagonal might break makes me feel paranoid, considering that they hold quite expensive eyepieces. 

In conclusion, what I want to say is that despite one can find high quality diagonal mirrors quite easily, this is not always the case regarding the diagonal body.

And the duties of a diagonals are two: 1) reflect the rays without reducing the image quality, and 2) holding eyepieces safely.

I wonder whether selecting a diagonal only based on the first point is actually worth, also in terms of money. It seems to me that this might be worth as long as one uses cheap and light eyepieces. Otherwise, saving £100 and risking 

to lose a 24Pan (£250)+diagonal(£50), does not seem a good strategy to me...

[John]

..... saving £100 and risking 

to lose a 24Pan (£250)+diagonal(£50), does not seem a good strategy to me...

Me neither !.

[F15Rules]

The main benefit of a one piece machined body like the TV Everbrite is that the nosepiece can't unscrew itself when loaded up with for example binoviewers and twin eyepieces (and maybe extension tubes)..

I learned this from bitter past experience!

Dave