New Diagonal for ST102

[davyludo]

Hi All,

Just got a Skywatcher ST102, which came with the 45 degree image erecting diagonal. 

I'd like to swap this out for a better quality 90 degree one (without breaking the bank). I don't have any 2" eyepieces and to be honest, I don't have plans to get any soon. I'll be using my X-cel LX 25mm which should give me about 3 degrees (by my calculations) - if I want wider, I'll be using binoculars. So I've been looking at 1.25" diagonals and think the following 2 seem reasonable for what I'm looking for:

https://www.harrisontelescopes.co.uk/acatalog/Revelation_Quartz_Dielectric_Diagonal_1.25_.html#SID=566

http://www.rothervalleyoptics.co.uk/altair-astro-125-dielectric-star-diagonal.html

I assume the price difference is because the Revelation version has a quartz mirror. I was wondering what peoples thoughts are on these diagonals and whether the quartz one is worth the extra money? Also is the quartz version much heavier?

I'm struggling to find the weights of diagonals - my concern is that I'm thinking about getting an AZ3 for camping adventures and don't want to make my scope back-end heavy...so trying to think about the weight I'd be adding (again, partly the reason I wasn't looking at 2" versions or eyepieces). 

Many thanks, 
Davy

[happy-kat]

Interesting thought on weight my Skywatcher erect image diagonal weighs nothing my WO dielectric diagonal must be pushing near three times heavier.

[davyludo]

20 minutes ago, happy-kat said:

Interesting thought on weight my Skywatcher erect image diagonal weighs nothing my WO dielectric diagonal must be pushing near three times heavier.

It was really when I was playing around with the scope on the AZ4 - I had the alt axis quite loose and noticed that the scope started to creep back itself as I got higher (I know I just need to tighten the alt axis or move dovetail further forward) but it got me thinking about back-end weight...which would be more of an issue on the AZ3 as I know people have come up with various counterweight systems for the AZ3 because of this problem. 

I know the diagonal I have just now will be a fair bit lighter than a new one as it's made of plastic - I assume ones about £50 will be made from metal. 

Is you WO dielectric a quartz version? Trying to judge whether quartz adds weight over the same size/quality non-quartz version. 

[happy-kat]

Interesting discussion.

Link

I only have the WO as FLO had it as an open box so was much cheaper.

[happy-kat]

With end caps. Not sure which version the box didn't say it is the one FLO sell 1.25".

WO 236 grams

Skywatcher 112 grams

Edit: I don't think it's quartz.

[Alan64]

You could add another mounting-plate on top of the AZ3's mounting plate, and forward a bit, then mount the tube-rings onto the secondary mounting-plate, and thereby balance the telescope with whichever new diagonal you choose, including a 2" if you so desire.

[Cosmic Geoff]

3 hours ago, davyludo said:

So I've been looking at 1.25" diagonals and think the following 2 seem reasonable for what I'm looking for:

https://www.harrisontelescopes.co.uk/acatalog/Revelation_Quartz_Dielectric_Diagonal_1.25_.html#SID=566

http://www.rothervalleyoptics.co.uk/altair-astro-125-dielectric-star-diagonal.html

I assume the price difference is because the Revelation version has a quartz mirror. I was wondering what peoples thoughts are on these diagonals and whether the quartz one is worth the extra money? Also is the quartz version much heavier?

I have one of these ST102's and by coincidence I just bought a 90 deg star diagonal for it - an inexpensive "Sky-watcher" diagonal from Astroboot.  I don't think that a short-focus achromat is the kind of telescope that merits a premium priced star diagonal, but it's your money, and you might want to use the diagonal in another telescope at some time. 

[davyludo]

3 minutes ago, Cosmic Geoff said:

I have one of these ST102's and by coincidence I just bought a 90 deg star diagonal for it - an inexpensive "Sky-watcher" diagonal from Astroboot.  I don't think that a short-focus achromat is the kind of telescope that merits a premium priced star diagonal, but it's your money, and you might want to use the diagonal in another telescope at some time. 

Hi Geoff, thanks for pointing that out. I hadn't thought about the fact that an expensive one might not be necessary for my short achromat. I guess I just assumed I'd need to move up to above the £50 region in order to see a difference. 

I was thinking about getting a MAK at some point next year to use for planets and lunar - thought it would compliment the ST102. I suppose if I got a decent diagonal now....it could be used for both.

Decisions decisions!

[davyludo]

9 minutes ago, Alan64 said:

You could add another mounting-plate on top of the AZ3's mounting plate, and forward a bit, then mount the tube-rings onto the secondary mounting-plate, and thereby balance the telescope with whichever new diagonal you choose, including a 2" if you so desire.

I've actually grabbed a second hand AZ3 and bought a dovetail clamp from eBay (found it mentioned in a few forums). I'm going to have to make a plate to fix the dovetail clamp to the AZ3 anyway....I hadn't thought about mounting it further forward. Might just do that to start with.

Thanks for that!

[Alan64]

Just now, davyludo said:

I've actually grabbed a second hand AZ3 and bought a dovetail clamp from eBay (found it mentioned in a few forums). I'm going to have to make a plate to fix the dovetail clamp to the AZ3 anyway....I hadn't thought about mounting it further forward. Might just do that to start with.

Thanks for that!

I first thought of mounting a Vixen-style clamp, but I didn't suggest it as I thought the other easier, perhaps.  You would then need a longer dovetail bar.  Actually go with the clamp if possible, as it would be far more versatile.

You've got it taken care of, in any event.

I need a longer dovetail-bar for this 80mm f/6...

...as it really swings back, with that 2" diagonal, let alone with an eyepiece inserted.

[davyludo]

32 minutes ago, Alan64 said:

I first thought of mounting a Vixen-style clamp, but I didn't suggest it as I thought the other easier, perhaps.  You would then need a longer dovetail bar.  Actually go with the clamp if possible, as it would be far more versatile.

You've got it taken care of, in any event.

I need a longer dovetail-bar for this 80mm f/6...

...as it really swings back, with that 2" diagonal, let alone with an eyepiece inserted.

The reason I'd gone with the dovetail clamp was because I'd like to use the mount with multiple scopes...Thought it would be easier if I just used dovetails all round.

That 2" looks like a beast, I can see why it swings back, especially when you add an eyepiece. That's kind of why I was thinking about just sticking with 1.25" for now. Trying to keep the ST102 as a lightweight setup that I can take away camping and walking. A couple of hundred grams here and there soon adds up.

 

Would you recommend a quartz version of diagonal? Or do you think I wouldn't really notice the difference with my wee ST102?

[davyludo]

Anyone have any experience with either of the diagonals that are linked in first post? Trying to decide whether to spend the money of just grab a cheap 90 degree from AstroBoot. 

Cheers,

Davy 

[Uplooker]

22 hours ago, davyludo said:

Hi Geoff, thanks for pointing that out. I hadn't thought about the fact that an expensive one might not be necessary for my short achromat. I guess I just assumed I'd need to move up to above the £50 region in order to see a difference. 

I was thinking about getting a MAK at some point next year to use for planets and lunar - thought it would compliment the ST102. I suppose if I got a decent diagonal now....it could be used for both.

Decisions decisions!

Hi Dave,

You will not go wrong with the Revelation diagonal. I had one in the past, since sold on. Very well made and does give good views.

My personal stance is to buy the best you can afford, within reason. By spending a bit more for the Revelation,rather than a cheap SW one, means that you can keep it for use on other better quality scopes.

[happy-kat]

Just read a related read diagonal and mak and you'll want to read Stu's past about prism and fast achro and CA. I've just removed a prism from my mini mak and the CA has gone.

Post at end of thread

[Alan64]

On 3/17/2017 at 11:44, davyludo said:

Would you recommend a quartz version of diagonal? Or do you think I wouldn't really notice the difference with my wee ST102?

Both diagonals are dielectric.  It's just that the Revelation has a quartz substrate, and that of the Altair Astro is of borosilicate-glass...

https://en.wikipedia.org/wiki/Borosilicate_glass

"Borosilicate glasses are known for having very low coefficients of thermal expansion..."

Quartz, too, has that quality, therefore I'd say that both are a toss-up.

You simply don't want the substrate to expand and contract due to variations in temperature, and deform the image in the process.  

Incidentally, if you'll look closely at the bodies of those diagonals, they appear identical, and probably made in the same factory overseas.  This one, too...

http://www.teleskop-express.de/shop/product_info.php/info/p1771_TS-Optics-1-25--TS-Optics-1-25--Star-Diagonal-with-ring-clamb---99----1-12-Lambda.html

[davyludo]

1 hour ago, Alan64 said:

Both diagonals are dielectric.  It's just that the Revelation has a quartz substrate, and that of the Altair Astro is of borosilicate-glass...

https://en.wikipedia.org/wiki/Borosilicate_glass

"Borosilicate glasses are known for having very low coefficients of thermal expansion..."

Quartz, too, has that quality, therefore I'd say that both are a toss-up.

You simply don't want the substrate to expand and contract due to variations in temperature, and deform the image in the process.  

Incidentally, if you'll look closely at the bodies of those diagonals, they appear identical, and probably made in the same factory overseas.  This one, too...

http://www.teleskop-express.de/shop/product_info.php/info/p1771_TS-Optics-1-25--TS-Optics-1-25--Star-Diagonal-with-ring-clamb---99----1-12-Lambda.html

Hi Alan, 

Thanks for the info. I've ended up going for the revelation as it seems a lot of people have good things to say about it. Figured if I bought a cheap one, I'd probably end up replacing it. Hopefully this one will last me a long time and be suitable for if I get a MAK in the future.

It's funny how the more you look into telescope accessories, the more you find that different brand names are produced in the same place! 

Cheers, 

Davy