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MimasDeathStar

Is a dielectric diagonal a good value upgrade?

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Hello all

Well I've been bitten by the astronomy bug it seems as I seem to be spending a worrying amount of time looking at astronomy retailers and thinking "ooohhh that would be nice, ooohh but so would that, maybe I'll just get one, or maybe that one instead, or maybe both!" and so on!

Anyway, I have a small 70mm Meade refractor. I really like it and have seen the wild duck cluster so far (although I'm still not sure why it is called that!)  I think I'm going to get a UHC filter to deal with light pollution but the internet doesn't seem to be unanimous on the relative merits of a dielectric diagonal for smaller relatively inexpensive scopes. If I understand it correctly, we're talking an increase in reflectivity from about 92% to 99% which sounds like a lot in theory but would it make much difference in reality?

It would cost about the same as the scope I bought (ooops!) but I guess it would be something I could take with me to a new scope if they're really good.

Anyway, if anyone has any opinions I'd be delighted to hear it!

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On a low cost scope few would bother upgrading to a dielectric diagonal. Most dielectric diagonals also have better build quality. And compression rings. The cheap diagonals that come with low cost scopes are plastic bodies.

However it is possible to get a low cost diagonal with good build quality. I have tested this one and it was actually quite good with a metal body. One I’d recommend as an upgrade for your scope.

http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Telescopes-Opticstar.asp?p=0_10_5_1_8_201

 

Edited by johninderby
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1 hour ago, johninderby said:

On a low cost scope few would bother upgrading to a dielectric diagonal. Most dielectric diagonals also have better build quality. And compression rings. The cheap diagonals that come with low cost scopes are plastic bodies.

However it is possible to get a low cost diagonal with good build quality. I have used this one and it was actually quite good with a metal body. One I’d recommend as an upgrade for your scope.

http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Telescopes-Opticstar.asp?p=0_10_5_1_8_201

 

That's handy, that's where I bought my refractor from! Thanks very much for the recommendation will get one of those!

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You are talking about a 7 % increase in reflected light, under otherwise perfect circumstances. What exactly are you expecting to gain? What are you missing?

If you have been bitten by _the bug_, by all means spend money, it's fun! But consider what for...

I would first look at eyepieces before investing in an upgrade for the diagonal. What do you have? How do they cover the feasible range of your scope and your interests? And most important, what about their quality? Maybe there is more to be gained here?

Sven
 

 

 

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29 minutes ago, freiform said:

You are talking about a 7 % increase in reflected light, under otherwise perfect circumstances. What exactly are you expecting to gain? What are you missing?

Ha ha very good questions! But I think the answer to all of those is: "I have no idea!!" so I thought it was worth asking. It sounds like this isn't an area that should worry me too much at the moment though. Thanks very much for the reply.

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I would not buy the filter nor the dielectric. U mentioned the filter will be as much as the whole scope. When using lp filters or nebula filters it will dim the view, and the more the bandwidth the more it darkens it.

So I'm not sure I would used a filter on a small scope like a 70mm.

The same with the diagonal if u will spend 2x the cost ad the scope then dont buy those 2 items upgrade to a much bigger scope like 100mm refractor.

I think that will help u more than a 70mm and filter

Joejaguar 

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You probably won't be able to tell the difference between 92% and 99%. Though I think Meade comes with erecting prism, then getting a star diagonal will be benefitial.

I woudn't bother with filter yet. It helps a little, but doesn't iliminate light pollution. With my 8" dob the difference is pretty marginal - it helps to bring out a little more detail or detect what can't be seen at all without a filter, but not even close to what it is like under dark skies. Plus with 70mm under light polluted skies you are pretty much limited to brighter clusters, and UHC won't help you with those. 

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I found my answer to a question now deleted.

Edited by Alan64

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6 hours ago, MimasDeathStar said:

Oh dear, was nothing to do with me I promise! 

I was only wondering as to the nature of that Opticstar diagonal.  I then found that it uses a mirror.  You can use a star-prism instead with your 70mm f/13 refractor.  I have the Celestron version of your telescope...

4c.jpg.69efa9b5561952d1ef49057899bd6424.jpg

I've used a Celestron star-prism with that one, and with my other refractors.  A prism is more durable, and with less light-scattering when viewing brighter objects.  This is the diagonal...

https://www.365astronomy.com/Celestron-Diagonal-Star-1.25-in.html 

You have to be careful when selecting a prism-diagonal, as there are the Amici erect-image types, and the star types.  That Celestron is a star type, and best for use at night, as is a star-mirror.  In that the Opticstar contains a mirror, then I assume that it is a star-mirror, and will serve.  The diagonal that came with your telescope is an Amici erect-image, and best for daytime/terrestrial use; birds in trees, ships at sea, that sort of thing.  You can use it at night, but on the smaller, brighter objects you may see the "Amici line" of the prism, and as an illuminated streak across the objects...

5ufVAEI.jpg

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One thing to be wary of with the cheap dielectric diagonals.  The locking screw or compression ring is often very close to the lip which causes many eyepieces with undercuts to be pushed up and out at an angle.

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I finally found the discount dielectric diagonal I was referring to above.  It is still listed on Amazon for $49.99.  What's deceptive is that you can't see the position of the 2" thumbscrew or compression ring from the photos relative to the top of the eyepiece holder.  They are very near to the end and work terribly with undercut 2" eyepieces as described above.  Otherwise, it's a fine diagonal.  It's a shame it's marred by poor design.  It is somewhat usable if you slip a parfocalizing ring or rubber O-ring on each 2" eyepiece prior to putting them in the eyepiece holder to lift them slightly out of the holder to allow the compression ring to align with the undercut.

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Seems to cheap I have bought these for 169 plus taxes almost 200, with the name brand models. I also just sold a brand new one just last week that came with my skywatcher 100ed f9 that I just got like 2 weeks ago.

I sold it for 125 it wasn't used I just didnt need it as I have my own but still has to be cheaper than someone buying from store.

So is skywatcher meade celestron and Orion just making 3x what they should off us? Or is this Amazon to cheap and it's not a real dielectric?

Joejaguar 

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I have seen comparison tests that do show that the cheap dielectric diagonals are not terrible but lack contrast in particular  compared to the big name brands. Also often the mirrors aren’t mounted well and some stick out into the light path blocking a bit of the aperture. The Orion and Celestron are not quite as good as say the WO or ES or GSO quartz diagonals.

Must be said though that when you get to the price point of the WO paying more doesn’t seem to make any real difference.

 

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4 hours ago, joe aguiar said:

Seems to cheap I have bought these for 169 plus taxes almost 200, with the name brand models. I also just sold a brand new one just last week that came with my skywatcher 100ed f9 that I just got like 2 weeks ago.

I sold it for 125 it wasn't used I just didnt need it as I have my own but still has to be cheaper than someone buying from store.

So is skywatcher meade celestron and Orion just making 3x what they should off us? Or is this Amazon to cheap and it's not a real dielectric?

Joejaguar 

It is definitely a more lightly built 2" diagonal than the GSO equivalent.  Optically, I didn't notice any major differences, but I also haven't done a critical back to back test of the two.  I'll add it to the list of things to do in my copious free time. 😉 

I was just looking for a low cost 2" diagonal for my daughter to take with her camping observing kit, but was unprepared for such a design oversight.

Edited by Louis D

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37 minutes ago, Louis D said:

It is definitely a more lightly built 2" diagonal than the GSO equivalent.  Optically, I didn't notice any major differences, but I also haven't done a critical back to back test of the two.  I'll add it to the list of things to do in my copious free time. 😉 

I was just looking for a low cost 2" diagonal for my daughter to take with her camping observing kit, but was unprepared for such a design oversight.

agree for low cost and most times the extra 7 to 9% wont do much anyway. our eyes cant detect anything under 9% anyway as it too small for eyes to process, a camera could but that's a different story.

I also have 2 or 3 none dieelectrics too and they are fine for normal use

anyway good buy for $50

joejaguar

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