Di-electric Star diagonal quality?

[spaceboy]

I am currently in the market for a star diagonal and although I am able to use a 2" diagonal with my set up a 1.25" would come in more handy as I have other scopes it could be used in. While browsing the net as you do I came across this http://geogdata.csun.edu/~voltaire/roland/dielectric.html and I remembered a similar comment being made some time ago on SGL regards 2" over 1.25" as the better bet but is this also the case when choosing a 1.25" diagonal with out di-electric coatings ??

[michael.h.f.wilkinson]

Regular 1.25" and 2" silvered/aluminized diagonals should perform equally as I understand it. Therefore, a good quality 1.25" diagonal should perform well, but the 1.25" supplied with cheaper scopes, and even with my C8 do not perform to the level of either my former WO 2" 99% reflection quartz dielectric diagonal, or that of the 97% reflection Denkmeier filter-switch diagonal. These are simply better made. I do not doubt that a TV 1.25" diagonal will be a cracking piece of kit, but then you knew that already

[Pig]

Most of the 2" come with a 1.25" adaptor.

If it were my decision then it would depend on how many 2" eyepieces I had.

Maybe 1 of each would suit you more

This is the one I have

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p89_TS-2--Zenitspiegel---99--Reflektion---Ringklemmung---2--Anschlus.html

[spaceboy]

I have now found some interesting comments being made about gold coated diagonals (see below) and how these perform well in achromatic refractors yet I am unable to find any such diagonals. I would have thought with so many people having achro refractors and spending a small fortune on fringe killers and di-electric diagonals, gold coated diagonals would have been more widely available if the improvements are to be had with such coatings.

http://www.astrosurf.com/luxorion/reports-stardiagonal.htm

http://uk.search.yahoo.com/r/_ylt=A0SO82Je4mZSjW0AzU1LBQx.;_ylu=X3oDMTBzcnZmYjNuBHNlYwNzcgRwb3MDMTAEY29sbwNncTEEdnRpZAM-/SIG=13iljiprr/EXP=1382503134/**http%3a//brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/colourfilters/colourfilters.pdf

[michael.h.f.wilkinson]

I think the gold coated ones also cost a small fortune. In my SCT it would be useless, so a decent 2" dieletric combined with a fringe killer might be the better option if you have multiple scopes

[spaceboy]

Just out of curiosity what are peoples views on the 1.25" di-electric diagonals as it is suggested that they do not perform as well as aluminium coated diagonals due to the edge drop off when coating the mirror with di-electric coatings??

[Peter Drew]

Not heard of that one before, I wouldn't have thought that the edge would come into play visually. I use a TV dielectric 1.25" diagonal in my C8, I haven't noticed a huge difference over the stock Celestron item but I do have the satisfaction of knowing that I'm still the "weak link in the chain". 

[spaceboy]

Not heard of that one before, I wouldn't have thought that the edge would come into play visually. I use a TV dielectric 1.25" diagonal in my C8, I haven't noticed a huge difference over the stock Celestron item but I do have the satisfaction of knowing that I'm still the "weak link in the chain". 

It mentions it in this article http://geogdata.csun.edu/~voltaire/roland/dielectric.html and I remember having a similar discussion on SGL. I will try to find the discussion that was had on here.

[John]

I've owned and used a few 1.25" diagonals including a William Optics dielectric, a Tele Vue Everbright and a Revelation Dielectric and they all seemed to perform well to my eyes. There is an internal stop within the WO one that restricts the FoV that low power / wide angle eyepieces can deliver but thats a mechanical issue.

I recall reading about the supposed performance advantage that a 2" could have at various times but I can't say I've experienced it myself.

[spaceboy]

Thanks John. I seem to remember you were in on the discussion about 2" over 1.25". It was a long time ago and I can't find the post but I remember I had posted a pic of my Skymax 127 with 2" diagonal and the debate started from there.

The discussion being the skymax draw tube? (not sure if this is the correct term for it)  only being 1.25" so where were the advantages of using a 2" diagonal. I am aware that Skywatcher did do a version of the Skymax 127 with a 2" diagonal which I am assuming was because there are advantages to be had over 1.25" even when there are restrictions that make using 2" EP's pointless??

[Peter Drew]

Thanks Spaceboy. Interesting analysis but I wouldn't get paranoid about it. 

[spaceboy]

What are peoples thoughts regards Quartz mirrors? Sorry for all the questions but I know a lot of the "this has this and that has that" can sometimes be sales gimmiks just to get that little bit extra cash out of us astronomy geeks

[John]

One of my 2" diagonals has "Quartz" printed on the body. I've never noticed any difference in it's performance against the other 2 that I have though.

[spaceboy]

Thanks John

[Naemeth]

I've got this one for my travel set-up:

http://www.telescopehouse.com/acatalog/Revelation_Dielectric_99__Quartz_1.25__Diagonal-1.html

Does the job and holds all my 1.25" EPs easily, a 2" diagonal is just too big and heavy to justify taking.

[Pig]

Just out of curiosity what are peoples views on the 1.25" di-electric diagonals as it is suggested that they do not perform as well as aluminium coated diagonals due to the edge drop off when coating the mirror with di-electric coatings??

that's a new one to me, I have not noticed any difference in a drop in quality