Diagonals...

[James]

Hi,

I'm thinking of replacing the stock diagonal that came with my Skywatcher Evostar 120mm F/8.3 refractor with a better one but wanted to pick the brains of the wise people (grovel) here...

I want to get a 2" diagonal, partly in case I get 2" eyepieces at some point and partly as I've heard that 2" diagonals are better in that mirror imperfections are going to be at the edge and therefore out of the way of the light I'm going to be looking at.

But... like everything there's choice, there's:

Televue's Everbrite: http://www.acecameras.co.uk/asp/web/recorprod/1/product/12639/cat/1358/ph/cat/keywords//recor/1/SearchFor//PT_ID/1/product.asp

William Optics:

http://www.acecameras.co.uk/asp/web/recorprod/1/product/11812/cat/1359/ph/cat/keywords//recor/1/SearchFor//PT_ID/1/product.asp

and there's this from FLO: http://www.firstlightoptics.co.uk/proddetail.php?prod=QD2incdiagonal

OK, the questions... considering the scope I have and that I use some quite good eyepieces (a couple of Panoptics and Pentax XW's):

Am I really going to notice a difference (in your opinion) in visual use or am I just dreaming up ways to spend money behind my wife's back. Is it worth going for a more expensive model (diagonal, not wife ) or will the diagonal from FLO be more than sufficient?

I was tempted to post something similar on CloudyNights but was too scared I'd start a thread that would degenerate into open warfare and get too caught up on minutiae

[GazOC]

All those diagonals have great reputations. Don't get rid of your 1.25" though, some kit will not come to focus using a 2" diagonal, its handy to have both.

[GordonCopestake]

The best answer to "will I notice a difference" is to train your 'scope on a tyical target, look through your normal eyepiece/diagonal setup and note the view. Then remove the diagonal and place the same eyepiece directly in the focuser and (attempt) to refocus. You may need an extension tube (or barlow with the element unscrewed). When you have focus (and have nearly broken your back) note the view. The view without the diagonal is the PERFECT view 100% reflectivity. If you notice a significant difference then you will benefit from a new diagonal. If you can't tell the difference then your money is better spent elsewhere.

IMO

[James]

Good idea Gordon - I will do just that (with all due consideration for my back!).

[FLO]

The one FLO sells is from the GSO factory and is the same under the skin as a number of premier brands. You are welcome to take one on approval and return it if you don't see a difference (you will ).

[John]

I upgraded from the standard Celestron 1.25 inch prism diagonal to 2 inch and 1.25 inch William Optics dielectric diagonals and there is a noticable improvement. That's not to say the Celestron diagonal is awful it's just that the images through the others seem to me to show a little more contrast and resolution.

John

[Brass n glass]

A dielectric should always do better because the image just bounces off the reflective surface, whereas with a prism it has to climb through a thick chunk of glass.

[John]

A dielectric should always do better because the image just bounces off the reflective surface, whereas with a prism it has to climb through a thick chunk of glass.

Ageed, but I found that the Celestron prism still performs better than the standard Skywatcher mirror diagonal which I think Maccers uses at the moment - so he should see an even bigger improvement

John

[James]

The one FLO sells is from the GSO factory and is the same under the skin as a number of premier brands. You are welcome to take one on approval and return it if you don't see a difference (you will ).

I think I will take you up on this Steve, I'll be in touch shortly! I might also get a chance tonight to try out Gordons suggestion to have a look through without the diagonal to see what difference that makes.

Ageed, but I found that the Celestron prism still performs better than the standard Skywatcher mirror diagonal which I think Maccers uses at the moment - so he should see an even bigger improvement

Cool... I'm convinced...

[The Warthog]

The best answer to "will I notice a difference" is to train your 'scope on a tyical target, look through your normal eyepiece/diagonal setup and note the view. Then remove the diagonal and place the same eyepiece directly in the focuser and (attempt) to refocus. You may need an extension tube (or barlow with the element unscrewed). When you have focus (and have nearly broken your back) note the view. The view without the diagonal is the PERFECT view 100% reflectivity. If you notice a significant difference then you will benefit from a new diagonal. If you can't tell the difference then your money is better spent elsewhere.

IMO

Very well put!