Which 2" diagonal for Celestron 9.25

[glass]

Hello I'm considering a good quality 2" erect image 90 degree diagonal, I realise they are not as good as a mirror diagonal but can I get one close to the quality without spending too much?

Thanks for any replies.

[YKSE]

A blant answer is NO.

Simpler erected (Amici) prism diagonals has very noticeable poorer light transmission falloff (I have a WO one for terestrial work). Even much more costly amici prism is judged to be not as good as good dielectrical ones, see the answers in #9 and #12 in this thread:

http://www.cloudynights.com/topic/502630-diagonals/?p=6634968

[glass]

Thanks,things to consider then.

[John]

To get one that even approaches the optical quality of a decent mirror diagonal would cost around £150 - £200 I think. The benefit would be that left and right would appear correctly orientated - the normal mirror diagonal produces an image with up and down as our eyes see them already. Taking into account even a slight degrading of image quality that seems a lot to pay for a relatively small benefit.

[glass]

It is a lot to pay but in a years time would I notice it had gone?! Of course I could look out for second hand but they seem rare to come buy. I'm thinking now of a quartz dielectric on Skys The Limit for around £70.

[brantuk]

Amici prisms are usually used for daytime observing where there's loads of light and upside down and right left orientation are important. In space at night it doesn't matter much how an object is orientated so regular diagonals tend to be used - dielectric is very popular. I have the WO dielectric which is great on my fracs, and also the Celestron one with matching Starbright coatings for my 925 - it's expensive but performance is excellent with the Sct.

You'll get a good condition WO dielectric for around £70-£85 on the used market - or wait for a retailer offer to come up. Check out UK Astro Buy Sell website for used bargains. Hth

[glass]

Thanks Brantuk

[John]

.....I I could look out for second hand but they seem rare to come by.....

I think thats because few people use them for astronomy, because of the drawbacks discussed.

[garryblueboy]

The Explore scientific 2" is Good value for money also I had one and compared it to my WO one and to be honest could see no noticable difference theese are around £50 -£60 on used market .

[John]

The Explore scientific 2" is Good value for money also I had one and compared it to my WO one and to be honest could see no noticable difference theese are around £50 -£60 on used market .

I see their 2" diagonal on the ES website but I can't see a correct image version ?.