Do high quality and/or large diagonals make a real difference on an SCT?

g__day (Matthew) · #1 23-10-2006, 10:33 PM

Guys I was pondering parking my standard diagonal for maybe a Williams Optics D-DIG2DS SCT 2" Dielectric diagonal with 1/10 wave, 99% reflectivity that Andrews sell for $259 (vs Astronomy Online for $349)! or maybe the 2" erecting prism D-EP90 for $315

I ponder do these diagonals make either or both viewing or imaging discernibly better - and if so under what conditions or what objects? Or are they really just a gimmick not worth the investment? My 80mm Megrez has one of the sorts of diagonals, and its contrast is terrific - but that might just be the quality of the optics of the scope.

What are peoples thoughts and experiences please!

h0ughy (David) · #2 23-10-2006, 10:41 PM

OK no gimmick the y do make a difference, you think that if all the surfaces within your scope were optically that efficient that you would gain nearly 10-20% more light at the eyepiece depending on conditions. I used the original Meade 2" diagonal and a WO 99% one and showed 3 people at duckadang last year with the same object (a galaxy - Spanish dancing one (not Tuesday nights on Prime)) and they picked the Wo one as the brightest, I then told them. the other diagonal was the 97% reflectivity one.

JM2CW

oh forgot to say that at each optical surface there is light loss due to interference and loss within the medium, and dispersion, but some smart cookie will have the actual facts somewhere

g__day (Matthew) · #3 23-10-2006, 11:04 PM

Thanks Houghty, another thought struck me too - can you readily connect this diagonal with a Williams Optics SCT 2" Crayford focuser with 2 speed microfocuser? I may get one of these two - especially if you can combine the two!

Striker (Tony) · #4 24-10-2006, 06:40 AM

There is 2 versions...the SCT diagonal and the standard 2" diagonal that simply slides into all 2" focuser such as the williams you mentioned or any other 2" focuser.

The SCT diagonal has a thread that will screw onto the visual back of your SCT...you probably wont want this diagonal if your planning on having a 2" focuser.

Go with a diagonal that has the standard housing for 2" focusers....which is the most common diagonal.

Merlin66 (Ken) · #5 24-10-2006, 07:01 AM

Remember to can have the best of both worlds if you have a SCT threaded diagonal, you can add a 2" adaptor ( about $25) and use it on 2" focussers.
This is what I did when I added the micro-fine zero shift 2" focusser to the Lx200. Now I can still use all the SCT "daggle-dolly's" ie flip mirror/ compressor/filters/ on the 2" connection.

acropolite (Phil) · #6 24-10-2006, 07:34 AM

Bintel have 2 inch Quartz dielectric diagonals for $149. They are very well made and possibly perform as well as their more expensive (WO) counterparts.

g__day (Matthew) · #7 24-10-2006, 10:49 AM

Great news too! I am keen to know if you can attach a Williams Optics focusser to the back of a Celestron C9.25 OTA. - EDIT - Just checked, says you can on the Williams Online Site.

Merlin - when you say uo added the micro-fine zero shift 2" focusser is that the shaft that goes on to replace the focus knob or is it the entire shaft that connects to the back of the OTA (where light goes through) that the diagonal attaches too?

Taa guys!

Merlin66 (Ken) · #8 24-10-2006, 12:46 PM

I've got the #1206 (?) Meade electric focusser on the knob and a #1209(?) crayford "zero-shift" on the SCT thread at the back of the cell. I rigged up a controller which can switch between them ( with DC braking to prevent over run!) I can then use the knob drive for quick focus and then switch to the other for fine focus. Works for me. The 2" adaptor I mentioned allows me to use all the SCT stuff with the crayford.

casstony · #9 24-10-2006, 01:26 PM

Why would one choose a GSO dielectric quartz diagonal ($150) over a BK7 diagonal ($95)? Would there be any noticeable difference?