A Question About Diagonals

5 years 5 months ago #101952 by lunartic
A Question About Diagonals was created by lunartic
Hi all

With my current set up, Celestron 9.25 SCT, I am using the mirror diagonal that came with the eyepiece kit that I purchased along with the scope, in my mind I feel that I am not getting the best out of the scope with this diagonal, to my eyes the sky does not look dark enough, and I am giving serious consideration to changing it for one of better quality. I have looked online for information about this particular diagonal, reflectivity, etc., but have come across nothing.

My question is this; is it worth the cost of buying another diagonal of better quality, or does it really not make so much of a difference?

Paul

Programming today is a race between software engineers striving to build bigger and better programs, and the universe trying to produce bigger and better idiots. So far, the universe is winning.

Rich Cook

Please Log in or Create an account to join the conversation.

5 years 5 months ago #101958 by flt158
Replied by flt158 on topic A Question About Diagonals
Hi Paul. I can only tell you I have Dielectric mirror diagonals on my scopes made by Orion. At the time they were of the 2nd highest standard of their range. I find them very effective.

Aubrey.

Please Log in or Create an account to join the conversation.

5 years 5 months ago - 5 years 5 months ago #101970 by dave_lillis
Replied by dave_lillis on topic A Question About Diagonals
What make is the diagonal?
It would want to be a particularity bad diagonal to give you a visible degradation of the image.
One thing that can sometimes help darken the fov is to use a good sized dew shield.

Dave L. on facebook , See my images in flickr
Chairman. Shannonside Astronomy Club (Limerick)

Carrying around my 20" obsession is going to kill me,
but what a way to go. :)
+ 12"LX200, MK67, Meade2045, 4"refractor

Please Log in or Create an account to join the conversation.

5 years 5 months ago #101976 by lunartic
Replied by lunartic on topic A Question About Diagonals
The diagonal is a Celestron make, perhaps it's just me, maybe I am thinking of other scopes I've owned that were of a faster focal length and believed that the view was somehow better.

This is the diagonal in question.

www.telescopes.com/telescope-accessories...gonalmirror2inch.cfm

Paul

Programming today is a race between software engineers striving to build bigger and better programs, and the universe trying to produce bigger and better idiots. So far, the universe is winning.

Rich Cook

Please Log in or Create an account to join the conversation.

5 years 5 months ago #101977 by dave_lillis
Replied by dave_lillis on topic A Question About Diagonals
I can't imagine that been a bad diagonal.
A bad diagonal would dim the star field, so would actually darken the field. A bright field is been caused by something else like light scatter or an actual bright sky.
What you can do is get a visual back where you can put the eyepiece directly into the back of the scope and not use a diagonal at all, that would be the ultimate test.

Dave L. on facebook , See my images in flickr
Chairman. Shannonside Astronomy Club (Limerick)

Carrying around my 20" obsession is going to kill me,
but what a way to go. :)
+ 12"LX200, MK67, Meade2045, 4"refractor

Please Log in or Create an account to join the conversation.

5 years 5 months ago - 5 years 5 months ago #101979 by stevie
Replied by stevie on topic A Question About Diagonals
Diagonals, and their ability to improve views, is one of those subjects which crop up constantly on other forums. Some believe that dielectric diagonals are a great improvement, and others reckon they are a waste of money. It seems to me that most Celestron diagonals, rather like most Skywatcher finderscopes and the eyepieces supplied with cheaper scopes generally, are poor quality, and rather let down the rest of the equipment. However, the diagonal you have seems pretty reasonable.

I use a William Optics diagonal in my Nexstar, and I think it does show a marked improvement over the original. A mate also bought a 2" Williams for his refractor, and he also thinks it is an improvement.

One possible solution would be to collimate the diagonal you already have, but you may need a refractor to do it. I did this with the diagonal on my TAL refractor., and the view improved considerably.

Make a paper circle for the front lens end of the refractor, and make a tiny hole in the centre. Take out the four screws at the back of the diagonal, there should be another four screws underneath. Put the diagonal into the eyepiece end, and put a red collimating laser into it. See where the laser hits the paper at the front. Mine was way off. Adjust the screws until the laser passes through the hole in the paper. I set up the scope so that it pointed towards a mirror, which meant I didn't have to keep going from one end to the other to see where the laser was hitting the paper.

I don't know if it would be possible to bounce the laser off the secondary mirror of the SCT and collimate it by centring the reflected light in the black dot at the centre of the collimator, rather like collimating a dob, but it might be worth trying.

stevie

Secretary NIAAS

Please Log in or Create an account to join the conversation.

5 years 5 months ago #101981 by mykc
Replied by mykc on topic A Question About Diagonals
That's very interesting Stevie. I had a (not cheap) diagonal in which the mirror had become unseated from its housing and there was obvious vignetting. Reseating the mirror was straightforward, but I was not aware of the proper collimation procedure you describe. I'm one of those people who does not notice a significant change in the view through 99% reflectivity diagonals versus the 90% versions.

I see that you have a 2" diagonal Paul, which prompts a couple of off-topic comments. Being fundamentally lazy, I hate changing eyepieces and adapters, so I use a 2" like yourself, and either 2" eyepieces or, for the shorted focal lengths, Hyperions which have both 1.25" and 2" sleeves so I never have to swap down to a 1.25" diagonal or use an adapter. Also, I work through the double star targets for a session in order of decreasing separation to minimise the number of time I need to swap eyepieces. How bad is that! :)

Mike

Celestron 280 mm f/10 SCT
CG-5 mount
Toolbox full of bits n' bobs
Thermal underwear

Please Log in or Create an account to join the conversation.

5 years 5 months ago - 5 years 5 months ago #101986 by stevie
Replied by stevie on topic A Question About Diagonals
Hi Mike

It's not necessarily the correct procedure, just one that worked for me. Probably a bit complicated, to be honest.

Here's another way, without having to use a telescope at all.


stevie

Secretary NIAAS
The following user(s) said Thank You: mykc

Please Log in or Create an account to join the conversation.

5 years 5 months ago #101990 by mykc
Replied by mykc on topic A Question About Diagonals
Excellent, thanks Stevie.

Mike

Celestron 280 mm f/10 SCT
CG-5 mount
Toolbox full of bits n' bobs
Thermal underwear

Please Log in or Create an account to join the conversation.

Time to create page: 0.091 seconds
Powered by Kunena Forum