SCT Eye Pieces 2" or 1.25"

[mickqueensland]

Hi All,

I am having some difficulty understanding the whole eye piece thing. I have done quite a bit of reading now so I have a basic grasp of magnification, TFOV, AFOV etc etc and I am trying to decide which way to go. I am planning on buying a Celestron 8SE scope soon and I want to get the right set of EPs first time round rather than wasting time and money learning the hard way.
First, I wear glasses so I want good relief, I'd say about 20mm (?). Also it looks like a wider field is better too, specially for the closer objects like Sun and Moon. Of course good optical quality would be desirable as I want to use these EPs for long time and I dont want to be frustrated after a few months use.
Second, as well as visual, I also want to use a CCD. I am considering an Orion Starshooter Solar System Color Imager 3 to hook up to my laptop. (or is that item just too cheap? 1/2" cmos ccd, 1.3 Mpixel, 5.2 micron pixel, colour)

What I need clarified is the difference between 2" and 1.25" EPs, and what I need to put a 2" EP on my 8SE scope? I guess this would be easier if I had the scope to look at but I dont yet. Celestron's website didnt have any info about changing to 2" from 1.25" (not that I could find anyway) I understand that a 2" EP will give me a larger Field Stop & Field Size but how important is that?
Do I need to match the Exit Pupil to the CCD diameter or should it be slightly larger?

Any other hints on whether to stay with the standard 1.25" or swap to 2" right away?

My head is spinning from reading so much stuff... :P

Cheers
Mick

[astro744]

Unless I'm mistaken the Celestron 8SE would come standard with a 1.25" visual back and 1.25" diagonal and perhaps one or two 1.25" eyepieces (maybe 25mm & 10mm). With this configuration you will only be able to use 1.25" eyepieces. The maximum field you will get with 1.25" is with a 32mm Plossl or 24mm Panoptic, both of which have a 27mm field stop diameter and will give you 0.77deg TFOV.

You can change the 1.25" visual back to a 2" version and add a 2" star diagonal and you can then use 2" eyepieces. A 35mm Panoptic would be a good choice and will give you 1.1deg. (A 41mm Panoptic is useable but you will get slight vignetting due to the opening at the rear of the SCT (visual back) alhough it may not be noticeable.

Note you could also use a f6.3 focal reducer and stay with 1.25". The reducer screws on first and then the visual back.

Stay with what the 'scope comes with for a while as you can always change and add to it later as the SCT is very versitile.

[sheeny]

I second that.

Al.

[mickqueensland]

Hi fellas,

thanks for the quick answers, astro & sheeny. I agree that using what it comes with is a reasonable idea for starters. However, the 8SE isnt exactly brimming with accessories. (hard to ***** at the asking price though :rofl:)

The 8SE comes with 1 EP, 25mm at 1.25" giving a magnification of 81x. It also has a 1.25" "Star Diagonal" (nb: The 8SE has a FL of 2032mm) There is no other info on the EP but I would assume it is a Celestron plossl with something like 52°, just a guess

I guess that 25mm a commonly used FL EP for an 8" SCT.

Looking at US ads I see that I could add a 2" Visual Back and a 2" Diagonal for about usd $100. So thats not bank breaking. I expect the EPs may be a tad more expensive though ;)
I also note that OPT sell their own range of 68° EPs and they are very reasonably priced. Almost too good to be true... Any thoughts on the quality?

Cheers
Mick

[sheeny]

I can't comment on the quality of OPT EPs, I haven't encountered them myself.

However, if the money is burning a hole in your pocket, I can recommend a 13mm Nagler Type 6:thumbsup:. The view is impressive.

Quality EPs you'll keep for life;).

Al.

[gb_astro]

Hi Mick.

The OPT 68deg. Superviews appear to be the same as the Superviews sold by Bintel in Australia under there own Bintel brand name and at a similar price, which should be less after freight charges.

However you would have to be a bit skeptical about quality when OPT say this on there own website when describing the Superviews:
"However, we'll be honest... at high magnification the image sharpness can become distorted at the edges of some manufacturer designs in some telescopes without corrective measures."
Still at that price it might be worth a gamble. Also a f10 scope like the Celestron 8SE can be very tolerant of poor eyepiece quality.

Some of the better (expensive) 20mm ER designs are the Pentax XWs, Tele Vue Radians or the Vixen LVWs.

I would have to agree with Astro744 though. Get the scope first, especially if you decide on higher quality eyepieces.
You get hands on experience plus more time for research before making a decision. Also you can buy just one eyepiece and try it. If you like it you can get more of that design. If you don't you get something else.
That's better than having three or four versions of a design you end up not liking.

gb.

[mickqueensland]

Hi,

cool, Sheeny, I checked out the good stuff and there are so many to choose from. One that caught my eye (joke lol) was the Vixen LV8-24mm Zoom with 15-19mm eye relief. This would give a power range of 85x-254x and AFOV 60°-40°

This sounds like a nice EP that does a lot in a single package for about $340. THis combined with the supplied EP would do most of what I want to begin with I think, or am I mistaken? Does anyone have any experience with them?

Cheers
Mick

[Harpspitfire]

i really dont care for 2"EP's, i got rid of mine- its true the rear cell on your 8e wont open fully to a 2" diagonal, i but i wouldnt worry about that, i got 2 older celestron 1.25 diagonals (stock) that are excellant performers, my newer stock 1.25 diagonal is a step down in quality, i got a feeling your diagonal will be of this type- i can recommend the astrotech 2" enchanced diagonal- mine was $79USD on sale- im not sure its made anymore but the 2" dielectric is $119USD

[astro744]

The Tele Vue 8-24mm zoom is also a good performer and well priced in AUS as is the Tele Vue 32mm Plossl. These two eyepieces both have good eye relief and the 32mm will give you a nice exit pupil and the widest TFOV in 1.25".

If you want a bit more AFOV, go the 24mm Panoptic instead of the 32mm Plossl but also add the zoom. I'd go the Plossl+zoom though and get a 1.25" UHC or O-III filter (or both) to go with the 32mm+zoom.

You may find the 8-24 zoom + 32mm is all you will ever need or at least for a while and even if you get other eyepieces the zoom is still very handy.

Note adding a f6.3 focal reducer has a similar effect on TFOV as going from 1.25" to 2". ( ie. 1.25/2 = 0.625) and you wont have the vignetting with the larger 2" eyepieces. You can add the focal reducer later if you feel you want more TFOV for certain objects or for shorter exposures in astrophotography.

[mickqueensland]

Hi all,

thanks astro and astro and harp. All recommendations taken on-board. Thanks again. I think I will pass on the 2" stuff for now. I will probably go for a zoom to begin with, in a good quality make and see how I go. I will also look at a focal reducer to 6.3 ish and a powermate about 2 or 2.5 and then maybe a 32mm plossl when funds become available again.

Now I have a plan, thanks for all advice and any more is still welcome. The range of choice of eye pieces is seemingly endless...

Cheers
Mick