eyepiece advice

[Guest memoryman]

I have a recently *revamped Meade LXD55 SN10 f4 scope (focal length *1007mm, primary mirror 254mm diameter) on an HEQ5 equatorial mount with extended counter weight rod, plus manual motor controller. 

 

I also own four eyepieces, namely a 1.25" Super Plossyl 40mm, that I use mainly for locating objects initially, plus a 2" TV Nagler type 4 17mm 82 degree eyepiece which is superb. A 1.25" Pentax SMC XL 10.5mm, again superb views and a 1.25" Williams Optics SPL 3mm. that, when skies are clear and seeing is good gives great views of the Moon, Planets and DSO's.  

 

To this collection I added a a Celestron Ultima 2x Barlow (bought second hand form a seller off UK Astronomy Buy & Sell), which extends my range to 20mm, 5.25mm and a very low probability of 1.5mm with the Williams Optics 3mm!! 

 

I would appreciate some advice on which eyepiece/s to buy to help with wide field low mag viewing of DSO's and whether I need (must be a good quality eyepiece as the scope is fast at f4) between the Nagler and the Pentax?

I think I need a 2" eyepiece of between 26mm and 35mm focal length and possibly a 14mm 1.25" eyepiece to complete my collection.

Do any of you with a lot of experience of eyepieces, think I'm on the right  track or if not, have you any suggestions as to eyepieces I should look at?

 

*I made a PLOP optimised a 6pt floating support cell for the clipectomied primary mirror, plus cleaning of same and re spotting of centre spot with Farpoint red triangle centre spot, fitting of a new Revelation Astro Crayford 10:1 focuser, plus cleaning of the corrector plate and the fitting of a compression spring between the secondary (also cleaned) and the the outside of the central support ring, which the tilt bolts push against.

 

Any advice will be appreciated.

[Tweedledee]

Hi Paul.

 

SN 10 F4!! Well, I didn't think there were anymore of those dinosaurs in existence.

I know why you need an extended counterweight rod.

If you use an eyepiece with an exit pupil larger than your dark adapted eye pupil, you will be wasting light and defeating the object, and will only get the light gathering power equivalent to a smaller telescope. If you are only interested in an extremely wide field, then a bigger exit pupil is ok, but you won't be benefitting from the full 10" aperture.

Let us assume that your dark adapted eye pupil is 6mm - it may be smaller. Therefore to fully utilise the aperture (ie. maximum light grasp) of an F4 telescope you need an eyepiece of focal length (eye pupil size x telescope focal ratio) ie; 6 x 4 = 24mm.

Currently my widest true field of view is provided by a 2" 23mm 82 degree Celestron Axiom LX. This gives me an exit pupil of 5.75mm at 44x with a 1.86 degree field on the 10" Schmidt Newt. The quality of the view is excellent across the bulk of the field of view and gives quite a wow factor.

For comparison, your 40mm 44 degree Super Plossl will give a 10mm exit pupil at 25x with a 1.73 degree field, but your 10" will only gather as much light as a 6" scope because the exit pupil is so big.

If, like me, you really like ultra wide fields and that wow factor, check out the 100, and 120 degree eyepieces from Explore Scientific and the Televue Ethos. They are well corrected at F4 and give the most amazing views.

Some eyepieces suit some people better than others, so before spending lots of money come to a dark site and try some of ours and see which suit you best.

 

Regarding Naglers and Pentax, I can only say that all the Naglers I have owned were superb, but I know some prefer the Pentax even though the Nagler has a wider apparent field.

If you need any help calculating the numbers, I would be happy to help.

 

Regards,

Pete.
 

[dawson]

Hi Paul. I don't know enough about anything to help, I'm sorry, but welcome. I used to work with an Andy Burtenshaw in Birmingham in the NHS; he was a lovely chap, if he's any relation to you say hello from me.

 

Good luck with the eye piece quest.

 

James

[Tweedledee]

Do you feel the PLOP optimised cell and other mods have significantly improved the scope?

 

I would be very interested to see a picture of the cell.

[catman161]

24mm TV panoptic would be my recommendation

[Guest memoryman]

Do you feel the PLOP optimised cell and other mods have significantly improved the scope?

 

I would be very interested to see a picture of the cell.

petersull:

I completed it between June and mid July last year (2013) and it works very well. The primary is held very firmly, but isn't constrained by the lateral and vertical supports which are separated from the mirror by a gap the thickness of a piece of A4 paper.  The mirror also moves smoothly on its 6 slippery 25mm wide round pads. After transporting it in my van over bumpy country roads, setting it up and using it for a couple of hours in lots of different orientations the collimation remains virtually spot on requiring just a minor tweak or two to get the Far Point triangle centre spot dead center in the reflective ring of my 2" Farpoint Cheshire (I'm a stickler for accuracy in this regard. My wife just says I faff about! :-)). One evening I even took the mirror cell out at my Astro clubs meeting to show people, who handled it turning it round and even upside down at times over the course of about an hour or so. When I reinserted the cell back in the OTA and checked the collimation it was still virtually spot on, which people found amazing!

After cleaning, replacing the centre spot with the Far Point triangle and fine tuning collimation the views are spectacular! At one meeting last August when viewing M13, I managed to magnify it using my Willams Optics SPL 3mm EP where the Globular Cluster occupied almost half the FOV and with averted vision the centre was filled with the bright points of light of individual stars! An experienced companion also witnessed the view and was equally amazed!

So yes it was worth every minute of the hours, days and weeks of mostly mental effort I devoted to the project and the end results confirm it! Now all I have to do is remember how to post images!!