Eyepiece Spacing

[Madanie7]

Hi All,
Just wondering if I could get input into this eye piece list as a goal.
Looking for good coverage for my Nexstar 6SE

No rhyme or reason except for I already have some Televue so kept with them and what I thought were "reasonable" magnification & TFOV jumps.

Panoptic 24mm 62.5x TFOV - 1.0 (already own)
Delos 17.3mm 86.7x TFOV - 0.81
Nagler 6 13mm 115.4x TFOV*- 0.67 (already own)
Nagler 6 9mm 166.7x TFOV - 0.47
Delos 8mm 187.5x TFOV - 0.38 or Nagler 6 7mm 214.3x TFOV - 0.37
Delos 6mm 250x TFOV - 0.29

Thanks
Brendan

[Kunama]

The Delos are much larger than your Nagler T6 and Pan24, especially the Delos 6mm. Why not stick with the Nagler T6 and Panoptics or maybe DeLite for the higher power options...

[ab1963]

Hi Brendan

Matt has given you some valuable advice about eyepiece weight so it would be wise to take it on board, I would not go with a 6mm of any flavour as the amount of times you will have seeing good enough to use it IMO and would go 7mm Nagler for the highest power then the 9mm Nagler that with the 13mm you have will probably end up your 2 most used eyepieces. Lastly i would get a 32mm Televue plossl for low power work a very nice ep in your scope.....

[Madanie7]

Thanks both for your advice, will certainly take on board.

I read somewhere about anything wider than the 24mm panoptic in my scope being wasted. I think it was the field stop of 27mm. I am still quite new to this so not really sure what it means.

[ab1963]

Tv plossl gives 47x with a 1.07 degree field of view and a 3.2 exit pupil. It is well tried in this particular scope

[Madanie7]

Thanks Andrew. Appreciate the help.

[astro744]

The Tele Vue 24mm Panoptic, 32mm Plossl and 40mm Plossl all have 27mm field stop diameters which also happens to be the largest possible within the constraints of a 1.25" barrel. See field stop (mm) column at http://www.televue.com/engine/TV3b_page.asp?id=214

Any eyepiece with different focal length but with the same field stop will give the same true field in a given telescope. What will change is the magnification and the apparent field of view.

In the three above the Panoptic has a 68 deg AFOV, 32mm (and below) Plossl 50 deg AFOV and the 40mm Plossl only 43 deg. AFOV. The Panoptic view is the most pleasing to most people being wider whereas the view through the 40mm is like looking through a narrow tube. All however give the same true field of view. See formula at bottom of above link to calculate true field of view (TFOV).

Now what you do get with the different eyepieces is a different exit pupil and for an f10 instrument this is important especially when using contrast and line filters as a larger exit pupil helps so the image is not too dim. Dark skies still required and preferred especially without filters otherwise the sky starts getting grey at larger exit pupils
At f10 a 24mm, 32mm & 40mm would give 2.4mm, 3.2mm, 4mm exit pupils respectively.

Exit pupil = eyepiece focal length / focal ratio. Also
Exit pupil = telescope aperture / magnification

You will get a lower power with the 32mm and 40mm but the same true field. I would get the N9T6 and N7T6 next for planets and planetary nebulae. The D8 does give that really nice magnification which on some nights 166x is not enough but over 200x is too much and you will find that for planetary viewing every mm of focal length makes a difference and sometimes you will be between focal lengths. You could get a 24-8mm zoom and use with a quality Barlow for fine tuning planetary magnifications. The Type 6 Naglers are quite small compared to the Delos. It's a pity the DeLites are in the same focal lengths as the Naglers and I believe this was done to complement the now discontinued Radians. Look out for a pre-loved 8mm Radian.

Whatever you choose, enjoy!

[Madanie7]

Thanks for the thorough explanation. Its much clearer now.

Cheers
Brendan

[Don Pensack]

Well, normally a 40% jump in magnification from one eyepiece to the next would be a decent place to start.
Starting with the 24mm (and I think you should have a 32mm Plössl for lower power), that would be: 24mm 17mm 12mm 8-9mm 6mm.
But many planetary/lunar/double star observers like their higher powers closer together because they'll be pressing against the limit dictated by seeing conditions.
They might say starting at your 13mm: 13mm...10mm..8mm..6mm
For general use, though, I don't really see you need another eyepiece.
Except maybe a 32mm Plössl for 47x.

[Madanie7]

Thanks Don. Sounds like the plossl might be a decent investment.