Eyepiece Selection For 150mm F8 Reflector - Advice?

[Alkaid]

Hi all,

I am looking for some advice if possible please regarding new eyepieces for the 150mm F8 Newtonian shown in my signature. I know it is a slow Newt, so cheaper eyepieces will work quite well in it, but to be honest the pieces I will buy are intended to stand me in good stead for many years, and are to be used with all future OTA purchases. So I want good ones in the £80 to £150 range say. I am perfectly happy with calculating magnifications, but I am un-familiar with calculating exit pupils, vignetting and other problems that may crop up with the eyepieces I have selected so far…and I also need to work out fields of view.

The OTA has a 2” Crayford focuser, with 1.25” adaptor.

Here are the eyepieces I have been looking at. I am mainly a lunar and planetary observer.

Baader Hyperion 8mm, with 14mm and 28mm fine tuning rings. Will give magnifications of:

8mm: x 150

6mm: x 200

5mm x 240 (For the Moon on good nights)

4.3mm x 279 (Within the capabilities of the scope, but probably not the seeing, however I am willing to try for fun).

Baader also provide field stop data, but I don’t know how this relates to my eyes, presume this just affects the field of view?

8mm: 10.7mm field stop

6mm: 8.6mm field stop

5mm: 7.1mm field stop

4.3mm: 6.1mm field stop

In 2” guise with the front 1.25” element removed from the 8mm hyperion, the focal length becomes 21.8mm yielding x 55 mag, and then the eye piece has a field stop of 30mm.

Also a very low power eyepiece for sky sweeping and DSO hunting when the mood takes me:

Skywatcher Panaview 38mm: x 31.5

Field stop: Don’t know.

Assuming I have normal eyes, will all of these eyepiece combo’s work well with this OTA? Or not?

Any comments appreciated as always.

Many thanks Steve

[rwilkey]

I wouldn't go below 6mm (200x) with your telescope, higher magnifications wil not be used very often and will therefore not be good value for money. Your general choices seem quite good but you might want to concentrate on medium and low power, for DSO's, unless you are interested in planetary. For the PanaView 38mm, I would suggest the 32mm for your low power needs instead.

[crazyjedi]

The Hyperions will work very well with your current scope and provide good views as will the Panaviews. However, if you do upgrade to a faster scope you may feel the need to upgrade to Meade or Explore Scientific (which both fall in to your price bracket (just)) for their wide field EPs or the excellent Televue plossls or Pentax XF range. If a wide FOV isn't an important factor for you. Many Dob owners (but not all) favour a wide FOV ep for planetary mainly because the planet stays in field for longer meaning fewer nudges whilst viewing.

There is always the second hand market to be explored to find some premium EPs at for reasonable price. I got myself a Teleview Radian for £115 who is pretty tidy

[part timer]

Bit late to this but,

I have the same type of scope and will tell you that fewer, better eyepieces is better than more but inferior eyepeices. I have loads and can increase magnification incrementally. However I started with just three and a barlow.

At f8 you may as well take advantage of the 2" focusser to get wide fields.

I seriously would take even two secondhand televues and a semi-decent barlow over all the hyperions and panavues put together.

I've only used the hyperions in all honesty but 'average' just about sums it up. The're not that cheap either.

The only eyepices i have never and will never feel the need to 'upgrade' are my televues and my Baader Ortho (and I hate orthos normally!). I can use them in every scope in all conditions and all magnifications and they will be used for life.

With some patience you can get two or three eyepieces of your chosen focal lengths second hand within budget from the plossls, radians, panoptics, or even (at the top end your budget) Naglers. All, even the plossls are worth two or three hyperions and others.

Others disagree I know but unless you want keep buying eyepieces and flogging them at a loss you may as well just get the best to start with.

[crazyjedi]

Bit late to this but,

I have the same type of scope and will tell you that fewer, better eyepieces is better than more but inferior eyepeices. I have loads and can increase magnification incrementally. However I started with just three and a barlow.

At f8 you may as well take advantage of the 2" focusser to get wide fields.

I seriously would take even two secondhand televues and a semi-decent barlow over all the hyperions and panavues put together.

I've only used the hyperions in all honesty but 'average' just about sums it up. The're not that cheap either.

The only eyepices i have never and will never feel the need to 'upgrade' are my televues and my Baader Ortho (and I hate orthos normally!). I can use them in every scope in all conditions and all magnifications and they will be used for life.

With some patience you can get two or three eyepieces of your chosen focal lengths second hand within budget from the plossls, radians, panoptics, or even (at the top end your budget) Naglers. All, even the plossls are worth two or three hyperions and others.

Others disagree I know but unless you want keep buying eyepieces and flogging them at a loss you may as well just get the best to start with.

Even though I can't afford all that is black and green , I do totally agree with this principal.

I have purchased the best quality lenses that I could (without incurring financial ruin or spousal repercussions)

I think for planetary work the BGO's are hard to beat (If you can find them anymore) especially when you consider how cheap they are, and there are quite alot of good lenses that can be had for the same price as a Hyperion particulalry on the second hand market.

[KaStern_Former_Member]

Hi Steve,

your 150/1200mm is an f/8 scope and f/8 is not very demanding for eyepieces.

The other advantage of f/8 is:

Coma does not be bothering, the diffraction limited field of view is relatively big.

I am un-familiar with calculating exit pupils

devide the eyepiece focal length by 8 and you have the resulting exit pupil (ep)

when used in your scope.

I recommend to take from about 0.66mm to about 6.6mm exit pupil.

The corresponding magnifications are from 225x to 22.5x

Knowing the field stop diameter you can calculate the true field of view

when used in your scope.

For example the 5mm eyepiece with 7.1mm field stop gives you

0.339° true field of view. The full Moon is about 0.5°

Cheers, Karsten