Wide FOV not for planetary observation?

[GotGazer]

Hi,

In many topics about eyepieces for planetary observation Plössls and Radians are often recommended.
Is that because an eyepiece with a lot of lenses cannot compete with one that has just a few lenses? 
Or are these recommendations based on the price of the eyepieces and a wide FOV is actually equal to a Plössl in terms of performance?
 

I'm asking because the next eyepiece I'll buy will probably be one that is good for planetary observation and I'll try to keep the number of eyepieces to a minimum.
Lets say I'm looking for an 8mm planetary eyepiece.
Thinking about 3 different approaches:

1. A 16mm wide FOV + a x2 Barlow  =  I will get a nice 16mm for DSO and an 8mm for planetary. (But there will be a lot of lenses for that 8mm combination.)
2. An 8mm  wide FOV  =  Could still be used for DSO but probably just an expensive planetary eyepiece.

3. An 8mm narrow FOV = Lower price but only for planetary observations.

Right now I have a c9.25 with a LVW 42mm and a few low quality plössl.

[ronin]

A wide FoV is to an extent unnecessary, you will be putting the planet in the middle and literally that will be the one and only aspect you will be looking at. You tend not to be admiring the stars surrounding Jupiter.

So you do not need the additional lens that enable a wide field.

Coating have improved a lot so there is less problems with scatter from the coatings but still the more of them then the worse some aberrations will get. So in that respect less glass air surfaces are useful.

So non-wide FoV simple eyepiece lend themselves to planetary observing, and they often cost less. Another "effect" is a planet in a wide FoV appears smaller.

[John]

Radians do have quite a lot of lenses - 6 or 7 depending on the focal length.

Personally I do like a wide field eyepiece when observing at high power because my scopes are on undriven, alt-azimuth mounts and the wide field helps with tracking at high power.

Modern glass and coating technologies mean that good quality and well designed wide field eyepieces can compete on contrast and sharpness with simpler designs although the better quality orthoscopics do just edge the more complex designs on light scatter.

Cost is a significant issue though with the complex wide field designs that can compete with the simpler designs costing much more than their "low glass" bretheren.

I honestly believe that the categorisation of eyepieces into "planetary" and "wide field" is getting very blurred these days. Not that "blurred" is a particularly good term to use in eyepiece discussion I guess .....

[Moonshane]

if you buy good quality, and especially with a slow scope, there's no reason not to buy wide field for planetary. personally I prefer narrower fields (plossls and BGOs) for solar system and doubles but this is just preference not necessity.

[Owmuchonomy]

Hi GotGazer I have the same telescope as you. For planetary observations I use an 8mm Baader Hyperion. I also purchased the Fine Tuning Rings with it so I can decrease the focal length to 4.3mm. This gives me great planetary views through this scope when the atmospheric seeing allows. There is the added advantage that you can connect a DSLR directly to the EP and do EP projection photography. See below taken in the Spring.

[GotGazer]

I didn't think it was possible to use eyepieces shorter than 8mm with a 9" SC 

The Baader 8mm with rings is really tempting.

- A lot of positive reviews

- An inexpensive way to go beyond 8mm which feels a bit risky

- Planetary photography within reach. (I do have a DSLR)

- I will get an eyepiece that can be used for fine tuning collimation

 

I will definitely keep an eye on this one.

[Pig]

My experiences using  9.25 SCT for planetary work lead me, eventually, down the path of using a narrower FOV eyepieces.

For example a SLV 25mm 50 degree FOV gave a bigger and much sharper views of Jupiter than those experienced using a Delos 17.3mm 72 degree FOV (this was a revelation to me) this approach applied across the whole range of sizes.

However, the Deloi were great for messier objects by comparison. I then purchased a short refractor and as a result solved this sky coverage issue when using the SLV's. So now I have great planetary close ups and great views of clusters etc...

I would advise people who purely want to view planets and the Moon to use good quality ortho type eyepieces or buy a different type of scope.

It all depends on what you want to get from the hobby, there are many options.

[Mr Spock]

I find the same with my C925. My most used eyepiece for planetary is the 10mm NLV follwed by the 8mm LVW.

The LVW has 65° but I use LVWs for their comfort rather than field of view.

If you are not bothered by a 40° field then a good orthoscopic is hard to beat.

[Moonshane]

This reminds me of what is presumably an optical illusion in that planets seem smaller in a wider field than a narrower field even though presumably the disk is the same diameter in the eyepiece.

[Pig]

Shane, I am not sure about the maths, but the effect is more planet to look at from the view available, in addition the magnification is lower with the eyepiece in my example so sharpness of detail is increased. It may be an optical illusion but it is a cheaper illusion

( sorry for going off topic to the OP)

[Moonshane]

I think we are on topic :0)

[Pig]

I did quite a bit of switching between eyepieces before I made the change from wide FOV eyepieces and to me there was a clear difference. The brain is a complex piece of equipment and I wouldn't be surprised if it were an illusion. Maybe someone with 2 scopes that are the same could conduct an experiment.

[John]

Having directly compared the views of planetary disks through scopes when testing eyepieces of the same focal length but with varying fields of view, I'm pretty confident that the apparent diameter of the planet in the eyepiece field remains the same. The amount of sky that frames the planetary disk does vary enormously between, say, an ortho and an Ethos though so that can create an optical illusion that the planetary disk is "smaller".

This is the same optical effect that makes the Moon's disk seem larger when it's  close to the horizon, the so called "Moon Illusion".

Most of the time I enjoy using my wide fields on the Moon Planets but I do keep a few simpler designs for when the mood takes me 

One very experienced observer who posts here says that his best ever views of Jupiter came with an Ethos eyepiece used with a 2x Powermate which = 14 pieces of glass !

Just as well the modern designs enable more glass to perform so well as it gives a chance for those who wear glasses to use short focal length eyepieces with some comfort

[Moonshane]

I think that some of the legends about best planetary performance come from experienced observers with high quality scopes at altitude in excellent conditions (often in the states). In these circumstances the extremely subtle differences of the most optimum eyepieces for planetary observing will naturally present themselves.

For the average observer with a standard albeit decent scope and cheap but decent eyepieces sat in their urban garden with average seeing any feasible features will be apparent with patience

[Pig]

I think that just about wraps and puts that one to bed for a while

[John]

Yep, can't argue with that

[bond19]

It's a personal thing regarding wide fields when viewing the planets. Personally I love how Jupiter just hangs in empty space in my Ethos 8mm (and x1.6 barlow) combo. It really frames the planet and it's moons perfectly. As for detail, well it's all there. I can even make out a couple of the moons as discs and some with a hint of colour (albeit very, very small discs) and just barley on the limits of being perceptible. So I agree that modern complex designs can rival simpler eyepieces. So with that in mind, I'll take a wider view every time.

[michael.h.f.wilkinson]

The point about aberrations getting worse with more glass is not quite convincing to me. Scatter can and will become worse as more glass-air interfaces are added in particular. Glass-glass interfaces are less troublesome. Coatings have reduced these problems to a great extent (but not entirely eliminated them). However, for all other aberrations additional surfaces give more degrees of freedom to reduce them. What I find particularly baffling is claims people make that an orthoscopic with a quality barlow beats modern long eye relief designs (the ones with a Smyth lens (a.k.a. Barlow when sold separately) followed by something which looks a lot like a plossl or ortho design, or latterly more Erfle like for more field width. As quality Barlows tend to be four element two group desings, the number of lenses/groups should match those in planetary EPs at least.  By matching the Smyth lens design to the rear unit you can in principle get better correction than by separating the designs of the Barlow and the EP. What is easily as important as good optics is good comfort. Take time to take in the image, relax, and tease out the detail. That helps MUCH more than the small gains you have from better optics.

Back to the issue of large FOV: on tracking scopes like mine, I do not mind a narrower FOV, but the XWs perform very well over their larger FOV, and are very comfortable. I am getting a 5mm SLV (mainly for planetary on the smaller F/6 scope, but also for good nights on Mars and the moon with the C8). I will see how it pans out. Regarding the SLV 25mm being sharper than the 17.3 Delos: I am not surprised that the contrast and sharpness appear larger at lower magnification. However, at higher mag you can tease out more detail.

[bingevader]

2. An 8mm  wide FOV  =  Could still be used for DSO but probably just an expensive planetary eyepiece.

IMHO it doesn't need to have a wide FOV or be an expensive planetary, or be of poor quality.

However, I am recommending a plossl!

My 8mm TV plossl was £40 second hand.

The magnification at this focal length, with a crisp image from side to side, gives a decent amount of viewing time in a static 'scope and the ER is still comfy without the specs.

[jetstream]

I don't think its the extra glass causing the issue, it may be increased distortion with increased AFOV, anyone wonder why TV EP's oval the moon/planets etc near the field edge? It is how TV chose to correct their eyepieces (and some others).http://www.televue.com/engine/TV3b_page.asp?return=Advice&id=113#.VHNI7WclGcw