How does a 8mm Hyperion perform on planets/Moon?

[Crusader]

I recently bought a 17mm Hyperion after sticking with the Orion Sirius Plossls that came with my XT10 for close to a year. My first reaction with the Hyperion was . It's huge in comparison to the Plossls and I absolutely love it. The eye relief is amazing and I love the large eye lens (if that's the correct term.

I'm thinking of now getting a 8mm Hyperion to use as a planetary EP. I'm tired of almost melding my eye to the 10mm Plossl to view something.

Can anyone give me some feedback on how the 8mm performs and if it's as comfortable to use as the 17mm?

[RobF (Rob)]

Hi,

I haven't used a 17mm Hyp, so can't compare, but do have an 8mm and very pleased with its views. I believe all the Hyp's are almost identical in design/weight. Hefty but nice field of view and eye relief as you say. I've had great views of some of the big southern globulars through mine, and the moon is nice too. View seems a little "smokey" (just a tad yellow) compared to a 6mm Televue Radian, but still nicely sharp.

8mm is a really nice med/high workhorse on my F5 1000mm Newt, but I find its nice sometimes to put in the 6mm Radian for a bit more detail when the seeing will allow.

Its going to depend on your other eyepieces, FL and viewing expectations too of course.

[Crusader]

Well, this will be for use in my XT10 with a 1200mm FL. Aside from the 17mm Hyperion I only have the standard 25mm and 10mm Plossl that came with the scope.

[JethroB76 (Jeff)]

I had the Hyperions from 21mm down to 8mm. Although they are big and heavy, they were all very comfortable to use; and all performed well for their price point - though the 13mm was my favourite.

IMO if I was buying again at that price I would buy the Hyperions or the Pentax XFs although the latter only comes in 8.5mm and 12mm. The XFs are slightly smaller AFOV at 60 but they are a better EP overall.

[bones]

I also think it might depend on your focal length. I have three hyperions being 17mm, 13mm and 8mm. With 2800mm focal length on my scope this brings the magnification up to approx 164x, 215x, and 350x respectively.

I'm only using the scope for observing. But when it comes to planetary and lunar observing I find I'm mainly using the 13mm. I have read before that around about 200x is the best to expect for planetary observing which is what I'm getting with the 13mm. I have found it harder to get a clear view with the 8mm. (I can see why I was once advised to not bother with a 5mm).

If your scope is has a 1200mm focal length then an 8mm would give you 150x. This should be o.k. for planetary observing in your situation. I'm not an expert in this stuff but someone else might want to back me up.

Overall I've found the hyperions a nice eyepiece. A little on the weighty side but what do you expect when you invest in glass?

Hope this helps.

[Wavytone]

The optimum eyepiece depends on your scope - and it depends on your visual acuity, too.

Ages ago I wrote a paper on this topic with Greg Thompson. The optimum magnification is that where, when you are looking closely, the image is reasonably bright and sharp and you are just beginning to discern airy disks round stars, or diffraction on sharp edges like the lunar disk limb. At this point you're seeing all the detail your scope can provide - more magnification only makes the image dimmer and enlarges the diffraction rings and you won't really see more details.

This magnification is a function of the spacing of the rods and cones in the fovea on your retina, vs the scale of the image projected on the retina by your scope.

For most people it works out to be between x1 to x1.2 per mm of aperture of the telescope. Thus for a typical 200mm aperture f/10 SCT, this sweet spot is around 200 to 220X, which means an eyepiece around 8 to 10mm focal length. Magnification of x1 to x1.2 per mm of aperture is pretty much the sweet spot for all scopes that produce very distinct Airy disks - SCT's, Newtonian reflectors and Maksutovs.

Some observers will wind the magnification up a tad beyond this - x1.5 is not uncommon - on a bright object like the moon it may be a bit more comfortable if the seeing is steady enough, but you won't really see more detail.

On the fast ED and APO refractors however, these don't produce such distinct Airy disks due to higher order achromatic abberations - though the image is sharp - very sharp - and will stand magnifications around x1.5 to x2 per mm of aperture before the image starts to deteriorate.

On my Maksutov (it's 180mm f/15) the 13mm Vixen LVW gives 208X - IMHO the optimum in most conditions. With a 10mm (270X) the image is starting to break down and with the 8mm (338X) its very soft, due to diffraction.

The same will be true regardless of whether its a Hyperion, TV or other eyepieces.

Greg and I had a very lengthy discussion about whether or not this same magnification is also the optimum for small faint extended objects such as planetaries and galaxies. We both suspected it is, though not exactly sure why.

[Backyard gazer (Don)]

I must agree with Bones about the 5mm Hyperion, I have one and I don't think it is of much use. The 13mm is much better and until recently was my preferred eyepiece.
I would suggest a look through a 8mm before buying if at all possible.

[Wavytone]

On the moon with an f/15 Mak I find my 13mm LVW is very nice - 208X from an 180mm aperture - and at this power images are good with a hint of diffraction.

If the seeing is steady it can be worth dropping the 8mm LVW in for a closer look (338X) at the planets, esp. Jupiter or Saturn, but diffraction effects are obvious and the image a tad soft.

This would scale with focal ratio for other scopes, if using a set of LVW's - they are remarkably consistent eyepieces across the range.

[Jules76 (Julian)]

Originally Posted by Wavytone

For most people it works out to be between x1 to x1.2 per mm of aperture of the telescope. Thus for a typical 200mm aperture f/10 SCT, this sweet spot is around 200 to 220X, which means an eyepiece around 8 to 10mm focal length. Magnification of x1 to x1.2 per mm of aperture is pretty much the sweet spot for all scopes that produce very distinct Airy disks - SCT's, Newtonian reflectors and Maksutovs.

Some observers will wind the magnification up a tad beyond this - x1.5 is not uncommon - on a bright object like the moon it may be a bit more comfortable if the seeing is steady enough, but you won't really see more detail.

I was under the impression that this "x1 to x1.2 per mm of aperture rule" was under average viewing conditions. When the seeing is really good you can expect more. At least this has been my experience.

In the past, seeing conditions in my backyard haven't been that great, so my 8mm Hyperion on my small 114m Reflector was pushing it (x112 @ 900mm focal length). So that seemed to confirm that "rule". However just recently the seeing conditions have been almost perfect for a few nights with this cooler weather and clear skies. I've been in fact able to push my scope further then what I expected. Using my 8mm Hyperion plus both finetuning rings (making it effectively a 4.3mm) I was getting a zoom of 209X with my 900mm focal length of my scope and it was still clear!

I was amazed. Viewing Saturn, I was now getting more detail then I had ever seen before with my scope. While the image was still small, I could now make out the ring across the body of Saturn (instead of just seeing it on the edges), and I could start makng out the moons (could see Titan clearly as a white dot, another was barely visable). This was something totally unexpected for me. If my maths is correct, I'm getting around x1.8 per mm aperture.


But anyway, getting back to the original question, the Hyperions are great eyepieces (I've also got the 17mm). I'd highly recommend you get the Hyperion Finetuning Rings as well. Allows you to try out extra magnification without purchasing more eyepieces, and effectively makes then 4 eyepieces in 1! Definately worked for me.

[Satchmo]

Originally Posted by Jules76

I was under the impression that this "x1 to x1.2 per mm of aperture rule" was under average viewing conditions. When the seeing is really good you can expect more. At least this has been my experience.

In good steady seeing X1 per mm of aperture will allow your eye to resolve the Airy Pattern. In poor seeing you will need more than this to catch glimpses of the disc and ring structure due to it boiling and breaking up. This equates to about 25X per inch.

When people talk about still gaining detail at magnifications of 50X or even 100X per inch, I just know they do not have great seeing as I call the point above which you can see the Airy pattern `image breakdown' . If you are looking at the trapezium in M42 for example at X300 you are clearly seeing the first diffraction ring around each star with a 12" scope, what is the point of increasing the power? I would be backing off th epower until the stars look like pinpoints.

Usually when people talk of using 100X per inch they are usually talking about looking at the Moon or Saturn , which seem at least from an aesthetic point of view to be able to stand much more magnification than is necessary.

[Wavytone]

Back to the OP for a moment - if the Hyperions are anything like my LVW's - the 8mm LVW is equally comfortable as my 13 and 22mm so yes I would expect the same of the Hyperion. Note however that the image quality off-axis of the Hyperions is known to be poorer than that of the LVW and if you can stretch the budget a little the 8mm is worth having; I do use my 8mm in my f/15 Maksutov on the moon and bright planets.

Originally Posted by Satchmo

Usually when people talk of using 100X per inch they are usually talking about looking at the Moon or Saturn

Because they are bright enough for the cones in the macula to work. In some respects the eye seems to have two modes of operation - one when there is enough light the cones kick in and we have colour vision; and a low-light monochromatic mode when we see with the rods alone and these have a very different spacing (closer) and are more sensitive than the cones. The angular spacing is fairly consistent from person to person.

The nominal figures I quoted are based on the magnification needed for you to be able to just detect the Airy pattern around stars using the rods in the macula region of your retina (the small part you use for direct vision).

The interesting part is that the spacing of the rods and cones in the macula is different - the cones are colour sensitive but they have two problems - they are a lot less sensitive, and their spacing is further apart - about 4X that of the rods in most individuals. When there is enough light for the cones to fire, the brain seems to prefer the image from the cones and ignores the image from the rods.

The Moon, Venus, Jupiter, Mars, Saturn and a few of the brighter stars down to mag 1.0 or so are bright enough to trigger the cones. Hence with a scope, where there is enough light for the cones to fire, you can also crank the magnification up beyond 2X per mm of aperture before you can clearly resolve the Airy disk using the cones in your retina.

Sadly humans inherited natures Mark I eyeball, with a pretty crappy lens optimised for an aperture around 1-2mm (bright light) and with the retina wired inside-out, which means its even more inefficient. At 6mm aperture most peoples eye typically has defects exceeding 1 wavelength, far from diffraction-limited. In many respects it's a great shame we did not inherit the Mark II eyeball, which birds have, optimised for full aperture at night and with the retina wired the right way round - more sensitive by an order of magnitude.

[Chippy (Nick)]

Interesting reading. Thanks for the information guys!

[RobF (Rob)]

Whew - just when I thought I could handle Aperture Fever, no I've got to avoid Eyeball Envy !

Definitely and interesting read re cones and rods - makes sense.

[Wavytone]

Originally Posted by RobF

I've got to avoid Eyeball Envy

What would be truly awesome is to bypass what nature gave us - eliminate the natural lens and the need for eyepieces - if we could have a surgically implanted 20 megapixel digital retina that works at 0.01 lux, and couple this digital eyeball to the prime focus of the scope.