XF8.5 or Baader Hyperion? (1 Viewer)

Hi everyone

My Pentax 65mm is very nice with BST Explorer 12mm. But besides having a greater FOV and being brighter, I cannot say it is better than my Nikon 50 ED at 30x.

I also have a BST Explorer 8 mm but am not satisfied with it. The eye relief and eye placement are very critical so it is too hard to use and I can't say it adds any improvement to the excellent 12 mm.

It would be nice to get a higher magnification with the Pentax but it has to be usable. I have considered the XW10 but haven't been able to try it, and if the scope is not up to the task, a lot of money is wasted.

Recently, I read that the XF8.5 is more than decent.
Should I buy one or choose the Baader Hyperion 8mm or maybe 10 mm?

Thanks in advance

//L

looksharp65 said:

Hi everyone

My Pentax 65mm is very nice with BST Explorer 12mm. But besides having a greater FOV and being brighter, I cannot say it is better than my Nikon 50 ED at 30x.

I also have a BST Explorer 8 mm but am not satisfied with it. The eye relief and eye placement are very critical so it is too hard to use and I can't say it adds any improvement to the excellent 12 mm.

It would be nice to get a higher magnification with the Pentax but it has to be usable. I have considered the XW10 but haven't been able to try it, and if the scope is not up to the task, a lot of money is wasted.

Recently, I read that the XF8.5 is more than decent.
Should I buy one or choose the Baader Hyperion 8mm or maybe 10 mm?

Thanks in advance

//L

Click to expand...

I had all three XF eyepieces when I had the PF65. The 12mm is definitely the sweet spot. The Hyperion 8-10mm are HUGE eyepieces, bigger/heavier than the XWs if memory serves. Stick with the much smaller/lighter XF.

looksharp65:

The Pentax XF 8.5 and 12mm EP's are very good EP's. However, they each only have 18mm of eye relief (OK if you do not wear eyeglasses) and they are rather expensive. I believe they discount around $150. For $150 you should be able to get two EP's that produce images of the same quality as the XF.

You might also consider that the 8.5 mm EP produces 46x in the little Pentax and that's about all that the 65 can deliver with good image quality. I found that my 8mm, TV Radian has very, very shallow depth of field in my PF-65 which makes it a royal pain in the ... to focus. You might want to consider staying above 8.5mm?

Baader Hyperion's are very big, another reason I like my small Vixen NLV's. I think Celestron X-Cel EP's (Currently on discontinued sale for $40) are about the same quality as the Pentax XF's and obviously an excellent buy. The new wider AFOV Celestron X-Cel LX's are $70. Both prices are from optcorp.com , they have a great selection of EP's. Good luck. Oh and I don't work for them -unfortunately.

bearclawthedonut

RJM,

in more than one place I've read that the 8.5 is a better performer than the 12 mm.
Did you find it usable or was it too dim? Hard to focus due to short DOF? Were there times when it undeniably enabled bird identification when the 12 mm was not enough?

bearclawthedonut,

from what I've read, the XF series was designed for these spotting scopes, and the 65 mm would produce a slightly larger exit pupil than the 80 mm.
So I reckon the 8,5 will not be useless. But my current 8 mm adds nothing to the equation but some weight, so I have to challenge the scope with a better eyepiece.

My Nikon ED50 and the Pentax with 12 mm are quite close in performance. That is why I want to get the most out of the Pentax in terms of magnification.
It feels a little silly to own two scopes that basically do the same work, but the Nikon with monopod is not so much heavier than the Pentax scope itself.

If I can avoid buying an 80 mm scope I would prefer so. But the odds may be against me - some of the birding here is done at very long distance and in low light.
Adding a C90 Mak, thus using three scopes, might help in those circumstances.
Then again, it will take some cerebration to pick the right scope for a given birding trip.

chasing extra magnification to "get the most out of" the scope is often counterproductive. In my experience (which echoes others) 30x is really the sweet spot for the PF-65. Pushing the Pentax from 32.5x (where you are currently) to 40x or more isn't going to yield that much more detail, just a dimmer, harder to focus image.

frankly, in your situation, I agree that the Pentax and Nikon are redundant. I would probably keep your favorite of the two "small" scopes and instead invest in a bigger scope if you want more magnification.

looksharp65 said:

RJM,

in more than one place I've read that the 8.5 is a better performer than the 12 mm.
Did you find it usable or was it too dim? Hard to focus due to short DOF? Were there times when it undeniably enabled bird identification when the 12 mm was not enough?

Click to expand...

I should say I sold my PF65ED v1 scope over 3yrs ago. My main interest is digiscoping and it just did not live up to my expectations. The CCD takes no prisoners and this scope showed too much CA in my pics. The PF80ED was MUCH better in this regard (but then I discovered it is really only ~70mm when focused at infinity!).

So I really can't remember how that eyepiece performed in the PF65ED. I do have a pretty serious astro hobby though and I liked both XFs alot for lunar observations. Eventually I needed more focal lengths and sold them for a full set of TMB Planetary eyepieces.

looksharp65:

The XF series was indeed designed specifically for the PF-65 scope and that's why Pentax produced an 8.5mm EP and not an 8mm EP. Any EP with a shorter focal length than 8.5 mm is pushing the little 65 beyond its practical capabilities. If you want an 8mm EP, I'll be glad to sell you my TV Radian for what I paid for it ($150 including shipping). A TV Radian is a considerably better EP than a Pentax XF EP.

In theory a 65mm scope can support up to 130x for astronomy usage. But that's on a perfect night. Most good nights might allow a maximum 80x to 95x with a 65mm scope. You can chase the 130x, but you'll never get to use it. As a daylight 65mm spotting scope Pentax (not me) decided to limit their high mag EP to 8.5mm (45.88x). You might want to take this into consideration when selecting a higher mag EP?

The Pentax XF 8.5 is a good EP; however, I believe it is over priced. RJM sold his two Pentax XF EP's and bought a "full set" of TMB Panetary EP's. By all means if you have your heart set on it - get the XF 8.5. You could certainly do a whole lot worse, but ...

bearclawthedonut

bearclawthedonut said:

looksharp65:
If you want an 8mm EP, I'll be glad to sell you my TV Radian for what I paid for it ($150 including shipping). A TV Radian is a considerably better EP than a Pentax XF EP.

Click to expand...

Now that's a very generous offer...If it had been a 10 mm I gladly would have accepted it.
This means I can get at least three very different eyepieces at roughly the same price - your Radian, a minty XF8.5 or a new Baader Hyperion.

The Nikon is subjectively sharper than my Pentax. If the Pentax will not add any detail above 32,5x all this cerebration is wasted.
I have decided not to challenge the optics gods, so I will not push the scope above 40x. So, a 10 mm will be what I will look for.

A Nikon 27x/40x/50x MC Wide with astro adapter would give about 38x with the Pentax and be useful for the Nikon too.
Other contenders are many, but I lean towards the $150 league.
If money were no issue, I would have bought the XW10 already.

Looksharp,

I don't think better eyepieces will extract any more detail. The trick is to determine what magnification brings the smallest details the scope can resolve up to a size that your eyesight acuity can easily see.

A really good 65mm telescope has resolution of about 1.8 arc seconds on a line pair per millimeter resolution chart. A person with 20/20 acuity can resolve about 120 arc seconds on the same chart, so it takes a minimum of 67x for that person to be able to see the full resolution of the scope and really a bit higher magnification, perhaps 80x, would make the task easier. However, in the real world the scope may not be that good and/or the viewer's eyesight acuity may be better. If the scope can only resolve 2 arc seconds and the viewer's eyesight acuity is 90 arc seconds (my acuity) then the minimum would be lowered to 45x (easier at 55x).

To determine how much magnification is useful (under ideal conditions) you need to know your own acuity and the resolving power of your particular scope specimen. BTW, the only measurements I've seen of eyepiece resolution suggest that most eyepieces, even cheap ones, appear to have center field resolution of around 60 arc seconds, equal to about 20/10 acuity. You can be virtually certain that the telescope objective, not the eyepiece, is what limits resolution at high magnification.

Henry

Thanks Henry

It seems I have not been enough clear when explaining my dilemma.

At the moment my two scopes have about the same reach, but as the Pentax has a larger aperture, it should be possible to get beyond 32,5x - even though I suspect it does not have as high resolution as the Nikon.

As well as it can provide a wider FOV and brighter image at the same magnification, it should be able to produce a wide image with the same brightness as the Nikon but at a higher magnification, right?

My 8mm/48,75x is too tricky to use - I never seem to find the right distance to the eye.
Kidney-beaning occurs all the time. Strangely, it seems as it does not fully disappear even when I get beyond the maximum eye-relief. Is this possible?
Furthermore, it's too dim and too soft (it over-powers the scope)

My 12 mm is wonderful on the scope but I still believe I can stretch the reach a little further by using a 10 mm eyepiece (39x).
Even if cheap eyepieces have enough resolution power in the center, they may be less than useful.
I want a 10 mm eyepiece with great eye relief, decent AFOV, high light transmission, sharp edges and so on. Above all, it must be comfortable to use and allow fast action.
Probably, the light output at 39x is close to the lower acceptable limit for me.

I never said that an expensive eyepiece would increase the central resolution, but the total image quality and absence of eye strain should mean the difference between "useless" and "very nice".

Btw, my visual acuity is somewhere around 20/16.

Thanks again Henry for your dedication to this forum.

Henry:

Those are really interesting points. However, I'm a bit confused by my PF-65's performance. The first EP that I used with it was a defective WO Zoom. It had oil spots on interior lens surfaces. Even so it was very sharp in the 16-32x range, but resolution appeared to drop off above 32x. I returned that EP and received a replacement new WO Zoom from Williams Optics. The second one was surprisingly sharp up to about 40x (but like the first one, the eye relief really dropped off above 30x) and then resolution droped off slightly to 45x +/- (although still useful) and then plumeted to poor resolution at it's maximum magnification of 52x.

The next EP that I purchased was a 12mm TV Radian - it was and still is excellent at 32.5x. Then, I got my 8 mm TV Radian and while it delivered almost 49x the depth of field was so small that it was very difficult to achieve a satisfactory focus. I sent it back to Tele Vue and they examined it and said it was fine; they suggested that I try it in an 85 or 90mm telescope. I then got a Vixen Click stop zoom (as changing EP's when using the WO Zoom was cumbersome). It also delivers very sharp images to about 40x +/- with increasing drop off in resolution above 45x. My next EP was a Vixen NLV 9mm which delivers very good to excellent resolution at 43.3x.

My conclusion was that my Pentax PF-65 is limitted to a maximum usefull magnification of 45x+/-. However, I recently purchased an Orion Shorty-Plus 2x, 1.25" Barlow and although I can not focus past 80 yards +/- with it, the produced image using my Vixen NLV 9mm at 86.7x was very, very good? Same with the Vixen CS Zoom at between 32.5-97.5x? If the scope is limited to approximately 2 arc seconds of resolution, how was I getting very good resolution at 86.7x and 97.5x? I had hoped to use this Barlow for some light Moon and planetary observation. The Barlow has already gone back to Adorama, but I remain puzzled.

Most people's acuity tends to drop off rather sharply once you exceed 1x per mm of aperture, i.e. 65x in the case of the Pentax. How did you perform your resolution tests?

RJM:

No resolution tests were performed. Just observing the delivered images.