12mm EP for 65PfEDII (1 Viewer)

Y

Yippeekiay

Well-known member

• Sep 8, 2009

• #1

Hi All,
Just discovered that a guy named Dawes figured out some resolution limits for given apetures and that my 65mm can (should be able to) handle up to a 33.6 magnification w/out maxing out. Oddly enough this coincides w/ my constant wish for more magnification in the field.
Now, seeing that the XW14 supports a cool 27.8x I'm hoping to boost the mag another 6x or so and since the XW's don't come in a 12mm (390/12=32.5x) and the 10mm would exceed thoretical (if not observed) limits, I was hoping someone would recommend a 12mm that's on par w/ them. So far the xl is the front runner.... Any ideas?

 

RJM

Don't Worry, Be Happy!

• Sep 8, 2009

• #2

You should get the eyepieces Pentax designed for the scope, the 12mm and 8.5mm XF.

cheers,
Rick

 

Y

Yippeekiay

Well-known member

• Sep 9, 2009

• #3

Not sure if I'd go down to an 8.5mm. Though 45x sounds tempting, it may be too far along the line of diminishing returns. From what I understand the 10mm seems too much also for a 65mm scope.
The 12mm is definitely next on the "to get" list. I was just wondering if there's other 12mm EP'S to look in to. Maybe some I've never heard of. The Televue radian or Nagler sounds interesting to start. I don't mind spending a little more for quality. (Can't always afford it but we do O.K.).
Thanks!

 

Can Popper

Well-known member

• Sep 9, 2009

• #4

The William Optics/Orion/Smart Astronomy planetary 12.5mm eyepiece also works pretty well. You can read FrankD's Celestron Regal thread and that was the best eyepiece he tested.

 

FrankD

Well-known member

• Sep 10, 2009

• #5

Ditto on what CP stated. I easily preferred that particular eyepiece to any of the others that were sent. Wide field of view, bright, sharp image with very little noticeable CA.

 

S

spyglass

Djoo c it? Wut wuzit?

• Sep 11, 2009

• #6

Now I use a 10.5XL on my PF65, giving 37x and it works like a charm. The beauty of the Pentax scopes is they'll take any 1.25" ep, which really opens up the possiblilties. Any of the fine Pentax XW's, their predecesors the XL's, anything from TeleVue, TMB, Tak, etc, work fine. If you're looking for a really good buy, I'd recommend the excellent Stratus line from Orion. I use a 17mm Stratus on my Orion 4" f6 astro scope, it gives 68* afov, 18mm eye relief, nearly edge-to-edge sharpness and first-rate resolution....for under $150. I'd considered selling all 3 XL's (10.5, 14 & 21) and replacing they with the comparable XW's, but other than a slight for increase, I see no difference, except the big price jump. The 10.5 gives 48x on my PF80, and that's about all you can ever use for terrestrial viewing, unless you have exceptional air quality, so I'm very content.

 

S

spyglass

Djoo c it? Wut wuzit?

• Sep 11, 2009

• #7

whoops, that should be "slight FOV increase".....

 

Y

Yippeekiay

Well-known member

• Sep 11, 2009

• #8

That sounds like it might be a winner.(10.5 xl) Though the 12.5 sounds nice, it's only a 3 or 4x jump and still a few mags shy of the target 33.6x. I think the optimum came to 11.75 (390/11.75=33.2) or so but I haven't found any right at that length. A few 11's popped up so I may try testing the resolution limit theory with one of those. (Anyone tried this one> http://telescopes.net/doc/2500/mftr/ES/item/EP8211-00 ) ??
I know I'm probably splitting hairs (10.5 to 11) and won't be able to tell the differences but hey, it's worth a shot. Normally I'm not one to buy/try and return but I may just make an exception for this.

 

RJM

Don't Worry, Be Happy!

• Sep 12, 2009

• #9

A more modern rule of thumb for maximum useful mag is to use 1x per 1mm of aperture for those folks with average vision. For scopes with superior optics and those folks with above average vision 2x per 1mm of aperture is easily possible. The Pentax 65ED is just an average optic that probably due to daytime atmospheric effects maxes out at ~45x.

Like I said the 12mm XF and 8.5mm XF were developed specifically for the Pentax 65ED optics. They are lightweight with excellent eyerelief to minimize fogging. The XL/XW series are certainly nice eyepieces, but they are expensive, BIG and HEAVY (~35% the weight of the scope!) For me the extra widefields they bring do not offset their disadvantages in such a small scope.

Rick

 

Last edited: Sep 12, 2009

Y

Yippeekiay

Well-known member

• Sep 13, 2009

• #10

So you think the 8.5xf is comparable to the 10.5xl, quality of view-wise?? Because I really would like the higher magnification and if the 8.5xf doesn't get too dim, that would be the way to go.

 

S

spyglass

Djoo c it? Wut wuzit?

• Sep 15, 2009

• #11

You'll likely hafta get an XL off ebay, as I doubt any dealers still have any in stock....but I'd get the best EP I could find for reasonable $, because that is largely what makes the scope. BVD had an excellent series of articles on this a while back. But for most birding, I've found 25-35x is all you need over 90% of the time, and the 2 XL's I mentioned will give you better views than the budget XF's, every time.