Pentax orthos- planetary eyepiece gems!

[mike bacanin]

I thought it might be interesting to serious planetary observers, to present a little article on Pentax orthoscopics.

I first came across these eyepieces a couple of years ago on Astromart. I did some google searches and it became apparent these are something special as far as planetary eyepieces go.

They were made in 5,6,7,9,12,and 18mm focal lengths.

all are .965 inch barrel size and require an adapter to use in std 1.25 inch holders/diagonals.

they are featherweights, quite a bit lighter than a typical ortho, and are beautifully made.

the tops are a rubber type material and so never feel icy cold to the touch.

fov is 42 degrees.

the thing that you first notice when looking through one is the razor sharp field stop, and then there is the famous pentax smc coating.

smc coatings are probably, bar the ZAO II's, the best eyepiece coatings ever produced.

so, what is so good about these little gems? well, first, the contrast! it is truly wonderful, i recall a view of mars with my previous mewlon 210 that showed the polar cap like it was pure white and very sharply defined.

the difference to say a typical ortho, is that it is like a thin veil has been lifted from over the image. The image has very rich saturation and ,very noticeable, a very dark sky background with hardly any scatter.

Having owned the legendary ZAO originals, there is really nothing between them in terms of image quality, just that the zeiss fov looked a little larger.

the inside of the pentax is very matt, and superbly baffled, which goes some way to explaining the high contrast.

eye relief is typically ortho, about 75% of focal length.

I now have the 6,7 and just acquired the very rare 9mm. I have owned the 12mm and 18mm.

I used nearly a couple of years ago apair of 12mm in denk binoviewers. The views were terrific.

As regards prices, well they are expensive used.

It is very hard to find them in the UK, in fact most advertised were ones i owned!

typically the 6, 7mm fetch $250 usd, and the 5,9,12,18mm around $300- $325 on Astromart. In context, about half the price of ZAO, but pretty much equal performance.

Big money indeed, but i have learned that if you want the absolute best planetary views, and can raise the funds, it is worth it.

Yes, these tiny little gems are real planetary powerhouses!!

Mike

[Doc]

A very interesting read.

I have never heard of these before but alas they are out of my price range.

But I do agree ortho's are spot on for planetary viewing.

[mike bacanin]

Hi Mick,

thanks!

Just also to say that the orthos typically available offer very good performance.

But if anyone ever finds themselves in a position to upgrade, these are great performers.

Mike

[philsail1]

They do sound excellent eyepieces Mike! I will definately go for a selection of those - if and when I ever have the funds!

I agree that "orthoscopics" are among the very best eyepieces for planetary views as I have a Celestron 18mm Orthoscopic, and it is the best eyepiece I have - even easily outperforming a Vixen Lanthanum for sharpness of views.

Regards,

philsail1

[FLO]

Interesting article Mike, I have yet to see one of the earlier Pentax orthoscopics.

Pentax do still offer two new-style Pentax XO orthoscopic eyepieces in 2.5mm(!) and 5mm focal lengths.

[The Warthog]

I``d like to see that, as I find my unbranded orthos to be excellent. Interesting...

[FLO]

For brightness, clarity and lack of distortions, orthos are excellent!

If Ernst Abbe (a designer for Carl Zeiss) had designed them today everybody would be talking about them but they were designed in the 1800's (for taking accurate measurements from microscope slides) so pass under most peoples radar undetected.

[GazOC]

People are very caught up on AFOV these days.

[John]

People are very caught up on AFOV these days.

If you are a dob user keeping an object in the narrow FoV of an Ortho or TMB Mono (even more so) can be a real chore at high powers.

I've tried some decent ortho's back to back with my T6 Naglers and could not see any difference in image quality - but the wide FoV and longer eye relief of the Naglers made them more comfortable to use - for me at least.

Cost-wise though the orthos won hands down of course - but they were not Pentax's.

John.

[FLO]

Yes, it is 'horses for course' and modern widefield eyepieces are very comfortable, as are the new breed of planetary eyepieces that incorporate optically matched multipliers for greater comfort/eye-relief.

I guess I am a fan of orthos as back when I started astronomy I was on a more restricted budget and orthoscopics were available for £15-25 secondhand on ebay. I quickly put together a set of the Japanese volcano-top orthoscopics along with some Plosssls and a couple of low-magnification Kellners. The performance per £ offered by those three designs is unbeatable!

[John]

I agree Steve, back in the early 1980's my 1st eyepieces were Vixen 1" orthos and some Unitron (USA) 1" plossls - they would be somewhat of a rarity now. The Vixen orthos in particular were exceptionally sharp albeit with tiny amounts of eye relief and minute eyelenses. They were also relatively cheap !.

John

[GazOC]

If you are a dob user keeping an object in the narrow FoV of an Ortho or TMB Mono (even more so) can be a real chore at high powers.

Thats very true, I only tend to use my Hyperions on my Dob...orthos are very frustrating both for the FOV and the eye relief in undriven scopes but a lot of time people don't even consider orthos for their driven scopes/ mounts when they would do a great job in a lot of cases.

[John]

Thats very true, I only tend to use my Hyperions on my Dob...orthos are very frustrating both for the FOV and the eye relief in undriven scopes but a lot of time people don't even consider orthos for their driven scopes/ mounts when they would do a great job in a lot of cases.

Agree entirely Gaz

If and when I get a scope on a driven mount again I'll treat myself to some Baader HD Orthos which seem to be the best if you can't run to Pentax Ortho's or TMB Monos. Mind you the Nagler 3-6mm Zoom is pretty tasty and sports a "whopping" 50 degree AFoV !.

John

[KaStern_Former_Member]

Hello Mike,

thanks for the intersting information!

5mm Pentax XO :

My pal Sven and me did a eyepiece/barlow comparison in witch the XO took part.

The 5mm XO did a phantastic job on both an 102/800mm Apochromat and a 200/1200mm Newt.

The views were very contrasty. It is well-baffled, very good coatings, excellent finish.

You can find the comparison there:

Barlow-Test

Sorry, in german, but a google translation may help.

Clear skies, Karsten

[mike bacanin]

Hi KaStern

thank you for that interesting link!

Regards

Mike

[lunator]

I'm a bit late to the discussion but I have to agree with the comments made so far.

I have a full set of ortho's and although the shorter ones are a bit much in terms of magnification on the OMC the longer focal lengths are fantastic for planets and double stars.

You can't really beat them in terms of value for money.

Cheers

Ian

[KaStern_Former_Member]

Hello Mike,

I am glad that you found my link to be helpful.

One thing to be added is the Pentax 5mm XO`s eyerelief:

It is only 3.6mm wich is about the same what a normal 5mm Ortho will have.

And so is the apparent field of view: 44°

You can find this information and a lens sheme on that site.

Unfortunately the XO eyepieces are discontinued. I found the 5mm to be very good.

But I really would like to read a comparison with one of the older SMC Orthos.

Regards, Karsten

[mike bacanin]

Actually i find the eye relief on the 5mm XO tolerable.

The sharpness is exceptional, but i have a feeling there would be very little between it and the 5mm smc ortho.

mike

[FLO]

Unfortunately the XO eyepieces are discontinued. I found the 5mm to be very good.

The Pentax XO orthoscopic is available here in the UK.

The Japanese-made Baader orthoscopics are also worth considering.

HTH

[KaStern_Former_Member]

Hello Steve,

thanks for the link. At the current Pound/Euro the Pentax Prices in GB are very interesting.

Regards, Karsten