Pentax X0 2.5mm

[jetstream]

Well, Ive suffered a moment of weakness...

Not uncommon with regard to astro equipment thats for sure. Ive found a new Pentax XO 2.5mm after a many year wait and the vendor passed it along to me at a nice price knowing that I'm a "collector" and not a re seller. I cant wait to compare it to the 2.4mm Vixen HR in the TSA120.

Now that I'm able to carry the AZEQ6 again the TSA120 is seeing a lot of use including another stunning lunar session last night.

Any experiences with the 2.5mm XO is great to hear.

Also great to hear are thoughts about the Pentax 3.5mm and the 4mm DeLite, feel free to wander in the thread... I always do

ps and now I'm sitting patiently under a spruce tree in the rain for the 5mm XO to wander by lol

( a reference to former hunting lol, glad I gave that nonsense up)

[markse68]

That was a lucky find! I've got one and like you would love a 5 to go with it as it would be amore useful/used ep for sure. On rare occasions I need 300x with my current scope I usually just barlow a 5mm celestron ultima which is a nice ep, but I have been using it more to try for the pup. It has very short eye relief and fogs up easily but excellent sharpness and great colour rendition on Mars for the mag. I should do more comparisons between it and the barlowed ultima. Wish Ricoh would bring them back and maybe some in between mags. And expand the XF range  . I have the 3.5 XW too- its a lovely ep for high power stuff and the extra fov and eye relief are welcome but it's huge by comparison and I'm liking more compact eps currently so haven't used it in a while. I used to use it with my 8" f8 for 460x on tight doubles and it was very sharp and completely free of internal reflections and glare

Mark

[Sunshine]

I have the 3.5 XW, it’s my main star splitter, almost exclusively for that purpose, razor sharp and comfortable to use.

[jetstream]

31 minutes ago, markse68 said:

very sharp and completely free of internal reflections and glare

This makes me smile 👍

[jetstream]

5 minutes ago, Sunshine said:

I have the 3.5 XW, it’s my main star splitter, almost exclusively for that purpose, razor sharp and comfortable to use.

This makes me smile too...👍

The mouse is hovering over one..

[nicholasastro]

14 minutes ago, jetstream said:

This makes me smile too...👍

The mouse is hovering over one..

The 2.5mm XO is a stunning eyepiece. I had my best ever view of Saturn at 687x where I could see the narrow Encke division (not just the minima) with it. Unbelievably good.

[jetstream]

48 minutes ago, nicholasastro said:

The 2.5mm XO is a stunning eyepiece. I had my best ever view of Saturn at 687x where I could see the narrow Encke division (not just the minima) with it. Unbelievably good.

Awesome!!

Cant wait to get it on Saturn myself a favourite of favourites. It can take on a ''chiselled glass" appearance in some scopes and I too have seen the division under great seeing.

[tom.yates]

Yes great eyepieces,  I have the 5XO

And it truly is fantastic. 

[Highburymark]

Congratulations Gerry. Fantastic find. Look forward to hearing your impressions. I’ve just bought a 5mm XO, but haven’t had chance to use it yet. I’m a big TOE fan, so will be interesting to see how the XO compares.

[Louis D]

The 3.5mm XW is probably the finest of the XW line.  No edge astigmatism, chromatism, or field curvature at f/5 to f/6 in my scopes.  It is sharp and contrasty across the field of view.  The problem for me is with the resultant tiny exit pupil and my floaters getting in the way of enjoying the view.  Eye relief is excellent for relaxed, extended viewing.

[jetstream]

1 hour ago, Highburymark said:

Congratulations Gerry. Fantastic find. Look forward to hearing your impressions. I’ve just bought a 5mm XO, but haven’t had chance to use it yet. I’m a big TOE fan, so will be interesting to see how the XO compares.

Thank you Mark !

Im eagerly waiting your impression of the XO vs TOE. Of course if you dont have time to do it I could always buy the XO from you

Nice equipment Mark, very nice.

[jetstream]

1 hour ago, Louis D said:

The 3.5mm XW is probably the finest of the XW line.  No edge astigmatism, chromatism, or field curvature at f/5 to f/6 in my scopes.  It is sharp and contrasty across the field of view.  The problem for me is with the resultant tiny exit pupil and my floaters getting in the way of enjoying the view.  Eye relief is excellent for relaxed, extended viewing.

Have you compared the 4mm DeLite to it Louis?

[Louis D]

2 hours ago, jetstream said:

Have you compared the 4mm DeLite to it Louis?

No, just the Svbony 3-8mm zoom at 3mm which actual 3.5mm.  The XW stomps all over it in eye relief, field of view, sharpness, and control of chromatic aberrations.  This should surprise no one.

I don't spend a lot of time at tiny exit pupils.  The only reason I picked up the XW was because Amazon dropped the price to $216 years ago, so it was too tempting to pass up.

[JeremyS]

Super find on the XO 2.5, Gerry 👍🏻

[jetstream]

19 minutes ago, JeremyS said:

Super find on the XO 2.5, Gerry 👍🏻

Thanks Jeremy, I'm excited! Could have used it tonight- another great session with the 120mm and the HR 2.4mm is quivering in its boots lol Heres the sky when we went for a sled ride late this aft a few km from the house.

[Sunshine]

Look at that setting, jealousy overload.

[Alan White]

Great find, there are some optical wonders about still.

The Vixen HR 3.4 is such an eyepiece, I passed my one on as someone was desperate and immediately regretted my decision.
I expect your find will be similar, but just don’t part with it.
 

[Highburymark]

I’ve reported this elsewhere several times, but I find XWs and Delites impossible to split at planetary powers. If you want width, go for the XW, if you want smaller size and weight, go for Delite. There’s a tiny bit of edge false colour in the XWs, but otherwise, both ranges are pretty much perfect, even in an F/6 scope. However, the TOEs (and presumably the HRs) clearly show intricate planetary detail more readily than either, as long as seeing is steady. What will be interesting is establishing how well the XO performs in this company. 
The main drawback with the XO is obviously eye relief - the TOEs are very comfortable by comparison (10mm ER rather than under 4mm), but it’s easy to hover above the lens so you’re not touching it with your eyelashes, but this really requires a tracking mount, as I only see (an estimated) 60% of the fov. To see the field stop, you need to get much closer, and make sure you don’t blink. In fact the 2.5mm XO has a tiny bit more eye relief than the 5mm.

[jetstream]

27 minutes ago, Highburymark said:

However, the TOEs (and presumably the HRs) clearly show intricate planetary detail more readily than either, as long as seeing is steady

Hmmm, this statement caught my attention and yes the HR's show more when conditions allow also. Going to check TOE focal length.

The mouse is in hover mode for a reason, thanks Mark!

[Louis D]

32 minutes ago, Highburymark said:

There’s a tiny bit of edge false colour in the XWs

Agreed on all but the 3.5mm.  Did you see chromatic aberration at the edge in your 3.5mm XW?  My 5.2mm XL is also free of color to the edge.  After seeing the chroma at the edge of the 7mm, I decided to keep the 5.2mm rather than "upgrade".

[jetstream]

Last night the seeing supported 375x with the 2.4mm HR. However Ive been playing with the VIP and nosepiece extensions and the 8mm Delos. I find for some reason this barlow can sharpen up eyepieces and it does in this case. Not to say the Delos isnt sharp its that the Zeiss barlow element really does work in this regard.

The 8mm Delos has the fieldstop .25" below the shoulder, which gives 1.67x effect. The 8D/900mm and 4.8mm effective fl EP gives 187X mag. A great mag but still to low. I wont bore everyone with all the configs I tried.

I did go all the way up to (61-15 +64)/64=1.7 (+1)=2.7x barlow.

This gave an excellent very sharp mag of 900/(8/2.7)= 304x with a great widefield view. I slid the EP with nose piece extensions up and down to fine tune the mag.  This gave a "zoom" of about 260X-300X .

I cant wait to compare the XO/HR to the barlowed Delos or Delite or whatever I come across.

ZAO maybe?

Edited March 5, 2023 by jetstream

[Don Pensack]

17 hours ago, Highburymark said:

Congratulations Gerry. Fantastic find. Look forward to hearing your impressions. I’ve just bought a 5mm XO, but haven’t had chance to use it yet. I’m a big TOE fan, so will be interesting to see how the XO compares.

Needs to at least have the dust blown off.  Lots of debris on that lens.

[nicholasastro]

On 04/03/2023 at 21:29, jetstream said:

Awesome!!

Cant wait to get it on Saturn myself a favourite of favourites. It can take on a ''chiselled glass" appearance in some scopes and I too have seen the division under great seeing.

Using my David Lukehurst dobsonian, the 2.58mm Pentax XO hits a sweet spot on Saturn when the seeing conditions support 687x , representing 43 times per inch. On the other hand, the 5.1mm Pentax XO yields 350x, about as much magnification as I would consider deploying on Jupiter for maintaining good contrast - I can go higher but don't necessarily see additional detail.

Many years ago, I carried out side by side comparisons between a 5mm TMB Supermonocentric and 5.1mm Pentax XO on Jupiter under exceptionally good seeing conditions. The images through the TMB Supermono were superb but I was actually surprised to see slightly more detail in the XO. The favourable conditions lasted throughout most of the night and I was careful to prolong the evaluation as much as I could to be certain that I was not mistaken.

In summary, I haven't experienced anything quite as good as the XOs, and that includes adding a Vixen HR into the mix.

[jetstream]

3 hours ago, nicholasastro said:

In summary, I haven't experienced anything quite as good as the XOs, and that includes adding a Vixen HR into the mix

Thank you for the excellent reply and now I'm really excited to try the XO... and really want the 5mm too!

[Highburymark]

Highest power I generally use with my TSA-120 is 360x with the TOE 2.5mm.  The 5mm XO (although some say it’s 5.1mm) will give me 180x - perfect for average evenings. But I bought it for better than average evenings! So I have the 1.5x Tak extender which will bump things up to 270x. Yes, it’s more glass, but then it turns the TSA into an F/11.25 planet killer.