New Masuyama 2" eyepieces

[MortonH]

The other day I read about some new Masuyama 2" eyepieces, including a 32mm 85º model that's had some reasonably favourable initial reviews.

http://agenaastro.com/masuyama-2-inch-eypiece-32mm-mop-32.html

http://www.cloudynights.com/topic/555445-initial-impression-masuyama-32-mm-85-degrees-under-the-sky/


Telescopes-Astronomy in SA will be selling them. Just got prices in their latest newsletter.

MOP-60 Masuyama 2" Eyepiece 60mm 46º - $820AUD
MOP-50 Masuyama 2" Eyepiece 50mm 53º - $695AUD
MOP-45 Masuyama 2" Eyepiece 45mm 53º - $576AUD
MOP-32 Masuyama 2" Eyepiece 32mm 85º - $490AUD (same cost as importing from Agena)

[Wavytone]

Hmm ... the 32 mm at 85 degree aFOV will be essentiallylimited by the inside diameter of the 2" barrel.

The rest are really only for people with seriously large scopes.

[ausastronomer]

Hi Morton,

This isn't a cheap eyepiece and I have some reservations about an eyepiece designers ability to design a 32mm 85 degree eyepiece with only 5 elements, offering a flat field view with good edge of field performance in medium to fast F ratio telescopes. Historically some pretty smart eyepiece designers including Carl Zeiss, Ernst Abbe, Heinrich Erfle and Al Nagler haven't been able to achieve this over the past 160 years. My guess is that these will be similar to the Widescans of a couple of decades ago which worked very well in medium to slow telescopes, particulalry slow refractors, but fell over in today's faster telescopes. I may be wrong, but I would want to try it out first at sub F6 F-ratios before I shelled my cash out.

Outside their EOF performance in fast telescopes, optically they should be very good, as were the Widescans.

The other focal lengths could work very well because they have a much narrower AFOV.

Cheers,
John B

[MortonH]

I agree John. I think this excerpt from one of the comments on CN sums it up:

Overall, it's a nice eyepiece, but with the field curvature caveat. I feel like I bought a 1990's, 65 degree eyepiece with a redesigned barrel allowing for 85 degrees, packaged in a beautiful Masuyama housing. Having the extra FoV is nice; having the extra FoV in focus would have been better.

[Wavytone]

John - fast scopes ?!? The 32mm maybe but the 60mm is only suitable for f/10 or longer focal ratios - and that means SCT, mak or refractors; not newtonians. And 60mm suggests big scopes - 50cm or more.

Very very few eyepieces are flat field - for good reason - most scopes aren't either. Being Japanese it's 10:1 they'd have designed to match the field curvature of such scopes which is opposite to that of newtonians.

Hence I'm not surprised at all to hear someone say half the field was not in focus - I'd bet they tried it in a Newtonian. Even a modest plossl would perform better.

[Wavytone]

John - 60mm in fast scopes ? Oh really !? The 32mm maybe but the 60mm is only suitable for f/10 or longer focal ratios - and that means SCT, mak or refractors; not newtonians.

If they had any sense they'd have designed to match the field curvature of such scopes which is opposite to that of newtonians.

Even in small refractors there is a question as to how wide the well corrected field is; outside that images will deteriorate extremely sharply.

Hence I'm not surprised at all to hear someone say half the field was not in focus.

And FWIW I have a no-name cheap $59 38mm 70 degree eyepiece that is a perfect match for my 130mm refractor, razor sharp to the edge. As far as I'm concerned anyone buying a masayuma is shelling out stupid money for a badge.

[ausastronomer]

Wavy,

At no point in time did I make any comment about using any of these eyepieces other than the 32mm in a fast telescope. I have been around long enough to know that a sub F6 scope will create too large an exit pupil for any of these eyepieces other than the 32mm. You may be able to use the 45mm in an F6 scope but it won't gain you anything that you can't do with a 35mm or 41mm Panoptic.



That comment is inaccurate. The field curvature of a catadioptic telescope is determined by the focal length of its primary mirror, not the overall F-ratio of the system. An F10 SCT will usually have a primary mirror with an F-Ratio of F2 to F2.5. For instance a Celestron C11 has an F2 Primary mirror with a focal length of 22" and it can exhibit significant field curvature with many eyepieces. That's why you use a field flattener with a SCT when imaging. Consequently these eyepieces may work well in an F10 refractor and not work well in an F10 SCT. You would need to try them on an individual telescope basis, not make a general speculative comment based solely on F-Ratio.



That comment is also inaccurate. Are you trying to tell me the 60mm wouldn't work well in the 15"/F12 (38cm) D & G refractor I have used on a couple of occasions, or the 6"/F12 D & G Refractor I have also used on a few occasions? Of course it would also work exceptionally well in the few remaining 4"/F15 (10cm) Unitron refractors still floating around.

Cheers,
John B

[hoverge]

Here's a friend of mine's review of the Masuyama 32mm being used on binoculars.
http://www.cloudynights.com/topic/562033-masuyama-on-binoscope/#entry7626669

[MortonH]

Somehow I missed that thread. Thanks for the link!

[anj026]

Hi Morton,

The 32mm is wonderful in f15 refractors. I bought mine on special from APM just before Xmas when they were discounted. I paid around $500AUD. The moderate weight and good transmission make for a great wide field deep sky eyepiece. The longer the focal length the better it performs.

[Wavytone]

Forget shelling out for expensive eyepieces. IMHO there are many excellent bargains to be had if you have the guts to "thrash and trash" - try what's out there, keep the good ones and onsell the not-so-good ones. I'll also admit to putting a few in the bin, I wouldn't even give them to my son to pull apart.

For example I bought a Prostar 2" 38mm 70-degree for a whole whopping $59... which is excellent in my refractors at f/7. Tack sharp, to the edge.

1/8 the cost of a Masuyama and a perfect low power eyepiece.