Note: This account is actually dated 10-14-12 and I'm recounting it here for you now.
With great anticipation, my pair of OPT branded 40mm GSO's arrived in the mail. Quick plug for OPT: they have great prices, quality merchandise and friendly and helpful staff. I have purchased quite a bit from them and will continue to do so in the future. To see what I mean visit www.optcorp.com. Even quicker disclaimer: I'm not affiliated in any way with OPT or receive any compensation from them whatsoever.
I've been wanting a pair of 40mm plossls for a long time and for various reasons.
- Because they exist
- To keep my pair of excellent GSO 32mm Plossls company in my eyepiece case
- To provide for lowest power scanning, extra eye relief and narrower AFOV which should make it easier to see the entire TFOV
- To get an even smaller image scale when using my binoviwers allowing me to see extended objects framed a bit easier without panning my eye around
- To increase the exit pupil when using on long FL telescopes to maximize the image brightness of those faint extended objects like the Veil nebula or North American nebula
- Because although my 1rPD 40mm Plossl is good optically I can't seem to find another one to complete a matched pair for my binoviewer
I already own a pair of GSO 32mm Plossls and they essentially do everything you can expect a quality plossl to do for you which is show you clean, low power views at the maximum True Field Of View (TFOV) in a 1.25" eyepiece with a minimum of optical aberrations. I was ridiculously close to buying a pair of these 40mm Plossls from the Astronomics booth two years ago at the NEAF Astronomy show in Rockland, NY but decided not to at the last minute. The logical side of me said: "Why get these when the TFOV is essentially the same as the 32mm Plossl which gives a higher power and consequentially more immersive view and higher contrast to boot?"
Well that nagging desire to ignore logic finally won out yet again and I found a great deal on a pair of these on the classified section of one my favorite Astronomy websites: Cloudy Nights (www.cloudynights.com). I've been frequenting CN since Astromart.com started charging a yearly fee to use their previously well used classified section. I don't think I'm alone in abandoning that site because if you go there and check how many listings there are per category, it pales in comparison with the tons of listings on CN. Hats off to the people at Astronomics.com for enhancing the astronomical community with such a great and free online resource!
Ok with all that out of the way - and straight off of the OPT website is this introduction to this eyepiece:
"The four element Plossl design is perhaps the most popular telescope eyepiece design on today's market and an all-around performer. The OPT Plossl provides excellent image quality, good eye relief and an apparent field of view of about 45 degrees. This well manufactured Plossl will deliver high contrast and pinpoint sharpness out to the edge of the field of view."
First thing I noticed: Open the boxes and you can see these are not small eyepieces. They are similar in girth to the GSO 32mm but even taller - see image below. I immediately compared them with my existing single 40mm 1rpd plossl (clone of Series 500) which happens to be an extremely sharp and bright EP even to the edge but is literally "barrel limited" and has an ugly field stop - being the actual chrome barrel itself! Some people claim the Series 500 label was made by the same factory that made the older Meade Series 3000 plossls but this is not confirmed. I also compared it with my 32mm GSO plossl. For those of you that aren't familiar with the GSO 32mm Plossl - it's a fantastic eyepiece with a clean field stop and does everything it's supposed to do right which is why it has survived a recent EP shake-up. I will write more on eyepiece shake-ups in a future post. The hope was that the 40mm GSO would be of similar quality to my 32mm GSO.
"The four element Plossl design is perhaps the most popular telescope eyepiece design on today's market and an all-around performer. The OPT Plossl provides excellent image quality, good eye relief and an apparent field of view of about 45 degrees. This well manufactured Plossl will deliver high contrast and pinpoint sharpness out to the edge of the field of view."
First thing I noticed: Open the boxes and you can see these are not small eyepieces. They are similar in girth to the GSO 32mm but even taller - see image below. I immediately compared them with my existing single 40mm 1rpd plossl (clone of Series 500) which happens to be an extremely sharp and bright EP even to the edge but is literally "barrel limited" and has an ugly field stop - being the actual chrome barrel itself! Some people claim the Series 500 label was made by the same factory that made the older Meade Series 3000 plossls but this is not confirmed. I also compared it with my 32mm GSO plossl. For those of you that aren't familiar with the GSO 32mm Plossl - it's a fantastic eyepiece with a clean field stop and does everything it's supposed to do right which is why it has survived a recent EP shake-up. I will write more on eyepiece shake-ups in a future post. The hope was that the 40mm GSO would be of similar quality to my 32mm GSO.
Coatings were all pristine and similar in color and uniformity to GSO 32's. Which is to say nice deep green coatings. Body and barrels looked very well executed and substantial.
I checked the AFOV (Apparent Field Of View) and TFOV first.
Using my seat of the pants method of determining AFOV - looking straight down the barrel of a given eyepiece in one eye, while alternating other eyepieces up to my other eye with an actual 40*, 45*, 48*, and 50* AFOV's I can merge both field stop circles to see which is larger, and by what amount. I then make a judgement call!
The AFOV of my older 40mm 1rpd is about 40* compared with the about 50* AFOV of my 32mm GSO. Huge difference when looking down the barrel. To ad insult to injury my 32mm GSO shows more actual TFOV than my 40mm 1rpd. Couple that with a MUCH more immersive experience and cleaner field stop the 32mm GSO trounces the 40mm 1rpd in virtually every way except for perceived image brightness which the 40 1rpd is clearly the winner -despite the 1rpd's lesser coatings of MgFl vs Fully Multicoatings of the 32 GSO. Perhaps the larger exit pupil produced by the 40mm vs the 32mm FL is helpful here.
Enter in the 40mm GSO. Its AFOV appears to be somewhere between 43*-45*. Noticeably larger than the 1rpd. OPT claims its AFOV is 45* which I'm not sure is even possible due to barrel limiting at this long Focal Length (FL). When comparing the TFOV between the GSO's 40 and 32, the 40 is actually a little greater! Shocker! Having slightly more TFOV than the GSO's 32mm is a huge bonus and I didn't expect this. As you may know, with eyepieces sometimes just minor incremental differences are difficult to achieve and you pay a lot for them. That is the law of diminishing returns and the astronomical community is chock full of incremental improvements for big $$$. This EP now delivers the widest TFOV out of all of my 1.25" EP's!
The AFOV of my older 40mm 1rpd is about 40* compared with the about 50* AFOV of my 32mm GSO. Huge difference when looking down the barrel. To ad insult to injury my 32mm GSO shows more actual TFOV than my 40mm 1rpd. Couple that with a MUCH more immersive experience and cleaner field stop the 32mm GSO trounces the 40mm 1rpd in virtually every way except for perceived image brightness which the 40 1rpd is clearly the winner -despite the 1rpd's lesser coatings of MgFl vs Fully Multicoatings of the 32 GSO. Perhaps the larger exit pupil produced by the 40mm vs the 32mm FL is helpful here.
Enter in the 40mm GSO. Its AFOV appears to be somewhere between 43*-45*. Noticeably larger than the 1rpd. OPT claims its AFOV is 45* which I'm not sure is even possible due to barrel limiting at this long Focal Length (FL). When comparing the TFOV between the GSO's 40 and 32, the 40 is actually a little greater! Shocker! Having slightly more TFOV than the GSO's 32mm is a huge bonus and I didn't expect this. As you may know, with eyepieces sometimes just minor incremental differences are difficult to achieve and you pay a lot for them. That is the law of diminishing returns and the astronomical community is chock full of incremental improvements for big $$$. This EP now delivers the widest TFOV out of all of my 1.25" EP's!
The AFOV effect is significantly more "normal" plossl looking than with the 1rpd. The 1rpd looks like you're viewing through a restricted tunnel with a nasty shiny and irregular field stop (chrome barrel threading). The GSO 40 looks like its approaching a normal plossl AFOV eventhough it is noticeably smaller, kind of like looking through a well-designed ortho. Bonus rounds: It's not like looking through a shiny pipe (sorry 1rpd). To be fair to the 1rpd 40mm, optically it shows a very bright and sharp field of stars. It just fails pretty hard at the field stop and abnormally small AFOV.
For your bino-viewing aficionados out there:
In the Denk Big Easy (26mm Clear Aperture) through the very fine and much loved AT106LE triplet APO refractor there is only minor vignetting. No more than with my GSO 32's which is to say workable. This is not an issue with my 26mm Meade Plossls or any shorter FL plossl in my set due to their smaller than 26mm field stops. There is massive eye relief when binoviewing so head placement is critical but it works if you're careful. The binoviewer usually ads eye relief because it employs a barlow element to help come to focus on a refractor. This barlow is what pushes out the eyerelief making viewing even more comfortable when using much shorter FL eyepieces. On the longer FL eyepieces this can be an issue though. I will have to do some testing on how well it'll work when using the binoviewer in my Celestron C11XLT though due to the massive eyerelief which may cause me to see the central obstruction - (There is a relationship with seeing the central obstruction of a reflecting telescope using long FL eyepieces and that effect is more pronounced the longer you go in FL of eyepiece and the greater the eye relief of that eyepiece)
Either way these are definitely keepers and I really like them! No more wondering if I should get a pair of 40mm Plossls, these will stay in my collection for the long term.
Editorial Update 10-20-13:
A year later, these have shown to be excellent performers showing sharp star fields to the edge of their well-defined field stop. They are fully up to the optical quality of my 32mm GSO plossls and produce excellent throughput and contrast with no ghosting even on bright stars. In truth, they aren't used as often as my 32mm Plossls but I'm an admitted eyepiece junkie and love making eyepiece comparisons when viewing objects. I swap eyepieces in and out of my diagonal frequently when viewing an object with the intent on finding the best eyepiece for a given night's conditions and depending on which object is being viewed and which telescope and accessories I'm using. The quest to find that elusive optimal combination of magnification, image scale and framing, brightness and contrast is part of the mission I'm on to best appreciate and study the object being viewed.
So, is a well-designed 40mm Plossl necessary for a complete eyepiece set? No, but If you've been bitten by the astro-bug yet...you know how that goes...
Editorial Update 10-20-13:
A year later, these have shown to be excellent performers showing sharp star fields to the edge of their well-defined field stop. They are fully up to the optical quality of my 32mm GSO plossls and produce excellent throughput and contrast with no ghosting even on bright stars. In truth, they aren't used as often as my 32mm Plossls but I'm an admitted eyepiece junkie and love making eyepiece comparisons when viewing objects. I swap eyepieces in and out of my diagonal frequently when viewing an object with the intent on finding the best eyepiece for a given night's conditions and depending on which object is being viewed and which telescope and accessories I'm using. The quest to find that elusive optimal combination of magnification, image scale and framing, brightness and contrast is part of the mission I'm on to best appreciate and study the object being viewed.
So, is a well-designed 40mm Plossl necessary for a complete eyepiece set? No, but If you've been bitten by the astro-bug yet...you know how that goes...
Clear skies!
EuropaWill
