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Various eyepiece review with PF-100ED (1 Viewer)

Can Popper

Well-known member
Various eyepiece reviewed with PF-100ED

I recently tested my whole eyepiece collection plus a binoviewer on my Pentax 100ED. The goal was to get what I will term the "Ultimate View" for a reasonable price. I like to use my scopes for astronomy, long range target shooting and birding so I purchased the 100ED as the scope that could be used for all 3.

The day I tested the eyepieces was a bit humid so high power views at long range may show atmospheric degradation and not reflect the true performance of the scope and eyepiece. I also had my wife look through the various eyepieces for a second opinion. For reference comparisons, I have a 114mm Bushnell Voyager Newtonian rich field (Edmund Astroscan knockoff), 90mm Konus OEM Maksutov, and 60mm Meade Kestrel refractor spotter.

The eyepieces tested were:
40mm GTO plossl (purchased off ebay)
32mm GTO plossl (ditto)
26mm GTO plossl (ditto)
20mm 65 degree William-Optics (came with binoviewer)
20mm SWA (purchased off ebay from Smart Astronomy)
15mm SWA (purchased off ebay from owl1)
11mm UWA (purchased off ebay from Smart Astronomy)
10mm GSO Superview (purchased directly from Smart Astronomy)
Pentax SMC zoom (8mm to 24mm)
Orion Ultrazoom (7mm to 21mm)
Scopetronix Zoom (7mm to 21mm)

Plus I tested a William Optics binoviewer, with and without the 1.6x barlow nosepiece.

Here are the results:
40mm GTO plossl - results in about 16x mag. Very long eyerelief (25mm+). Clear and bright views. Around 6.3mm exit pupil. Probably great for digiscoping. Eyepiece is clean with no dust between lenses.
32mm GTO plossl - results in about 20x mag. The very best, bright view out of all eyepieces tested. Long eyerelief. Exit pupil around 5.1mm. An absolute delight. Eyepiece is clean with no dust between lenses.
26mm GTO plossl - results in about 24x mag. Nice bright view with good eyerelief. Brightness not perceived to be as bright as 32mm plossl probably because of smaller exit pupil of 4.2mm. Eyepiece is clean with no dust between lenses.
20mm William-Opt Widefield eyepiece. - results in 32x mag. Nice wide bright clear contrasty views. Decent eyerelief. Eyepiece is clean with no dust between lenses.
20mm SWA - results in 32x mag. Nice wide bright clear contrasty views. Decent eyerelief. Eyepiece contains some dust between lenses which detracts from the "being there" experience.
15mm SWA - results in 42x mag. Nice wide bright clear contrasty views. Decent eyerelief. Eyepiece contains some dust between lenses which detracts from the "being there" experience.
11mm UWA - eyepiece does not come to focus in 100ED, an F6.3 system. Also doesn't work in my Voyager a F4.3 system. Simply not enough "in-focus" on the two scopes. Only scope it works on is the F12.3 Maksutov.
10mm Superview - results in 63x mag. Atmospheric conditions that day probably resulted in more degraded view. Less dusty than SWA's but not as clean as plossls and Williams eyepieces. Eyerelief is decent and field of view is still pleasant.
Pentax SMC zoom - variable mags from 26x to 79x. One big mother! Not as heavy as it looks (whew!) Good eyerelief though eyes are harder to position due to such a big eyepiece. Very good color, as good as the plossls. View at higher mags resemble the 10mm Superview probably because of slight haze due to atmospheric conditions. Like all zooms, less field of view at low mags and wide field of view at high mags.
Orion Ultrazoom - variable mags from 30x to 90x. I love this eyepiece on my Bushnell Voyager, clear, bright and widest views of all zooms tested but it just isn't appropriate for the Pentax 100ED. Eyerelief is too short to use as a spotting scope eyepiece. Also works poorly on my 90mm Maksutov.
Scopetronix Zoom - variable mags from 30x to 90x. I hated this eyepiece on my Bushnell Voyager because its field of view was quite narrow in comparison to the Orion Ultrazoom but it really redeems itself on the Pentax 100ED. Has longest eyerelief of all zoom eyepieces tested. I can see why Scopetronix sells it as a solution for zoom digiscoping. Fairly clear, clean, and bright due to it being fully multicoated. Atmospheric degradation to image at high powers. Smallest zoom out of three tested. A decent zoom spotting scope eyepiece and only $60 to boot. People with the smaller Pentax spotters should seriously consider this as a substitute to the SMC if they want to save on weight and money.

Now onto the binoviewer....
When I plugged the binoviewer in, it didn't look out of place at all. Probably because the Pentax SMC was such a big eyepiece. I tested it using the two included 20mm Williams-Optics eyepieces.

First without the 1.6x barlow nosepiece, the binoviewer config would not come to focus at all. Second with the included 1.6x barlow attached, would only come to focus on objects out to 10ft. Had the same problem on my Bushnell Voyager as well. The only scope the binoviewer would come to focus on is the F12.3 Maksutov and this is without the 1.6x barlow nosepiece. However, the Maksutov's focal length is 1200mm so with the 20mm eyepieces, I get 60x mag and an exit pupil of 1.5mm which makes it difficult to align both eyes with the eyepieces.

I felt frustrated and went checking on the CloudyNights website for a solution and found people recommended using Seibert Optics OCA's to get the binoviewers to come to focus with any scope, even spotting scopes. After looking through Seibert's website, I ordered the 1.25x OCA which are guaranteed to bring any scope to focus. I chose the 1.25x because I didn't want the OCA's adding too much to the eyepieces' magnification. I will post a review when I get the Seibert OCA and test them with the various eyepieces.
 
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Hi Can Popper
I'd appreciate your advice re plossls on the PF65ED. I'm relatively new to all this interchangeable lens stuff and to date I've steered clear of Plossls because I've been put off by their small dia top elements (whatever the proper name for that is!)

Should I worry? on the other hand would this characteristic help with digiscoping? - my Casio Exilim Pro 600 vignettes badly with all my current lenses - would a Plossl help do you think?

any advice greatly appreciated.

Can't find any reference to the Scopetronic zoom which you rate so highly, here in the UK, which is a shame, as it sounds a very good piece of kit

John
 
Hi John,
The plossls only have small top lens when being operated at high powers. At the very low powers, their lenses are just as big as any. Just use the three lowest power plossls and you'll be fine.

I'll post some digiscoped pictures I took with my 40mm plossl. It is extremely easy to digiscope with due to its very wide bright views and long eyerelief. I'll even post some digiscoped pictures I took with the Pentax SMC zoom which were not nearly as good as the plossl and much more difficult to do as a comparison.

My GTO plossls came from this website:
http://www.handsonoptics.com/ep_gto.html

A digiscoping accessory I'll probably get which should work great with the low power plossls would be this:
http://www.telescope.com/shopping/p...e=PRODUCT&iMainCat=6&iSubCat=29&iProductID=65

The way I've been digiscoping is simply to hold my Fuji F10 digital camera to the low powered plossl eyepieces and zooming the camera up to its max mag (scope is tripod mounted). Then I focus the scope while looking at the camera's LCD screen. My hands do shake a bit but the image coming out of the low power plossl is so large and the eyerelief so long I still manage to get many decent to good pictures. The universal camera mount should help take me to the next level by removing my handshake so I can concentrate exclusively on focusing the scope.

You can find the scopetronix zoom on this page. Also look at the plossl pictures at the top of this link. The three lowest power plossls all have very large eye lenses.
http://www.scopetronix.com/ep.htm
 
.. lots of really helpful info here, which has got me thinking.

Any advice as what 'low powered' should mean for my PF65ED?

GTO lenses don't seem that readily available over here (at least not on eBay) but I've got a US based seller listing the 32mm at £18 and the 15mm at £14 - that's including shipping!

I like the look of that digiscoping bracket too - I wonder if it will allow you to swing away the camera?

Kicking myself now looking at the adapters for the Nikon Coolpix range that allow the camera to couple directly to eyepieces; I sold my 995 shortly before buying my PF65 (which I love!)

Off to Holland for a few days this week and the joy of the PF65 is, that, together with my Velbon CF tripod I can easily carry them as hand baggage on the ship and do some sea watching, without getting shoulder ache!

John
 
Well, I ran some quick calculations.

When I say "low power", I generally mean the eyepiece. In astronomy, eyepieces of the fl of 20mm and higher (as in 40mm) are considered "low power". Naturally, the scope you stick it on will determine the final magnification.

Medium power consist of the range of 10mm to <= 20mm. And high power eyepieces are less than 10mm.

If you stick the 40mm plossl on the 65ED, you will get a final magnification of about 10x. But remember, to digiscope, you have to optically zoom your camera to max (2x-3x or whatever it is capable of) so the final magnification is 10x times 2x-3x or 20x to 30x which is fine. Digital zoom usually works poorly for digiscoping so stay away from those cameras.

From my tests, it is eyerelief and exit pupil that counts for digiscoping. Minimal digiscoping eyerelief (where you are pushing your camera's lens right up to the eyepiece's exit lens) is 20mm. More eyerelief is better.

Secondary impact is exit pupil. A larger exit pupil makes it easier to position the camera for digiscoping (and also brighter images). To calculate exit pupil size, take the aperture of your scope, in this case 65mm, and divided by final mag, with 40mm plossl about 10x. For the 65mm scope and 40mm plossl that works out to 6.5 mm exit pupil which is great.

For your case, you really don't need the GTO brand plossl. Any "low power" plossl with long eyerelief (in our case the 25mm,26mm, 32mm, and 40mm) would work well.

I only recommended GTO because the lens are clean and eyepiece cheap but most decent priced low power plossl should just be as good. If you read my eyepiece review from above, some of the cheaper eyepieces have dust between the lens which may or may not degrade the digiscope image.
 
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As promised, here are some digiscoped pictures I took with the 40mm plossl using a Fuji F10 camera. The camera was set to natural light mode so it could auto adjust itself up to ISO1600.

My 100ED was mounted to a tripod and I used my hands to hold the camera, adjust the focus on the Pentax, and snap the picture.

For the first picture, you can see the one drawback to the Plossl. Notice how the fence appears a bit convex. On the Siebert Optics website test of the plossls, a slightly curved field is one of its features: http://www.siebertoptics.com/SiebertOptics-eyepiececomparisons.html

Of course without straightlines, the slightly curved field isn't really noticeable as you can see in the second picture.
 

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John Fleet said:
Can't find any reference to the Scopetronic zoom which you rate so highly, here in the UK, which is a shame, as it sounds a very good piece of kit

John

Hi John. I got digiscoping stuff from that company. Just look at the scopetronix homepage to find that zoom eyepiece..............

www.scopetronix.com

You can find both the eyepeice plus various digiscoping adapters (including one for the camera you mentioned). They deliver outside the USA too.
 
Hi Stu,
thanks for that; I'm not keen on paying $190 plus shipping for the bespoke solution! I'd rather put that towards a new camera. Might go for their zoom mind you, depending on how reasonable their shipping is.

Question for Can: (and Stu too!)

I've just tried handholding the Casio to a no brand 15mm lens which came with the Pentax. Still a lot of vignetting at the max optical zoom. So, if I were to buy the 32mm Celestron Plossl, advertised as being the same lens as the GTO, which is apparently only about £18 delivered, I calculate as follows:

Focal length of Pentax is (I believe) 390 mm. therefore magnification = 12.18
Exit pupil = 65/12.18 = 5.33

How does that sound as a potential digiscoping set up? - with the four x optical zoom on the camera, would that mean I'd be digiscoping at up to x 48? - sounds a bit powerful?

should I try and find a 40mm Plossl giving about 10 x magnification and a 6.66 mm exit pupil and thereretical mag of up to 40 x?

... John
 
If your no brand 15mm eyepiece has the specs of this 15mm:
http://store.yahoo.com/yhst-1469288697390/15suwianey.html

It would be no wonder you are getting vignetting; the eyerelief is only 13mm and the minimum acceptable eyerelief in my tests is 20mm.

Let me try digiscoping with my Scopetronix Zoom today and I'll let you know how well it works (I'll try out both my modern Fuji F10 and my old Fuji A300). On their website, they say it can work for digiscoping but it wasn't an optimal solution. It's eyerelief certainly meets the minimal 20mm digiscoping specs. On mine, it feels like it has longer eyerelief than the Pentax SMC zoom which has eyerelief listed at 20mm.

Your calculations certainly seems correct. One spec you fail to mention which you can look up on the handsonoptics.com website is the eyerelief for the 32mm plossl. There, the specs are "32mm FL, True 4 Element Plossl, 51 degrees FOV, 24mm ER Full Multicoated Rubber Eyeguard" and the eyerelief is the "24mm ER" portion which exceeds our 20mm minimum ER requirement.

So setup wise, you should be good to go with this eyepiece. Instead of buying a scopetronix zoom, you can use your camera as the zoom lens with the fixed 32mm plossl or 40mm plossl; just zoom in and out with the camera to adjust final magnification. The setup's potential combined mag of 40x approaches the optical limits of the 65ED as things stand.

Just another personal comment/opinion: the plossl eyepieces are cheap enough where you can use the 40mm as the permanent digiscoping setup and the 32 mm (or zoom) for viewing. I am thinking about getting the Orion Universal Camera mount and leaving it permanently attached to my 40mm plossl. I would use the 32mm (or zoom) for viewing (in my review, the 32mm works great for visual viewing) and then switching in the 40mm/camera mount/digital camera setup once I locate a target I'd like to photograph. My reasoning is once I have the camera aligned just right to the eyepiece thru the Orion Mount, I would loath to remove and later fumble around trying to find the proper alignment again. By just swapping the 32mm with the 40mm/camera assembly, I should be able to do lightning quick digiscoping.
 
Can

Good to know I'm getting my head around the math!
This is the Plossl I'm looking at:
http://cgi.ebay.co.uk/NEW-CELESTRON...oryZ3636QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

doesn't state any eye relief. Looking on the Celestron web site I can't find anything to match the eBay item; the neared match seems to be the Omni series 32mm, which has 22mm of eye relief, so would seem to a good contender?

I agree with your comments re having a lens permanently coupled to the digicam, however one issue with the Casio is that the lens retracts/extends when powering up/off, so that might complicate things slightly, but the ease of changing lenses on the Pentax is certainly a big plus point in my opinion.

Looking forward to seeing your zoom test results; I do have an 8mm - 24mm , which I tend to use as my prime lens at the moment.

John
 
Well, on the handsonoptics website, they say the Celestron is just a rebranded GTO. Thus the specs should be identical so this should be fine. In fact, that one on ebay looks eerily like my GTO. It's probably all the same OEM being rebranded again and again anyways.

I think the lens retraction and the different zoom levels on the camera shouldn't affect the alignment to a degree which you can't correct simply by changing the focus on the 65ED scope. I'll need to get the Orion universal mount to be sure.

Since you already got a 8mm-24mm zoom plus a 15mm, all you are missing is a long eyerelief eyepiece and Orion mount for digiscoping. What I like about such a combo is it can all be had for <$80. Inexpensive, yet effective.
 
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As promised,
Here are the pictures I took through the Scopetronix zoom eyepiece. The first one is with the zoom set at 21mm or 30x. The second pic was taken at 15mm or 42x. The last picture was taken at 7mm or 90x.

Now what I need is a steadier hand and maybe some black felt paper to wrap around the light path to improve my contrast.
 

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Can
Looks very promising! - I've ordered the 32mm, so we'll see how that goes. Neither my zoom or my 12.5mm prime work at all well as previously mentioned with lots of vignetting, so if the Plossl is OK in that regard I'll be encouraged to go for the Scopetronic. Were your photos taken coupled to the PF65ED? One plus for the Casio should be its remote control, which should obviate the need for a cable release....


John
 
I took my pictures with the zoom coupled to the Pentax 100ED. I think the large aperture may be why I was able to get almost a magnifying glass view of the leaves when I set the zoom to 7mm or 90x. When the camera's magnification is taken into account, the third picture is actually a 180x picture.
 
I tried out digiscoping with one of the eBay eyepieces today. The one I used was the 15mm SWA that can be purchased from owl1/Smart Astronomy on eBay.

This eyepiece has a wide 70 degree field of view but only 13mm of eyerelief. Thus, digiscoping with this eyepiece is not recommended.

That being said, my Fuji F10 is a very forgiving digital camera. By sitting the camera lens right on top of the eye lens of the 15mm SWA, I still managed to pull off some digiscoped pictures.

The pictures even had better contrast than the ones I took with the scopetronix zoom because sitting the front of my camera on the eyepiece prevented stray light from leaking in from the sides and can be held in place by hand steadier.

Apparently the dust in the eyepiece did not impact the digiscoped images much.
 

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Hi can popper . Please make sure to post your findings with the Seibert oca & binoviewer as i have a Burgess BV & hope to use it with the forthcoming 100 pf .
Thanks Brian.
 
Thanks for the interest.

I will as soon as I get it from Seibert. They are taking their sweet time shipping it to me. Believe me, I am real anxious to get it.

I was at the gun range today and was reading the finer print below the fine print on the targets posted 100 yards away with the 100ED and SMC zoom. And with the 5mm Stratus, the targets looked like I was standing in front of them a feet away.

Just imagine what the binoviewers can do (if they work, that is...).
 
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In my above posts, I think I've gone over exhaustively how eyerelief is important for digiscoping compatibility. Other posts have noted how the exit pupil affects the amount of light the camera receives and thus the shutter speed and picture clarity.

One other eyepiece specification I think I've neglected to explore was the implications of an eyepiece's field of view on digiscoping. To restate, is there any advantage to using an eyepiece whose field of view is, say, 70 degrees over an eyepiece whose field of view is 45 degrees if both eyepieces have the same 20mm eyerelief and 32mm focal length?

To find an anwser, I tested my 40mm plossl, 32mm plossl, 26mm plossl, 20mm SWA, and 20mm Williams by digiscoping through them with the zoom on my Fuji F10 digital camera set to 1X or no zoom. The scope used was the Pentax 100ED. The picture results are posted at the bottom of this message.

As the reader can see, the narrower field of view eyepieces such as the Plossl resulted in a "circle" type of view when the camera is set at no zoom; thus, to get a full field image, the Plossls mush be used with quite a bit of camera zoom to take full field pictures. Meanwhile, the wide field eyepiece the 70 degree SWA allows full field digiscoping without using any zoom at all. The slightly narrower field 66 degree Williams allows full field digiscoping with just a little zoom.

In conclusion, eyepieces with field of views of 70 degrees or greater allows the user the distinct advantage of doing full field digiscoping without the use of camera zoom. This also by inference points out the weakness of zoom eyepieces where camera zoom must be used to achieve full field digiscoping. This test also validates the Pentax spotters unique value proposition to the aspiring digiscoper.
 

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Just for grins,
I decided to take a few pictures through my Orion Lanthanum 2.3mm eyepiece. This is the most powerful eyepiece, magnification wise, on the market so it will act as a good indicator of my Pentax 100ED's optical quality. The eyepiece combined with my scope gives a power of 274X; well beyond the 1X per mm of aperture rule for useful magnification on spotting scopes.

The first picture is of a holly tree located 40 yards away. The second is of leaves on a climbing vine located 75 yards away. The camera was set to no zoom and held by hand to the eyepiece.

Two things to note when comparing the pics from expensive lanthanum to my pics from the cheaper plossls are the sharp to the edge and very sharp field stop pics on the lanthanum.

*EDIT* Added new pic taken through Lanthanum with use of Universal Digiscoping Adapter. It is of an insect on a twig 75 yards away.
 

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Can Popper said:
Just for grins,
I decided to take a few pictures through my Orion Lanthanum 2.3mm eyepiece. This is the most powerful eyepiece, magnification wise, on the market so it will act as a good indicator of my Pentax 100ED's optical quality. The eyepiece combined with my scope gives a power of 274X; well beyond the 1X per mm of aperture rule for useful magnification on spotting scopes.

The first picture is of a holly tree located 40 yards away. The second is of leaves on a tree located 100 yards away. The camera was set to no zoom and held by hand to the eyepiece.

Two things to note when comparing the pics from expensive lanthanum to my pics from the cheaper plossls are the sharp to the edge and very sharp field stop pics on the lanthanum.

CP,
I wonder if your choice of subject matter could not have been better...

Your subject matter exist in a 3 dimensional space with great depth as well as width and height. At 274x your depth of field is approaching the point of vanishing.

So naturally only those very few object that arbitrally happen to fall within this very shallow DOF are really in focus while most objects will be out of focus. This gives an over-all impression of softness that does not necessarily reflect the true performance of your eps or scope.

SF
 
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