Pentax 100 ed Spotting Scope? (1 Viewer)

medinabrit said:

I have one & like it very much.
The pentax eye pieces are second to none .But of course you can use any 1.25 EP.with it.

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That's been my opinion as well.

medinabrit said:

I should mention that i also have Miyauchi saturn 71mm ,Garrett 100mm 45degree & Vixen 80 BT binoculars ,
Some of these can go as high as x115 for the Miyas & about 75 for the others BUT IF IT RAINS I HAVE TO GET THEM INSIDE.
If your viewing is under cover all the time i would definately consider something like the Garrett or Vixen big bins .They are cheaper than the Pentax & use I.25 EP,s like the scope but you need 2 of them.
The Miyauchis are the best but no longer available.

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Wow, nice toys! The BT80s will take any 1 1/4" EPs? Have you used BT125s?
I've heard mixed reviews on them.

medinabrit said:

But for really great viewing the 10 14 & 20mm pentax XW,s are the ones to have.

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I use those same EPs on my PF80 and it's hard to imagine a better view.
Do you have any other spotting scopes or have you compared the Pentax' against say, Swarovski, Kowa, or other high end scopes with their fixed EPs?
I'd like to hear of that comparison.

I have a Pentax 100 and wasn't all that impressed with it. My Swaro STS80HD gives better results. It's also a pain to handle and needs a heavy duty tripod and head .I would look at the new Kowa 88 too. Neil.

I have the Nikon 82. 60, & 50mm fieldsdscopes .& two Takahashi astro scopes.
The sky 90 & the FS60.Also a Vixen 80 SS.& a televue 60.
I think the Pentaxes are exellent & great value compared to the Euro scopes.
When used with the XW EP,s the are probably equal to any.
I believe that the EP is the most important element & the Pentax along with the TV EPs are a hard act to follow,
Ive stated on this forum before i believe that snobbery plays a part in the choice of scopes & binos.
If it didnt many more birders would be using Canon IS binos.
Brian.

medinabrit said:

I have the Nikon 82. 60, & 50mm fieldsdscopes .& two Takahashi astro scopes.
The sky 90 & the FS60.Also a Vixen 80 SS.& a televue 60.
I think the Pentaxes are exellent & great value compared to the Euro scopes.
When used with the XW EP,s the are probably equal to any.
I believe that the EP is the most important element & the Pentax along with the TV EPs are a hard act to follow,
Ive stated on this forum before i believe that snobbery plays a part in the choice of scopes & binos.
If it didnt many more birders would be using Canon IS binos.
Brian.

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Brian,
A nice collection of scopes and telescopes. How would you rank them with bird observation and digiscoping in mind?
I have the 20mm XW eyepiece for my 100 mm scope and I tested it in the Swarovski (using the telescope eyepiece adapter ). Not much in it but I gave the Swaro the nod due to slightly better contrast, particularly against the light where the Pentax showed some fringing ( the Swaros don't ).
Here is a test taken over about 300 metres from the window of my apartment . Neil.
ps these are out of the camera, crop only. Pentax on the left , Swaro on the right.

Neil, its not only contrast and CA but also resolution. So I think your Pentax 100ED has collimation issues or perhaps your focus was off. The 20mm aperture advantage is too large for the 80mm Swaro to outresolve the 100ED on the fine details that you pics show.

Hold on...maybe the 100ED use the same focus system the 80ED uses!? I discovered my 80ED actually becomes a ~70ED when focused at infinity.

Rick

RJM said:

Neil, its not only contrast and CA but also resolution. So I think your Pentax 100ED has collimation issues or perhaps your focus was off. The 20mm aperture advantage is too large for the 80mm Swaro to outresolve the 100ED on the fine details that you pics show.

Hold on...maybe the 100ED use the same focus system the 80ED uses!? I discovered my 80ED actually becomes a ~70ED when focused at infinity.

Rick

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Rick,
I was surprised at the results too. I will get the Pentax checked out.
Neil.

RJM said:

Hold on...maybe the 100ED use the same focus system the 80ED uses!? I discovered my 80ED actually becomes a ~70ED when focused at infinity.

Rick

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I'd like to know more about this as you've mentioned it twice and I'm not aware of this issue. If you could Rick, why not start another thread about this so as to not take this one any farther afield.

medinabrit said:

I think the Pentaxes are exellent & great value compared to the Euro scopes.

Ive stated on this forum before i believe that snobbery plays a part in the choice of scopes & binos.

Brian.

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Well said Brian.

Without getting into a long interminable, sterile technical discussion I post these without comment.

All taken with a Pentax 100mm spotter+Ca-35 DSLR adapter+Pentax camera.

Beautiful photos .
They show how good the Pentax optics are.
Brian.
PS photographer pretty good to.

Kevin Conville said:

I'd like to know more about this as you've mentioned it twice and I'm not aware of this issue. If you could Rick, why not start another thread about this so as to not take this one any farther afield.

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Hi Kevin,

I first noticed this effect with the Pentax 80ED. But the truth is, ALL the fieldscopes I have checked (Pentax 80ED, Nikon ED82, Kowa TSN663) show vignetting. I have not checked my Nikon EDIII or ED50.

You can see this effect in few ways. Note the effect may become less pronounced as you move from low to high power eyepieces.

First you can see the exit pupil change size as focus is moved from one extreme to the next. Since the focal length of the lens and eyepiece is fixed, we can assume light entering the objective lens is being "variably" obstructed somehow.

You can also look down the objective and watch the exit pupil change shape or maybe disappear as your eye moves towards the edge. The amount will vary with focus position.

Finally, the most revealing test comes from pointing the eyepiece towards a white wall in low light from a distance of about 15cm and shining a laser down the objective and watch for changes in the projected exit pupil while moving the laser from the center towards the edge. Basically, you will see the projected pupil go from round to "D" shaped starting from about 50% out from the center. This is actually the real shocker as it shows the exit pupil is not fully illuminated by as much as 50%!

By measuring the changes in projected exit pupil you make some estimates regarding the "true" unobstructed aperture of your scope.

Mechanical vignetting seems to be quite common in most all binoculars and some recent refractors coming out of China, so it not surprising to see it in fieldscopes.

Hope this helps,
Rick

Rick,

I consider the type of vignetting that you describe to be vignetting of the field, rather than the exit pupil. One source of confusion comes from interpreting the laser test. I've found that what is projected on the wall behind the eyepiece is not an image of the exit pupil, but the eyepiece fieldstop. In any case this kind of vignetting causes a very gradual dimming toward the edge of the field, not a complete stop down of the aperture. All binoculars show it to some extent and I wouldn't be surprised to see it at low magnification in spotters with prisms, especially if the field is wide.

As you probably know that kind of vignetting has been a contentious subject both here and at Cloudy Nights, so I really don't want to get into it again, but I've also found that the Pentax 80ED suffers from the worse problem of an actual aperture stopdown at close distances. I measured the true aperture as less than 70mm at the closest focus (as I recall about 30'?). This happens because the focusing system uses a moving prism with an aperture that is large enough at its infinity focus position but increasingly stops down the objective as the prism is moved toward the close focus position. Other scopes that use this focusing system (like the Pentax 100 ED) probably show the same effect, but perhaps not all to the same extent. The optics of the 100mm Pentax appear to be very similar to the 80mm, just scaled up (f/6.3, with an air spaced doublet up front and a third small element down the barrel close to the prism), so I would expect it to behave a lot like the 80.

I've spent only a little time with the 100mm Pentax. I was not much impressed with the one I saw. It had obviously lower resolution than the 90mm scope I compared it to that day (Tak SKY90), but as always, there may be better samples out there. I've also found the Pentax zoom to be inferior to other zoom eyepieces I own (Zeiss, Swarovski, Nikon, Baader). High magnification in the Pentax zoom was particularly unimpressive with excessive lateral CA close to the field center and loss of contrast and sharpness compared to other zooms.

Henry

henry link said:

As you probably know that kind of vignetting has been a contentious subject both here and at Cloudy Nights, so I really don't want to get into it again, but I've also found that the Pentax 80ED suffers from the worse problem of an actual aperture stopdown at close distances. I measured the true aperture as less than 70mm at the closest focus...

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Hey Henry, nice to see you chime in. Did you measure this from differences in exit pupil size at focus extremes or some other method?

I agree probably best not to go too far down this rabbit hole, especially since it seems vignetting may actually be an industry-wide design "feature." Given how "fast" these optics have to be to meet size/weight/ergonomic design parameters of field use, a little vignetting is probably a good thing.

As we know, all optics are a design compromise and consumer optics are built to a price point first and formost. When used under the typical magnification limitations imposed by their comaptible eyepieces, I'd bet all fieldscopes deliver acceptable images unless they have suffered from some misalignment of the optics.

Frankly, if one is happy with the views best not to spend time testing the optic as chances are you could discover something that will "mentally" ruin any further enjoyment from the scope.

cheers,
Rick

Rick,

I measure aperture directly by placing a transparent ruler across the objective and then viewing the exit pupil with a magnifier held behind the scope eyepiece. That magnifies the exit pupil image enough to read the ruler.

I use various telescope eyepieces for magnifiers. Often they need to be used backwards to reach focus on the exit pupil. About 30mm FL usually works well.

Henry

Henry i think that you would find that just about any spotting scope would be a bit inferior to the sky 90.
Im fortunate to have the sky 90 ,FS60 & the Tak astronomer 22x60.
They are all hard to beat in their size classes.
Reason for having the PF 100. Water & drop proof [im pretty clumsy]
Brian.

Hi Brian,

I think some of the current birding scopes do pretty well compared to the SKY90. A Kowa 883 I recently tested was better overall than my SKY90 (much better color correction) and the best Zeiss 85mm Diascope I've tested was approximately as good. From what I've read I wouldn't be surprised to find Nikon 82EDs with lower aberrations. The SKY90 is a nice telescope, but I think only so much can be expected from an f/5.6 doublet, even with Fluorite.

BTW, have you noticed the discussions on Astromart and CN about prism diagonals vs. mirrors in ED telescopes? I've found that the SKY90 is an example of a scope that benefits from using a prism instead of a mirror. The spherical under correction and red CA are largely eliminated, although with some addition of blue CA as a trade-off. The FS60C might benefit also.

Henry

Thanks Henry .I have never had the opportunaty to look thru a Kowa 883 .
But there is an Amish fellow about 30 miles from me [Time & Optics].
So maybe he,ll let me have look thru.
I do have the Nikon field scope ed,s though.
I did read some of the stuff about the prism diags.
I shall try to obtain one .
Is there any that you could recommend ?
Thanks Brian.

henry link said:

Rick,

I measure aperture directly by placing a transparent ruler across the objective and then viewing the exit pupil with a magnifier held behind the scope eyepiece. That magnifies the exit pupil image enough to read the ruler.

I use various telescope eyepieces for magnifiers. Often they need to be used backwards to reach focus on the exit pupil. About 30mm FL usually works well.

Henry

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Thanks for sharing your expertise Henry. I used your method to test my Pentax 80ED and Nikon ED82 off my veranda today.

With the Pentax I used a TV 24mm Panoptic for the eyepiece and Celestron 25mm Plossl as my magnifier. At the focuser extremes, the ruler went from ~77mm to 60mm! Using my laser range finder I focused on points at my typical 100m, 40m, and 15m observing/digiscoping distances. I saw readings of 73mm, 70mm and 66mm respectively. However, reversing the roles of the Panoptic and Plossl gave me slightly differently results. I then tried a few other eyepiece variations and also saw some different results. But in no case did I ever see the full 80mm. I also noticed if I tilted my eye right or left I could see "beyond" the obstruction to see the full 80mm.

Next I tested the Nikon ED82 with the 30xWDS eyepiece and 25mm Plossl magnifier. At both focus extremes and at the three focus points the aperture reading stayed the same at ~81mm. Seeing no change, I did no further testing with eyepiece variations.

cheers,
Rick

Rick,

Thanks for doing those measurements. I briefly tested that scope (straight version with the Pentax zoom eyepiece) a few years ago and couldn't remember the exact results. The aperture stop down problem appears to be worse than I remembered. Is your scope straight or angled? The problem might be worse in the angled version.

As you discovered, the eye needs to be centered and held as still as possible using that technique. If the eye moves too much while reading the ruler at each edge that will cause the obstructing aperture to move back and forth and give a false reading that is too large. I suppose using different eyepieces in the scope must produce slightly different results, something I didn't try.

I would be surprised to see this problem in a scope with an internal focusing lens like the Nikon. The focusing lens would have to be grossly undersized to obstruct the aperture.

Henry

medinabrit said:

I did read some of the stuff about the prism diags.
I shall try to obtain one .
Is there any that you could recommend ?
Thanks Brian.

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Brian,

I can't see much difference in the effect with different prisms. I've tried everything from a cheap Meade prism to a very expensive Zeiss/Baader in the SKY90. Clive Gibbons at CN has done the most with this. He prefers an old Celestron with his scope. The Tak prism should be optically good and is mechanically nicer than the cheapies.

Henry

Thanks for the info Henry.
We are fortunate to have you on bird forum.
Brian.