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PENTAX PF – 100ED. Assessment (1 Viewer)


Well-known member

Like motor cars, optical equipment can arouse passions in a man, consequently birdwatchers’ opinions are not always subjective or dispassionate.

The first question you need to ask your self is – ‘What type of bird watcher am I?’

If you walk miles and miles in tough country or are a quick glance tick-it-off bird watcher go for light weight. Remember a mighty telescope requires a strong tripod and head adding considerably to the weight.

If you are an aesthetic bird watcher who stands or sits for hours scrutinizing every detail of your chosen subject, or weight is not a problem because you enjoy rude health, consider a big one.

The other thing not to forget is that the top of the range telescopes are all good - you are in the BMW/Lexus/Mercedes bracket so there is not much chance of disappointment.

Now to Pentax.
For many years I have deferred buying a telescope because none delivered the quality I demanded and I considered that bird watching telescopes were let down by inferior eyepieces.
Pentax have been producing eyepieces for astronomers for a long time, and these achieved a reputation as the ones to use if you were at all serious about the hobby. They are WATERTIGHT-unusual in astronomy, if not unique.
Because they are designed for astronomy they have a 1 ¼ inch (31.7mm) fitting - the projecting tube that slides into the telescope - thus taking advantage of every last vestige of light the objective lens is delivering.
So there you have it – class-leading eyepieces with nothing watertight to put them in.

Eventually Pentax took the logical step of producing a Nitrogen purged tube with the necessary correction lenses - astronomers live in an inverted world with fewer lenses, hence more light admission. But they kept it secret. I wrote to them - no reply, none of the UK dealers I asked had heard of it. Finally after many months I tracked one down.

Now I am using a PF - 100ED.
Verdict - EXCELLENT.

I have three eyepieces:
22 1/2 x
26-78x zoom.
22 ½ x is my favored one for all round watching. The light admission is wonderful, superb color definition, sharp, bright. A walk-into image with a good field of view and depth of field.
This eyepiece can be used without the tripod. I can rest the shoe on the aperture in a hide – another plus point as there is often no room to stand the tripod.
Don’t let the 22 1/2x deceive you. When other watchers have used it and asked what magnification it is I invite then to guess - the answers range from 32x to 45x, the majority being mid to high 30s.

45x comes next in order of preference. Inevitably the field of view suffers as the price of the higher magnification but the rest of the attributes are all there.

The technique that has evolved for me – the 22 1/2x stays on the telescope permanently then when I find something that needs closer scrutiny I change to 45x. It is so easy, it takes but a moment.

The zoom. Measured against the straight eyepieces, optically it is disappointing. It just does not deliver the image quality of the other two. Add the fact that the field of view at 26x is the same as the straight 45x it is only used for an extremely long reach and not always then, as often the power is negated by poor air quality.
I suspect Pentax have built it to a price rather than a standard knowing that bird watchers wouldn’t/couldn’t pay the price of the quality/cost of production/limited market equation (astronomers would never use a zoom).
However other birdwatchers who have used the zoom say it is good and don’t share the same degree of disappointment.

After using the telescope for some minutes a Northern gent said.
“Why man it brings deed bords alive”

Since I obtained the Pentax another route has come onto the market which might go some way to mitigate the optical quality verses weight problem.
Swarovski are now producing an adapter which enables astronomical 1 ¼ in eyepieces to be married to their new generation of bodies.
In the hopes of testing one I have contacted a few dealers but they didn’t know what I was talking about.
That could be a subject for the forum “Dealers and their lack of product knowledge.”

If you are still reading, here are a few even more tedious facts:

100mm Objective lens.
Length 20-22ins (510-520mm) depending on eyepeice
Weight 92 ozs 2600g

22 ½x eyepiece:
Field of view at 1000m 42m. 1000yds 126ft.
Exit pupil diameter 4.4mm.
Eye relief infinitely adjustable to 20mm.
Weight 12 ozs 340g.

45x eyepiece:
Field of view at 1000m 26m. 1000yds 78ft.
Exit pupil diameter 2.2mm.
Eye relief infinitely adjustable to 20mm.
Weight 12.7 ozs 360g.

The zoom 25-78x:
Field of view at 1000m 26m.- 14m 1000yds 78ft –42ft.
Exit pupil diameter 3.9mm –1.3mm.
Eye relief infinitely adjustable to 20mm.
Weight 19.4 ozs 550g.

Paulyoly who lives in Florida and appears on these pages is using a CoolPix 990 married to the Pentax PF- 80ED which uses the same eyepieces.

To put the telescope’s capability into more everyday terms – at 160 yds at 22 ½x the barbs on a barbed wire fence are just discernable but 1inch lettering carved on a wooden footpath sign is crystal clear.

At 160 yds at 45x the twist of the barbs are pin sharp.
With the same magnification, stone work and roof tiles are very clear at 1 1/2 miles.

Using the zoom at 78x a Z bend road sign can be read at 3 ¼ miles but is not pin sharp.

Finally, the debit side.
The telescope, +22 1/2x eyepiece, tripod and head weighs 16 ½ lbs – 7.5k. Add the other two eyepieces, binoculars, stool, picnic, two bottles of wine and it becomes rather heavy.
Fortunately I have a manservant.

Gordon Boreham-Styffe.
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Art Thorn

Well-known member
This is not about Pentax, but you have raised the interesting question of Swaro's 1.25 adapter. Has anyone tried it? I just purchased a second-hand ST 80 and have some truely excellent Televue Naglers (currently on sale). If the adapter idea works, I'll keep the 13mm Nagler, which will give me about 38x, very wide field viewing.

Art Thorn

Well-known member
Thanks Gordon. I'm going to try it. Now that I have the scope, I have to say I am mildly disappointed with the narrow field of view through the zoom eyepice. I really want to get my 13mm Nagler on it and see what it looks like!


New member
Thanks for your post Gordon - I have been seriously thinking of buying a PF-80ED for the reasons of the eyepiece choice and other reviews I have read on the scope seem very favourable. As you say birders even like the zoom eyepiece... how do you rate Pentax with TeleVue for eyepiece quality/price ?


Well-known member
Dear Tates,

Welcome to the forum. You have made a wise decision in joining this group of enthusiasts. They all must have signed the Hippocratic oath for the dissemination of knowledge.

After an introduction like that the rest of this letter will be a disappointment as I am unable to answer your question.

Some time ago I wrote to Tele Vue asking if their eyepieces were waterproof with a view to marrying them to a watertight birdy tube but didn’t receive a reply so went no further.
My limited research only produced the Pentax eyepiece as being watertight.

I did try a Tele Vue eyepiece at an astronomy happening but it was seriously let down by the inferior telescope it was attached to. Unfortunately the dew arrived so the astro party packed up before I could experiment and compare. (Their kit was not waterproof)

I suggest you contact ACE Optics they have an astro department as well as a bird watching one. I have always found them very knowledgeable and helpful.

G B-S.


Steve Campsall
You've given an honest assessment of the Pentax zoom eyepiece - and, in fact, an assessment, I believe, that applies to a very similar extent to all current birding zoom eyepieces. The best available for field of view is probably the Swarovski but twist it to 60x and a similar thing happens as you have found with the Pentax (which, like my Nikon ED82, igoes well beyond 60x).

Only in the best lighting conditions and after a few moments of eye-acclimatisation can it seem to be good enough. But change it then to any fixed wide angle eyepiece and the zoom seems like a rather poor relation.
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Quacked up Member
Out of interest why is Pentax so underused over here? There bins get rave reviews in the states but over here you don't see them and if you flip through the adverts in the magazines they are barely mentioned.


Steve Campsall
There are plenty in camera shops - I think they sell well to non-birders, Pete (got it right, notice!). My wife has a pair of pocket Pentaxes and, for the price, they're quite good and great for a seat in the gods.

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