Posts Made By: John Huntley

I have recently brought a number of EP's that date from the 1980's including circle-v and circle-t Ortho's in 9, 12.5 and 18mm, a 25mm Kellner and a 32mm Erfle. All these are 1.25 inch.

Up til now I have got used to using modern Plossl's of various FL's but now I have tried the older EP's I'm not entirely sure now that newer is always the best.

Although the older EP's have smaller fields of view in the main and I guess the coatings are not as efficient as modern designs, it seems to me that they are simply nicer to use in some ways. For one thing the conical tops lift the eye lens up to the eye whereas the modern plossls have flat or even slightly dish shaped (ie: shorter FL Ultimas) tops so you seem to have to search for the eye lens.

Another factor for me is that the lesser fields of view (often 45 rather than 50 degrees) are easlier to view without pushing your eye right up to the lens and seem (to me at any rate) to put less demand on the eye.

I guess that my f10 refractor is less demanding than short FL scopes which might struggle with the older EP's but does anyone else think that some of these older EP's have some advantages over the newer designs ?.

John,
England

On my 32mm 1.25 inch Celestron Erfle the barrel length (ie: the chrome part) seems very long compared to my other EP's. I can understand why the top part of the EP is long (5 elements plus air spaces to fit in) but I can't understand the purpose behind the long barrel.

In my mirror diagonal, if I drop the erfle in for the full length of it's barrel, it would be resting on the mirror which I obviously want to avoid.

Is there any reason for the long barrel ?.

John,
England

I have one of the older type TAL 25mm Plossl's. It seems to have a wider field of view than other EP's of this type that I have used and I have seen opinions expressed that these older TAL 25mm's should be actually classified as Konigs.

What is the difference beween the plossl and konig designs ? - presumably more than just a wider field stop ?.

My estimate is that the EP has a 55-60 degree AF. It seems to perform very nicely which is the bottom line of course !.

John,
England

I have acquired a cemented 80mm achro objective lens in a mount - it came from an old spotting scope.

I would like to use the lens to make a rich-field astro scope but I'd like to know it's focal length as accurately as possible - is there any straightforward way of working this out ?. I would guess it to be somewhere between f5 / f6 but I guess I'll need to know more accurately than that.

Thanks.

John,
England