CN FORUMS ARCHIVE Telescope Reviews: IMPORTANT ! ep info !

With a rare break in the rain around lunchtime , I took the opportunity to begin what is likely to be many experiments and observations with the new eyepieces , barlows and adaptors I've recently ordered .

My first one was to test the performance of a TeleVue 20mm Plossl in the straight through Zeiss 85 Diascope .

Although very pleased with the overall sharpness and contrast , I quickly noticed what I considered to be excessive pin - cushion distortion .

Vertical TV aerials when viewed from around 100 metres distance bowed considerably when placed anywhere outside around 80% from ON - AXIS , radially speaking , and when placed at the top and bottom of the field of view , the magnification increase of a large chimney cowl was VERY noticeable -- I would estimate at least 10% different than from the centre .

Disappointed and intrigued by this , I then put the same TV 20mm Plossl into the TeleVue 76 scope , and to my surprise and great sense of relief , this excessive pin - cushioning all but disappeared completely !

I learned something at that moment .

In my technical ignorance , I'd always presumed that an aberration such as pin - cushion was a result of EYEPIECE design .

Clearly this is NOT the case at all !

I can only presume that SOMETHING in the Zeiss Diascope , presumably the prism system , is causing that remarkable difference , and it is something which needs to be kept in mind if and when anyone makes any claims about this or that make and model of eyepiece .

ALWAYS CONSIDER THE TYPE OF SCOPE ( or indeed binocular ) in which the eyepieces are being tested and rated !

Of equal interest , but even more disappointing to me , is the following .

Yesterday's jubilant announcement of mine , that the TeleVue Radian was going to spend a LOT of time in my Zeiss Diascope , has proved to be based on false optimism and unthorough testing .

In fact , the Radian will NOT come to focus in the Zeiss Diascope at any distance beyond about 400 metres :-(

The Radian eyepiece is so long that there in insufficient IN FOCUS travel in the Zeiss housing to accomodate it .

I'm 100% certain this is bound to be the case also with any TeleVue Panoptic or Nagler eyepieces , or indeed with any of the larget eyepieces , such as the Pentax XWs .

As if in consolation , upon re - checking , I found the TeleVue 20mm Plossl DOES indeed come to focus at infinity , with a little to spare too .

These discoveries have amounted to something of a set - back for my original hopes and expectations of using the new accessories -- but one thing is for sure -- my initial impression rating of the TeleVue 76 scope has only been elevated further still .

Already , I think I can say with 90% certainty , that the TeleVue 76 with TeleVue eyepieces provides crisper , sharper , more aberration - free images than the Zeiss Diascope , regardless of WHICH eyepiece could be used with the Diascope .

This comes no GREAT surprise to me , to be honest , as the absence of prisms alone ought to give a considerable edge to the TeleVue 76 .

However , that is NOT true , for example , of my Helios 105 f5 scope when used with a diagonal only -- THAT still doesn't produce images as sharp and colour - free as the Zeiss scope .

I HAVE detected a little CA through the TeleVue 76 , through both the TV 20mm Plossl and the 18mm TV Radian , with more in the latter than the former , but it is VERY VERY minor .

I'm still greatly loking forward to the arrival of the TeleVue 32mm Plossl , the 2x and 3x barlows ( which I'm now doubtful are going to be of much use in the Zeiss scope ) and the Zeiss astro adaptor , which I'm optimistic of being able to use with the TeleVue scope .

I will keep this thread updated if anyone is interested .

Kenny

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Milton Wilcox R.I.P