Tolles eyepiece put to the test

[Dawson]

On a visit to see Alan Heath in early 2017 we got talking about eyepieces; I’ve only ever really used Plossls. Alan told me about the Tolles eyepiece, which had been affectionately known as the poor man’s Orthoscopic. Alan said the views of the planets he had achieved with his old Tolles eyepieces were amongst some of the best he’d ever seen, though had got rid of his Tolles many years ago.

I decided it would be nice to track down a Tolles for Alan, and set about a search.

None of the avenues I tried came up with any results and so I posted a thread in the BAA Forum last summer. Roy Hughes sent me an email in response to the thread and said he had a ¼” Tolles (6mm) and very kindly offered it to me for free after I explained what it was for.

1/4" Tolles eyepiece

I gave the Tolles  to Alan last year and he was overjoyed with it. He said he would make use of it and out of interest compare it to his other eyepieces.

In April Alan did a comparison of the Tolles with a monocentric and a Plossl. He typed up his results which I have scanned and include here (with Alan’s consent), along with an image of the Tolles eyepiece with some plumbers tape around the RAS thread so it sits nicely in a 1.25” focuser.

I’m very grateful to Roy for sending me the eyepiece and also to Alan for educating me.

Attachments:

1. 

   Tolles.JPG
   

2. 

   AWH-Tolles.jpg
   

3. 

   AWH-Tolles_0.jpg
   

[Roy Hughes]

Interesting results.

With only two surfaces the tolles was always considered to be “bright”, but of course at that time these eypieces were not coated.

There seems to be a problem with the post, the image of the results just shows a broken image symbol, however the click through to your members page works OK.

Roy.

[Dawson]

Roy

Thanks for the message. Yes, it is interesting. I suspect you could conduct some transmission tests to numerically compare the light transmission of the three eyepieces. I guess I could do this with one of my CMOS cameras, but not sure how sensitive it would be to the differences between them and probably difficult to standardise the alignment etc between the light source, eyepiece and sensor. Maybe a project for a rainy month… But we are both very grateful for the Tolles.

As for the broken image, the image appears fine on my browser (Chrome) as the screen shot hopefully shows. The image of the results is hosted on my members page as when I tried to upload it to the forum the forum algorithms resized it to 640×480 and the text was not legible, so I cheated and linked to a higher resolution version allowed by the members pages. There may be a way to get higher resolution images in the forum, as I’ll ask the clever technical guys. If the image preview isn’t showing for you, it may be your browser; maybe try a different browser. Having said that, I’ve just looked on my iPhone and the images doesn’t display there. 

Regards

James

[Author]

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