It is currently Tue Nov 20, 2018 12:51 am


Post new topic Reply to topic  [ 18 posts ]  Go to page Previous  1, 2
Author Message
PostPosted: Thu Nov 01, 2018 8:33 pm 
Offline

Joined: Mon Jan 18, 2010 9:25 am
Posts: 5215
The problem with using afocal teleconverters is that they are fixed focus.
So, unless both eyes need zero dioptre correction, apart from astigmatism, one needs to wear glasses.
If one has little accommodation the view is out of focus for most.

The Nikon's above lose field when wearing glasses.
I can minimise this by using Minolta camera eyepiece correction lenses. I think it was the Minolta MD ones that fit perfectly into the recess at the back. The Minolta AF ones being a little big. This loses much less field than wearing glasses.

The Konica Minolta 1.5x (1.65x for me) loses no field with small glasses of the right correction, possibly my computer screen glasses.

So opera glasses that focus are better, but may not give the maximum field size. They may also vignet.
However, very large aperture afocal teleconverters probably give impressive monocular views. Possibly a Ricoh one was very large, I can't remember.

Regards,
David


Top
 Profile Send private message  
 
PostPosted: Mon Nov 05, 2018 10:41 am 
Offline

Joined: Mon Jan 09, 2006 11:05 am
Posts: 5021
Location: Lancashire
We haven't mentioned the "field glass". These are bigger than the opera glass and were used by the military before the prismatic binocular came in. Does anyone have any experience with the field glass?

_________________
brian


Top
 Profile Send private message  
 
PostPosted: Mon Nov 05, 2018 5:34 pm 
Offline

Joined: Mon Jan 18, 2010 9:25 am
Posts: 5215
Yes, Brian.

They are a pain.
Big and narrow fields.
They were made in vast numbers, and usually cost about £15 now.
Many names, often just the shop selling them.

They were still used in the 1920s and 1930s, but Porroprism binoculars are smaller, better and have wider fields.
To get a wide field, a field glass or opera glass needs large objectives.
Without huge objectives the fields can be tiny, especially if one wears glasses.

Regards,
David


Top
 Profile Send private message  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 18 posts ]  Go to page Previous  1, 2

All times are UTC


Who is online

Users browsing this forum: Bing [Bot] and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group