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Nikon EDG focal length and EMA adapter (1 Viewer)

L

lflip

Active member
What is the focal length of an EDG 65 and 85 scope?
I am not sure if it is 400 and 500 mm. That's less than the ED III and ED82.
The EDG scopes are bigger than the fieldscopes.

Has anybody used a fieldscope eyepiece with an EMA adapter on a EDG scope?

Is the view in some way limited compared using the eyepiece mounted on a fieldscope?

Leo
 
lflip said:
What is the focal length of an EDG 65 and 85 scope?
I am not sure if it is 400 and 500 mm. That's less than the ED III and ED82.
The EDG scopes are bigger than the fieldscopes.

Has anybody used a fieldscope eyepiece with an EMA adapter on a EDG scope?

Is the view in some way limited compared using the eyepiece mounted on a fieldscope?

Leo
Click to expand...

Good question. I'd like to know as well.

Steve
 
ED82 fieldscope fl=525mm
Fieldscope Eyepieces
30x fl=17.5mm
38x fl=14mm
50x fl=10.5mm
75x fl=7mm


We can assum the EDG eyepieces (by their designations and identical magnifications) have the same focal lengths as the fieldscope eyepieces so the EDG85 has the same 525mm focal length as the ED82.
 
Jason, there is a long history of using Nikon fieldscope eyepieces with astro telescopes of known focal length. It is just a matter of measuring the exit pupil of the fieldscope eyepiece in a telescope of known focal length and with that data you can determine magnification of the eyepiece (objective lens ÷ exit pupil) and from that eyepiece magnification data you determine the focal length of the eyepieces (known telescope focal length ÷ eyepiece magnification).

The focal length of an unknown scope is simply the focal length of the eyepiece x magnification.
 
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The length of the Nikon EDG 65 is 313 mm while the ED III has a length of 279 mm. The size of the EDG 85 is about 15% more than the ED82.

Because of this difference in size I thought that this would go together with a change in the focal length.

Perhaps the Nikon USA representative, who now and then pays a visit to this forum, can shed some light on this issue.


Leo
 
The physical length of the scope does not always correlate with the focal length. If I am not mistaken the prism design can play a part as well the design of the entire optical train.
 
horukuru said:
How to calculate focal length of scope ? What I know, with FSA-L2 adapter, the EDG85 starts at 500mm f5.9 for FX camera.
Click to expand...

You can not calculate the FL of the scope ,unless You have its f/ number and aperture...or the exact FL of the eyepiece and magnification..However You can calculate the Eyepiece FL based in the eyepiece AFOV and the scope magnification ratio or the eyepiece Field stop....then You can calculate the scope FL!


http://www.cloudynights.com/item.php?item_id=2591
 
I continue the discussion started from message #15 in this thread: http://www.birdforum.net/showthread.php?p=2682150#post2682150 , because I think the topic do fit very well into this thread, where some of the questions that have arised in the other thread were already discussed here hoping you all do agree.

Rick, I see your point but still think there are a couple of aspects that doesn't fit together. You say the Nikon Fieldscope 82 and the Nikon EDG 85 do have the same focal length of 525mm. They only differ by their lens size of 3mm. The Fieldscope is made of aluminium and the EDG is made of a lighter magnesium alloy. In spite of this the difference in length and weight between both Nikon scopes is much greater than with any other type of spotting scopes that do share the same focal length but differ in objective size much more. I collected a couple of examples and hope, as this is a table, it is readable.

Name-weightsmall -weightbig-lengthsmall-lengthbig-deltaweight-delta length
Leica Apo Televid 65-82 1123-1469-302-328-346-26
Swarovski ATS HD 65-80-1130-1350-325-355-220-30
Kowa Prominar 77-88 1330-1520-318-343 -190- 25
Nikon Fieldscope ED-A- EDG 85 A 1670-2030-339-398-360-59

Theses numbers do suggest for me that either the Nikon scopes do not have the same focal length and because of this the EDG is so much longer than its fieldscope counterpart or something else is going on here that has to be discussed and elaborated further.

Steve
 
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Steve, FYI the EDG is still an aluminum tube. With that I have said all I know and care to further say on the subject of the EDG fieldscopes. They just don't interest me.
 
lflip said:
What is the focal length of an EDG 65 and 85 scope?
I am not sure if it is 400 and 500 mm. That's less than the ED III and ED82.
The EDG scopes are bigger than the fieldscopes.

Has anybody used a fieldscope eyepiece with an EMA adapter on a EDG scope?

Is the view in some way limited compared using the eyepiece mounted on a fieldscope?

Leo
Click to expand...

Leo,

What I have been told is that the focal length can be achieved by measuring the length of the barrel. What I am not sure about is exactly where you measure from. Of course, that number would change depending on your zoom/eyepiece magnification. I realize this doesn't help too much, but I wanted to try.

Take care,
Mike Freiberg
Nikon's Birding Market Specialist
 
Mike..No external measurement is going to tell You the focal lenght of the scope.The lenght of the Tube is only part of it,then You would have to measure the whole path of the light inside the prism..The Eyepiece has nothing to do with the focal lenght of the scope..The Eyepiece has its own focal lengt,..the division of the Scope´s focal lenght between the Eyepiece´s focal lenght gives as a result The magnification...In the case of a Zoom the focal lenght varies by mechanical means,sliding the bottom glass elements up and down ............525/7=75X..525/21=25X..(fieldscope ED82 / MCII zoom in this example)..
Dont You guys ,in Nikon USA, know the Focal lenght of the EDG Spotting scope?...dont tell me that the designers in Japan told you to get a ruler and measure the tube,,sounds like a joke
 
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