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Fieldscope ED III depth of field issue

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Old Wednesday 2nd September 2015, 19:05   #1
devans1
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Fieldscope ED III depth of field issue

Hi all

I've recently got myself the ed III with the 30x eyepiece.

I didn't have the option to try before buying but I have heard nothing but good things about the scope so wasn't too concerned.

Initial views backed this up as it does give a great image for it's size and price.

After a bit more of a play however, I find the depth of field ridiculously shallow, to the point where it is difficult to focus properly as no sooner is an object in focus, it moves out of focus. I have used a wide range of scopes over the years and have never come across one as sensitive as this.

Has anyone else found this to be an issue? I've look through the threads and can't find much more than a brief mention of it so I assume it's not a common issue with ed III users.

Would using a different eyepiece change things? I prefer to use fixed eyepieces and 30x is my preferred choice but would consider the zoom or a lower mag eyepiece if it would make things better.

Any views would be appreciated.

David
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Old Wednesday 2nd September 2015, 20:56   #2
mayoayo
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I owned the ED III ,not for a long time,but enough to use it in a good number of outings..truly i cant remember the scope to be better or worse in that regard than other scopes .If anything its focal ratio being f/7 should increase the depth of field ..i know this is true with camera lenses,but i am not sure if the inclusion of prisms and the ocular in the system would actually have the opposite effect..
One thing i know for sure is that depth of field gets more and more shallow the closer you focus..and increases gradually focussing towards infinity...Have you noticed if your scope performance changed a lot at different distances.?
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Old Wednesday 2nd September 2015, 21:21   #3
devans1
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Quote:
Originally Posted by mayoayo View Post
..Have you noticed if your scope performance changed a lot at different distances.?
It's the same throughout the focus range as far as I can tell, very frustrating.
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Old Wednesday 2nd September 2015, 22:13   #4
Hermann
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Depth of field depends solely on the magnification. The problem you're experiencing is probably that you're not used to the focusser of the EDIII. Once you get used to it you shouldn't have these problems anymore.

That said, for general use I prefer smaller magnifications than 30x simply because of the larger depth of field.

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Old Thursday 3rd September 2015, 21:11   #5
mayoayo
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Quote:
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Depth of field depends solely on the magnification.

Hermann
I see..so what causes the shallow field at close distance,is in fact increased magnification ,"macro" effect if you wish....
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Old Friday 4th September 2015, 17:00   #6
sjackal
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Longer focal length generally results in shallower depth of field.
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Old Saturday 5th September 2015, 11:53   #7
Hermann
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Longer focal length generally results in shallower depth of field.
The influence of focal length is negligible in scopes and binoculars. Check one of the textbooks on optics.

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Old Saturday 5th September 2015, 19:36   #8
devans1
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I gave the scope a good workout today and have to say that it gives a fantastic view IMO.

I am not convinced with the depth of field that the 30x eyepiece gives you though. When I was watching birds that were relatively close it wasn't a big deal but when getting on to birds in the middle to far distance I repeatedly struggled to get them in focus, repeatedly focusing past and back again. Maybe I will get used to it in time and I appear to be in the minority regarding this issue.

I would like to try the scope out with the zoom eyepiece or maybe one of the lower mag DS eyepieces to see the difference though.
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Old Saturday 5th September 2015, 20:47   #9
Vespobuteo
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I gave the scope a good workout today and have to say that it gives a fantastic view IMO.

I am not convinced with the depth of field that the 30x eyepiece gives you though. When I was watching birds that were relatively close it wasn't a big deal but when getting on to birds in the middle to far distance I repeatedly struggled to get them in focus, repeatedly focusing past and back again. Maybe I will get used to it in time and I appear to be in the minority regarding this issue.

I would like to try the scope out with the zoom eyepiece or maybe one of the lower mag DS eyepieces to see the difference though.
I owned the EDIII for many years and used the 30x MC wide EP most of the time, the focus wheel is pretty fast and as you say it might be an issue,
but with some training I think you will appreciate the rapid focuser,
and the feel in the Nikon focus wheels I think is top-notch,
(even better than my current scope of another make...)
a helical focuser is always a compromise between speed and accuracy (hmm..I guess all focusers are..)

The nikon zoom is another beast, it's very sharp but FOV is a bit narrow, and not the best with glasses, but could be worth testing it out though, nice to have some extra reach at 60x, or a bigger exit pupil in low light, or the lower 20x mag in warm summer days.

the wide DS eyepieces (24x) will give you better DOF, but also less reach,
but it might suit your type of birding better,

for me the 30x was the most used EP,

Last edited by Vespobuteo : Saturday 5th September 2015 at 20:52.
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Old Saturday 5th September 2015, 22:00   #10
devans1
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Originally Posted by Vespobuteo View Post

the wide DS eyepieces (24x) will give you better DOF, but also less reach,
but it might suit your type of birding better,

for me the 30x was the most used EP,
Thanks for the input vespo, the zoom and the 24x DS are the two I'd like to try. Secondhand fieldscope eyepieces seem pretty few and far between though.
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Old Saturday 5th September 2015, 22:52   #11
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Originally Posted by devans1 View Post
Thanks for the input vespo, the zoom and the 24x DS are the two I'd like to try. Secondhand fieldscope eyepieces seem pretty few and far between though.
check out eBay,
lot of fieldscope gear right now,
but get the MC II zoom, (MC I is not as good)


24x DS:

http://www.ebay.com/itm/Nikon-Fields...item5b02dbf160

the zoom:

http://www.ebay.com/itm/NEW-Nikon-Fi...item3f51947c45

and a used one from US

http://www.ebay.com/itm/Nikon-Fields...item2a57a3e63a

Last edited by Vespobuteo : Saturday 5th September 2015 at 23:01.
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Old Thursday 17th September 2015, 15:42   #12
DiDi
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I recently got a MCII zoom for my IIIED from the wex used section and its great. I only struggle with focusing when its at the long end of the zoom and in poor light, rest of the time its fine.
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Old Thursday 17th September 2015, 16:13   #13
Hermann
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Originally Posted by Vespobuteo View Post
check out eBay,
lot of fieldscope gear right now,
but get the MC II zoom, (MC I is not as good)
I've got both, and the difference is there, but it's by no means great. Slightly better contrast in the MCII, slightly better edges. But you've got to look pretty hard to see the differences.

Hermann
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Old Sunday 27th September 2015, 04:05   #14
sjackal
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I have a MC1 for cheap if you want shoot me an PM.
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