Re: Televue 85
- From: "Alan French" <adfrenchremoveallthis@xxxxxxxxxxxx>
- Date: Sun, 25 Sep 2005 19:09:02 GMT
<rmorea@xxxxxxxxxxx> wrote in message
news:1127669117.041401.307140@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Hi!
>
> I originally posted this on sci.astro.amateur, but it may also apply
> here since I think this scope is sometimes used by birders, albiet it
> is considered a bit too big for easy mobility... If anyone has
> comments, I am interested.
>
> --------------------------------
>
> I just bought a new Televue 85. Just for the heck of it, I attempted
> the
> dollar bill test as explained by the Better View Desired webpage.
>
> Basically the test works like this. Tape a $1 bill to a fence (or
> whatever) with the back side facing outward. Set your scope up to view
> it. Notice with your naked eye that the shading under the word ONE on
> the back of the dollar bill is actually a series of closely spaced
> lines. For me, I can distinguish individual lines from about 18 inches
> or so.
>
> At 50x, which is a 12mm Radian, I can distinguish these lines from
> about 45 feet. Now, this would seem quite fine to me, and I am
> basically satisfied. But it is less than what was reported for the
> Better Views Desired reference scope, a Nikon 78mm Fieldscope, which
> resolved the lines from about 75 feet at 56x.
>
> Reasons could be anything from the reviewer has better eyes, he is a
> better observer, he used a newer dollar bill, his standard for *seeing*
> the lines is different from mine, the difference between 50x and 56x,
> or his scope is better than mine.
>
> Strangely, it doesn't bother me so much if I have worse eyes but a
> worse scope would be terrible! OK, so thats not logical. Has anyone
> else tried this test with a TV-85? Care to share the results?
Craig,
I have a couple of comments, having used a 90mm APO for birding and
astronomy for some time. I am also familiar with and have used the TV85
(have not seen the Nikon however).
First of all, it is very hard to make comparions separated in time and
space, and done by different observers. Your eyes may well differ from
those of Stephen Ingraham. You are, however, getting up to magnifications
where the eye does not play a big role.
A big problem with such tests is that you have neither the proper controls
over illumination or target contrast. Better illumination would generally
result in a better result, as would a higher contrast target. As you
mention - the age and wear of the bill would change the contrast of the
printing on it.
Deciding when lines are resolved, which you also mention, is a serious
problem. In testing using resolution targets some folks suggest lines
should be considered perfectly resolved when they are both well defined and
show no hint of fuzziness. Most folks look to see when they can simply tell
there are two lines - and this can be a tough call.
If you are happy with the scope, I wouldn't fret over this. I thoroughly
enjoy the views through my little 90mm APO.
Clear skies, Alan
.
- References:
- Televue 85
- From: rmorea
- Televue 85
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