Would this be a waste of money? (1 Viewer)

[Stino]

Hi All,
I usually go birding with Kowa 6.5x32 binoculars which I love for their light weight and large field of view. I sometimes feel the need for a bit more magnification than 6.5x. I want it to be very lightweight for hiking and I could place whatever I get on a light monopod that I already have and can carry on my belt. I came across the 12x55 GoSky monocular on Amazon. It has good reviews from the general public, but I am wondering if for birding it is just going to be a waste of money? I am not looking for Leica/Zeiss performance at this price point of course. Just something decent that won't break after a few weeks of use. Here is the link to it: LINK . What do you think?

 

[jring]

Hi,

ok, let me start with a general remark and that is 12x is a fairly difficult intermediate magnification which will be too high to hold steady even for those who habitually use 10x bins and on the other hand why bother with that low magnification on a tripod...

Let's have a look at the numbers for the 12x55mm mono:

• Prism: BAK4
• Field of view: 325ft/1000yds
• Field Angle: 6.5 Degrees
• Minimun Focus Distance: 2.5mm
• Exit Pupil: 4.2mm
• Exit Relief: 18mm
• Dimensions(in): 2.19(L)x3.25(W)x5.45(H) Weight: 15.85oz

55mm aperture divided by 12x gives an exit pupil of 4.6mm - either the real magnification is 13x or the true aperture is 50mm... my money is on the latter solution.

True field in ft at 1000 yd = true field in degrees x 52.5 = 6.5 x 52.5 = 341 ft/1000yds... close but no cigar.

Apparent field of view in degrees is roughly true field of view in degrees times magnification resulting in 6.5x12 = 78 degree... a very respectable value for an ultra wide angle astro EP...

Unfortunately there is a little joke about eyepieces among astro nerds going like this:

wide apparent field of view, good eye relief, compact eyepiece - choose any two!

The reason for this is that some basic geometry shows that the eyelens diameter a, exit pupil size p, the eye relief r and the apparent field of view alpha are roughly connected as follows - see the following link for some drawings - http://www.mira.org/ascc/pages/lectures/fabform.htm

a - p / r = 2 tan (alpha / 2)

if we solve for the eyelens diameter a we get

a = 2 * r * tan (alpha / 2) + p = 2 * 18mm * tan (78/2) + 4.2mm = 33.4mm

which is a value befitting an ultra wide angle astro EP... for example my APM 12.5mm 84 deg afov EP has 35mm or so. The only problem is that this eyepiece weights 550g which is a bit more than the 15.85oz or 450g stated for the whole 12x55 mono...
It is also 120mm long just for the eyepiece as compared to the 5.45" or 138mm for stated for the monocular...

Go figure...

Joachim

 

[Stino]

Hi,

ok, let me start with a general remark and that is 12x is a fairly difficult intermediate magnification which will be too high to hold steady even for those who habitually use 10x bins and on the other hand why bother with that low magnification on a tripod...

Let's have a look at the numbers for the 12x55mm mono:

• Prism: BAK4
• Field of view: 325ft/1000yds
• Field Angle: 6.5 Degrees
• Minimun Focus Distance: 2.5mm
• Exit Pupil: 4.2mm
• Exit Relief: 18mm
• Dimensions(in): 2.19(L)x3.25(W)x5.45(H) Weight: 15.85oz

55mm aperture divided by 12x gives an exit pupil of 4.6mm - either the real magnification is 13x or the true aperture is 50mm... my money is on the latter solution.

True field in ft at 1000 yd = true field in degrees x 52.5 = 6.5 x 52.5 = 341 ft/1000yds... close but no cigar.

Apparent field of view in degrees is roughly true field of view in degrees times magnification resulting in 6.5x12 = 78 degree... a very respectable value for an ultra wide angle astro EP...

Unfortunately there is a little joke about eyepieces among astro nerds going like this:

wide apparent field of view, good eye relief, compact eyepiece - choose any two!

The reason for this is that some basic geometry shows that the eyelens diameter a, exit pupil size p, the eye relief r and the apparent field of view alpha are roughly connected as follows - see the following link for some drawings - http://www.mira.org/ascc/pages/lectures/fabform.htm

a - p / r = 2 tan (alpha / 2)

if we solve for the eyelens diameter a we get

a = 2 * r * tan (alpha / 2) + p = 2 * 18mm * tan (78/2) + 4.2mm = 33.4mm

which is a value befitting an ultra wide angle astro EP... for example my APM 12.5mm 84 deg afov EP has 35mm or so. The only problem is that this eyepiece weights 550g which is a bit more than the 15.85oz or 450g stated for the whole 12x55 mono...
It is also 120mm long just for the eyepiece as compared to the 5.45" or 138mm for stated for the monocular...

Go figure...

Joachim

Thank you for all that info Joachim! I am also considering the Leupold 10-20x40 scope. This is much more expensive, but probably more reliable.
I have a kowa 60mm scope with tripod, but I often don't feel like carrying it. Hence my search for something small that would work on my monopod.

 

[jring]

Thank you for all that info Joachim! I am also considering the Leupold 10-20x40 scope. This is much more expensive, but probably more reliable.
I have a kowa 60mm scope with tripod, but I often don't feel like carrying it. Hence my search for something small that would work on my monopod.

Hi,

The Leupold is probably less of a fake than that Amazon special, but still the magnification range is in that awkward space between hand-held and with support.

Kowa 501 or 502 then maybe? Same weight as the others, a more useful 20-40x50 format and price about halfway between the other two... The example I looked trough managed to impress me.

Joachim

 

[Stino]

Hi,

The Leupold is probably less of a fake than that Amazon special, but still the magnification range is in that awkward space between hand-held and with support.

Kowa 501 or 502 then maybe? Same weight as the others, a more useful 20-40x50 format and price about halfway between the other two... The example I looked trough managed to impress me.

Joachim

I'm worried that 20 to 40x will be too shaky for a monopod?

 

[jring]

Can't say, don't have a monopod... but Nikon ED50 with 27x seems to be popular for that, so cannot be too bad...

Joachim

 

[KC Foggin]

And I'm just going to jump in here and wish you a warm welcome to you from those of us on staff here at BirdForum

We're glad you found us and please join in wherever you like

 

[dries1]

Stino,

I would save your money, since getting a good sample is in all likelihood 50/50.

Andy W.

 

[Binastro]

I have 10x,12x,15x and 20x50 Chinese monoculars.

All have stiction in the focus.

They are available in at least eight different brand names, probably much more.

Optically they are O.K. but not brilliant.

One thing they have in common is over the top advert claims.

I don't know if the one linked here is basically the same or more upmarket.

Perhaps an image stabilized monocular might suit.

Or a Canon 10x30 Mk2 IS binocular.

Regards,
B

 

[Stino]

I thought I should give an update on what I ended up doing. I decided not to buy a monocular. Instead, right after my posts here I came across a 20x widefield eyepiece on ebay for my kowa tsn 603 telescope. I got that and tried it on my light weight Polaroid monopod with manfrotto 234 head. 20x is reasonably stable I found so far. A little bit of shakes, but manageable. And the whole thing (60mm telescope, head and monopod) is so light that I don't mind bringing it with me all the time. The scope was originally on a heavy tripod and I always left it at home because of that. So problem solved!