odd binocular specifications?

[Astronomist]

A few months ago I got a pair of 60mm tasco binoculars for free at a car boot sale, the seller told me they were 'seeing double' and I could have them if I could fix them. I just got around to recollimating  them a  few days ago, and they are actually surprisingly good for what they are. 

However, on the back they say '90x60'. If my understanding is correct this should mean 60mm aperture and 90x magnification, which they are not.

please could someone help shed light on this

Edited May 11, 2023 by Astronomist

[Callred1975]

In my opinion, they are most likely knockoffs.  I’ve seen similar binos with outrageous numbers like that on them before (100x100, 200x200, etc).

Hope that helps.

[Peter Drew]

I tend to agree.  Interesting coatings.      🙂

[bosun21]

I have never seen anything like this designation on binoculars. It looks like a counterfeit binocular IMO.

[Louis D]

It seems odd to make a knockoff of a Tasco binocular rather than a knockoff of a premium brand.  For reference, what sort of counterfeiter would make knockoffs of purses costing under $100?  The whole point of counterfeiting is to make huge profit margins, and that isn't going to happen making knockoffs of low-end products like Tasco.

My guess is that the same factory that makes Tasco had blems or extra product produced after they finished a run of official Tasco or similar binoculars and sold them as a lot to a jobber to recoup some of their losses.  The jobber may have had the printing added after receiving the lot.  That would explain why the collimation was off, assuming it wasn't due to mishandling by the original purchaser.

[bosun21]

1 hour ago, Louis D said:

It seems odd to make a knockoff of a Tasco binocular rather than a knockoff of a premium brand.  For reference, what sort of counterfeiter would make knockoffs of purses costing under $100?  The whole point of counterfeiting is to make huge profit margins, and that isn't going to happen making knockoffs of low-end products like Tasco.

My guess is that the same factory that makes Tasco had blems or extra product produced after they finished a run of official Tasco or similar binoculars and sold them as a lot to a jobber to recoup some of their losses.  The jobber may have had the printing added after receiving the lot.  That would explain why the collimation was off, assuming it wasn't due to mishandling by the original purchaser.

Some of the older Tasco binoculars were made by Vixen and were not that cheap. If that’s not the case then what is the answer to the strange designation?

[Astronomist]

Thanks for your replies, so the numbers are most likely blatant lies then. Interesting you should mention the coatings @Peter Drew, I was only just thinking  they might make good ERFs... 

[DaveL59]

Likely it's square-mm of the eyepiece lenses, probably the sum of both too, just to get a nice big number to draw in the unsuspecting.

[Astronomist]

it has 20mm eye lenses, so the area in mm of each of them is 314mm squared...

[Louis D]

Here's a Tasco 60x35 on Mercari.  What's the 60 supposed to mean?

Is the 8° the apparent or true field of view?  At 60x, an 8° TFOV would be impossible.  An 8° AFOV would be miserable to use.

If I'm doing my trig correctly, a 76 meter field at 3000 meters amounts to a 1.45° TFOV, not 8° TFOV.  Assuming a 50° AFOV, that would amount to 34x, not 60x.

[Astronomist]

21 hours ago, Louis D said:

Is the 8° the apparent or true field of view?

I can only assume it must be true field, since 8^o AFOV would as you say be like looking through a pinhole. I suppose this is another pair of rip off binos like mine. In any case 60x mag at 35mm aperture would be very dim, blurry and impossible to hand hold.

<edit> I fount  these on eBay that seem to be the same as the aforementioned ones but advertising a much more realistic 8x21

Edited May 11, 2023 by Astronomist

[Louis D]

I had my doubts about the 35 meaning 35mm objectives as well.  I figured it was either an 8x21 or 10x25.  So, basically, they got absolutely nothing right with their numbers on those bins, either.

[Astronomist]

It seems these cheap manufacturers just make it all up as they go along, i cant see Leica or Zeiss doing that.

[Louis D]

The original bins appear to be 10x50 and very similar to these ebay and amazon listings.

Apparently, the factory would print whatever you wanted on them for the right price.

[Franklin]

Glad they didn't cost you anything. 

[Paz]

The red coating on the front is what they put on lower quality binoculars to make the CA less obvious in the views, I think by by chopping out the red end. The first astronomy kit I ever had was a pair of binoculars of this nature I received as a present. I thought they were epic at the time, I saw Jupiter and the 4 moons and was amazed! These binoculars are now in bits having been dismantled in the furtherance of scientific discovery.

You could work out the specifications fairly accurately as follows...

Measure the diameter of the objective lense directly (A) (but note this assumes no internal field stops - they are another trick to improve the views through a poor optic)

Measure the diameter of the exit pupil (B).

Then A/B = magnification (M).

Then the the normal specification for the binoculars would be M x A.

You can find the exit pupil by pointing the binoculars up at the clear blue sky (but not near the sun) and putting some paper or tracing paper behind the eyepiece where your eye would be. You will see a circle of light on it. Move the paper in and out until the circle is sharp and focused - that is the right spot to measure its diameter. If for example it is 10x magnification then the exit pupil would be 6mm if the objective was 60mm etc..

Edited May 12, 2023 by Paz

[F15Rules]

And very likely too the 60mm aperture isn't really 60mm, probably stopped down a fair bit.

Still, you got them for nothing!😊👍

Dave

[doublevodka]

A quick Google image search dug up this old thread with some very similar-looking bins, so I suspect like the ones in that thread they are around 12x60

For free they are a bargain in my book 👍

[Astronomist]

9 hours ago, Paz said:

The red coating on the front is what they put on lower quality binoculars to make the CA less obvious in the views, I think by by chopping out the red end

very interesting @Paz, i never knew that was why those coatings where used, I think they need it as the aperture is 58.5mm at around f4.1 with no internal stops, even with weird coatings it is a little colourful at the edges. I have measured the exit pupil to be 6mm, so magnification is around 10x.

[Astrobits]

In order to get the unsuspecting customer to purchase cheap bins the manufacturers/suppliers often quote AREA magnification not the usual linear to make them appear super powerful. So technically they are not exactly dishonest. 10 x 50 bins have an area mag of 100 so could be quoted as 100 x 50. For those quoted as 90 x 60 just take the square root of 90 for the normal mag,= 9.5 approx, not abnormal for 60mm bins. The square root of 60 is 7.7 so those are probably similar to other 8 x 35's.

Nigel