• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Spotting Scope Resolution Chart Comparison (1 Viewer)

yakyakgoose

Well-known member
I came across a review that included the chart attached above. I specifically am interested in where the Vortex Razor 65 HD was ranked in the resolution chart. If you notice, the 65 ranked only a few steps behind the ATX and Kowa 80+mm scopes. The Nikon 50ed came further back, I'm assuming due to the much smaller objective.

My question is can we assume that the Razor 85 (not the 65) would resolve closer if not the same as the ATX and Kowa? I would think it would have to be at least a couple steps better than the 65.
 

Attachments

  • targetresults.jpg
    targetresults.jpg
    72.3 KB · Views: 308
Predictions like that don't work in the real world because different specimens of the same scope have a wide range of resolution measurements running from lemons to cherries.

If we accept the measurements in this review, then none of these scope units was very good. Below are their resolution measurements converted to arc seconds and a number that shows how close they are to diffraction limited (resolution in arc seconds multiplied by the diameter of the objective lens in millimeters). A diffraction limited scope will be about 116/Diameter when using a line pair chart like the USAF 1951. The higher the number the worse the optics. I wouldn't buy an expensive scope unless it resolved around 120/D. I've measured Swaro ATX and Kowa 883s at around 120/D. I would consider 125-135/D mediocre and anything much above that a lemon.

Nikon ED50 - 2.8", 140/D
Vortex Razor 65 - 2.25". 146/D
Swarovski ATS80HD - 1.79", 143/D
Swarovski ATX85 - 1.59, 135/D
Kowa TSN-884 - 1.59", 140/D
 
Last edited:
Adding to what Henry says, the review resolution tests were conducted at a fixed 50 yard distance. When distance is kept fixed, the steps between elements in the chart are nearly 17%, which makes meaningful comparisons between scopes of nearly similar apertures impossible. Additionally, any atmospheric disturbance will introduce a random error which is exceedingly difficult to control for. 50 yds. likely means outdoors, which likely means atmospheric disturbance did influence the results.

Resolution chart testing is very valuable, but numerical results unfortunately do not tell us as much as we'd like them to. Carefully conducted tests can be very accurate, even ones done outside of a lab, but even then they only give accurate information about the particular scope specimen being tested, as Henry pointed out.

Kimmo
 
Hi Kimmo,

Resolution chart testing is very valuable, but numerical results unfortunately do not tell us as much as we'd like them to. Carefully conducted tests can be very accurate, even ones done outside of a lab, but even then they only give accurate information about the particular scope specimen being tested, as Henry pointed out.

I wonder if there is a description of the test procedure available somewhere on this forum. I found Henry's explanation quite interesting, and am idly wondering now how difficult it would be to test my optics to see how good they are (or if I don't manage to get that much accuracy, at least to confirm that they are not total lemons ;-)

Regards,

Henning
 
I agree with Kimmo. I sometimes use an outdoor setup of about 30 yards, with the target and the scopes placed well above a grass lawn. I make certain the the air is steady enough by including a diffraction limited reference scope. As Kimmo pointed out, because of the large gaps between elements, a really accurate measurement with the USAF 1951 requires tweaking the distance of each scope to arrive at a similar "just barely resolved" result for each.
 
Hi Kimmo,



I wonder if there is a description of the test procedure available somewhere on this forum. I found Henry's explanation quite interesting, and am idly wondering now how difficult it would be to test my optics to see how good they are (or if I don't manage to get that much accuracy, at least to confirm that they are not total lemons ;-)

Regards,

Henning

I heartily concur -- I'd love to test how good my scope is compare to an expectation of 120/D
 
Did they just use maximum zoom on the standard eyepiece? If so, that would give an average estimate for the tester's visual acuity of 20/16 with a best result at 20/15 and tell you very little about the scopes optical resolution.

David
 
No not yet, I got my hands on one to check it out through a local hunting organisation and was impressed. Currently dealing with FedEx and wherever the heck they dropped it off at :/
 
So I found it.....in my apartment office's clubhouse refrigerator!

It had been packaged in some kind of turkey box so the apartment thought it was a food package and stuck it in the fridge.

Sometimes I go down there to raid any leftover beer that's been left in there, imagine my surprise when next to the beer was a box with my apartment number written on the side. Beer and an ice cold scope...thats a good day!
 
Last edited:
Warning! This thread is more than 6 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Users who are viewing this thread

Back
Top