henry link
Well-known member
The Brunton ICON 25-50x 80mm scope I ordered from Botach.com arrived yesterday. The foam lined Brunton scope box had simply been wrapped in a plastic shipping bag and there was no Botach paperwork included. Fortunately, I haven’t detected any signs of damage.
Weather is poor here, so it will be Monday before I can really start my normal outdoor tests. Here are a few initial impressions for those who are thinking of moving quickly while these are still available for $599.
Normally indoor tests at 30 feet would be good enough to reach conclusions about resolution and aberrations, but this scope has an odd behavior at close range. Many scopes show somewhat higher spherical aberration at close distance because the spherical correction is designed to be optimum at infinity focus, but I’ve never seen SA increase as dramatically at close focus as it does in this scope. It’s unacceptable (about ½ wave) at 30’ and gets worse at the closest focusing distance of 15’. I haven’t yet conducted a proper star-test at long distance, but I can see from comparing it to other scopes looking casually at distant objects from my deck that the image improves considerably at distances above 100’. This behavior might be explained by a unique objective design. There is a fixed triplet up front, but it is combined with a positive focusing doublet. Every other scope I’ve seen with a focusing lens has used a negative doublet.
On the plus side, longitudinal chromatic aberration at any distance is extremely well corrected, well enough for me to suspect that the “SD” glass is probably one of the Fluorite equivalents, like Ohara FPL-53. But, on the other hand the 25-50x eyepiece is afflicted with a large dose of lateral CA, fortunately not impinging on the center of the field, but quite vivid on high contrast edges by about 1/3 of the way to the edge.
I can say at this point that the eyepiece does have a nice wide apparent field, about 55º at 25x and close to 80º at 50x. Off axis sharpness is adequate, but not impressive. The eye relief is quite consistent over the zoom range, about 20mm from the glass, 16mm from the eyecup rim.
I’ll post in more detail later (which might include some revisions to these initial impressions), but for those who are thinking of buying one from Botach I would say that this is certainly no $4000 scope, with the possible exception of longitudinal CA, which is very well corrected. While I've seen specimens of alpha scopes that were worse than this one at long distances, I think its real optical competition would be Vortex, Zen-ray, etc. at about two to three times the $599 price. I think if you get a good one and it survives shipment from Botach it will hold its own very well in that company, at least at distances beyond 100'.
Weather is poor here, so it will be Monday before I can really start my normal outdoor tests. Here are a few initial impressions for those who are thinking of moving quickly while these are still available for $599.
Normally indoor tests at 30 feet would be good enough to reach conclusions about resolution and aberrations, but this scope has an odd behavior at close range. Many scopes show somewhat higher spherical aberration at close distance because the spherical correction is designed to be optimum at infinity focus, but I’ve never seen SA increase as dramatically at close focus as it does in this scope. It’s unacceptable (about ½ wave) at 30’ and gets worse at the closest focusing distance of 15’. I haven’t yet conducted a proper star-test at long distance, but I can see from comparing it to other scopes looking casually at distant objects from my deck that the image improves considerably at distances above 100’. This behavior might be explained by a unique objective design. There is a fixed triplet up front, but it is combined with a positive focusing doublet. Every other scope I’ve seen with a focusing lens has used a negative doublet.
On the plus side, longitudinal chromatic aberration at any distance is extremely well corrected, well enough for me to suspect that the “SD” glass is probably one of the Fluorite equivalents, like Ohara FPL-53. But, on the other hand the 25-50x eyepiece is afflicted with a large dose of lateral CA, fortunately not impinging on the center of the field, but quite vivid on high contrast edges by about 1/3 of the way to the edge.
I can say at this point that the eyepiece does have a nice wide apparent field, about 55º at 25x and close to 80º at 50x. Off axis sharpness is adequate, but not impressive. The eye relief is quite consistent over the zoom range, about 20mm from the glass, 16mm from the eyecup rim.
I’ll post in more detail later (which might include some revisions to these initial impressions), but for those who are thinking of buying one from Botach I would say that this is certainly no $4000 scope, with the possible exception of longitudinal CA, which is very well corrected. While I've seen specimens of alpha scopes that were worse than this one at long distances, I think its real optical competition would be Vortex, Zen-ray, etc. at about two to three times the $599 price. I think if you get a good one and it survives shipment from Botach it will hold its own very well in that company, at least at distances beyond 100'.
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