Swampy Sam
Well-known member
Just wondering what you guys thought? Smaller aperture show more details than larger aperture on hot days?
I asked a similar question last year.Just wondering what you guys thought? Smaller aperture show more details than larger aperture on hot days?
"In hindsight I wish I would have placed a mask on the larger scope's objective."
That's a perfect summary.Since smaller scopes have usually been easier to manufacture to stricter quality standards, they used to generally have lower aberrations than bigger scopes and would perform better, or at least not degrade as much relatively speaking, when seeing was poor. In heat haze, a scope with lots of aberrations (spherical aberration, coma, astigmatism) will show a significantly worse image and be harder to focus than a scope with low aberrations, irrespective of whether they are the same size or same or different makes or models.
How did you do the actual testing? and, did you just go to a shop and run the gamut of their scopes?When I went through the process of acquiring my previous "reference scope," a Nikon Fieldscope ED 82 A, one of my testing methods was to compare specimen directly against a known super-low-aberration specimen of a Fieldscope ED 78. Not until I found a sample with even more close to perfect optics, did it out-perform the smaller scope in heat-haze.
I think this is spot on.Besides all said I add 2 details:
- usually smaller scopes have less minimum magnifications so looking better within hot days, due to lower magnifications;
I dont think depth of field really comes into play much here as thermal waves are more of a lateral refraction problem rather than a light path difference from the refractive index (as evidenced by the fact that similar things are seen in astronomy which is certainly all done beyond the hyperfocal distance). Also objective diameter does not play a big role in DOF as has been discussed ad nauseam in the binocular forum.
- being all equal, smaller scopes work better since have higher depth of field, so are less affected by thermal waves.
Did you duplicate the test in good seeing conditions? Is it possible you are just increasing the resolution by stopping down your scope (ie increasing the f/ of the scope) or using only the best central part of your eye by reducing the size of the exit pupil?
- Within my search for different solutions, I tested a 80mm triplet apo-refractor that was used for bird dslr photography and had a manual aperture regulation (with a circular guillotine, as on tele-lenses...), and visual image quality and resolution increased reducing aperture within bad seeing conditions!