Is aperture still king even during the day?
Posted 10 November 2013 - 03:04 PM
Posted 10 November 2013 - 04:58 PM
My honest answer simply has to be "I'm afraid I don't really know", having never had the pleasure of looking through anything larger than 102mm in the daytime.
It may well be that if viewing something only a short distance away, e.g a bird 50 feet away(when mirage caused by rising heat etc. doesn't play a significant role)a view of that bird with a magnification of around 100x, through a 4mm exit-pupil, provided by a 400mm APO(if such a thing exists!) would blow away all else available.
I can easily imagine there will be some locations, at certain times of day and year, when temperatures and atmospheric conditions are most favourable, where a similar set-up would undoubtedly yield similarly superlative views above and beyond anything currently available.
However, MOST of the time, in MOST locations, for MOST people, "optimum" magnification of objects or scenery from several miles distance is invariably restricted to around 40x, because of the "mirage" or atmospheric "haze".
So, if we stick to a desired exit-pupil of 4mm(my personal favourite), then I would guestimate that a 160mm objective size would probably provide very close to "as good as it is going to get".
Purely speculative, of course, but as I said, this is a very interesting question, which around nine years ago, on this very forum, would almost certainly have attracted a more duly deserving array of responses than it almost certainly, and most sadly, will now.
Posted 10 November 2013 - 06:05 PM
My exit pupil tolerance is about 2 mm. Below that and I find that colours and contrast go out the window fast.
So I guess that means I could probably be happier with a 120 mm scope (or the 107 I already have) than with the 80 mm I'm typically using in the daytime.
Either way I think on most days there won't be any practical difference between a 100mm and 120 mm scope - that's a small difference in aperture anyway. But I have found myself using 138x in my 80mm in daytime and really wishing I had an 8" scope to put the colour back onto the deer I was watching on the next mountain.
The remaining question is, do you want to have the aperture available for those few days when the higher magnification works fine, but knowing that on many days your lugging around a heavier instrument for nothing.
To the OP: since you have a 114mm scope, please use it several times in daytime with and without a 95mm aperture mask, and then please come and tell us what you found.
Posted 11 November 2013 - 01:15 AM
Posted 11 November 2013 - 06:20 AM
I don't think the difference you noticed in sharpness in going from 114 to 120 is related to the aperture. It's either the inherent optical quality of the scopes, or the suitability for fast f/ ratios of the eyepieces you're using.
The Tak 102NSV is only going to be about 2" shorter than the ED120, right?
Posted 11 November 2013 - 12:14 PM
After using the ED120 for a few months now I'd say my max size and weight for a day time scope would be 12 pounds(bare ota) and about 30 inches long. Anything longer then 30 inches doesn't fit in my current backpack and an ota over 12 pounds would probably require my to get a new mount.
Back to the topic at hand. It sounds like one needs to consider more then just aperture but in general the more the aperture the better even when used during the day. At least this is what seemed to be implied from mooreorless's post even though I couldn't get the link to work.
So far I have a hard time seeing a difference at the eye piece between the ED114 and ED120. Besides the increased magnification of the ED120 the only other major difference is the color tone. I have yet to use either of the scopes at dusk or dawn so there might be a bigger difference during these times of day. Videoscoping is where I start to see the differences in the sharpness and clarity between the two but as stated earlier this might have nothing to do with aperture. I'll try and post some pics or videos of the differences I'm getting between the two scopes.
As far as masking the ED114 I actually have an iris in that scope and the more close the iris the sharper the scope gets to a certain point at least but at the cost of color vibrancy and detail. The only problem with this is that I currently have no way to tell how much I am masking the scope with the iris so I don't know at what aperture that I'm getting my best results at. I'll have to do some more experimenting when I get the time. Hopefully I can get a hold of a Tak fs-102nsv soon enough to compare with the other two scope as well.
Posted 11 November 2013 - 12:25 PM
I simply based my 40x "optimum" magnification figure on impressions and results after using the 20-60x zoom lens on my Zeiss 85mm Diascope for around 6 years.
Perhaps the "slightly above 2mm exit-pupil" had as much to do with that as anything else, but there were definitely many days when I felt there was absolutely nothing gained and a little lost by tweaking the zoom up to 50x.
Posted 11 November 2013 - 12:58 PM
In full daylight, an excellent 60 mm. scope gives just as good views as an excellent 100 mm. scope. In daylight, atmospheric heat waves often limit top magnification to 40X or even 20-25X. 60x is considered to be the top useful magnification for diurnal terrestrial use.
Well-heeled forest birders, owlers, and crepuscular birders often haul around 80-100 mm. apochromatic spotting scopes, but I see a lot more 60-80 mm. achromatic scopes used by birders in the field, because of budgetary restraints. It's also likely sheer size and weight limit birders' ability or willingness to haul around a 100 mm. scope and tripod.
Posted 11 November 2013 - 01:31 PM
Posted 12 November 2013 - 10:23 AM
Many birders prefer 30X for most situations .... which does not mean that in those "perfect days" can be reached with good resolution at 50X-60X or some more ....As for the size of the telescope I think there is now a trend towards smaller diameters ..
Posted 17 November 2013 - 02:14 PM
Posted 17 November 2013 - 03:17 PM
Posted 17 November 2013 - 06:30 PM
Did it tolerate that? :-)
Posted 20 November 2013 - 11:35 PM
Posted 21 November 2013 - 10:45 AM
I've been doing a few test with aperture masks on my 114mm scope but I wasn't satisfied with the results. Mainly because masking a scope slows it down and I'd like to compare different apertures with similar focal ratios. So I just bought a Sky 90 to compare with the 114mm scope it should be here next Monday. Both are very fast scopes with the 114 at f/5.3 and the 90 at f/5.6. Comparing these two scopes should help cure my curiosity.
Posted 21 November 2013 - 01:35 PM
Posted 22 November 2013 - 05:53 PM
Posted 28 November 2013 - 09:50 AM
I've only been able to use the Sky90 during the middle of the day and during that time I find I like the Sky90 just a bit better then my Vixen 114. Contrast and sharpness are just a hair better with the Tak and the overall view is just more pleasing to me. So far the only EP used has been a 30mm leitz and a 12mm Ortho so I have yet to push the tak to see how it performs at higher powers. The main test for me and my uses will be to see how the Tak does during dusk and dawn timeframes and how well the Sky90 will do with videoscoping.
Posted 29 November 2013 - 06:02 AM
Posted 29 November 2013 - 11:27 PM
Posted 30 November 2013 - 04:37 AM
Only bad thing is that I can't reach infinity with my modified diagonal with iris and mag switch.
I am quite sure that if the iris is in the diagonal then it is close to the focal plane and would not act as an aperture mask.
As a birder, I think aperture choices are made on the basis of portability rather than maximum possible performance. Some situations allow for high magnifications but hauling around a 120mm refractor and tripod is quite a task..
As far as the typical 60x limit on spotting scopes, there are probably a lot of reasons for that, the need for a more stable mount at higher mags, various optical compromises induced by the more complex light paths and optics as well as the generally poor seeing..
Posted 30 November 2013 - 06:50 AM
Another restriction would be an exit pupil below around 1mm being undesirable for the majority of people and daytime situations.
Posted 30 November 2013 - 11:24 AM