نقل قول:
نوشته اصلی توسط
Chik
متشکرم از جواب . پس این که عمق میدان در دوربین های فول فریم خیلی متفاوت با دوربین های کراپ دار هست چی؟ برای بدست آوردن f واقعی در دوربینهای کراپ دار از چه فرمولی باید استفاده کرد؟ فرض کنیم با یک لنز 200 با f:2.8 روی دوربین فول فریم عکس میگریم. خوب اگه همان لنز را روی دوربین کراپ 1.6 ببندیم جدا از مسئله فاصله کانونی چه میزان در عمق میدن تاثیر میکذاره؟ یعنی در کراپ 1.6 این 2.8 از نظر سخت افزاری به چه عددی تغییر میکنه؟
یک سوال دیگه. اگه ما یک لنز EF-S را روی فول فریم ییندیم چه اتفاقی میافته؟(همیشه برام سوال بوده)
ممنونم
سلام:
در مورد قسمت دوم کاوه عزیز اشاره کرد
در مورد قسمت اول فرمایش شما ( قسمت بولد شده ) هیچ وقت تغییر نمیکند...
نقل قول:
If Gertrude Stein had been a photographer she might have said "f2 is f2 is f2". The maximum aperture of a lens is constant. The f-stop is given by the focal length divided by the aperture size. If you have a lens with a focal length of 100mm and a physical aperture of 50mm, it's an f2 lens and will produce an image with a brightness determined by the fact that it's an f2 lens. Since neither the actual physical focal length nor the actual physical aperture change the when the lens is mounted on a camera, it's always an f2 lens. It doesn't matter if you use it on a full frame camera, an APS-C camera or and 8x10 camera. If it's f2, it's f2. Of course the angle of view that is recorded will be different for different formats and unless the lens was designed for 8x10, if you use it with an 8x10 camera you'll get a tiny image in the middle of a field of black, but the actual image brightness won't change because the lens will always be f2.
For an equivalent field of view, the physical aperture of an EF-S lens designed for an APS-C camera will be smaller than that for a full frame lens, but that's because the focal lengths will be different. It's not actually related to the format of the camera attached to the lens. Thus a 50mm lens on an APS-C camera gives the same field of view as an 80mm lens on a full frame camera and so you can consider them to be "equivalent", though obviously they are in fact different since they have different focal lengths. If they were both f2, then the physical aperture of the 50mm lens would be 25mmm and that of the 80mm lens would be 40mm, so the crop sensor lens would be smaller and have a physically smaller aperture even though they were both f2. This is a point which causes some confusion, but the bottom line is that if you mount a lens marked "50mm f2" on an APS-C crop camera or a full frame camera, it's f2 on both of them and it's 50mm on both of them. The so called "1.6x digital multiplier" is really a factor which affects the field of view which is recorded and which does depend on format size. It does not affect the aperture and it does not affect the true focal length of the lens.
Crop Sensor (APS-C) Cameras and Lens Confusion
کد:
http://www.bobatkins.com/photography/tutorials/crop_sensor_cameras_and_lenses.html
کنترل عمق میدان روی دوربین های فول فریم بهتر است ( این بهتر بودن الزاما به معنای عمق میدان بیشتر نیست ) بنظرم برای دیافراگم معادل ( که در این مثال ممکن است بیشتر بدرد نورسنجی بخورد ) روی دوربین های کراپ هیچ وقت دنبال آن نگردید چون ممکن است با اعداد صدم و هزارم روبرو باشید. و تاثیر آن بسیار ناچیز.
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