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Thread: 100mm + 1.6x Crop factor not = 160mm

  1. #1
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    Question 100mm + 1.6x Crop factor not = 160mm

    Hi,

    Just like to clarify this:

    If you have a 100mm lens, and add on to a DSLR with 1.6x crop factor, your effective focal length is NOT 160mm but a cropped 100mm picture only right? So if its like this we can still abide to the 1/focal length shutter speed right?

    It's made me wonder if this is true or not because here and other forums people keep saying that with a 1.6x or 1.3x crop factor need to shoot at 1/1.6x focal length or 1/1.3x focal length...

    And also your effective focal length is still 100mm, not 160mm because the magnification isn't there compared to a say 160mm lens right?

    Someone correct me...
    The equipment can only bring you so far - the rest of the photographic journey is done by you.

  2. #2

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    That is correct. You get a field of view equivalent to a 160mm lens, but the focal length is still 100mm. The 1/focal length rule still holds true, and you don't x1.6 for that either

  3. #3

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    No.
    Yes, it's cropped.
    No, it's not 1/100s for a 100mm lens, but 1/160s.
    Because you'll be enlarging the cropped area, thus all shakes will be enlarged also.

  4. #4
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    Quote Originally Posted by AReality
    No.
    Yes, it's cropped.
    No, it's not 1/100s for a 100mm lens, but 1/160s.
    Because you'll be enlarging the cropped area, thus all shakes will be enlarged also.
    But isn't it like taking a piece of fill, covering parts with black tape to make it 1.6x Crop factor and shoot? Isn't it the same?

    Now you really got me confused...
    The equipment can only bring you so far - the rest of the photographic journey is done by you.

  5. #5
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    Quote Originally Posted by AReality
    No.
    Yes, it's cropped.
    No, it's not 1/100s for a 100mm lens, but 1/160s.
    Because you'll be enlarging the cropped area, thus all shakes will be enlarged also.
    Dun really agree... If I shoot with a FF body at 100mm, then I crop to 1.6, does it mean that I need to take into consideration of the possible cropping that I am going to do, i.e in this case at 1/160, instead of normally 1/100???

    This something that really puzzled me...

  6. #6

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    1/focal length refers to the physical focal length, 100mm in this example. The cropped field of view of 160mm is still taken physically on a 100mm lens, thus my reasoning is that it shouldn't change the 1/focal length rule, right?

  7. #7
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    If that is the case, can I shoot 1/70sec with a prosumer camera which has actual focal lenght of 6-70mm lens ( 35mm equ = 35-420mm ) and get sharp picture ? Don't think so, why would the maker provide IS for a 6-70mm lens ?

    I'm not able to get sharp picture when I shoot 1/70sec without IS.

    The crop factor still applies, 1 / focal-lenght x 1.6

    Read here :http://www.photo.net/bboard/q-and-a-...?msg_id=006fBv

  8. #8

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    Quote Originally Posted by AReality
    No.
    Yes, it's cropped.
    No, it's not 1/100s for a 100mm lens, but 1/160s.
    Because you'll be enlarging the cropped area, thus all shakes will be enlarged also.
    i dun think its right, if your theroy of 'enlarging the cropped area' is true, than lots of ppl are going to complaint abt DSLR with smaller than 35mm field of view sensors makes all lenses slower by a few stops.

    anyway i have used the 1.6 crops cameras for more than a year now, and in the real field test for all angles from 17-200mm i never have a problem with blurness when i follow the 1x orginal focal length rule not with the crop factor taken to account. You still need proper techinque for any camera, even with IS lenses.

    24mm 1/25- 1/30
    35mm 1/30- 1/40
    50mm 1/50-1/60
    85mm 1/80
    105mm 1/100
    135mm 1/125- 160
    200mm 1/200

    still sharp enough all the time with proper shooting techniques!
    Last edited by Belle&Sebastain; 9th October 2004 at 12:18 AM.

  9. #9

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    Full frame Sensor size :36mm x 24mm
    1.6x Sensor size : 22.5mm x 15mm

    The fact is the image captured is cropped.
    So when u print it on 4R (6"x4"), you're effectively enlarging the 1.6x more than the full frame.

    Students, so far so clear?

  10. #10

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    Just look thru a full-frame and a APS-C sized viewfinder, with both cameras attached with maybe a 300mm lens. Then shake. The APS-C sized viewfinder will show more drastic shake as it is magnified.

  11. #11

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    Quote Originally Posted by AReality
    Full frame Sensor size :36mm x 24mm
    1.6x Sensor size : 22.5mm x 15mm

    The fact is the image captured is cropped.
    So when u print it on 4R (6"x4"), you're effectively enlarging the 1.6x more than the full frame.

    Students, so far so clear?
    print, not shooting time.
    if i shoot anything and crop later, i need not not additional shutter speed for the crop out picture right?

  12. #12

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    Since you're enlarging your image more than a FF sensor, all handshakes, blurs, are also magnified.

  13. #13

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    Quote Originally Posted by Belle&Sebastain
    anyway i have used the 1.6 crops cameras for more than a year now, and in the real field test for all angles from 17-200mm i never have a problem with blurness when i follow the 1x orginal focal length rule not with the crop factor taken to account. You still need proper techinque for any camera, even with IS lenses.

    24mm 1/25- 1/30
    35mm 1/30- 1/40
    50mm 1/50-1/60
    85mm 1/80
    105mm 1/100
    135mm 1/125- 160
    200mm 1/200

    still sharp enough all the time with proper shooting techniques!
    Have you tried it in comparision with a full-frame/film camera of a comparable class?

    1/focal length rule is just a guide, you being able to handhold at a particular speed has no relevance on the issue unless you are certain that you get identical results on a full-frame.

  14. #14

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    Quote Originally Posted by Zerstorer
    Have you tried it in comparision with a full-frame/film camera of a comparable class?

    1/focal length rule is just a guide, you being able to handhold at a particular speed has no relevance on the issue unless you are certain that you get identical results on a full-frame.
    yes i do..... film slr, i practice the 1 x real focal length on all my slr (FM2) onwards 2000 since day 1, i break the rules when possible (IS or low light) but mainly if i shoot with the focal lengths with the shutter speeds i mention above i get sharp pictures until today with dslr.

    for myself only if will drive me nuts to have to use 1/80 instead of 1/60 to normaly shoot with a 50mm lens. that's 1/3 stop less.

    in theory what you guys say maybe right about the 1/focal length rule x 1.6 on dslr camera but in practise i dun follow, until today that has not caused any problems for my pictures
    Last edited by Belle&Sebastain; 9th October 2004 at 01:12 AM.

  15. #15

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    Quote Originally Posted by Belle&Sebastain
    yes i do..... film slr
    How was the comparison made? Scanned film or prints? If scanned, were they viewed at the same resolution?

    Personally I find that the crop factor does magnify shake. I can shoot at significantly lower speeds on film without noticable shake, even when viewing high resolution scans.

    Easiest illustration would be digicams, they require far higher shutter speeds than their physical focal lengths indicate.

  16. #16

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    Quote Originally Posted by Belle&Sebastain
    yes i do..... film slr, i practice the 1 x real focal length on all my slr (FM2) onwards 2000 since day 1, i break the rules when possible (IS or low light) but mainly if i shoot with the focal lengths with the shutter speeds i mention above i get sharp pictures until today with dslr.

    in theory what you guys say maybe right about the 1/focal length rule x 1.6 on dslr camera but in practise i dun follow, until today that has not caused any problems for my pictures
    That's where we differ. I don't follow any rules, I just find my personal handholding limit for each camera lens combination that I have and then it becomes a personal guide.

    Perhaps you could have taken shots at even lower shutter speeds with your FM2?

    for myself only if will drive me nuts to have to use 1/80 instead of 1/60 to normaly shoot with a 50mm lens. that's 1/3 stop less.
    It's not that bad isn't it? Take note that your effective field of view is basically that of a 80mm or so, so in essence you have not lost anything.

    Or rather, that extra focal length was not gained without a cost.
    Last edited by Zerstorer; 9th October 2004 at 01:23 AM.

  17. #17
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    Personally, I'm with AReality on this one. I think this crop not multiplier issue is greatly overstated; it is certainly true, but I think the practical differences are few and far between and relatively speaking fairly insignificant.

    With regards to the issue at hand, the increased cropping effect means that the errors get magnified too. Same thing if you shot a full frame image, cropped it to the smaller sensor size, and then compared them. The shots should be identical.

    And Belle&Sebastain, please no offence meant just because I hold a different viewpoint to your good self, and I hope you don't take offence and start complaining about me again.

  18. #18

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    Quote Originally Posted by Jed

    And Belle&Sebastain, please no offence meant just because I hold a different viewpoint to your good self, and I hope you don't take offence and start complaining about me again.
    no offence Jed, we all have our viewpoints, you made your valid points.

    i will not complain about you again, if ever.

  19. #19

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    It's all about magnification. If you are going to use full 100% pixels, better follow the 1/160s route.

    Meanwhile, just this Wed, i published a full 6MP frame resized for web (600 pixels tall) on the intranet, it was taken at 1/5s at 75mm (112.5 effective) at 2.8, ISO 1600, handheld but braced. 100% crops would not have made it.

    This is also to say that there won't be any difference in the end result even if i shot at 1500x1000 resolution.

  20. #20

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    OT abit...

    i assume perspective does not change on a x1.6 right?

    eg.we all know that a 100mm used on a film slr is just nice for portraits.
    but on a dslr, if i use a 60mm (x1.6=96mm) will i get the same nice portrait, perspective wise?
    or must i still use the 100mm but stand way back to shoot the portrait?

    thanks.
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