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A little confused about focal length, m4/3, and adapters..

Discussion in 'Adapted Lenses' started by jpaek, Mar 9, 2010.

  1. jpaek

    jpaek Mu-43 Rookie

    11
    Mar 9, 2010
    Canada
    I've read up quite a bit about m4/3rds but I'm still a little confused regarding focal length and crop factor...

    So.. my sources are telling me that m4/3rds have a crop factor of about 2 relative to 35mm sensors. That leads to focal lengths being doubled??? What does that mean? So.. if I'm using a 14mm lens, its an equivalent of using a 28mm lens on a 35mm??

    I'm all interested in this because I'm really looking for a wide-angle lens to use with my E-P1. If I want a 20mm lens.. should I be looking for a 10mm lens then??

    Also... does the use of adapters further increase the focal lengths???? For example, if I use an adapter to use a 28mm Nikon lens.. would it be 56mm? or even larger?

    Thank you in advance. I want to know exactly what I'm getting when I buy my next lens/adapter.

    *EDIT* Forgot to ask my main question... Does this narrow the FOV????
     
  2. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Your guess is correct. There's a 2x crop factor...just double the focal length.
    So the panny 20mm is a 40mm on a 35mm camera format.
    The adapter does not change the focal length any more than the 2x factor.....

    We are all waiting for that 10mm (20)..... there's a 14 (28) due out very soon...
    shooter
     
  3. jpaek

    jpaek Mu-43 Rookie

    11
    Mar 9, 2010
    Canada
    Ah... so with focal lengths doubled... that would narrow the field of view.. correct?? (relative to a 35mm)
     
  4. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Yes, correct. Think like this.....
    on your 35mm you love a 35mm Field Of View.
    on the m4/3, you need a 17mm (OLY 17mm 2.8) to equal that.
    Remember...35mm is a 3/2 aspect and 4/3 is 4/3 aspect so the rectangle is different but the FOV is equal.
     
  5. jpaek

    jpaek Mu-43 Rookie

    11
    Mar 9, 2010
    Canada
    Hm.. then what is considered a wide-angle lens on a m4/3rds? I heard lens under 28mm are considered wide angle lens. Does that mean only 14mm and below are considered wide angle lens?

    Sorry.. I'm awfully confused by all this, but I appreciate your patience and answers shooter :)
     
  6. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    Well, that's a personal point of view. I'll speak for myself and probably many others.
    For me, 35mm is my natural FOV on a 35mm Leica. So wide for me is 28mm or maybe 24mm. I have both but never use them.
    I would suggest you find your personal FOV and go from there.

    The kit zoomies are 14mm- either 42 or 45mm. The 14mm equates to 28mm on a 35mm camera. That should be considered wide but some would consider that very wide.

    Do you have the kit zoom lens? If so, I can teach you how to find your personal FOV.
    That should be the starting point and without knowing what it is, you'll never find out what other lenses you should have.

    I'm just back from the street shoot so it's bed time for me...I'll be up and about around 0600 est. I'll subscribe to this thread, you do the same...then we can continue here and maybe get some others involved...

    Good night...see ya in the am...
    shooter
     
    • Like Like x 1
  7. jpaek

    jpaek Mu-43 Rookie

    11
    Mar 9, 2010
    Canada
    Yep, I got the 14-42mm kit lens.

    I hardly use the zoom at all. To be honest, at 14mm it doesn't seem that wide to me. Its hard to make a judgement when I haven't had any experience with any other lens though. :confused:
     
  8. IronChef

    IronChef New to Mu-43

    6
    Mar 7, 2010
    Hi jpaek,

    I too was a bit confused on this subject. I (personally) found it helpful to do a scene comparison with another camera that I was more familiar with comparing the lcd screens side by side. The kit zoom at 14mm matched the other cameras angle of view at 28mm, but before I compared I was imagining otherwise.

    There is a multiplication in the aperture also that you may wish to consider.

    Regards
    IC
     
  9. BBW

    BBW Super Moderator Emeritus

    Thanks for starting this thread jpaek. I'm particularly interested to read what Don has to say about finding one's personal field of view.

    Don, when you wake up and have your requisite coffee, etc.... I remember your writing about this before and should have asked then for more explanation.

    IronChef, regarding the multiplication in the aperture - can you expand on that a bit? No pun intended...:wink:
     
  10. Streetshooter

    Streetshooter Administrator Emeritus

    Dec 15, 2009
    Phila, Pa USA
    BB,
    The change in fstop is only related to depth of field.
    The fstop itself is part of the exposure equation and is the same with any lens/format.
     
  11. BBW

    BBW Super Moderator Emeritus

    That's what I thought, but IronChef made me start to wonder if there was something I didn't know. It's all his fault.:wink:

    So tell us about how to find our personal field of view - when you're ready.
     
  12. ballfresno

    ballfresno Mu-43 Regular

    30
    Feb 11, 2010
    West Sussex, UK
    The aperture is a property of the lens as is the focal length. The only that changes is what percentage of the image circle the lens projects is actually captured by the recording surface. An m43 sized sensor covers roughly half of the area a 35mm film would cover (roughly because the proportions are also different, 4:3 versus 3:2) and hence leads to an apparent doubling of the focal length (or equivalent narrowing of the field of view) but all that is happening is that you are cropping the image you keep.

    The aperture only affects the amount of light hitting the surface of the recording medium and that does not change (in terms of light per unit of area) so an f/2.8 lens is still an f/2.8 lens no matter what it is mounted on. An adaptor that has no optical element will not affect this (in general; you could of course think of an adaptor with a very constricted circle for light to get through...). However, depth of focus is affected by how much you enlarge the resulting image.

    What some person considers wide may not be wide to another. For me, the 14mm focal length on an m43 camera is wide; 20-25mm is normal.
     
    • Like Like x 1
  13. Claudiobass

    Claudiobass New to Mu-43

    7
    Jul 9, 2010
    I was wondering if the length of the adapter increase the focal length, because the lens is far to the sensor, croping more than 2x.

    Would someone help me to understand it?

    Thank you in advance
     
  14. photoSmart42

    photoSmart42 Mu-43 Top Veteran

    628
    Feb 12, 2010
    San Diego, CA
    No, the adapters simply place the rear lens element at the correct distance from the sensor for which the lens was designed in order to end up with a focused image on your sensor. So for example my FD adapter on my GH1 places an FD lens the same exact distance from my sensor as it would be if it were directly attached to a Canon FD film camera.

    The focal length is a function strictly of the lens. The crop is a function of the sensor size relative to the 35mm/FF size. You can add converters and extension tubes in order to reduce your FOV (thereby increasing magnification), but you sacrifice your infinity focus when you do that.
     
  15. pdh

    pdh Mu-43 Top Veteran

    598
    May 6, 2010
    the OP hasn't seemed to take you up on this offer, but I'm interested and sure others might be too ...
     
    • Like Like x 1
  16. dwig

    dwig Mu-43 Top Veteran

    621
    Jun 26, 2010
    Key West FL
    WRONG WRONG WRONG... The focal length is NOT doubled. All that changes is the field of view (FOV) as a result of the sensor being smaller than traditional 35mm full frame.

    Its this thinking of the focal length being changed that creates all of this confusion. Focal length is an attribute of the lens and is NEVER altered by the body, nor is it altered by any simple mount adapter. It takes optical elements, such as those in tele extenders and closeup lenses, to alter a lens' focal length.

    If by "want a 20mm lens" you mean "want the look of a 20mm lens on 35mm" they yes, you want a roughly a 10mm lens on 4/3rds or m4/3.

    I say "roughly" because the 2x crop factor is based on the two formats' native aspect ratios and these ratios are different. The diagonals of the formats are compared when calculating the crop factor, but its usually the long dimension or the short dimension that is important when taking pictures. If you compare the long dimensions with the m4/3 image cropped to the 3:2 aspect ratio of 35mm FF you will find the crop factor slightly higher and that it would take a 9-9.5mm lens to match the FOV of a 20mm lens on 35mmFF. On the other hand, if you crop both to the aspect ratio of an 8x10 print the crop factor would be lower and a roughly 11mm lens would replicate the FOV of the 20mm on 35mmFF. This is true for any 4/3rds or m4/3 camera with the exception of the Panasonic GH-1. Its crop factor remains 2x at 4:3, 3:2, and 16:9.
     
  17. supermeera

    supermeera New to Mu-43

    8
    Feb 1, 2010
    I too was confused by the 'crop factor', but I think I definitely have a better idea of what they mean now.

    Just to give a few suggestion on wide angle lenses, as I've been doing some research into a wide angle lens to do landscape shots, I've read through various reviews on the web that the Vivitar 7mm (to be used with an adapter), Samyang 8mm, and Olympus 9-18mm (native m 4/3) has yielded some very good results. In fact there are threads already on this forum showing sample pictures from most of these lenses. However I am hoping to pick up an old Canon FD wide angle lens to try out on my Panasonic GF1, although manual I think it will be able to give you a wide angle lens and a cheap price!
     
  18. Krang

    Krang Mu-43 Veteran

    202
    Feb 19, 2010
    This can be quite difficult, since the most common wide lenses in FD mount are 24-28mm. And when you transfer that to the crop factor of m4/3 it's just a "normal" lens of relative focal length around 50mm.

    Of course there are some wider FD mount lenses, but they are rare, and thus more expensive.

    The advent of under 20 to 15mm lenses really came into existence only after the digital age. Because of the smaller sensors, like APS-C and 4/3. During the film age there wasn't a lot of interchangeable lens cameras that used film smaller than 35mm.

    I Hope that you find this babble somewhat coherent :)
     
  19. dwig

    dwig Mu-43 Top Veteran

    621
    Jun 26, 2010
    Key West FL
    Adapting lenses from larger formats (e.g. 35mm full frame film) generally works well for lenses that are longer than "normal" (normal = a focal length equal to the diagonal measure of the sensor/film image = about 20mm for m4/3). Finding a lens made for 35mm FF with a short enough focal length to be a truly wide angle lens on m4/3 will be a challenge and will prove to be rather expensive in almost all cases.
     
  20. photoSmart42

    photoSmart42 Mu-43 Top Veteran

    628
    Feb 12, 2010
    San Diego, CA
    Don't confuse fish-eye lenses with wide-angle lenses. Very different types of lenses and effects. WA and UWA lenses are assumed to do their best to remain rectilinear with minimum distortion. As others have said, UWA lenses made for film are in the realm of 14-24mm, and even the older ones are still expensive enough to make you consider the advantages of a native m4/3 UWA lens like the 9-18 or the 7-14 (I know, I've looked). At best you can get a reasonably priced Canon FL 19mm lens that's rectilinear, but even at 19mm that's still inside the FOV of your 14-45 kit lens, so probably not worth it.