Focusing inaccuracy with Bessa R4M

Discussion in 'Rangefinder Forum' started by osprey48, Nov 23, 2008.

  1. osprey48

    osprey48 Member

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    Apologies if this has been covered on this forum in the past, but I can't find any direct references to it.

    I'm thinking of buying a Bessa R4M, because of its compact size, and would be a good camera to take on travels with just a 35mm or 28mm lens. However, I've read in a couple of reviews that because of the short rangefinder distance, accurate focusing with 35mm-50mm lenses isnt possible, or is at least very difficult. Can anyone share their personal experiences of this, and is it really much of a problem? Or is it just reviewers trying to think of something negative to say just to balance their reviews up?
     
  2. ElrodCod

    ElrodCod Member

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    I've read that there could be focusing issues with the 90 at the close end of it's focusing range because of the short rangefinder base of the Bessas but I haven't seen any firsthand reports of this with any of the shorter lenses. I have a Bessa R2 and haven't had any problems with my 35mm and 75mm lenses.
     
  3. Alex Bishop-Thorpe

    Alex Bishop-Thorpe Member

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    There shouldn't be any problem at all with 35-50mm lenses. Remember that the R4 was designed for use with wide lenses - lenses longer than the 75 would perhaps be the problem
     
  4. Graham.b

    Graham.b Member

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    I have a 'R' and can say there are no prob's with this one. I use a 35 near on all the time.
     
  5. haris

    haris Guest

    I have R2A, and never was able to get completelly "focused" image focusing at infinity (that is, when focused to infinity, and looking at very distant object through viewfinder, there is double picture in "yellow spot" in viewfinder, never images combined in one sharp image). But, when focused on near(er) object, there are no those problems and focusing allways is acurate. And it happens with mine both 35mmPII and 75mm lenses.

    That is short rangefinder base problem I was told.
     
  6. ElrodCod

    ElrodCod Member

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    The difference is in the viewfinder magnification. The rangefinder base is the same as the other Rs.

    That's an adjustment issue that's not related to how wide the rangefinder base is. It's fairly common for the Bessas to get bumped out of alignment. Do a search here for info on a DIY fix. http://www.rangefinderforum.com/forums/forumdisplay.php?f=28
     
  7. haris

    haris Guest

    Thanks ElrodCod.

    I have tested camera (biggest aperture opening, focusing on wall graffitti, and another test with pages of daily newspspers on wall, and moving from closest focusing fistance by one meter at time away from wall) and all photographs were sharp. That is why I didin't pay too much attention to it.
     
  8. John W

    John W Member

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    The big difference that rangefinder effective base length (EBL) will make is with fine focusing accuracy when depth of field is shallow. The RF will appear to be in focus, but due to the limited EBL the lens' focus will be off from the intended focus plane. You won't be able to notice a problem with pretty much any RF lens when DOF is not overly shallow (e.g. you'll never notice a problem at f/8). But when running wide-open apertures, especially at longer focal lengths, critical focusing may be off. Esp. lenses like the Noctilux 50/1, Summilux 75/1.4, and the Zeiss Ikon 85/2, require a good EBL at max aperture due to shallow DOF.

    To make ElrodCod's point completely clear, it's worth noting that the EBL is the physical RF base length times the viewfinder magnification. As noted, the Bessa R2/R3/R4 physical baselengths are all the same, the only difference is in the VF magnification. The R4A/R4M cameras by design have a x0.52 magnification (i.e. wider) than the other Bessa's (e.g. compare to the x1.0 VF magnification in an R3M). The R4's tradeoff is reduced EBL since the magnification factor is relatively smaller.
     
    Last edited by a moderator: Nov 27, 2008
  9. waileong

    waileong Member

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    There's a difference between focusing inaccuracy and vertical/horizontal rangefinder alignment.

    That your images do not line up at infinity is an alignment issue.

    Focusing accuracy is dependent basically on the effective baselength.

    50 mm lenses on the R4M should be ok for F2 and higher.
     
  10. haris

    haris Guest

    Thanks, but now I am confused:

    If camera have alignment issue, but I don't have problem using it, and focusing is corect, what is exactly alignment problem then?
     
  11. Leigh Youdale

    Leigh Youdale Member

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    With a 35mm focal length lens you're unlikely to even need to focus at all, the depth of field will be so great. It's a non-issue but something that technical purists like to debate. Just go and take photos.
     
  12. nemo999

    nemo999 Member

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    Rangefinders focus by bringing 2 patches into left/right alignment. If this is out, you will get unsharp pictures. It is also possible for the 2 patches to have poor up/down alignment. If this is the case, it has no effect on sharpness but is annoying to look at.