Scopes in poor light

Discussion in 'General Airgun Chat' started by Artfull-Bodger, Aug 2, 2010.

  1. Artfull-Bodger

    Artfull-Bodger Member

    Joined:
    Feb 7, 2010
    Messages:
    309
    Location:
    Llantrisant
    Guys I have heard from a few people lately about FT scope rangefinding shifting in poor lighting, at Avon Hawks last Sunday a couple of the guys hit low due to ranging about 2yds short!

    now we have all heard of temp shift but has anyone reaserched what causes this phenomenon, it seems to affect different makes yet is it the scopes, or is it the shooters eyesight compensating for the light?

    is it spectacle wearers who see this or do guys with 20/20 vision also see short ranging?

    Mike
     
  2. NJR 100

    NJR 100 Because I`m AWESIME !!

    Joined:
    Aug 10, 2009
    Messages:
    5,577
    Location:
    Skewen
    Club:
    Avon Hawks, Tondu, Oaktree
    Which guys and what scopes were they using?
     
  3. Artfull-Bodger

    Artfull-Bodger Member

    Joined:
    Feb 7, 2010
    Messages:
    309
    Location:
    Llantrisant
    Jason and Nigel both use Diamonds I believe, yet jason was short ranging Nigel not, work that one out?

    I was talking to a guy at Newbury a few weeks back who had a Burris and he mentioned low light shift whilst we were talking about temps?
     
  4. NJR 100

    NJR 100 Because I`m AWESIME !!

    Joined:
    Aug 10, 2009
    Messages:
    5,577
    Location:
    Skewen
    Club:
    Avon Hawks, Tondu, Oaktree
    its not unknown for a scope to give different readings in bright light or low light, or with a black target as apposed to a white target.

    Its as the old saying goes, about knowing your equipment.

    Or use the Forse:D
     
  5. RobF

    RobF Administrator Staff Member

    Joined:
    Mar 4, 2010
    Messages:
    11,976
    Location:
    Poole, Dorset
    Club:
    Parkstone Gun Club, South Dorset FTC, Southampton Buccaneers
    Light can affect the eye because of a couple of reasons... one, light changes make the pupil open or close, which can affect how you focus your eye ( if you notice a cat before it's about to pounce, it's pupils open right up, because it's using this to create a very shallow depth of field to help it determine the range... like FT shooters do)...

    the other problem is that you detect a range by focus, and what tells you focus the best is contrast... funnily enough, because the eye is most sensitive to yellow, the best contrast is between yellow and black, and the eye can be overloaded with the mix of colours that make up white.. but that aside, by lowering the light, you lower the brightest part of the image, which gives you less contrast...which gives you less idea of good focus... which can lead to error.

    people rangefind in different ways... and different scopes do... at some point, there is a band of which it's hard or impossible (it varies) to determine a change of focus... fine detail helps determine this better, because it's the first to go in and out of focus, but there's a point/band where your eye my not be able to see this change. Some determine the range on the middle of this band, where they determine absolute focus is, some use the edge of this band, either before or ahead of the range, but the edge of where they can determine no difference... so when the light changes, it might change where this band or edge is determined... if you come up, or come down on the range, it will probably affect if you range short or long on target.

    Its personal really to you, your scope, and how you use it (ie what you focus on)... and it may be something you need to learn (if it happens to you) or something you don't. For me, irrespective of what of my scope's i'm using, i use string frays or very fine detail to work off, and the plate is the last resort... and I don't (he says grabbing mahogany) have a problem with dark/light even with the old custom shops. (that said, the custom shops had difficulty on bright white n hazy conditions where i couldn't pic out a sting fray).

    I've noticed when comparing scopes, that some handle deep dark colours better at the expense of contrast on brighter subjects, and others the opposite.
     
  6. Artfull-Bodger

    Artfull-Bodger Member

    Joined:
    Feb 7, 2010
    Messages:
    309
    Location:
    Llantrisant
    Good post Rob, the only time I have seen a difference is when I did my scope set up on white card targets, then it ranged short on everything else, since then I mark up my sidewheel on wood using the neutral coloured grain/bark detail to focus on!

    Your reply has pretty much fleshed out where I was going, I was wondering if the brighter target causing the pupil to close produced enough of a focal shift compared to when the pupil is wider looking at a darker image?
    I was thinking along the lines of a cameras arperture there!

    many thanks for that Rob, something to think about.

    Mike.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice