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Weird Lens

Discussion in 'photo' started by JemHayward, Jul 14, 2020.

  1. JemHayward

    JemHayward pfm Member

    It was my birthday last weekend, and as usual, we can't find anything to buy each other that we haven't got, actually need, or can afford. This has resulted in such romantic gestures as a potato peeler (from my wife) and a finger pointing trowel (from me to my wife). This year much the same, so after the Porsche and the electric mountain bike were rejected I went onto Amazon to look at photographic accessories I've not actually got, and definitely need. This inevitably leads to Neewer, and I found a useful clamp thingy that clamps your camera to things... then I spotted what looked like the 7-Artisans 25mm f1.8 lens Fuji fit, £47.99, so I added that to my list, and she took the bait. Having queried my previous lens spending (£800 for the Fuji 90 f2 led to a 'discussion') - I was now asked how a £50 could be any good, and I explained that wasn't the point.
    It's arrived, and it is a bit quirky, and I think 'faulty', but I don't think I'll send it back, as the fault is something I'd not encounter in normal use.
    Here it is at f16
    [​IMG]_E3F6638 by Jem Hayward, on Flickr
    f4
    [​IMG]_E3F6640 by Jem Hayward, on Flickr
    f2
    [​IMG]_E3F6642 by Jem Hayward, on Flickr

    Other apertures on my Flickr photostream, though the exif is totally fictitious, they are in order f16,f8, f5.6, f4, f2.8, f2, f1.8

    Basically at f16 something goes horribly wrong in the centre. As the aperture widens you get more vignette, and the corners are always distorted and blurry, but centrally at wider apertures it's pretty good. I'm going to use this zone focussed at f5.6 as a 'street' lens, if and when I'm allowed out in public again.

    Fun lens and for £50 who can moan.
     
  2. stevec67

    stevec67 pfm Member

    I'd back it. It's junk. If you want distortion buy a clip on fisheye for your phone for £3. For £50 I want a lens that works.
     
    mansr, tuga and narabdela like this.
  3. JemHayward

    JemHayward pfm Member

    It's pretty good distortion wise if you look at the brickwork, the vignette may be annoying sometimes, but I add vignette to a lot of my images anyway.
     
  4. Mr Perceptive

    Mr Perceptive Perceptive Member

    The 7artisans lens I have played with did exhibit some vignetting, but not that magenta ball you have at F16, definitely faulty, buts its your choice if it goes back or not. The distortion towards the corners on 6641 is quite nasty as well, personally I'd send it back, otherwise it will just be an expensive paperweight
     
  5. JemHayward

    JemHayward pfm Member

    I think I may, as it's definitely not right, I know quite a lot about lenses and have collimated a couple with a degree of success, but I'm at a loss as to what may cause the purple blur at f16 - it's not an aperture I'd use, but this must be causing other more subtle issues.
     
  6. Mark_R

    Mark_R pfm Member

    I think these hot spots are caused by multiple reflections between the sensor and the rear element of the lens. Is the back surface of the rear element quite flat, or slightly concave? They can be seen with some old 35mm film lenses used on digital. They only become apparent at small apertures since the light is then much more collimated so the multiple reflection can build up. The lens is probably not faulty as such, just not a good design. Mind you, do you really need to use it at f16? The stronger vignetting at larger aperture is also par for the course. And the weak corner performance is inevitable for the price.
     
  7. JemHayward

    JemHayward pfm Member

    Indeed, that makes sense, and yes, the rear element is relatively flat, but I've seen images on the internet using this lens that doesn't show the effect.
     
  8. JemHayward

    JemHayward pfm Member

    I'm going to return it and order another. If it's the same, I'll keep it as I like a lot of the other things the lens does, and have lots of lenses so this will sit with my Helios 58, and Jupiter in the quirky lens pile.. If I want perfection I have Fuji primes at 16, 27, 35 and 90 and Zeiss primes at 50 and 135. And a few others!

    [​IMG]_E3F6652 by Jem Hayward, on Flickr
     
  9. SteveG

    SteveG pfm Member

    From what I've read the quality control is supposed to be poor on those lenses, but if you get a good one the centre performance is supposed to be decent although they're never going to be any good at the corners. It's very, very cheap though so probably worth returning it and seeing if you can get a decent one as a replacement.

    I've got a 24mm F1.8 (a Sigma) and it's quite a useful lens in low light conditions i.e. reasonably fast, reasonably wide (on full-frame) and a decent performance wide open. It's not a small lens though. One of my regrets is selling the Pentax FA* 24mm F2 that I had back in my film days. It was a lot smaller and a very good performer, and now I've got a FF Pentax DSLR it'd be seeing a lot of use.
     
  10. JemHayward

    JemHayward pfm Member

    Indeed, I built my Helios 58 from two and got it working rather well. I have a Fujinon 27 f2.8 pancake lens which is stunning but it won't flare, vignette or distort, so the 25 has a purpose, creatively.
     
  11. SteveG

    SteveG pfm Member

    I'm got a Helios 58mm and mine seems a reasonably decent performer although I don't think I've used it on a FF body yet so don't know what the corners are like.

    I've got loads of wierd and wonderful Eastern bloc lenses - mostly in M42 or Pentax K but a few Leica screw mount ones as well. They can be a bit temperamental but can still get some decent results. Favourites are a Porst 55m F1.2 (in Pentax K) and the Solgor 135mm F2 (I have two of those - one that's in great condition and one with a touch of fungus). They're quite fun to use wide open as while they're not that sharp wide open the out of focus rendering is nice. The 37mm F2.8 Mir-1B is a nice lens as well, as are some of the Meyer Optik ones (the 100mm Trioplan is one I like a lot and the 30mm Lydith is also good). Ok some of the ones I bought have been crap, but none of them were expensive either.

    I must dig some of them out and give them a try on the K1 as I don't think I've tried many of them FF.
     
  12. Stunsworth

    Stunsworth pfm Member

    IR hotspot causing the central issue?

    What I’ve seen of this brand of lenses they all seem to perform poorly at the edges - that’s what costs the real money in lens design and manufacture.

    Currently it’s unusable IMHO. I’d send it back, if the replacement is the same get a refund.
     
  13. Space is the Place

    Space is the Place pfm Member

    Are you sure it's not... a ghost!

    Or the Aura of the the washing line? Purple means Loving with a touch of magical!

    [​IMG]
     
  14. JemHayward

    JemHayward pfm Member

    Lens exchanged and new one arrived today. Still some purple sensor reflection at f16 but no distortions. The price you pay for such a cheap lens is that you need to do the QC yourself!
    [​IMG]f16 by Jem Hayward, on Flickr
     
  15. Mr Perceptive

    Mr Perceptive Perceptive Member

    A zine of Dr Who images then.................
     
  16. Stunsworth

    Stunsworth pfm Member

    Oh dear. Useless for colour work.
     
  17. JemHayward

    JemHayward pfm Member

    Indeed, but I rarely use f16 and mostly do mono, so it's a keeper!
     
  18. JemHayward

    JemHayward pfm Member

    Eastern block lenses were often classic designs built poorly, so can vary from being very good, to pretty awful, as QC was very much seen as optional. The Helios 58 as a design was not bad at all, but I've seen some examples that are really poor. I bought a cheap Dixons plastic bodied telephoto for my Zenit B in the late 70s and it was really good. I then bought a 'better' camera - with a different mount, so sold the lens, and bought another with a bayonet mount. It was nowhere near as good. So I had a 'better' camera that made no difference to the image quality (maybe better exposure accuracy) and now a worse lens. Important lesson learned. I've generally bought the best lenses I can afford, but something quirky appeals as most of my lenses are essentially characterless perfection.
     
  19. richardkendell

    richardkendell pfm Member

    As a matter of interest what lens distortion or defect would result in the purple patch?
     
  20. JemHayward

    JemHayward pfm Member

    I think it's a reflection off the sensor hitting a relatively flat rear element.
     

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