18 August 2018 at 3:30 pm #574112
Its often said that the Samyang 14mm f2.8 lens manual lens is a bargain for doing wide field images of starfields and landscapes. With the smaller frame size of a Canon 1100D or Canon 700D series cameras it gives a field 90 degrees across, while on a full frame Canon 5D it gives a whopping 110degree field of view. Its a very clever design of more than 10 lenses with multiple glass types, coatings and even aspheric lenses. Typically, they appear on the second hand market for a bit over £200 – the cost of lenses has risen significantly since the referendum.
But these are mass production items – assembling that many components accurately and maintaining build quality is non-trivial. There will be poor batches, there will be poor random examples and the camera they sit on may be duff too – the CCD being non-perpendicular to the optics by as little as 50microns can be enough to mess things up the performance of such a wide angle lens.
So, when I bought one second hand – with guarantee happily – I wasnt suprised that things were not quite right. I took a 10s exposure of the summer triangle and the surrounding sky and then looked closely at the shape of star images off the central axis.
The image attached shows the view at the left top corner of the image and at the top right of the image. The difference is very obvious. Pretty much the whole of the left side and centre of the image was superb. Really good for the cost of the lens – the Canon equivalent costs 7x as much.
Suffice to say its going back to the supplier. Though I am looking for another as I borrowed a Samyang from Mark Radice a few months ago and that gave a great response across the whole field.
Moral of story – don’t believe in perfect manufacturing. When you get a new lens – test it immediately.
What has everyone elses experience been with this sort of thing?
Attachments:20 August 2018 at 3:25 pm #579897James DawsonParticipant
My 14mm Samyang has some aberration at the edge when the iris is wide open; I’d just assumed this was the common given the enormous field of view and the relative affordability of the lens.
James21 August 2018 at 1:07 am #579902John BellParticipant
Here’s the top left corner of one of my Perseid frames 14th at 00:47. It isn’t tracked. There is some difference between the trails at the corner and at the opposite corner (approx the centre of the screen) My main worry is vignetting but that’s the geometry of the aperture and is similar with any lens. but like James I am happy to compromise affordability and quality.22 August 2018 at 7:14 pm #579904
Could you post some excerpts from the corners please so we can compare?
Also, is it symmetric? Are all 4 corners similarly distorted?22 August 2018 at 7:16 pm #579903
Any chance you could post examples from those corners please?
Perhaps the lens I borrowed previously was an outlier i.e. unusually good? In that the distortion was about 25% of the extent I found with my lens.
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