Pages: [1]   Go Down

Author Topic: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops  (Read 679 times)

danielc

  • Newbie
  • *
  • Offline Offline
  • Posts: 45

Hi Guys,

Just wanting to check whether this issue is common to this lens or if I have a damaged/bad copy.

My issue really started showing up once I upgraded to the D850 from the D810, It was occasionally noticeable with the D810 but not as much, I assume due to the lesser detail.

It's primarily showing up when shooting at F2.8-5.6, and almost completely gone at F8.

Here is an example from Vivid in Sydney the other night: 1600 ISO and unedited but you get the idea.

Full size -


100% crop of focused area:


100% crop of right hand side


100% crop of left side


100% crop of bottom (acceptable)


And here is a 100% crop of a similar shot at F8 (edited) it's not perfect but it's pretty good.


Is it just the lens or is it my copy? It's a few years old now so no chance of swapping it out. Tempted to get a Prime but I really do use most of the range from 15-30 regularly, plus I have a Lucroit adapter for this lens to fit my 165mm filters which will be another expense if I swap...

Can it be entirely resolved by only shooting at F8 - F12? It's generally what I do but low light gets sketchy.

EDIT:
Here is an example at F5, ISO 64, 15 Sec exposure.
Middle 100%


Right 100%


Left 100% - You can see the gradient from in focus to out here from right to left. This should all be hyperfocal?
« Last Edit: June 21, 2018, 07:57:50 AM by danielc »
Logged

BernardLanguillier

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 11234
    • http://www.flickr.com/photos/bernardlanguillier/sets/
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #1 on: June 22, 2018, 01:01:03 AM »

You are worried by the softness in the corners around f4?

Isn't it simply the combination of:
- a lens that is very good but not excellent in the corners
- a non perfectly flat field near infinity

I am not shocked by what you are seeing franckly.

Cheers,
Bernard

Shiftworker

  • Newbie
  • *
  • Offline Offline
  • Posts: 32
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #2 on: June 22, 2018, 02:04:04 AM »

Even good primes often need stopping down to middle apertures to get peak edge and corner resolution. Also try focusing off center or slightly beyond infinity as often depth of focus is slightly thicker in the center than at the edges so you can trade a very small (even unnoticeable) loss of center resolution for a larger and  noticeable gain in edge resolution.
BTW - what you are seeing is not focus shift but a curved focus plane. Focus shift is where the plane of focus moves/changes shape at different apertures and in some cases lenses can get worse when they are stopped down.....
« Last Edit: June 22, 2018, 02:07:12 AM by Shiftworker »
Logged

danielc

  • Newbie
  • *
  • Offline Offline
  • Posts: 45
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #3 on: June 22, 2018, 09:03:54 AM »

You are worried by the softness in the corners around f4?

Isn't it simply the combination of:
- a lens that is very good but not excellent in the corners
- a non perfectly flat field near infinity

I am not shocked by what you are seeing franckly.

Cheers,
Bernard

It's not so much softness as unusable mush for my high quality landscape images. Even at F8 the edges aren't perfect which is unfortunate considering a decent amount of my time is spent at quite low light.
Logged

danielc

  • Newbie
  • *
  • Offline Offline
  • Posts: 45
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #4 on: June 22, 2018, 09:04:43 AM »

Even good primes often need stopping down to middle apertures to get peak edge and corner resolution. Also try focusing off center or slightly beyond infinity as often depth of focus is slightly thicker in the center than at the edges so you can trade a very small (even unnoticeable) loss of center resolution for a larger and  noticeable gain in edge resolution.
BTW - what you are seeing is not focus shift but a curved focus plane. Focus shift is where the plane of focus moves/changes shape at different apertures and in some cases lenses can get worse when they are stopped down.....

Rightio, thanks a lot for the explanation. I have started focusing more off centre to make sure most of the shot is in focus. Thanks for the advice.

Logged

BernardLanguillier

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 11234
    • http://www.flickr.com/photos/bernardlanguillier/sets/
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #5 on: June 22, 2018, 09:17:34 AM »

It's not so much softness as unusable mush for my high quality landscape images. Even at F8 the edges aren't perfect which is unfortunate considering a decent amount of my time is spent at quite low light.

I don't think it is realistic to expect perfect corners from this lens. You would probably have been better off with the Nikon 14-24mm f2.8 or with a combination of the Sigma 14mm f1.8 prime and a Nikon 20mm f1.8.

Cheers,
Bernard

NancyP

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2374
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #6 on: June 22, 2018, 11:58:31 AM »

Research landscape astrophotography users of this lens. This is a popular lens for the landscape astro crowd. Note also that Tamron has had some manufacturing variability in the past. And here's a post by Uncle Roger, with MTFs and field curvatures (n = 5):
https://www.lensrentals.com/blog/2015/02/just-the-lenses-tamron-15-30mm-f2-8/
Logged

MichaelEzra

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 957
    • https://www.michaelezra.com
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #7 on: June 23, 2018, 02:27:05 PM »

Daniel, I have this lens and been using in on D800e. The lens is very, very sharp - and all the way to the extreme corners.

However, this lens exhibits very strong field curvature. The design of this lens is more suitable for photographing interiors as the focus field literally wraps the walls.
This lens also allows to keep one's feet and far horizon in focus, but it cannot keep the entire horizon line in perfect focus, as towards the edges (and corners) of the frame the focus field curves to close proximity towards the camera.

To an extend this can be mitigated with the increased depth of field, however, that will not entirely compensate for lack of focus on distant objects at the edges of the frame.
With proper use, this lens if excellent for what it is designed to do.
Logged

danielc

  • Newbie
  • *
  • Offline Offline
  • Posts: 45
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #8 on: June 23, 2018, 08:08:52 PM »

Daniel, I have this lens and been using in on D800e. The lens is very, very sharp - and all the way to the extreme corners.

However, this lens exhibits very strong field curvature. The design of this lens is more suitable for photographing interiors as the focus field literally wraps the walls.
This lens also allows to keep one's feet and far horizon in focus, but it cannot keep the entire horizon line in perfect focus, as towards the edges (and corners) of the frame the focus field curves to close proximity towards the camera.

To an extend this can be mitigated with the increased depth of field, however, that will not entirely compensate for lack of focus on distant objects at the edges of the frame.
With proper use, this lens if excellent for what it is designed to do.

I don't understand how you can say it's sharp to the extreme corners despite the focus field wrapping inwards. By definition unless you are photographing something like an interior that wraps back towards you it cannot be sharp to the extreme corners.

I don't agree that it was designed only for interior architecture photo's.

For the immediate future I will compensate for this lens weaknesses by off centre focussing, using as large a depth of field as possible in the light conditions, and I will start researching better alternatives that suit my use more, such as the Nikon 14-24 or a prime. 

If I had of seen that lensrentals lens review earlier specifically the field curvature I wouldn't have bought this lens. I bought it for its renowned sharpness.

Suggestions for lenses that will suit me perfectly (apart from the obvious Nikon 14-24)?
Logged

MichaelEzra

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 957
    • https://www.michaelezra.com
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #9 on: June 23, 2018, 08:13:14 PM »

It is sharp where it is designed to be sharp, just not where you expected it to be.
Make this test - shoot a building far away, pointing camera horizontally and in portrait orientation, use 15mm.
Focus on the building in the center of the frame. Examine the ground in the bottom of the frame - it will be tack sharp.
Now, imagine that you are shooting the horizon and expecting that the edges of the horizon will be sharp - how can they be? The lens is not designed to focus on distant subjects at the edges of the frame.
« Last Edit: June 23, 2018, 08:16:27 PM by MichaelEzra »
Logged

BernardLanguillier

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 11234
    • http://www.flickr.com/photos/bernardlanguillier/sets/
Re: Tamron 15-30/2.8 on Nikon D850 - Focus shift on edges at low F/Stops
« Reply #10 on: June 24, 2018, 05:39:09 AM »

Suggestions for lenses that will suit me perfectly (apart from the obvious Nikon 14-24)?

As proposed above, a combination of 2 excellent primes such as the Sigma 14mm f1.8 and Nikon 20mm f1.8.

Or wait a bit since nikon is quite likely to update soon the 10 years old 14-24mm f2.8 (now lens rental just called that 10 years old lens the best ultrawide zoom, so it is still very good obviously).

Cheers,
Bernard
« Last Edit: June 26, 2018, 08:15:10 AM by BernardLanguillier »
Logged
Pages: [1]   Go Up