Help on lens calibration

Calibrate Sigma?

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Encorez

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Hi guys,

This is my first thread in a discussion section so if there is anything I did that's against the rules, just let me know and I will edit it immediately!

I had been having focus problems on my Nikon 50mm f1.8g. Plus, I recently purchased a Sigma 17-50mm f2.8 which (based on what I read) is notorious for focus problems so I looked up a bit on calibration and did a simple test myself.

What I did was,
- Set my D3200 on my tripod facing the focus test chart on the wall (beside the window at about 1pm)
- Shot 3 shots (RAW) using live view and 3 shots with the viewfinder
- 2 sec self-timer at ISO 100 using center focus point
- Did this for each of my 3 lens
(1)50mm f1.8g Nikon
(2)18-55mm f3.5-5.6 kit lens
(3)17-50mm f2.8 Sigma
- Reduced sharpening in Lightroom to 0

and here are the results I got,
(I only posted 1 live view and 1 viewfinder shot for each lens, but there are more samples in my flickr album - YH, on Flickr)

- Nikon 18-55mm f3.5-5.6 at 48mm f5.6
Live view - https://farm2.staticflickr.com/1602/23720951754_9a03f64f42_o.jpg
Viewfinder - https://farm2.staticflickr.com/1631/24266644931_221d405820_o.jpg

- Nikon 50mm f1.8g at 50mm f1.8
Live view - https://farm2.staticflickr.com/1699/24349119875_4e7c52b795_o.jpg
Viewfinder - https://farm2.staticflickr.com/1470/23981336769_e62c9a09e7_o.jpg

- Sigma 17-50mm f2.8 OS DC HSM at 50mm f2.8
Live View - https://farm2.staticflickr.com/1707/24240917042_ae79a9f311_o.jpg
Viewfinder - https://farm2.staticflickr.com/1689/23722324473_3ab8dd01d9_o.jpg

I am interested in trying out portraiture so sharp focus is really important. The 50mm prime probably needs re-calibration but I am not sure about the Sigma. It seems to have a tiny bit of rear focusing although I don't know if that tiny bit really matters in practice. I am hoping to get some of your advice. Should I bring it down for calibration?
 
Zoom lenses are virtually impossible to fine tune especially with the D3200 as Nikon omits the ability to adjust auto focus fine tuning in it's entry level D3xxx and D5xxx bodies. Therefore it has to be done by a Nikon certified repair center or if you have steady hands it can be done yourself using mirror lockup and a small allen wrench. The adjustment screw is on the side of the mirror box behind the mirror and just in front of the camera's sensor (not for the faint of heart or shacky handed). Also the adjustment is very very sensitive and getting an exact adjustment is a very tidious process.

The reason zooms are so diffucult is because of the way they are made. Because the lens elements inside move, this changes the characteristcs of the lens with regards to focus. You can adjust your fine tuning for the wide end, but then it's highly likely that the long end will be out of adjustment.
 
Yeah bringing it to the respective service centers for calibration is the better choice.. I definitely don't have very stable hands.

But I am unsure if the phase focus on the Sigma still can be improved by calibration.

Someone told me that smaller apertures are used in studio portraiture so focus matters less. I am more interested in street and environmental portraiture so I am guessing aperture would matter more in these genre?


Sent from my iPhone using Tapatalk
 
Had to fine tune my 50mm 1.4 art with the Sigma dock the other day. The lenses focus was way off, but i was able to correct it within a few hours. :)
 
I looked at your test shots...these are all what I would think are acceptable. You shot these from close distance and wide-open...that is a supremely difficult challenge for a non-macro lens. I think all of these are within acceptable tolerance for wide-open shots at close range.

Shots made at f/1.8 or f/2.8 on a zoom lens are not going to look anywhere near as crisp as shots made with the lens stopped down two full stops from wide-open. I think you might be looking at these images a bit too much, with too much concern over the test chart photos. How do "real photos" look?
 
Someone told me that smaller apertures are used in studio portraiture so focus matters less.
Then someone gave you bad information.
Middle apertures are mostly used in studio portraiture, not the smaller apertures.
 
Had to fine tune my 50mm 1.4 art with the Sigma dock the other day. The lenses focus was way off, but i was able to correct it within a few hours. :)
Hey! That's cool but I read somewhere that the dock only works on the newer lens?

Then someone gave you bad information.
Middle apertures are mostly used in studio portraiture, not the smaller apertures.
Hi Kmh, yeah I think what he meant was probably "smaller than the widest" aperture.
 
Shots made at f/1.8 or f/2.8 on a zoom lens are not going to look anywhere near as crisp as shots made with the lens stopped down two full stops from wide-open. I think you might be looking at these images a bit too much, with too much concern over the test chart photos. How do "real photos" look?

Hi Derrel, thanks for taking your time to look at the photos. I still couldn't get the focus right for the 50mm so I'll probably be bringing it down for calibration but this is what I took with the new Sigma. It seems sharp to me though I am not sure if it can still be improved.

by YH, on Flickr
 
Had to fine tune my 50mm 1.4 art with the Sigma dock the other day. The lenses focus was way off, but i was able to correct it within a few hours. :)
Hey! That's cool but I read somewhere that the dock only works on the newer lens?

Then someone gave you bad information.
Middle apertures are mostly used in studio portraiture, not the smaller apertures.
Hi Kmh, yeah I think what he meant was probably "smaller than the widest" aperture.
Unfortunately that's true. The Sigma dock is a pretty nifty little gadget that does what it advertises.

Here are the following compatible lenses with the dock:
20mm F1.4 DG HSM
24mm F1.4 DG HSM
35mm F1.4 DG HSM
30mm F1.4 DC HSM
18-35mm F1.8 DC HSM
24-35mm F2 D HSM
24-105mm F4 DG OS HSM
50mm F1.4 DG HSM
17-70mm F2.8-4 DC MACRO OS HSM / DC MACRO HSM
18-200mm F3.5-6.3 DC MACRO OS HSM / DC MACRO HSM
18-300mm F3.5-6.3 DC MACRO OS HSM
150-600mm F5-6.3 DG OS HSM
120-300mm F2.8 DG OS HSM
150-600mm F5-6.3 DG OS HSM
 

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