Sony Digital Camera Forums
Sony DSLR, SLT, NEX, & Mirrorless Discussion => Full Frame Sony Alpha Camera Discussion => Topic started by: AScot on March 25, 2012, 08:32:09 AM
After two years of owning the A850, I finally got around to Micro adjusting most of my full frame lenses. :( Results seem to be very good and to have improved most of my lenses to the point that I doubt if I would purchase another camera that did not have this feature. I do expect that I may have to readjust some lenses slightly as time goes by. All reading were taken with the camera on a tripod and using 2 second delay with mirror lockup. Micro adjusting can be performed on the A850/A900 cameras and I believe the A77.
Here are my results
Sony 28-75mm F/2.8 SAM = -5
Sony 70-300mm F/4.5-5.6 G SSM = -2
Minolta 28-135mm F/4-4.5 = -2
Minolta 70-210mm F/4 (Beercan) = -7
Minolta 28mm F/2.8 = -3
Minolta 50mm F/1.7 = -0
Minolta 100mm F/2.8 macro = -1
Minolta 300mm F/4 HS-APO G = -3
Minolta 500mm F/8 reflex = -16
Sigma 21-35mm F3.5-4.1 = -3
The first thing I noticed is that all adjustments were negative numbers. Could this indicate that most, if not all lenses, suffer from back focus problems (rather than front focus) to varying degrees. However it may just be a coincidence.
I also noticed that prime lenses were by far the easiest to adjust, having only one focal length. I checked them at maximum aperture and at around f8, also at close to the MFD and at a distance, depending on the focal length and type of lens (macro etc) and found little to no difference at these extremes.
Zoom lenses however varied a little bit at minimum, middle and maximum focal lengths, but mostly only by -1 to -2. I settled on the adjustment required for the sharpest result at max. aperture and at the focal length that I use most for the particular lens being tested.
I also found that all lens adjustments could vary by a very small amount if I focused the lens to infinity and/or to close focus prior to taking the reading. From that I realized that this is not an exact science but rather an exercise in compromise.
The Sony 28-75mm F/2.8 SAM required -5 which was a surprise, as it is my newest lens. The Minolta 70-210mm F/4 (Beercan) required -7, not a surprise for such an old lens. The oldest lens however, the Minolta 28-135mm F/4-4.5, only required -2.
By far the biggest surprise was the Minolta 500mm F/8 reflex at -16. Perhaps that is why I never used it much, hopefully it will earn it's keep from now on. When first tested, bearing in mind that at f8 it had a relatively large depth of field, all of the sharp area was in the positive or back focus range.
Sharp focus, although not the only requirement for a good lens, is possibly the most important, certainly the most discussed. So I think this test and adjustment was time well spent.
Could you tell us how you performed the test?
Very interesting results. I wonder if others have similar experiences...john
My theory is that all manufactures invent this future to reduce cost and bad reputation. Almost 30% of the owners were complaining of FF(frond focus) or BF (back focus). With this future customers are satisfied and manufactures don't need to receive/send & adjust a camera and at the end the customer was again not satisfied because the adjustment was made with different lens than the s own.With Minolta 7D Minolta was asking to send camera and lens together.
I will try to post also my results but definitely different since the manufacture release a cameras & lens in the market for sale with tolerance for example +/-2. If the focus results is within this range the camera/lens goes for sale.
The problem appears when lets say a lens is from manufacture -2 and the camera is also -2 then you have a total difference of -4. Here you need to make microfocus adjustment to reduse the difference from the manufacture tolerance.
Rex, these are the results for my lens and for my camera only. Others with the same camera and same lenses will have different results, that is a given that surely does not need repeating. I am showing my results just for information, some may find it of interest, you may not. The manufacturers did not invent this feature just to reduce cost and to avoid a bad reputation, they were getting a bad reputation! This feature was brought out to try and reduce the necessity to send both your camera and your lenses away for as much as six weeks. Only a misinformed beginner would send only his lens for adjustment without also sending his camera. Your theory does not hold water with me and is cynical beyond belief.
I have found a definite improvement in the lenses that I have adjusted and subsequently tried under real life shooting (not many yet), especially the 500mm reflex. So I am initially happy and as I test the remaining lenses under real life conditions I will find out if my initial happiness is justified. I am not so naive as to think that this will solve all my focusing problems, but it is a start, a start that could be easily undone by simply dropping my camera bag. :(
Stef, I should have added that the focus target was a 45o target downloaded from the internet, you have seen it before. I was very careful to ensure that each lens was centred at the correct height and perpendicular to the focus point on the target. I have a floor area inside my house that has a 50 foot unobstructed view, so wind or weather were not factors. The target was illuminated by daylight from two large windows. The camera was mounted on a tripod with a ball & socket head equipped with bubble levels and the target was mounted on a second tripod. I set the camera up at varying distances from the target, depending on the lens being tested. Two second delay with mirror lockup was used and camera was on spot focus. Most shutter speeds were faster than the inverse of the focal length being used. All filters were removed from the lenses. Other pertinent data is as previously noted in my original post.
Testing ten lenses at varying apertures, focal lengths and distances from the target, together with removing the flash card and loading the results into the computer after each lens test, was a very time consuming process, not one I will repeat again soon.
Thanks very much Ascot for your explanation!
One thing though...Be very careful when you update your firmware...all the adjustment data will be lost!!! So you have to note down the adjustment settings as in Ascot's case above and you will have to put them in once again after having upgraded to your new firmware!
A good point Stef. I doubt that A850/A900 users need be concerned :D A77 and future camera owners surely will.
Interesting results AScot! I've been planning to do same measurements, but been too busy (read lazy :-) ).
Thanks for the explanation of test.
Rex......Only a misinformed beginner would send only his lens for adjustment without also sending his camera. Your theory does not hold water with me and is cynical beyond belief.
AScot your English is very advance for me to understand what you exactly mean but from my writting i didn't mean that these setting is for everybody the same :)
Yes manufacture save money with these future and customer are satisfied since they don't need to send there equipment away for 4 weeks but some customer may be more satisfied when the lens camera combination doesn't need at all any adjustment :)