panorama software,virtual tour software
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2006-12-14
#1

How to read lens MTF chart

There has been some discussion about the quality issues of the Sigma 8mm f4 and f3.5 fisheye lens.  One of the ways to determine the lens performance is to evaluate its MTF [Modular Transference Function] chart.  Any lens manufacturer will at some point during its design will subject it to laboratory testing.  They will generate an MTF chart.  Canon does it.  Nikon does it [on the Japanese site].  And now Sigma has started putting it on their website. 

So what will an MTF chart do for us ?  It will help us determine if the hunk of glass we are holding in our hands will give us those beautiful sharp crisp images that we need.  The MTF chart is objective approach to determine if the lens will produce great contrast and sharp qualities.  An MTF chart should be available for all their lens types not just a fisheye lens we see below.

The MTF chart essentially shows us of all the light that enters the front end of the lens how much and what quality makes it to the back end where it is registered on your cameras sensor.

The chart and lens (f4) is layed out below.  Left side vertical scale is on the 0 center axis of the lens and it is measured from 0.0 to 1.0.

0.8 to 1.0 Excellent
0.5 to 0.8 is good lens performance.
0.50 and below is poor lens performance.  
PLEASE DISREGARD the rating labels I wrote on the chart.

The bottom horizontal scale starts at 0 -> 5, 10, 15 and 20.  This is the horizontal lens axis from lens center to the far right side of the lens edge rim.

 The test shows how many lines per millimeter the human eye can determine along this horizontal axis. 

Red solid line is Contrast at 15 lines per millimeter. 
Red dotted is Contrast 30 lines per millimeter.

Green solid line is Sharpness at 15 lines per millimeter
Green dotted is Sharpness 30 lines per millimeter

With some lab tests in your hand you can now go into a camera shop and feel comfortable that you KNOW that the lens you are about to buy WILL be sharp and produce those amazingly crisp panoramas.

Compare the solid green sharpness curve at 15 lines per millimeter between the F3.5 and F4.0.

I do not think there is any doubt that the Sigma 8 F3.5 is a sharper lens.  So I called my favorite local camera shop and ordered the F3.5 lens.  He did call back and cheerfully explained that it is now back ordered until middle of January 2007.  Thats ok.. thats only 30 days from now.  We do not leave for our Cancun project until 15 February. 

By the way.. the F3.5 like the F.4.0 will fit the Agnos RingTS8 pan head.

NOW please, would someone go and find the MTF for the Nikkor 10.5 and post it here on the forum ?

Source information
Sigmaphoto.com/ Lenses
http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3319&navigator=4

Luminous-Landscape - MTF Explained
http://luminous-landscape.com/tutorials/understanding-series/understanding-mtf.shtml


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Dave
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2006-12-15
#2
agnos is having reporting having trouble with the ring on the 3.5 sigma, it ends up fixed on the focus ring which is less than ideal. But they say they are working on a solution and will provide it free to afected customers.
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2006-12-15
#3

Yes this is true,  I talked with Agno's this afternoon.

 


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2006-12-14
#4

daves, on what camera are you gonna put the sigma 3.5 ?

if u get a chance, check ur  forum Inbox


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2006-12-14
#5

To answer your question. 

Yes, I did read your private message earlier today.  I am holding off answering until I get more information.  It might not apply to our situation.

We will probably use it on either of our Canon Rebel XT (350d) or the Canon 20d.  Most likely use in on our Canon 5d. 

Oh I found the Nikkor 10.5 MTF chart.  Notice that both solid lines for the Contrast and Sharpness stay above the .8 all the way across the lens face.

http://www.nikon-image.com/jpn/products/lens/dx/singlefocal/af_dx_fisheye_ed_105mmf28g.htm


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2006-12-14
#6

when u get it,  if u get a chance to do a 3 shot interior with tiles  with the 5d, let me know.

now that ur a canon man,

you notice big differences between those 3 models?

i reckon the 5d stands out more simply cuz is full frame.

im wondering if anybody has the rebel xt with the self cleaning/vibrating sensor.

i think you dave have the previous model before they implemented that feature.


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2006-12-14
#7

Yes.  that one is the XTi or 400d

The Xt is my wifes camera.  I was using the 20d.  Then we got the 5d.  So now we use the 20d and the Canon 10-22 for still shots and the 5d with Sigma.

If I could find someone here in the US that wanted to buy the XT.. we might consider selling it.  Then we would upgrade to the 400d XTi.


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