Micro-adjustment with teleconverters

[Nancy Bell]

It is recommended that to micro-adjust a 400 mm lens the target should be set approx. 33 ft. away. Should this distant be changed when I put on the 1.4 teleconverter to determine the micro-adjustment?

[Jay Gould]

Hi Peter,

The distance supported by the LA Distance Tool: http://www.whibalhost.com/lensalign/ldt/index.html is 25 x the focal length.

Have you done any testing to compare applying MA at the minimum focus distance and at the recommended 25 x FL?

Living in a caravan I have had a problem finding a decent place to do the LA, for example with my 70-200 at 200 + 2.0 would = 32' according to the distance tool.

Cheers, Jay

[Alan Lillich]

Nancy,

Yes, you should account for a TC, and you should ignore the body crop factor. You can make the math easier also. The LensAlign folks recommend at least 25 times the focal length, but it does not have to be exact. I use 1 foot per 10mm of focal length, which works out to about 33x. So a 400 with 1.4 TC works out to 56 feet.

You can see the LensAlign FAQ here:
http://www.mtdhelp.com/kb/lensalign-how-to

The TC question is here:
http://www.mtdhelp.com/kb/lensalign-how-to/do-i-consider-the-tele-converter-when-calculating-distance

Alan

[Charles Glatzer]

I can tell you if the primary lens is in need of adjustment, it will also be in need with the converter.

Chas

[Alan Lillich]

Chas,

The body crop will of course affect the size of the target in the frame. My memory was a little off, it is 30.5x to get 1 foot per 10 mm of focal length. Using that multiplier, here are full frame (D700) and 1.5 crop (D300) images - about 10.5 feet with a 105 mm lens - hand held, not overly concerned about being exact. The target is a LensAlign Mk 2. These are not focus tuning shots, just size in frame shots.

Alan

[Jay Gould]

I am very happy to hear about doing it at MFD.

May I then assume that if MFD works then any comfortable distance between MFD (the closest you would apply MA, and the distance recommended by the Distance Tool (DT) (the longest distance you would set up for MA application) would also work?

Peter, currently I am in Thailand (very rainy Thailand) for three weeks. I brought with my various lenses, two tripods, and the MKII.

The longest distance I can create from the camera to the MKII is 30'.

For the moment my longest focal length would be my 70-200 + 2.0X = 400 = 40' using the 10' rule.

Peter, based upon your suggestion, with 70-200, for example, without either extender I can setup at 20' (the Distance Tool recommendation), and with either extender leave the setup at 20' since that distance will be between the MFD and the DT recommendation; correct?

Thanks, Jay

[Mike Vanecek]

Jay, Performing MA at minimum focus distance gets the LA tool in full view. Using 25x minimum focus distance with my 800mm lens would mean 150m or close to 500ft. For the large lenses this rule is useless (atmospheric interferences etc). I have done my MA on my tele lenses at (close to ) minimum focus distance with great results. My suggestion is to do your MA at different distances and do the field test: you will find the optimum somewhere. Remember that at whatever distance you are adjusting, once you use the lens at another distance, the tolerances will vary (never mind temp, humidity, bumping your lens, etc)
Am I interpreting your comment correctly, you use ~66 feet (or 80 feet) for doing the MA on the 800?

Thank you.

Mike

[Blake Cook]

If you set MA with stacked TC's the camera will remember only the TC on the lens. The camera MA memory doesn't see the second TC, which means the body will auto-set the same MA for Lens +2x TC as lens + 2x and 1.4x stacked.

None of this matters if you manual focus, but the 1D4 will auto-focus with a 300 f/2.8 IS +2x +1.4x in good light and not so good light if you get it in the ball park manually.