Which of these looks sharper/better to you?

Started 2 months ago | Polls thread
TheSonyEnthusiast
TheSonyEnthusiast Regular Member • Posts: 259
Re: Which of these looks sharper/better to you?

StefanD wrote:

TheSonyEnthusiast wrote:

kiwi2 wrote:

TheSonyEnthusiast wrote:

The first shot is mine and I think the reason the first photo has the moon periphery out of focus is because teleconverter shrinks the already narrow depth of field of the 70-400.

I don't think you'd be having a DoF issue with something 400,000 kilometres away. It looks more like motion blur. Don't forget the moon is constantly moving across the frame unless you are tracking it on a EQ mount.

With the TC the f-ratio become slower and it exaggerates lens softness. What was the ISO and shutter speed?

While I will admit the shot was at 1/20 of a second, if it were motion blur it would affect the sharpness across the entire image. The reason I think it may be depth of field is due to the preciseness necessary in manually focusing; I took a series of shots barely nudging the focus each time toward infinity, and a fraction of a millimeter either way resulted in less resolved craters.

According to this DoF calculator, the DoF of a 600mm lens at f/8 focussed at the moon (384402000m) ranges from 1500m to infinity. That should be enough to have the whole moon in focus.

What's on paper and in practice do not necessarily match up.  The distances denoted on a lens's DoF window go up logarithmically, and different makes and models of lenses have different depths of field.  According to the DoF window on a typical lens itself, I should be able to have something at an "infinite distance" (I.e. Moon) in focus across a slight range of focus barrel movement as long as infinity is within that.  Usually DOF finders have markings for F8 and F32, and that would be for the lens itself (case in point, I could go narrower with F5.6); if you threw a teleconverter on a 1.4 teleconverter and smallest f-stop were 5.6, the range in focus would be for F8 now, for the F8 on the rangefinder window, thats now f11, etc, so your depth of field is different between between your lens at F32 vs with a teleconverter stopped at F32, the former will have more depth to its focus than the latter.

With the SAL70400G2 though, that isn't the case as there is no DOF indicator in the rangefinder window; there is only a black line denoting the focus (see photo below), which is no surprise because the depth of field on the lens is so shallow that Sony engineers probably felt putting a range on it would be pointless.

With the teleconverter attached, *any deviation* of the focus barrel either left or right from a specific point pushes it out of focus.  Which should be no surprise given then narrow window that is made narrower by teleconverter use, the logarithmic scale of distance to infinity, and the moon being *just before* infinity.  If you have a 70400G2, SAL14TC and an a99M2, try it and you'll see what I'm talking about.

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