Steve Spencer
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 p.1 #3 · Thoughts on MFD and MWD of the new Sony FE 100mm f/2.8 Macro GM Lens | |
Erictator wrote:
I started this as a reply to another thread but thought it might be better posted on its own to not hijack that one with my ramblings.
I know I am probably an idiot for caring or bothering to check or not already knowing this, but I went through the exercise so I could fully understand the relationship between MFD (Minimum Focus Distance) to the sensor vs/ MWD (Minimum Working Distance) to the front lens element at the various Magnifications of the new Sony Macro.
Why? Just because... and to get a rough idea if having 1.4x Magnification gave any useful "extra" working distance at 1:1 or other lower magnifications to justify the potential purchase of the new macro to myself compared to lenses I already own.
So, I started by finding the PDF of the manual on Sony's website and found this tidbit:
https://live.staticflickr.com/65535/54866842552_fe0a7cd916_z.jpg
Now that is to the sensor, so the other tidbit picked up was that while the MFD is 10.2 Inches, the MWD is 3.5 Inches, so a difference of 6.7 inches.
So, to make a chart of MWD based on Magnification, what we get is this:
1.4x = .26 Meters = 10.26 Inch MFD to Sensor, but 3.5 Inches MWD to front element
1.0x = .28 Meters = 11.02 Inch MFD to Sensor but 4.32 Inches MWD to front element
0.5x = .37 Meters = 14.56 Inch MFD to Sensor but 7.86 Inches MWD to front element
0.2x = .67 Meters = 26.37 Inch MFD to Sensor but 19.67 Inches MWD to front element
OK, so that was fun, but how does that help us? Well, for those of us chasing bees, butterfly's, lizards, frogs, whatever little creatures that we don't want to spook, MWD matters, as well as the actual magnification ratio at that distance and now we can compare it to stuff we already might have on the shelf:
For instance, comparing the above to my Sony 70-200MM 2.8 GMII at the 70mm end of the zoom range:
0.30x = .40 meters = 15.74 inch MFD to sensor but 7.75 Inches MWD to front element
And at the 200mm end of the zoom range:
0.263x= .82 meters = 32.28 inch MFD to sensor but 24.28 Inches MWD to the front element
Yes, the 1.4x and 2.0 TC will add magnification, but with the same MFD. There is no chart to see what the new Magnification is at various distances with TC other than the max Magnification at the MFD, but you can guestimate it will extend the working distance by about the ratio of the chosen TC to get the previous mag ratio that it would have had sans TC, right? I'm not willing to make another chart for the mental exercise, heh.
Can anyone here corroborate my math/findings? I "think" I have this correct...?
If so, I may have just talked myself out of a new lens... because my existing lens on a 61MP sensor is pretty much giving me the same thing I will get with the new macro at the longer shooting distances I would typically use to shoot the kinds of subjects I shoot (meaning I'd still be cropping in post with both lenses at those distances), and I can always put my 1.4x TC on my existing lens for more Magnification also.
Hope that wasn't too much of a ramble and made sense, heh.
Eric...Show more →
A far as I can tell your math is right, but there is one factor you will want to consider that will change the MWD calculations. Keep in mind when you add a TC you not only increase magnification, but you increase the length of the lens. I believe when you add a TC the MFD is the same, but the MWD won't be because the lens is now longer. The MFD is to the sensor and you need to subtract the new length of the lens with the TC attached from the MFD to get the MWD. So for the new 100mm Macro GM instead of subtracting 6.7 inches from the MFD to get the MWD, you will need to subtract 6.7 inches plus the length added to the lens because the TC is attached.
I think for a lot of folks who do this type of shooting, the lens they will be comparing this new Macro to is the 70-200 f/4 G II Macro. The 100mm GM macro will be better if you need the extra magnification it provides, but if the 70-200 f/4 G II Macro provides enough magnification it will provide a little bit longer MWD. For example, the MFD for the 70-200 f/4 G II Macro at 200mm is .42m, and the length of the lens is .205m, so I believe the MWD at .5X magnification and 200mm would be about .22M or about 8.5 inches which compares to 7.86 inches for the 100 GM Macro at .5X magnification. So, the 70-200 f/4 G II Macro gets you a little more working distance, but not a lot.
If someone wants a longer MWD and .35X is enough magnification, however, then I think the Sony lens they should consider is the 100-400 f/4.5-5.6 GM. It will provide over 30 inches of working distance at .35X. That much longer working distance can be quite useful for some types of shooting and if one adds the 1.4X TC, they can still get .5X magnification with that lens.
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At least they let us cheat and use a slide rule in that class (yeah, I'm old... ) but I did get to use the Texas Instruments TI30 towards the end of those classes as calculators became more accepted, they cared more about you knowing how to get the answer and what formula to use than the math in those electronics classes.