I thought I would like to see if I could check out the above statement. I therefore looked at the 12-35mm f2.8 pana lens, which is a relatively heavy m4/3 lens: 305g, 74mm long.
Nikon FX 24-85mm f/2.8-4D IF is a somewhat similar lens even though it is not constant f: 545 g, 83mm
Nikon FX 28-70mm f/2.8 ED-IF is probably a more fair comparison given that it is the constant f2.8: 935g, 122 mm long.
For DX, I could not find a single fast lens with a comparable range. I did find 18-55mm f/3.5-5.6G VR II: 195g, 66mm -- however the fair comparison for Panasonic would be something like 14-42mm F3.5-5.6 II ASPH Mega OIS: 110g, 49mm.
In conclusion, from almost 2x to 3x the weight when comparing smaller nikon lenses to comparable reach pana lenses.
Niels
Hi Neils
The general point I was trying to make was that on the smaller focal lengths I can't see how 75g to 150g weight difference makes much of a difference in lens selection but I generally only carry a maximum of two lenses at a time. There are also some very heavy short focal length lenses weighing over 1000g.
There are quite a few, often heated, discussions on equivalency on Dpreview forums. The aperture has a big influence on the size and weight of the lens as does the sensor size. You are quite right that sticking to 2.8 on both results in lighter M4/3 lenses. However, I have no problem with 3.5 and those lenses are similar in weight to the 2.8 M4/3 lenses. 3.5 also seems to be the starting point for the more common DX lenses
You already mentioned the Nikon AF-S DX Nikkor 18-55mm f/3.5-5.6G VR II weighs 195g. I have the Pany 12-35 and before that had the old 14-140 at 460g. Both were fine for me weight wise. Probably not fair to compare the 12-35 to the Nikkor as the Pany is a better build but the image quality of the original 14-140 was not great so it's a fair comparison.
At a longer focal length, the Nikon AF-S DX Nikkor 18-140mm f/3.5-5.6G ED VR weighs 490 g 78x97mm vs the new Pany Panasonic Lumix G Vario 14-140mm F3.5-5.6 ASPH. / Power O.I.S 265g 67x75mm results in a greater weight difference of 230g and more bulk. Interesting that the weight of the Nikkor is similar to the weight of the old Pany 14-140 at 460g.
Comparing the Pany 100-300 to a DX offering makes an interesting case,
Panasonic Lumix G Vario 100-300mm F4-5.6 OIS 520g 74x126mm
Nikon AF-S DX Nikkor 18-300mm F3.5-6.3G ED VR 550g 79x99mm
Both are almost the same in weight and bulk. In the end this is where I have ended up. With no new tele zoom lenses (I don't want a prime lens) in either PANY, OLY or Sony E mount coming up anytime soon and me not wanting to wait any longer I took the plunge yesterday.
I pre-ordered the Nikon D5500 body and the 18-300 zoom. The end result; what I have now, GH3 + Pany 100-300 (550+520=1070g) to what I will be using D5500 + Nikkor 18-300 (420+550=970g). About the same in weight but with the convenience of a superzoom bridge camera. No lens changes on my trip in March. This gives me the same coverage I have now with the 12-35 and the 100-600. I expect the quality to be good enough for me but I am sorry to give up the EVF.
This doesn't work for everyone but it works for me.
Paul