Small sensor vs Large sensor: Why lenses decided which i will buy. (Long post)

Started Dec 15, 2013 | Discussions thread
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Ontario Gone
Ontario Gone Senior Member • Posts: 4,183
Small sensor vs Large sensor: Why lenses decided which i will buy. (Long post)

Preface: Disclaimer- this is all done in a FWIW point of view. Many will have different needs, likely most, so i only post this as help to the few who may be buying by the same criteria.

So i am patiently waiting for the post holiday season to get here, if there are after xmas sales i want to see them (plus this is when the wife gets small work bonusĀ  ). This gave me time to study as well. I am tied to no system, although i have a few sony apsc A-mount lenses, but all in all i am buying free of bias. I am not the type to spend thousands apon thousands on this, i don't make money from my gear and i have kids and other expenses. I will not be subscribing to the LBA club, i might have 3-5 lenses total, to cover the basic FL and that's about it. I will never buy the $2500 FOTM glass. So, i try to find the best bargain within my budget, which led me to a few choices.

As i have discussed in other threads, i am very pleased with the specs of the GX7, it's fantastic in almost every way. Almost, as the one thing that could improve is sensor size. Of course this would defeat the whole MFT system idea, but im just dreaming of the all around perfect camera. So i must decide, IQ or features. Small sensor MFT, or large sensor FF ect. Then i start looking at systems as a whole, meaning glass as well. Remember, everything i share here has been all along, filtered through my budget. When i say "best" i am not talking best overall, because there is always better if you are willing to spend more.

I shoot a lot of low light, family indoors ect. Low light AF is important, as is the ability to get sufficient SS. I know the 6D is good in both these areas, and it happens to be only $1500 on B&H. This however is approaching my limit for this purchase, which means i would likely get just one lens with it, perhaps a 50mm for a walk around, and then another in a few months time. So then i must decide, is the feature set i like so much on the GX7 (focus peaking, LV, nice EVF, silent mode, great video ect) worth giving up the great FF noise performance and IQ? Just to be precise, i decided to window shop the glass i WOULD most likely buy in each scenario, since glass is half the equation. It does no good to assess a system based on lenses you will never pay for.

According to DXO, both the 6D and D610 for example, are nearly exactly 2 stops better SNR than the GX7, judging them at around ISO 3200. Of course, the thing with light is, if you have a lens that is two stops faster, which allows you to set ISO two stops lower and match SS, the difference is closer to even, and actually, the DR is better on the GX7 when ISO is 2 under both the FF. So, i checked lens prices and rez charts. Remember, i know i am not paying $2k for any Canon glass, so my options to fill the FL gaps are going to be more of the non pro quality. I want a WA, 50mm equiv walk around, 80-100mm or so portrait, and a 200mm+ for the rest.

The 6D has great low light AF and is on sale, so does the $670 difference allow me to get better glass overall for MFT, or will lenses be even enough that the FF sensor has the advantage? The Canon 50mm F1.8 II would be my first buy, as it's only $110. It is decent at F2.8, below that it is horribad. But, the price is low, and i won't be spending much more than that up front, and later i still won't be spending huge amounts on any lens. That lens is good for a walk around, and puts my total purchase at over $1600. The GX7 is $830 body only. So what can i get for $770?

The Pany 25mm F1.4 is $530, but i will need it to be usable wide open to make up the two stops of ISO and match the 6D with a F2.8. Well, it is, in fact it's sharper. Here are some 3d rez charts from

Good in the center, but the Pany is far better across the frame.

Just to show what it looks like even at F2, F1.8 is a bit worse, not usable by my standards.

So in adding all this up, the 6D + 50mm comes to just over $1600, where the GX7 + 25mm is around $1360. Both have the same 50mm equiv lenses, and both will net the same SS at the same SNR for any given scene, but the Pany ends up saving $250 and the lens is better. Now i am aware this is only comparing the purchases with a single lens and with a price cap, but this is my budget vs my camera requirements. However, when i look at other lens comparisons of future purchase, the same thing happens. MFT has lenses that are so good at the wide ends, they end up negating the ISO advantage of larger sensors. The Olympus 45mm F1.8 is only $350 and would serve as my 90mm portrait. The Pany 14mm F2.5 would be my landscape. Both lenses are nearly as sharp as the Pany 25. This leaves only a tele to worry about, and i have a temporary fix for that, as my sony 75-300 only needs a $65 adapter to use.

Over and over i compare the FL that i will need to fill, and if i am to stay within my budget each time, the FF lenses just don't perform at fast apertures. I have known this for a while really but never compared side by side with MFT. The point is, if the lenses are not good at F1.4 or 1.8, or at least not good enough for me to want to use, they are losing the ISO advantage FF has. This has been a very long winded way of saying glass IQ really really matters, especially at the fast end if that's what you need.

To put a stamp on it, the actual features of the GX7 (and other MFT cameras, EM1 ect) are so good that if there was no IQ advantage to be had for larger sensors, the choice is a no brainer. Turns out, for my budget and needs, there isn't an advantage. In closing i will say again, if you have more to spend, or plan on buying the expensive Canon glass that is better at the fast end, you may indeed be able to take advantage of the FF sensor, but you will pay so much more for it. For somebody like me who refuses to spend a fortune for a hobby, it was the MFT glass that made the difference.

I imagine this will get all kinds of opinions, feel free to let the poo fly.

 Ontario Gone's gear list:Ontario Gone's gear list
Nikon D7000 Canon EOS 70D Nikon AF-S DX Nikkor 35mm F1.8G Nikon AF-S Nikkor 50mm f/1.8G Canon EF 40mm f/2.8 STM
Canon EOS 6D Nikon D610 Olympus E-M1 Panasonic Lumix DMC-GX7
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