DX Lenses should be brighter/faster than FX lenses

heartyfisher

Cool! more announcements on the Tokina lense today. Looks like it could make a nice wide aperture kit for a D500. Shame that Nikon is not playing in that field .. :-(

New Tokina 14-20 F2, Sigma 18-35 F1.8, Tamron 60 F2.0 Macro(portrait), Sigma 50-100 F1.8.

Seems that it is clear that DX can really have Wider Aperture lenses than FX and they have been artificially restricted for years ! Too bad that its about to be overrun by mirrorless :-(

snakebunk

Ironheart said:

http://www.lensrentals.com/blog/2010/07/how-autofocus-often-works
http://www.lensrentals.com/blog/2014/02/why-you-cant-optically-test-your-lens-with-autofocus
http://www.lensrentals.com/blog/2012/07/autofocus-reality-part-1-center-point-single-shot-accuracy

I really recommend all 4 parts of the last article, but these should be enough to burst anyone's autofocus bubble )
I agree with @Paperman, it's a wonder it works at all....

Thank you, I have now read all articles and find them informative. However, I found no explanation for how a lens can be bad at focusing in low light (which was the discussion I had with spraynpray).

In other words: A lens can focus fast or slow, it can be accurate or inaccurate and it can work good or bad with a certain camera, but I do not see how darkness can affect the autofocus of a lens.

moreorless

I think you can see part of the problem with these recent Sigma F/1.8 zooms. Yes the max aperture is impressive but it comes at the cost of a much more limited range than the FX equivalent.

My guess is that getting the equivalent amount of light into a smaller imgae circle is simply a more complex optical task.

WestEndFoto

I don't think it has anything to do with the size of the image circle. Nikon's best zooms have more limited ranges than their budget zooms. It is just tradeoffs between cost, size, engineering etc.

moreorless

The Sigma 18-35mm is what roughly 28-53mm? that's much more limited that the typical 24-70mm F/2.8 that its the equivalent of aperture wise. The new 50-100mm is also obviously much more limited in range than a 70-200mm F/2.8.

The DX lenses are pretty much the same size as the FX but again my guess is that getting F/1.8 into a smaller area with higher quality for the higher pixel density is a more difficult task.

Ontop of that as well don't you have an issue with light loss around F/2 and below with fast lenses on digital? with FX I think this is less of an issue for most people as pretty much everyone shooting faster than F/2.8 is doing so mainly to control DOF but with DX your still looking at shooting for low light ability below that and perhaps not getting what you [aid for.

DaveyJ

Lens WE will use on the D500: 16-80 Nikkor, 10-20 Sigma, 10-17 Tokina, 12-24 Nikkor, 55-300 Nikkor, 70-300 Nikkor, and a 200-500 Nikkor. None of the lens we own are super fast. The 35 f1.8 Nikkor we own will not be used. It sits on a D90? We will not be adding to our Nikon lens unless some offering looks really great for wide of field photos. We are planning on using fast cards.....and we are waiting for Ikelite to announce a UW housing and ports for the two widest listed lens. The 10-20Sigma, and 10-17 Tokina. This is based on user preference from divers using mostly the D7100, not that many went UW with the D7200. We are after the speed, etc.. And will buy it with a three year protection plan. When I get (if I do) a D500 as the grandparent, I will pass,on the protection plan as I will keep using my Nikon1 AW 1 UW and Go Pros, leaving my latest Nikon DSLR for land use and less danger. Right now I don't see huge difference in our D7200 and D7100. So that means the fast primes in DX don't pose on lens we demand or will buy. The above lens have served extremely well and we are satisfied with all aspects of their service. I might even take a D7300 instead of a D500 second camera for my one personal use as I think a little better video might be on a D7300 over the D7100 I use as daily camera. Fast DX primes have no attraction here.

retread

My shooting is mostly wildlife and sports. My DX lenses are the Tokina 11-20 and the Sigma 17-50, it is more a normal zoom. I then go to FX with the Nikkor 24-70 and 70-200. For primes I have AI and AIS from my film bodies that I still like but only use if I have time to play. After the D500 I plan to add a D810 or D8XX when the time comes.

heartyfisher

Before the amazing sigma 1.8 zooms there were no fast zooms that fast, not even F2.0 zooms
Even the "standard" F2.8 Zooms and primes were "restricted" in range and aperture because of the aberrations wide open. so You would expect some trade offs for having F1.8 Zooms at all. (Having said that the first F2.8 or 3.5 zooms were all very restricted in range as well)

The argument that these DX 1.8 zooms have limited value compared to the FX F2.8 counterparts seem to be illogical ( biased ? ) as its obvious that the F1.8 is 1.5 stops (ie almost 3 times ) brighter than F2.8 the only way you can say that the F2.8 zooms are almost as good is if you want thin DOF then F2.8FX is almost as good as F1.8 DX. otherwise in any other criteria the F1.8 Zooms are better. ( except for the range :-) but that is restricted by IQ aberation of wide aperture lenses )

Do I really need to spell out the advantages of having a lense that is 3 times brighter? when needed/wanted I think the restrictions are a good compromise.

Re: "Light loss on digital below F2". That is related to the angle of light hitting the edge of a sensor from a lense. It effects FX much more than DX. and newer sensor are also less effected because of the shorter distance between the microlenses/colour filters to the actual silicon sensor, especially the ones with offset micro-lenses. I am not sure if Nikon has offset micro lenses etc yet on their DSLRs but I do know that the Coolpix A had it and there was some "Nikon fairy dust" sprinkled on the D810 vs D800. [ I am hopeful this fairy dust recipe got to the D500 !! ;-) ]

Msmoto

Earlier in the thread I had joked about NAS and purchasing equipment. However, I fully agree, cash in hand is an excellent policy before purchasing any camera gear. And, I believe we need to exam carefully our requirements before the purchase as well.