f/1,7, f/2. Why? Differences?

[papasito]

I have seen some brands with both 50 mm lenses (or 55 mm sometimes), the 1,7 and the 2 versions.

In almost all the brands, the f/1,7 have 6/5 scheme and the f/2 have 6/4 one.

Also the f/2 should be 50 mm lenses and the f/1,7 were first a55 mm and then 50 mm.

Well, what is the differences en IQ among the f/2 and the f/1,7 lenses if this exists?

Thanks for read.

Horacio.

[Gerald]

Normal F1.7 and F1.8 lenses are small developments of F2 lenses. In general, all these lenses are based on the 6-element 4 or 5-group Double Gauss optical structure. The main motivation to launch a F1.7 or F1.8 lens was marketing, for so the lens manufacturer could tell it had a faster lens that competitor's F2. To be fair, Leica is one of the few manufacturers that has always been true to the normal lenses with F2 aperture.

In practice, the differences between the F1.7 lenses, F1.8 and F2 are in general too small to be considered.

[JJB]

Hola Horacio. Given that we're no longer limited to film with an ISO of 400 or 800, I don't know how meaningful the difference between 1.7, 1.8, and 2 is. I usually go up a stop or two from wide open, so the potential rewards are further diminished. While I appreciate a 50/1.4 for certain applications, much of the time a 1.8 or 2 is just as good. I do find that on a cropped sensor camera, there is a difference between 50 and 55mm when I compose my photos.

I agree, that much of this minor variation can be explained by marketing competition.

[Mos6502]

As has been stated above, breaking through f/2 into the 1-point-something range was a big deal when it came to marketing cameras. The mentality that "faster equals better" was marketed, so having a 1.9 or 1.8 lens instead of f/2 was important.

Without knowing which lenses in particular you are asking about I will comment that in my opinion, generally, the 1.8 and 1.7 lenses do not perform as well as their f/2 relatives, especially when used wide open. Unlike 1.4 lenses which needed another element or two to perform adequately, most of the lenses between f/2 and f/1.4 are just "stretched" six element designs.

The reason for so many companies making 55mm lenses instead of 50mm lenses was to provide a 1:1 viewfinder image (ie. life size). Building a viewfinder that would give 1:1 viewing with a 50mm lens was more difficult and only a few companies decided it was worth the effort, this difficulty was exacerbated when viewfinders needed to incorporate exposure needles, aperture indicators, etc. which mean reducing the magnification of the viewfinder image to fit in all the other "info" around it.

[Oldhand]

These are all good answers Horacio.
There is so little difference between f1.8 and f2 lenses that either would give similar results.
I have read somewhere that in the case of the Takumar, the f2 and f1.8 were the same lens but the f2 was simply aperture limited for marketing purposes. I don't know how true that is but it would not surprise me at all.
Almost all 50/55/58mm lenses with a maximum aperture around f2 will be good, although some render colour and bokeh differently.
OH

[memetph]

Yes those Taks 1.8 and 2 are the same lens. There were sold with the SP 500 and 1000.

[papasito]

Thanks guys.

I read in some reportes of lenses that the 1,7 have better IQ that their brothers of f/2.

In that way the rokkors, Super takumar o SMC ones, rikenons M42, Yashicas M42, perhaps the mamiyas too.

And was rare to me that if they are all the same lenses /F/1,7 and F/2 versions) they have not the same IQ.

[paulhofseth]

In this context it is interesting that in 1968 the Swiss optics specialist Kern in Aarau went against the then current marketing fashions and recalculated their apochromatic 1,8\50 Macro-Switar and replaced it with a 1,9 version.

p.

[luisalegria]

Some later (late 1970's-90's) f/2 lenses are actually simplified 5-element formulas.
For example the Pentax M and A 50/2 . This was not considered a particularly sharp lens.

The Pentax M and A 50/1.7 have 6 elements.

[IAZA]

I tried Zenitar 50/1,7, which is said earlier than zenitar 50/2, The later has more plastic stuff, sharp, contrasty etc. But I prefer 1,7 one smooth rendering, sharp also.

[Lightshow]

[papasito]

[papasito]

In mamiya brand, there were two versions of the 1,8/55.

The first, chrome nose (TL version) had 6/4 scheme.

After it, the all black (from DTL to SX) lens had 6/5 scheme.

The F/2 had (from DTL to SX) ever 6/4 scheme.

Horacio.

[Mr G]

Another consideration of faster lenses is the amount of light in the viewfinder, a real consideration when trying to focus in low light. Tessar's, Domiplan's etc are even slower at 2.8, although fine lenses.
Smaller, faster and lighter seems to be the norm these days usually at the expense of build quality, just my opinion.

[dimitrygo]

[paulhofseth]

Two small additiona to the info on that netsite;

* before the "fat mount" Macro Switars and their "medium mount" auto aperture predecessors, there was an even earlier "slim mount" manual aperture version introduced in 1951 with more or less the same dimensions as the early Alpa-Xenon.

* Some of the Switars -i forget which batch- must have had slightly different data since they used Thorium glass - which the later ones did not use.

p.

[Pancolart]

Perhaps this topic is good answer why F1.7: http://forum.mflenses.com/auto-rikenon-1-7-50-ouch-t68523.html
Last photos would be somehow harder to make with F2.0 speed.

[Lightshow]