Difference between Pentax f/1.4 and f/1.7

Hi,
I have my eye on a 50mm f1.4. Some say the 50mm f.17 is better but I'm' drawn by the extra speed.
Would anyone be able to post some pics comparing the difference between f1.4 and f1.7 at:
a. low light
b bokeh

Thanks,
Pa.

How do you (or they) "mean better" ?

Better relates to the f1.7 design having a flatter field and higher resolution.

The f1.4 version has higher contrast and is faster.

This is all related to what the expectation was as reagrds usage. It was assumed the f1.4 was a low light reportage lens and that the f1.7 was the one people would generally have and generally abuse with optical add ons, close up devices, etc.

Of course if you want a low light reportage lens then the f1.4 is better.

For me in this age of good quality digital ISO the cost difference between f1.4 and f1.7 is somewhat negated for 1/2 a stop, is using ISO 100 any better than using ISO 160 (or 800 v 1200)? If your looking for narrow depth of field, again there is not much of a difference to justify the extra cost of the f1.4.

Both are fantastic lenses but as John mentions ifyou want to play around with addons the f1.7 is the better option and contrast can be manipulated in camera or in post.

And there is no point buying f/1.4 unless you are going to use f/1.4!

I love my f/2.8 zooms and shoot a lot of pictures very wide open (occasionally stopping down to f/4.0). And then you find you are having to use very high shutter speeds. But simply changing to a lens with a wider aperture for any other reason is rarely worth it.

Well there's certainly a difference worth having between my f/1.2 and f/1.4. I also have an f/1.7 and when I get time I'll do some comparison shots for bokeh, etc

Personally I think the best thing to so is take all our subjective comments into consideration and then look around the Tinterweb for example pics from any lens you are considering. Then you can choose on floats your boat.

It's been documented on this board previously that digital sensors can't see f/1.4 they can only see it as f/1.7 anyway and the focusing screens see both as about f/2.5. The only slight advantage with an f/1.4 and it may not apply across the board is that a 50mm A f/1.4 lets through slightly more light at every stop than the 50mm A f/1.7...... it's a maximum of about 0.3 stops, well inside the tolerance of the metering system.

I can't speak for anyone else's experience but my K20D sensor can certainly see the difference between 1.2 and 1.4 and 1.7 - I haven't tested my 1.2 on my K-5 yet. but I'll add that test to the list of things to do and note aperture differences on the same shot


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Agreed here. I can never realise the beauty of the 1.2 DOF and bokeh until I actually look at the pic.


Personally I think it's a mistake to judge lenses entirely on technical data. These lens have different characters.

I'm also sceptical about this statement since I can definitely see a difference between 1.4 and 1.7.

I don't see where that's coming from either, it doesn't appear to make any sense.

this whole no difference between 1.7 and 1.4 comes from a luminous landscape article: luminous landscape article.

while i follow the reasoning, i think his explanation is jumping to conclusions. i can certainly see a difference between 1.7 and 1.4.

i would always go for the f/1.4. i'm a speed-freak. every little counts. sharpness and field-curvature means little to me, so long as it's 'good', it's 'good enough', and most primes are good enough. it's all about the background rendering.

I think that's all highly dubious, but unfortunately the internet being what it is it gets repeated until it becomes a fact...

The manufacturers will set their sensor sensitivity so that it closely approximates the ISO value, but we should remember it isn't film. It's a sensor and behaves in a different way.

The main effect of the aperture is on DOF and this will be significantly different at f1.4

From Mr Luminous Landscape ....

"In other words, the "marginal" light rays coming in at a large angle from near the edges of the large aperture are completely lost."

This is clearly nonsense from my experience with the K20D and my f/1.2 v. 1.4 ( both apartures outside Mr Luminous Landscape's window of sensor pickup angles )

At 1.4 in the OOF regions you can see the facets of the aperture blades at 1.4, while at 1.2 the 'bokeh' is perfectly round as the lens is wide open

Mr Luminous Landscape is claiming that these sensor tubes are acting as an aperture limit.

As his tests are with a Canon machine I have just messaged my Canon shooting buddy, who recently bought an F/1.2 50mm and asked him he would do a test at 1.2,1.4 and 1.7

I thought it might be something to do with the smaller area of a cropped sensor compared to a frame of film?

All I know is that with my Samyang 85mm f1.4 I get a very bright viewfinder and it's dead easy to focus manually!

I don't see any reference in this thread saying there is no difference between f1.4 and f1.7 and I've never herard of Luminous landscapes