50mm FA1.4 vs FA1.7
The f1.4 is a reportage/low light lens and as such has high contrast but lower micro-detail. So you would expect high MTF20 results and moderately high MTF50 results. It will not have as flat a field at close distances and is not ideal for attaching to bellows.
The f1.7 design will have higher micro-detail and a flatter field, so it's the lens to abuse for multiple purposes.
However, although the two lenses differ in detail, they are both excellent lenses.
The lenses I find much more to my taste are the 43mm f1.9 Limited and the 40mm f2.8 Limited. Lenses are more than just technical results and some will suit individual photographers better than others.
Best regards, John
Although I've never used the 1.7 version I can vouch for an increase in IQ on the 1.4 when a hood is added... Images are certainly more 'contrasty' making them at least 'look' sharper... Without the hood f2 was as wide as I'd go but I now have no qualms about shooting at 1.4...
Screw-on 49mm metal hood - less than a fiver from ebay including shipping from China -

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Digital:
Pentax K5- Vivitar 19mm 3.8; FA35mm f2; D-Xenon 100mm macro f2.8; DA50-200mm WR...
Flash:
Yongnuo YN-560; Vivitar 285HV; Cactus V4 triggers...
Film:
Pentax-MX & M50mm f1.4; Spottie & 55mm f1.8; MG & M40mm 2.8...
http://www.flickr.com/photos/daveholmesphotos/
Best regards, John
I was trying to balance the loss in speed with the extra sharpness but sounds like its a bit more complicated. I had assumed they were largely the same design.
Certainly agree that its not all about the numbers, I just don't want to buy another lense that doesn't bring something new to the table.
I think the kit-lens should also come with a hood provided to be honest...
But I've taken us off topic...
If someone offered me a swap for the 1.7 version against my 1.4... I'd say no... That extra tiny bit of speed could make or break the shot...
........................................................................
Digital:
Pentax K5- Vivitar 19mm 3.8; FA35mm f2; D-Xenon 100mm macro f2.8; DA50-200mm WR...
Flash:
Yongnuo YN-560; Vivitar 285HV; Cactus V4 triggers...
Film:
Pentax-MX & M50mm f1.4; Spottie & 55mm f1.8; MG & M40mm 2.8...
http://www.flickr.com/photos/daveholmesphotos/
Sigma 30mm 1.4 ?
Gets good reviews (some say not sharp in corners - but that's not why you buy a 1.4 lens IMO) and a very usable focal length...
........................................................................
Digital:
Pentax K5- Vivitar 19mm 3.8; FA35mm f2; D-Xenon 100mm macro f2.8; DA50-200mm WR...
Flash:
Yongnuo YN-560; Vivitar 285HV; Cactus V4 triggers...
Film:
Pentax-MX & M50mm f1.4; Spottie & 55mm f1.8; MG & M40mm 2.8...
http://www.flickr.com/photos/daveholmesphotos/
Best regards, John
The 18-55 is now relegated to the 'stuffbag' in the cupboard anyway, so no great loss

........................................................................
Digital:
Pentax K5- Vivitar 19mm 3.8; FA35mm f2; D-Xenon 100mm macro f2.8; DA50-200mm WR...
Flash:
Yongnuo YN-560; Vivitar 285HV; Cactus V4 triggers...
Film:
Pentax-MX & M50mm f1.4; Spottie & 55mm f1.8; MG & M40mm 2.8...
http://www.flickr.com/photos/daveholmesphotos/
DA35-LTD-Macro brings something really unique to the table in similar focal length... Slower AF (its a macro so much longer focus throw) but by all accounts a great 'do it all' favourite...
Just planting seeds...
........................................................................
Digital:
Pentax K5- Vivitar 19mm 3.8; FA35mm f2; D-Xenon 100mm macro f2.8; DA50-200mm WR...
Flash:
Yongnuo YN-560; Vivitar 285HV; Cactus V4 triggers...
Film:
Pentax-MX & M50mm f1.4; Spottie & 55mm f1.8; MG & M40mm 2.8...
http://www.flickr.com/photos/daveholmesphotos/
In an ideal world the 31mm Ltd should offer the best of both worlds!
[link=https://500px.com/will_brealey/[/link]
The sigma 30mm 1.4 is an interesting option, will look into it.
I have one and love it. As I bought specifically got shallow DOF shots I rarely use it stopped down below 1.4, although it's a great performer when you do. Highly recommended.
Some great examples here
[i]Bodies: 1x K-5IIs, 2x K-5, Sony TX-5, Nokia 808
Lenses: Pentax DA 10-17mm ED(IF) Fish Eye, Pentax DA 14mm f/2.8, Sigma 17-70mm f/2.8, Pentax-A 28mm f/2.8, Sigma 30mm F1.4 EX DC, Pentax-A 50mm f/1.2, Pentax-A 50mm f/1.4, Pentax-FA 50mm f/1.4, Pentax-A 50mm f/1.7, Pentax DA* 50-135mm f/2.8, Sigma 135-400mm APO DG, and more ..
Flash: AF-540FGZ, Vivitar 283
Actually, I tell a lie, I have an M 50mm attached to my Super-A which will be swapped for an A version if I can find one at a decent (cheap) price.
Peter E Smith
My flickr Photostream
My 2 lens kit K-x came with hood for 50-200(WR) and without on the DA18-55???
The 18-55 is now relegated to the 'stuffbag' in the cupboard anyway, so no great loss

The 18-55 that came with the K-x is the DA-L version and hence no hood. The 50-200WR is not a DA-L (kit) lens and hence has a hood

Pentax K10D + Vivitar 55/2.8 macro + Super Takumar 55/1.8 + SuperMultiCoated Takumar 85/1.8 + SuperMultiCoated Takumar 135/3.5 + SuperMultiCoated Takumar 200/4 + Super Takumar 300/4
Pentax K100D + DA18-55ALII + DA55-300
Pentax K5 + FA31Ltd + M50/1.7 + DFA100WR + M120/2.8 (+ DA18-55WR at occasion)
gunner
Member
Kent
I have an FA1.4 and I'm generally happy with it. However, I've been looking at an FA1.7 and have heard that it's generally thought to be the better lense - particularly when looking at sharpness at wide apertures.