Pentax/Sigma 50 f1.4 Comparison
A sharper lens won't give you an increased DOF at the same aperture. It just means that the part of the image that is in focus will be sharper.
You need to either be careful and skilful with what you put in focus with a shallow DOF, or use a small enough aperture (large enough f number) that all of your subject is easily in focus.
Anyway, Pentax 1.4 lenses are no sharper than what you have already at around f1.8 or f2. I don't know about the Sigma. I hear the new Pentax 55mm f1.4 is sharp at f1.4, but it's a very expensive lens.
~Pete
Thanks for replying so quickly.
What I wrote may be misleading, as I'm comfortable with how DOF works, and how it becomes even more shallow (and critical) with increased aperture.
My thread is more to do with the benefits of using autofocus on a lens such as the 50mm f1.4 : is autofocus better than manual at achieving sharpness? We have to assume of course that neither the photographer or the subject moves after focusing.
Also, I guess the autofocus is quicker than manual.
My real question to the forum though is just about the Sigma lens itself, to ask if anyone has experience of using it.
Many thanks.
Alan.
Camera: K20D.
Lenses: Pentax DA* 55mm f1.4 SDM, Pentax DA* 16-50 SDM, Pentax 18-250 SMC DA, Pentax-M 50mm f1.7, Sigma 70-300 F4-5.6 DG macro.
Flash: Pentax AF360.
I find MF sometimes more accurate than AF when the subject is well lit and shows up clearly through the viewfinder - even more so with a Katz Eye focusing screen, but also with the standard screen.
(I have an MF 50mm f1.7 and a AF 50mm f1.4, Pentaxes).
~Pete
As this appears to have been a 'slow' thread, I gather there aren't too many Sigma 50mm f1.4 owners within the Pentax Forum. Interesting!
Anyway, I very much appreciate your input about your own experience of the auto & manual lenses. It's enough for me to probably delay a while and just keep going with the old manual lens, which btw, I think is excellent.
Have to see what else I can spend my money on!

Cheers.
Alan.
Camera: K20D.
Lenses: Pentax DA* 55mm f1.4 SDM, Pentax DA* 16-50 SDM, Pentax 18-250 SMC DA, Pentax-M 50mm f1.7, Sigma 70-300 F4-5.6 DG macro.
Flash: Pentax AF360.

Joining the Q
I suspect I would prefer the Nikkor to the Sigma, and that probably I would also prefer the Pentax for the same reasons.
Best regards, John
If you want to see if AF would help, then try using trap focus. Set your camera to AF-C and it'll only let you take a picture when it thinks the lens is in focus (this only works for manual lenses).
Stevo, I will try 'Trap Focus'; that looks like it could be very useful.
Presently, I've just left the camera on AF-S, although it does beep and give me the red square when, I presume, it thinks it's in focus. I'll try the experiment to see what the difference is.
Shim. Thanks for that link to the review of the Sigma lens. Excellent reading, and I certainly wouldn't be too unhappy now about spending the extra on the Sigma lens.
Changing subjects completely, I followed-up the thread about Jessops selling off stock yesterday, and bought my first flash-gun, the Pentax AF360. I'd been reading the excellent material recently on this forum about flash photography, and had just about made my mind up that I'd go for the AF360 anyway...so it was nice to get it for £121 inc. p&p.
Flash photography, now there's a can-o-worms!

Many thanks to all.
Alan.
Camera: K20D.
Lenses: Pentax DA* 55mm f1.4 SDM, Pentax DA* 16-50 SDM, Pentax 18-250 SMC DA, Pentax-M 50mm f1.7, Sigma 70-300 F4-5.6 DG macro.
Flash: Pentax AF360.
although it does beep and give me the red square when, I presume, it thinks it's in focus.
This is a common misunderstanding. The red square only shows where the camera is focusing, not that it's in focus. Focus confirmation is indicated by the green hexagon at the bottom of the viewfinder. If the green hexagon is steady then focus has been found.
Best regards, John
~Pete
Best regards, John
I should have known that already! Indeed, I have read that in the camera's manual. Doh!
I feel a bit silly now, but in my defence, I'm trying to take in a lot of info at the moment!

I shall have another play when I get home tonight.
BTW, John, it's Paul Nemeth I work with, not Paul Jones. I think my subconscious had seen Paul Jones on your camera club's website.
Regards.
Alan.
Camera: K20D.
Lenses: Pentax DA* 55mm f1.4 SDM, Pentax DA* 16-50 SDM, Pentax 18-250 SMC DA, Pentax-M 50mm f1.7, Sigma 70-300 F4-5.6 DG macro.
Flash: Pentax AF360.
I did some tests last night with my K20D and Pentax-m 50mm f1.7 lens.
No problems I'm pleased to say!
Stevo/John, I found that the 'in-focus' beep/red-square/green hexagon behaved the same regardless of whether the camera was set to AP-S or AP-C. But it was nice to be fully aware of how these 3 indicators worked.
I found the focusing (on the centre of a flower) to be very sharp (zooming using the camera's screen and roller-wheel) although not always! I'm pretty steady at hand-held phtotgraphy, but I guess at f1.7 even the slightest movement is enough to affect the sharpness.
I did all of this using the camera's M mode of course, which I find is a pleasure to use, especially the top display's indication of light-metering/exposure. Also, using M mode, it's very easy to adjust the shutter-speed and the ISO to suit.
Which brings me on to another point: I have found that the ISO can be easily manually set using the OK button and front wheel together. This is a really handy usable feature. Is this common knowledge, as I've NOT found this feature in the manual...or am I just being dim again?!

Regards to all.
Alan Lowe-Jones.
Camera: K20D.
Lenses: Pentax DA* 55mm f1.4 SDM, Pentax DA* 16-50 SDM, Pentax 18-250 SMC DA, Pentax-M 50mm f1.7, Sigma 70-300 F4-5.6 DG macro.
Flash: Pentax AF360.
salixarbour
Member
South Cheshire
As a newbie and recent recruit to the Pentax fold, I recently bought my first Prime lens, an old Pentax-M 50mm f1.7 from Ebay, in excellent condition. I am now really enjoying the experience of being able to shoot indoors (at this dull time of year) whilst also creating images containing lots of bokeh.
I'm not too upset either at having to manually focus. However, when I roll the rear wheel and zoom in to check for sharpness on the camera's screen, I do notice that I don't always achieve the subject sharpness I'd like. I gather this is not unusual as even tiny head movements (after focusing) can affect this sharpness. I do get lucky sometimes though!
It's therefore possibly time for me to consider buying one of the modern-day equivalents: either the Pentax 50mm f1.4, or the Sigma.
I have to admit that whilst the Sigma is considerably more expensive, it does appear to be a 'better' lens. Perhaps that statement is a tad naïve,
but my question is; does anyone in the forum have experience of using this lens, or indeed, just an informed opinion...unlike myself!
Regards.
Alan Lowe-Jones.
Camera: K20D.
Lenses: Pentax DA* 55mm f1.4 SDM, Pentax DA* 16-50 SDM, Pentax 18-250 SMC DA, Pentax-M 50mm f1.7, Sigma 70-300 F4-5.6 DG macro.
Flash: Pentax AF360.