[fizzyvimto]

Just got this lens this week. Not taken too many shots with it. Here is one I did to test its sharpness etc. What do you think? This is a HDR.

[fizzyvimto]

I took a few more shots on a walk today:

[dadipentak]

[fizzyvimto]

A few night shots I took yesterday evening:

[Digitalis]

just a question to the 8-16mm usergroup - has anyone used this particular lens with the astrotracer function on the Pentax O-GPS?


FYI, fizzyvimto. you really should downscale your images before posting them.

[steve1307]

just a question to the 8-16mm usergroup - has anyone used this particular lens with the astrotracer function on the Pentax O-GPS?

Hi Doug, I'd try it out right now for you but it's cloudy here and there is not a star in sight, no moon either (sank below the horizon 1 hr ago), so I couldn't give you any visual confirmation if it worked. Tomorrow night?

Technically I suspect it would function OK from 10 to 16mm with the FL in the exif. Below 10mm, who knows what the O-GPS1 might do?

As it is wide angle this may allow the full 5minute maximum exposure within the travel of the sensor movement before getting trails.

Also since the field of view is so wide, I'd wonder what the corners would be like. With the movement of the sensor is 2 dimensional in the sensor plane, perpendicular to the axis of the lens (ie thru the centre point) so would we get accurate points at the centre portion and trails at the edge due to the field curvature?

[steve1307]

just a question to the 8-16mm usergroup - has anyone used this particular lens with the astrotracer function on the Pentax O-GPS?

I just ran some quick tests (nothing special) in my back yard.
The Astrotracer function worked with Sigma 8-16 @8mm. The orientation (heading) is 203deg (SSW). South celestial pole is about 1/3 from the left and halfway vertically up the frame.

Processing in LR4 to show brightest stars Highlights +100, Blacks -40. This did hide some of the fainter stars and nebula which could only just seen in the image. I hoped to bring out the brightest stars more clearly against a darker sky.



8mm 300sec Astrotracer ON



8mm 300sec GPS OFF


Notes: The "lines" on the right side is my TV antenna (not a UFO ).
There's a huge gum tree obscuring the sky on the left of the shot.
An aircraft flew through the Astrotracer shot on the right side.

In the Astrotracer shot the stars in the centre of the frame are rendered as points pretty much as expected, but in the corners trails are apparent. It could be difficult to see in 1024pixels wide but the trails are "radiating" out from the centre and are longer, the further they are from the centre of the image.

In the standard shot the star trails are apparent as expected in the image and "rotating" around the pole ( with the longest trails on the right side of the image which is furthest from the southern pole)

Testing at 11mm which the K-5IIs can read directly in the exif gave a similar result except 2 planes when right thru the middle of the shot within the 5minute exposure.

I also tried orientations directly west (away from the south pole rotation) and got similar results with accurate point stars in the centre of the frame and trails lengtening out to the corners of the wider field of view. The length of the light trails varies with the distance from the centre of the frame and the orientation of the camera which determines in which direction the sensor moves to get the points in the centre so the trails are different lengths from one side of the frame to the other.


Would i bother with using the 8-16 with astrotracer again? Well yes, but not with the maximum 5minutes exposure as the trails are distracting and noticable. This means it (or any other UWA) wouldn't work for photographing dimmer objects, nebula or more distant clusters. It's a pretty slooooowww lens anyway.

I have done 5 minute exposures with an FA43 and had no issue with trails.


FA43 300sec Astrotracer ON


With longer FL of course there is limit to the exposure time as the sensor will move more quickly and reach the end of its "travel limit" before a 5minute exposure



DFA100mm 90sec Astrotracer ON.

---

Last edited by steve1307; 09-10-2013 at 06:10 AM.

[Digitalis]

Thank you very much for your information on the O-GPS astrotracer functionality with the Sigma 8-16mm, I have other lenses like the FA31, 50mm f/1.2, FA77 and my FA*400mm f/2.8 that should also be very useful with the astrotracer.

[civiletti]

I did not get much chance to use the 8-16 at Yellowstone with the walkways and tourists all around, but it was the only way to capture this entire pool at West Thumb Geyser Basin. At 8mm and f8:

[normhead]

Cross posted from post your photos..

We started the day with a trip to the park for a guided hike where the big topic seemed to be tree sex. This guy is a tree sex expert apparently, although he didn't know if Beech trees were hetero or bi.



We finished the night at our favourite camsite where awesome ribs done on an oak fire were washed down with a few beers.









Today it's all rain and thunder, so we're lucky we got another night in.

[dadipentak]

Cross posted from post your photos..

Gorgeous!

[fizzyvimto]

Here are some architecture shots I took on Saturday with this lens:

[NickLarsson]

Sigma 8-16 @ 13mm

[snipenekkid]

shot this today, handheld, noise exaggerated rather than suppressed for effect.

K5, Sigma 8-16mm @ 8mm (maybe 9mm I don't remember looking), f10, 1/80, ISO500, YN560 III on hotshoe for ambient fill


Same in BW just because:


Not the final version of that image but rather more a let's play with the 8-16mm today and see what's what. 135 shots later annnnnd, well ya know.

[johnc]

Hi - been out with the 8-16 together with the 16-50 and 50-135 today. Here's my favourite 8-16 shot. Yes - a single exposure... and less heavily processed than you might think!



Hope you like this flight of fantasy!

John C