Rokinon 8mm F3.5 Ultra Wide Aspherical Fisheye Lens for Pentax

This was the lens that, for better or worse, was recommended as the best pairing for under $1K. Hoo boy. Results were very out of focus, despite all of my efforts when shooting in a great dark sky location in Puerto Rico. Like fishing, I took my time and enjoyed the occasion so I wasn't too put off at the time. But after getting home and trying everything, every single shot looks like it was shot through gauze on an astonishingly poor quality cell phone. In fact, I was able to get some shots with my iPhone of the bright starfield, but not this great camera (which is brilliant in all else with the kit lens).

Having enjoyed successful sessions with other cameras (Sony Alpha, Samsung NX), I know this camera can do it. Astrotracer was correctly calibrated, and all settings as were recommended in other threads were meticulously set. Then, when success was clearly elusive, I gingerly modified the focus to just below infinity, F-stop, bulb to various other increments. All produced abysmal results.

What could've gone wrong?

Thanks!

[SteveinSLC]

Did you purposely use a focus of less than inifinity? Stars are all at infinity, you shouldn't use less than unless the markings on your lens are off(which they can be).
But for stars you should focus by using live view to zoom in on a bright star. Adjust the focus until you the star is as small and sharp as possible...that's what you should consider infinity.
Also some of the reviews I saw of this indicated that it was soft until f5.6, so if you were shooting wide open, that also might be part of the issue.

I'd choose the 14mm or 16mm Samyang's over the fisheye for astro.

[Adam]

Your best bet would be to use live view magnification to verify correct focus.

Also, with a lens as wide as the 8mm fisheye, the astrotracer will likely produce blurry corners and only allow for relatively short exposures (perhaps in the 15-30 second range). A bit of trial-and-error would definitely be the way to go in ensuring that the focus is correct, and the exposure time reasonable.

[Derek]

In daylight with Live View and LV magnification focus on something as far away as you can see.

Tape the focus ring at that point using "gaffer's tape" on some other type that doesn't leave a lot of residue.
Use just enough tape that you won't jostle it of position in the dark.

I do this with any lens that I want to use for stars, etc.

[Trickortreat]

Samyang 16mm f2 would be the best astro lens you can buy for pentax.

[SteveinSLC]

Samyang 16mm f2 would be the best astro lens you can buy for pentax.

Or the 24/1.4.

Though the 15-30 and perhaps the 11-18 may also be equally good, though more expensive and in the case of the 15-30, much larger.

Thanks everyone! Duh! Why didn't I think of gaffer's tape? Probably because I was in Puerto Rico and actually trying to vacation vs fixation!

Couldn't find a Samyang 16mm in a K-Mount, though they do have a 14/2.8. Rokinon has a 16, but aren't they about the same? And good to know that I can be disabused of the whole fisheye notion.

I think I was trying to futz with focus as trial and error as infinity was producing the gauzy effect just as much as a step back - just figuring that something could've been off.

Thanks everyone! I was a little intimidated that as a relative noob to K-Mounts and getting astro right, I'd fall all over myself. You are all incredibly kind.

[Adam]

Yup, Rokinon and Samyang are the same. Which is marketed where varies, but the product doesn't.

[Trickortreat]

Or the 24/1.4.

Though the 15-30 and perhaps the 11-18 may also be equally good, though more expensive and in the case of the 15-30, much larger.

Hmmm.. i find 24mm to be to wide for landscapes.
Id rather go with sigma 18-35mm f1.8 and use it at widest end

[JensE]

My 8mm FE only considerably sharpens up at f/5.6. And I had to significantly adjust the focus scale (screw under the focus ring rubber clamps it).
Maybe yours is similar.

My 12mm FE however is sharp across the frame (K-1) even fully open at f/2.8.

[ecostigny]

My first try at astrophotography yielded blurry results because the lens (a Sigma 17-70 f2.8-4.5) allowed me to focus past infinity in manual focusing mode. Once I realized my mistake, I was able to get reasonably sharp pictures (See example below, exposed using the ETTR technique).

My biggest constraint now is the light pollution on the Connecticut shoreline; this web site suggests I have to do some driving if I want some darker skies: Light pollution map

I've heard good things about the Samyang 14mm and 16mm lenses for astrophotography. Maybe some day...

I found this series of articles to be very helpful in getting started: How to Do Basic Backyard Astrophotography, Part I: Introduction | B&H Explora

Enjoy!

[aslyfox]

. . . I found this series of articles to be very helpful in getting started: How to Do Basic Backyard Astrophotography, Part I: Introduction | B&H Explora

. . .

I recommend reviewing this series:

Astrophotography Series Announcement
A six-part tutorial series
By K David in Articles and Tips on Feb 22, 2015

Read more at: Astrophotography Series Announcement - Articles and Tips | PentaxForums.com

[kiwi_jono]

Mostly covered above already but really the 8mm can be use in this scenario if you want a really wide view but:
1. Probably best to avoid astrotracer (but can be used with some success for smaller exposures say < 20s)
2. Ideally needs to be stopped down to at least f5.6 (otherwise very soft corners and not very sharp center either). This might need to lift your ISO in order to get a short enough shutter time (unless you are going for star trails)
3. Focus needs to be right. The 8mm is known for having an incorrectly set infinity focus stop, and I know mine never focused anywhere near infinity (until I adjusted it). Do some tests in daylight against distant objects.

[Martin KP]

Rokinon 8mm F3.5 Ultra Wide Aspherical Fisheye Lens for Pentax

This was the lens that, for better or worse, was recommended as the best pairing for under $1K. Hoo boy. Results were very out of focus, despite all of my efforts when shooting in a great dark sky location in Puerto Rico. Like fishing, I took my time and enjoyed the occasion so I wasn't too put off at the time. But after getting home and trying everything, every single shot looks like it was shot through gauze on an astonishingly poor quality cell phone. In fact, I was able to get some shots with my iPhone of the bright starfield, but not this great camera (which is brilliant in all else with the kit lens).

Having enjoyed successful sessions with other cameras (Sony Alpha, Samsung NX), I know this camera can do it. Astrotracer was correctly calibrated, and all settings as were recommended in other threads were meticulously set. Then, when success was clearly elusive, I gingerly modified the focus to just below infinity, F-stop, bulb to various other increments. All produced abysmal results.

What could've gone wrong?

Thanks!

I don't know the answer, but will do after the Astro course. It starts next week.

[SSGGeezer]

Red enhancing filters also help with distant city lights. B and W have multiple sizes. They and Bahtinov masks in differing sizes for focusing are available at B and H.