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06-24-2012, 12:15 AM   #1
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Wide angle 1.4 - 2.0???

Good day yall!

Ben Canales' photography inspired me to shoot astrophotohpgraphy. His lens is a canon 24 1.4. Any chance there is an option for my k-5 k-mount or even m42?

The criteria for my search are 2 things:
- f1.4 to 2
- 15-17mm (for a 24mm equiv)

I hope there's a lens out there that will Have these specs!
-Scott

06-24-2012, 12:28 AM   #2
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Not many options in the Pentax world. The closer might be the DA 14 f2.8, which is sort of slow compared to your criteria. There is the Samyang 14 f2,8 as well. If you aim for speed and can give up a bit of wideness, the Sigma 20 f1.8 can be an option. I suggest you read reviews of those lenses as they have their own characters.
06-24-2012, 01:18 AM   #3
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Your not going to find a 15-17mm f/1.4 - f/2 lens in Pentaxland. The closest would be a Sigma 20mm 1/.8 otherwise go Canon or Nikon
06-24-2012, 02:20 AM   #4
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there was a prototype 20mm f/1.4 made in the 1980's - apparently there is a hood available for it, but the lens as of yet has not been seen..by anyone.

06-24-2012, 04:22 AM   #5
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Micro four thirds may be the way to go?
M.ZUIKO DIGITAL ED 12mm f2.0 | OLYMPUS E-SYSTEM | Olympus Imaging Asia
or amazing 17.5 f/0.95 (that's "equal" to 24mm on APS approx)
Four Thirds | Micro Four Thirds | Products(Lenses)

Or four thirds will let you get f/2 with a zoom.
ZUIKO DIGITAL ED 14-35mm F2.0 SWD | Digital SLR | Olympus Imaging Asia
06-24-2012, 04:56 AM   #6
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Pentax generally is making fairly slow lenses. And at that focal length you will be hard pressed to find many fast lenses at all. You will have to choose between a bigger focal length and fast (up to 35mm, maybe even 50mm, with f1.4 or f1.7) and a wide lens but slower (like the 14mm f2.8)
Also, the newly announced K-30 camera will have an astrophotography mode where it moves the sensor according to the GPS in such a fashion that the stars stay dots. That would eliminate the need for a very wide angle (usually you want a wide angle so you can have a longer exposure without the stars turning into lines).
OR you can get a tripod head that moves with the sky (I forget what its called) and you can use a slow lens at whatever focal length. But that might be harder to come by.

Oh, and I don't think micro 4/3 is the answer, because it has smaller sensors and might have higher pixel density, focal length equivalence, and noise.

edit: Also, there are many astrophotgraphy tutorials on the net, some might give you more tips.
06-24-2012, 04:57 AM   #7
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fact is the Canon 24mm f1.4 cost arpund 1.500$

the closest is the Samyang 24mm f1.4 (no AF) at 700$

in the less than 20mm range, you won't find anything very fast.

Anyway, you need to stop the lens a little bit to get the minimum sharpness required most of the time.


And you can do some sky shots with a 24-28-35 lens, and it will be nice too.
06-24-2012, 05:22 AM   #8
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Why do you need a 1.4 or 2 to shoot astro anyways? I always thought astro was shot stopped down for sharpness.

06-24-2012, 06:06 AM   #9
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stop down and use astro-tracer mode? with the gps unit thing
06-24-2012, 06:53 AM   #10
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QuoteOriginally posted by JinDesu Quote
Why do you need a 1.4 or 2 to shoot astro anyways? I always thought astro was shot stopped down for sharpness.
exactly, I recommend buying the Pentax GPS astrotracer - because it is substantially cheaper than most f/1.4~f/1.2 lenses out there.
06-24-2012, 06:55 AM   #11
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QuoteOriginally posted by JinDesu Quote
Why do you need a 1.4 or 2 to shoot astro anyways? I always thought astro was shot stopped down for sharpness.
you can stop down lenses but not to much.

the exposure time should not exceed : "275 / focal lengt" if you don't want star trail.
06-24-2012, 07:07 AM   #12
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QuoteOriginally posted by Scootatheschool1990 Quote
Good day yall!

Ben Canales' photography inspired me to shoot astrophotohpgraphy. His lens is a canon 24 1.4. Any chance there is an option for my k-5 k-mount or even m42?

The criteria for my search are 2 things:
- f1.4 to 2
- 15-17mm (for a 24mm equiv)
Do you mean 35mm equivalent? And is a lens in that criteria even optically possible with reasonable IQ?
06-24-2012, 08:28 AM   #13
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QuoteOriginally posted by Scootatheschool1990 Quote
Good day yall!

Ben Canales' photography inspired me to shoot astrophotohpgraphy. His lens is a canon 24 1.4. Any chance there is an option for my k-5 k-mount or even m42?

The criteria for my search are 2 things:
- f1.4 to 2
- 15-17mm (for a 24mm equiv)

I hope there's a lens out there that will Have these specs!
-Scott
What Ben Canales is saying is to capture as much light as possible. With Canon you can go full frame with a relatively fast wide lens, along with the highest useable ISO. He is just using the most appropriate equipment - he choose Canon.

Now just because he is using a 24/f1.4 lens does not mean that you need to look at the exact equivalent field of view for the K5's cropped sensor - a 24mm lens is still a 24mm lens regardless of sensor size. Just about the best you can do (in terms of fast and wide) is the K 28/f2 lens (its the same lens as the Zeiss 28mm f2 Distagon that has a cult following). Remember that 24 to 28mm is about the widest you can go with the least amount of distortion.

Use what you have in terms of speed and width, then work up to where you want to go based on your equipment (or possibly move to another that has the lenses you desire - however, its expensive).

You can compensate and trade capabilities for what Pentax has available. The O-GPS unit with astrotracking will provide you with additional time, however since it stabilizes the moving stars (removing the trails), it will essentially blur the landscape (since it is not moving).

06-24-2012, 08:45 AM   #14
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When photographing stars, which are point objects represented by one or just a few pixels on the sensor, the f-stop does not play any role in the exposure for that star. It is only the shutter speed and ISO.
06-24-2012, 09:06 AM   #15
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QuoteOriginally posted by demp10 Quote
When photographing stars, which are point objects represented by one or just a few pixels on the sensor, the f-stop does not play any role in the exposure for that star........
The f-stop plays a dominant role in exposure, even for a point source of light. The light emitted by a star spreads uniformly in space and the total amount that gets into the camera is proportional to the actual open area of the aperture; which is proportional to 1/(f-stop)^2.

That's why large diameter telescopes are used for astronomy.

Dave in Iowa
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