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04-20-2012, 08:43 PM   #16
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QuoteOriginally posted by liukaitc Quote
I do not think there is any ultra-wide angle lens (<16mm) faster than f2.8...
something like sigma 10-20 f3.5 is consider pretty fast for a ultra-wide angle lens.
Thanks for the reply............. There is a Samyang 14mm F2.8 (link above) but I agree. If F3.5 was ok this Sigma lens looks very good.

I think the diffference with the F Stop is the amount of time required for the exposure. The higher the F Stop means the longer the shutter needs to stay open and as the northern lights are moving, the shot will not be as clear. Another way around it I suppose is going to a higher ISO (& Noise Reduction) so I might be limited with the Pentax K10D (800 is probably Ok but I think it would struggle with noise @ 1600 Max ISO)

04-20-2012, 08:52 PM   #17
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people use ultra-wide angle lens mostly for lanscape
if you shoot outdoor, slow F-stop is not a problem, because you usually stop down anyway.
If it is indoor, then you would use tripod with longer exposure time to get best result, so slow f-stop is not a problem again.
you would need fast f-stop if you do a lot handheld low light photography. otherwise you might get away with a slow ultra-wide angle lens.
04-20-2012, 09:01 PM   #18
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I will be there in December so even though I am shooting outside, it will be very dark (only about 2 hrs daylight and between New Moon & 1st Qtr) I will have my tripod & use the remote shutter which will help but the shutter will be open for a loooonng Time.........

Here is an extract from Patrick's excellent article on exposure required:

Approximate exposure times in relation to f/stop @ 400ISO – varies based on ambient light.

Camera Lens F-stop Time
Canon EF 24mm L f/1.4 7.5 seconds
Canon EF 35mm L f/2.0 15 seconds
Canon EF 24mm f/2.8 30 seconds
Canon EF 16-35mm Lf/2.8 30 seconds
Canon EF 10-22mm f/3.5 50 seconds
04-20-2012, 09:02 PM   #19
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Just to give you an idea of how the 10-17 fish-eye can work for landscape, here are two recent shots.
At 13mm


At 15mm


A flat stretch of horizon in the centre and hills, slopes, foreground detail, etc along the edge can disguise the curve. It is not a fast lens but with the curve of the element more light does tend to come in.

04-20-2012, 09:12 PM   #20
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Thanks Joe.......... I can see what you mean.

It's just the F Stop will kill the clarity of the shot as the Northern Lights are moving. (At F3.5 Patrick is saying the exposure = 50 seconds @ ISO 400)

I am positive now that I need something at least F2.8
04-20-2012, 11:52 PM - 2 Likes   #21
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QuoteOriginally posted by Chook Quote
There is a Samyang 14mm F2.8 (link above) but I agree. If F3.5 was ok this Sigma lens looks very good.
QuoteOriginally posted by Chook Quote
I am positive now that I need something at least F2.8
Here is an AOV (angle of view) table for a few lenses mentioned. The numbers apply to a Pentax dSLR with a sensor diagonal of 28.1mm.

* Samyang 14/2.8 (rectilinear) = 90 degrees
* Sigma 10-20/3.5 @10mm = 109 degrees
* Zenitar 16/2.8 (slightly FE) = 99 degrees
* DA10-17 @10mm (very FE) = 175 degrees

Yeah, the DA10-17 specs say 180, but that's on a nominal APS-C sensor diagonal of 30.1mm. 175 is the reality.

The DA10-17 is f/3.5 @10mm. Don't think that it's slow. Think about the 1/FL rule. It applies to rectilinear lenses and says we get acceptable sharpness with a shutter speed of one divided by the focal length. So you get the same sharpness with a 50mm lens @1/50 second and a 10mm lens @1/10 second. The DA10-17 @10mm is effectively 2mm, so you'd get the same sharpness @1/2 second.

You quoted this Camera Lens F-stop Time table entry: Canon EF 24mm L f/1.4 7.5 seconds. The aperture difference between the Canon 24/1.4 and the DA10-17 @10/3.5 is 2.6 stops or about 6x the light transmission. But the 1/FL difference is 24mm/2mm= 12x or 3.6 stops. The DA10-17 would be able to take the same exposure as the Canon in half the time, 3.75 seconds. And it would cover virtually the entire sky, whereas the 24mm prime on a FF camera would only see 84 degrees, about like a 15mm rectilinear on a Pentax dSLR.

Cut to the chase: To get a desired level of sharpness, a longer lens must be faster than a shorter lens. It's not the focal length, but the angle of view. A lens with a very wide AOV can use a very slow shutter. The numbers above show that a 10/3.5 fisheye on APS-C is twice as 'fast' as a 24/1.4 rectilinear on FF. Even the Zenitar 16/2.8 on APS-C is slightly 'faster' than the FF Canon. Also, the DA10-17 @10/3.5 is twice as 'fast' as the Sigma 10-20/3.5 @10mm. Keep all this in mind if you want short sharp exposures. Have fun!

Last edited by RioRico; 04-21-2012 at 12:03 AM.
04-21-2012, 12:50 AM   #22
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Wow

I have only had my Digital SLR 3 months now and can hardly understand what all this means.

I am very happy to learn as I will only get one shot at this so very keen to get it right.

If I don't understand it correctly please let me know as I am still learning.

I appreciate your detailed response and if I follow the logic it sounds like you are recommending a 10mm F3.5 Fisheye or the DA10-17 because of both the AOV & the amount of light it collects will reduce the time required for exposure (whereas I have been focussing purely on the F Stop).

I may be way off track here but It appears I need to somehow multiply the F Stop effect & the AOV to get time for exposure?

It also sounds like I may be wrong about the Fisheye lens as the AOV of these may also help me get a better shot.

I really like your "Cut To The Chase" comment............. So here goes.

Which one would you choose if you were going to the Arctic Circle with a Pentax K10D and wanted a wide angle lens to take a photo of the Northern Lights ???

I am really grateful for the responses.

P.S. What does "Slightly FE" "Very FE" Mean.


QuoteOriginally posted by RioRico Quote
Here is an AOV (angle of view) table for a few lenses mentioned. The numbers apply to a Pentax dSLR with a sensor diagonal of 28.1mm.

* Samyang 14/2.8 (rectilinear) = 90 degrees
* Sigma 10-20/3.5 @10mm = 109 degrees
* Zenitar 16/2.8 (slightly FE) = 99 degrees
* DA10-17 @10mm (very FE) = 175 degrees

Yeah, the DA10-17 specs say 180, but that's on a nominal APS-C sensor diagonal of 30.1mm. 175 is the reality.

The DA10-17 is f/3.5 @10mm. Don't think that it's slow. Think about the 1/FL rule. It applies to rectilinear lenses and says we get acceptable sharpness with a shutter speed of one divided by the focal length. So you get the same sharpness with a 50mm lens @1/50 second and a 10mm lens @1/10 second. The DA10-17 @10mm is effectively 2mm, so you'd get the same sharpness @1/2 second.

You quoted this Camera Lens F-stop Time table entry: Canon EF 24mm L f/1.4 7.5 seconds. The aperture difference between the Canon 24/1.4 and the DA10-17 @10/3.5 is 2.6 stops or about 6x the light transmission. But the 1/FL difference is 24mm/2mm= 12x or 3.6 stops. The DA10-17 would be able to take the same exposure as the Canon in half the time, 3.75 seconds. And it would cover virtually the entire sky, whereas the 24mm prime on a FF camera would only see 84 degrees, about like a 15mm rectilinear on a Pentax dSLR.

Cut to the chase: To get a desired level of sharpness, a longer lens must be faster than a shorter lens. It's not the focal length, but the angle of view. A lens with a very wide AOV can use a very slow shutter. The numbers above show that a 10/3.5 fisheye on APS-C is twice as 'fast' as a 24/1.4 rectilinear on FF. Even the Zenitar 16/2.8 on APS-C is slightly 'faster' than the FF Canon. Also, the DA10-17 @10/3.5 is twice as 'fast' as the Sigma 10-20/3.5 @10mm. Keep all this in mind if you want short sharp exposures. Have fun!

Last edited by Chook; 04-21-2012 at 01:43 AM.
04-21-2012, 01:50 AM   #23
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Sorry if your head hurts. And thanks for my 550th thumbs-up!

QuoteOriginally posted by Chook Quote
I may be way off track here but It appears I need to somehow multiply the F Stop effect & the AOV to get time for exposure?
Sort of. Rather, consider the aperture and the AOV when *comparing* exposure settings for different lenses. So we can use the same shutter speed with a 175 degree DA10-17 fisheye @10/4 as we would with a 87 degree Samyang 14/2.8 and get the same motion-stopping effect. Double the AOV equates to double (half?) the EV. Did I explain that well? I hope so.

It's simpler to think of just rectilinears. A 28mm lens has half the AOV of a 14mm lens and so needs twice the shutter speed at the same aperture to have the same motion-stopping effect -- thus the 1/FL rule.

Comparing rectilinears with fisheyes (FE!) we can only consider AOVs. Let's see, what would be a comparable rule? On APS-C, 20mm=70 degrees; 80mm=20 degrees; 300mm= 5 degrees. How to build a 1/FL equation from these data points? Now MY head hurts!

QuoteQuote:
It also sounds like I may be wrong about the Fisheye lens as the AOV of these may also help me get a better shot.

I really like your "Cut To The Chase" comment............. So here goes.

Which one would you choose if you were going to the Arctic Circle with a Pentax K10D and wanted a wide angle lens to take a photo of the Northern Lights ???
Luckily, I have more than one lens for my K20D. I would take my DA10-17 for full-sky shots; and my Zenitar 16/2.8 for quarter-sky shots, because the DA10-17 is only f/4.5 (2.3 stops slower) @16mm. I'd take other lenses too, like my Tamron 10-24 and Vivitar-Komine 24/2. But those two fisheyes would be best for short sharp exposures.

If I didn't have the Zenitar and I wanted something comparable but not fishy, I'd get the Samyang 14/2.8, or the DA14/2.8 if I could afford it. Those rectilinear 14's are 90 degrees; the Zenitar is 99 degrees. Close enough.

And for ultimate fisheye, I'd put my cheap 0.25x FE adapter onto my DA18-55 @18/3.5 for a somewhat distorted full-circle image. Yeah, that's equivalent to a 4.5mm FE! But I wouldn't expect high-quality images from that.

QuoteQuote:
P.S. What does "Slightly FE" "Very FE" Mean.
FE is fisheye. 10mm is very fishy. 16-17mm are slightly fishy. Hope this all helps!


Last edited by RioRico; 04-21-2012 at 01:57 AM.
04-21-2012, 02:17 AM   #24
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QuoteOriginally posted by RioRico Quote

Luckily, I have more than one lens for my K20D. I would take my DA10-17 for full-sky shots; and my Zenitar 16/2.8 for quarter-sky shots, because the DA10-17 is only f/4.5 (2.3 stops slower) @16mm. I'd take other lenses too, like my Tamron 10-24, but those two fisheyes would be best for short sharp exposures. And for ultimate fisheye, I'd put my cheap 0.25x adapter onto my DA18-55 @18/3.5 for a somewhat distorted full-circle image.

If I didn't have the Zenitar and I wanted something comparable but not fishy, I'd get the Samyang 14/2.8, or the DA14/2.8 if I could afford it. Those rectilinear 14's are 90 degrees; the Zenitar is 99 degrees. Close enough.
The cut to the chase hase helped me greatly thank you.

I think I might be fairly close to what I need with just a couple of low cost additions.

The same guy that is selling the Samyang 14/2.8 is also selling one of those adapters I could use use on my DA18-55 @18/3.5.

ODS Samyang 14mm f2.8 Wide Lens for Pentax K20D K200D K-m K-7 K20 K200 K2000 | eBay

ODS 0.22x Super Wide Fisheye Lens for Pentax K20D K200D K-m K-7 K20 K200 K2000 | eBay

How does that sound ??

Is it close or do I also need to get a 10-17 Fisheye ??

Cheers,
Arthur
04-21-2012, 03:28 AM   #25
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QuoteOriginally posted by Chook Quote
The same guy that is selling the Samyang 14/2.8 is also selling one of those adapters I could use use on my DA18-55 @18/3.5.

ODS Samyang 14mm f2.8 Wide Lens for Pentax K20D K200D K-m K-7 K20 K200 K2000 | eBay

ODS 0.22x Super Wide Fisheye Lens for Pentax K20D K200D K-m K-7 K20 K200 K2000 | eBay

How does that sound ??
The Samyang looks good. I am *very* suspicious of that 0.22x strap-on. My eBay 0.25x cost me US$20 shipped from China to USA just a few months ago. The AUS$130 price on the 0.22x seems excessive, especially since such optics have toy-like quality. Mine is marked "Precision Design Super AF Fisheye" and shouldn't be hard to find. Any such adapter will give results that are dramatic but not optically good.

QuoteQuote:
Is it close or do I also need to get a 10-17 Fisheye ??
Like I said, the 14/2.8 or Zenitar 16/2.8 will be good for fast sharp quarter-sky photos. The DA10-17 at its widest will be better for full-sky photos. The longer lenses can be aimed to where you think aurorae will appear, and will give finer detail. The DA10-17 @10mm need only be aimed straight up, and will give more expansive vistas.

Another way to look at it: You need more luck with the Samyang or Zenitar than with the DA10-17. Cheers!
04-21-2012, 10:00 AM - 2 Likes   #26
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Good Morning,

At times its pretty difficult to try to respond to threads at an appropriate level, because there is so little information initially available. So, now with a bit more information consisting of a K10 with 3 months experience, I think we can help you a bit better. We want to see some absolutely spectacular images, and you also want to have a great time with your grandkids - sounds like a great trip!!!

With all of that in mind, let's touch on the three basics.... and all of these are inter-related. Its a game of wack-a-mole - where you push it down here and then over there it pops up.
  • ISO - is an indication of the sensor's sensitivity. The higher the number the more sensitive the sensor becomes. However, with increased sensitivity, noise also is increased. Think of a radio, by turning up the volume - the radio station get louder, however the background hiss also becomes more noticeable. ISO 100 is usually the base, ISO 200 is twice as sensitive and ISO 400 is 4 times as sensitive (as ISO 100).
  • Aperture - is the hole in the lens that lets the light into the camera and on to the sensor. Take a look at this site (especially the picture up in the corner)...f stops have numbers like f2.8, f4, f5.6, f8, f11 Going from f2.8 to f4, cuts the amount of light in half. In fact, going from one whole f stop number to the next one, cuts the light in half.
  • Shutter Speed - is the amount of time the shutter is open, letting light in to hit the sensor. The longer the shutter is open, the more motion of the view will be recorded. This may not be bad. Think of a waterfall, taking a image with a fast shutter will get an image of the water frozen in time, however a longer shutter speed will record a much softer image - something that is milkey smooth. So you the photographer can essentially do both and everything in between.

A K10 is a somewhat older camera body (near professional level). Its only real drawback is that the sensor is a couple of generations out of date, and thus is very good at ISO 100, 200 and up to about 400. Past 400, its is going to get noisy at 800 and really noisy at 1600. But it is workable. I am going to guess that you are not going to want to go past 400. The lens table from the site earlier, bases everything at ISO 400. Just as a note, you may want to experiment with ISO 800 and try some noise reduction software. That would be something to look into. So, what that does is to leave you with the ability to vary the f stop (aperture) of the lens along with the shutter speed.

Here is a set of camera simulators, that you can play with, that will demonstrate the inter-relationships between ISO, aperture and shutter speed.Homework - Sorry about this - but we want to see some really nice images of the Northern Lights!!! I don't know where you live but, here are some suggestions...
  • Out in the Country - Night sky shooting. Try taking images of the moon, and the stars. Try for silhouettes of the country landscape at night against the sky during blue and or golden hours. Here is a site that explains...
  • Urban - Shoot city or urban evening lights, from a hill side or hill top. Just something, anything.
  • City - anywhere in the city in the evening and at night.
The key here is to get some practice and see how the images turns out. The great thing here is to go take some evening pictures of anything, come back home and load them up and take a look at them. Figure out what you want to do different, or what you feel you did not get to your liking, and then try again. Remember, each of the pictures has all the information embedded in it as to the lens, f stop, shutter time, so you can really see what is going on. The software that came with the camera has all of this capability built in, or you can down load PhotoMe for free (just google it). Get familiar with the camera and lens - any lens will do here. Use the tripod, take a small flash light and setup, aim, focus, and then determine the shutter speed. Also, remember to dial in the 2 second delay, so that the mirror will lift up, wait 2 seconds for the vibration to settle and then it takes the picture. Also, remember to disable the shake reduction when on the tripod. At times you may need to go into manual focus and / or manual mode. Also, you may want to experiment with bracketing. What bracketing is - is a camera setup where by it takes 3 to 5 images in quick succession automatically, with each image at a different exposure value, i.e., normal +1 exposure, -1 exposure, +2 exposures and -2 exposures. the reason why I suggest this is that you get a series of 3 to 5 images and you can then select the best one afterwards with out a whole lot of setup and tinkering with the camera.

Here is the manual for the K10. Its a soft manual. You can search for the word bracketing and it will indicate what to do to set it up.

You have 8 months at 4 weeks or 32 weeks to practice till showtime. A little practice will provide a wonderful return of great pictures.

hope that helps.....

Last edited by interested_observer; 04-21-2012 at 10:17 AM.
04-21-2012, 12:55 PM   #27
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Thanks for the advice..............I plan to do a lot of research & practice beforehand to get the most out of the trip. Those simulations will help greatly also. I like the idea of the "Bracketing" feature you mention so will definitely look into that. I have another lens from my old Ricoh XR6 35mm Camera that I might try also with the Fisheye Adaptor. It has a really wide aperature with an F Stop of 2 but is long @ 50mm Ricoh XR Rikenon 50mm f/2.0 Lens Reviews - Ricoh Lenses - Pentax Lens Review Database

Cheers,
Arthur

Last edited by Chook; 04-21-2012 at 01:58 PM.
04-23-2012, 01:01 PM   #28
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Thanks everyone for all the advice..................... I found a Pentax 10 - 17mm at a great price online so bit the bullet and grabbed it.

eBay Australia: Buy new & used fashion, electronics & home d?r

Will have time to see if a Pentax 14mm 2.8 comes up also (if not I can get the Samyang locally)
04-23-2012, 01:18 PM   #29
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QuoteOriginally posted by Chook Quote
Thanks everyone for all the advice..................... I found a Pentax 10 - 17mm at a great price online so bit the bullet and grabbed it.
[...]
Will have time to see if a Pentax 14mm 2.8 comes up also (if not I can get the Samyang locally)
You will find the DA10-17 to be astounding. You will also find a 14mm rectilinear to be a bit longer, with narrower FOV, than the DA10-17 @17mm, but rather faster. You just missed a Zenitar 16/2.8 at an astonishingly low price in the Marketplace here. Priced at US$115; I should have grabbed it just to resell it for almost twice as much! But I'm not greedy, oh no.

I sometimes mention that the DA10-17 is the lens that drove me to Pentax. Back when I was deciding how to upgrade from my advanced P&S, I knew that what I wanted to do that it couldn't do were 1) ultrawide, 2) ultralong, and 3) ultrafast. Ultrawide was most critical; EVERYBODY had long and fast lenses at reasonable prices, but UWs were tricky four years ago. No UW rectilinear zooms; few fisheye zooms, and those were horribly expensive. All except the DA, and a Zuiko; but the Zuiko was only for 4/3 cameras with their teensy-weensy itty-bitty little sensors.

So now I'm here because the DA10-17 was there. Even with four years' inflation, its price is about the same, so it's actually a bit cheaper now. Mine is always in my carry bag because I can never know ahead of time when NOTHING ELSE WILL DO. Have fun with yours!
04-24-2012, 02:00 PM   #30
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I think you'll need to change mount to achieve your hearts desire, oh and up your budget.
Nikon 6mm f/2.8 lens
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