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10-12-2010, 02:23 PM   #46
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QuoteOriginally posted by Rondec Quote
It is interesting. I don't own any of these lenses -- not really a wide angle shooter, but looking at Amazon's web site, it appears that the Sigma at 10mm takes in 102 degrees angle of view, while the Pentax at 12mm takes in 99 degrees. That just doesn't sound like a whole lot to me, but I guess at close quarters maybe it would make a difference.

The things that impress me about the Pentax 12-24, looking at photos, is the control of the distortion and the sharpness of the photos.
QuoteOriginally posted by Rondec Quote
Thanks for the correction. I took the numbers from the listing for the K mount version of the Sigma 10-20 on Amazon, but I guess it must be listed incorrectly.
when you look at the 119 degree FOV vs 99 degrees for the 12-24 my math suggests this represents about a 10% change. si stepping back a step or so is only if you are 20 feet away, if the subject is bigger, and you are more than 20 feet away, you have to step back more, and many interiors are less than 20 feet side to side to start with so there is probably not a step back possible. IMO.

But then again, in addition to the 10-20, I have now aquired an 8mm fisheye

10-12-2010, 07:35 PM   #47
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QuoteOriginally posted by Lowell Goudge Quote
when you look at the 119 degree FOV vs 99 degrees for the 12-24 my math suggests this represents about a 10% change. si stepping back a step or so is only if you are 20 feet away, if the subject is bigger, and you are more than 20 feet away, you have to step back more, and many interiors are less than 20 feet side to side to start with so there is probably not a step back possible. IMO.

But then again, in addition to the 10-20, I have now aquired an 8mm fisheye
Was it the Samyang/Rokinon/Bower/Vivitar/Pro-Optic 8mm f/3.5 fisheye? The lens seems pretty cool... and an inexpensive way to play with a fisheye and determine if it's something one really likes.
10-13-2010, 04:48 AM   #48
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QuoteOriginally posted by pop4 Quote
Note that the image only compares FOV, and does not take into account the changes in perspective
Perspective doesn't change, no matter what focal length you use. It only changes if you (or your subject / other objects in the scene) change location, e.g. you move closer. Photons don't change their path just because you zoom from 17mm to 35mm
10-13-2010, 05:24 AM   #49
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QuoteOriginally posted by simico Quote
QuoteOriginally posted by pop4 Quote
Note that the image only compares FOV, and does not take into account the changes in perspective
Perspective doesn't change, no matter what focal length you use. It only changes if you (or your subject / other objects in the scene) change location, e.g. you move closer. Photons don't change their path just because you zoom from 17mm to 35mm
True for your (human) perspective, but that's not entirely true of the perspective that reaches the film (sensor) plane and makes it into the image, though. Ultrawides make distant stuff seem smaller with respect to the overall image than a telephoto would. See Wide-angle lens - Wikipedia, the free encyclopedia - look at the blue bottle's size compared to the red one.

10-13-2010, 05:32 AM   #50
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QuoteOriginally posted by Nass Quote
True for your (human) perspective, but that's not entirely true of the perspective that reaches the film (sensor) plane and makes it into the image, though. Ultrawides make distant stuff seem smaller with respect to the overall image than a telephoto would. See Wide-angle lens - Wikipedia, the free encyclopedia - look at the blue bottle's size compared to the red one.
it is true for lenses as well

Enlarge a crop from the central FOV equivelent of a 50mm or 100mm lens from a UA exposure and the perspective has not changed one bit.

It will only change if you relocate the camera to change the relitive distance of camera to subject to background.

what changes is magnification and field of view but not perspective.
10-13-2010, 05:42 AM   #51
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QuoteOriginally posted by Nass Quote
QuoteOriginally posted by simico Quote
Perspective doesn't change, no matter what focal length you use. It only changes if you (or your subject / other objects in the scene) change location, e.g. you move closer. Photons don't change their path just because you zoom from 17mm to 35mm
True for your (human) perspective, but that's not entirely true of the perspective that reaches the film (sensor) plane and makes it into the image, though. Ultrawides make distant stuff seem smaller with respect to the overall image than a telephoto would. See Wide-angle lens - Wikipedia, the free encyclopedia - look at the blue bottle's size compared to the red one.
UWA are same if you use them at same "zoom" as tele lens...
- But then you don't have a UWA lens any more...

This link is IMHO best to explain it:
Digital Photography Tutorial: Focal Length - TrustedReviews - TrustedReviews

If you want full frame picture of a face then you have to be pretty close with UWA lens and much further away with tele lens. If you take a photo with the UWA lens from the same location as the tele lens then the face will be very small. Cropping will also result in distortions different from the tele lens, given an different lens is used and will of course be dependent on where the face was placed in the frame... And photon still go the same way, just other photons are capture by your camera...
10-13-2010, 05:43 AM   #52
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QuoteOriginally posted by Lowell Goudge Quote
it is true for lenses as well

Enlarge a crop from the central FOV equivelent of a 50mm or 100mm lens from a UA exposure and the perspective has not changed one bit.

It will only change if you relocate the camera to change the relitive distance of camera to subject to background.

what changes is magnification and field of view but not perspective.
Are we talking about perspective distortion only and excluding lens distortion?
10-13-2010, 05:58 AM   #53
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Hm. How embarassing. This is something I'll need to test myself because you know, I could have sworn this was the case. One of many things I struggle with using ultrawides is distant mountains that are 10 pixels high and rocks that are 1000 pixels across.

Update - it's an illusion. See http://www.patricktaylor.com/1988


Last edited by Nass; 10-13-2010 at 06:25 AM.
10-13-2010, 06:04 AM   #54
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QuoteOriginally posted by pop4 Quote
Here's a chart I did a while back with my Sigma 10-20mm. It's a bit rough and there's no 12mm, but I think it provides a rough idea of what you're after, and also notice the BIG difference between 16mm, and 10mm.


Note that the image only compares FOV, and does not take into account the changes in perspective and the 'compression' effect of longer lenses.
Thanks for the image. I can see some perspective in the picture for the difference mm in focal length.
10-13-2010, 10:32 AM   #55
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QuoteOriginally posted by Biro Quote
Was it the Samyang/Rokinon/Bower/Vivitar/Pro-Optic 8mm f/3.5 fisheye? The lens seems pretty cool... and an inexpensive way to play with a fisheye and determine if it's something one really likes.
Yes it is, mine is the pro-optic variant

It has had several good workouts lately. what I can advise is as follows:

With respect to overall quality it is pretty well built, the only complaint about this lens is that it cannot take filters, where as the more expensive fish-eye lenses take rear filters. Having said that it has pretty good contrast and flair is very well controlled. you can almpst point this lens into the sun and not have an issue, shich is important because with a 180 degree FOV the sun is almost impossible to keep out of the frame.

CA is also well controlled, where there is perhaps a 1-2 pixel CA band apparent at times (on my K10D).

Purple fringing is also not a real issue, but I did see some true purple fringing by pointing the lens at the hole in the center of a cathedral dome and the bright blue sky outside, and about 16ev lower lighting inside. the hole is surrounded by a really nice? purple band. this range of esposure overload is unusual however.

overall, it is a pretty good toy for the price, and comes in KA mouont so all auto exposure modes work. DOF is so large that focusing is almost redundant,.
10-13-2010, 10:49 AM   #56
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QuoteQuote:
Eruditass: I would've probably gone for the 12-24mm if it was the same price in K-mount as other mounts...

Yes, my thoughts as well!
10-13-2010, 10:54 AM   #57
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Fwiw, I have the 10-17 and I've bemoaned the possibility of filters myself more than once. But I did come across this Lee thing which will work for some of the fisheye lengths, not 8mm 180 obviously though: Lee Filters SW150 Filter Holder
10-13-2010, 11:01 AM   #58
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QuoteOriginally posted by Nass Quote
Fwiw, I have the 10-17 and I've bemoaned the possibility of filters myself more than once. But I did come across this Lee thing which will work for some of the fisheye lengths, not 8mm 180 obviously though: Lee Filters SW150 Filter Holder
Cokin also makes one. You may be able to find it cheaper, but the Lee filters give better quality. I've read some reviews where people complained about a color cast on the Cokin filters. I have the Lee ND filters and these things are great for landscapes where a Circular Grad. ND would be difficult to use.

How To Use Graduated Filters

One downside with using them is on a tripod with a windy day. They do create some wind drag on the camera and that makes it hard to keep it perfectly still.
10-13-2010, 07:12 PM   #59
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QuoteOriginally posted by Nass Quote
Hm. How embarassing. This is something I'll need to test myself because you know, I could have sworn this was the case. One of many things I struggle with using ultrawides is distant mountains that are 10 pixels high and rocks that are 1000 pixels across.

Update - it's an illusion. See Telephoto Perspective Compression
- At center of the lenses the location won't change much, but the shapes do:

Cropping is not same as zooming, it is real!!!
Digital Photography Tutorial: Focal Length - TrustedReviews - TrustedReviews





You can't call this lens distortion...
- With a UWA you look kind of side ways
- With a tele lens you kind of narrow view and magnify

Portrait lenses (for glamor applications) are typically longer to make people (faces) look slim (and support some distance)
10-13-2010, 07:21 PM   #60
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QuoteOriginally posted by r0ckstarr Quote
Cokin also makes one. You may be able to find it cheaper, but the Lee filters give better quality. I've read some reviews where people complained about a color cast on the Cokin filters. I have the Lee ND filters and these things are great for landscapes where a Circular Grad. ND would be difficult to use.

How To Use Graduated Filters

One downside with using them is on a tripod with a windy day. They do create some wind drag on the camera and that makes it hard to keep it perfectly still.
I can understand the "kick" of using graduated filters, doing it optical rather than digital, but am curious if is actually really needed for dynamic range or you just do it for the fun / habit.
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