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04-22-2010, 01:12 PM   #61
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QuoteOriginally posted by kacansas03 Quote
As I have said elsewhere you are a real asset to this community for Pentax users in addition to being a leader in the Millionth contest.
Thanks so much! I get a lot of help and have learnt so much on the net. It's only fair I give back at least as much as I have taken.

As for the contest, I mistakenly thought it ended at one million posts. Today I have hardly been online and the same will be true this weekend. I'm afraid no-one needs to do too much to knock me out of the rankings. Unless I suddenly have a change of heart and develop my spamming techniques.

04-22-2010, 02:09 PM   #62
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Hey! It's me, the other leader! :-P

I hope that rparmar can keep up and get the first or second place to share with me though, so nobody else make any more posts until we can make that happen!

Anywho...honestly I would go with the Sigma because it's sharper, and the 2mm longer on the wide end definitely makes a difference at that wide of an angle, but if you want the Pentax and can afford it then go for it! It's an overall better lens.
04-22-2010, 08:21 PM   #63
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in the k7, the sigma is really 15mm, not 10mm, due to the sensor (?) Could anyone verify
04-22-2010, 08:24 PM   #64
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QuoteOriginally posted by jdiritto Quote
in the k7, the sigma is really 15mm, not 10mm, due to the sensor (?) Could anyone verify
Ah the old crop factor confusion. It's really 10mm, but when you put it on the K-7 which has an APS-C sized sensor, it gives you the field of view of 15mm. So it's really a 15-30mm lens when it's on the K-7, but if it were on a full frame camera, then it would be 10mm. I know it's confusing, I'm not even sure if I explained that right actually.

04-22-2010, 08:43 PM   #65
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QuoteOriginally posted by jct us101 Quote
Ah the old crop factor confusion. It's really 10mm, but when you put it on the K-7 which has an APS-C sized sensor, it gives you the field of view of 15mm. So it's really a 15-30mm lens when it's on the K-7, but if it were on a full frame camera, then it would be 10mm. I know it's confusing, I'm not even sure if I explained that right actually.
See rparmar's FOV equivalents list lower down in this thread. It should give you the range of Field Of View for the 10 to 20 mm focal length zoom lens.
04-22-2010, 08:46 PM   #66
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QuoteOriginally posted by kacansas03 Quote
See rparmar's FOV equivalents list lower down in this thread. It should give you the range of Field Of View for the 10 to 20 mm focal length zoom lens.
You're talking about the Sigma 10-20mm right? Yes. and no. Oh the K-7 where the sensor has a 1.5x focal length multiplier, then the Sigma 10-20mm ACTS as a 15-30mm because if you multiply each number by 1.5 then that is what you get.
04-22-2010, 08:52 PM   #67
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QuoteOriginally posted by jct us101 Quote
You're talking about the Sigma 10-20mm right? Yes. and no. Oh the K-7 where the sensor has a 1.5x focal length multiplier, then the Sigma 10-20mm ACTS as a 15-30mm because if you multiply each number by 1.5 then that is what you get.
Quite right dude. On of the small reasons I like Pentax digital over Canon and a bigger reason to prefer it over the Lumix G1 2.0 crop factor. With that last one you look through a 16 mm and all the sudden it like looking through a 35 mm lens. Big difference. I hear the Lumix is great for telephoto shooting but and actual wide angle that has a 24 mm FOV is really a 12 mm fisheye. HHHMM not for me it isn't.!!
04-22-2010, 09:06 PM   #68
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QuoteOriginally posted by JP_Seattle Quote
. but the DA 10-17 is the lens that makes those "WOW" photos.
You are exactly right about that.

04-23-2010, 05:04 PM   #69
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Soo, the siigma 10-20 will capture at 10 on the k7 (?), but the view finder displays it as a 15? or was I right when I originally stated the 10 is really 15 on the k7 due to the sensor? (thus making the pentax 12-24/10-17 wider)


I am looking to test drive a lens rental during a trip to hawaii before purchasing at a later date - I have the 18-55 kit lens and a few longer/macros to borrow from a family member (gotta love that!!) I think having something to get a little wider than 18mm will be great for certain opportunities

I would love the fov with the 10-17, I'm just not so sure on hwo I feel about the fish eye effect, but after learning about the panorama feature in cs4, it has be thinking I should opt to rent the 10-17 fish eye, and use the 18+ stitching for anything I want wider.. so many potential options!

Last edited by jdiritto; 04-23-2010 at 05:10 PM.
04-23-2010, 05:35 PM   #70
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QuoteOriginally posted by jdiritto Quote
Soo, the siigma 10-20 will capture at 10 on the k7 (?), but the view finder displays it as a 15? or was I right when I originally stated the 10 is really 15 on the k7 due to the sensor? (thus making the pentax 12-24/10-17 wider)
This way of thinking is just confusing. The following might help.

1. A 24mm focal length lens is always a 24mm focal length lens. The camera does not magically change its optics. Which is obvious if you think about it.

2. Due to the film / sensor size, the camera sees more or less of the image circle the lens gives it. An APS-C camera sees less by a factor of 1.5. (Unfortunately this is called the crop factor, a confusing term.)

3. This results in a field of view (FOV) that is 1.5 times smaller. So we can talk about FOV equivalent lenses.

Bottom line: An APS-C camera prevents you from having the same ultra-wide FOV you'd get on full-frame.
04-23-2010, 06:24 PM   #71
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QuoteOriginally posted by jdiritto Quote
Soo, the siigma 10-20 will capture at 10 on the k7 (?), but the view finder displays it as a 15? or was I right when I originally stated the 10 is really 15 on the k7 due to the sensor? (thus making the pentax 12-24/10-17 wider)


I am looking to test drive a lens rental during a trip to hawaii before purchasing at a later date - I have the 18-55 kit lens and a few longer/macros to borrow from a family member (gotta love that!!) I think having something to get a little wider than 18mm will be great for certain opportunities

I would love the fov with the 10-17, I'm just not so sure on hwo I feel about the fish eye effect, but after learning about the panorama feature in cs4, it has be thinking I should opt to rent the 10-17 fish eye, and use the 18+ stitching for anything I want wider.. so many potential options!
None of what you said is accurate. The lens is a 10 mm focal length to 20 mm focal length as an example. If mounted on a full 35 mm frame film camera the view that the film or the view finder (which looks Through the lens remember) is the 10 to 20 mm field. Now when you mount the lens on a digital camera with a reduced sensor size that sensor can not "see" as wide of a field because some is cut off on the sides and top and bottom hence the "crop factor". On Pentax digital bodies to date the factor is 1.5. This means that when viewing the image it is smaller side to side, top to bottom, than a film image or full sized sensor image therefore it is cropped. It is the same effect as using the crop tools within photo editing software or laying something on top of a print of the picture that cuts off all the sides. So when you look at the picture or through the viewfinder you are seeing a smaller area than you would with a film camera. We Pentax owners are lucky in that for us it is an exact 1.5 so you multiply the actual focal length by 1.5 and you get the effective field of view so it is like looking though a lens that is longer however it is not the same as telephoto magnification. A 200 mm telephoto lens still gives about a 4 power magnification even though the angles of view through the lens are equal to a 300 mm lens. The list below in the thread gives you the effective field of view on a Pentax cropped sensor digital body. The reason they build the sensors smaller is they cost a lot less.
04-23-2010, 06:27 PM   #72
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QuoteOriginally posted by rparmar Quote
This way of thinking is just confusing. The following might help.

1. A 24mm focal length lens is always a 24mm focal length lens. The camera does not magically change its optics. Which is obvious if you think about it.

2. Due to the film / sensor size, the camera sees more or less of the image circle the lens gives it. An APS-C camera sees less by a factor of 1.5. (Unfortunately this is called the crop factor, a confusing term.)

3. This results in a field of view (FOV) that is 1.5 times smaller. So we can talk about FOV equivalent lenses.

Bottom line: An APS-C camera prevents you from having the same ultra-wide FOV you'd get on full-frame.
Just remember rparmar that it works the same on telephoto as on wide angle. You just can not see as wide an area with a crop sensor camera.
04-23-2010, 08:41 PM   #73
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QuoteOriginally posted by jdiritto Quote
Soo, the siigma 10-20 will capture at 10 on the k7 (?)
All 10mm lenses capture at 10mm on all cameras. Focal length never changes just because of the "crop factor". If you don't own a film camera, you can safely forget you ever heard that term. It's just not relevant to 99% of photographers.

QuoteQuote:
or was I right when I originally stated the 10 is really 15 on the k7 due to the sensor? (thus making the pentax 12-24/10-17 wider)
No. Again, 10mm is 10mm, and 12mm is 12mm. 10mm is *always* wider than 12mm when both are mounted to a given camera. 10mm on a K-7 might not be wider than 12mm on a film camera, but if you don't own a film camera with a 12mm lens, this is not relevant to you.

Last edited by Marc Sabatella; 04-24-2010 at 08:39 PM.
04-24-2010, 05:14 AM   #74
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QuoteOriginally posted by kacansas03 Quote
Just remember rparmar that it works the same on telephoto as on wide angle. You just can not see as wide an area with a crop sensor camera.
Sure. I only addressed wide angle since that is the topic of the thread. But all lenses of all focal lengths work exactly the same way. So a 200mm focal is always a 200mm focal, but on APS-C once sees only the central area, making it "appear" in FOV like a 300mm. But that's only because you're missing all the rest of the image that would be in the wider FOV. Crop an image of a full-frame and you end up with the same picture. (Which is where the "crop factor" term comes from.)

In a way, it is a shame all lenses for a given system are not measured in terms of field of view, since that is what everyone actually cares about. That only weakness of that system would be when using the same lens on different systems... which few enough people do.
04-24-2010, 02:01 PM   #75
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My wide angle

Well I have decided that I need to do more research for I really don't like the fisheye effect but yet I also know I liked the FOV of a 24 when using film. I also know I wanted a wider view and knew that a 20 could be bought that wouldn't have the distortion. I never got a chance to try that kind of lens. I am now thinking I should narrow down the list and then rent the lenses, I hope, and try them on my K100D. But first figure out by looking at specs for various lenses just what FOV I wish to capture. All the information I am getting from this thread is very, very valuable to me. Thank You everyone.!!
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