Re: Determining a Focal Length
On Fri, 22 Dec 2006, Shel Belinkoff wrote: No, the distances aren't precise, but I can get a more accurate idea the next time I drive past the scene. I think I'll put the Lufkin in the Domke on my way out later t'nite. How about a FF body with the 18mm on it? If it works you know what you need. Kostas -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
I think you need the angle of view more than field of view. the formula for AOV is AOF = 2*tan^(-1)/(F/2*f) where F is the size of the sensor f is the focal length. You'll have to use some algebra to rearrange the terms to solve for f. I'm just feeling too lazy... Shel Belinkoff wrote: There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. Shel -- Things should be made as simple as possible -- but no simpler. --Albert Einstein -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
On 12/24/06, P. J. Alling [EMAIL PROTECTED] wrote: I think you need the angle of view more than field of view. the formula for AOV is AOF = 2*tan^(-1)/(F/2*f) where F is the size of the sensor f is the focal length. You'll have to use some algebra to rearrange the terms to solve for f. I'm just feeling too lazy... f = B / (2xtan(AOF / 2)) I got it from here: http://www.mhohner.de/formulas.php Dave (also too lazy to work it out) -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
RE: Determining a Focal Length
No trig. is needed for this kind of calculation. If you know object size and distance, then all you need to know is that the object distance/object size = focal length/sensor size. Solving the equation, focal length needed = (object distance/object size) * (sensor size in mm) jco -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of David Savage Sent: Saturday, December 23, 2006 9:28 PM To: Pentax-Discuss Mail List Subject: Re: Determining a Focal Length On 12/24/06, P. J. Alling [EMAIL PROTECTED] wrote: I think you need the angle of view more than field of view. the formula for AOV is AOF = 2*tan^(-1)/(F/2*f) where F is the size of the sensor f is the focal length. You'll have to use some algebra to rearrange the terms to solve for f. I'm just feeling too lazy... f = B / (2xtan(AOF / 2)) I got it from here: http://www.mhohner.de/formulas.php Dave (also too lazy to work it out) -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Determining a Focal Length
There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. Shel -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
On 23/12/06, Shel Belinkoff [EMAIL PROTECTED] wrote: There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. f-calc http://tangentsoft.net/fcalc/ For an APS frame you'd need about 15mm and for a FF you'd need about 18mm -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
RE: Determining a Focal Length
Basic trigonometry. God, even the numbers are the easiest possible to calculate (dont even need a calculator for that baby). You need a 90 degree lens horizontally to just cover the object. The way to calculate f.l. is to use same ratios of film/sensor size to focal length as object size to object distance. Since your object distance is half the object size, your focal length needs to be half the sensor horizontal size which means a 18mm lens for FF 35mm film or a 12mm lens for APS digital. Even wider f.l. for slightly more coverage than the object itself. jco -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Shel Belinkoff Sent: Friday, December 22, 2006 3:53 PM To: PDML Subject: Determining a Focal Length There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. Shel -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
On 23/12/06, J. C. O'Connell [EMAIL PROTECTED] wrote: Basic trigonometry. God, even the numbers are the easiest possible to calculate (dont even need a calculator for that baby). You need a 90 degree lens horizontally to just cover the object. The way to calculate f.l. is to use same ratios of film/sensor size to focal length as object size to object distance. Since your object distance is half the object size, your focal length needs to be half the sensor horizontal size which means a 18mm lens for FF 35mm film or a 12mm lens for APS digital. Even wider f.l. for slightly more coverage than the object itself. Try again. A 12mm lens on APS format at 6' from the subject will provide a resultant horizontal field of view of 15' -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
Smacking forehead! I've got f-calc on this machine. Thanks for the reminder. Shel [Original Message] From: Digital Image Studio Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. f-calc http://tangentsoft.net/fcalc/ For an APS frame you'd need about 15mm and for a FF you'd need about 18mm -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
On 23/12/06, Shel Belinkoff [EMAIL PROTECTED] wrote: Smacking forehead! I've got f-calc on this machine. Thanks for the reminder. I've got another handy one for you: http://www.bobatkins.com/photography/technical/depth_of_field_calc.html -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
And the DA 14/2.8. Paul On Dec 22, 2006, at 6:58 PM, John Francis wrote: On Fri, Dec 22, 2006 at 12:53:26PM -0800, Shel Belinkoff wrote: There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. So, as you know now, for APS-C the answer is somewhere around 15mm (give or take; I assume your distances quoted above aren't absolutely precise). That leaves you with three or four choices: o The A 15mm o A DA 16-45, if you can get away with a 16mm o The DA 10-17 fisheye zoom, if distortion is OK (although you can defish the image digitally) o The DA 12-24; probably your best choice. I don't know what access you have to loaner lenses, but if you decide on the fisheye I've now got one of those in my bag :-) -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
Oops :-) On Fri, Dec 22, 2006 at 07:01:13PM -0500, Paul Stenquist wrote: And the DA 14/2.8. Paul On Dec 22, 2006, at 6:58 PM, John Francis wrote: On Fri, Dec 22, 2006 at 12:53:26PM -0800, Shel Belinkoff wrote: There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. So, as you know now, for APS-C the answer is somewhere around 15mm (give or take; I assume your distances quoted above aren't absolutely precise). That leaves you with three or four choices: o The A 15mm o A DA 16-45, if you can get away with a 16mm o The DA 10-17 fisheye zoom, if distortion is OK (although you can defish the image digitally) o The DA 12-24; probably your best choice. I don't know what access you have to loaner lenses, but if you decide on the fisheye I've now got one of those in my bag :-) -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
On Fri, Dec 22, 2006 at 12:53:26PM -0800, Shel Belinkoff wrote: There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. So, as you know now, for APS-C the answer is somewhere around 15mm (give or take; I assume your distances quoted above aren't absolutely precise). That leaves you with three or four choices: o The A 15mm o A DA 16-45, if you can get away with a 16mm o The DA 10-17 fisheye zoom, if distortion is OK (although you can defish the image digitally) o The DA 12-24; probably your best choice. I don't know what access you have to loaner lenses, but if you decide on the fisheye I've now got one of those in my bag :-) -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
RE: Determining a Focal Length
14mm will not be wide enough, you need 12mm maximum for APS based on the 2/3 f.l. factor vs. the 18mm FF lens. jco -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Stenquist Sent: Friday, December 22, 2006 7:01 PM To: Pentax-Discuss Mail List Subject: Re: Determining a Focal Length And the DA 14/2.8. Paul On Dec 22, 2006, at 6:58 PM, John Francis wrote: On Fri, Dec 22, 2006 at 12:53:26PM -0800, Shel Belinkoff wrote: There is a photo I'd like to make, but the widest lens I have is still too long as it forces me to include an undesirable object in the frame and I don't want to mess around with cloning the object out of the scene. I will need to borrow a wider lens, but I don't know what focal length would work. Is there a way to determine the focal length I need based on the subject distance and framing I want using the longer lens. I know how close I must get to the subject to eliminate the unwanted element. Perhaps a formula of some sort? For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. So, as you know now, for APS-C the answer is somewhere around 15mm (give or take; I assume your distances quoted above aren't absolutely precise). That leaves you with three or four choices: o The A 15mm o A DA 16-45, if you can get away with a 16mm o The DA 10-17 fisheye zoom, if distortion is OK (although you can defish the image digitally) o The DA 12-24; probably your best choice. I don't know what access you have to loaner lenses, but if you decide on the fisheye I've now got one of those in my bag :-) -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
RE: Determining a Focal Length
nope, what you gave was impossible. 18mm and 15mm are not possible (the lengths you provided) because Pentax APS always needs a lens 2/3 the length of FF 35mm for same angle of view. I dont care what calculator you used, it's wrong if it told you 18mm for FF and 15mm for APS were the same angle of view, because they arent. jco -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Digital Image Studio Sent: Friday, December 22, 2006 4:51 PM To: Pentax-Discuss Mail List Subject: Re: Determining a Focal Length On 23/12/06, J. C. O'Connell [EMAIL PROTECTED] wrote: Basic trigonometry. God, even the numbers are the easiest possible to calculate (dont even need a calculator for that baby). You need a 90 degree lens horizontally to just cover the object. The way to calculate f.l. is to use same ratios of film/sensor size to focal length as object size to object distance. Since your object distance is half the object size, your focal length needs to be half the sensor horizontal size which means a 18mm lens for FF 35mm film or a 12mm lens for APS digital. Even wider f.l. for slightly more coverage than the object itself. Try again. A 12mm lens on APS format at 6' from the subject will provide a resultant horizontal field of view of 15' -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
On 23/12/06, J. C. O'Connell [EMAIL PROTECTED] wrote: nope, what you gave was impossible. 18mm and 15mm are not possible (the lengths you provided) because Pentax APS always needs a lens 2/3 the length of FF 35mm for same angle of view. I dont care what calculator you used, it's wrong if it told you 18mm for FF and 15mm for APS were the same angle of view, because they arent. I just calculated it by hand and you are correct John. The app that I used to calculate the values used an actual APS frame size rather than the so called Pentax digital APS frame size (23.5mm x 15.7mm). -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
Hi John, No, the distances aren't precise, but I can get a more accurate idea the next time I drive past the scene. I think I'll put the Lufkin in the Domke on my way out later t'nite. There's also the DA 14/2.8 which, along with the 12-24, seems like the best option. Congrats on the 12-24 ... I think Paul has one and that he's quite satisfied with it. I tried Godfrey's 14/2.8 and liked it quite a bit. I've got to study the scene a bit and see when the light's right. This may not even be the right time of tear for the photo ... gotta watch where the sun is, y'know ;-)) Shel [Original Message] From: John Francis So, as you know now, for APS-C the answer is somewhere around 15mm (give or take; I assume your distances quoted above aren't absolutely precise). That leaves you with three or four choices: o The A 15mm o A DA 16-45, if you can get away with a 16mm o The DA 10-17 fisheye zoom, if distortion is OK (although you can defish the image digitally) o The DA 12-24; probably your best choice. I don't know what access you have to loaner lenses, but if you decide on the fisheye I've now got one of those in my bag :-) -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
RE: Determining a Focal Length
the numbers you gave call for a 12mm lens. If they are correct, then 14mm wont work. Dont forget, 12 vs 14 for a Pentax DSLR is the same as 24mm vs 28mm for FF. They are signifigantly different angles at that range on a Pentax DSLR. 2mm can make the difference between working and not working when you get that short. jco -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Shel Belinkoff Sent: Friday, December 22, 2006 7:52 PM To: Pentax-Discuss Mail List Subject: Re: Determining a Focal Length Hi John, No, the distances aren't precise, but I can get a more accurate idea the next time I drive past the scene. I think I'll put the Lufkin in the Domke on my way out later t'nite. There's also the DA 14/2.8 which, along with the 12-24, seems like the best option. Congrats on the 12-24 ... I think Paul has one and that he's quite satisfied with it. I tried Godfrey's 14/2.8 and liked it quite a bit. I've got to study the scene a bit and see when the light's right. This may not even be the right time of tear for the photo ... gotta watch where the sun is, y'know ;-)) Shel [Original Message] From: John Francis So, as you know now, for APS-C the answer is somewhere around 15mm (give or take; I assume your distances quoted above aren't absolutely precise). That leaves you with three or four choices: o The A 15mm o A DA 16-45, if you can get away with a 16mm o The DA 10-17 fisheye zoom, if distortion is OK (although you can defish the image digitally) o The DA 12-24; probably your best choice. I don't know what access you have to loaner lenses, but if you decide on the fisheye I've now got one of those in my bag :-) -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
Re: Determining a Focal Length
- Original Message - From: Shel Belinkoff Subject: Determining a Focal Length For what it's worth, the subject is about 12-feet long and I have to get about six feet from it. Presuming you want to use the DSLR, you will need either the 10-17 fish-eye or possibly the 12-24 might go wide enough. I just tried lining up half my house width, which is about 12 feet and found with the 14/2.8, I needed to be about 8' back from the wall, yet with the 10-17, I was at 6 feet with the FL set to just past 14mm. William Robb -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
