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#1
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Extension Tube + 400mm lens question
Okay, got the Canon 400 5.6L in today. Though its primary use will be
mounted on my 10D for bird shots at distance, if I wanted to take hummingbird photos from about 10 feet, what size extension tube would I need? Is there a formula for figuring this out? The minimum focus distance on this lens is 3.5 meters. Additionally, I see that Kenko makes a set of extension tubes 12mm, 20mm and 36mm. Should I just get a set or will just one tube satisfy my need/want? Additionally, am I correct in thinking that the magnification from one of these tubes will be the same as just adding the length of the tube to the focal length of the lens? TIA -- Eric Miller millereric at bellsouth dot net Convictions are more dangerous enemies of truth than lies. - Freidrich Neitsche |
#2
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I have a Canon 12.5 and a 25 mm extension tube. Both work fine, both are
pretty cheap. I use them only rarely, but your use may vary depending on interest. I am not sure if I understand the second question. I get improved short focus, but the extra magnification is mostly just secondary to being able to get closer to the subject. There are no lenses in those extension tubes, just air and electrical connections for the motor/camera. When I used them for stacking lenses, they were just added to allow the lenses to fit together. Dave "Eric Miller" wrote in message . .. Okay, got the Canon 400 5.6L in today. Though its primary use will be mounted on my 10D for bird shots at distance, if I wanted to take hummingbird photos from about 10 feet, what size extension tube would I need? Is there a formula for figuring this out? The minimum focus distance on this lens is 3.5 meters. Additionally, I see that Kenko makes a set of extension tubes 12mm, 20mm and 36mm. Should I just get a set or will just one tube satisfy my need/want? Additionally, am I correct in thinking that the magnification from one of these tubes will be the same as just adding the length of the tube to the focal length of the lens? TIA -- Eric Miller millereric at bellsouth dot net Convictions are more dangerous enemies of truth than lies. - Freidrich Neitsche |
#3
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Eric Miller wrote:
Okay, got the Canon 400 5.6L in today. Though its primary use will be mounted on my 10D for bird shots at distance, if I wanted to take hummingbird photos from about 10 feet, what size extension tube would I need? Is there a formula for figuring this out? The minimum focus distance on this lens is 3.5 meters. Additionally, I see that Kenko makes a set of extension tubes 12mm, 20mm and 36mm. Should I just get a set or will just one tube satisfy my need/want? Additionally, am I correct in thinking that the magnification from one of these tubes will be the same as just adding the length of the tube to the focal length of the lens? TIA -- Eric Miller Ok, basic formula: 1/u + 1/v = 1/f, where u=object distance from lens, v=image distance from lens, f=focal length of lens. Using a rearrangement of this formula, at the closest focusing distance (cfd) of 3.5 meters, the effective lens extension is 51mm. Adding a 48mm extension tube (12mm + 36mm), the effective lens extension is 48mm with the lens at infinity, and 99mm when the lens is at cfd. Referring to the formula again, object distance with 48mm extension is 3.733 meters, and 2.016 meters with 99mm extension. So, focusing range with a 48mm tube is from 3.7 meters to 2 meters more or less. Colin D. |
#4
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Eric Miller wrote:
Okay, got the Canon 400 5.6L in today. Though its primary use will be mounted on my 10D for bird shots at distance, if I wanted to take hummingbird photos from about 10 feet, what size extension tube would I need? Is there a formula for figuring this out? The minimum focus distance on this lens is 3.5 meters. Additionally, I see that Kenko makes a set of extension tubes 12mm, 20mm and 36mm. Should I just get a set or will just one tube satisfy my need/want? Additionally, am I correct in thinking that the magnification from one of these tubes will be the same as just adding the length of the tube to the focal length of the lens? TIA -- Eric Miller Ok, basic formula: 1/u + 1/v = 1/f, where u=object distance from lens, v=image distance from lens, f=focal length of lens. Using a rearrangement of this formula, at the closest focusing distance (cfd) of 3.5 meters, the effective lens extension is 51mm. Adding a 48mm extension tube (12mm + 36mm), the effective lens extension is 48mm with the lens at infinity, and 99mm when the lens is at cfd. Referring to the formula again, object distance with 48mm extension is 3.733 meters, and 2.016 meters with 99mm extension. So, focusing range with a 48mm tube is from 3.7 meters to 2 meters more or less. Colin D. |
#5
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-- I see that Kenko makes a set of extension tubes 12mm, 20mm and 36mm. Should I just get a set or will just one tube satisfy my need/want? I really like the Kenko set of tubes. use them quite a bit. I'm to the point now that I have to consider a macro lens because of the time it take to figure out the right extension for a project. I would get the Kenko set over individual Canon tubes. You have no glass to worry about Ray Creveling http://www.blackcatblog.com --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.745 / Virus Database: 497 - Release Date: 8/27/2004 |
#6
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-- I see that Kenko makes a set of extension tubes 12mm, 20mm and 36mm. Should I just get a set or will just one tube satisfy my need/want? I really like the Kenko set of tubes. use them quite a bit. I'm to the point now that I have to consider a macro lens because of the time it take to figure out the right extension for a project. I would get the Kenko set over individual Canon tubes. You have no glass to worry about Ray Creveling http://www.blackcatblog.com --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.745 / Virus Database: 497 - Release Date: 8/27/2004 |
#7
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If my calculations are correct, a 25mm tube will allow the 400 to focus from
8 to 22 feet. Someone posted a formula for the math below. But remember that internal focus lenses shorten the focal length at closer distances. So focal length plus extension at close up is always equal to focal length at infinity. I suggest that you forget the off brand tubes and buy the Canon. I haven't checked all the different brands but as far as I can tell the Canon will attach to the 400 much more securely - you can check this yourself in the store. Sorry due to spam I shall not provide a valid e-mail address. Please reply to group with questions or comments. "Eric Miller" wrote in message . .. Okay, got the Canon 400 5.6L in today. Though its primary use will be mounted on my 10D for bird shots at distance, if I wanted to take hummingbird photos from about 10 feet, what size extension tube would I |
#8
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If my calculations are correct, a 25mm tube will allow the 400 to focus from
8 to 22 feet. Someone posted a formula for the math below. But remember that internal focus lenses shorten the focal length at closer distances. So focal length plus extension at close up is always equal to focal length at infinity. I suggest that you forget the off brand tubes and buy the Canon. I haven't checked all the different brands but as far as I can tell the Canon will attach to the 400 much more securely - you can check this yourself in the store. Sorry due to spam I shall not provide a valid e-mail address. Please reply to group with questions or comments. "Eric Miller" wrote in message . .. Okay, got the Canon 400 5.6L in today. Though its primary use will be mounted on my 10D for bird shots at distance, if I wanted to take hummingbird photos from about 10 feet, what size extension tube would I |
#9
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Colin D wrote:
Eric Miller wrote: Okay, got the Canon 400 5.6L in today. Though its primary use will be mounted on my 10D for bird shots at distance, if I wanted to take hummingbird photos from about 10 feet, what size extension tube would I need? Is there a formula for figuring this out? The minimum focus distance on this lens is 3.5 meters. Additionally, I see that Kenko makes a set of extension tubes 12mm, 20mm and 36mm. Should I just get a set or will just one tube satisfy my need/want? Additionally, am I correct in thinking that the magnification from one of these tubes will be the same as just adding the length of the tube to the focal length of the lens? TIA -- Eric Miller Ok, basic formula: 1/u + 1/v = 1/f, where u=object distance from lens, v=image distance from lens, f=focal length of lens. Using a rearrangement of this formula, at the closest focusing distance (cfd) of 3.5 meters, the effective lens extension is 51mm. Adding a 48mm extension tube (12mm + 36mm), the effective lens extension is 48mm with the lens at infinity, and 99mm when the lens is at cfd. Referring to the formula again, object distance with 48mm extension is 3.733 meters, and 2.016 meters with 99mm extension. So, focusing range with a 48mm tube is from 3.7 meters to 2 meters more or less. Colin D. OK, an update on my previous. I belatedly realized that the 400mm probably uses internal focusing, so instead of racking the lens out by 51 mm from the film plane, the focal length of the lens is shortened sufficiently to focus on 3.5 meters. The question becomes, what reduction in focal length will cause a 400mm lens to focus at 3.5 meters? Since the object distance = 3500mm and the image distance remains at 400mm, then 1/f = 1/u +1/v, or 1/3500 + 1/400 = 1/358.9, so the effective focal length shortens to 359mm approx. If we add 48mm of tube in now, the image distance becomes 448mm, so now 1/u = 1/f - 1/v, or 1/u = 1/359 - 1/448, = 1/1807.1 Therefore, object distance at cfd is 1.8 meters approximately, so with an internal focusing lens, the range is 3.7 meters to 1.8 meters approximately. Colin D. |
#10
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Colin D wrote:
Eric Miller wrote: Okay, got the Canon 400 5.6L in today. Though its primary use will be mounted on my 10D for bird shots at distance, if I wanted to take hummingbird photos from about 10 feet, what size extension tube would I need? Is there a formula for figuring this out? The minimum focus distance on this lens is 3.5 meters. Additionally, I see that Kenko makes a set of extension tubes 12mm, 20mm and 36mm. Should I just get a set or will just one tube satisfy my need/want? Additionally, am I correct in thinking that the magnification from one of these tubes will be the same as just adding the length of the tube to the focal length of the lens? TIA -- Eric Miller Ok, basic formula: 1/u + 1/v = 1/f, where u=object distance from lens, v=image distance from lens, f=focal length of lens. Using a rearrangement of this formula, at the closest focusing distance (cfd) of 3.5 meters, the effective lens extension is 51mm. Adding a 48mm extension tube (12mm + 36mm), the effective lens extension is 48mm with the lens at infinity, and 99mm when the lens is at cfd. Referring to the formula again, object distance with 48mm extension is 3.733 meters, and 2.016 meters with 99mm extension. So, focusing range with a 48mm tube is from 3.7 meters to 2 meters more or less. Colin D. OK, an update on my previous. I belatedly realized that the 400mm probably uses internal focusing, so instead of racking the lens out by 51 mm from the film plane, the focal length of the lens is shortened sufficiently to focus on 3.5 meters. The question becomes, what reduction in focal length will cause a 400mm lens to focus at 3.5 meters? Since the object distance = 3500mm and the image distance remains at 400mm, then 1/f = 1/u +1/v, or 1/3500 + 1/400 = 1/358.9, so the effective focal length shortens to 359mm approx. If we add 48mm of tube in now, the image distance becomes 448mm, so now 1/u = 1/f - 1/v, or 1/u = 1/359 - 1/448, = 1/1807.1 Therefore, object distance at cfd is 1.8 meters approximately, so with an internal focusing lens, the range is 3.7 meters to 1.8 meters approximately. Colin D. |
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