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03-27-2013, 07:36 AM   #16
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QuoteOriginally posted by Racer X 69 Quote
If I used a lens with a shorter focal length, on the bellows or extension tubes, will it net a wider angle of view, or a narrower angle of view, given the distance from then front lens element remains unchanged from one lens to another?
"Working distance" is the standard term for the distance from the front of the lens to the subject. Longer focal length lenses give you more working distance for a given magnification. However, in the macro realm longer focal lengths also require greater extension to achieve a given magnification.

So to answer your question is actually rather complicated. Switching to a shorter focal length while preserving the working distance will require you to reduce the extension, and the end result will be a lower magnification image. But in general we care a lot more about the magnification than the precise working distance. In your example with the orchid you're getting more magnification than you want. You can reduce the magnification by using less extension, or by using a longer focal length lens.

Another way to think about it is handling -- very short working distances are awkward, but so are very large amounts of extension. For any given magnification there's a tradeoff between the two. Using a longer focal length gives you a more comfortable working distance; using a shorter focal length lets you get away with less extension. Since, for this example at least, you're dealing with relatively low magnification (well under 1:1), the extension required is quite small and you'll probably find a longer focal length lens easier to work with.

03-27-2013, 07:50 AM   #17
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QuoteOriginally posted by Anvh Quote
Your drawing has a little fault, what is named field of view is angle of view.
The width of the frame at the focus point is the FOV, but like DMS said that is the same for the same magnification.
Oh, I see it now. I'm not surprised that I made a mistake, if you only knew how many mistakes I was about to do when I drew that!
03-27-2013, 01:57 PM   #18
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Oh you drew it yourself?
It looks actually pretty good! =]

If you want to improve it, it could be very useful.
The only other " fault" i could find would be focus distance, it's not measured from the front of the lens but from the lens mount. So you could maybe add a camera to indicate that?
For the rest i might conect magnification to maginifcation of the subject, your way is not wrong though so you could leave it like that.
03-27-2013, 02:04 PM   #19
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QuoteOriginally posted by Anvh Quote
The only other " fault" i could find would be focus distance, it's not measured from the front of the lens but from the lens mount.
Actually, it's measured to film plane or sensor plane. Most film cameras had a mark on the top of the camera indicating the film plane.

03-27-2013, 02:11 PM   #20
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Oh really i thought it was from the mount, thanks for the correction.
03-27-2013, 02:56 PM   #21
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QuoteOriginally posted by Anvh Quote
Oh you drew it yourself?
It looks actually pretty good! =]

If you want to improve it, it could be very useful.
The only other " fault" i could find would be focus distance, it's not measured from the front of the lens but from the lens mount. So you could maybe add a camera to indicate that?
For the rest i might conect magnification to maginifcation of the subject, your way is not wrong though so you could leave it like that.
Yeah, and I really dislike MS Paint, especially when I'm tired with a touchpad. :P
Feel free to use it and improve it as you like!
03-28-2013, 04:08 AM   #22
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wow ms paint even.
Don't have enough time, need to finish 3 series for print in a magazine, before next week ends...

QuoteOriginally posted by Parallax Quote
Actually, it's measured to film plane or sensor plane. Most film cameras had a mark on the top of the camera indicating the film plane.
btw the K7, K5 and 645D also has this mark, so not just film camera's

03-28-2013, 08:51 AM   #23
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QuoteOriginally posted by baro-nite Quote
"Working distance" is the standard term for the distance from the front of the lens to the subject. Longer focal length lenses give you more working distance for a given magnification. However, in the macro realm longer focal lengths also require greater extension to achieve a given magnification.

So to answer your question is actually rather complicated. Switching to a shorter focal length while preserving the working distance will require you to reduce the extension, and the end result will be a lower magnification image. But in general we care a lot more about the magnification than the precise working distance. In your example with the orchid you're getting more magnification than you want. You can reduce the magnification by using less extension, or by using a longer focal length lens.

Another way to think about it is handling -- very short working distances are awkward, but so are very large amounts of extension. For any given magnification there's a tradeoff between the two. Using a longer focal length gives you a more comfortable working distance; using a shorter focal length lets you get away with less extension. Since, for this example at least, you're dealing with relatively low magnification (well under 1:1), the extension required is quite small and you'll probably find a longer focal length lens easier to work with.
I think this response gets the closest to answering my original question. I think.

Some of the points made I was aware of, but did not really consider in the overall macro process.

What I need to know (I think) is what focal length lens will give me more working area than I have with the M lens (which is set at 80mm in macro for the pictures I posted).

Would a 20mm or 28mm M or A series work, or do I need to go the other way and try a 120mm or 150mm M or A lens?
03-28-2013, 10:40 AM   #24
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QuoteOriginally posted by Racer X 69 Quote
What I need to know (I think) is what focal length lens will give me more working area than I have with the M lens (which is set at 80mm in macro for the pictures I posted).
Here's an example of a 28mm lens (M28/2.8) on a moderate amount of extension (Pentax #2 manual tube, not quite 20mm):



So, short focal length lens plus not very much extension already gives considerable magnification, more than you would want for your orchid shot. Have you tried putting the 40-80 on your shortest extension tube? The bellows even at minimum is quite a bit of extension.
03-28-2013, 01:22 PM   #25
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QuoteOriginally posted by baro-nite Quote
Have you tried putting the 40-80 on your shortest extension tube?
Yes, even though I didn't take any shots, I did try several combinations of lens, extension tubes, and varied the focal length of the lens from 40mm to 80mm, and viewed it through the camera. I found the lens looked the best set at the 80mm macro mode in all the various setups, so when I did record some images it was at 80mm.

Having just the one manual lens and only really checking it at 80mm, I didn't really see any difference in the width and height of the images within the area that could be brought into focus. The two shots I posted are from the shortest bellows setting and then the lens by itself. It looks like quite a jump from one to the other, and there surely must be a lens that will get me somewhere in between.

Even though I suck at math, perhaps there is a way to calculate the focal length I'm looking for.

Or I could just buy a 20mm or 28mm and a 150mm or 200mm M, A or FA lens and set it all up an take some pictures.
03-28-2013, 01:37 PM   #26
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In this magnification range (relatively low, say 1:3, or a subject size of APS-C of around 2x3 inches), you'll have finer control over setting the magnification by using a longer lens. The bellows gives you finer control than tubes, of course, but you then you are already starting with 30-some mm of extension. So to use the bellows in this range of magnifications you want something longer than 100mm. Either that, or a bellows lens (can only be used on a bellows); Pentax did make a 100mm bellows lens but they aren't that common.
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