'MACRO' pound coins
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cowasaki
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effectively it is about the inverse-square law! As the distance increases so does the magnification. This will depend on the camera/lens combination but it will always increase. I fancy a set of baffles or a telescopic tube. I might even have a mess and look at making one..... Where is that sticky back plastic, fairy bottle and packing tape?
The inverse square law only deals with distance i.e. doubling the distance between the light and the subject results in one quarter of the light hitting the subject.
If there was a law to link distance and magnification then magnification would be directly linked to the inverse square law. Otherwise I think magnification is just a confounding factor.
If there was a law to link distance and magnification then magnification would be directly linked to the inverse square law. Otherwise I think magnification is just a confounding factor.
pxl8 gave a really good example: using a 25mm tube on a 50mm lens will give a different magnification than if used on a 100mm lens, however the amount of light loss is the same. Therefore light loss cannot be attributed to magnification, it is just a confounding factor.
Another example just off the top of my head, people who drink at pubs get lung cancer. This is not true as drinking in pubs is a confounding factor to smoking.
Another example just off the top of my head, people who drink at pubs get lung cancer. This is not true as drinking in pubs is a confounding factor to smoking.
cowasaki
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Magnification is directly linked to distance as can be seen from either diagram. Whether it is perceived to be a confounding factor or not does not really matter. The point is that as the magnification is increased the amount of light hitting the sensor decreases which was what I was saying originally due to the reason I originally stated. You can look at it from either way but if you just explain it using distance as the important factor then it has a tendency to look like you are saying that light itself reduces in intensity as it moves through space which it doesn't (it spreads out so you see less). Either way explains the principal and I am sure that anyone reading this thread now understands how/why this happens.
cowasaki
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If you look at my responses I have said "for the same camera/lens combination" and as magnification increases the amount of light at the other end decreases. If the magnifcation is 8X then then light reduction is 8X8 (8x in each direction) ie one 64th. This does not require anyone to know distance, lens or anything else it is a simple mathematical principal.
cowasaki
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Because the lens is giving the same amount of light across the area. On a smaller sensor you are only looking at a small part of it. The cropped sensor is not magnifying anything it is just a small subset of a full frame sensor in the same position.
yep I agree, for the same lens combination that is in fact what happens. As distance increase so does magnification, therefore the further away the tube takes the lens the higher the magnification and also the less amount of light hitting the sensor.
What we are trying to point out is that it is not magnification per se but it's actually the distance which causes the light to be loss due to the spread of flux/energy. This spread of flux is constant with distance that's why the amount of light hitting the sensor at a certain distance from the subject is the same no matter what magnification.
But we are just going round in circles, end of the day the extension tubes takes the lens further away from the sensor, thus giving a larger magnification due to the extra distance which will result in less light hitting the sensor.
What we are trying to point out is that it is not magnification per se but it's actually the distance which causes the light to be loss due to the spread of flux/energy. This spread of flux is constant with distance that's why the amount of light hitting the sensor at a certain distance from the subject is the same no matter what magnification.
But we are just going round in circles, end of the day the extension tubes takes the lens further away from the sensor, thus giving a larger magnification due to the extra distance which will result in less light hitting the sensor.
cowasaki
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This is getting silly, it is like arguing over how far you can throw a round rock made of granite and one person saying it depends on the weight of the rock and another saying it depends on the size. They are effectively arguing the same thing as the size increases so does the weight. In our example as the distance increases so does the magnification. I chose to relate the light loss to magnification on the basis that it is much easier to explain WHY there is a light loss when you explain it this way ie 8x mag produces 64th the amount of light. Yes I agree it is due to distance but distance increases the magnification so as you increase magnification you increase light loss.
:bang::bang::bang::bang::bang::bang:
:bang::bang::bang::bang::bang::bang:
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Magnification will affect the amount of light and in the way you described but compensating for that doesn't compensate for the light loss from the addition of the tubes.
If you have a "normal" macro lens and point it at a evenly lit white wall at 1:2 (half life size) and take a reading and then take another reading at 1:1 you'll get a lower reading. This is the effect of magnification because you are looking at a smaller subject area so less light will be reflected into the lens.
It's got nothing to to do with the image circle projected onto the sensor/film plane as that stays the same size, it's just the result of how much light can enter the front of the lens. If you were to have infinite magnification then then amount of light reflected back would be infinitely small.
This doesn't compensate for the addition of tube. The inverse square law deals with the spreading of light (except colminated light from a laser, etc) and that spread happens along the length of the tube - the longer the tube the more the light will spread and the greater the reduction in light hitting the sensor. Don't be fooled into thinking that because the light has been focused it won't spread, that's only true if the light is a parallel beam like a laser.
If you have a "normal" macro lens and point it at a evenly lit white wall at 1:2 (half life size) and take a reading and then take another reading at 1:1 you'll get a lower reading. This is the effect of magnification because you are looking at a smaller subject area so less light will be reflected into the lens.
It's got nothing to to do with the image circle projected onto the sensor/film plane as that stays the same size, it's just the result of how much light can enter the front of the lens. If you were to have infinite magnification then then amount of light reflected back would be infinitely small.
This doesn't compensate for the addition of tube. The inverse square law deals with the spreading of light (except colminated light from a laser, etc) and that spread happens along the length of the tube - the longer the tube the more the light will spread and the greater the reduction in light hitting the sensor. Don't be fooled into thinking that because the light has been focused it won't spread, that's only true if the light is a parallel beam like a laser.
cowasaki
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Nobody is talking about any form of compensation. If you increase the distance you increase the magnification therefore using the simple example of a macro tube distance and magnifcation are TOTALLY linked and you could talk about either.
Yes I understand this but using the lens in this manner is using lenses to focus that light. This changes everything and has nothing to do with the SIMPLE model we were looking at originally ie MACRO TUBES.
I am only talking about magnification due to distance not using lenses. I am STILL agreeing with you! I understand about lasers and this is one of the reasons I chose to talk about the light loss in this way. Your description seemed to be saying originally that light reduced due to distance which would mean that the power of a laser would reduce in the same way. My explanation is sound for the macro tube which is what I was explaining!
cowasaki
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It is quite clear from my diagram that I understand this principal. I just chose to explain it in a manner that I thought people might understand more easily. People getting hung up on whether it is because of distance or magnification is not really relevant in this simple example as both are inextricably linked. As long as it is clear there is a light loss due to distance OR magnification does not matter either - there is a light loss and it is proportional to EITHER as they are both linked. The diagram shows how the tubes work. :bonk::bonk:
cowasaki
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If you are referring to the sides of the macro shot it is due to the depth of field. As you increase the f number you increase the amount of the picture that is in focus. As you decrease the f number you reduce the amount that is in focus. With macro shots this can make a big difference. I have been taking lots of jewellery shots as my wife makes it. If I have too low an f number then half a ring can be in focus and half not!
yep, the lower the F number the bigger the aperture but the shallower the depth of field.
However in this shot I used extension tubes, when using extension tubes you can focus more closely in on the subject but the depth of field becomes very shallow. It's a lot easier to make things blur than to get things in focus.
I think I shot this with a f/8 value.
However in this shot I used extension tubes, when using extension tubes you can focus more closely in on the subject but the depth of field becomes very shallow. It's a lot easier to make things blur than to get things in focus.
I think I shot this with a f/8 value.
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They're linked but that doesn't mean the light loss is due to the magnification.
Increased Distance = Magnifcation & Light Loss
You can't say that Increased Magnification = Light Loss because that simply isn't true. The same thing that causes the increase in magnification ALSO causes the light loss.
Apart from anything else in order to calculate the light loss you need to know the distance of extension. If you wanted to calculate it from the amount of magnification you'd still have to work out the extension in order to use the inverse square law - which, as we all know by now, is based on DISTANCE
If you allow people to believe that then they'll want to know how much light loss there is based on the magnification, ie.
Q: If I use a 25mm tube on a 50mm lens which gives me 0.5x magnification how much light loss will there be?
A: Approx. 1 stop.
Q: If I used 50mm of tubes on a 100mm lens which also gives me 0.5x magnification how much light loss will there be?
A: Approx 2 stops.
Q: Why is the light loss different if the magnification is the same?
A: Because it's the simple explanation... :bonk:
cowasaki
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I have already explained this several times, but you could apply simple algebraic techniques to your equation and make any of the three items the principal of the equation! I was never trying to give a total explanation of the working of lenses, cameras, lasers, light etc etc just that there would be a loss equal to the square of the magnification! Just that.
Apart from anything else in order to calculate the light loss you need to know the distance of extension. If you wanted to calculate it from the amount of magnification you'd still have to work out the extension in order to use the inverse square law - which, as we all know by now, is based on DISTANCE
OR it can also be based on my calculation! ie 8x mag = 8x8 times light loss
If we JUST look at magnification:
you have a macro tube on a 60mm lens giving a magnification of 8 then the light loss is 63/64ths.
you have a macro tube on a 105mm lens giving a magnification of 8 then the light loss is 63/64ths
(but these would be different tubes!)
I TOTALLY APPRECIATE WHAT YOU ARE SAYING (and you are not wrong either in your descriptions but...)!
I am not WRONG we could argue over which way of describing it is best and I would accept this quite happily. My explanation is sound for the example it was used for.
I have a high degree of understanding of physics but I wont pretend to say I am necessarily explaining it the best way - just the way that seems best to me! I was just trying to explain a simple thing using laymans terms without going into lots of detail and causing confusion! (which I think we have done now!)
cowasaki
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I agree completely. I have better things to do than go round and round in circles arguing the SAME THING.
At least anyone reading this will now understand that you get a light loss due to macro tubes and this depends on the length and/or magnification which was all that we were both saying.
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The magnification of a 50mm lens with 25mm of tubes is 0.5x
The magnification of a 100mm lens of 50mm of tubes is also 0.5x
According to your formula the light loss for these would be the same when in fact it's one stop more for the 100mm lens.
:shrug:
Just for clarity
a 100mm lens with 25mm of tubes has a mag of 0.25x so accordingly it should have less light loss than the 50mm lens, again not so.
:shrug:
cowasaki
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I am talking about percentage light loss over what is there originally (on the same lens). I was bored with this arguement whilst it was still 1 page.
You can argue with yourself now I can't be bothered wasting any more time with this. I am sure the person who asked about them can see how they work and that lots of light is lost. You understand it and so do I so i'll leave it at that and unsubscribe from the thread! Your time is obviously worth less than mine!
