Adapters light loss?

I was looking at getting an extension tube for my adapted FD MF for my 135,200mm lenses used on NEX-5n. As their close focusing distance is a little longer then I am use to. Probably only need a 10-12mm to cater for the difference I want. I understand I would lose infinity but that's ok.

I was having a quick look at them and noticed a mention of light loss. I didn't know this happened as there is no glass in extension tubes and all they do is increase the distance from the film/sensor and therefore allow for closer focusing. But the increased distance also means light loss.

This lead me to thinking. Considering the NEX's or m4/3s (I use both) difference in distance between sensor and lens does this mean a potential greater or less light loss or does the adapter make the distance exactly the same as it would be on the original FD FF system and therefore no difference at all?

First thoughts are the adapter would have to create the same distance but thinking about it as long as infinity is achieved it wouldn't matter. Potentially there could be a difference. So is it to our dis/advantage?

Hi, the answer is simple. Adapted lenses are mounted the same distance from the sensor on both m4/3 and the NEX.

--
A rose by any other name is still a chicken.

Sorry just to emphasise I am talking about the adapter alone increasing or decreasing the distance regardless of extension tube attached.

seachicken2000 said:

Hi, the answer is simple. Adapted lenses are mounted the same distance from the sensor on both m4/3 and the NEX.

--
A rose by any other name is still a chicken.

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Like I said that seems like the obvious answer but potentially there could be a difference and it may even vary from adapter to adapter. You seem very confident in your answer.

siejones said:

Like I said that seems like the obvious answer but potentially there could be a difference and it may even vary from adapter to adapter. You seem very confident in your answer.

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Adapters do differ slightly in the distance they put the lens from the sensor, but only because they're badly made.

If you think about it, when a lens focuses light from infinity, it is focusing parallel rays to a point Xmm from the lens. So you have no choice but to place the sensor at that point, if you want the lens to focus properly at infinity.

--
A rose by any other name is still a chicken.

But if you placed the lens closer to the sensor then surely you could just focus to infinity and beyond (sorry had to say it) but would lose some some of your closer focus distance. The Lens would be closer to the sensor and therefore you are gaining more light?

siejones said:

But if you placed the lens closer to the sensor then surely you could just focus to infinity and beyond (sorry had to say it) but would lose some some of your closer focus distance. The Lens would be closer to the sensor and therefore you are gaining more light?

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LOL, OK I think I get your idea. Now you are making me think.
I still don't think you gain any more light.

Here's why: take the simplest lens, a single element convex lens (focal length 50mm) that you focus by moving backwards and forwards. Let's say it's focused at infinity on a sensor, so it's 50mm from the sensor.

Now apply your idea, and move the lens closer to the sensor. The image is now brighter (yes!!!), but blurred (drat). We can refocus the lens by moving it to 50mm from the sensor. Once refocused we're back in the same state we started at, and no light has been gained (double drat).

--
A rose by any other name is still a chicken.

seachicken2000 said:

LOL, OK I think I get your idea. Now you are making me think.
I still don't think you gain any more light.

Here's why: take the simplest lens, a single element convex lens (focal length 50mm) that you focus by moving backwards and forwards. Let's say it's focused at infinity on a sensor, so it's 50mm from the sensor.

Now apply your idea, and move the lens closer to the sensor. The image is now brighter (yes!!!), but blurred (drat). We can refocus the lens by moving it to 50mm from the sensor. Once refocused we're back in the same state we started at, and no light has been gained (double drat).

Click to expand...

Ahh well a single element lens is surely changing the game. Yes you won't be able to refocus the lens after you have shortened the distance but only because you only have one element. In fact the only way to refocus this lens at all when the element distance was changed would be to move the cameras distance in relation to the subject.

With multiple elements the rear element does not move so moving it's distance from the sensor will still allow you to focus.

I can see the new marketing ploys already:

"Make your 300mm F4 into an F2.8 with out revolutionary new short adapters!"

{small print}
"loss of closer focusing may apply"



I have been looking on the net at the calculations and to be honest it looks like the differences in light loss/gain would not be by much. Apparently you would have to move the lens 40% the focal length away from the camera to lose a stop of light. That much movement would have too much of an impact on focus range to be useful and in most cases you couldn't shorten it enough to have a whole stop of light gain.

I don't think 12mm of extension tube would lose me much on a 135,200 or 300mm lens.

Interesting though

Two other points to ponder

• adapter sample variation is usually in the order of a fraction of a mm, not significant in terms of light loss/gain
• extension tubes allow macro-style close focus, but not much more beyond that e.g. Minolta Rokkor 50/1.4 + ext. tubes:

Alan

siejones said:

I was looking at getting an extension tube for my adapted FD MF for my 135,200mm lenses used on NEX-5n. As their close focusing distance is a little longer then I am use to. Probably only need a 10-12mm to cater for the difference I want. I understand I would lose infinity but that's ok.

I was having a quick look at them and noticed a mention of light loss. I didn't know this happened as there is no glass in extension tubes and all they do is increase the distance from the film/sensor and therefore allow for closer focusing. But the increased distance also means light loss.

Click to expand...

This is true also of focussing in the normal range, at least with a traditional lens where the whole lens moves to and fro to focus. (Some newer lenses just shift internal elements.)

As you move the lens away from the sensor, to focus closer, it gives an image over a larger area. Because the same amount of light is spread out over a larger area, it is dimmer. The extra area is outside the edges of the sensor or film.

(The same happens when you move a projector further away from the screen. As the lens of the projector gets further away, the picture becomes bigger and dimmer.)

At normal distances the effect is small, but as you add extension tubes to get into the macro focussing region it becomes more and more noticeable. Of course the camera's automatic exposure will still give the correct exposure, but to do so it may set a slower shutter speed or wider aperture.

siejones said:

This lead me to thinking. Considering the NEX's or m4/3s (I use both) difference in distance between sensor and lens does this mean a potential greater or less light loss or does the adapter make the distance exactly the same as it would be on the original FD FF system and therefore no difference at all?

First thoughts are the adapter would have to create the same distance but thinking about it as long as infinity is achieved it wouldn't matter. Potentially there could be a difference. So is it to our dis/advantage?

Click to expand...

You're over thinking this. There will be no light loss.

just consider this:

• in order to have one step less light you'd need to use ET of the length equal to lens' FL (eg. 50mm for 50/1.4 lens, so it will be effectively f/2 wide open);
• machining tolerances on a good (to passable) adapter will be of fractions of millimeters;
• as the adapter must preserve a native FD of each lens (the actual value of FD is immaterial, and will be different for each native mount type, eg. 44mm for EF, 27.95mm for Leitz-M, etc.) otherwise there will be no infinity focusing; there is no light loss at the native flange distance;

jpr2
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Comments and critique are always welcome!
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I would say that this question points to about two stops of brain loss:

Learning loss, Physics understanding loss, mental acuity loss, you name it. An adapter is nothing but a bunch of air to set the lens at the lens' proper distance to the sensor.

What happened by design in the lens' camera of origin, to sit at xx mm from the film/sensor, is achieved by the air filled adapter tube when on a shorter lens flange distance camera body.

It is like moving the driver seat into the proper distance-to-steering-wheel position in a car.

Sorry. Two stops of brain loss have been diagnosed here. Sorry.

uhligfd said:

I would say that this question points to about two stops of brain loss:

Learning loss, Physics understanding loss, mental acuity loss, you name it. An adapter is nothing but a bunch of air to set the lens at the lens' proper distance to the sensor.

What happened by design in the lens' camera of origin, to sit at xx mm from the film/sensor, is achieved by the air filled adapter tube when on a shorter lens flange distance camera body.

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He is talking about adding an extension tube as well as the adaptor. This is what will give some light loss - but not much if the tube is short.

uhligfd said:

I would say that this question points to about two stops of brain loss:

Learning loss, Physics understanding loss, mental acuity loss, you name it. An adapter is nothing but a bunch of air to set the lens at the lens' proper distance to the sensor.

What happened by design in the lens' camera of origin, to sit at xx mm from the film/sensor, is achieved by the air filled adapter tube when on a shorter lens flange distance camera body.

It is like moving the driver seat into the proper distance-to-steering-wheel position in a car.

Sorry. Two stops of brain loss have been diagnosed here. Sorry.

Click to expand...

Ahh the usual DPReview troll. I thought I would drag one of you sad idiot's from the darkened holes you scurry from. A typical example of the weak minded individual who has to accuse others of being dumb so they can feel better about themselves.

Did you bother to read what I have said? Trolls like you rarely do. They only see an opportunity to attack.

At which point did I say I was under the impression there was anything but air in the adapter? Obviously adapters are made to create the same distance as the system they are adapting. Considering most of these adapters are cheaply manufactured ebay no named brands do you really think there won't be slight differences in the distance?

I asked the question to hear ideas about this and maybe even if there was a possibility this could be used to our advantage and at the sacrifice of close focusing you could shorten the distance to gain more light.

Since asking the question I have learnt the differences would be small not be worth the effort.

I could have researched all this on the net but this is a forum is it not? A place where anybody regardless of their experience in the given subject can ask questions or debate a point. It's idiots like you that ruin that experience and therefore ruin DPreview forums. There are probably many users that are to scared to ask questions because they have seen dumb tossers like you abusing others.

Ask yourself this brainiac. If a man is born and bred on a secluded island and he does not know the answer to 1+1. Is he thick, stupid, unintelligent or is he just uneducated? Just because you don't know something it doesn't make you stupid. If you had any kind of intelligence you would have worked this out for yourself.

Just f&^k off back into hole you worm!

Sorry about getting you all so wonderfully mad at me.

Extension tubes shift the lens forward. There is the old optical formula 1/a + 1/b = 1/f, so a shorter extension tube loses less light and gains less magnification and vice versa.

THIS has nothing, nothing to do with sensor or film size. Period. Sorry, and I will take one brain loss back; but keep the other one, if you please.

uhligfd said:

Sorry about getting you all so wonderfully mad at me.

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I can't stand abusive forum trolls who throw unprovoked abuse at people they do not know. I can't imagine you do that out in the real world. You wouldn't last very long if you did. Does the protection of internet anonymity make you tougher? To me it makes you an idiot....period!

Now as for your answer. I will answer in you with the same attitude you deal out. Maybe that's all you understand.

uhligfd said:

Extension tubes shift the lens forward. There is the old optical formula 1/a + 1/b = 1/f, so a shorter extension tube loses less light and gains less magnification and vice versa.

Click to expand...

Have you bothered to read the replies to my original post? We have already established the whys and wherefores. Where did I reply I was having trouble understanding it?

uhligfd said:

THIS has nothing, nothing to do with sensor or film size. Period. Sorry, and I will take one brain loss back; but keep the other one, if you please.

Click to expand...

Where did I mention film/sensor size? Are you seeing things? Making things up in your head maybe?

If you really have a valid interesting point to make you need to READ more carefully. Go slower and you might understand instead of quickly rushing to conclusions and attacking.

As your replies have proven I don't think it's my intelligence that is in question here. In my experience real intellectuals don't go around accusing others of being dumb. Why? Because they have nothing to prove to anyone. Get it!