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Author Topic: Extension Tube Compression?  (Read 964 times)
JabariHunt
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« on: February 25, 2013, 02:16:56 AM »
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Suppose you are using an 80mm lens with an extension tube that has a magnification factor of 1.5.  This should effectively make a 120mm lens as far as focal length (as well as decrease the minimum focusing distance).  However, will you still have the same "compression effect" as you would if you were using an actual 120mm lens?  Also, how is overall sharpness affected?

I'm just trying to get a better understanding of extension tubes in general before I purchase one...
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Pics2
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« Reply #1 on: February 25, 2013, 03:58:31 AM »
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I think it's better to use 120mm macro for macro work for one simple reason - it's made for that.
Generally, 80mm lens is not performing its best at close distances and 120mm macro does.
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HarperPhotos
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« Reply #2 on: February 25, 2013, 04:08:04 AM »
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Hello,

An extension tube doesn’t magnify the lens it is attached to like a tele converter does. All it does is to move the lens further away from the film/CCD plane which makes it possible to focus closer to objects. It will still be a 80mm lens.

Cheers

Simon
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Simon Harper
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Rob C
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« Reply #3 on: February 25, 2013, 04:22:26 AM »
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If you intend to photograph people, I wouldn't advise an extension tube.

I tried the shortest one that Hassy made on my 4/150mm because I wanted to make larger headshots: it sucked, not because of quality, but because of distortion from getting too close. I would avoid getting nearer than about 5.5ft - 6ft for heads.

In my case, a 180mm would have been better, but the only one I had owned was for a Mamiya TLR which I flogged to buy the Hassy 4/150mm... Hassy didn't offer a 180mm in those early(ish) days.

Rob C
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JabariHunt
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« Reply #4 on: February 25, 2013, 04:46:03 AM »
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I think it's better to use 120mm macro for macro work for one simple reason - it's made for that.
Generally, 80mm lens is not performing its best at close distances and 120mm macro does.

This would primarily be for headshots & portraits, at least as a substitute until I can get a 150mm or 210mm.

Hello,

An extension tube doesn’t magnify the lens it is attached to like a tele converter does. All it does is to move the lens further away from the film/CCD plane which makes it possible to focus closer to objects. It will still be a 80mm lens.

Cheers

Simon

I understand there is no optical element that magnifies, but there is a magnification factor due to the increased distance of the lens from the sensor/film.  That, and the decreased focusing distance, are the main two reasons people use extension tubes, no?

If you intend to photograph people, I wouldn't advise an extension tube.

I tried the shortest one that Hassy made on my 4/150mm because I wanted to make larger headshots: it sucked, not because of quality, but because of distortion from getting too close. I would avoid getting nearer than about 5.5ft - 6ft for heads.

In my case, a 180mm would have been better, but the only one I had owned was for a Mamiya TLR which I flogged to buy the Hassy 4/150mm... Hassy didn't offer a 180mm in those early(ish) days.

Rob C

Interesting...I was thinking the 150mm would be good for headshots & portraits.  I also didn't know they made a 180mm.  As I mentioned above, I'm debating between the 150mm and 210mm.  I'll probably rent both and compare in order to decide.
« Last Edit: February 25, 2013, 04:48:13 AM by JabariHunt » Logged
BartvanderWolf
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« Reply #5 on: February 25, 2013, 06:15:55 AM »
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I understand there is no optical element that magnifies, but there is a magnification factor due to the increased distance of the lens from the sensor/film.  That, and the decreased focusing distance, are the main two reasons people use extension tubes, no?

Focusing close-up requires more distance between the ecxit pupil and the sensor plane. To achieve that, if the lens doesn't allow such a close focusing distance, an extention tube can be used.

The tube itself doesn't change the focal length or perspective, but focusing from a shorter distance, does change the perspective because the entrance pupil gets closer to the subject, i.e. you've changed the perspective by shooting from a different position.

Cheers,
Bart
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Rob C
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« Reply #6 on: February 25, 2013, 09:24:12 AM »
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Interesting...I was thinking the 150mm would be good for headshots & portraits.  I also didn't know they made a 180mm.  As I mentioned above, I'm debating between the 150mm and 210mm.  I'll probably rent both and compare in order to decide.



Remember, I was writing about the 500 Series Hassy; I'm not into the digital versions and have little idea of the focal lengths provided for them...

Good luck -

Rob C
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TMARK
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« Reply #7 on: February 25, 2013, 09:26:12 AM »
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What system are you using?

On the Hass V system for head shots at 6x6 I use the 150 and a 21mm tube.  I use the 80 with an 8mm or 10mm tube sometimes.  be aware that the range of focus is much decreased.

Lately I use the 80mm CF and the 150mm CF on the d800 and crop to 4:3.  Works well without tubes.
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JabariHunt
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« Reply #8 on: February 25, 2013, 12:09:44 PM »
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Remember, I was writing about the 500 Series Hassy; I'm not into the digital versions and have little idea of the focal lengths provided for them...

Good luck -

Rob C

What system are you using?

On the Hass V system for head shots at 6x6 I use the 150 and a 21mm tube.  I use the 80 with an 8mm or 10mm tube sometimes.  be aware that the range of focus is much decreased.

Lately I use the 80mm CF and the 150mm CF on the d800 and crop to 4:3.  Works well without tubes.


I'm thinking of purchasing one for both the H1 and RZ67...
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TMARK
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« Reply #9 on: February 25, 2013, 12:36:19 PM »
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I'm thinking of purchasing one for both the H1 and RZ67...

For the RZ, the 180 and 250 are fantastic.  The bellows allows you to focus closely.  No need for tubes.  the 150 is a fantastic lens but a little wide for head shots on an RZ at 6x7, but perfect for a DB.
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FredBGG
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« Reply #10 on: February 25, 2013, 02:19:19 PM »
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There is no one focal length lens that is "perfect" for portraits. I would say that the closest are the 70-200 2.8 zooms
from Canon or Nikon.
Different faces benefit from different focal lengths.
Also how close you are cropping on the face makes a big difference.

With the high resolution and pixel count of MF (as well as top of the line 35mm DSLR) you can get away with cropping the file in post
to get the right level of compression for the type of face you are photographing.

Here is a interesting comparison made by Stephen Eastwood

http://stepheneastwood.com/tutorials/lensdistortion/strippage.htm

It's with 35mm DSLR, but the same applies to medium format, just convert the focal length.

I would also add that more or less compression also effects the feel of an image or at lest supports/reinforces it.

That said a 150mm on a digital back is a good lens for portraits on most faces and if you are not shooting too close.







« Last Edit: February 25, 2013, 02:21:01 PM by FredBGG » Logged
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