In what order..........?


coker

Link Posted 05/02/2020 - 16:20
Given that they, together, give the magnification ratio & the subject distance I need, does it matter -- the order in which they are mounted behind the 100 mm D FA Macro.....?

Jessops 31mm PK/AF ext. tube,

Tamron 1.4x Pz-AF MC4 converter.

Thanks in anticipation,

Roger.
The more I look, the more there is to see!

bforbes

Link Posted 05/02/2020 - 18:31
No logic to it, but I'd automatically go Lens - Converter - Tube.
Barrie
Too Old To Die Young

http://www.pentaxphotogallery.com/artists/barrieforbes
https://www.flickr.com/photos/189482630@N03/

davidwozhere

Link Posted 05/02/2020 - 23:17
Yes. The tube simply causes the light emerging from the focusing device to travel further, making it "expand", thus magnifying the original result. The converter, being part of the focusing mechanism, should be with the lens. ....... That's my logic - or lack of it.
Both the *istDS and the K5 are incurably addicted to old glass

My page on Photocrowd - link

vic cross

Link Posted 06/02/2020 - 17:52
Sorry to butt in. Same sort of question. What happens if you put "TUBE/TUBES" behind a 90mm Tamron macro lens?. Does it make it even more macro?. I've only tried my macro lens a couple of times so I'm not sure how it all works. Maybe I'll have another go sometime with a little help from my friends at PU.
CHEERS Vic.
Born again biker with lots of Pentax bits. Every day I wake up is a good day. I'm so old I don't even buy green bananas.

bforbes

Link Posted 06/02/2020 - 18:00
vic cross wrote:
Sorry to butt in. Same sort of question. What happens if you put "TUBE/TUBES" behind a 90mm Tamron macro lens?. Does it make it even more macro?. I've only tried my macro lens a couple of times so I'm not sure how it all works. Maybe I'll have another go sometime with a little help from my friends at PU.
CHEERS Vic.

As I understand it, the tubes reduce the close focus distance
Barrie
Too Old To Die Young

http://www.pentaxphotogallery.com/artists/barrieforbes
https://www.flickr.com/photos/189482630@N03/

coker

Link Posted 06/02/2020 - 18:49
I've asked this before, but I don't remember the answer......

If you have a lens of F/L "x", if you put X mm of tubes behind it, you get 1:1 on the sensor.
50mm of ext. behind a 50mm F/L lens gives 1:1, etc., etc.

My 100mm D FA Macro gives me 1:1 anyway.
What does it give me if I use 100mm of tubes with it ?

Answers on a fax roll please to

Roger.

ps
Yes Vic, they'll all focus closer.
But at what rate?
The more I look, the more there is to see!
Last Edited by coker on 06/02/2020 - 18:52

bforbes

Link Posted 06/02/2020 - 18:53
the short version - 2:1?
Barrie
Too Old To Die Young

http://www.pentaxphotogallery.com/artists/barrieforbes
https://www.flickr.com/photos/189482630@N03/

Lubbyman

Link Posted 06/02/2020 - 22:31
bforbes wrote:
the short version - 2:1?

According to my book that has lots of formulae and says what buttons to press on a pocket calculator ---- Youre RIGHT!

More generally, adding 2 x FL gives 3:1, 3 x FL gives 4:1 etc.

The book does point out that the formulae are exact only for thin lenses (vague memories of school physics here!) and are only approximate for real lenses.

Whether you can get 1:1 by adding 50mm tubes to a 50mm lens depends on how close it will let you focus. You can get 1:1 from a 50mm lens without tubes - it's called a 50mm macro lens. The difference between that and a standard 50mm is the macro lets you focus close enough to get 1:1.

Steve

derek897

Link Posted 06/02/2020 - 23:15
Ok I'll butt in here too,
I have absolutely no formulas to back up my experience, only my results, and for me. While adding tubes certainly does allow closer focusing, it also increases the magnification,
Much the same as you would when using a handheld magnifying glass, by moving it closer or further away, more tubes pushes the lens further from the sensor, thus increasing the magnification.
An easy way to test this is to take a shot at 1:1 if your lens allows, with no tubes of a ruler, on the mm side. It should match your sensor dimensions, then add tubes. And try again,

More tubes = more magnification from my trials anyway, that's why I use bellows, it's like a variable extension tube.

My tuppence worth, for what it's worth.
I know what i like, If not always why.

Lubbyman

Link Posted 07/02/2020 - 13:34
derek897 wrote:
My tuppence worth....

Isn't it Euros in Wicklow? Or do you know something that hasn't hit the headlines yet???

You're absolutely right, of course, about magnification and closer focusing. The closer the subject is to the lens, the bigger the image and thus magnification. When the subject is closer than the minimum focus distance, the image is formed behind the sensor (hence the image on the sensor is blurred). Tubes or bellows move the lens away from the sensor and the in-focus image towards it. Move it by the right distance and the in-focus image falls on the sensor. As you say, it's just like a handheld magnifying glass.

Now how does reversing a lens work...

Steve

takuman

Link Posted 07/02/2020 - 14:35
Please, please stop. I now have the most awful headache
Just passing thru

derek897

Link Posted 07/02/2020 - 14:53
Lubbyman wrote:
derek897 wrote:
My tuppence worth....

Isn't it Euros in Wicklow? Or do you know something that hasn't hit the headlines yet???

You're absolutely right, of course, about magnification and closer focusing. The closer the subject is to the lens, the bigger the image and thus magnification. When the subject is closer than the minimum focus distance, the image is formed behind the sensor (hence the image on the sensor is blurred). Tubes or bellows move the lens away from the sensor and the in-focus image towards it. Move it by the right distance and the in-focus image falls on the sensor. As you say, it's just like a handheld magnifying glass.

Now how does reversing a lens work...

Steve

Oh that's much easier. all that is, is ....................

I know what i like, If not always why.
Last Edited by derek897 on 07/02/2020 - 14:54

davidwozhere

Link Posted 08/02/2020 - 02:03
I agree with Derek. If you are going to use longer extensions, stick it on a bellows. You can happily carry it around with you!
Both the *istDS and the K5 are incurably addicted to old glass

My page on Photocrowd - link
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