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Prime lenses with internal focus or rear focus?
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PostPosted: Wed Jan 13, 2021 4:25 pm    Post subject: Reply with quote
stevemark wrote:
benadamx wrote:
on a whim, i purchased an Accurar 35mm f/2.5 on ebay, because it was $10 and it looked cool, turns out it is one of the earliest japanese retrofocal lenses https://burntembers.com/2017/12/23/fujitar-p-c-35mm-f2-5-asahiflex-lens-test/


"Retrofocus" and "Rear Focus" is not the same ... !

S

I assumed not.
I have loads of retrofocus lenses but I don't think I have any 'rear focus'.
Before this thread rear focus is a term I'd not even heard of, am I right in thinking its focusing by moving the rear group independently of the remainder?

Most of my lenses are block focusing, but I do have some that are internal focusing, (and loads with no focus at all in the lens itself)...


PostPosted: Wed Jan 13, 2021 5:29 pm    Post subject: Reply with quote
...

Last edited by Blazer0ne on Tue Feb 22, 2022 6:08 pm; edited 1 time in total


PostPosted: Wed Jan 13, 2021 7:00 pm    Post subject: Reply with quote
Not to be a complete idiot or anything, but isn't Nikon's rear focusing a variant of internal focusing? The effect's the same and so is the underlying process. The lens focuses closer than infinity by reducing its focal length without changing extension.

Re prime lenses that are IF, don't forget the 200/4 MicroNikkor AIS. Early reviews of it characterized it as fixed focal length zoom lens.


PostPosted: Wed Jan 13, 2021 7:42 pm    Post subject: Reply with quote
Blazer0ne wrote:
55 wrote:


#1


I like where they are going here.

As a bonus, along with Internal Focus, this lens includes Bokeh.

All the mumbo jumbo PR/marketing nonsense aside the Samyang 50 f1.4 is a fine lens: https://www.flickr.com/photos/131684321@N03/albums/72157714844267418
Wink


PostPosted: Wed Jan 13, 2021 10:25 pm    Post subject: Re: Prime lenses with internal focus or rear focus? Reply with quote
redimp wrote:
Hello everyone, I am on a lookout for lenses that feature internal focusing and rear focusing.!


You are looking for a lense with IF and RF ?
That's right?

Rear focus (RF) is a variation of internal focusing (IF).
The opposite construction is the Fixed Rear Element Extension. Here, only the front lens or the front elements are extended, the rear element remains rigid.


PostPosted: Thu Jan 14, 2021 1:19 am    Post subject: Reply with quote
tomasg wrote:
All the mumbo jumbo PR/marketing nonsense aside the Samyang 50 f1.4 is a fine lens: https://www.flickr.com/photos/131684321@N03/albums/72157714844267418
Wink


Excellent, tomasg. Like 1


PostPosted: Sat Jan 16, 2021 6:27 pm    Post subject: Reply with quote
DConvert wrote:

I have loads of retrofocus lenses but I don't think I have any 'rear focus'.
Before this thread rear focus is a term I'd not even heard of, am I right in thinking its focusing by moving the rear group independently of the remainder?


Yes, exactly. You may check the Minolta patents on their AF 2.8/24mm and 2.8/20mm lenses, or Haruo Sato's article on the Nikkor AF 2.8/80mm (https://imaging.nikon.com/history/story/0023/index.htm).

S


PostPosted: Wed Jun 14, 2023 3:42 pm    Post subject: Re: Prime lenses with internal focus or rear focus? Reply with quote
paolos wrote:
redimp wrote:
Hello everyone, I am on a lookout for lenses that feature internal focusing and rear focusing.!


You are looking for a lense with IF and RF ?
That's right?

Rear focus (RF) is a variation of internal focusing (IF).
The opposite construction is the Fixed Rear Element Extension. Here, only the front lens or the front elements are extended, the rear element remains rigid.


Vivitar 100mm 1:2.8 MC 1:1 Macro Telephoto No.22nnnnnn is example of "Fixed Rear Element Extension" construction (fixed-position rear element). Made by Kino (Kiron).

#1


PostPosted: Wed Jun 14, 2023 9:45 pm    Post subject: Re: Prime lenses with internal focus or rear focus? Reply with quote
visualopsins wrote:


Vivitar 100mm 1:2.8 MC 1:1 Macro Telephoto No.22nnnnnn is example of "Fixed Rear Element Extension" construction (fixed-position rear element). Made by Kino (Kiron).
[/url]


Basically a (fixed) teleconverter with a moving gauss type normal lens in front. Helps to reduce the necessay movement when focusing, reduces the overall length and improves close range correction. The same principle was used for several other 100mm/105 mm macro lenses, eg the Micro Nikkor AiS 2.8/105mm and the Zeiss CY 2.8/100 Macro, and the Leitz Apo Macro 2.8/100mm.

S


PostPosted: Wed Jun 14, 2023 10:11 pm    Post subject: Re: Prime lenses with internal focus or rear focus? Reply with quote
stevemark wrote:
visualopsins wrote:


Vivitar 100mm 1:2.8 MC 1:1 Macro Telephoto No.22nnnnnn is example of "Fixed Rear Element Extension" construction (fixed-position rear element). Made by Kino (Kiron).
[/url]


Basically a (fixed) teleconverter with a moving gauss type normal lens in front. Helps to reduce the necessay movement when focusing, reduces the overall length and improves close range correction. The same principle was used for several other 100mm/105 mm macro lenses, eg the Micro Nikkor AiS 2.8/105mm and the Zeiss CY 2.8/100 Macro, and the Leitz Apo Macro 2.8/100mm.

S


Thank you! know of any lens diagrams?


PostPosted: Thu Jun 15, 2023 1:12 am    Post subject: Reply with quote
Never mind

https://lens-db.com/vivitar-100mm-f28-mc-macro-s-n-22xxxxxx-1986/


(I don't see a "teleconverter"?)


PostPosted: Thu Jun 15, 2023 9:13 am    Post subject: Reply with quote
visualopsins wrote:
Never mind

(I don't see a "teleconverter"?)


This may help you:


It's the lens section of the AF Micro Nikkor 2.8/105mm. The master lens - basically something like a 2/70mm double gauss - is shown in yellow, the three lens teleconverter (a simple triplet) in red. Be aware the teleconverter group in its entirety is negative. If you look at the curvatures alone, you might assume it to be positive, but in this case the negative center lens of the triplet is made from a high refractive glass, while the two positive lenses of the teleconverter group are made from a low refracting (and probably low dispersive) glass. Altogether the three red lenses act as a negative group and thus as a teleconverter. As with the Kiron 2.8/105mm, the teleconverter group of the Nikkor does not move while focusing.

Now lets look at the Kiron:

It has a "inverted Ernostar" type master lens (yellow) and simple negative doublet (instead od a triplet which allows for better correction) acting as a teleconverter.

Now how do I know that is is in fact acting as a teleconverter?

If you are focusing an ordinary 100mm lens from "infinity" to "1:1", you have to increase the distance between sensor/film and lens by 100mm. Measuring the extension of the Kiron 2.8/105mm Macro reveals that the master lens extends only about 70mm - which means the master lens has a focal length of about 70mm, and the red doublet must act as an 1.5x tele converter.

I hope you understand now what I had been writing yesterday. More detailed information can be found e. g. in Nikos "1001 Nikkor Tales" (look for the 60mm and 105mm Micro Nikkors) as well as in Marco Cavinas writing about the Zeiss 2.8/100mm Macro. There's also coresponding information about the Leica APO Macro 2.8/100mm, but I don't remember where I saw it.

S


PostPosted: Thu Jun 15, 2023 11:18 am    Post subject: Reply with quote
Thank you! Thank you! Thank you!


PostPosted: Fri Jun 16, 2023 12:26 am    Post subject: Reply with quote
stevemark wrote:

This may help you:...


Thank you! Proof of a great explanation is when even I can understand it. Friends Thank You Dog
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