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Ever seen a Minolta RF Rokkor 800mm f/8 cut in half?
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PostPosted: Fri Jun 24, 2022 1:54 pm    Post subject: Ever seen a Minolta RF Rokkor 800mm f/8 cut in half? Reply with quote

https://postimg.cc/McT1YczY

Well, now you have!

Or maybe you've read the book it's from anyway- 写真レンズの基礎と発展 by 小倉 敏布 (Fundamentals and development of photographic lenses, by Toshifumi Ogura)

This doesn't contain as many lens diagrams as I thought it would, but half/most of it is an educational book about lens technology/design anyway. It will be scanned in at some point but just thought to share this part right now.


PostPosted: Fri Jun 24, 2022 2:14 pm    Post subject: Reply with quote
Interesting: I find that the lever to focus by moving the front mirror is much easier than using a helix to focus

p.


PostPosted: Fri Jun 24, 2022 2:31 pm    Post subject: Reply with quote
Not cut in half; made in half Wink

(production of these "cut-in-half" lenses is a very special engineering skill).

I have this one (a whole one Wink ); the cut-in-half image is very useful should any future servicing be required!

Note details such as the clearance around the first lens for centering of the primary lens & secondary mirror combo.

Focus is by moving the secondary mirror, the helicoid cover has a rod control sticking out through a slot on the side of the lens (not visible).

Also not easily visible is that the last element is an interchangeable screw-in colour filter, the second-last element is one of a dedicated pair of f/8 (clear) and f/16 (NDx4) slide-in filters that slide in from the side.


PostPosted: Fri Jun 24, 2022 3:28 pm    Post subject: Reply with quote
This is one of the lenses that I watch for on e-bay. Someday, maybe, I may find a bargain and have money available at the same time.


PostPosted: Fri Jun 24, 2022 4:05 pm    Post subject: Reply with quote
It could have been cut in half, Royal Ordnance at Leeds once cut an entire Centurion tank in half, it's still on display somewhere.

If you can cut a 50 tonne battle tank in half....


PostPosted: Fri Jun 24, 2022 4:05 pm    Post subject: Reply with quote
jamaeolus wrote:
This is one of the lenses that I watch for on e-bay. Someday, maybe, I may find a bargain and have money available at the same time.


Patience is the name of the game here; bargains do sometimes turn up.

Make sure it comes with the slide-in "f/8" and "f/16" filters, which will be almost impossible to find as separate items (these are a pair of slide-in Clear & NDx4 filters, so don't really change the f-stop, they just reduce the exposure and affect SA). The screw-in colour filters for the back are the same ones as for Minolta's RF 250mm / 500mm mirror lenses and are much easier to find should they be missing. The screw-in NDx4 filter of the RF 250mm / 500mm lenses can also be used to double-up on the NDx4 filtering for the RF 800mm, so you can shoot at "f/32" should you want to.

Needless to say that the older black "RF ROKKOR" version of the 800mm is significantly more affordable than the later white RF 800mm version, but the optics are exactly the same, down to the coatings if you get a late ROKKOR sample. The white ones often also have paint damage thanks to the pleather front cap, whereas the older black ones are often in pristine condition.


PostPosted: Fri Jun 24, 2022 4:13 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
It could have been cut in half, Royal Ordnance at Leeds once cut an entire Centurion tank in half, it's still on display somewhere.

If you can cut a 50 tonne battle tank in half....


Best to check there isn't a shell left in the barrel before you do that!

I can imagine the Corporal handing a hacksaw to the Private; "got a job for you!" Laugh 1


PostPosted: Fri Jun 24, 2022 4:17 pm    Post subject: Reply with quote
Also, Minolta specifies a particular glass type for the clear filter at the rear. Presumably due to the calculations of dispersion & sperical aberration being upset if another inferior type is used.

p.
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