[BandeauRouge]

the manual if read correctly tells me not to use a 50/mm f1.7 or f1.4 reveresed, but in some spots it also tells me NOT to use these lenses at ALL with the bellows...

so in theory what lens do i want to get

[kypfer]

the manual if read correctly …

For which camera?

[K2 to K50]

And which model of Pentax bellows?
To get useful answers, you need to be more specific in the information you provide.

[titrisol]

Why not?
Those bellows are just air gaps to increase magnification.

I don;t have the A series, but my guess is that all the markings and scales are for the 50mm used in "forward" position,
Objects will have to be almost touching the lens; and focusing might be painful but I don;t see why not

[wkraus]

If you are referring to the Auto Bellows-A manual, it never says you should not use the 50mm f/1.7. Rather, it has detailed recommendations on how to use it. It does however say that the f/1.2 and f/1.4 lenses are not so good due to their field curvature at large magnifications. There are also recommendations on other suitable lenses.

[Not a Number]

My copy of the manual just says the f1.4 and f1.2 are unsharp for flat subjects and shouldn't be used for flat subjects at 1× or highter.

The f1.7 is shown on the reversed lens magnification tables.

[mlag]

Didn’t the older bellows have specific 100mm bellows lenses without focus rings, like these
Bellows-Takumar/Super-Multi-Coated Bellows Takumar 100mm F4 Reviews - M42 Screwmount Telephoto Primes - Pentax Lens Reviews & Lens Database

Bellows-Takumar/Super-Multi-Coated Bellows Takumar 100mm F4 Reviews - M42 Screwmount Telephoto Primes - Pentax Lens Reviews & Lens Database

[titrisol]

This bellows lenses were a convenience, but any lens can be used. Taking into account that there are advantages and disadvantages on using certain lenses (curved field, too dark, etc)

I have a few of those "bellows" lenses from the Polaroid copy cameras (Tominon M40mount) that I got when those cameras were replaced by digital in the early 00s.
But I dont see much difference in use when compared to a normal lens, as they are usually set to infinity anyway. I guess I could also use lenses from the old folding cameras that were unit focusing (same principle).

Didn’t the older bellows have specific 100mm bellows lenses without focus rings, like these

[Wheatfield]

Didn’t the older bellows have specific 100mm bellows lenses without focus rings, like these
[url=https://www.pentaxforums.com/lensreviews/Bellows-Takumar-Super-Multi-Coated-Bellows-TAKUMAR-100mm-F4.html]Bellows-Takumar/Super-Multi-Coated Bellows Takumar 100mm F4 Reviews - M42 Screwmount Telephoto Primes - Pentax Lens Reviews & Lens Database

The bellows lenses were 100mm macro lenses with no focusing helicoid, in effect, a 100mm enlarging lens.

[Not a Number]

There's a 100mm bellows lens in K-mount as well.

I suggest you look at Murray O'Neill excellent eBook on Pentax Macro:

https://www.pentaxforums.com/articles/photo-articles/pentax-macro-accessory-ebook.html

[Wheatfield]

There's a 100mm bellows lens in K-mount as well.

I suggest you look at Murray O'Neill excellent eBook on Pentax Macro:

The Pentax Macro eBook - Articles and Tips | PentaxForums.com

I have both the M42 and K mount bellows lenses. I suspect the optical formula is the same for both, though I could be wrong. I haven't had the opportunity to use the K mount lens as I picked it up when I was in buying a new camera, which is taking up my time at the moment.
I think I lucked out and got it from a guy who couldn't mount the bellows it was attached to to a DSLR because of a redundant aperture control lever on the back of the adapter that would have fouled on the prism extension on a DSLR unless a #2 extension tube was used.
I paid about 1/5 of the going rate for it, and got a free cheap bellows in the bargain.

[Not a Number]

I got my K-mount version off eBay for $49 free shipping. Near mint condition. As soon as I saw the listing I bought it.