[brbob1]

There are several of these big lenses listed on eBay that state "missing rear mount". My question is this. Are the rear mounts on Pentax lenses interchangeable? would a mount off off a cheap 50mm f2 fit on the big 500mm lens. Either the K bayonet mounts or the older M42 mounts.

Sounds too good to be true but I thought I would ask.

[Not a Number]

I don't think so. I believe the rear mount is on a module so you can change the rear filters.

[monochrome]

There are several of these big lenses listed on eBay that state "missing rear mount". My question is this. Are the rear mounts on Pentax lenses interchangeable? would a mount off off a cheap 50mm f2 fit on the big 500mm lens. Either the K bayonet mounts or the older M42 mounts.

Sounds too good to be true but I thought I would ask.

I haven’t looked at the specific eBay sales you reference, but take care what you bid on. The Takumar and SMC 500/4.5 and 1000/8 have a Mount Tube that is removed to screw a standard filter into the optical path at the rear end of the lens. Over time many of these mount tubes have been modified* to fit cameras other than K-mount, such that people buy a good lens copy with a “foreign modified” terminus, find a lesser copy with a proper K-Mount, scavenge the mount tube and sell the lesser lens sans mount tube. The lens is ABSOLUTELY USELESS without the Mount Tube. Be certain the selller includes mount tube, and be certain the mount tube is K-mount terminated.



* Around 1970 the Associated Press converted from Pentax to Nikon as their standard reportage body. Apparently one of their lens technicians converted the mount tubes for a couple dozen Takumar 500/4.5’s to a Nikon bayonet terminus using a T-Mount threaded joinery and a T > F Nikon converter. At one time I owned one of those lenses and was able to convert it back using a Vivitar T > K converter.

[brbob1]

I haven’t looked at the specific eBay sales you reference, but take care what you bid on. The Takumar and SMC 500/4.5 and 1000/8 have a Mount Tube that is removed to screw a standard filter into the optical path at the rear end of the lens. Over time many of these mount tubes have been modified* to fit cameras other than K-mount, such that people buy a good lens copy with a “foreign modified” terminus, find a lesser copy with a proper K-Mount, scavenge the mount tube and sell the lesser lens sans mount tube. The lens is ABSOLUTELY USELESS without the Mount Tube. Be certain the selller includes mount tube, and be certain the mount tube is K-mount terminated.



* Around 1970 the Associated Press converted from Pentax to Nikon as their standard reportage body. Apparently one of their lens technicians converted the mount tubes for a couple dozen Takumar 500/4.5’s to a Nikon bayonet terminus using a T-Mount threaded joinery and a T > F Nikon converter. At one time I owned one of those lenses and was able to convert it back using a Vivitar T > K converter.

Good advice. Thank you

[marcusBMG]

I have a junk "any-name" 400mm f6.3, the mount end on these unscrew leaving a tube with a t-mount set up. So then it would just be a matter cutting it to the right length and attaching it. Depends what the original attachment is. Access to a good lathe would be ideal but I've improvised in the past see here.

[brbob1]

I have a junk "any-name" 400mm f6.3, the mount end on these unscrew leaving a tube with a t-mount set up. So then it would just be a matter cutting it to the right length and attaching it. Depends what the original attachment is. Access to a good lathe would be ideal but I've improvised in the past see here.

Nice. I'm not that brave, even though I do have access to a lathe. I just bought a nice SMC Pentax 500mm tonight from Japan off ebay. Didn't have any issues and it looks brand new. Can't wait to try it out. Thanks everyone for responding so quickly. This is a great forum.
just got my Pentax K-70 and I'm having a ball. Love it.

[catfishjohn]

That lens is fun to use. Depending on your setup you might want to check out a " Telephoto Prism Lens Bracket" on EBay. It supports both camera and lens and gives a lot of adjustment to balance. Requires Arca Swiss clamp on your tripod.