I posted up recently in the Pentax forum on an issue around Tamron FD Adaptors for their Adaptall lenses. Thought this would be an appropriate place to repost - Its kind of a lenses thing but I think it would get lost in amongst all the digital boys wunderkind stuff. Its kind of related to the camera as well because a Tamron adaptor isn't much use without both a lens and a camera - Mods I shall let you decide Recently I acquired an FTb camera and as I didn't have many Canon lenses (actually make that none) and as I have a fairly big range of bodies (Nikon both AI and Pre AI, Pentax, Olympus, M42 etc) and as I happen to dislike Canon nFD lenses as they are nigh on impossible to repair I looked for something else. All of my camera bodies have to fulfil three criteria (its assumed they work ). The criteria are; Cant have been made later than 1980 and ideally mid 1970s Must have been 'historic' or market changers or 'best of' Must be mechanical only (apart from light meters) I will flex on some areas if there is a good reason. For instance I have an AE-1 and a Nikon F-301 as they were market changing cameras - the AE-1 has historical value as well as the moment when it all started to go downhill. the F-301 because it radically changed Nikons outlook on things (certainly changed the Nikon fanboys outlook )and was the last wholly designed and made by Nikon camera (allegedly) but I also happen to love it as a camera. All of this makes for a tough time when buying accessories and lenses Anyway - back to the Canon FTb and AE-1 and a lack of lenses. I was trawling eBay and came across a whacky Tamron Zoom. You don't see many of these - a macro focusing 38-100 - Tamron only made them for about 2 years but the lens was the right period and mint so I parted with the shekels and waited for the lens to arrive. As advertised it came with a Pentax K Adaptall 2 and its beautiful, near perfect condition, worked a treat on my Pentax KX, K1000 and even on my ratty old Chinon CE5 so how hard could it be to get a Tamron Adapall for it - easy peasey - just buy one off the bay and Bobs your mothers brother. So I do some reading and everyone says 'Oh yeah - Adaptall is forward and backward compatible and don't buy the Adaptall 1 adaptors because they are unreliable' so I go buy an Adaptall 2 adaptor and it fits on and seems to work. After a few minutes fiddling about I declare myself happy.........and then I notice something. When its hooked to the FTB and I press the DOF Preview the lens doesn't seem to stop down to where I would think f16 should be. So I flip the switch that puts the lens to manual mode (handy that) and theres the proof. The FTBs DOF is not stopping the lens down fully to F16 - its more like F8. Much experimenting takes place to find out why- the FTBs own FL lens is fine. So I try it on the AE-1 and its the same - doesn't stop down fully to the smaller apertures. I try the AE-1 on Auto and find that the apertures stops erratically - maybe F8, maybe F11, maybe f16 (rarely). So whats the problem ? Well I go buy an Adaptall 1 adaptor and as fans of the FD fitting might now the Adaptall 1 adaptors are aperture specific - if you have an f3.5 lens you need a 3.5 adaptor otherwise the camera will be wrong footed on its metering. Part of the Adaptall 2 deal was to get over this so you didn't have to have specific adaptors for FD, Konica and Minolta MD fittings (which was kind of messing up the sales pitch for Tamron hence the AD2 adaptors and lenses) Put the AD1 adaptor on and - peal of trumpets, heavenly choirs singing - all is fine. So why doesn't the AD2 work - well after much ado I worked it out. There are two springs on the FD adaptor. One of them holds the aperture actuator open, the second one acts as a kind of relief so that when the lens is fully stopped down it stops the cameras actuator putting any more pressure onto the actuating lever by offering a 'buffer' to slow the cameras actuator down rather than having a hard stop - basically the cameras actuator can keep on going but its decoupled from the lens mechanics This I suspect, and its only speculation, must be because the Canons aperture actuator has a specific need to not be blocked suddenly. Pentax, Minolta MC and Olympus have a kind of 'run' out - when the lens is fully stopped the actuator still has some spring left in it to the cameras actuator lever isn't suddenly hitting anything solid at the end of its run. So why do the AD1 and AD2 adaptors differ - its simple - firstly the spring in an AD2 lens is a lot lighter than it is in any of the AD1s I have tested ( I tested 5-7x AD1s and 3x AD2 lenses ) plus the relief spring in the AD2 adaptor is much weaker than the relief spring in an AD1. The consequence is that when you press the DOF or the camera stops down the lens the relief spring in an AD2 adaptor when mated to an AD1 lens simply lets go and relieves pressure before the lens has fully stopped due to the much stronger springs in the lens. It will stop down but just not to the right aperture and that will depends on just how strong/weak the springs in the lens AND the springs in the adaptor are. For instance on a 24mm AD1 lens none of the AD2 adaptors can even get it halfway closed when its set for minimum aperture. On a 135mm AD1 I have some of the AD2 adaptors can get it to close to minimum aperture but not all the way. When you do this with an AE-1 on auto you get weird aperture stop downs - its literally random once its under auto control as to what aperture the camera stops to when you have an AD2 adaptor and an AD1 lens. I have tried this with about 10x AD2 adaptors and my 5-7 AD1 lenses and not one of them will make an AD1 lens work right apart from a very old and clapped out AD1 Zoom where the lens springs are very weak and the whole lens is held together with prayer. So in a nutshell if you want too buy old Tamron AD1 glass make sure you can source the appropriate AD1 adaptor for it - some aperture values don't show up very often. I never saw for instance a 2.8 adaptor while I was shopping for these. Heres my FTb with the bonkers Tamron lens that started this whole thing off.