*ist with fixed aperture lens

I have a *ist and an MZ6 camera, and like them both. However, I find the MZ6 lens compatability, or rather, abilitiy to use K lenses, without the Aperture priority setting rather useful.

I have a Centon mirror lens with fixed f8 aperture, but am unable to get the *ist to operate with it, whereas, the MZ6 has no problem. Another thread puts this inability of the *ist down to the lack of electrical contacts, but why then does the MZ6 operate correctly. OK, the viewfinder doesn't relay the aperture information, but the exposure is correct. Not so the *ist.

Anybody got any idea how to make the *ist work correctly with this lens?

The *ist is intended to work with lenses of the "A" series and later, and only when set on "A". This is because on the *ist the camera controls the aperture, not the lens.

There is a custom function that allows use of aperture rings - have a go at enabling this function and it might be OK.

Custom Function 17 allows you to press the shutter with the lens set on an aperture other than 'A'. The camera will only meter at full aperture so thats what you have to keep in mind when using lenses at settings other than 'A', however yours is a fixed aperture so you should have little problem. I have found the custom functions of the IST extremely useful especially the one where you leave it leaves the film leader out after rewinding... i used to do that with my mz60 by popping open the cover when the counter reached zero ! dont know if that was healthy for the camera though.

Yes, I've tried function 17, and this allows the shutter to be fired with this lens. However, the exposure is wrong, and the camera seems unable to work out, or be told what the lens aperture is.

Are there any electrical contacts on the mount of the lens? If this is a very old manual focus lens perhaps it is just not compatible, although I can't see why there would be a problem with any of the more conventional Pentax bodies. The *ist is, of course, different in that it uses lenses without an aperture ring.

Thats not strictly true. The ist will take any lens with the 'A' setting on the aperture ring and even those without. There are manual focus lenses in current production with the 'A' setting and even with the old ones you can use them by making the appropriate exposure compensation in your head .. 1,2,3 stops however many f-stops you got it clicked to away from full. Although I bought the body on its own,The camera retailers here package pentax bodies with sigma lenses and rarely with actual pentax lenses so I have yet to see an FAJ lens (this the one with no aperture ring?) with the cameras being all electronic there is no need for an aperture ring. I think it is a good idea and tidies up the lens a bit I would imagine especially for digital SLR.

Sure, but I do think that the *ist is more logically used with the appropriate lenses. The other Pentax camera bodies arguably are more versatile with a wider variety of older lenses.

If I remember correctly, the Centon mirror lens uses a T-mount (like my Ohnar slide duplicator). My T-mount has no electronic contacts whatsoever although I believe there may be an AF version which I guess would have.

Hope that's in some way relevant!

Thanks for the information. Yes, the Centon lens uses a T mount adapter.

I've just checked it out again. The MZ6 is quite happy with the aperture of the lens, but the *ist acts as though it's a lot larger aperture, about f4 instead of f8. Neither camera will let you adjust the shutter speed in the Tv setting, but will let you set it when set to fully manual.

In manual mode, the MZ6 gives accurate exposure metering, but the *ist exposure meter is blank.

I guess that if I ever have to use it on the *ist, I'll have to rely on my Sekonic exposure meter, and use Manual exposure setting.

As I have had Pantax since 1980, I have a collection of lenses. Fortunately, a number are PKA lenses, so are quite useful for the *ist. This is the only focal length I can't cover with a PKA lens.

The Tv setting is shutter priority auto exposure, which means you set the shutter speed and the camera sets the aperture on the lens. It can only do this with an A series or later lens with the appropriate electronic contacts in the lens mount.

Your T mount lens is totally manual and you can only hope to use it in the manual settings or in the Av programme, where you set the aperture and the camera sets the appropriate shutter speed. The *ist might be able to do this as well as the other bodies - have a go and see if it works, but do change the custom function to allow use of apertures on a lens.