Fixed aperture exposure problems

In my collection of older lenses for my K100D are two with no aperture control. A 500mm CAT and a 1000-4000mm telescope with T2 mount.
With both of these I've found my camera consistantly underexposes by a good 2 stops.
I can understand my manual apertures are not read on the crippled mount, but surely this doesn't apply when the lens is fixed aperture...

Is there a work around, without just over-riding the exposure (2 stops is as far as it goes, and it can get left on if I change lenses in a hurry)

Mike

Hi - have you tried adjusting your Ev by a couple of stops to compensate?

I think that's what petrochemist is saying when he says "2 stops is as far as it goes". I've often wished the EV comp could do more then +2 or -2.

Indeed it is.

But I also can't see why EV comp should be required. With fixed aperture the TTL metering should have no option but to have the right aperture!

I feel EV comp should be for situations where the background requires compensation to get the subject right, not as a leave on whilst I'm using this lens.

When photographing Superbike racing, there's not a lot of time for checking things.

Mike

Is it the same in the different metering modes? And are you shooting in AV?

The K7 goes +5 or -5 EV compensation.

Most modes default to Aperture priority without an A setting.
I get the same results in the specialist modes (sport, autoprogram & macro all defaulting to AV) or AV itself.

TV, M & B would depend more on me, than the metering, I suspect

Unfortunately my bank balance doesn't go to the K7...
Perhaps they'll drop enough in price in 5 years

Why not shoot in manual? you can then see up to three stops compensation, of course after three stops you wont know where you are unless you do the math

When I'm using these long lenses it tends to be for fast moving subjects (Usualy motor racing or birds on the wing) and I have enough of a problem trying to get them focused (or even in frame :blush to adjust exposures on the fly.

When I asked about metering I meant is it the same in spot/center weight/matrix etc.

Thanks for the tip Clarky! That was something I didn't know. Makes me seriously consider a K7 now!!! (Thanks I previously had no interest in it)

Thanks for the clarification Tim.
I think they've all been matrix metered, I'll give the other modes a go...

with these lenses you won't get Pattern metering, the camera can only do spot and centre weighted without electric contacts. If it's set to pattern, it'll default to centre weighted.

My guess is that you're looking at some pretty small apertures with the lenses you mention. I find that the cameras tend to underexpose when the light hitting the meter gets very low.

Also with birds on the wing it's possible that your background is bright vs a relatively small, dark foreground. This will confuse the metering system and cause underexposure. If you post some examples we might be able to help more from there.

I've just confirmed the lack of pattern metering (which was a surprise).
No difference for either center weighted or spot.

The 500 is F8, (fairly standard) and the scope is F16 at 1000mm (not very usable beyond that.
Backgrounds on all have been fairly neutral.
The birds have been across a lake with trees for a background, with nothing usable.
The bikes with tarmac & grass for most of the background, have actually given me some reasonable shots. They are a bit noisy due to higher iso use, and rather soft focus if they're in the middle of sliding off the track (those few meters closer)
Even test shots of a blank word document (PC monitor white screen) are severely underexposed.

It's a limitation of the system, and even the instruction book warns that exposures may not be accurate.

It's really a matter of the amount of backwards compatibility that can be expected. You can use almost any lens going back over 40 years and some working around is only to be expected.

Other marques do not have the flexibility that Pentax offer, even though it's not perfect.