Soften up some Blu-Tak by leaving it stuck to the side of a
kettle that's recently boiled or hold near to a fire/radiator.

Roll it into lengths about 5mm diam.

Stick it on the edge of the filter rim, so the rim is fully
covered.

Place lens perpedicular to a Formica topped or glass table.

Push down so Blu-Tak grips the table.

Unscrew carefully by turning lens.

Don't do it again

These RF-602's link are very good as a shutter release. They have red and green LED's that light up to show half and full press and work up to about 100M.

To change the channels you have to destroy the plastic cover over the switches.... not really a problem

Hi David, you might well get a lot of acceptable pictures, just as I would get a lot of acceptable pictures if I used a constant f/8 at 1/200th but light transmission of lenses does vary... it's a fact you can't get away from A multi-coated lens will always transmit more light than a single coated lens. A lens that vignettes very heavily also transmits less light and no camera metering will know about that.

Even lenses of the same focal length from the same maker and from the same era/series don't transmit the same amount of light.

This is the difference between the Pentax-A Series 50mm's f/1.7 and f/1.4 at f/4 using Av and Expodisc they should be the same, but there's almost half a stop difference in the final result and compensation is needed to balance them out. I cut and pasted the crop from one onto the other. Sorry I can't remember which was which (done sometime ago on a K20D), but my final conclusion was that the f/1.4 was better for poor light. One lens needed a + correction the other -


-




I've just tested a SMC Takumar 35mm f/3.5 and found that it meters correctly with a K-5 at f/8 which is great because that's the aperture I would use it with. It underexposes by half a stop wide open. OK f/8 to f/16.


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Even the film cameras didn't always meter correctly with all lenses

The link I gave above was from 2009.... This is more recent with a graph of a K-7 as well. link

I use an Expodisk and set the WB off it 1st using the sky then a shot at each aperture using Av if possible, Manual (Green Button) if not.

I then read the RGB value for each shot and compare it to my expected value of 117R 117G 117B.

I then estimate the correction needed say +0.7 and do another test to make sure that I get around 117R 117G 117B

This is the rough result from such a test:

==================================================
K-5
Pentax_A 50mm f/1.7

WB Custom via Expodisc

Av Aperture set from Dial

f/1.7 114 112 126
f/2.0 108 106 120
f/2.8 099 097 110
f/4.0 105 101 115
f/5.6 102 100 113
f/8.0 102 100 113
f/11 105 103 106

WB Set again from Expodisc

f/11 106 106 108
f/4.0 105 105 107

Seems OK from f/2.0
All slightly too dark
===========================================

It would look at 1st glance that f/1.7 is correct, but
all other apertures are too dark, so knowing that f/1.7
should be out anyway I would apply a compensation factor
and use f/4 to f/11 for metering.

This is a Pentax-A lens which is quite well behaved.
Pentax-M lenses can be quite erratic.

This was a Pentax-K lens.
Note: WB out and results are not really usable
=========================================================
K-5
Pentax_K 28mm f/3.5

WB Auto via Expodisc
Seems way out time 6:30pm
possibly too late in the day

Aperture set from lens

f/3.5 116 128 152
f/4.0 116 128 150
f/5.6 129 141 163 Consistent from f/5.6
f/8.0 133 144 166
f/11 132 143 165
f/16 134 145 165
f/22 132 143 161


Seems OK from f/5.6
All slightly too light

Redone setting WB via Custom
Note: shots were done backwards f/5.6 to f/3.5

f/3.5 130 130 132
f/4.0 122 122 124
f/5.6 145 145 145
=====================================================

I eventually settled on using f/8 and -0.7 compensation:

GREY BRACKETED TEST
====================
AWB? showed right on camera

-->>> CORRECT F/8 -0.7 ManExp 116R 116G 116B
==============================================


A Sigma 24mm f/2.8 Test gave:

==============================================
GREY EACH STOP TEST
====================
AWB? showed WRONG
Custom WB hard to set. Non of the shots were right for bright sunlight.

f/2.8 120 118 139 Heavy vignette
f/4 165 163 184 Still vignettes to 126 in corner
f/5.6 169 169 193 Corner OK 154 ::::: Try to meter at f/5.6
f/8 180 178 199
f/11 178 176 197
f/16 186 183 202
f/22 186 182 199
=======================================================

So you can see there is a massive variation Lens to Lens
and it takes quite a bit of time to test each lens

These were just pastes of early tests. I'm now more
careful setting the WB correctly, because I need the
RGB values to be very close to each other.

There's a lot of nonsense being posted in this thread about people not having ANY exposure problems with lenses on Pentax cameras when it's well documented that there is

This thread link is one of many showing graphs etc. explaining the problems.

No two lenses meter the same either you have to carry out tests and decide on what aperture to meter on and what compensation to give.

TIP: Use an aperture that doesn't require compensation often f/5.6

Don't meter wide open on any lens below f/2.4 your pics will be far too dark. Again it's well documented..... try Giggle!

'M' lenses don't meter correctly with the green button
(Search the US forum for details).

You could just meter at say f/4 or f/5.6 and apply a constant each time to give the correct exposure.

You didn't say if you wanted AF or MF Gary?

If MF a Macro lens is almost useless as a telephoto The focusing scale from say 3m to INF is usually only a few mm's and difficult to set accurately. A proper tele lens such as the 100mm f/2.8 'M' turns through about 40mm from 3m to INF

Mark Cassino mentions this on his site. I'm surprised the people on here don't know this Where's Pentax_Expert when he's
needed

=======================================================
Review from Mark Cassino Site:
SMC-M 100mm f2.8: Great lens, Small, great optics. This is a nice lens for portrait work or general shooting - much smaller than a 100mm macro and with a focusing mechanism that allows you to fine tune distant subjects as opposed to close ones.
=======================================================

That's the Olympus one which can be picked up for about £25. The Pentax Refconverter shows a switchable 1x 2x view the correct way round and is by far the best way to manually focus the camera.

The KPS 1.3x is the best of the small fixed magnifiers.

If anybody wants to sell the rubber eyepiece off one of these please send me a PM mine's gone missing

Never used any of the Sigma's but they are probably reasonable/good quality. Probably Sigma's biggest sellers. Earlier models like the Synchro II 28-70mm manual focus got good reviews.

Sorry it is the SMC (proper) version. It only has the name on the focus window. The inferior version has Pentax-F on the lens barrel.

The edge performance on the graphs was almost Exc. at f/8
That was better than the F 28mm f/2.8 and the F 50mm f/1.4

The F 35-70mm scored very similar to the 28-80mm
Unusual to see such high edge performance from zooms.