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08-05-2012, 09:28 PM   #1
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How can Pentax improve TAv mode to be a killer feature

Many people like us turn to Pentax for budget, not just saving that little on Digital bodies, but for its rich feature and mind-blowing designs.
Meanwhile, Pentax is famous for compatibility with its own manual lens and adaptability with many other manual lenses.

One brilliant feature I like nowadays on K5/K7 is the TAv mode, which works with many "A" aperture FA/FA* and even manual lens.
The major selling point is the body can auto seek a proper ISO value, after some smart auto metering, to suit current Shutter speed, aperture, and maybe focal length. However, this won't work when manual lens without "A" aperture mode is used, or those having "A" but set to other aperture values manually.

This is killing the potential of many legendary manual lens of our collections, expecially now Pentax has already fixes its AF logic issues which has brought up our hope to make the best out of our lens collections, expecially those not-so-cheap but very good primes.

Maybe Pentax markting guys will tell their leaders that consumers should be led to buy new auto lenses. But when you ask real hard-core Pentax fans, we don't think so.

When Canon/Nikon are working their ass out to lure us into their camps by improving every aspect in their digital body, Pentax software guys can easily improve this killer feature by letting us set an nominal Aperture value (F1.2~F22) in manual mode dials (just like setting focal length with manual lens in K5/K7), then activate TAv logic based on these values, set manually, to decide ISO for best exposure. If the logic requires more, you can simply allow people to set in customization functions.

Pentax fans, when you play with some PK manual lens with/without an "A" on aperture ring, with this TAv mode on the dial, you will know why I am so gunhole about this feature...

08-07-2012, 10:39 AM - 1 Like   #2
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I would prefer more NEW high quality glass in the Pentax lineup rather than using OLD glass.
08-07-2012, 11:31 AM   #3
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QuoteOriginally posted by robinhook Quote
Many people like us turn to Pentax for budget, not just saving that little on Digital bodies, but for its rich feature and mind-blowing designs.
Meanwhile, Pentax is famous for compatibility with its own manual lens and adaptability with many other manual lenses.

One brilliant feature I like nowadays on K5/K7 is the TAv mode, which works with many "A" aperture FA/FA* and even manual lens.
The major selling point is the body can auto seek a proper ISO value, after some smart auto metering, to suit current Shutter speed, aperture, and maybe focal length. However, this won't work when manual lens without "A" aperture mode is used, or those having "A" but set to other aperture values manually.

This is killing the potential of many legendary manual lens of our collections, expecially now Pentax has already fixes its AF logic issues which has brought up our hope to make the best out of our lens collections, expecially those not-so-cheap but very good primes.

Maybe Pentax markting guys will tell their leaders that consumers should be led to buy new auto lenses. But when you ask real hard-core Pentax fans, we don't think so.

When Canon/Nikon are working their ass out to lure us into their camps by improving every aspect in their digital body, Pentax software guys can easily improve this killer feature by letting us set an nominal Aperture value (F1.2~F22) in manual mode dials (just like setting focal length with manual lens in K5/K7), then activate TAv logic based on these values, set manually, to decide ISO for best exposure. If the logic requires more, you can simply allow people to set in customization functions.

Pentax fans, when you play with some PK manual lens with/without an "A" on aperture ring, with this TAv mode on the dial, you will know why I am so gunhole about this feature...
Pentax just has to release a body with a mount that is not crippled to allow that
08-07-2012, 02:13 PM   #4
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Being that I was a manual film guy, I've never understood the "crippled mount" thing.

08-07-2012, 04:21 PM   #5
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QuoteOriginally posted by robinhook Quote
One brilliant feature I like nowadays on K5/K7 is the TAv mode, which works with many "A" aperture FA/FA* and even manual lens.
The major selling point is the body can auto seek a proper ISO value, after some smart auto metering, to suit current Shutter speed, aperture, and maybe focal length.
Focal length is irrelevant in TAv mode.
08-07-2012, 06:24 PM   #6
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QuoteOriginally posted by robinhook Quote
...Pentax software guys can easily improve this killer feature by letting us set an nominal Aperture value (F1.2~F22) in manual mode dials (just like setting focal length with manual lens in K5/K7), then activate TAv logic based on these values, set manually, to decide ISO for best exposure. If the logic requires more, you can simply allow people to set in customization functions...
It is a bit more complicated than entering the min/max f-stop values (essentially the information encoded in the 5 pins of "A" and newer lenses). The old (pre "A") lenses (with the exception of a couple late models) have aperture lever movements proportional to the diameter of the iris, while the A, F, FA and D are proportional to the area of the iris.

Unless the lever position that sets the aperture is re-calibrated for non-linear movements, gross exposure errors (more than 1 stop) will occur especially in middle f-stops.

It is very possible though to build correction tables, or even calculate the non-linear lever position on the fly given the f-range and the selected f-stop.

Even better, Pentax should have built a database of all the non-A lenses with the name and all the parameters so all we'll have to pick is the name. For example you pick "SMC PENTAX-M 1:1.7 50mm" and the camera loads the data for focal length 50mm, max f-stop 1.7, min f-stop 22, and the exact lever positioning for each 1/3 or 1/2 f-stop steps.
08-07-2012, 06:29 PM   #7
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I wish that TAv would give me faster shutter speeds before over exposing once ISO has reached the minimum. Effectively the shutter speed should become the minimum shutter speed.
08-07-2012, 07:24 PM   #8
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I can see why a product manager wouldn't want to add this feature (tell the camera you're using a K or M series lens, and it would then work as expected)... there's less profit in selling a camera than in selling a camera and lenses for it, right? At least, I'd expect that thinking before the GXR M-mount proved to be successful.

The GXR-M is basically a camera designed solely for 3rd party lenses. And, as far as I can tell, it is the only thing keeping the GXR series alive. Designing a camera to accept lenses that you won't profit from can still be profitable. (At least, I hope the GXR-M is profitable.) So, design a camera specifically for old glass. Program it to be user-friendly, expect your users to be comfortable with F-stops, shutter speeds, and selecting the lens that's currently mounted. Heck, design it to automatically correct for vignetting, CA, and other distortion--once specific test images have been shot at specific settings. Make lens settings downloadable. Have official programs for Pentax and Takumar lenses. Once you've done that, have had that camera on the market for 6 months or a year, add that programming to your other cameras. No marginal cost, right? The Q, K, and 645 cameras could all benefit from being adaptable to other lenses, methinks, and not just in usability but also in sales volume.

Then sell those system lenses to folks who want more automation. Sure, it won't benefit sales of the 55-200 much, but I'd bet you'd see more sales of the 31 Limited.

08-07-2012, 09:15 PM   #9
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QuoteOriginally posted by twitch Quote
I wish that TAv would give me faster shutter speeds before over exposing once ISO has reached the minimum. Effectively the shutter speed should become the minimum shutter speed.
What you really want is Nikon style minimum shutter speed in Auto ISO settings.
08-07-2012, 09:34 PM   #10
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QuoteOriginally posted by tabl10s Quote
Being that I was a manual film guy, I've never understood the "crippled mount" thing.
On an uncrippled mount, the movement of the aperture blades is done with a different mechanism in the lens. If you put the lens in A, it's all about the camera moving the aperture lever. If you turn the ring off A, it's all in the lens. Two systems that are supposed to produce an identical result are either redundant or a source of trouble. It makes sense that they'd eliminate one. Aperture rings start to suck in the later lenses anyway, and they have all those parts that launch into space when disassembled.

My idea was to have the camera capable of reading an RFID tag which could be placed on an M or older lens. The tag would tell the camera all about the lens, how the lever works, etc. You could buy the tags from Pentax, say for $20. That should be way more than the cost of manufacturing plus some research, and turn old lenses into a profit center.
08-07-2012, 10:00 PM   #11
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Why not have the camera calibrate the curve?

Mount the lens, enter name and some details such as minimum and maximum aperture. Set the camera and lens in a fixed position, either on a tripod or set on a platform of some kind. The body cycles the aperture lever over it's throw. It knows that at one extreme it is open, the other closed. It creates a table with the position of the lever and stops.

It could also save the focal length for SR purposes. When you mount the lens, you select the defined lenses and they work like an A type. Could also correct any focus screen exposure flaws.

The same strategy could be used for adjusting focus offsets. Use the CDAF to calibrate the pdaf system.
08-07-2012, 10:24 PM   #12
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QuoteOriginally posted by demp10 Quote
It is a bit more complicated than entering the min/max f-stop values (essentially the information encoded in the 5 pins of "A" and newer lenses). The old (pre "A") lenses (with the exception of a couple late models) have aperture lever movements proportional to the diameter of the iris, while the A, F, FA and D are proportional to the area of the iris.

Unless the lever position that sets the aperture is re-calibrated for non-linear movements, gross exposure errors (more than 1 stop) will occur especially in middle f-stops.
Not to hijack this thread, but going slightly off topic, I didn't know about this difference. So, does this mean that mounting K or M lenses on an 'A' body (or A lenses on an pre-A body) will result in inaccurate in camera meter readings?


Christian
08-08-2012, 01:06 AM   #13
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QuoteOriginally posted by demp10 Quote
It is a bit more complicated than entering the min/max f-stop values (essentially the information encoded in the 5 pins of "A" and newer lenses). The old (pre "A") lenses (with the exception of a couple late models) have aperture lever movements proportional to the diameter of the iris, while the A, F, FA and D are proportional to the area of the iris.

Unless the lever position that sets the aperture is re-calibrated for non-linear movements, gross exposure errors (more than 1 stop) will occur especially in middle f-stops.

It is very possible though to build correction tables, or even calculate the non-linear lever position on the fly given the f-range and the selected f-stop.

Even better, Pentax should have built a database of all the non-A lenses with the name and all the parameters so all we'll have to pick is the name. For example you pick "SMC PENTAX-M 1:1.7 50mm" and the camera loads the data for focal length 50mm, max f-stop 1.7, min f-stop 22, and the exact lever positioning for each 1/3 or 1/2 f-stop steps.
Then let me point out something about levers : when i use my super A with a K or M lens, then the body have no info about the lens used, right.

However what ever the aperture i choose, i always get right exposed picture.

When i use my "A" lens on a selected aperture, my picture are still perfectly exposed.

My point is, no matter the way the lever allow the body to calculate the exposure.
Fact is that the A series body, and particularly my SuperA body can "calculate" on it's'own how to expose well pictures. So it shouldn't be hard at all to include this in a modern dslr.
08-08-2012, 04:42 AM   #14
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QuoteOriginally posted by aurele Quote
Then let me point out something about levers : when i use my super A with a K or M lens, then the body have no info about the lens used, right.

However what ever the aperture i choose, i always get right exposed picture.

When i use my "A" lens on a selected aperture, my picture are still perfectly exposed.

My point is, no matter the way the lever allow the body to calculate the exposure.
Fact is that the A series body, and particularly my SuperA body can "calculate" on it's'own how to expose well pictures. So it shouldn't be hard at all to include this in a modern dslr.
That's because your Super A does not have a crippled K mount...
The crippled mount lacks the "feedback" aperture lever, that tells the body the relative aperture used (relative being the number of stops between wide open and the current aperture).
Old bodies don't need the wide aperture value to calculate proper metering, just this relative value between the wide open position and what the user wants. If the lens reports a 3 stops difference, then the camera will adapt the shutter value accordingly from what it metered.

Say that the camera meters the scene at 1/200 (with the lens wide open), and the "feedback" lever is at its -3 stops position. then the camera knows that a properly metered picture can be made using 1/25, without ever knowing its wide open aperture...
08-08-2012, 07:32 AM   #15
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QuoteOriginally posted by aurele Quote
Then let me point out something about levers : when i use my super A with a K or M lens, then the body have no info about the lens used, right.

However what ever the aperture i choose, i always get right exposed picture.

When i use my "A" lens on a selected aperture, my picture are still perfectly exposed.

My point is, no matter the way the lever allow the body to calculate the exposure.
Fact is that the A series body, and particularly my SuperA body can "calculate" on it's'own how to expose well pictures. So it shouldn't be hard at all to include this in a modern dslr.
Lenses have a secondary recessed lever that turns as you stop down the lens. Uncrippled mounts in older cameras, connect that lever to a network or resistors that adjust the exposure as needed.

The camera still has no idea what lens, how fast is it, how far it can be stopped down or what f-stop you are using. The meter in the camera measures light with the lens wide open and then compensates based on the secondary lever that tell the body how many f-stops the aperture is stopped down from the wide open position. It is all relative.
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