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04-06-2018, 11:59 PM   #1
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Poor flash performance with A series lens on K-3 compared to DA series

I have both a Pentax 50 1.7 A lens and Pentax DA 50 1.8 lens.

Close up, using the internal flash on a K-3 in PROGRAM mode the DA exposes perfectly but the A lens shot is always severely overexposed (the aperture and shutter speed settings are either identical or very close in both cases as I have it set to the "A" setting).

This only occurs with close up photos. With normal range photos the exposure is fine.

Does any one know why? Is this normal for A series lenses?

Bar AF, shouldn't the A series lens just operate in the same way as a DA lens?

Thank you!


Last edited by Theov39; 04-07-2018 at 11:29 AM.
04-07-2018, 12:23 AM - 1 Like   #2
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Aperture is mechanical. On old lenses it can get slower to move (and close). It's just one example of product wear over time.
04-07-2018, 01:11 AM - 3 Likes   #3
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P-TTL automatic flash exposure mode is not compatible with manual focus lenses, only autofocus. A series types allow the aperture control, but flash exposures can be expected to be inconsistent.
04-07-2018, 03:14 AM - 1 Like   #4
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QuoteOriginally posted by mcgregni Quote
P-TTL automatic flash exposure mode is not compatible with manual focus lenses, only autofocus. A series types allow the aperture control, but flash exposures can be expected to be inconsistent.
I didn't know that. Thanks for that. I'll stop trying or wondering what I am doing wrong.

04-07-2018, 06:49 AM - 3 Likes   #5
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You can use the manual flash settings on your K3, and you should be able to tweak things to get exactly whats needed. You'd need to take a test shot or two and adjust the flash power accordingly. I'd recommend Manual camera mode also, with a fixed ISO, for the most consistent results with flash. However, you may find that Av mode (with fixed ISO) is good too. The less variables you introduce into the equation then the most reliable will be your flash and ambient exposure balancing. For that reason I don't think P mode or anything with auto-ISO is a good idea.
04-07-2018, 07:05 AM - 3 Likes   #6
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QuoteOriginally posted by mcgregni Quote
P-TTL automatic flash exposure mode is not compatible with manual focus lenses, only autofocus. A series types allow the aperture control, but flash exposures can be expected to be inconsistent.
I have to differ on this point. I have several A-series lenses (both Pentax and non-Pentax brand) and they all expose well in all the auto-exposure modes (including with built-in flash) as long as they are on the "A" setting on the aperture ring. This is with all my Pentax DSLR bodies.

If you are not getting good automatic exposure with the aperture ring in the "A" setting, make sure the electrical contacts on the base of the lens and the lens mount of the camera are clean. Wipe both with a dry lint-free cloth.

However, as mentioned, it is possible your aperture ring is not free and snappy, so there is a delayed closing of the aperture. One way to test this is to remove the lens, set the aperture to the smallest aperture (e.g., f16), pull back on the aperture lever with your fingertip to open the aperture then let loose of the aperture lever. The aperture should instantly snap closed. If it's sluggish, that's a problem. Another way to test more critically with the camera is to put the camera in Av mode, with the aperture on the lens in the "A" position, then with the Av dial, set an aperture of wide open, or nearly wide open (say f2), pop up the flash and take an exposure. It should be a fairly good exposure. Now dial a stopped-down aperture (say f16) and take an exposure of the same object at the same distance with the flash popped up, and see if the exposure is good. If it is significantly overexposed, your aperture may be sluggish. However, note that not every lens is perfect, and some over- or under-expose slightly because of aperture nonlinearities, but it should be fairly close if all is working properly. I have found on all my DSLR bodies that I prefer a -0.3 exposure adjustment of my built-in flash to help prevent blowing highlights in high-contrast subjects.

I hope this helps.

-Joe-

-Joe-

Last edited by k0og; 04-07-2018 at 07:15 AM.
04-07-2018, 08:09 AM - 1 Like   #7
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QuoteOriginally posted by mcgregni Quote
A series types allow the aperture control, but flash exposures can be expected to be inconsistent.
I think the "can be expected" part is not a general fact at all.
Pentax aperture on an A lens and on a FA lens, when using manual focus is not different in any way I am aware of.
04-07-2018, 09:07 AM   #8
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QuoteOriginally posted by mcgregni Quote
You can use the manual flash settings on your K3, and you should be able to tweak things to get exactly whats needed. You'd need to take a test shot or two and adjust the flash power accordingly. I'd recommend Manual camera mode also, with a fixed ISO, for the most consistent results with flash. However, you may find that Av mode (with fixed ISO) is good too. The less variables you introduce into the equation then the most reliable will be your flash and ambient exposure balancing. For that reason I don't think P mode or anything with auto-ISO is a good idea.
Thank you. That is very helpful. I'll try that.

---------- Post added 04-07-18 at 09:11 AM ----------

QuoteOriginally posted by k0og Quote
I have to differ on this point. I have several A-series lenses (both Pentax and non-Pentax brand) and they all expose well in all the auto-exposure modes (including with built-in flash) as long as they are on the "A" setting on the aperture ring. This is with all my Pentax DSLR bodies.

If you are not getting good automatic exposure with the aperture ring in the "A" setting, make sure the electrical contacts on the base of the lens and the lens mount of the camera are clean. Wipe both with a dry lint-free cloth. -Joe-
Thanks Joe. That is very helpful. At normal range (say more than 5 feet away), the A lens shots are the same as the DA shots and the exposure is fine which seems to suggest that the lens is working as it should. This just occurs at close up shots. Anyway, I will try your suggestions and see if that improves things.

04-07-2018, 09:14 AM - 1 Like   #9
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P-TTL works with manual focus "A" lenses as long as they are set to the "A" mode. This can be confirmed from the info screens or the EXIF data which indicate P-TTL. However it will not work as reliably as with AF lenses. It would appear the chip on the AF lenses supplies the P-TTL system some data for optimal performance.
04-07-2018, 09:36 AM - 1 Like   #10
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QuoteOriginally posted by Not a Number Quote
However it will not work as reliably as with AF lenses. It would appear the chip on the AF lenses supplies the P-TTL system some data for optimal performance.

Yes, this is the crux of it. There is no publically available technical data that I've ever become aware of that details exactly what the difference is between say, data transmitted via the mount with an A series type, or an F, FA, Da, etc. There is some evidence from references in the flash manuals that the focal length and focal point are part of it (obviously providing subject distance info), and indeed the flash manuals do specify 'distance' as being part of the P-TTL flash calculations for the pre-flash (ie calculated before the pre-flash - the pre-flash itself providing feedback on the surface reflectivity).


When I raised this question after the first edition of my 'Pentax Flash Guide', there was some extensive discussions and testing (kindly carried out by the member Ole, but with contributions from many other experienced people here). I was able to draw a firm conclusion that the A series types did not provide fully reliable and P-TTL exposures performance, this varying of course depending on ISOs and apertures, plus the different camera bodies also. It was certainly enough to conclude that this reference from the Flash Manual should be considered correct :


AF-540FGZII Manual, Page 25 P-TTL Auto Flash .....
"5 Confirm that the subject is within the effective flash range
and the Ready lamp is lit. Then take a picture.The correct flash output is obtained in P-TTL mode only
when the flash unit is used with autofocus lenses".



04-07-2018, 09:36 AM - 1 Like   #11
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QuoteOriginally posted by Theov39 Quote
Thanks Joe. That is very helpful. At normal range (say more than 5 feet away), the A lens shots are the same as the DA shots and the exposure is fine which seems to suggest that the lens is working as it should. This just occurs at close up shots. Anyway, I will try your suggestions and see if that improves things.
A possible explanation as to why the close-up shots are overexposing is that at closer ranges the lens needs to stop down more due to higher light values in the P-TTL pre-flash light measurement, and if there is a sluggish aperture mechanism it may be not quite closing all the way by the time of exposure hence overexposing the shot. Yet, at greater distances the aperture would not close down much if at all, hence the aperture is responsive enough to close correctly by the time of exposure.

-Joe-
04-07-2018, 09:39 AM - 1 Like   #12
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Autofocus lenses tell the camera distance. A series do not. For what I do I see the difference mostly in close up photography. Using my 50mm 2.8A lens with my 1.4x A converter gives me overexposure with flash. Using my generic or Pentax 100mm AF macro lenses gives good results.
04-07-2018, 09:46 AM - 1 Like   #13
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QuoteOriginally posted by mcgregni Quote
AF-540FGZII Manual, Page 25 P-TTL Auto Flash .....
"5 Confirm that the subject is within the effective flash range
and the Ready lamp is lit. Then take a picture.The correct flash output is obtained in P-TTL mode only
when the flash unit is used with autofocus lenses".



I don't have an AF-540FGZ of any kind, but find with the built-in flash all my A-series lenses expose properly at all useable distances (including close-up, as long as I don't have the ISO pushed too high beyond P-TTL adjustment range for closeups) with all my Pentax DSLR bodies. There may be some other factor related to AF as you mention with the AF-540FGZ series flashes, but I don't think that applies to the built-in flash since it does not have AF capabilities like the 540 does. That's been my experience with my bodies and A-series lenses.

-Joe-
04-07-2018, 09:54 AM - 1 Like   #14
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I feel that the P-TTL flash exposure measurement process would likely be exactly the same for a built-in flash and an accessory flash. The K3 Manual does not specifically have the same instruction regarding P-TTL and autofocus, but it does have this passage (relating to use of the built-in flash) :

K3 Manual, Page 44 : ...
"The shutter speed is locked at 1/180 seconds when a lens
other than a DA, DA L, D FA, FA J, FA or F lens is used"


So, the A series is missing, therefore we know this statement to be untrue .... however, by deduction, is this not an indication also that they consider the manual focus lenses including the A series to be not compatible .... ?

However, this is somewhat contradicted in the table on page 86, where it shows P-TTL Auto Flash as being "available" (??)

"*1 Available only when using a DA, DA L, D FA, FA J, FA, F or A lens"




All very confusing. I'm not sure if there is any absolute conclusion to draw from this, or whether this is the result of developments and mis-communicationsover time as Pentax passed from one owner to the next .... ? So, the P-TTL mode is "available" with an A lens (yes, we always knew that), but with the accessory flashes "the correct flash output is obtained only with autofocus lenses" ....


My quite blunt interpretation of it comes from the point of view of a Guide book. I don't doubt that people have obtained good results from P-TTL with A series lenses, but I guess you couldn't make a claim against Ricoh for a warranty fix if it wasn't working well.

Last edited by mcgregni; 04-07-2018 at 10:06 AM.
04-07-2018, 11:33 AM   #15
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QuoteOriginally posted by pentaxus Quote
Autofocus lenses tell the camera distance. A series do not. For what I do I see the difference mostly in close up photography. Using my 50mm 2.8A lens with my 1.4x A converter gives me overexposure with flash. Using my generic or Pentax 100mm AF macro lenses gives good results.
That would make sense (Nikon lenses also do this) and is also in line with the suggestions here that the chip in AF provides better P-TTL responsiveness. In a way it is not surprising, You would expect the chips to be improved over time.

---------- Post added 04-07-18 at 11:36 AM ----------

QuoteOriginally posted by Not a Number Quote
P-TTL works with manual focus "A" lenses as long as they are set to the "A" mode. This can be confirmed from the info screens or the EXIF data which indicate P-TTL. However it will not work as reliably as with AF lenses. It would appear the chip on the AF lenses supplies the P-TTL system some data for optimal performance.
That is definitely the case with Nikon lenses and, indeed, they used to badge their lenses that provided the distance information with a "D". I suspect it is the same with Pentax.
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