Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
12-10-2008, 02:41 PM   #1
Senior Member




Join Date: Mar 2008
Posts: 285
How do you use flash with M lenses?

As most Pentaxians will know, M lenses can not be used with P-TTL flash. Flash alway fires at full power. Negative flash power compensation is also not possible, as is slow syncro and trailing curtain (IIRC).

I'd love to be able to use flash to a certain extent at least, because there are very nice and affordable M lenses especially for portraits.

How do you solve that problem? Sure, selling all M glass and buy all FA Limited would be one solution - pricey, though

Are there more creative approaches? Do any of you use grey filters on lens and/or in front of the flash? Any other cool ideas out there?

12-10-2008, 02:50 PM   #2
Veteran Member
arpaagent's Avatar

Join Date: Sep 2008
Location: Raleigh, NC
Photos: Gallery
Posts: 777
You won't be able to use your onboard flash with M series lenses on a digital body, unless you can somehow stop the lens down enough to get just the amount of light.

You can, however, use M lenses if you have an external flash that supports "Auto" mode, as most do. These flashes can be set to measure their own light output and cut off at the right time. You would just need to set your M lens to the correct aperture, and put your camera into manual mode, at a speed low enough (<1/180 for example on the K200D) that will sync with the flash. I have used older flashes (Pentax AF280T) like this and it works fine. The auto mode on these older flashes is pretty reliable and is quite usable. Not quite as worry-free as P-TTL, but works well under most situations, including bouncing off of ceilings and walls.
12-10-2008, 03:07 PM   #3
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,394
I use an *istD

I find myself contnually recommending that if people want a second / back up 6MP camera, they should get an *istD. Why? because it is fully TTL capable, both with hot shoe and internal flash.

NO other DSLR can do that.

If you are using a K10D yoru best option is to get an AF540 FGZ and use it in Auto mode (that's right, it has its own flash sensor just like the old days)
12-10-2008, 03:13 PM   #4
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,093
As hinted above, you will have to do it the old fashioned way. According to the K10D owner's manual, the guide number table is:



Code:
ISO                Guide Number
-------------------------------
100 11
200 15.6
400 22
800 31
1600 44
-------------------------------
Aperture = guide number / shooting distance (meters)

So for ISO 200 at 3 meters the aperture is f/5.2 (may be safely rounded to f/5.6)

In practice, I make a quick guess, do a test shot, chimp the histogram, and adjust accordingly.

Steve


Last edited by stevebrot; 12-10-2008 at 03:22 PM.
12-10-2008, 03:30 PM   #5
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,093
QuoteOriginally posted by arpaagent Quote
You won't be able to use your onboard flash with M series lenses on a digital body, unless you can somehow stop the lens down enough to get just the amount of light.

You can, however, use M lenses if you have an external flash that supports "Auto" mode, as most do. These flashes can be set to measure their own light output and cut off at the right time. You would just need to set your M lens to the correct aperture, and put your camera into manual mode, at a speed low enough (<1/180 for example on the K200D) that will sync with the flash. I have used older flashes (Pentax AF280T) like this and it works fine. The auto mode on these older flashes is pretty reliable and is quite usable. Not quite as worry-free as P-TTL, but works well under most situations, including bouncing off of ceilings and walls.
A note of caution regarding external flash. Many older (and some newer) flashes have an overly high trigger voltage that may damage the circuitry of your camera. There have been a number of threads on this forum on the issue. There are also a few resources on the Web that have tables of known voltages.
Photo Strobe Trigger Voltages
There is some discussion about where the upper threshold of safety lies and I would be the last to make any suggestions, though there is some thought that under 7.8V is safe. (My old Vivitar flash measured in at 140V!)

Steve

P.S. You might also want to check out this poll https://www.pentaxforums.com/forums/pentax-camera-accessories/43200-flash-tri...nown-work.html

Last edited by stevebrot; 12-10-2008 at 04:00 PM.
12-10-2008, 08:29 PM   #6
Senior Member




Join Date: Jan 2007
Location: Upstate New York, US
Photos: Albums
Posts: 223
I've used my AF540 in manual mode with a manual lens before. I mostly just calculated power by eye (1/1, 1/2, 1/4, 1/8, or 1/16). Take a few test shots to get the feel, and it doesn't seem too hard to get it right that way. You should be able to do this with older flashes too, but you should watch the trigger voltage as Steve mentioned.
12-11-2008, 12:55 AM   #7
Veteran Member




Join Date: Jul 2008
Location: Var, South of France
Photos: Albums
Posts: 1,071
Hello,

Well, in fact, you can trick the camera into thinking it has an A lens attached... Just short the A and Data electrical contacts on the mount, and Tadaaaaa! you've just enabled P-TTL and matrix metering (Focus point still stays centered, though).

It'll will even transform some PK-M lenses into PK-A (not all, you'll have to try!). To do this, just set the aperture ring on the smallest aperture available.

Only downside for m42 and pure PK-M (those not working as PK-A): you have to select the biggest aperture available on the body, or the pics will be overexposed.
12-11-2008, 02:33 AM   #8
Veteran Member
Mike Cash's Avatar

Join Date: Jan 2007
Location: Japan
Photos: Gallery
Posts: 6,952
QuoteOriginally posted by arpaagent Quote
You won't be able to use your onboard flash with M series lenses on a digital body
I don't like to do it, but I have used onboard flash with M lenses and M42 lenses. You just have to know the GN and guesstimate your subject distance to get you in the ballpark of the correct aperture. Then review your histogram and adjust accordingly.

The option you outline of using external flashes with an auto feature is far preferable.

12-11-2008, 02:53 AM   #9
Veteran Member




Join Date: Aug 2007
Location: England
Posts: 309
QuoteOriginally posted by dlacouture Quote
Well, in fact, you can trick the camera into thinking it has an A lens attached... Just short the A and Data electrical contacts on the mount, and Tadaaaaa!
Huh? With K and M lenses the mount on ther lens is metal, so all the contacts will be shorted. IIRC this is how the body detects that the lens is K or M rather than an A or later. Si IMO shorting the A and Data pins will do nothing because they are already shorted.

Perhaps you are thinking about this modification? Mark Roberts actually insulates part of the mount so that the camera can determine the maximum and minimum aperture.

QuoteQuote:
you've just enabled P-TTL and matrix metering (Focus point still stays centered, though).
P-TTL means that the camera sends test flashes, and meters, then it adjusts the flash accordingly, do you see this with your modification?

When you say you get matrix metering, are you saying that you can set the camera to the matrix metering setting?

QuoteQuote:
It'll will even transform some PK-M lenses into PK-A (not all, you'll have to try!). To do this, just set the aperture ring on the smallest aperture available. Only downside for m42 and pure PK-M (those not working as PK-A): you have to select the biggest aperture available on the body, or the pics will be overexposed.
If you have to use the smallest aperture then it means that the flash is using full power. This means that there is no metering from the body, so P-TTL is not working. If you could use any aperture (and you can change the flash power for the on-board flash using the menu) then it would mean that P-TTL is working.

Richard
12-11-2008, 05:35 AM   #10
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,394
QuoteOriginally posted by CFWhitman Quote
I've used my AF540 in manual mode with a manual lens before. I mostly just calculated power by eye (1/1, 1/2, 1/4, 1/8, or 1/16). Take a few test shots to get the feel, and it doesn't seem too hard to get it right that way. You should be able to do this with older flashes too, but you should watch the trigger voltage as Steve mentioned.
I'm surprised you didn't select Auto mode on the AF540, it has it's own sensor, and all you have to do on the flash is set the F-stop you set thelens to, the camera sends the ISO, and you are all set.
12-11-2008, 05:46 AM   #11
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,394
lets just clarify a little, I've been there
QuoteOriginally posted by richard64 Quote
Huh? With K and M lenses the mount on ther lens is metal, so all the contacts will be shorted. IIRC this is how the body detects that the lens is K or M rather than an A or later. Si IMO shorting the A and Data pins will do nothing because they are already shorted
no not all contacts touch the mount, the one that tells the camera that the lens is automatic apature (3rd from the locking pin) is recessed on the camera body, the pin must stick out from the lens
QuoteQuote:
Perhaps you are thinking about this modification? Mark Roberts actually insulates part of the mount so that the camera can determine the maximum and minimum aperture.
this does not work, because the DSLRs disable matrix metering if the lens is out of auto apature mode I think mark roberts also states this only works on film bodies
QuoteQuote:


P-TTL means that the camera sends test flashes, and meters, then it adjusts the flash accordingly, do you see this with your modification?

When you say you get matrix metering, are you saying that you can set the camera to the matrix metering setting?
if it is working, but you need the lens in auto mode to do this, meaning that you have to also short the third pin from the lens locking pin, and that causes all sorts of other problems. Specifically the camera now thinks it has an A lens, and tries to figure out the metering based on the other contacts, and gets it wrong. Also, when you short the A poin, the apature activation lever operates to the extent necessary to set the F stop on an A lens, which is not the same as a manual apature (Non A) lens

QuoteQuote:

If you have to use the smallest aperture then it means that the flash is using full power. This means that there is no metering from the body, so P-TTL is not working. If you could use any aperture (and you can change the flash power for the on-board flash using the menu) then it would mean that P-TTL is working.

Richard
All of these work arounds in my opinion are a waste of time. I did an experiment where I actually converted a lens to A from K mount, by marking the apatures according to the Mark Roberts instructions AND adding the pin for Automatic apature. Did it work, sort of, but exposure is all over the map. Why? Because the apature activation lever on a non A lens controls the apature differently. Most Non A lenses have the apature change diameter linearly with motion of this lever, where A lenses have the area change linearly with this lever. As a result the converted Non A lens got the exposure wrong at every setting varrying from -1.5 stops at max apature to +2 stops at min apature. In other words, it was almost useless.

If you are serious about flash work with non A lenses, as I said earlier, you have at this point 2 options, get an *istD (or DS but on the DS the internal flash isnot TTL capable) or get an AF540 FGZ and use it in the Auto mode.
12-11-2008, 06:32 AM   #12
roy
Inactive Account
roy's Avatar

Join Date: Sep 2006
Location: D/FW area, Tx.
Photos: Gallery
Posts: 1,712
the DS also works in TTL. that's why i'll keep mine..
this subject is my only peeve with pentax. all but the D&DS will not work in TTL. you can get around it but ti still PMO that they did this.


QuoteOriginally posted by Lowell Goudge Quote
I find myself contnually recommending that if people want a second / back up 6MP camera, they should get an *istD. Why? because it is fully TTL capable, both with hot shoe and internal flash.

NO other DSLR can do that.

If you are using a K10D yoru best option is to get an AF540 FGZ and use it in Auto mode (that's right, it has its own flash sensor just like the old days)
12-11-2008, 06:50 AM   #13
Veteran Member
Mike Cash's Avatar

Join Date: Jan 2007
Location: Japan
Photos: Gallery
Posts: 6,952
QuoteOriginally posted by Lowell Goudge Quote
If you are serious about flash work with non A lenses, as I said earlier, you have at this point 2 options, get an *istD (or DS but on the DS the internal flash isnot TTL capable) or get an AF540 FGZ and use it in the Auto mode.
Or any of several other flashes that have an auto mode.
12-11-2008, 07:02 AM   #14
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,394
QuoteOriginally posted by roy Quote
the DS also works in TTL. that's why i'll keep mine..
this subject is my only peeve with pentax. all but the D&DS will not work in TTL. you can get around it but ti still PMO that they did this.
Roy

does the internal flash on teh DS work also in TTL mode, SOmeone posted earlier it did not.

I know the *istD does.

As per your pet peeve, my wish list for the next high end, i.e. K30D is that it returns with the TTL sensor reading off the sensor plane. Why, not because I like to use old glass, but because for wildlife, the preflash disturbes the subject, and sometimes the pose is lost, and the lag that preflash adds results in less perfext shots. For wildlife, TTL is the only way to go.
12-11-2008, 07:59 AM   #15
Pentaxian
bdery's Avatar

Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 5,753
The best advice is, indeed, to get a flash that has an auto Thyristor mode, and set the exposure parameters accordingly. No problems then.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
flash, k-mount, lenses, pentax lens, power, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Lenses, lenses, lenses... and a flash! pbo Sold Items 18 05-28-2009 04:35 PM
Built-In Flash + Old Lenses k100d Pentax DSLR Discussion 18 04-06-2008 04:39 PM
No wireless flash with M lenses? AndrewShirley Flashes, Lighting, and Studio 0 03-09-2008 02:27 PM



All times are GMT -7. The time now is 08:04 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top