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11-09-2019, 05:11 AM   #1
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Bulb time setting on K-70

I want to use the Bulb setting on my K-70 for long exposure with a Lee Super Stopper (15 stop) filter. However, I can't seem to get the exposure timing right. If the table on the Lee filter documentation indicates I need an exposure of one minute for the equivalent of 1/500th of a second normal exposure without the filter, I'm setting the camera to B, setting the aperture with the rear dial, pressing the O on the top of the camera so the duration time is displayed, setting the exposure time to one minute with the front dial, and then pressing the Shutter. The shutter is opening for the one-minute duration, but then the shutter appears to close and I get a flashing orange light for the same duration as the shutter was open for. This results in the picture taken being over exposed. It appears that I'm getting a "double time". I'm getting better results by setting the exposure to 30 seconds. i.e. half of what Lee prescribe. I've had exactly the same results when I've tried longer timings, ie. Lee say 4 minutes for a /125th sec, so I set Bulb to 2 minutes and I get 2 minutes of open shutter plus t minutes of flashing orange light, and the results are pretty good.

Why am I having to set Bulb exposure to half the Lee prescribed time? When my colleagues using Canon and Nikon do this with the same filter, and comparable apertures etc., they set their Bulb exposure exactly as Lee define.

11-09-2019, 05:17 AM   #2
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I think the flashing orange is in-camera dark processing.
11-09-2019, 05:52 AM - 1 Like   #3
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Yes after a long exposure the camera will do dark frame subtraction to eliminate noise. Your picture is not being overexposed during this process.

The question is however "why are you getting overexposed pictures. Might help if you post three images.... one at 1/500 (no filter) / one at 60 seconds/ one at 30 seconds.

Are you ensuring no stray light is entering either the viewfinder or around the gap between the filter and the lens. You need to be shielding both these areas from light.

Remember that the difference between 30 and 60 seconds may sound like a lot, but is only one stop.
11-09-2019, 06:01 AM   #4
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Is your ISO set the same as your friends? Upload a file here with full exif. Jpg is fine.

11-09-2019, 07:50 AM   #5
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You can turn the in camera dark frame subtraction off (NR off in the menu) but if you can spare the time leave it on.

As for the correct exposure time - > 15 stops - > multiply your shutter speed with 2^15=32768
Using your example: 1/125 sec will become 32768/125 sec = 4 min 22 sec

As mentioned it's important to prevent light leakes for such long exposures
11-09-2019, 09:15 AM   #6
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I put a dark object, such as a dark end of a sock over the viewfinder when I do longer exposures to avoid light leak into the sensor/image. As stated above, the camera will do a noise reduction function for approximately the same time as the amount of time the shutter was open for the shot.

If you do not cover the viewfinder during longer exposures, you may get over exposure and/or streaking in the image. As I mentioned I put an end of a dark sock over my viewfinder, due to the fact that placing and removing the actual viewfinder that came with the camera may be more tedious and time consuming.
11-09-2019, 09:40 AM   #7
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QuoteOriginally posted by C_Jones Quote
due to the fact that placing and removing the actual viewfinder that came with the camera may be more tedious and time consuming.
This is why landscape photographers chew gum
11-09-2019, 12:02 PM   #8
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QuoteOriginally posted by pschlute Quote
This is why landscape photographers chew gum
Since I lost the original cover I use tape (when not in use sticking above the flash)

11-09-2019, 03:25 PM   #9
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Thanks for your replies. I can confirm that no stray light is getting in past the filter, I'm using a Lee filter in the first slot of a Lee adaptor. I learnt the technique on a photography course, and the instructor watching me confirmed I was doing everything right, but he wasn't familiar with Pentax. Everybody else was using Canon or Nikon wheer their Bulb settings were set as the Lee 'table' suggested. The instructor also confirmed that on the longer exposure pictures I took, where the Lee filter 'table' (I was using a class-room provided Super-Stopper at the time) said four minutes for the equivalent duration without the filter, and when the K-70 was set to four minutes, it had the shutter open for four minutes, and then a further four minutes of orange flashing light. The result was a white-out over-exposure. As indicated earlier, if I set the exposure time for a half of what Lee indicate then in the case of four minutes, if I set it for two, I get two minutes of exposure, and two minutes of orange flashing light, with a decent result. When I took the picture uploaded I only had a ten stop Big-Stopper with me. To try and get the longest exposure possible, without a filter I set the ISO to 100 with F29 giving me 1/15sec. A Lee big-stopper says 1 minute for 1/15sec. I took the attached at a 30 second exposure, with 100 ISO, and F29, the camera opened the shutter for 30 seconds and flashed the orange light for a further 30.
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11-09-2019, 03:33 PM - 1 Like   #10
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QuoteOriginally posted by pschlute Quote
This is why landscape photographers chew gum
I use gaffer's tape.
11-09-2019, 03:47 PM   #11
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QuoteOriginally posted by Bob Lee Quote
Thanks for your replies
Hi Bob

Can only really help if you post some examples of where things dont work out. So please post a picture at 1/500 (without filter) and at 60 sec and 30 sec. Then we will be able to see.

I use Lee filters all the time with the K1.
11-09-2019, 03:55 PM   #12
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It also looks like you are getting some vibration. make sure nothing is dangling and turn off anti vibration (stabilization )because the camera will try to correct in long exposure and cause slight vibration. I was shooting long exposure with an 8 stop and when I got home didn't find a single file that was tack sharp, not because the camera wasn't on a sturdy tripod and not because anything was dangling.

Turn off the long exposure noise reduction, it will help a bit using it but not enough to make it a must use option. The long exposure noise reduction is doubling your time.

Leaving the stabilization active caused slight vibration causing the file not to be tack sharp.

Last edited by kevinWE; 11-09-2019 at 05:41 PM.
11-10-2019, 03:37 AM   #13
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QuoteOriginally posted by Bob Lee Quote
it had the shutter open for four minutes, and then a further four minutes of orange flashing light.
I am guessing you mean the orange LED on the back of the camera indicating writing operations on the SD card? That would be somewhat weird in my opinion because it only flashes for a short time after the exposure + NR is done and not the whole time NR is running. NR can be turned off (at my K-3 it can be found in the quick menu by pushing the Info button)

As mentioned before to fully understand the problem it might be good to see a picture taken before and after you applied the filter.
SR should be deactivated too (I think it is by default turned off when using the 2 sec timer or M.UP, I am not so sure about the 12 sec timer though)
11-10-2019, 08:26 AM   #14
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The not-sharp part of the image could be the forum software scaling... Iím viewing it on my phone so itís hard for me to be critical of the sharpness.

Did you do anything else to your sample? Or is it basically straight out of camera? Exposure here looks OK to me, depending on what youíre after.

It may just be that your lens behavior is slightly different from the Nikon/Canon folks. You could test that by running the comparison with the lenses at f5.6 or something. That would rule out the lens aperture stopping down differently.

You could swap filters with someone and test again, ruling out sample variation in the filters.

And you could test in low light with no filter and see if ISO 100 on your camera is just different at long exposures...

Oh, and the orange light should be the dark frame subtraction. It is done with the shutter closed so there should be no extra exposure happening there. The camera is just trying to find sensor hot spots and such to reduce noise.

On an unrelated note, you seem to have a couple of dust specks on your sensor...

Good luck,

-Eric
11-10-2019, 09:45 AM   #15
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Hi, the ..908 and ..952 shots show the non-filter and filter/bulb settings I'm using.

358 is a non-filtered picure at 1/125 and F14. 359 us with the 15 stop Super Stopper filter where 1/125sec = 4 minutes on Bulb, 360 is the same pic but at 2 minutes. Both at F14, ISO 400

362 is 1/125 F13, 363 is 4 mins F13.

372 is 1/25 F8, 373 is F8 2mins.

For every picture taken with Bulb, the apearture opens for the set time, and then the orange light flashes for the same duration. Which, for a 4 minute picture takes a very long time.

@Othar - the SD card is a 170MB/s SanDisk Extreme Pro, so there shouldn't be any delay in the writing time to the card.

@TwoUptons - The dust spec is in the lens, so I'm hoping Father Christmas brings me a replacement.

Not sure what I'm doing wrong, too easy to blame the camera.
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