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04-14-2023, 08:57 AM   #1
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Long Exposure Issue

Hello,
I'm new to this forum and am hoping that someone can identify the problem I'm experiencing and hopefully offer some help. I have owned a Pentax K-70 for about 2 1/2 years now and never noticed any problems. In January I purchased a K&F Concept Nano-X Pro ND1000 neutral density filter for long exposures with my DA18-135 lens. I have noticed that on exposures longer than about 15 seconds there is a distinct line at the bottom of the image, about 1/8 of the way into the frame (left side in portrait orientation). The line starts at this point and fades in towards the center of the image. It is much more noticeable when I stack a circular polarizing filter on the ND filter, but is still there without the polarizer. I'm attaching 3 sample images. The first is an approximately 3 minute exposure with polarizer and is the most obvious example. The next is 60 sec without the polarizer and 65 sec with the polarizer. The line is clearly present in the bottom right on both images. All 3 are with the ND filter.

Today I experimented with 3 minute exposures in a dark room with the DA18-135 lens, a DA55-300 PLM lens, and a DA50 lens. I tested each lens without any filters and at f18 and f2 or f3.5. I did not notice the line in any of these images. However, the images were all very dark and I may not have allowed for enough light.

I don't see how the filters themselves could cause this issue. Any idea if it is a problem with the camera itself (light leak?!?!) or the lens? Thanks in advance,

Erik

Attached Images
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PENTAX K-70  Photo 
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PENTAX K-70  Photo 
View Picture EXIF
PENTAX K-70  Photo 
04-14-2023, 09:12 AM - 5 Likes   #2
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QuoteOriginally posted by EHogan Quote
I don't see how the filters themselves could cause this issue. Any idea if it is a problem with the camera itself (light leak?!?!) or the lens? Thanks in advance
First question is how are you covering the viewfinder during the long exposure ?

Second question is do you have Long Exposure NR turned on ?


My first guess is it is viewfinder light leak. In portrait orientation, which way up was the camera ? I am guessing shutter button south ?

Last edited by pschlute; 04-14-2023 at 09:36 AM.
04-14-2023, 09:45 AM - 1 Like   #3
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Thanks for the quick reply! The NR is turned on (auto). I'm (maybe obviously) new to long exposures and hadn't heard of covering the viewfinder, so its been completely uncovered. I just did some quick research and I bet this is exactly the problem. I'll do some more tests and report back, but in the meantime I welcome any more insight!
04-14-2023, 10:06 AM - 3 Likes   #4
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QuoteOriginally posted by EHogan Quote
Thanks for the quick reply! The NR is turned on (auto). I'm (maybe obviously) new to long exposures and hadn't heard of covering the viewfinder, so its been completely uncovered. I just did some quick research and I bet this is exactly the problem. I'll do some more tests and report back, but in the meantime I welcome any more insight!
Yes, when doing long exposures, the mirror is up and the foam seals will stop light getting from the viewfinder to the sensor and ruining the shot....but only up to a point

The problem is most apparent when the sun is bright and behind you....so shining right into the viewfinder.

The best way to deal with it is to remove the viewfinder eyepiece and slot in the viewfinder cover (little plastic thing that comes with the camera), but in practice, and depending on length of exposure a thumb over the viewfinder or hand shielding it will usually work.

ps. there is also a good reason why long exposure photographers chew gum !. Just make sure not to actually touch the camera during exposure.

04-14-2023, 08:50 PM - 1 Like   #5
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I also think it is light entering the viewfinder. And you notice it more when you are using a ND filter blocking light entering the lens. So more of the light captured in the image will be from the viewfinder.
04-15-2023, 06:44 AM - 2 Likes   #6
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I did a test shot this morning with the sun at the viewfinder. I couldn't find the viewfinder cover that came with the camera, so covered the eyepiece with the opening of a black microfiber cloth sack and cinched it down with the drawstring. 100% this was the issue. I'm extremely grateful for the help! Now to keep looking for the cover and find better alternate methods to cover the eyepiece that don't involve residue from tape. Or gum . Thanks again!
04-15-2023, 11:02 AM   #7
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QuoteOriginally posted by EHogan Quote
better alternate methods to cover the eyepiece that don't involve residue from tape. Or gum . Thanks again!
I have done plenty of long exposures using ND filters, and to be honest shielding using my hand or a lens cloth or a baseball cap all work well. Obviously the longer the exposure, the more robust your shielding needs to be.

Glad to be of help.

04-16-2023, 08:41 AM   #8
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QuoteOriginally posted by pschlute Quote
The best way to deal with it is to remove the viewfinder eyepiece and slot in the viewfinder cover (little plastic thing that comes with the camera)
I have a K-70, as does the OP. When did Pentax start supplying a viewfinder cover with the K-70? Neither the OP or myself have one.
04-16-2023, 11:00 AM   #9
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I'm fairly certain my camera did not come with a viewfinder cover. I searched the internet and could not find one for sale at a reliable retailer. However, I did find a simple work around. I found a thin piece of black plastic (rigid but flexible, not plastic bag) and cut it into a small rectangle. This easily slips under the rubber of the eye cup to hold it in place over the viewfinder. The square would be easy to lose, but are simple to make and I can always have multiple with me. Hope that helps!
04-16-2023, 12:01 PM   #10
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QuoteOriginally posted by Dale H. Cook Quote
I have a K-70, as does the OP. When did Pentax start supplying a viewfinder cover with the K-70? Neither the OP or myself have one.
I cannot truthfully answer that.

All I know is that my MX; Z-1; DS; K10D; and K-1 and K-1 II all came with them.
04-16-2023, 12:06 PM   #11
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QuoteOriginally posted by pschlute Quote
I cannot truthfully answer that.

All I know is that my MX; Z-1; DS; K10D; and K-1 and K-1 II all came with them.
Looks like the K70/KF do not come with them.

You can buy them in the UK for £10.... or do what I do and use your hand
04-16-2023, 12:24 PM   #12
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I believe entry level cameras do not include VF cover, but higher end cameras usually do.

What is included with the camera should be listed in the manual.
04-16-2023, 03:12 PM   #13
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QuoteOriginally posted by EHogan Quote
I found a thin piece of black plastic (rigid but flexible, not plastic bag) and cut it into a small rectangle. This easily slips under the rubber of the eye cup to hold it in place over the viewfinder. The square would be easy to lose, but are simple to make and I can always have multiple with me.
I may make one, in case I want to try long exposures with ND filters on my K-70. I almost always have my O-GPS2 GPS unit mounted on my hot shoe, so I keep the hot shoe cover in an unused SD card pouch under the lid of my Lowepro camera bag. If I make a viewfinder cover it can be stored in the same pouch.

Last edited by Dale H. Cook; 04-16-2023 at 03:48 PM.
04-25-2023, 06:29 AM   #14
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For a VF cover, I have pieces of black gaffer tape stuck to various things including tripod legs, lens hoods of my most used landscape and macro lenses, and ND filter cases. I figure that I'm bound to have one of those items with me for long exposures or tripod work.
04-25-2023, 01:21 PM   #15
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It appears that the viewfinder cover for the K-1000 will fit the K-70 and KF. My K-70 viewfinder hood fits fine on my K-1000. I have a K-1000 viewfinder cover on the way.
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