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07-03-2018, 07:20 AM   #16
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QuoteOriginally posted by bhbrake Quote
Not entirely. Aperture is the diameter of the opening in the lens that lets the light through, and it is measured in gauge kind of like wire. (Smaller number is a bigger opening). It is called the f-stop. The lower the f-stop number, the more light comes in while the shutter is open and the narrow the depth of focus is. The ISO is the sensitivity of the sensor/film setting and the larger the number more sensitive and therefore the faster an image can be recorded. Higher the ISO, the grainier the image. The relationship of ISO number to quality of image is inverse. Shutter speed is just how long the shutter is open to allow light through.
Therefore, to maintain an exposure value (ev), high shutter speed requires low f-stop and high ISO. High f-stop requires low shutter speed and high ISO. High ISO allows high shutter speed and high f-stop.
Essentially, all three actions affect the amount of light getting to the sensor. If you want a high quality image, then low ISO (100-400) is the goal, and if you need a lot of field depth from a high f-stop, you are going to need a long exposure and a really steady hand...also known as a tripod.😁
Wow, I have so much to learn Thank you for your help!!

---------- Post added 07-03-18 at 07:23 AM ----------

QuoteOriginally posted by Qman Quote
It might help to know what kind of photos you'd like to capture with long exposure. You could use it at night for city lights or stars. Or you could use long exposure to show motion blur of a dog or a car passing by. Or you could use it to make flowing water look smooth. Or you could even make people disappear from a busy street. Each of these photos will require different techniques. Some of them will require an ND filter. Most will require a tripod. Let us know what type of photo you want to try and we can give some suggestions for how to capture the shot you want.
This is a good point! I am interesting in shooting water flowing because I am near lots of waterfalls

---------- Post added 07-03-18 at 07:25 AM ----------

QuoteOriginally posted by UncleVanya Quote
Buy this book:
Understanding Exposure, Fourth Edition: How to Shoot Great Photographs with Any Camera: Bryan Peterson: 9781607748502: amazon.com: Books?tag=pentaxforums-20& (use affliate links from the forum however to help the site)


Basic theory:

ISO (yes sensitivity) + aperture + shutter speed = an exposure. A given calculation for an exposure will result in a particular value chosen for all three. Making adjustments to any of them without changing in a related way others will result in an exposure with more light or one with less light than the original calculated exposure (we can pretend and call this the normal exposure for now). More light = overexposure; less light = underexposure from the "normal" one calculated. Note I'm not saying how this was calculated - you can use the camera meter, the sunny 16 rule, a light meter, etc.

Assume ISO is set to 100 and isn't changing (not set to AUTO ISO).
Assume the "normal" exposure calculated was 1/125s at f/8.
If you wanted to have less depth of field and were willing to adjust aperture - if you lowered f/8 to f/5.6 you would have increased the light by 1 "stop". This could be compensated by reducing the time of the shutter opening to 1/2 (every stop is based on this factor in time) so the new "normal" would be ISO 100, f/5.6, 1/250s. The same can be accomplished by moving the ISO so you could keep 1/125s if you adjusted to ISO 50 - but most cameras won't go that low. Alternatively if the original ISO had been 1600 and the same exposure you could lower it to 800. The only value that isn't adjusted in direct multiples of 2 is aperture which is based around ratios of openings and does relate back to 2x the light but the numbers are a bit weirder. In aperture 2x = 2 stops. So f/4 to f/8 is two stops with f/5.6 between.

It's a lot to absorb.

Neutral Density filters simply take away light and add the need for more stops of light to come from the camera so you can take a bright beach and shoot a long exposure with shallow depth of field if you want. The combinations are quite large but don't get overwhelmed. Start with the image you want to make, take a benchmark "normal" shot and look at the exposure parameters the camera set for you. Let's say it was ISO 1600, f/4, 1/250s. To get a blurred effect you might want a 1/2 sec exposure lets say. Adding light from 1/250 to 1/125 to 1/60 to 1/30 to 1/15 to 1/8 to 1/4 to 1/2 is a lot of stops (7 to be exact). You could drop from ISO 1600 to ISO 800 to ISO 400 to ISO 200 to ISO 100 (4 stops), then you could change aperture from f/4 to f/5.6 to f/8 to f/11 (3 more stops) to get the effect you wanted. (These numbers are just made up btw - the ratios are right but the numbers are just pulled out of thin air.)

Another important fact: time is in ratios of 1/time - so the larger numbers are smaller values. Aperture is a ratio of size of the opening to the focal length so again larger numbers represent smaller openings with less light admitted. ISO is a value that goes up with increased sensitivity so increasing ISO makes the needed light for a given exposure go down.

Higher ISO = higher noise (to a degree)
Higher Aperture = more depth of field, likely higher sharpness to a point and then loss of sharpness due to magical fun called diffraction
Higher shutter speeds = faster action can be stopped, flashes will not sync easily over a set value based on the camera, etc.

This is only scratching the surface.
Thank you so much for taking your time to really explain these concepts. These forums are so helpful for a beginner such as myself!

07-03-2018, 07:30 AM   #17
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There are actually two ways to do long exposures on a K-70. One way is traditional by using an ND filter (and either a timed exposure or remote triggering) and the other way is to use the built-in multiple exposure facility with averaging processing. (f.i. taking thirty one-second exposures and having the camera average them into the equivalent of one single 30 second exposure)
07-03-2018, 07:38 AM - 1 Like   #18
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QuoteOriginally posted by newmikey Quote
There are actually two ways to do long exposures on a K-70. One way is traditional by using an ND filter (and either a timed exposure or remote triggering) and the other way is to use the built-in multiple exposure facility with averaging processing. (f.i. taking thirty one-second exposures and having the camera average them into the equivalent of one single 30 second exposure)
Is there a good thread or tutorial on this feature? I've used it some but I'm not accomplished. I'd love to see more details on it on a Pentax centric article.
07-03-2018, 09:09 AM - 1 Like   #19
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One guide is set your camera to Av mode ISO auto range 100-3200 for indoor trials.
When you turn the edial it changes the speed.
Slow speed from .3 sec. to 6000 sec is shown and can be selected depending on the F number shown.

Or set to Tv mode to change only the speed you like.


Last edited by Penview52; 07-03-2018 at 09:18 AM. Reason: correction
07-03-2018, 10:04 AM   #20
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QuoteOriginally posted by Penview52 Quote
One guide is set your camera to Av mode ISO auto range 100-3200 for indoor trials.
When you turn the edial it changes the speed.
Slow speed from .3 sec. to 6000 sec is shown and can be selected depending on the F number shown.

Or set to Tv mode to change only the speed you like.
Confused... can't we set the lower bound shutter speed as low as 30 seconds?
07-03-2018, 10:19 AM - 1 Like   #21
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Waterfalls! Ok, here's some basics, using an ND filter
.
Equipment: Camera, Tripod, ND filter. ND filters allow less light to enter the camera. They are available as either fixed or variable. Starting out, the variable ones are handy since you won't know how much light you want to block. You'll likely get a circular one that screws onto the front of your lens. You need to look at the filter ring size that is printed on the front of your lens. For example, the 18-55mm lens requires a 52mm diameter filter. Or, the 18-135mm lens requires a 62mm. If you have more than one lens then decide which lens you are more likely to use for the waterfall photos and just buy the right size for that lens. These filters will usually vary between ND3 and ND400. ND3 only allows 1/3 of the light to pass through it. ND400 allows only 1/400th of the light to pass through it. You can set the variable filter to anywhere between these values. Note that you can also buy an ND filter that is fixed to just one value, like ND4.

Technique (there are many ways to do this but I'll give you one method to keep it simple):
1. Set your camera up on the tripod. Put it into the Self-Timer (2 sec) mode using the 4-way controller buttons (button to the right of OK button, watch on the screen and hit the right button twice, then down button, then right button, then OK). This prevents you from shaking the camera when you click the shutter. Do not mount the ND filter yet.
2. Turn the top dial to M mode (manual shutter and aperture). Hit the ISO button and rotate the little dial to the right of the viewfinder to set the ISO to a low number, like 100 or 200. Zoom your lens to the focal length that gives you the framing that you're looking for and compose the shot. Now you need to adjust the aperture to what you want by rotating the same dial that you used to adjust the ISO. If you aren't sure, then try something between F5.6 and F8.0. Now press the little green button on the top of the camera near the power on switch. That will set the shutter speed automatically. Take the photo, either through the viewfinder or in Live View.
3. Review the photo on-screen to make sure the exposure and focus are what you want. If not, make adjustments and take more photos until you're satisfied.
3. Switch the camera to manual focus (switch on the body to the left of the lens mount). Focusing can be a problem with ND filters so this ensures your shot will be good, as long as you don't change the zoom or move the camera. Mount the ND filter and adjust it to somewhere in the middle of its range of darkness.
4. The green button will set a slower shutter speed, but it may not be accurate. Use live view and judge the exposure by how it looks on-screen. If it's too dark or too light then rotate the dial just in front of and below the shutter button. This will change the shutter speed. When it looks good on screen then take the photo. Review the photo and make more adjustments to the shutter speed if necessary. Note that you can do this more precisely if you know the exact setting of your ND filter, but for now the Live View method will work just fine.
5. Do this again with the ND filter set lighter and darker. The darker it is, the smoother the water.
6. Some ND filters will change the colors in your photos. If this happens, you can use post processing software to adjust the colors back to normal. This is another reason why you took the first photo with no filter. It gives you a reference to adjust the colors. Again, there are other ways to adjust the color, but this will work for now.

Note that if the shutter needs to be slower than 30sec you will need to go into bulb mode. If all you want is to smooth the water out then you don't really need to go longer than 30s. If it is requiring more than 30s for proper exposure then you can either make your ND filter lighter, or use a higher ISO number, or use a numerically smaller aperture number. Also note that on a windy day trees and leaves will be moving so they will also be blurred. It then becomes a compromise between smoothing the water and keeping the leaves reasonably sharp.
Have fun with it!
07-03-2018, 12:40 PM   #22
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" ...Confused... can't we set the lower bound shutter speed as low as 30 seconds? "




In Av mode, choosing 1/30 seconds can be attained depending on the F number that it is in match, if not you can not attain 1/30 sec.
Example: at F 29 the speed is 1/25 sec. ISO auto, indoor trial.

07-03-2018, 01:02 PM   #23
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QuoteOriginally posted by Penview52 Quote
" ...Confused... can't we set the lower bound shutter speed as low as 30 seconds? "




In Av mode, choosing 1/30 seconds can be attained depending on the F number that it is in match, if not you can not attain 1/30 sec.
Example: at F 29 the speed is 1/25 sec. ISO auto, indoor trial.
I think we are talking at cross purposes. I'm sitting looking at my camera (K-3) set to ISO 100, with F stop set to f/29 and I am seeing 20 seconds - not 1/20th of a second. I often in the field at rational f/stops get 4 second exposures in Av mode. I'm really confused by what you are trying to say. I can place my hand close to the front of my indirectly lit room (lights are off outside sunlight is reflected off trees and sky etc.) and get 30 seconds without covering it completely.

AUTO iso is a whole different can of worms. It won't typically allow the shutter speed to fall that far if the ISO range can help it. In this light it immediately jumped to ISO 6400 and got me to between 0.3 seconds and 1 second.

EDIT: rereading the original post I'm not sure what slow speed 0.3 sec to 6000 seconds is representing. I can't get more than 30 seconds without using the bulb functions but I could be missing a feature. I misunderstood you I think originally.
07-03-2018, 03:03 PM - 1 Like   #24
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QuoteOriginally posted by steve_k Quote
Welcome. I would also recommend buying the K-70 eBook for sale on this site. It will explain a lot.
I second that. The book is a far better read than the Pentax manual.
07-04-2018, 08:17 AM   #25
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" Confused... can't we set the lower bound shutter speed as low as 30 seconds? "

You need to get out of the building under bright day and adjust two parameters: F stop and Speed to attain the desired speed with ISO auto.

No manual/catalogs that explain how to do this- search at youtube videos.
07-04-2018, 10:10 AM   #26
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QuoteOriginally posted by Penview52 Quote
" Confused... can't we set the lower bound shutter speed as low as 30 seconds? "

You need to get out of the building under bright day and adjust two parameters: F stop and Speed to attain the desired speed with ISO auto.

No manual/catalogs that explain how to do this- search at youtube videos.

You realize I have nearly 40 years of photographic experience and used many manual cameras including meterless one's right? See my signature for more detail.

The comment which was amended was because the post I responded to confused me into misreading it as having implied we couldn't get lower than 0.3 seconds in Av mode. I realized my confusion and corrected my post. I think you are now misreading me.
07-04-2018, 07:09 PM - 1 Like   #27
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QuoteOriginally posted by Qman Quote
Waterfalls! Ok, here's some basics, using an ND filter
.
Equipment: Camera, Tripod, ND filter. ND filters allow less light to enter the camera. They are available as either fixed or variable. Starting out, the variable ones are handy since you won't know how much light you want to block. You'll likely get a circular one that screws onto the front of your lens. You need to look at the filter ring size that is printed on the front of your lens. For example, the 18-55mm lens requires a 52mm diameter filter. Or, the 18-135mm lens requires a 62mm. If you have more than one lens then decide which lens you are more likely to use for the waterfall photos and just buy the right size for that lens. These filters will usually vary between ND3 and ND400. ND3 only allows 1/3 of the light to pass through it. ND400 allows only 1/400th of the light to pass through it. You can set the variable filter to anywhere between these values. Note that you can also buy an ND filter that is fixed to just one value, like ND4.

Technique (there are many ways to do this but I'll give you one method to keep it simple):
1. Set your camera up on the tripod. Put it into the Self-Timer (2 sec) mode using the 4-way controller buttons (button to the right of OK button, watch on the screen and hit the right button twice, then down button, then right button, then OK). This prevents you from shaking the camera when you click the shutter. Do not mount the ND filter yet.
2. Turn the top dial to M mode (manual shutter and aperture). Hit the ISO button and rotate the little dial to the right of the viewfinder to set the ISO to a low number, like 100 or 200. Zoom your lens to the focal length that gives you the framing that you're looking for and compose the shot. Now you need to adjust the aperture to what you want by rotating the same dial that you used to adjust the ISO. If you aren't sure, then try something between F5.6 and F8.0. Now press the little green button on the top of the camera near the power on switch. That will set the shutter speed automatically. Take the photo, either through the viewfinder or in Live View.
3. Review the photo on-screen to make sure the exposure and focus are what you want. If not, make adjustments and take more photos until you're satisfied.
3. Switch the camera to manual focus (switch on the body to the left of the lens mount). Focusing can be a problem with ND filters so this ensures your shot will be good, as long as you don't change the zoom or move the camera. Mount the ND filter and adjust it to somewhere in the middle of its range of darkness.
4. The green button will set a slower shutter speed, but it may not be accurate. Use live view and judge the exposure by how it looks on-screen. If it's too dark or too light then rotate the dial just in front of and below the shutter button. This will change the shutter speed. When it looks good on screen then take the photo. Review the photo and make more adjustments to the shutter speed if necessary. Note that you can do this more precisely if you know the exact setting of your ND filter, but for now the Live View method will work just fine.
5. Do this again with the ND filter set lighter and darker. The darker it is, the smoother the water.
6. Some ND filters will change the colors in your photos. If this happens, you can use post processing software to adjust the colors back to normal. This is another reason why you took the first photo with no filter. It gives you a reference to adjust the colors. Again, there are other ways to adjust the color, but this will work for now.

Note that if the shutter needs to be slower than 30sec you will need to go into bulb mode. If all you want is to smooth the water out then you don't really need to go longer than 30s. If it is requiring more than 30s for proper exposure then you can either make your ND filter lighter, or use a higher ISO number, or use a numerically smaller aperture number. Also note that on a windy day trees and leaves will be moving so they will also be blurred. It then becomes a compromise between smoothing the water and keeping the leaves reasonably sharp.
Have fun with it!
This post really helped me out! Thank you so much!
07-04-2018, 11:41 PM - 1 Like   #28
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Glad to hear it was useful. Let us know how it goes. If you don't have a filter yet you can still practice the steps so that you can see how the M mode and green button work. Ask questions if anything doesn't make sense.
07-06-2018, 02:03 PM - 1 Like   #29
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One word of caution on variable density round ND filters- as far as I have seen, nearly half the range produces a dark X pattern when used on wide angle lenses. I believe most of the tests I read produced significant issues below 35mm on APS-C cameras like the K70
07-06-2018, 07:49 PM   #30
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Very true. I haven't had the dreaded X on the 18-55. Either I have a good filter, or 18mm isn't wide enough. But for my 14mm I use a single density filter to avoid the X.
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