Aperture - Affect in apparent focus - Infinity

[bubbawny]

Hi friends:

I just got a Canon 5D Mark IV. Worked long and hard to save enough for it. The only lens I have for it ATM is the Canon EF 50mm F1.4 (an unbelievably sharp lens).

I went out the other night to do some low-light photography at the Buffalo Waterfront at and after sunset through the blue hour.

My settings varied from ISO 400 through 3200, F22 through F2.8, shutter speed various. Some of the shots came out great. Exposure was fine, noise was introduced at higher ISOs, obviously.

My question is regarding APERTURE specifically.

If I have my lens set on INFINITY (set via the window on the side of the lens), would a wider aperture affect apparent focus in distant subjects.

For example, I was standing about 100-150 YARDS away from the Buffalo Lighthouse. I adjusted for exposure mostly using aperture and ISO. Because sail boats were still going by, I want to have a fast enough shutter to not have motion blur.

As the blue hour crept in, I had to go to lower and lower ISO, ultimately down to about F2.8. (I don't go lower on this lens because CA is awful as it nears F2.0 and lower.).

When I look at the shots in Lightroom, the lighthouse when zoomed in seems out of focus.

So my question is really this:

With a subject > 100 yards away, will lower apertures reduce it's apparent focus?

This lens is incredibly sharp. As an amateur, it is without a doubt, the sharpest I've ever personally had.

But to me, the details on the lighthouse seemed soft even before i adjusted noise in post processing.

To be honest, the photos look really good in small form. But I guess what I'm trying to understand is how to have distant subjects in clearer (e.g., sharper) focus.

or is it a case where the focal range of the lens comes into play? I only have a 50 prime, so I've nothing to test against.

I guess what I'm getting at is how to have distant stationary subjects >100 yards away in a landscape shot have greater sharpness.

When I do candids with this lens, the sharpness is just stunning and unbelievable. But for mid-range landscape subjects, it's ok. Nothing to write home about.

Anyways, just trying to learn if I made a mistake on trying to keep a 100 yard + subject to be sharp by setting the aperture down to low? Should I have kept the Aperture at F8 or higher and simply adjusted Shutterspeed instead in order to get the lighthouse in greater sharp detail?

[DanK]

That lens should be quite sharp at f/2.8. How did you focus? What was the shutter speed, and did you use a tripod and remote release? Posting the image, with a link to the full-size image, and these details would make it more practical to figure out what is going on.

One guess: on many modern lenses (I don't own a copy of that one), the physical hard stop is not necessarily proper infinity focus.

[NorthernFocus]

...One guess: on many modern lenses (I don't own a copy of that one), the physical hard stop is not necessarily proper infinity focus.

Yes if you're focusing manually this may be an issue. This was mentioned recently in another thread. Modern lenses aren't really designed for manual focus, in spite of that feature being available to us. What you may be experiencing is simply DOF effects and the focus plane not actually being where you thought it was/intended for it to be. Playing around with a DOF calculator like the one here on CiC may be informative.

You may find it to be better technique to use the camera's AF and then switching to manual if you want to freeze focus. Or set up the camera to use "back button focus" and disable focus with the shutter release. That makes it easy to focus and recompose.

[Manfred M]

The old manual focus lenses had a hard stop at the infinity setting, which was set up and adjusted on an optical bench. Modern autofocus lenses with internal focusing motors use the lens markings as a general high level indicator and tend to be somewhat inaccurate. These lenses were never designed for you to use these focal distance markings for focusing and including them does lead to confusion as to what they are for.

If you want to validate the "exact" location of where the lens focuses on infinity, the best way to do so is to set your camera on a tripod and either use a single focus point on an "infinite" distance subject or use a magnified live view to achieve this. Note where the actual infinity focus occurs, as this should be consistent.

[bubbawny]

Thanks for the info.

I will attempt the shot again tonight or tomorrow night. I will use LIVE VIEW to try to identify and mark the location in the window as the infinity point, and to return to that marking when I am taking subsequent shots as the blue hour deepens. I will also set the "BACK BUTTON FOCUS". Been intending to. Just haven't gotten to it yet. I will also ensure use of a remote release/tripod. All the basics.

A quick use of the DOF calculator shows that this subject would be in the infinity area for all F-stops on my 50MM. So it still begs the question whether a low f-stop (F2.8) vs. a higher F-stop (f11+) would have the items in the INFINITY area in any greater focus?

Here's a sample of the photo I took. Sorry it's a low rez copy from my FB site. I'll have to get the original and upload it later along with the settings.

Note: I did use LR to do some post-processing: Set LENS correction (Distortion, etc.). Cropped a smidge (not much really). Adjusted luminence to reduce noice a bit. Can't remember what else.

When I took the shot, I did under-expose a bit. This was to increase color as described in "Understanding Exposure" by Bryan Peterson. I think this perhaps has been making it a bit harder for the camera to do autofocus. It doesn't hunt like my 70D does. But again, that's why I want to resort to ensuring I have the lens manually and precisely set for infinity.

FWIW, I'm just an amateur. Trying to learn through practice and study. I'm sure I'm making mistakes. But the more I come to know and understand, hopefully the better shots I get and the fewer mistakes I make due to ignorance.

[DanK]

A quick use of the DOF calculator shows that this subject would be in the infinity area for all F-stops on my 50MM. So it still begs the question whether a low f-stop (F2.8) vs. a higher F-stop (f11+) would have the items in the INFINITY area in any greater focus?

Stopping down will not give you any greater sharpness at the plane of focus. In fact, stopping down far enough will begin to reduce sharpness because of diffraction. Note that none of us gave you answers pointing to aperture. We all pointed to focusing errors. If you don't have a problem with the lens, I would bet that the problem is either that the plane of focus isn't where you want or that you have camera motion.

I don't think you will be able post a full-sized image here, but you can post a link to it.

[NorthernFocus]

...A quick use of the DOF calculator shows that this subject would be in the infinity area for all F-stops on my 50MM. So it still begs the question whether a low f-stop (F2.8) vs. a higher F-stop (f11+) would have the items in the INFINITY area in any greater focus?

Sorry I didn't articulate more clearly in recommending the DOF calculator. What I meant was to familiarize yourself with the concept by playing around with it. Focal plane means just that. There is a plane in space on which all objects are at optimum focus. EVERYTHING not on that plane is less than optimum focus that the capture system can produce.The DOF calculator is based on human perception when looking at an image printed at 8x10. If you are going to use full resolution "pixel peeping" as your standard or plan to produce very large prints then yes, smaller apertures will produce sharper results on objects farther from the focal plane. Though at some point diffraction may become an issue as DanK pointed out.

...When I took the shot, I did under-expose a bit... I think this perhaps has been making it a bit harder for the camera to do autofocus.

This won't affect focus on an optical viewfinder. The camera focuses at max aperture regardless of exposure setting. Not sure about live view depending on camera model.

[ajohnw]

There is another view on resolution and depth of field. Rather obscure but worth noting.

http://www.trenholm.org/hmmerk/DOFR.html

In your case say you focused precisely on the lighthouse the resolution can be calculated at that point and then at fractional distances that are nearer. In other words 1/2 the distance, 1/4 or what ever.

In some ways it's far more useful than hyperfocal distance.

John
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[Stagecoach]

Hi Bob,

For the shot you have posted I would ask why you chose not to use AF to determine focus on the lighthouse?

It is a perfect target for the AF system, and with your 50mm f/1.4 you should have been able to rely upon it totally.

Edit : Added

I would also question the 'usefulness' of trying to determine and mark the infinity position on your lens for general photography. What are you going to use as an 'infinity' target'?

As an example if I focus accurately on the moon (infinity?), subjects a few hundred yards away from the camera are going to be OOF. If I focus accurately on the sea horizon (infinity?), subjects nearer to the camera are going to be OOF, the amount varying dependent upon aperture.

With a modern lens it only requires minute rotation at the far end to make a drastic differences in focus of nearer objects.

As someone that has often shot in low (after/before sunset/sunrise) to extremely low (under the moon as the only source of light) I have found the best 'focusing' procedure is to focus on your closer subjects whilst having a reasonable knowledge of the DoFs you will attain at a few FLs and apertures. With this method it is far easier to get both near and far objects sharp.

[Manfred M]

Silly question; is this image from a raw or a jpeg?

If it comes from a raw, did you do any import sharpening to counter demosaicing / AA filter (I believe the Mk IV has one)? If not, might this be the issue?

[bubbawny]

So I went out again tonight. I put the 5DMKIV on a tripod. I got the device paired with my smart phone and used the EOS app to take shots...mainly using the smartphone as a wireless shutter release.

A couple things:

I am, I think at my knowledge limit here, regarding trying to get this lighthouse in better focus.

I let the LIVE VIEW determine the focus. While there was adquate light, the camera easily focused on the lighthouse. After the sun set and the blue hour kicked in, it did have some trouble.

Before I went out, I used live view to focus on distant trees on a hill, trees a couple hundred yards away, and trees about 50 yards away. Looking at the little window on the lens, each shot seemed to be precisely in the same point. And, as the one poster indicated, none of the shots focused at the INFINITY marker on the lens. They all were a couple millimeters shy. In fact, I could still spin the focus ring to move the marker to the INFINITY LINE and beyond (begging the question: Why can it travel past the infinity marker, and, what's the point anyways if the markers are not accurate?

In taking many progressive shots, I noticed that the lighthouse was in pretty good focus, though as I had to go to higher ISO, details quickly disappeared.

I love learning and doing low-light photography. But as I said, I'm probably beyond my knowledge depth here to make any sense of things at this point. The Live View seemed to help. But I don't know that the pictures really are any better.

In fact, in studying the photos, post-processing, the issue seems to be more of the ISO than anything. With ISOs 800 and up, the noise interefered with the details on the light house. Correcting for luminence noise in LR smoothed the details even further, as one would expect.

I'm going to post some of the RAW files some where for people to take a peak, and to share some thoughts. Again, I am an amateur trying to learn.

I also have to read up on PLANE OF FOCUS. I have a rudimentary understanding of it, and of hyperfocal distance, apparent focus and such. But I clearly do not understand how to calculate where the exact plane of focus will be for a given set of settings.

I'm not a glass freak, nor am I obsessed with "tack sharp" imagery. Just trying to learn how to get greater level of sharpness in low light.

Here's a couple shots from tonight. I'll get RAW files up somewhere to share so you can see the raw data and meta data.

I really appreciate all of you contributing towards my learning. It is very much appreciated. I know from past experiences, that the learning process takes work and time and effort. I am sure with my practice and study that I'll gain better knowledge and capability.

Not there yet. Don't expect it to be easy. Will keep persisting and keep at it!





and for fun...this is my son!

[Stagecoach]

Hi Bob,

Three questions first before going into any more details;

a) In processing and downloading these three images, have you applied any sharpening procedures if they were RAW files? ( refer to Manfred's question)

b) What were the settings of each image, Speed, Aperture and ISO?

c) With these two boat pics where did you focus the camera on?

Edit :

When I do candids with this lens, the sharpness is just stunning and unbelievable. But for mid-range landscape subjects, it's ok. Nothing to write home about.

This initial comment is confusing things a bit at present because I would assume you are using the same PP procedure roughly for all your images

Further thoughts and diagnosis;

a) Minor sharpening to theses Jpegs makes a considerable improvement to their apparent sharpness.

b) The depth of focus, determined by aperture used, in these two lighthouse images in this light condition along with the shutter speed to freeze the boat movement would have required a high ISO. A high ISO is not your friend when trying to achieve a sharp final image, but unavoidable at times.

c) Atmospherics when shooting over water can affect sharpness.

[Manfred M]

I let the LIVE VIEW determine the focus. While there was adquate light, the camera easily focused on the lighthouse. After the sun set and the blue hour kicked in, it did have some trouble.

There are two ways to use LiveView to focus. The first is to use the contrast detect, as you appear to have done. This is slower, but generally more accurate than the phase detect when you look through the camera's viewfinder. Because it relies on contrast, it does not work well in low light.

The second way it is used and is the "best" way to do low light photography is to use it for manual focusing. Increase the magnification until you get a clear view of part of your subject (likely somewhere near the light on the lighthouse and manually focus until this is sharp. The magnification might look noisy / grainy, but it's pretty easy to see when the focus is sharpest. Short of shooting tethered, this is the best focus method you are likely to get in low light shooting.

Before I went out, I used live view to focus on distant trees on a hill, trees a couple hundred yards away, and trees about 50 yards away. Looking at the little window on the lens, each shot seemed to be precisely in the same point. And, as the one poster indicated, none of the shots focused at the INFINITY marker on the lens. They all were a couple millimeters shy. In fact, I could still spin the focus ring to move the marker to the INFINITY LINE and beyond (begging the question: Why can it travel past the infinity marker, and, what's the point anyways if the markers are not accurate?

Good question for the camera manufacturers regarding why they have markings. Some low end lenses don't.

The reason for this running past the infinity mark is a cost savings for the camera / lens maker. Old lenses with a hard stop had an additional manufacturing step during lens assembly where the lenses were manually calibrated on an optical bench with electronic measuring equipment and the hard stop was set this way. With autofocus, the manufacturers let the lens figure this out using autofocus to figure this out. It works in most shooting conditions and the method I suggested above works in low light.

In taking many progressive shots, I noticed that the lighthouse was in pretty good focus, though as I had to go to higher ISO, details quickly disappeared.

The base ISO gives you the highest dynamic range, highest colour depth and lowest noise. Crank up the gain (which is all that is really happening when you increase ISO), the image quality starts to deteriorate.

In fact, in studying the photos, post-processing, the issue seems to be more of the ISO than anything. With ISOs 800 and up, the noise interefered with the details on the light house. Correcting for luminence noise in LR smoothed the details even further, as one would expect.

While noise reduction algorithms have gotten better, they all use a technique often referred to as pixel smearing to some extent. Apply noise reduction and you will get a slightly less sharp image. A good workflow is to apply noise reduction to the raw data with NO sharpening and then sharpen the image in PP after import. That way you are not sharpening the noise.

I'm going to post some of the RAW files some where for people to take a peak, and to share some thoughts. Again, I am an amateur trying to learn.

Raw files are data and have to be converted to image files for people to see them. Nicely said, posting raw data won't work. Sending someone raw files through some other means (email, DropBox, etc.) is the only way I know of sharing raw files.

I also have to read up on PLANE OF FOCUS. I have a rudimentary understanding of it, and of hyperfocal distance, apparent focus and such. But I clearly do not understand how to calculate where the exact plane of focus will be for a given set of settings.

You've got that a bit backwards. The focusing operation, whether you set it with autofocus or manually defines the focus plant. Everything else falls out from that move.

[NorthernFocus]

Cute pooch.

[bubbawny]

The second way it is used and is the "best" way to do low light photography is to use it for manual focusing. Increase the magnification until you get a clear view of part of your subject (likely somewhere near the light on the lighthouse and manually focus until this is sharp. The magnification might look noisy / grainy, but it's pretty easy to see when the focus is sharpest. Short of shooting tethered, this is the best focus method you are likely to get in low light shooting.

Wow...that's really a good idea! I never would have thought of that.

I'm 52 and have presbyopia. Looking through the viewfinder and trying to focus is not easy because the view port is difficult for me to see. Looking on the back screen (or on the iPhone with the phone connected) with Live View is turning out to be very helpful.

i was reading up on blue hour photography. Seems like the general approach is mid-range F-stop (f8-f11), low ISO, long shutter (3 seconds plus). I'll have to experiment some more.

FWIW, I wanted to say how much I appreciated the time you took to share what you did throughout this thread. It was very valuable. I genuinely appreciate you taking the time to help impart some knowledge!

[Manfred M]

Wow...that's really a good idea! I never would have thought of that.

I didn't think of it either, but the technique was suggested to me by another member here at CiC

I'm 52 and have presbyopia. Looking through the viewfinder and trying to focus is not easy because the view port is difficult for me to see. Looking on the back screen (or on the iPhone with the phone connected) with Live View is turning out to be very helpful.

You are not alone with that issue (I've been wearing glasses for over 50 years and have 10 years on you) so can appreciate what you are saying. The real issue is that there are ways to work around issues like presbyopia with a bit of practice. I find a smart phone screen and the screen on the back of the camera to be roughly equivalent. A tablet or laptop are even better, but the laptop works better in studio work.

i was reading up on blue hour photography. Seems like the general approach is mid-range F-stop (f8-f11), low ISO, long shutter (3 seconds plus). I'll have to experiment some more.

Low ISO, I agree with. I very rarely shoot at below f/8 and if I am shooting with an ultra wide angle lens, I will often shoot at f/4 or even wide open. It really depends on the focal length I am using and how I have framed my subject. The shutter speed is really an outcome of the aperture I have chosen to shoot with and the ISO I decided to use. A good sturdy tripod is also very important. If your camera supports "mirror up" shooting, it can help with those types of shutter speeds too.

FWIW, I wanted to say how much I appreciated the time you took to share what you did throughout this thread. It was very valuable. I genuinely appreciate you taking the time to help impart some knowledge!

No problem. This is a learning site and I think you have noticed that the members here are more than will to share ideas and try to help.


Here is a blue hour pano I did a few months ago (right at the end of blue hour). ISO 100, f/8 36mm focal length (FF camera) and 2 sec exposure. I seem to remember this was about 10 stitched images. Some of the ideas I shared with you, including the focusing technique, were used when I took this image.

[bubbawny]

Stunning photo! Thanks for sharing!

Pano...now there's an idea! Having only a 50MM prime with a narrower FOV, I'll have to give that a shot. I used to have a Ultra Wide lens, but is EF-S and doesn't work with 5DMKIV. Saving up for Ultra Wide. But that's months away.

Seriously, though I'll have to really think about a pano shot or two to begin exploring. The lighthouse shots of the Buffalo Waterfront really call for it. Where the lighthouse sits, and where you can stand to get a shot, leaves the setting sun out off the frame to the right. But with a pano shot and some stitching, well perhaps I can pull it together!

Tonight, I think, will be the end of the unusual summer-like weather here in Buffalo. We've been in the low 90F. Normally, it's high 60s. So I've been enjoying getting out and pretending it's summer! (I loathe winter! But I live in Buffalo and there's no getting around the coming cold and snow! Just have to hang in there and wait until next Spring!) Tonight will be a nice night for some more captures and practice!




Really appreciate you taking the time!

[Thlayle]

Bob,

I will suggest a couple of ideas that may be relevant, and hopefully not too redundant, given all the other great advice already given.

I am also an amateur and I do a lot of low light and nighttime shooting. I am shooting with a Canon T2i and for most of my shots like this one and ones after twilight hours have passed, I use a 14 mm, f2.8 and focus manually (I have to; it's a Roknion a though excellent for astrophotography it doesn't sync with the auto settings on my camera).

No matter what lens I am using though, I have found the infinity setting to NOT work for me. With the 14mm I am using, I pretty much can hit the hyperfocal and that does it for me. But again, I seem to almost never use the infinity setting with any of my lenses.

Also, someone asked about ALL of your settings, including the shutter speed. With low light shots and long exposures, there's of course the issue of any vibrations or small movements, even with a tripod. And if you are using a tripod, turn off the image stabilization. I can say both from experience, and the directions that came with my lenses (that I only read AFTER having issues), that not turning off the image stabilization when using the tripod has a high likelihood of messing things up.

Then I think you can sometimes get other problems that I think are somehow attributable to "atmosphere" -- especially in urban settings. I know many others here at CIC can comment on whether or not, or how, this comes into play. I believe temperature gradients, wind, and air pollution all can influence how sharp the shot will look when you are out there.

Randy

[Pica]

Hello Manfred,
Some sunshine from Scandinavia to you:

I want to convey that I have had my camera in front of me and tried the method of manual focusing with the use of LiveView right now. Background is that I have been contemplating the matter of focusing when capturing seascape here at low light.

Appreciate this hot tip. Hope this information makes you glad to learn.

Regards Pica

There are two ways to use LiveView to focus. ...

The second way it is used and is the "best" way to do low light photography is to use it for manual focusing. Increase the magnification until you get a clear view of part of your subject (likely somewhere near the light on the lighthouse and manually focus until this is sharp. The magnification might look noisy / grainy, but it's pretty easy to see when the focus is sharpest. Short of shooting tethered, this is the best focus method you are likely to get in low light shooting.

[dem]

But I clearly do not understand how to calculate where the exact plane of focus will be for a given set of settings...

You don't calculate it, you just focus on what you want to be in focus - the plane is going to run through your subject parallel to the sensor. Then you can use the distance to this plane as an input for camera-subject distance in one of these DOF calculators to calculate how far away from the plane things are still going to look sharp. Do not rely on the calculators too much though because their idea of acceptable sharpness (normally defined by a circle of confusion hidden somewhere in the settings) might not be the same as yours.

A steady tripod, mirror lock up, remote release, OIS is off, low ISO and you are good to go. The second example you have posted looks like it is all working for you now. Panoramas next