Canon 300hs and *HUGE* f-stop/aperture numbers

I thought I would make a new thread on the topic of the Canon 300hs apparently choosing ridiculously high f-stop numbers (like f14) when most Canons will not go above f8.0, causing very very soft images due to diffraction.

Original post -

Jinwons said:

I'm not that impressed by outdoor shots of 300HS so far. I get 2~3 somewhat blurry or soft shots out of 10 shots despite my best effort to hold it steady and messing around with AF, IS settings. Even the good sharp shots fall short of my ZS7 in details, sharpness a bit. Maybe I'm so used to seeing excellent outdoor shots of ZS7.
...

...then I realized that some of them got very low lens speeds like F/11~F/14. Looks like 300HS has its own mind on choosing lens, shutter speed. Sometimes it does high F/number, slow shutter and the other times it does low F/number, fast shutter speed combination even at the same shooting location. Although the total exposure is similar, bigger F/number+slow shutter speed causes soft images due to bigger diffraction spot and longer exposure. Unfortunately there is no way to control this behavior as 300HS doesn't have ASM modes.

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I was going to the camera store (National Camera Exchange) to look at some other stuff, so I thought I would check this out while I was there. I grabbed a 300hs and tried to reproduce these absurdly high apertures.

I couldn't get it to do it at all, initially. It wouldn't go above f8.0. I went as far as setting the camera to spot focus, small focus area, and pointing it directly at a light - it (correctly) wouldn't do it. In this photo I used pointed the 300hs at an LED light I keep in my pocket and the camera maxed out at 1/2000 f8.0 iso100 and wouldn't bump up aperture up above that at all (actually I didn't get it in the picture, but just before this the text turned orange suggesting the camera couldn't go above this) -





It would not go above f8.0 no matter what I was pointing the camera at.

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Here's what's funny - when I wrote this:

PaulRivers said:

My point was the it's very weird for a Canon to do that...

Every now and then there's some weird bug where, like, you set the white balance to tungsten and it incidentally changes some other settings that means you get super high apertures or something. I was just suggesting doing "reset all" then trying it out and seeing if you got the same behavior.

It's not impossible that it's a faulty one, but in my opinion that kind of behavior is usually a firmware bug that affects all of the same model, not something that just went wrong with your unit.

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I'm take a second to mention that the other poster wrote back -

Jinwons said:

Regarding the settings in 300HS that might cause this, I don't think your guess makes sensor much to explain it. I've only used smart auto for some and predominantly P mode with only focus, EV, icontrast changed. P mode still does automatic exposure with ISO, lens speed, exposure time no matter how we change other settings in there. Anyway I did reset and made a few changes on focus, ev and it's back the same setting basically. Doesn't make any differences. I believe this is firmware bug at least in my 300HS.

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Obviously he felt my guess that changing some sort of setting doesn't even make much sense!

...though, it sounds like he did try it, and he uploaded photos, so I can't give him to much crap, and thus I'm also writing back. :-D

I was finally able to reproduce the bizarrely high f-stop readings - by using the zoom. As soon as I started zooming, suddenly the camera was more than happy to jump up to absurdly high f-stops just as Jinwons had pointed out -









I'd like to hear back from other people who own a 300hs - do you find the same thing? Does the f-stop stay reasonable (f8.0 and below) when you don't zoom, but jumps up above that in bright light when you do zoom?

For reference, here's the original thread -
http://forums.dpreview.com/forums/readflat.asp?forum=1010&thread=38249204&page=2

And here's a thread with pics showing the effects of diffraction on the s95, a totally different camera, but since you can see the effects at f8.0 you can imagine how bad they get by f14 -

http://forums.dpreview.com/forums/readflat.asp?forum=1010&message=37655165&changemode=1

I appreciate your taking time with 300HS to find out this. Basically what you found is that 300HS has 8.0 max f/number (min aperture) at wide and 17.0 at telephoto end. Canon says 2.7 min f/no (max aperture) at wide and 5.9 at telephoto. Most manufacturer's don't state max f/number (min aperture) range of lens, only max aperture range from wide to telephoto.

Your finding simply means that 300HS lens stop can vary from 2.7 to 8.0 at wide and from 5.9 to 17.0 at telephoto end. It's good to know this info. But it doesn't really explain why 300HS sometimes chooses high f/number rather than small f/number at certain focal length under bright outdoor. I reviewed my samples with high f/numbers and they are mostly taken at 2X~3X zoom with f/numbers 11 to 14. So this fall in the range of max f/numbers you found. I also got some f/8.0 shots from wide end of zoom as it's the max f/number it can get at wide end.

So I still think that iContrast was the main reason behind this high f/number (slow lens stop) exposures under bright outdoors. I noticed that it impacts the exposure parameters like ISO, shutter speed too. Panasonic does only post processing with iExposure, not really varying the actual exposure parameters. But iContrast in Canon seems to vary exposure parameters and it sometimes choose slow lens stop in doing so.

Jinwons said:

I appreciate your taking time with 300HS to find out this. Basically what you found is that 300HS has 8.0 max f/number (min aperture) at wide and 17.0 at telephoto end. Canon says 2.7 min f/no (max aperture) at wide and 5.9 at telephoto. Most manufacturer's don't state max f/number (min aperture) range of lens, only max aperture range from wide to telephoto.

Your finding simply means that 300HS lens stop can vary from 2.7 to 8.0 at wide and from 5.9 to 17.0 at telephoto end. It's good to know this info. But it doesn't really explain why 300HS sometimes chooses high f/number rather than small f/number at certain focal length under bright outdoor. I reviewed my samples with high f/numbers and they are mostly taken at 2X~3X zoom with f/numbers 11 to 14. So this fall in the range of max f/numbers you found. I also got some f/8.0 shots from wide end of zoom as it's the max f/number it can get at wide end.

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Could you please list at least one model of compact camera that behaves that way?

I haven't seen one, I've never seen that be the case. For both my Canon s90 and s95 f8.0 is the max, and it doesn't matter how much you zoom at all - f8.0 is the uniformly the largest number you can get regardless of whether you're at wide angle or at fully zoomed - I even just double checked in aperture priority mode.

Here's a link to another Canon camera that's of a cheaper / lower class than the s95, the sd4000 -

http://www.usa.canon.com/cusa/consumer/products/cameras/digital_cameras/powershot_sd4000_is#Specifications

Maximum Aperture
f/2.0 (W) / f/5.3 (T)
The following f/numbers are available in Av:

W: f/2.0/2.2/2.5/2.8/3.2/3.5/4.0/4.5/5.0/5.6/6.3/7.1/ 8.0
T: f/5.3/5.6/6.3/7.1/ 8.0

Notice that at both wide angle and telephoto, the maximum aperture priority you can get is f8.0.

Since you replied in the other thread that your idea is "not new stuff to anyone with basic understanding on the camera lens", I feel an obligation to respond that perhaps you've never actually tried it on a compact camera before?

I haven't seen a Canon compact that will ever go above f8.0 no matter how you're zoomed before, assumably because of the issues you've seen in your photos - diffraction starts to overwhelm the image quality above f8.0 on a compact. In my opinion this is a bug, and that bug is that the camera isn't supposed to go above f8.0 but it does.

Jinwons said:

So I still think that iContrast was the main reason behind this high f/number (slow lens stop) exposures under bright outdoors. I noticed that it impacts the exposure parameters like ISO, shutter speed too. Panasonic does only post processing with iExposure, not really varying the actual exposure parameters. But iContrast in Canon seems to vary exposure parameters and it sometimes choose slow lens stop in doing so.

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If iContrast was the problem, then turning off iContrast would eliminate all instance of the f-stop number going above f8.0. But it either just reduces it - or you just didn't zoom as much on your second trip out.

I don't think you really understand the definition of lens aperture stop number. In case you didn't know, it defined as effective focal length divided by physical stop diameter. So for the fixed lens stop diameter, it's always bigger at telephoto because focal length is longer.

This is how it works in principle you can't argue with. I don't know why Canon made S95, SD4000 in such way that it doesn't go beyond F/8.0 even at telephoto end. But I know plenty of other brand P&S that can go way above F/10.0 at telephoto including my ZS7, WX9. If you are curious, just ask any one with Sony, Panasonic P&S. Looks like your experience is limited to Canon. This is nothing new to me. But being able to go above f/10.0 doesn't mean that camera should use that always unless it's pointed at bright sources.

Jinwons said:

I don't think you really understand the definition of lens aperture stop number. In case you didn't know, it defined as effective focal length divided by physical stop diameter. So for the fixed lens stop diameter, it's always bigger at telephoto because focal length is longer.

This is how it works in principle you can't argue with. I don't know why Canon made S95, SD4000 in such way that it doesn't go beyond F/8.0 even at telephoto end. But I know plenty of other brand P&S that can go way above F/10.0 at telephoto including my ZS7, WX9. If you are curious, just ask any one with Sony, Panasonic P&S. Looks like your experience is limited to Canon. This is nothing new to me. But being able to go above f/10.0 doesn't mean that camera should use that always unless it's pointed at bright sources.

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I don't know what we'd be disagreeing about then. You're taking an argumentative tone, but saying nearly the same thing that I'm saying - that the camera shouldn't be choosing high f-stop values when it could raise the shutter speed instead, because doing so is resulting in unnecessarily soft photos. That's - almost exactly what I'm saying as well.

My point is that no other Canon compacts that I know of will go above f8.0 regardless of how much or little you zoom - assumably exactly because of the diffraction issue you are experiencing in your photos. Whether a lens itself is capable of going up farther is really rather irrelevant - based on the both that this is causing serious softness issues, and that no other Canon's behave in this way, I think it's a bug in the firmware that allows the camera to do this. It's either that, or it is totally new behavior for Canon cameras.

Either way, as shown by your original post and subsequent "soft" pictures, the camera really shouldn't be doing this.

Sigh~, you really think I was taking argumentative tone? Look at our previous comments exchanged to see who was doing that.

Anyhow I just rechecked my ZS7 lens stop range in A-priority mode and it also stops at 4.9 at telephoto end the, same as wide end. Pansonic site says so. But from my experience it can definitely shoot above F/10.0 in P mode if there are very bright spots in frame. This tells me that camera can stop down further beyond the A-mode spec range if it senses bright spots to help with DR and prevent sensor damage. I got the similar experiences with Sony, Samsung cams too. It's a bit surprising to me that Canons would never go above f/8.0 no matter what. It maybe so in the spec, but what about real world? Are you 100% certain that it will stop at f/8.0 in auto or P mode even on extreme bright scene?

Jinwons said:

Sigh~, you really think I was taking argumentative tone? Look at our previous comments exchanged to see who was doing that.

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That is entirely possible, and my apologies if I did. I need a new laptop, and I've been reading through a 227 page thread on the model I'm looking at, and it may have resulted in my replies being kind of terse and ending up sounding confrontational. I also have seen a number of times where someone suggests something (like try turning off iContrast), and someone comes back and says "oh that solved it!" when it didn't solve it at all, they just didn't do the thing that made the problem happen for that test run - that person who's done that has sometimes been me. lol, maybe it makes me kind of terse just thinking about having done it myself. And reading through 227 pages of info makes me feel...a little uptight, lol.

Anyways, I'll try to write less like that. :-D No "for sure" promises until next week when I get done with laptop ordering, haha.

Jinwons said:

Anyhow I just rechecked my ZS7 lens stop range in A-priority mode and it also stops at 4.9 at telephoto end the, same as wide end.

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I'm not sure I'm correctly understanding what you mean here - you mean it won't go above f4.9? Like, it won't do f8.0?

Jinwons said:

Pansonic site says so. But from my experience it can definitely shoot above F/10.0 in P mode if there are very bright spots in frame. This tells me that camera can stop down further beyond the A-mode spec range if it senses bright spots to help with DR and prevent sensor damage. I got the similar experiences with Sony, Samsung cams too. It's a bit surprising to me that Canons would never go above f/8.0 no matter what. It maybe so in the spec, but what about real world? Are you 100% certain that it will stop at f/8.0 in auto or P mode even on extreme bright scene?

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I am 100% certain that on my s90 and s95, the aperture will never go above f8.0 in P mode, yes. Actually...to be fair, I guess technically it's like 99% certain, lol, since I'm not going back through my entire collection of photos to check...but I took shots on the beach in Mexico where it was very, very bright, and at both wide angle and full zoom, and the aperture would not go above f8.0, despite the other settings being iso80 and about 1/400. The reason I know they didn't is because I noticed unusual softness to the photos at 100% so I was going through the pictures specs and checking out the aperture it used.

I was actually kind of annoyed with the camera as it should have lowered the aperture and raised the shutter speed and my images would have been a little sharper.

The exposure limit on the s90 (and s95) is iso80 f8.0 1/1600. I have never encountered light so bright that the camera has reached this limit - iso80 f8.0 and 1/500 in Mexico was about the brightest I've ever encountered. Maybe I should try shooting into the headlights of my car, haha...hmm.

(continued below)

PaulRivers said:

PaulRivers said:

Pansonic site says so. But from my experience it can definitely shoot above F/10.0 in P mode if there are very bright spots in frame. This tells me that camera can stop down further beyond the A-mode spec range if it senses bright spots to help with DR and prevent sensor damage.

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This is one of those points where I'm afraid I'll sound argumentative...

With Canon at least, I've read repeatedly that if you install "CHDK" you can access hugely faster shutter speeds than you can otherwise get on your camera on any Canon compact. I think it tops off around 1/100,000 - though I'm not sure on that one. I know it's way bigger than the 1/1600 or 1/2000 you usually get.

Regarding exposure, protecting the sensor, dynamic range, etc, as far as I know you have two choices -

1. Increase the shutter speed. This really doesn't have any negative side effects once the shutter speed has reached like 1/250 anyways (I mean that it's a very rare shot where there's any difference in the photo between 1/250 and say 1/4000 - you've already frozen all the action anyways).

2. Close down the aperture. This increases the depth of field in the pic (though on a compact it's often huge already so, like increasing shutter speed, this often doesn't have any practical effect). But it also makes the image softer once you get beyond the ideal aperture for the lens (about f4.0 on a lot of compacts).

My point is that I don't know why the camera would choose to close the aperture beyond it's normal limit to protect the sensor. And I don't think changing the aperture would help with dynamic range any more or less than choosing a better shutter speed would...you know? The camera is almost certainly capable of both higher shutter speeds and smaller apertures than it allows you to set. Better choice would be to up the shutter speed, as far as I know.

I think I had a point with that...but I lost it. Hmm.

I think what we agree on is -
1. When you're not zoomed at all, the camera will not go above f8.0.

2. When you do zoom, the camera goes above f8.0 and I think we both agree the 300hs does so necessarily - there's no need to go to f11.0 when the shutter speed is only 1/250, on a camera where the shutter speed can go as high as 1/2,000.

3. This results in soft, blurry pictures which would be sharp given the conditions if the camera had chosen to use better apertures.

So I think we both agree that the camera choosing these large apertures, under the conditions you're shooting in is bad, or buggy behavior.

In my opinion, since all the other Canon's I know of are limited to f8.0 regardless of zoom range, as well as because I think it is odd it is limited to f8.0 at wide angle, but higher f-stops once you start zooming (I do realize the lens might physically only do f8.0 at wide but do other apertures at other zoom levels, but I just think that is very odd that it's the usual f8.0 limit at wide angle) I think it's some sort of bug where they somehow missed testing the max aperture once you started zooming. I do realize your point about the lens doing different apertures at different zoom lengths, it's not that I think that is not possible, it's that other Canon compacts do not behave in this way (and since behaving this ways is obviously causing problems, that was your original problem, I don't think it's just something they decided they would change for fun or something, you know?).

The ZS7 is limited to f/6.3 at all zoom settings. When zooming, the aperture doesn't suddenly close down either.

Jinwons said:

But I know plenty of other brand P&S that can go way above F/10.0 at telephoto including my ZS7

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Diffraction is controlled by aperture diameter and the diameter is bigger at telephoto.

PaulRivers said:

In my opinion, since all the other Canon's I know of are limited to f8.0 regardless of zoom range, as well as because I think it is odd it is limited to f8.0 at wide angle, but higher f-stops once you start zooming (I do realize the lens might physically only do f8.0 at wide but do other apertures at other zoom levels, but I just think that is very odd that it's the usual f8.0 limit at wide angle)

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http://www.flickr.com/photos/techoutsider

Those are probably "effective" aperture numbers. Meaning they slide out an ND filter rather than changing the iris. No need to worry much about diffraction. It seems like lots of these tiny cameras do this trick. If you want to test it, point the camera at a bright light source and listen for the click. On my Panasonic FX30 I could actually see the filter sliding into place. You might even see "ND" displayed on the screen (my SD4000 does this).

OK. I pretty much agree on everything of what you said in long posts. I will answer couple questions for you that I didn't make clear. Also I admit that I was wrong on how ZS7 behaves with zoom.

What I meant for ZS7 stopping at F/4.9 is that it's the max aperture setting at the telephoto end in A-priority mode. It can go up to F/6.3 in both wide end and telephoto, similar to S95 going up to 8.0 from both end of zoom.

But I was wrong in saying that ZS7 can shoot above F/10.0. Like TechOutsider pointed out, ZS7 never goes above F/6.3 at any optical zoom. I got some high F/number shots from Samsung P&S (SL720, WB600) and mistook some of them as Panasonic pictures. Sorry about my error. Hmm, so it's good to know that even Panasonic travel zoom camera behaves like Canon S95 regarding F/number vs zoom focal length. Anyway my 300HS surely behaves differently with F/number range going up with focal length. I believe most Sony, Samsung cams are behaving this way too. I wonder if new Canon siblings to 300HS like 500HS, 100HS behave this way too as they are very similar except slight difference in lens.

Finally to double check this findings to test, I just took my 300HS and ZS7 to my parking lot and pointed them toward far hill over canyon on the west side of where I live at around 6pm. Sun was just above the frame on the sky, so the scene was very bright from sun light. I focused on the hill with max telephoto in two cameras. As I expected my 300HS took telephoto shot with F/17! But my ZS7 took telephoto shot at F/6.3.

It's nice to see you chime in! A Panasonic expert.

TechOutsider said:

The ZS7 is limited to f/6.3 at all zoom settings. When zooming, the aperture doesn't suddenly close down either.

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You are right. I admitted my mistake to OP as well. I also tested it by shooting at bright hill this evening.

TechOutsider said:

Diffraction is controlled by aperture diameter and the diameter is bigger at telephoto.
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http://www.flickr.com/photos/techoutsider

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For plane aperture diffraction, yes only diameter of hole matters. But for focusing lens like in camera, it's actually F/number that determines diffraction spot size at focal plane. It's linearly proportional to F/number.

Jinwons said:

As I expected my 300HS took telephoto shot with F/17! But my ZS7 took telephoto shot at F/6.3.

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Well I think we both agree that that is messed up behavior. The Canon is doing something unwanted (and unusual for a Canon compact) by choosing such huge apertures when clearly it could raise the shutter speed.

PaulRivers said:

Jinwons said:

As I expected my 300HS took telephoto shot with F/17! But my ZS7 took telephoto shot at F/6.3.

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Well I think we both agree that that is messed up behavior. The Canon is doing something unwanted (and unusual for a Canon compact) by choosing such huge apertures when clearly it could raise the shutter speed.

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It's unusual behavior for Canon and possibly Panasonic too as ZS7 is this way apparently. However, I have seen others like Samsung, Sony cams doing this before, shooting above F/10 under bright outdoors. I have those shots and can post here too. So it's a little less surprising to me than you. My gripe with 300HS was just that rate of it choosing high F/number seems a bit higher than normal with icontrast. Now that I keep iContrast off, chance of doing that is lower though it still does that for very bright objects as both you and I verified.

I read somewhere that Sony is using ND filter type of aperture to reduce the intensity on sensor to level of equivalent F/numbers. This way it reduces light intensity on sensor but doesn't actually reduce physical stop diameter to cause diffraction issue. My Sony WX9 does predominantly high F/number shots > F/10 under bright outdoors, but it goes below F/3.0 most of time indoors. Sony spec site says that it has hybrid stop consisting of physical iris and ND filters. So I guess that it might be using ND filters to reduce light intensity to effectively high F/numbers without causing severe diffraction. Since these new Canons (100HS, 300HS, 500HS) are employing the same type of CMOS 1/2.33" sensor, I think it's possible that Canon implemented similar kind of lens stop in them.