Gary's Parries 15/10/06

October 15, 2006 | Mark Goldstein | Gary's Parries | Comment |

Gary's ParriesThis week’s Gary’s Parries topics are:

1. Getting Close With Add-On Lenses
2. Electronic Shutters In Full Bloom
3. Picassa Ducks Out On DVD Recording

Introducing this week’s Gary’s Parries column. Everything you always wanted to know about digital cameras, but were afraid to ask. No question too difficult, or too easy. As a Senior Principal Software Engineer, and a former Assistant Professor of Computer Information Systems, as well as a recording studio owner/operator, inventor, and now, a digital camera enthusiast, GARY has more digital camera knowledge in his entire brain than most people have in their little finger. In the unlikely event that GARY would not know the answer to your question, he will answer it anyway, true to the spirit of the word “Parries”, a fencing term which, in this context, implies “cleverly evasive answers”. So let your imagination run wild. Email all your nagging digital camera questions to: [email protected] , and then, En Garde!

You may also attach to your email an ORIGINAL PHOTO of your choosing. A preview of the photo will be displayed with your question, and a full-sized version will be just a click away. No personal information will be published with your question unless you specifically include it in the text or attached photo of your email, which may be further edited for grammar, content, or other reasons.


garys_parries_151006_q1.jpgHi Gary,

Try this question out for size!

I have used add-on wide-angle and 2x telephoto lens converters on my Canon PowerShot A95, without being impressed with the results. Will I ever get good results with these add-on lenses?

Currently I have a Panasonic Lumix DMC-FZ30, which is giving me great results, but lacks wide-angle so I am thinking of getting one for it.

Ian Copple

“When you read this and smell the coffee that’s Synaesthesia!”

*** ANSWER 1

Great tasting question, Ian. :)

As you may or may not be aware, all converter (a.k.a. add-on) lenses will cause some loss of image sharpness and contrast, but depending on the quality of the lens, this is usually minimal. However, without knowing more about the types of converters you are using, as well as about the specific problems you are having using them with your Canon A95, I will have to answer your question in the general case.

There are four types of problems that typically occur with converter lenses:
(1) Images appear soft
(2) Images exhibit barrel distortion
(3) Images exhibit vignetting
(4) Images exhibit unexpected shadow areas

Problem (1) - Image softness can be caused by improper spacing between the camera lens and the converter lens. If you are using only A95 factory accessories, namely, the Canon LA-DC52D converter lens adapter, Canon WC-DC52C 0.7x wide converter lens, and Canon TC-DC52A 1.75x tele-converter lens, improper spacing is unlikely. However, since you are using a 2x tele-converter, which is NOT an A95 factory accessory, image softness is a very likely possibility.

Fortunately, there are custom spacers you can purchase to adapt alternative converter lenses to your A95. To see an example of the effectiveness of such spacers, check out these LensMate A95 webpages for the Raynox 6600 .66x Wide Converter and Canon TC-DC52 2.4x Tele-Converter (made for A70).

Problem (2) - Barrel distortion, where the normally straight lines of an image appear curved, is a result of the curved surfaces of the lens elements causing different parts of the image to be reproduced with slightly different magnifications. Generally, lenses use paired elements with inversely matched curvatures to cancel out the barrel distortion of each, so the use of a single element converter lens can add considerable distortion to an image.

Fortunately, there are numerous computer software applications to correct for this barrel distortion in post-processing. To see an example of the effectiveness of such software, check out this LensMate A95 webpage for the Raynox 720 .72x Wide Converter w/ and w/o Factorsys Debarrelizer.

Problem (3) - Vignetting, where the periphery of an image appears darker than its center, is caused by the barrel of the converter lens partially blocking the incoming light rays emanating from the edges of an image.

Fortunately, there are two ways to minimize such ‘mechanical’ vignetting: (a) zoom the A95 lens to its full telephoto position and leave it there; and (b) stop the A95 lens down as far as possible. Admittedly, neither of these is an ideal solution.

Problem (4) - Shadows appearing at the bottom of an image when using an internal flash are caused by light from the flash being partially blocked by the large size of the converter lens. The larger the converter lens, the worse the problem.

Fortunately, there is one way to remedy this problem (short of using no flash at all), use an external flash. Unfortunately, if the converter lens is also partially blocking the A95’s flash sensor, even an external flash may not work properly. Similarly, a large converter lens could block the camera’s AF assist lamp, in which case its auto-focus may not work properly, as well.

If you are having problems specifically with your 2x tele-converter, my Canon A95 guru, Myron, suggests as a workaround that you closely compare your results with similar shots made without the use of a tele-converter, but with the additional 2x zoom and corresponding crop accomplished in post-processing using, for example, Photoshop. If the post-processed images look better than the images made with the tele-converter, then why bother?

Unfortunately, Myron does not have an equivalent workaround for a wide converter. However, if you are still considering the purchase of a wide converter for your Panasonic Lumix DMC-FZ30, you may want to check out last week’s Gary’s Parries (see comments 9 thru 13), where Nick in Japan explains that he leaves a Canon 0.7x wide converter attached to his FZ30 - ALL THE TIME - with very good results, albeit not without some post-processing.

[Note: Thank you, Nick, for sharing this vacation photo taken with an FZ30 and attached Canon 0.7x wide converter, although I presume this was not a wide-angle shot :). – Ed.]



I wonder why you need a mechanical shutter for a digital camera?

I can understand why you need different apertures: to get different depths of field, and to adjust the amount of light striking the image sensor. But why can’t the processor just save the present image that is projected on the LCD? Isn’t that what it does in movie mode?

Anders Tiberg

*** ANSWER 2

Excellent question, Anders, and a bit of a paradox. The ‘Parries’ answer would be that you certainly do not ‘need’ a mechanical shutter for a digital camera, as is evidenced by the overwhelming majority of digital cameras that do not have one. But more to the point of your question, why would anyone ‘want’ a mechanical shutter on a digital camera, especially when you consider its disadvantages?

There are numerous disadvantages to mechanical shutters, including: (1) they are slower than electronic shutters, which can limit a camera’s top shutter speed; (2) they are less accurate than electronic shutters; (3) they require more battery power than electronic shutters; (4) they are, unlike electronic shutters, susceptible to wear and mechanical failure; and (5) for digital cameras that use the combination of a mechanical shutter to cover the low shutter speeds, and an electronic shutter to cover the high shutter speeds, they are an added expense, particularly when you consider that an electronic shutter is capable of covering the camera’s entire range of shutter speeds.

Yet, many high-end cameras do have mechanical shutters, so you would think there has to be SOME advantage to them … and you would be right. The main advantage of mechanical shutters is improved image quality. With mechanical shutters, light strikes the CCD only during the time of exposure; however, with electronic shutters, light strikes the CCD continuously (i.e., even before the exposure starts, and then even after the exposure ends). Due to this ‘extended’ exposure time, there are two problematic phenomena that arise with electronic shutters.

One such problematic phenomenon is called ‘bloom’. This is when the pixels of an image’s high-contrast areas become saturated with charge due to their longer exposure to light, which in turn causes them to overflow to adjacent pixels, thereby making the image’s high-contrast areas appear larger than actual size (i.e., bloom). A mechanical shutter completely eliminates this problem by enabling the exposure to start with totally dark pixels, so as not to become so easily saturated.

Another problematic phenomenon of electronic shutters is called ‘smear’. This is caused by light continuing to strike the CCD after an exposure is complete, even while its image data is being transferred from the CCD, which in turn alters (i.e., smears) the image during the transfer process. The longer the transfer, the larger the smear effect. Once again, a mechanical shutter completely eliminates the problem by enabling the transfer to be carried out in total darkness, so as not to alter the image.

The bottom line is this. With today’s circuit technology, it is certainly feasible to produce a standalone, electronically-shuttered CCD that can (1) instantaneously drain all charge from the pixels immediately prior to an exposure (equivalent to the totally dark exposure start of a mechanical shutter), and (2) instantaneously latch all image data immediately after an exposure (equivalent to the totally dark data transfer of a mechanical shutter); however, the additional circuitry required to enable such capabilities would significantly decrease the percentage of photosensitive material at each photosite, and thus lead to smaller and noisier pixels.

Even so, with the current state of CMOS Image Sensor technology, mechanical shutters for digital cameras are just a ‘click’ away from extinction. :)

[Note: Thank you, Anders, for submitting this photo taken with a Canon PowerShot S1 IS, which appropriately has a combination mechanical + electronic shutter. – Ed.]


garys_parries_151006_q3.jpgWithout spending $100, how can I record my digital camera videos from Picassa to DVD?

Thank you,

[Note: Picassa DVDs are currently incompatible with home DVD players. – Ed.]

*** ANSWER 3

Gordon, how’s $39.99 sound? You can download the ACDSee 9 Photo Manager to burn your Picassa videos to DVD, and then watch them on your home DVD system.

DISCLAIMER: As you may know, I am a Mac user. So, to play it safe, I would suggest taking advantage of ACDSee’s ‘free trial offer’ before buying this Windows-only software solely on my recommendation. :)

[Note: Another photo from Nick, this one shot with a Canon 20D while playing “Sea Of Heartbreak” from his van to get the duck’s attention (Nick’s Photography Tip #9). – Ed.]

[Column photo “The Photographer” by Brenda LaFleur of Brenda LaFleur Photography.]