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Advanced Questions
by Chuck McKern

With over 12 years of retail and professional experience Chuck thought he'd heard it all - until he took this job.

Send us your questions for either the Beginner or Advanced columns by clicking HERE.  Please include as much detail about the technique, camera, lens, or film as you can so Chuck can answer your questions.

I was interested to read your explanation of the differences in colour rendition of the same image on paper and on a computer monitor - "your monitor is an illuminated image while printed images are reflected images". Does the same reasoning explain why the colours of a print look different when viewed on a lightbox and when viewed normally?


Light boxes are designed for viewing negatives and transparencies and have a tendency to "weaken" colors in photographs. This is because the paper is not designed to transmit light through it. However, if you view a photograph under daylight then look at it under florescent and finally tungsten light, you will notice that the colors do vary. This has to do with color temperature of the lighting that is being reflected off the photograph and how it is reflecting the colors in the photo.

The same thing occurs when viewing negatives and transparencies on a light box. The actual colors that you see will vary depending on the color temperature of the bulbs in the light box. Believe it or not, most light boxes are not daylight corrected. This is primarily due to the cost of the daylight bulbs compared to the normal fluorescent bulbs.

I need a new shoe for the Achiever 623LCD flash that will fit a Canon. Is there anyone in the USA I can call/write and order another one. Please help.

Thank you,
Jim Carroll

I would refer you to Tempe Camera Repair in Tempe Arizona. They offer a full line of repair services including a machine shop so they may be able to help you out. Visit their web site at

Be sure to email or call their repair department before you send your flash unit.

I have a Nikon N70. I shoot race car pictures, mostly for my own enjoyment, although every so often the drivers buy them from me or they end up in the paper I write for. It's all daytime shooting.

I use Fuji 800 and have been taking pictures of race cars for something like 8-10 years.

The current lens I use is the 28mm-300mm Sigma lens. Got this one so I don't have to bounce between the 28-80 and the 70-300mm. Love this lens.

The question I have is: I read somewhere about teleconverters. Don't know a thing about them but it sounded interesting. First and most important, do they work with telephoto lenses? Do the teleconverters add a lot of weight to the lens?

I honestly thought of a 100-400mm Sigma, but the weight was really what held me back.

Any help you could send my way would be great, I'm going to Bristol's Winston Cup race and would like to purchase it before that time if it's a viable option.


Teleconverters can be a great way to increase the magnification of lenses without having to invest in another lens. There are several things that you need to know about them first.

The weight issue is really not worth talking about. Teleconverters typically do not weigh that more than a couple of ounces. More important is their effect on the speed of the lens. Most auto focus lenses with a 5.6 aperture, or smaller, will loose their auto focus capability when adding a teleconverter. This may be a total loss of auto focus or a tendency for the auto focus to "hunt" in and out several times before finally focusing. The reason for this is that teleconverters "loose" light. Typically speaking, a 2x converter will cause a loss of about two stops. This would make an f/5.6 lens the equivalent of an f/11 lens. In your case it could be the difference between getting a shot and getting a blur.

You also want to take into consideration stability at that magnification. Put a 2x converter on your 28-300, this will effectively make it a 56-600mm lens. Unless you have very steady hands, you'll need a tripod or monopod for added support.

The most common converter types are the 2x converter mentioned above and 1.4x converters. A 1.4x converter would turn your lens into a 39-420mm lens. With a 1.4x converter you'll only lose about 1.5 stops of light and it's more likely you'll preserve auto focus operation.

Another thing to consider is the fact that your lens already covers a wide range of focal lengths. Physics dictate that the lens has to give up a bit of sharpness somewhere. With these wide range zooms it's usually at the longer focal lengths. Any teleconverter will add a bit of softness to the image. This will be most noticeable at 600mm in your case. That said, every lens design reacts differently to the use of a teleconverter. Some lenses will show virtually no visible difference in image quality while with others it will be quite noticeable. Your best bet is to find a camera shop that will let you try a converter in the parking lot for a few shots before you buy. If the shots look good - go for it. 

I know the mirror on my 35mm SLR is very delicate and have only cleaned it when absolutely necessary using a photographers blower brush. Upon inspection I noticed a smudge mark on the mirror (from where, I can only imagine) I keep my blower brush clean and stored in its own container and exercise great care when exposing the mirror to change a lens. My question; Is there a method to clean this type of smudge mark from the mirror myself, or is this best left to a technician at tune up time?

Keith Roenspiess

Since anything on the mirror does not effect the image being recorded, I would just let it go until the camera goes into the shop for one reason or another. If the smudge is really bad, you can clean it with a slightly diluted lens cleaner and be very careful not to put much pressure on the mirror while cleaning it. The pressure is where most people get into trouble. If possible, use a clean Q-tip, or similar swab, to wipe off the smudge, and then use the blower brush to get rid of any lint left behind. Just do yourself, and your camera a favor and be VERY gentle.

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