Using a Digital8 camcorder, recently started exploring telephoto and wide-angle lenses and a UV filter. I'm running into issues with both of them impacting image clarity particularly when zoomed in. Wonder if it's due to principles of optics I'm not familiar with, low quality lenses, or some other issue.
Camera is a Sony TRV-730. In all examples the camera and added lenses were freshly cleaned with lens cleaner and microfiber cloth. The sample frames are screen shots off Virtualdub, deinterlaced using Avisynth QTGMC.
With the telephoto I find it kills clarity in the image. In this case a Vivitar Series 1 2.2 x 37mm lens.
At full 25x optical zoom without the telephoto lens
Same zoom with the telephoto - image becomes hazy overall with pronounced blurring on the sides.
I notice that the issue isn't particularly pronounced at a lesser zoom. For example:
But very obvious when at full zoom.
Same zoom no tele lens. Big difference in overall clarity.
Also run into a problem with a wide angle lens - in this case a Sony VCL-0637H .06 wide conversion lens. The image takes an overall hit on sharpness, particularly pronounced at the sides.
At max zoom without the wide lens.
Max zoom with the wide lens.
Again, not too much impact on the image with the zoom backed off.
I notice that overall the Sony wide lens looks better when zoomed out than an Albinar .45x 37mm that uses a macro attachment.
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Are you using only optical zoom? Once you've reached the limit of the optical zoom the camera starts using digital zoom. That blurs the picture since you are zooming into fewer and fewer pixels of the digitized frame.
It's very common for lenses to have barrel and pincushion distortions at the extremes. And blurring at the edges.
Last edited by jagabo; 8th May 2014 at 11:31.
Those are are more rightly termed, "diopter lenses". They are aftermarket add-ons that provide additional magnification factors (>1x for Telephoto, < 1/X for wide-angle). They are usually labeled as such, along with the mag factors.
Regular lenses are precision pieces of engineering. They are made up of multiple lens element components and anti-reflective and corrective coatings, in even the simplest of prime lenses, much less an extreme powered zoom lens. All of this has to be coordinated, calculated, and built to extremely fine tolerances in order for the individual lens elements to work in concert with each other and to correct and NOT magnify aberrations.
Diopter lenses do not have the advantage that a single, complete traditional lens has in its manufacture. It is an "afterthought", a last-ditch emergency attempt at getting magnification BEYOND the capability of the standard lens. With this "opportunity" comes compromises. There can be no precise alignment with the original lens - you don't even know EXACTLY how close the diopter will lie WRT the original lens when it is mounted. And tolerances on the original lens are measured in microns, not millimeters. Plus the curvatures and coatings are no longer "coordinated" when paired with the original lens (which is probably built by a different manufacturer).
All this adds up to losing the "tightness" of the optics. This is just the way things work when you use Diopter lenses, as opposed to just replacing the original lens with a whole new lens assembly. Of course, that might not be possible with your camera. That is the reasoning behind the bonus of using interchangeable lenses in such things as DSLRs and eCinema cams.
There are websites which explain and exemplify this difference: do a google search on "diopter lens abberations" or similar and you should likely find examples which mirror your own experience.
Disappointing as I'm sure it is to hear, these are the facts. Does that make them useless? No, but they are really only to be used in a pinch, and only within certain "safe" zoom ranges. Otherwise, the abberations start getting greatly magnified, and in uneven ways (making it even more noticeable). If you don't have a cam that supports interchangeable lenses, or if you are already at the limit of your existing lens toolkit, these, combined with adjustment of your distance and digital post-production zooming will have to suffice.
BTW, jagabo'smention about optical vs. digital zoom is still a valid one to consider as well.
Some of the more expensive screw-on adapters >$200, are designed for zoom through, but the cheapies generally distort.
I must be blind because I see no differences in the quality of the images.
A "UV" filter, or Neutral Density Filter, cuts the exposure a lot too, so you have to bump up the f-stop to compensate. But that camera may not be able to open the aperture very much.
So depending on the filter density, there might be a built in bottleneck.
There's no solution to a marginal camera, other than to get rid of it. Try to pass it off to an unsuspecting new film buff for a couple hundred.
Last edited by budwzr; 8th May 2014 at 16:01.
And adding a UV filter (if it's the same as an Olde Fashioned") camera, will add another layer of glass to confuse the camera
Yes, but UV and similar filters are PARALLEL-facing instruments and so don't mess with the convergence/divergence of focus (barring refraction due to medium change) and so they are MUCH more "transparent" and inoccuous with aberrations. Plus, they generally have much higher quality coatings on them than what I've seen with diopter lenses (probably because they are meant to be used much more often and so are expected of more demanding use).
I like these Digital8 cameras a lot - the one feature I really wish they had is a viewscreen that presents a clear and accurate representation of what the camera is recording. As it is it gives you a general idea but it's really hard to gauge exposure and focus. I've overexposed things that looked okay on the viewscreen.
Also wish it shot in progressive so I didn't have to go through the drill of deinterlacing to get progressive video.