Edge-Softness with Sony VCL-HG1758 Telextender
 

The Sony VCL-HG1758 is a commonly-used telextender with the VX2100 and its close relatives. I've had one for 2.5 years and have been generally pleased with it. However, I have recently been paying more attention to the edges of my frames and have realized that this telex blurs them to quite an extent. It gives a sharp image in the center of a frame and since that is usually where viewers are looking, I've previously failed to see how bad the edges are.

I've used the HG1758 with several camcorders and two digital still cameras and have seen the same problem with them all. These cameras have good edge-sharpness when there's no added lens.

I have a Raynox DCR-2020PRO telextender that gives 2.2X magnification, that cost just a little more than half of the HG1758's price. It gives sharp images all the way to the edges and on a 7-MegaPixel digital camera, doesn't degrade the resolution of the basic lens by more than a slight and tolerable bit. It provides 26.4X magnification on the VX2100 at full zoom.

Since Sony puts such nice basic lenses on most of its cameras, I'm puzzled by this problem on such an expensive telextender. Of course, similar complaints have been made by people who have used a couple of other brands of telextenders with the same 58mm mounting thread size. Now, my Raynox telex seems my only option for extra magnification with my camcorders. But, it vignettes badly at any setting below about 85% full zoom, so it isn't a practical solution for general shooting. In the area between 12X and 22X in magnification, I have no unflawed lens capabilities.

There's a newer Sony telextender, the VCL-DH1758, that is intended for use on their digital still cameras that have 58mm filter threads. Several expert users have said this telex gives high-resolution images, even on a 7-MegaPixel camera. It might work on a VX2100, but I may have to buy one to test out how sharp it is at the frame edges. It's less expensive, with an MSRP of $150. and a street price of around $100. to $125. I'd like to hear from anyone who has bought it.

If you want to see a couple of pictures showing the soft edges using the HG1758, I've posted two on a telextender thread on the Under Water, Over Land Forum and there's another shot showing the sharp image with the Raynox telex. You need to download the full-sized images to see what I've described.

Steve, I start by saying I haven't used the HG1758 tele-extender, but its numbers suggest it's a 1.7x 58 mm attachment, and Sony's specification lists it as a 5 element lens assembled in three groups. So this is an expensive lens as far as converters go, and the performance you describe might well be caused by damage. A fall or a hard knock, maybe?

Raynox sure make some good lenses these days and their web site showing the effects is excellent.

http://raynox.co.jp/english/video/vx2000/index.htm

The DH1758 has been designed around still cameras that use bigger chips and generally shorter optical zooms. I see no reason why it wouldn't work on your camcorder, but I wouldn't go laying down the cash without trying it out first. You sound like a critical bloke like me, so get some money back guarantee before you shell out.

tom.

Tom, by going back and looking closely at footage I shot the first day I had the HG1758, right out of the box, I can see the same edge-softness, although in the center and 2/3 of the way to the sides, it's very sharp.

Judging by the DCR-2020PRO I have now and by a 2.5X, narrower-barreled telex from Raynox I had 18 years ago, they can make some very good add-on lenses. I just looked at some old S-VHS recordings I made with the 2.5X back then and as I remembered, it was optically good, although it vignetted below about 60% full zoom. This older lens kissed the pavement, as I left it on the roof of my car------a careless type of mistake I haven't made since.

Raynox does have a website that is filled with the kinds of data and pictures you'd like to see about all products. Most manufacturers don't bother to go into much detail these days. I guess they figure since electronics sales are so high, that they don't need to do it. The much greater amount of people who use cameras and camcorders has apparently lowered their average level of technical interest in what they buy.
http://raynox.co.jp/english/video/vx2000/index.htm

Actually, the DH1758 is specifically produced for the H1/H2/H5 digital camera models and they all have 12X zooms. This telex is relatively cheap, but every user who has discussed it on forums, is very positive about its performance and sharpness of image. Looking at the photos they post from its use, I can generally see pretty good sharpness to the edges. However, it's hard to judge how much edge-softness on some of the pictures I see from other people, might be due to the shallow DOF at full zoom. More often than not, the objects at the sides of pictures were at a different distance away, than the center subject. When I refer to the edge-softness of my own pictures, these are ones where the side-objects were at the same range as the center. I'm waiting until a local store has it in stock, so I can easily return it, if it doesn't pass my personal test, which will include using it on my VX2100 and DCR-H5, as well as an Olympus C-2100UZ camera.

I used a 1.7x Olympus extended with a 58mm thread intended for their still camera, it worked great on my trv900. I got a great deal on ebay for a century optics 2x and really couldn't see the difference. Just a thought.

Duane

Adding converter lenses puts you in a bit of a quandry Steve. Cameras with tiny 1"/3 chips really require that you don't stop down below f/5.6 because of the loss of sharpness due to diffraction, yet as you've seen, it's the wide apertures that tend to show up the faults of adding converter lenses.

Remember that your VX2100's lens has 12 elements (two of them asphericics) and three beam splitting prisms between your subject and the chips. Adding a further 5 elements (the 1758) is not to be taken lightly.

The converter lens is quite often way off axis, as the filter thread is not necessarily concentric with the camera's zoom. It's close, but the tolerances are huge vs the lens assembly itself. Also, a lens with 5 elements can have one or more of the elements knocked out of alignment, and my suspicions are that your 1758 came to you faulty.

So you need good reason to use any converter lens in my view, and invariably the good reason is for wideangle perespective control and telephoto reach and compression.

If you treat your screen as a painter's canvas I really think you shouldn't get too hyped up about edge definition. If your film is worth watching then the last thing on any viewer's mind is the worry over edge chromatic aberation. Much more obvious lens failings such as vignetting and barrel distortion will be noticed by many more.

Of course I appreciate your concern over edge to edge sharpness, it's just that I feel we can get a bit carried away by it. Here's a for instance. I tested the series of Red Eye wide-angles for the VX/PD, and my conclusions were dissappointing to say the least. Yet those lenses are used worldwide by a great many videographers. They don't really care about the blurry edges - it's the effect they're after, and such a wide-angle delivers the goods.

tom.

More Tests and a Change of Opinion
 

I've done some more tests with the Sony VCL-HG1758 telextender, with all my cameras and especially with the VX2100. I need to apologize for making such an issue of the edge-softness I was seeing with this telex, as I now realize it was appearing almost entirely on my new Sony digital camera, the DCR-H5. This camera and the 1758 telex are apparently not optically matched well enough to give good edge-sharpness. However, by examining pictures I shot today on the Memory mode in the VX2100 camcorder, with the HG1758 attached, I don't see more than a small and insignificant softness at the sides, at any zoom position where the telex doesn't cause vignetting. On many pictures, I couldn't detect any edge-sotness at all. Most of the edge-softness I was seeing previously with the telex and the camcorder, was due mostly to the side objects being out of the depth-of-focus range of the center subjects.

So, I made a mistake in expecting a video telex lens to work flawlessly on a smaller digital camera lens and then extending this observation to see problems that really weren't there when I used it on a camcorder. I believe Sony designed the HG1758 specifically for the VX2000 and four other models with similar features, including the VX2100. Again, I regret criticizing the performance of this telex, because of my trying to use it in a way it wasn't intended to do. I believe I can continue to use it and have good results with my VX2100.

Actually, the telex allows for very sharp images in the center portion of a frame on the small DCR-H5 camera, showing that its glass can pass more resolution than a camcorder would ever need. It's just out to the sides, that the incompatibility of a very large telex and a small basic camera lens shows itself.