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First Light
01-14-2006, 01:07 AM
Description
This is another popular super-telephoto lens in Tamron's "Super Performance" (SP) line. The current model is the 55BB and at the time of this writing it costs about US$462 at Adorama (http://www.adorama.com/TM5008.html?searchinfo=Tamron%20500mm&item_no=2). It's a catadioptric lens. These kinds of lenses are also called "reflex" or "mirror" lenses because they use mirrors to fold the focal length into a shorter lens body. This Tamron 500mm has two silver evaporation coated reflective mirrors. The lens body is all metal and seems very rugged. The photos below show the lens without its hood. You can see the large rear mirror in the right photo. The black disk in the middle of the lens covers the smaller front mirror.

http://fourthirdsphoto.com/components/com_simpleboard/uploaded/images/T500a.jpg

http://fourthirdsphoto.com/components/com_simpleboard/uploaded/images/T500c.jpg

Another unique characteristic of catadioptric lenses is their fixed aperture. This lens has an aperture of f8.0 and it cannot be changed. This means that there are only two ways to control the exposure: (1) by adjusting the shutter speed, and (2) by adding one or more neutral density (ND) filters. However, the latter would seldom be needed since an f8.0 aperture is fairly small, giving the lens a moderate sensitivity to light. An exception would be solar photography when a special (and expensive) 82mm front ND4 solar filter would be needed to protect both the photographer and camera from concentrated sunlight---remember that the lens acts as a magnifier---including both visible and infrared wavelengths.

Unfortunately, this lens is not available with a 4/3rds mount. Instead, it comes with Tamron's universal Adaptall-2 mount. The Adaptall-2 mount does not connect directly to a camera. Rather, you add one of Tamron's Adaptall-to-camera adapters. In this case you must use their Adaptall-OM adapter and mount it to your 4/3rds camera via one of the OM-to-4/3rds adapters (like the Olympus MF-1).

This is a popular "moon lens" because you can take great shots of the moon with it. There is no equivalent with a 4/3rds mount---the 4/3rds lens with the longest focal length is the Zuiko Digital (ZD) 300mm f2.8 ED lens. Since this Tamron is not a 4/3rds lens, you must operate your camera in either Manual or Aperture Priority mode and focus manually. This, along with its modest aperture, make it a poor choice for action shots that require fast shutter speeds and rapid changes in focus (although an E-1 equipped with a third-party split-prism focusing screen can help quite a bit with focus). Even still, I wouldn't recommend this lens if you plan to snap quick shots of moving critters owing to its manual focus.

One of the big advantages of a catadioptric lens is its small size and light weight. This makes this lens very comfortable to shoot by hand. However, with such a long focal length and a 2x focal length factor on a 4/3rds camera, you would need to shoot at about 1/1000th second or faster in order to avoid motion blur. That will be very difficult with its fixed f8.0 aperture unless you are outdoors in very bright sunlight. Therefore, a tripod or monopod will be needed most of the time with this lens.

Since this lens has been in production for quite a while, many used ones are available. Previous models can be purchased at a fraction of their new cost. For this test I purchased a used model 55B in very good condition for only US$87 on eBay.

The big question is, how well does it work on a 4/3rds camera? Remember that this Tamron 500mm lens is designed for film cameras so its image circle is sized for a 35mm film frame. With a 4/3rds camera, only half that diameter is used and, as a result, you can expect the image to be slightly less bright compared to a lens that focuses all of its light onto a 4/3rds image sensor at the same f-stop.


Specifications (model 55BB )
- Focal length (FL): 500mm
- Angle of view (AOV): 5 degrees (2.5 degrees on a 4/3rds camera)
- Aperture range: f8.0
- Lens construction: 4 groups, 7 elements
- Coating: BBAR multiple-layer coating
- Minimum focus: 5.6 ft (1.7 m) from the focus plane
- Filter size: 82mm (front), 30.5mm (rear)
- Length without hood: 4.25 inches (108mm) with front filter
- Length with hood: 6.625 inches (169mm)
- Weight: 18.9 oz (0.535 kg).

The following photo shows the lens, hood, front lens cap and tripod mount. My older 55B model allows the tripod mount to be quickly removed by two thumbscrews. The rotating tripod mount collar stays on the lens and uses a single thumbscrew to lock the position of the lens. An 82mm Tamron "Normal" filter is shown mounted to the front of the lens. Also shown is an SP 2x teleconverter that normally ships with some lens kits. This 2x teleconverter turns it into a 1000mm f16 lens.


http://fourthirdsphoto.com/components/com_simpleboard/uploaded/images/T500b.jpg

I tested the lens with this teleconverter as well as a Tamron 140F 1.4x tele and an Olympus EC-14 1.4x tele. The two Tamron teleconverters are designed exclusively for this and Tamron's SP 300mm f2.8 LD IF lens. They mount between the Adaptall-2 mount and the Adaptall-to-camera mount. That means you have to remove the Adaptall-OM adapter each time you want to add a Tamron teleconverter. It doesn't take very long to do so but it is annoying because it requires that you carefully align one of the two aperture scale pins even though this lens has a fixed aperture (the teleconverters each include a second aperture scale which displays the true aperture value with the teleconverter).

This Tamron 500mm lens also has a rear filter. In my older 55B, the filter screws onto the back of the lens underneath the Adaptall-2 mount. You have to remove the Adaptall-2 mount to change the filter. I think the current 55BB model has a sliding tray mount for the rear filter which makes it much easier to change. A rear filter should normally be installed when the lens is used and mine had the standard Tamron "normal" filter.


Measurements
My measurements are based on the Imatest (http://www.imatest.com/) system (version 1.6.3). The camera was mounted on a tripod and located an appropriate distance away from each of several precision test targets. All tests were performed with my Olympus E-1 with an MF-1 OM adapter and an RM-CB1 remote shutter release cable. My E-1 is outfitted with a Katz Eye Optics split-prism focusing screen and an HLD-2 battery grip. The mirror was locked up (anti-shock mode) for each shot.

During the sharpness tests the lens had to be located a sizeable distance from the test target. With a focal length of 1000mm with the 2x teleconverter it was necessary to perform these tests outdoors. Fortunately, the sky was overcast, transforming the sun into a diffuse light source.

Sharpness - The easiest way to measure the sharpness or resolution of a lens is with a camera. However, this makes the camera a part of the measurement. That means we are measuring the lens and camera together---the camera cannot be removed from the measurement. For this reason it would be best to use a camera whose image sensor has the highest available resolution. That's why PhotoZone uses an E-300 for its 4/3rds lens measurements. I don't have an E-300 or E-500 (both 8 megapixel cameras) so I used my trusty E-1 (a 5 megapixel camera). Therefore the values I measured will not be the highest possible.

Fortunately, this should not present a problem because we are not making absolute measurements of the lens' optical resolution. What we are doing is making relative measurements where we compare one lens to another on the same camera. I chose to use my award-winning ZD 150mm f2.0 ED lens for these comparisons because: (1) it is recognized as a very high quality, high resolution lens and (2) it is the best telephoto lens that I own.

There are several measures of image sharpness and before we can compare results, we have to make sure that we use the same measure. I chose to measure MTF50 in lw/ph. The MTF50 is the "modulation transfer function" or spatial frequency where the contrast drops to half (50%) of its low-frequency value. I know that sounds technical and you don't need to understand it because as long as you read my tests, I'll always measure the same thing so we can compare "apples to apples". But readers of my review should not compare my results to those of another reviewer unless they first make certain that they measured MTF50 also. As for "lw/ph", it is the units and it means line widths per picture height. Lw/ph is calculated as follows: lw/ph = 2 x lp/mm x picture height. Where lp/mm is the number of line pairs per millimeter and the picture height is also in millimeters. I won't bore you with any more technobabble. Suffice it to say that if you want to compare someone else's sharpness measurements to mine, they need to measure MTF50 in lw/ph using an E-1 camera. For more information about measurements, see Imatest (http://www.imatest.com).

Since this lens has a fixed f8.0 aperture, I measured its sharpness at just the one f-stop. The following results show the sharpness of the lens with and without its filter and teleconverters:


http://fourthirdsphoto.com/components/com_simpleboard/uploaded/images/T5001.jpg

Notice that I made two measurements for each test. First, I measured the sharpness in the center of the field of view (FOV). Second, I measured the sharpness in one of the corners of the FOV (I used the lower left corner). That way you can see whether a lens is sharper in the center or at a corner.

This lens has only mediocre sharpness without its front "normal" filter. With its filter, the sharpness improves and is good but not great. Still, it's better than all other catadioptric lenses that I've measured so far on an E-1. Such a significant and positive effect by the filter was unexpected. I recommend always using this lens with Tamron's 82mm front "normal" filter.

Some readers may ask what the MTF50 numbers mean in practical terms. An MTF50 less than 1000 lw/ph should be considered "bad" or "poor" because it will produce a very soft picture with low contrast. You need at least 1150 lw/ph before the picture begins to look "good" and I'd rather see 1450 lw/ph or more. This lens measured almost 1300 lw/ph in the center of the FOV.

The remaining portion of the graph shows the sharpness with the various teleconverters, starting with the Tamron 140F 1.4x tele, followed by the included Tamron SP 2x tele, and lastly the Olympus Digital EC-14 1.4x tele. All three teleconverters were measured without the lens front filter so you can expect the sharpness to improve a bit if the filter is included (recommended). Still, the sharpness takes a big hit with any of these three teleconverters so you can expect soft pictures with low contrast. As a result, I recommend avoiding teleconverters with this lens.

Note that the teleconverters change both the focal length and the f-stop of the lens. The two 1.4x teleconverters change the lens to a 700mm f11 lens. The 2x teleconverter changes the lens to a 1000mm f16 lens. The reduced apertures (higher f-stops) partly explain the lower sharpness because diffraction increases as the f-stop value increases and diffraction softens the picture.

Now, the moment we've all been waiting for... How does the Tamron 500mm f8.0 compare to the ZD 150mm f2.0? The next graph shows:


http://fourthirdsphoto.com/components/com_simpleboard/uploaded/images/T5002.jpg

Notice the amazingly strong sharpness of the ZD 150mm all the way down to f2.0. That is phenomenal. See my second ZD 150mm review (http://www.fourthirdsphoto.com/vbb/showthread.php?t=146) for all of my test results. There's no way that the Tamron lens can approach the sharpness of the ZD lens at or below f8.0. But is the Tamron lens bad? I don't think so. Using a scale of poor-mediocre-okay-good-very good-excellent, I rate the sharpness of this lens between "okay" and "good".

Chromatic Aberration (CA) - This test measures color fringing and it wasn't really necessary because a characteristic of catadioptric lenses is no CA. It measured so low as to be totally "insignificant".

Distortion - This test measures whether or not parts of the image are bent, stretched or squished. An extreme example would be the barrel distortion that is common to some wide-angle lenses like a "fisheye" lens. To measure it, a grid pattern of equally spaced horizontal and vertical lines are photographed and measured. This Tamron 500mm lens is basically free of distorion by itself or when it is used with a Tamron teleconverter. The highest deviation I measured was 0.138% which is very small. The distortion was noticeably higher when the lens was used with the Olympus EC-14 teleconverter. However, the highest deviation was -0.962% which is still modest.

Vignetting - This test measures the light drop-off near the corners of the picture. I used worse-case conditions with the lens focused to infinity. The lens exhibited very little vignetting---no more than -0.35 f-stops (or EV). Most of the time it was less than -0.24 f-stops which is quite good. The low vignetting is probably due to the fact that only the center half of the lens is being used on a 4/3rds camera and most vignetting, if it exists, probably occurs outside this area closer to the edge of the lens image circle.


Conclusions
Pros - This is a well-made super-telephoto lens with a strong metal body, no CA, low distortion and low vignetting. It accepts both front and rear filters. The small size of the rear filters can save money. Some kits include a 2x teleconverter. It has a built-in rotating tripod mount and nice metal hood.

Cons - Since it is not a 4/3rds lens, it must be manually focused and you cannot use the Program or Shutter Priority modes of your camera. The sharpness is okay but it is not that great---a super high-grade 4/3rds ZD lens is much sharper. The rear filter is awkward to change because you have to remove the Adaptall-2 mount to access it. The lens is not weatherproof. The lens tripod mount is not useable if a battery grip is installed on your camera because the mount is located too close to the camera body (fortunately, the lens is light and short enough that the camera tripod mount is sufficient).

On balance, I think this lens manages to squeak by with a "good" rating.


Copyright 2006 by Harris Technologies, Inc. All rights reserved.

jebir
01-14-2006, 03:04 AM
Hi FL,

once again a great review! Thanks!

I think that you really do all of us a great favour. I am sure that these reviews of 'old' third party lenses will increase the popularity of this site (and hopefully also the 4/3 system) as the interest for 4/3 cameras grows.

Best, Jens

Renko
02-25-2006, 05:21 PM
Great review FL! It echos most of my experience with this lens.

I have a couple of questions...

I was very surprised to see the increased sharpness with the front filter, kind of expected the reverse to be true. Do you have any more information about this "normal" filter? I don't have one with mine.

Also, were the tests conducted with a normal rear filter or without and if with then did you try without? I have had varied results and I'm just realising that perhaps this was becuase I had removed the rear filter at one stage.

Thanks, Jon

First Light
02-25-2006, 08:53 PM
Thanks Jon,

I don't have any information about the front "normal" filter. It was a Tamron filter that they made for the lens. I assume that it is a multicoated UV filter. Why did it appear to improve the sharpness of photos? My guess it that the extra multicoatings are the answer. They probably attenuate stray reflections that would otherwise reduce the contrast of the lens (and therefore reduce the sharpness). But this is just a guess. As I wrote in my review, I was surprised with the results, too.

As for a rear filter, yes, the lens also had a rear filter (I think that I explained this in my review). Unlike newer models of this lens which allow you to easily slide a rear filter in and out, my lens required you to remove the Adaptall-2 adapter in order to access and unscrew the rear filter. It has a Tamron "normal" rear filter just like the front. I left it on for all measurements. As I understand it, most of these type lenses are intended to have a rear filter installed all of the time.

Renko
02-27-2006, 03:09 AM
Your assumption about the multi-coating on the front filter sounds like a pretty good one. I think I'll try and get a good UV filter and see how it affects the performance. Wonder if the same could apply for other legacy lenses, hmmm... If I manage to get one I'll let you all know how I got on.

I didn't realise the newer versions had the drop in filter but then I've never seen a newer version of the lens :) Good to know.

I think your right, the rear filter is meant to be in place all the time. (Have memories of reading this in the manual as well) I was just curious.

ziuko
02-28-2006, 08:17 AM
I actually have this lens and the 2x converter and OM mount in a velvet lined Tamron Box, I have owned the lens with my OM system for years (too many !) but have only used it twice.

I need to get the om -4/3 converter to use it, but considering how little I have used it, I should sell it if anybody wants to make me a reasonable offer. I will have to post it from Australia , but I receive stuff from the USA ok so shouldnt be a problem.

The lens is in mint condition, not a mark on it.

Ziuko

jebir
03-01-2006, 01:17 AM
Your assumption about the multi-coating on the front filter sounds like a pretty good one. I think I'll try and get a good UV filter and see how it affects the performance. Wonder if the same could apply for other legacy lenses, hmmm...

Hi Renko and FL,

FWIW, my Tokina AT-X 300/2.8 is equipped with a 112 mm front filter that was supplied with the lens when it once was new. In the manual for the lens it specifically says that the front (and rear) filters should be mounted at all times for best performance.

Even a flat slab of glass will add some, although small, amount of chromatic aberration. I can thus see a reason for designing an expensive high resolution lens to correct for that added CA by including the filter as an optical element in the design process. That would allow the owner to protect the front element with a filter while maintain the highest image quality. Of course then, if the filter is removed, it will mean that the CA that was corrected for will show up again and deterioate the image somewhat.

Such a filter must of course be multicoated in order to reduce flare as much as possible. I don't see how two added surfaces per se can improve the optical performance even if they are multicoated - it ought to be what's in-between the surfaces that improves the image quality.

Just a thought on this filter improvement effect.

Cheers, Jens.

First Light
03-01-2006, 02:53 AM
Hi Jens,

Your explanation seems plausible for a normal refracter lens. But I thought that catadioptric lenses were naturally free of CA. If they are, then it would seem that the front filter would not reduce something that wasn't there to begin with.

Is that correct (that catadioptric lenses are naturally CA-free)?

jebir
03-01-2006, 02:57 PM
Hi First Light,


Is that correct (that catadioptric lenses are naturally CA-free)?

I checked up on that and, in summary, the idea with catadioptric lenses is to compensate spherical abberations of the mirror system by use of refracting lenses up front and/or in the rear. If the mirror geometry is correct and the lenses are chosen and manufactured correctly, their inherent CA can be made to cancel each other in the final image. However, in reality, compromises have to be made in order to save weight, size, and light transmission which may lead to deviations from that ideal case.

So, not all mirror lenses are CA-free. I guess that one gets what one pays for in that respect - as usual.

Coming back to the improvement with the filter, I agree that my explanation is far fetched for this lens as the filter is sold separately as an accessory.

Cheers, Jens.

First Light
03-01-2006, 03:14 PM
Thanks Jens! You are becoming the "go to" guy for difficult lens questions. I'm very glad you're here.

Alfredo
07-18-2006, 06:31 PM
Thanks FL.
Splendid analysis.
My little contribution:
http://www.telecable.es/personales/jubotas1/policarbonato/TeleYmacro.htm

Greetings:
Alfredo
Oviedo - Spain