Oddball Lens #1

Over the years I've accumulated quite a few "oddball" lenses. Lenses which are uncommon, rare, one-of-a-kind, or simply bizarre. I haven't posted anything in a while, and figure a fun series of oddities would be an interesting enough way to get back into this.

Minolta AF Reflex 500mm F8

Today I’ll be taking a look at an adapted Minolta A-mount to Sony E-mount lens: the Minolta AF Reflex 500mm F8. There were three versions of this lens—the original A-mount (used here), a Vectis-mount model, and a Sony version that’s nearly identical to the original but with slightly newer coatings. The Minolta 500mm Reflex was introduced in 1989, and discontinued in 2010. 

Using SLR lenses this old is always a little quirky, and it feels even stranger adapting one to a modern mirrorless body. In my case, I’m adapting it to my Sony A7RII and A7RIII (I’ve been moving away from Micro Four Thirds—maybe I’ll do a separate post on that!).

There are a couple of adapters that work with the A7RII/III: the Sony LA-EA3 and LA-EA4. The LA-EA3 can autofocus with some Sony lenses and a few third-party options. It uses the camera’s sensor for focusing, while relying on the lens’s own motor. The LA-EA4, on the other hand, uses a pellicle mirror—cutting the light by about a third—but it can drive much older glass. The Minolta 500mm works with the LA-EA4.

On this camera, the adapter + lens combo looks a little unbalanced, but it’s really not bad at all. Considering it’s a 500mm, it’s surprisingly small and light.

Autofocus is snappy on the LA-EA4, though it only uses the center point. Continuous AF works, and it does a decent job, but it can be tricky keeping that lone center point locked on moving subjects like birds.

Being a catadioptric design, its effective light-gathering ability is lower than that of an equivalent refractive lens for two main reasons:

• A mirror reflects less light than a lens can transmit (85%-95% for the mirror vs 95%-99% for the lens)
• The center mirror obstructs the center of the aperture, blocking about a third of the light.

Some quick math: at F8, if the central mirror blocks about one-third of the light, that’s roughly a 1/3-stop loss. Each stop corresponds to multiplying the F-number by √2, so losing X stops means multiplying by (√2)^X.

If we estimate ~30% loss from the secondary mirror and another ~10% from reflection inefficiencies, that’s about 40% total loss (60% transmission). In stop terms, that’s ~0.4 stops darker. Converting to a T-stop:

T ≈ 8 × (√2)^0.4 ≈ F9.1

Keep in mind, we’re using the LA-EA4 with this lens, which has a pellicle mirror—so we lose about a third of the light there as well. In practice, that means our 500mm F8 is gathering light more like an F10 or even F11 lens.

The aperture cannot be changed - it's fixed at F8. This leaves the exposure triangle balanced on the shutter speed and ISO only. For that reason, the lens works best on bright days where you don't have to bump the ISO too high.

If you were expecting to shoot at ISO 800, you’ll actually need something closer to ISO 1250 to maintain the same exposure.

The lens comes with pop in filters in the rear. A clear filter and a 4-stop ND filter.

The case has held up quite well. A padded leatherette covered protective tube.

A view from the front. 67mm filter thread. The "hood" is rubber coated metal, currently screwed in.

 

On Left: the filter insert pulled out. The button on the side turns AF on/off.
On Right: Minolta 500mm F8 Reflex mounted on A7RIIIusing the LA-EA4 adapter. Tamron 70-300, and vintage Canon 50mm F1.4 FD on either side for size comparison.

Image Quality

I've used catadiatropic lenses before. While I've appreciated their size, I've generally gotten better image resolution from standard refractive lenses at shorter focal lengths. I'll have to admit some surprise seeing the clarity of this lens though. I really didn't expect it to be this capable. I had recently tried the "modern" Tokina SZ 500mm F8 and was quite disappointed, so this old lens not only besting it with the versatility of AF but also with IQ is a wonderful surprise!

While I was impressed with the image quality, that’s only in the context of other catadioptric lenses. I'm curious how it holds up against refractive glass. I generally use two zooms for wildlife: an old adapted Tamron SP 150–600mm and a more modern Tamron 70–300mm Di III RXD. As much as I like oddballs, I’m going to guess the little Tamron 70–300mm can outresolve the Minolta 500mm. That’s fine though, since the Minolta usually goes for around $150–200 (adapter not included).

Let's compare the 500mm reflex with the compact 70-300mm Tamron RXD and an old Tamron 150-600mm (Sony-A adapted via LA-EA3). I scaled down the 500mm and 150-600mm images to match the pixel pitch of the 70-300mm. I could scale up too, but for this cormorant, it's a difficult subject with the dark shaded body.

Minolta 500mm Reflex

Tamron 70-300mm

Tamron 150-600mm SP

The old formula does a decent job of capturing fine detail, but it struggles with local contrast, giving the impression that it resolves less than the 70–300mm. The donut-shaped bokeh also makes the plane of focus appear thinner than it really is.

Let's focus on just the head.

Minolta 500mm Reflex

Tamron 70-300mm RXD

Tamron 150-600mm SP @600mm

I've ordered the images in increasing amounts of resolved detail. It's not surprising that the 70-300mm and 150-600mm outsolve the old cat. There's a bit of a loss in contrast with the cat, and it does seem to affect darker areas more. Might be helpful to overexpose a little and adjust in post.

Here's a picture of container ships across the bay.

It's an easier subject. Let's focus on a few containers. This time I've scaled up the image.

Minolta 500mm Reflex
F8, 1/1000, ISO 800

Tamron 70-300mm RXD
F8, 1/1000, ISO 500

Tamron 150-600mm SP @500mm
F8, 1/1000, ISO 640

Here, the 70–300mm loses to the 500mm F8 in resolution. The container on the lower left has a serial number that’s readable in the 150–600mm shot (483113). The 500mm reflex lens has lower local contrast and requires more sharpening—the text is legible, but barely. The 70–300mm image is completely unreadable. The MGW/TARE/NET labels on the lower right container show a similar pattern. Scaling the 70–300mm image back to its original size didn’t help.

Bottom line: the Minolta 500mm Reflex lens does return more detail than the modern 70–300mm under good conditions. The 70–300mm under-exposed a little as its wider field of view captured more of the bright sky. The 500mm Reflex was noticeably darker, so a higher ISO was needed. Keep in mind that about a third of the light is lost to the pellicle in the LA-EA4 adapter, with another ~30% blocked by the catadioptric lens’s center mirror.

Corner resolution of the 500mm is better than the center.

Minolta 500mm Reflex

Tamron 150-600mm @500mm

Tamron 70-300mm @300mm, upscaled to match

Here the reflex lens puts up an amazing result, somehow delivering much more resolution than my other 2 main tele lenses. The 70-300mm also shows it's modern chops, rivaling, and surpassing the 150-600mm (although with the 70-300, it's not quite at the corner since it has a wider view).

Sample Photos:

This won't be complete without some proper sample photos. Picking and choosing a few examples helps, but doesn't show how it performs in practice. Blogger resizes my pictures more than i'd like unfortunately.

After processing to increase the contrast, fine feather detail can be resolved. 1/1000, ISO 320.

Just The bokeh can be distracting. Normally the progression of sharp subject to blurring forground/background isolates the subject giving it pop. It's a bit harder to give it pop when the blur is a well defined donut.

Squirrel on the grass. You can see how the bokeh transitions to the foreground and background. On a higher contrast photo, it can become more distracting. ISO 1000, 1/200.

These mallards visited my park every day for a week. The blur of the background duck doesn't look too bad here. ISO 1000, 1/200.

The Minolta 500mm F8 Reflex and LA-EA4 AF system work well enough to capture birds in flight. The lens is light, making tracking with the center focus-point fairly easy. Stand back when you look at this photo, and don't look at the details - look at the sky. You'll see an odd ring. This vignette is an odd pattern, being less intense at the very corner.  1/400, ISO 200.  

A view across the bay at the Newark docks, and the airport control tower. Had to cut through a fair amount of haze in post.

Another squirrel. Not a crop. Long focal length let me get close enough to fill the frame. 1/500, ISO 1000.

Expect to brighten up your images - not just with this lens, but in general, photographing birds with darker plumage against bright backgrounds can leave you with some work in post. See finished shot below...

One of my favorite starling photos. 1/500, ISO 800 - but brightened up a LOT in post. I've learned to be unafraid to abuse the RAWs - They're proven that they can take it!

Tree swallow. This is more of a test of the LA-EA4's AF, and how it can shoot through the tight space of these leaves and branches to pinpoint the bird's eye. 1/500, ISO 500.

Summary - Minolta 500mm F8 Reflex:

• The lens is quite light, and barely longer than the 70-300mm.
• Can out-resolve the modern 70-300mm, but has lower contrast, often losing details in darker areas.
• Is quite dark - With the LA-EA4 also requiring some of the light for focusing, expect to bump ISO by 50% at least.
• The LA-EA4 only gives the center focus point with this. While I like the pinpoint accuracy, it does lack the versatility the A7RIII's focus system can deliver.
• Edge detail is quite good. Perhaps it makes sense to offset shots taken with this lens.
• No chromatic aberration correction is nice. 
• The LA-EA4 is expensive. It's ~$150-$200 on ebay at this time. That adds to the cost of this lens.
• If given a choice between this and the 70-300mm, I would probably opt for the 70-300mm RXD. The modern optics are quite good, and while it does lose out on resolution, it's not a huge gap. The AF capability is quite good.
• There's an odd vignette that can stand out depending on the way the image is processed.

If you're someone that likes collecting lenses, this is not simply a lens to have for its history, but actually capable. 

From a collector's standpoint, there aren't any other autofocus reflex lenses out there. 

If your goal is "cheap", and you already have the LA-EA4 (or LA-EA5 and more modern camera) then this lens is a pretty good deal. Ebay has it going for $120-$180. Just be aware that you'll want to tweak the final image in post for the low contrast and center sharpness. Perceived sharpness is a combination of two things. The first is the lens resolution of course. The second is local contrast. While this lens does have pretty decent resolution (especially away from the center), it does not have great contrast. Luckily, that can be corrected from RAW.