Mirror Lenses

From and advanced amateur.
Why are refractor lenses preferred in photography over mirror (reflector) enses? Color aberation, as I understand it, is the nemesis of traditional lenses and that's why we have "coatings". Reflector lenses have less chromatic aberration and lens internal "stuff" which greatly reduces weight. Packing a large telephoto on one's back, weight-wise, seems a factor for photography in remote places. I guess VR would be an issue? But technique with any telephoto is also important. There must be other reasons why the reflector (especially "catadiopric" sp? which makes a really short lens) is not available. I have a 500 mm Nikkor-Reflex from ancient times which is very short and very light weight. I have not used it much on by D-300. Comments appreciated.
the fisch

That's a good question Larry. The only mirror lenses I've seen are pretty cheap ones, so I don't know what a good one would be like. I'd guess the reasons you don't see reflector lenses are because of the same disadvantages that reflector telescopes have - they're less robust, and need to be cleaned and aligned a little more perfectly.

I think the biggest problem, photography-wise, is that the bokeh of the lens makes all these little blurry donuts that aren't very attractive (some people think they're downright horrible). (Here's a good example - the No Parking signs).

Still, they could certainly be compact, and I don't quite understand why there isn't a compact telephoto or two out there from Canon or Nikon.

I've got the Nikkor Reflex 500mm F/8 and have faithfully tried it alongside my other lenses with each successive generation of camera bodies since I bought it in the 1960's. It's just about my last choice in lenses for quite a few reasons.

It's not contrasty enough for my tastes except in very bright light- just about useless in low light because the low contrast seems to team up with a tendency to softness to yield really poor results.

That f/8 fixed aperture is a millstone around your neck. You need a wider aperture in low light and you do not have the option of closing down or opening up to manage shutter speeds for specific effects in a variety of lighting conditions.

Have fun changing filters!

For whatever reason it has noticeably less DOF than my 500 f/4 shot at f/8.

Out of focus highlights are distinct donuts. Kind of a neat effect when you're shooting cityscapes at night with all the points of light, but not something I'd ever consider for landscape or wildlife any time there's anything but a pretty uniform background.

An 80-200 f/2.8 or 300 f/4 with extenders is really no heavier, and will knock the sox off the reflex 500 for image quality, even while they're much more versatile.

Edit- I forgot a BIGGY:

It's really dark looking through the viewfinder, making critical focusing in low light a royal PITA, kind of like strapping a polarizing filter onto a lens in low light. Ick.

A few reasons:

1) You're limited to one aperture setting
2) Many people dislike the "donut" effect in out-of-focus areas
3) No AF

Guy

Hank and David,

Thanks for the reply. You bring several good points. I honestly have not used this lens much but did not like the photos I was getting. Donuts are distinct! Focus on the D300 is probably best done with the green focus verification light; not sure how that works in dim light. I wonder if the limitions are not in the lens itself. Afterall, astronomers use reflectors almost exclusively. The don't seem to have contrast and color issues???? Hank, I'm from Kansas but have been to AK 9 times since 1993. Rivers: Clearwater, Delta, W.Fk. Mclaren, S.Fk. Koyukuk and Saganirvirtok (sp?). The "Greatland", eh???? Clearwater and Mclaren are non-motorized. Can you say "bow and stern" line for about 25 miles! I have a canoe and motor stored in North Pole at a friends house. Getting to old to pull.

I think the distinction for astronomers is that they're working with very high contrast, and for pro uses they're using (and paying for) much higher quality gear than the Nikkor Reflex. They're also working with rock solid "tripods" and no subject movement.

Those are great rivers! Lands and waters are getting a bit crowded up here for my tastes and traditions, so non-motorized waters and lands hold special appeal for me. Thankfully the run-of-the-mill outdoor recreator is lazy and gasoline dependent. You have to look a little harder to find the wilderness these days, but it's there.

When I was shooting film, I had a Minolta 500mm reflex used mainly for bird photography for about ten years. I had all the same problems outlined by Hank. In very bright light and still conditions, it was decent at best. When I switched to digital, I went with Canon and only the best lenses ($$$). What a difference!

In my experience, there's really nothing you can do to make a reflex lens perform like the best for outdoor photography.

OK then. It appears the comments are that reflector lenses aren't as good. Vibration I understand and alway a problem with telephotos, even VR. Now, as far as quality, I have Questar 3.5 inch catadioptric, mirror and lens combo and option. The quality is unsurpassable for the mirror. I still have color saturation problems; contrast??? I'm shooting "to the right" on histogram. Can that be maniupulated in the post photo process. I've not had good luck in doing that but have begun playing with RAW using Nikon Capure NX2. Since I'm not proficient at this, any opinions on processing for contrast, etc. on photos taken with mirror lens? And, anyone want to buy a Nikkor Reflex?? (grins).

You can certainly "repair" the contrast and saturation issues to a degree in post processing, but it takes a fair degree of proficiency and a well calibrated system to avoid "plastic" or artificial results. For my tastes there's also a significant loss of detail tied to the lack of contrast, especially in the coats of animals and other areas where fine pattern in subtle colors are required for best results.

And as for sales potential of a Reflex lens, why do you think I still have mine after 40 years of limited use? It certainly isn't sentimental reasons. Heck, I have given it away twice to friends and it always seems to wander back home.

FWIW I've used a Celestron 1000mm Catadioptic with my old Canon AE-1. The lack of contrast was a problem. I was able to mitigate it by going to the local hardware store and buying a large hose clamp and rubber sewer pipe fitting. It fit nicely as a lens hood - but it sure was ugly!! You might try some sort of lens hood on your Questar and see if it helps with the contrast problem.

OK, we have a contrast problem. I still have not played with the Questar that much. It has a built-in lens hood and for closer shots a diaphragm to put on the scope to reduce the aperature (vignetting?). I'll do some shots this weekend and report if I have any observation. However, it sounds like you all have those observations down pat alredy. Question: How does contrast relate to detail? If the detail is there, can the contrast be created. I have no question the Questar will match the detail of the finest lenes. It would seem to me that empty contrast without detail seems to be without merit.

“… As they like to say on Wall Street, the goal is to leave you with only your socks and a smile…” -- Review and Outlook, Wall Street Journal, Pushovers at the Fed, 25 March 2008, pg. A22

"Question: How does contrast relate to detail? If the detail is there, can the contrast be created."

Depending on which way it flops, when you're losing contrast you can also lose detail in the light or dark areas. When subtle values are at risk, as say on a deer hide with both black and white hairs as well as brown, with loss of contrast, something has to give. You can easily lose detail if the image is not "contrasty" enough. Bump the contrast in post-processing, but it won't draw up detail that's not recorded at the time of capture.

One aberration that is difficult to correct in reflectors is coma. This is noticeable at the edges of the frame. While there are designs that can correct for this, notably the Ritchey Chretien, they generally must be hand-figured and therefore very expensive. A rule in amateur astronomy is that if you want the most light-gathering power for your buck, go for a reflector. If you want the most image quality, get a refractor (with ED glass).

Alex, what I get from your post is that reflector lenses are more difficult to configure correctly and hence more expensive? Does a very high quality reflector produce the same results as a high quality refractor? If not, is there an understandable physical reason besides "coatings"? Chromatic aberation, which could affect contrast and detail (I think) spoken of in previous posts, is corrected in refractor lenses with coatings of various types. Do these, through the correction process (light bending?) add to detail and contrast as a result? If putting the spectrum of colors on a single focal plane equally is the ideal it would seem that all the plus-factors for a good photo would be there also, regardless of lens type. The Questar lens has no comma--very high quality and very expensive. Appreciate the intereset. I'm going to play around this weekend if the light is good (storms in my area forecast) and do some comparison. In passing, I took a photo of a bald eagle last January with an 18-200 Nikon (not known for its quality as well as the 70-200?) . This was a snapshot (I dropped my pack, racked the lens out and released the shutter-AF of course) at probably 200 mm. The detail was amazing. The bird was at least 250 yard distant and the bird's eye could be esily discerned (even the pupil) in enlargements shot with the large format jpeg. Suble detail in the feathers could also be distinguished. I say this because modern refractor lenses are really "there" in most cases.