Celestron 500mm f/5.6 mirror lens quality?

[dan_smith]

A friend has come to me asking about a Celestron 500mm f/5.6 mirror

lens for bird photography. I know from experience that most mirror

lenses aren't nearly as good as prime glass. He knows this also but

is looking at a limited budget & a desire to get a tele that might do

OK, if not really well for small prints from negs. Anyone out there

have any experience with the Celestron mirror lens & whether it will

focus close enough to be useful or is actually close in quality to

Tamron/Tokina/Sigma 400 tele lenses?

He is using a Canon EOS Rebel. Will he have trouble with it since

this mirror lens is manual focus only?

[bobatkins]

I'm not sure the extra 100mm would be worth loss of AF and aperture control. Manual focus on a Rebel could be tricky for some people (it has a plain screen, no split image focus or other assist device and the electronic focus indicator doesn't work with MF lenses). For most people a used 3rd party APO lens would be a better buy.

 

BTW if you really want to go cheap Adorama have a "Pro-Optic" 500mm f5.6 mirror lens for $210. If your standards are low enough and/or your print size is small enough and you think you can MF it, I hear it produces OK, if not spectacular, images. I really don't think it would be the best route to go though.

[jeff_drew3]

I've used inexpensive mirror optics before and find them wanting in almost every way other than price. Even the T/T/S 400 teles differ in quality. The Sigma 400 APO is significantly better than the much cheaper Tokina 400mm. But, if one doesn't use it a lot, makes small enlargements, a mirror optic gets one by. Resale new ones is poor!

[thomas_jakubowski]

Dan,

 

I purchased a ProMaster 500 mm mirror lens (f/8) (Schmidt-Cassegraine)last summer for use on an Olympus OM-1n camera; the photos that it help me to produce sold for $100 each at my very first photo exhibition. This lens let me take pictures like nothing I have produced before.

 

Let's get some things straight. This lens is hard to use, primarily because it is a fixed f-stop; exposure is controlled solely through shutter speed. Focusing is an issue too, because the depth-of-field is narrow; also, you need a tripod to stabilize things.

 

So much for the bad news. Because I have something of a background in optics, I recognized that reflective lens systems are devoid of chromatic and spheric abberations, neatly side-stepping these very important refractive optics issues. Light reflects off only two surfaces, then goes on to the imaging optics (1 or 2 refractive lenses).

 

On the other hand, a typical refractive lens of such long focal length may involve 15-20 elements, each with its own coating(s). Light travels through these lenses, through each coating, and the light hitting the film ultimately has been refracted 30 - 40 times. That's why these lenses cost so much; they must be engineered to minimize (minimize, not eliminate) chromatic and spherical abberations. And lets not forget about the light loss going through so many elements and surfaces.

 

I LOVE this lens. Everybody told me not to buy it because it was so hard to use. OK, everybody is entitled to their opinion. The trick here was to use that narrow depth of field to my advantage. Only the subject of interest was in focus; everyting in back or in front of it was highly blurred. The blurring gave an aura of mystery to each photo. That's why people were willing to buy them from me to hang on their walls.

 

 

I can only tell you that when I showed my photos to others (photographers as well as lay folk), the responses ranged from "...Oh my..." to gasps of disbelief. I'm not joking about this. It was quite rewarding to see these responses - it made all the hard work worth while.

 

Regards,

 

TJ

[thomas_jakubowski]

Dan,

 

Forgot to mention: the mirror lens was engineered for use as a macro lens as well as long-distance. I take photos of objects as close as 8 foot away.

 

Regards,

 

TJ

[bobatkins]

A few points:

 

Depth of field depends only on focal length and aperture. A mirror 500/8 has exactly the same depth of field as a refractive 500mm lens at f8.

 

A "typical" 500mm refractive lens has maybe 6 or 7 elements, not 15-20 (e.g. Canon 500/4.5L). Transmission through a multicoated element averages about 96-98%. Reflection from an aluminized mirror averages about 90%. Even mirror lenses have to use two or three refractive elements for purposes such as field flattening.

 

Mirror lenses suffer from most of the same aberrations as

refractive lenses, with the exception of chromatic aberration.

They show coma, astigmatism, field curvature and distortion as

well as spherical aberration (depending on design). They

also show increased image degradation due to diffraction from

the large central obstruction which is present in all

commercial mirror lenses.

 

Many mirror lenses focus quite close (this is easier to do in a compound design as less movement of the

optics is needed). This doesn't really make them "macro" lenses though

as aberrations tend to get worse when close focused. I have a Tamron

500/8 SP lens which has 1:3 "macro" capability, but image quality drops.

 

I'm not saying mirror lenses aren't sometimes useful,

just that they're not magic...and they certainly

don't outperform or equal a good refractive lens in any area

except for price!

[george_rhodes]

I've used three different brand catadioptric mirror lenses over the years and was not very impressed with any of them, at least for my purposes. The thing that really limited the usefulness of the lenses for me was the way out of focus highlighted areas appear as little doughnuts in the final image. Of course, if you're looking for this particular effect for creative purposes, it can be a plus, but those little rings of light seemed to be there too many times when they detracted from the image. Also, mirror lenses don't perform well with a teleconverter. In my opinion, for what it's worth, there are simply too many better optical alternatives today to justify a mirror lens, especially for nature work. I think the Sigma 400 would be far superior for your friend's purposes.

[william_kazak]

<p>I saw a photo in Life magazine when I was young. The mirror lens isolated the athlete and the background was compelling. The photog was stationary on a tripod. Eventually, I acquired about three different mtrror lenses. Hard to use them. The f stop is not the t stop. Depth of focus/field was so tiny as to make it almost impossible. You need fast shutter speeds. Moving subjects, forget about it or get really lucky. So dark thru the viewfinder; typically they are F8 or F6.3 at 500mm. I have a Celestron 300mm F5.6 right now. Very compact. Pop Photo used to publish resolution numbers and they were always rather low for mirror lenses.</p>

[srspeck]

<p>I have never used the Celestron 500mm f5.6, but still have a Celestrion C90 1000mm F11 that I purchased in the mid 70s. It is reasonably sharp, if you can get it focused and use a solid support, but not in the same class as my Reflex-Nikkor 500mm F8. If you need inexpensive reach, that is the lens I would recommend. Check Ebay. Of course you do have to live with the donuts.</p><div></div>

[Mike Gammill]

The 500 mm f5.6 has a larger central obstruction than the f8 version so contrast suffers. Also the deeply curved front

meniscus corrects abberations in primary mirror but provides optimal correction for a specific spacing between primary and

secondary mirror. Since mirror lenses focus by moving the primary you will only have best correction at a specific distance.

The 500mm Reflex Nikkor is about as good as they get. The Minolta Rokkor and other camera makers generally have

good mirror lenses. I've gotten good results with my 600mm f8 Sigma mirror lens.

[dan_fromm2]

<p>Steve, I bought a C-90 in 1978. It is the worst lens I've ever owned, had terrible astigmatism. It couldn't bring a grid's vertical and horizontal lines into focus at the same time. Eventually I gave it up, sent it to Celestron to be made right. They replaced it under warranty, the replacement is the second-worst lens I've ever owned.</p>

<p>Back then Celestron's QC was very poor. I'm glad you got one that was even usable, think you were very lucky.</p>