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08-06-2012, 01:33 PM   #1
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Mirror Lenses: Benefits?

Apart from being amazingly cheap for some of the focal lengths, what might be a benefit in having a mirror lens. I really am quite naive with regard to how they work, as opposed to regular, hideously expensive long lenses... and given that I can't afford a DA*200 or 300, have been considering a mirror lens.

What sorts of things must one be careful of? Is the quality really bad? Are some better than others? How would you know which to get? Do you need extra adapters or not?

Mirror lenses and I have never met, but I think we might, soon.

08-06-2012, 01:39 PM   #2
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They are incredibly light in comparison to traditional lenses as well as being physically smaller.

They generate a doughnut bokeh that some dislike. They have a fixed f-stop and require a great deal of light to get descent contrast. They typically don't produce anything close to good results until the object focused on is pretty far away from the lens.

There are very poor ones out there and some, like the Tamron BB's, that people think rather well of.

Most of the current ones use a T-mound adapter. There are some reviews in the Lens section that can help you learn more.
08-06-2012, 02:52 PM   #3
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Because the light is reflecting off mirrors instead of through glass, there's no CA. Newer lens and glass designs limit this problem, but many older lenses have it to some degree.

The low weight means a low total mass for the camera/lens/tripod. I've read warnings about the lower mass meaning less damping of vibrations. I think that might be true if you already have a great tripod that can handle a large lens. If you have a cheap tripod, the mirror lens should be well within its weight limit. I find the mirror lenses work better on my cheap tripods than longer, heavy lenses.

They are all (or at least the ones that mount on a Pentax) manual focus. They're not as long as conventional telephotos but fatter.

The donut bokeh looks really bad in photos of a bird in tree branches. Even if you are the most bokeh-insensitive photographer, it's distracting. But many other shots will not be a problem.

With the fixed aperture, you can't stop down for more depth of field. That makes focus critical for nearby subjects.

I have the Tamron Adaptall-2 500mm f8 55BB, and it's known for having good contrast for a mirror lens. It also focuses closer than some. I can even use it with an Adaptall 01F 2X TC sometimes. The contrast helps with focus. A good mirror lens is much more useful than a cheap one.

At 500mm, atmosphere is a significant contributor to sharpness and contrast. You can only limit that effect by moving closer. People with $8000 lenses will have the same issues.
08-06-2012, 03:31 PM   #4
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QuoteOriginally posted by Just1MoreDave Quote
Because the light is reflecting off mirrors instead of through glass, there's no CA.
I think any mirror lens has at least one refractive element, to correct for spherical distortion. So there is the possibility of some CA.

Mirror lenses also typically have a pretty small effective aperture, so that the main focusing difficulty is the darkness of the VF image. (I say this not from experience; I've never used one.)

08-06-2012, 03:57 PM   #5
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QuoteOriginally posted by baro-nite Quote
I think any mirror lens has at least one refractive element, to correct for spherical distortion. So there is the possibility of some CA.

Mirror lenses also typically have a pretty small effective aperture, so that the main focusing difficulty is the darkness of the VF image. (I say this not from experience; I've never used one.)
The majority are either f6.3 or f8.
08-06-2012, 04:09 PM   #6
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QuoteOriginally posted by kyteflyer Quote
Mirror lenses and I have never met, but I think we might, soon.
The main advantages are lightness and size. Disadvantages are the doughnut bokeh and a susceptibility to veiling flare which kills contrast. The standard size is a 500mm/f8, but there are 300mm/f5.6 around. Unless you really need 500mm I'd recommend finding a cheap 300mm one - much easier to use handheld and to focus. A really deep hood is a must though.

Scroll through the https://www.pentaxforums.com/forums/lens-clubs/71775-mirror-lens-club.html thread to see how good (and bad) they are.

I have a cheap Super Paragon 300mm/f5.6 and it is quite reasonable - if you are careful how you use it.
08-06-2012, 04:10 PM   #7
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QuoteOriginally posted by baro-nite Quote
I think any mirror lens has at least one refractive element, to correct for spherical distortion. So there is the possibility of some CA.

Mirror lenses also typically have a pretty small effective aperture, so that the main focusing difficulty is the darkness of the VF image. (I say this not from experience; I've never used one.)
I've often wondered about the CA. Most (all?) mirrors have some glass elements at the back of the lens, however by the time the image reaches there, I presume it is formed to a point where it reduces the CA to insignificant levels compared with the focal length (i.e. the mirrors have done most of the work).

I've also heard mirrors are less resistant to shocks, if the mirrors are knocked out of alignment (collimation) it makes a significant reduction to the image.

I have the Tamron AD2 500/8 55B, it's my longest lens and gives me a focal length I wouldn't otherwise have, I don't use it often (on APS-C it is really too long for many uses). Handling any lens of this focal length needs patience, practice and a degree of luck but the dimmer viewfinder image doesn't help in lowish light.

Some examples I've got - on it's own and with various tele-convertors: Cruising airliners and experiments with teleconvertors
08-06-2012, 08:05 PM   #8
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Thanks, guys, and for the links. On looking at many of the shots, it seems to me they are quite hazy, especially with those taken of very distant objects. Also, I kinda like that funky bokeh Could be fun in some shots! And worked really well in kh's flickr page ... the shot of the couple on the bench seat. I liked that

08-08-2012, 01:23 PM   #9
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Hazy can be good sometimes. Last night when I saw the moon, I grabbed the mirror lens and tripod and snapped this (no cropping):

08-08-2012, 09:42 PM   #10
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QuoteOriginally posted by Just1MoreDave Quote
Hazy can be good sometimes. Last night when I saw the moon, I grabbed the mirror lens and tripod and snapped this (no cropping):
yeah, thats pretty cool
08-08-2012, 10:14 PM   #11
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QuoteOriginally posted by kyteflyer Quote
Apart from being amazingly cheap for some of the focal lengths, what might be a benefit in having a mirror lens. I really am quite naive with regard to how they work, as opposed to regular, hideously expensive long lenses... and given that I can't afford a DA*200 or 300, have been considering a mirror lens.

What sorts of things must one be careful of? Is the quality really bad? Are some better than others? How would you know which to get? Do you need extra adapters or not?

Mirror lenses and I have never met, but I think we might, soon.
I collected some bits I know on the topic of mirror lenses here.

In a nutshell - you can't beat a good mirror lens except by getting a high end telephoto and then you jump in another price bracket.

Here are a couple of samples:



08-08-2012, 10:23 PM   #12
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I own a 500/8 mirror that rarely gets used any more. I have had a few good shots from it so I know it's capable but I have had difficulty focusing and also holding it steady. It's light but 500mm is still very long and I can't really hand hold it and get a steady shot. I bought it for shooting my daughters crew team when she was in college for a copuple of courses that were pretty far out on the water. It did the job but I can honestly say that crops from my 300 were better.
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