Mirror lens question

Sodak · Apr 10, 2009

I'm looking on ebay for new lenses and I see this:

Bower 500mm/1000mm Mirror Lens.

Buy it now $169.

My gut tells me that these cant be worth a hoot, can they? Does anyone have experiences they can share using this type of lens?

AlexColeman · Apr 10, 2009

No good. Just search for previous topics.

tirediron · Apr 11, 2009

They're heavy, slow (Typically f8) and especially in the cheaper ones, really dodgy optical quality. Unless you have to pack 1000mm into a relatively small package, can shoot in very bright light, and aren't super-fussy about the overal quality, walk away.

Sodak · Apr 11, 2009

AlexColeman said:
No good. Just search for previous topics.

Thanks. I didn't remember seeing them talked about in this forum, but I've only been around about 3 months.

I shall flee in earnest with my cash secured.

Dwig · Apr 11, 2009

Sodak said:
I'm looking on ebay for new lenses and I see this:

Bower 500mm/1000mm Mirror Lens.

Buy it now $169.

My gut tells me that these cant be worth a hoot, can they? Does anyone have experiences they can share using this type of lens?

Mirror lenses are a mixed bag. On the plus side:

1. generally reasonably high resolution, particularily in the center
2. very light for their focal length
3. very compact for their focal length
4. generally focus closer than conventional lenses of the same focal length

On the negative side:

5. very prone to flare
6. the world's worst bokeh
7. generally slow (modestly small maximum aperture)
8. no iris to adjust aperture; you always shoot at maximum
9. with very, very, very few exceptions (I believe there was only 1), they are manual focus.

The bokeh (quality of out-of-focus portion of image) problem manifests itself as donut or crescent shaped out-of-focus highlights. These can overlap creating a rather annoying background when shooting against a complex background (e.g. leaves with small spots of sky showing through). A single bird against a blank sky or with a few clouds, on the other hand, doesn't generaly display any flaws.

#1 and #5 mix to yield what you see as "sharpness". Sharpness doesn't exist in the real world; it is the impression you get when your brain combines the contrast between the tones on either side of the edge with the width of the edge as the one tone blurs into the other. When shooting in low flare situations, mirror lenses tent to produce images that look "sharp". In high flare situations (e.g. backlight, reflective objects in the shot, ...) the percieved sharpness drops of fast.

Add to all of this that the Bower brand is not known for high quality optical, the lens you list is probably not a great option.

Katier · Apr 11, 2009

tirediron said:
They're heavy, slow (Typically f8) and especially in the cheaper ones, really dodgy optical quality. Unless you have to pack 1000mm into a relatively small package, can shoot in very bright light, and aren't super-fussy about the overal quality, walk away.

The speed isn't really an issue, most outdoors shooting is done at f8 ( heck LF often shoot at f16 or F22 regardless of the light ) or slower.