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Offline Danzig

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Mirror lenses
« on: June 28, 2011, 04:58:12 PM »
Hi all, fresh to the site and forum, but would like to tap into your knowledge for some advice...

I'm thinking of purchasing a 500mm Mirror lens for my a390 for wildlife and maybe some motor sport/astro use.

Has anyone had experience with these and can you recommend a make? Pros and cons please...

Thanks in advance!
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Offline subbu68

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Re: Mirror lenses
« Reply #1 on: June 28, 2011, 05:34:31 PM »
From my little knowledge about telescopes, mirror 'lenses' (should we call them lenses?) have no chromatic abberation. The  normal refractive lenses suffer from this and warrant the ED and APO elements to control it.
 
Mirrors do have spherical abberation that the manufacturers must have controlled using parabolic mirrors.

They need secondary mirrors at the front to reflect the light received at the primary mirror to the camera sensor. These mirrors might have been supported at the front of the 'lens' and these supports introduce spikes due to diffraction. If the camera manufacturers have some other technique to include the secondary mirror on the inner surface of front correction lens I do not know. If so that would avoid spikes.

The secondary mirrors occupy certain area obstructing the light path. This means lesser light than a normal lens of same diameter as light collection is directly proportional to area of the collector lens or in effect diameter. This reduced area reduces the contrast.

Any user might throw better light than my theories.

For astro use you would need faster lens that would be available in refractors generally. A good APO telescope with T ring adaptor.

Cheers
Subbu
« Last Edit: June 28, 2011, 05:38:19 PM by subbu68 »
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Subbu (Subramoniam)

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Offline Danzig

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Re: Mirror lenses
« Reply #2 on: June 28, 2011, 05:47:20 PM »
Cheers for the info, am currently using a Meade Maksutov-Cassegrain & Orion Reflector via a T mount for the Astro stuff, but wanted something a little more portable..?

Be good to hear from anyone who's currently using a Mirror..?
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Offline subbu68

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Re: Mirror lenses
« Reply #3 on: June 28, 2011, 06:05:51 PM »
Aha, then you could advise me on astro use. I have a Skywatcher 4", 1000mm Acro. What all should I get to mount my A200?
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Subbu (Subramoniam)

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Offline PhilBee

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Re: Mirror lenses
« Reply #4 on: June 28, 2011, 06:53:50 PM »
Hi Danzig, I have only previously used a 300mm mirror for a film camera but the principles are the same.

Pros, smaller and more lightweight than non mirror equivalent, less room needed in the gadget bag. Sony 500mm is autofocus. Not as obstrusive as a non mirror so more candid.

Cons, fixed apature, usually f8+ unless you add small supplied filters to increase. As a result usually a darker image in the viewfinder. Unlike the brokeh of a normal lens the brokeh of a mirror lens will record highlights as 'doughnuts' as a result of the mirror therefore it's a 'love them or hate them' thing.

Don't be tempted by the cheap 'T' mount mirrors of Samyang(?) etc which get a mediocre feedback at best. 

Mirrors have their place but in limited uses, and I've never seen a sports photographer with one. Maybe you could check out the Sigma  200(?) to 500mm 'bigma' zoom which is apparently highly regarded?

Best of luck!
Don't you just love helping other folk spend their money :-)
Phil
« Last Edit: June 28, 2011, 06:58:04 PM by PhilBee »
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Offline Danzig

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Re: Mirror lenses
« Reply #5 on: June 28, 2011, 09:39:12 PM »
Subbo68- Skywatcher should do a camera mount for that scope, if not try Broadhurst Clarkson & Fuller or Orion Optics as all Reflectors have the same mount (into the eyepiece holder) via the usual T2 mount.

http://www.telescopehouse.com/acatalog/Online_Catalogue_Camera_Adaptors_15.html
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Offline subbu68

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Re: Mirror lenses
« Reply #6 on: June 29, 2011, 04:51:54 AM »
Thanks Danzig.

I am looking to order some photo accessories from BH Photo as they are the only ones shipping to the UAE and cheaper than getting from the UK. Thought would add what is required for mating the camera to the scope in the same shipment. Had missed these when I ordered some EPs and diagonal for my scope from Agena Astro.

A T-ring to the scope and a Minolta / SONY Alpha adaptor would do?
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Subbu (Subramoniam)

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Offline GeirJ

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Re: Mirror lenses
« Reply #7 on: June 29, 2011, 09:18:02 AM »
I have had the Sony 500mm mirror lens for about 1/2 year and used it a few times on the a850. It is one of the lenses I am not going to sell (I am selling some lenses at the moment to finance a 70-400mm G), but I would not regard it as a lens for fast moving action. I tried it out at an airshow about a month ago and this was not a great success. I ended up using the Sigma 100-300mm F4, sometimes with 1.4 TC. I got some sharp pictures of a hovering Sea King helicopter with the 500mm, but fast moving planes were difficult. The AF is not all that fast and there is no focus limiter, so the autofocus hunted more or less the whole time.
Still, it is a nice lens, not too expensive and compact and lightweight, but you need practice to use it to its full advantage.
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Offline Fud

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Re: Mirror lenses
« Reply #8 on: June 29, 2011, 10:17:05 AM »
Quote from: subbu68 on June 29, 2011, 04:51:54 AM
A T-ring to the scope and a Minolta / SONY Alpha adaptor would do?

Yep that is what you need - at least that is what I got to fit to my celestron.

As for the 500 mirror I did have one for a while but because of the F8 and poor UK light I didn't use it that much.  I believe Clive used his for a while for wildlife but since he's gone to G glass I don't think he uses it - I know it does suffer from doughnuts in the background
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Offline JimA

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Re: Mirror lenses
« Reply #9 on: June 29, 2011, 06:48:31 PM »
dont even think about anything other than minolta/sony

in the UK its a sunny day lens, contrast is not high and f8 is pretty low but it does autofocus its not the fastest lens I own 

Bokeh is ok unless there is a bright out of focus point which then becomes a doughnut

But all these cons are nothing compared to the fact that other 500s weigh 10x more esp when you factor in a tripod and I ain't carrying that sort of weight around all day. The mirror just sits in the bag  with the kit lens, a 10-20 sigma, a 50mm f1.4 and a beercan that covers most situations. If the light is low I swap the mirror and beercan for a 70-210 f2.8. That covers most situations     

I posted a couple of hand held shots last week
http://www.dynaxdigital.com/images-to-share/gotcha/   

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Offline Gordon McGeachie

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Re: Mirror lenses
« Reply #10 on: June 29, 2011, 09:36:41 PM »
Many years ago I had the Tamron 500 mirror in Minolta MD mount.............

what a lens that was, I loved the lack of weight so much that I would not hesitate to try out the Minolta/Sony one.

as long as you know the restrictions etc, then it should do..........

I used my old one for airshows and it did great................
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Offline Lez60

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Re: Mirror lenses
« Reply #11 on: July 01, 2011, 03:58:22 PM »
Sony/Minolta 500mm lens for me. As others have said, it's reasonably light, easy to handle and the best bit: autofocus. This really makes a difference when compared to other manufacturers manual focus lenses.

They don't come up for sale very often but they're worth waiting for unless, of course you want a new one.

Quite a few photos have been posted taken with this lens. (images to share). Enter sony 500mm reflex in search box on home page.

Les.

« Last Edit: July 02, 2011, 10:11:17 AM by Lez60 »
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Offline balacau

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Re: Mirror lenses
« Reply #12 on: July 05, 2011, 06:35:34 AM »
I'm a current user of Sony's 500mm Reflex F8 mirror lens.  It was bought originally only for the range as I did not understand the concept (or potential benefits) of a mirror lens.  As far as I was concerned, it is a 500mm lens in a compact and fairly light-weight package which would give me additional reach if required.  What's not to like?

And all I can really say is that it worked and continues to work very well indeed.  Certainly much easier to cart around than the 50-500mm Bigma when you are travelling around; along with some other glass too.  It does, however, require a fair bit of light to work with otherwise the AF will not lock.

I also have a purely manual Sigma F8 600mm mirror that I bought off eBay.  Its not something I really use "seriously", more for playing around really but still not a bad piece of kit either.  The lens hood is only rivalled in size by Tamron's 180mm macro...

My view on mirror lens usage is that if you can get away with using just that focal length and fixtured aperture, then you should be alright.  Modern equivelent primes are faster but also far more expensive unless you are talking about the ultra-large mirrors which are rare.  I did find one Minolta 1600mm mirror up for grabs, asking price was £2100.  That's a speciality lens if ever I saw one, but then again so is a 600mm F4 I suppose!

Best regards

Gavin
« Last Edit: July 05, 2011, 06:38:08 AM by balacau »
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