Anybody ever removed the front element of a mirror lens?

cheekygeek · Joined: 05 Aug 2008 Posts: 183

Greetings all,
Just wanted to know if anyone has any experience removing the front lens element on a mirror lens. It looks like it should be the easiest thing ever (just held in by front retaining ring).

Is it really that simple, or are there some "gotchas"?

It appears that a dab of superglue has been applied to the front retaining ring threads (two spots opposite each other). Do you just crack that when you turn the ring off, or do you apply a drop of acetone or something to soften it up first?

I just obtained a bargain Tamron SP 52BB (500mm f8 mirror lens) and it appears that there is a little haze on the back side of the front element. I took a chance that I could salvage it and paid $50.

Thanks in advance, for any words of wisdom.
Smile

shauttra · Joined: 17 Nov 2009 Posts: 778 Location: Latvia

I think it is easy, as you said - you should remove only one front ring.
Mirror lenses have very simple construction.When i replaced grease for my MTO-1000 i need to screw out only one screw, and I divided it into two parts.Thats all Smile

Attila · Expire: 2025-11-18

Little haze will not impact picture quality I am pretty sure.

LucisPictor · Expire: 2013-12-03

I'd be careful. Mirror lenses need perfect alignment, otherwise their performance deteriorates badly.

cheekygeek · Joined: 05 Aug 2008 Posts: 183

Thanks for the replies.

The following link is a corner crop (actual pixels) of the upper righthand corner:
http://www.flickr.com/photos/pixelsmithy/5431812190/

of this photo:

before cleaning. Smile

CarbonR · Posted: Wed Feb 09, 2011 8:15 pm Post subject:

I removed the front element (or, let's say, window) of the 6X7 1000/8 (180mm diameter), don't had any problems but this lens seems to have a quite odd construction (mirror seems to be in two glass element, as a sandwich)

Lloydy · Expire: 2022-01-01

My friend who repairs optical equipment for the military tried to clean the fungus from my Canon FD 500 mirror lens, and he did clear most of it.

But he had to stop cleaning the mirror because the silver finish was so thin that there was a very real danger of damaging it.
Being a professional he tested a minute area and didn't go any further.

The lens is useable once again, even though there are still visible traces of fungus, but at least the mirror is still intact.

visualopsins · Expire: 2025-04-11

Results like that I'd be inclined to leave it alone! Very Happy

Otherwise:

CarbonR · Posted: Wed Feb 09, 2011 9:47 pm Post subject:

The 6X7 1000/8 is even more different : I could not touche the miror Shocked

cheekygeek · Joined: 05 Aug 2008 Posts: 183

Thanks for the replies.

Here is an indoor shot taken with it (high iso)

The Welder (Test of Tamron SP 52BB) by ~Pixelsmithy, on Flickr

This shot was taken from approx. 41 meters (45 yds) away from the subject. The central obstruction of the mirror lens gives you semi-transparent edges of objects inside the plane of focus, as seen by the red toolbox that is only about 20 ft from the camera.

wupdigoj · Joined: 18 Mar 2010 Posts: 85

I can confirm that cleaning a mirror is much more risky than a lens. I have some experience cleaning a telescope mirrors. Your lens seems to perform very well, so I would leave it alone.

Javier

pat donnelly · Posted: Wed Feb 16, 2011 12:01 pm Post subject: Mirror

I forget which is which, if I ever knew, but some probably most, mirror lenses are silvered on the surface and therefore cannot be "cleansed" except by damaging the silver.
The silver may be mercury. Dangerous ....

Just dust off?

Good results from a good lens!

beachboy2 · Posted: Thu Feb 17, 2011 9:12 am Post subject:

"The silver may be mercury. Dangerous .... "
I doubt it. The more modern version is aluminium. Owners of astronomical reflectors have been known to clean/polish mirrors and even re-coat silver mirrors if I remember correctly from my amateur telescope making days . You can google sites with advice on how to clean mirrors. Of course the the often quoted advice of if the lens takes OK pictures, don't mess around with it still applies.
bb2