[gibikote]

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Hi

Being a very comfortable user of the Tamron 500mm f8 mirror lens, I am on the lookout for a faster mirror lens, which lead me to this on ebay

SIGMA 400MM F5.6 TELEPHOTO LENS PENTAX MOUNT FAULTY | eBay

The seller has shown us some pics of what he guesses might be fungus. But the last pic shows some grainy brown stuff.

* Is this fungus.. can fungus look like this? I always have seen it to be white, hazy or cob-web like.

* Is this (whatever) be reversed / can the lens be restored? I get the feeling that mirror lenses are more difficult to handle and clean.

* Is this item worth considering?
This has been reviewed as average/poor on the forum here.

I have read some nice reviews of the Rokinon 6.3, which might be an option; but this one is 5.6 - not many visible.


Thanks.
Sridhar

[Blue]

Sridhar,,

IF you get it cheap enough and can have it cleaned it may be worth it. But that is an IF. It would cost me about $80 U.S.D. to get a mirror cleaned. Note that the 'if' is bold, italicized and underlined.

[Just1MoreDave]

* Is this (whatever) be reversed / can the lens be restored? I get the feeling that mirror lenses are more difficult to handle and clean.

I assumed that mirror lenses were constructed like the mirrors in cameras, that is, the reflective surface is right there on top, like a lens coating. That would make cleaning really difficult, because that kind of surface is easy to damage.

The Tamron Adaptall-2 isn't built that way, so cleaning is easy. I don't know if that applies to any other mirror lenses. I wonder if it's possible for a front-silvered mirror to be multi-coated, as the Sigma says. That mught be a sign that it's like the Tamron.

The lens itself is less complicated so the odds are better that you can access the surfaces that need cleaning.

I think in terms of doing the repair myself, and therefore, whether the repair is possible. If you intend to get a professional repair, you might get a rough estimate before bidding. Then it's just a matter of adding the repair cost to the bid to see the full price.

[jstevewhite]

Hi

Being a very comfortable user of the Tamron 500mm f8 mirror lens, I am on the lookout for a faster mirror lens, which lead me to this on ebay

SIGMA 400MM F5.6 TELEPHOTO LENS PENTAX MOUNT FAULTY | eBay

The seller has shown us some pics of what he guesses might be fungus. But the last pic shows some grainy brown stuff.

* Is this fungus.. can fungus look like this? I always have seen it to be white, hazy or cob-web like.

* Is this (whatever) be reversed / can the lens be restored? I get the feeling that mirror lenses are more difficult to handle and clean.

* Is this item worth considering?
This has been reviewed as average/poor on the forum here.

I have read some nice reviews of the Rokinon 6.3, which might be an option; but this one is 5.6 - not many visible.


Thanks.
Sridhar

If you can get it cheap enough, it might be worth a shot. If the actual mirror surface has fungus, though, you're probably not going to get a good result. That said, if the glass is not pitted, you might be able to get a telescope shop to re-silver the mirror.

Coatings on the mirror surfaces are a marketing device, as mirrors do not suffer from the CA that refractive surfaces do, as all wavelengths of light reflect at the same angle, even though they don't refract at the same angle. (mirrors are apochromatic by physics rather than by design). Some mirrors (so called "solid mirrors") have a solid optical glass tube with the reflective surface on the concave back surface. Some mirror lenses use active refractive optics as well; there's a considerable variance in design.

Frankly, I'd give it a shot and see if I could score it for, say, $30. You might even be able to re-silver the elements yourself if you can get to 'em, and have a nice lens for not much money. Otherwise you're out $30, which is about my limit for 'experiments'.

[gibikote]

Thanks everyone for your thoughts and suggestions.
I shall see what is available locally in terms of repair, re-silvering etc.

-Sridhar

[Laurentiu Cristofor]

Yuck. This looks worse than the sample I got and I was disappointed with its performance. I thought that it being faster than my Tokina 500/8, it might be more usable. But it was less sharp, so it didn't matter it was faster - I couldn't get any keepers with it. I would skip it. It would probably be a better idea to get the Samyang 500/6.3 instead.

[jstevewhite]

Yuck. This looks worse than the sample I got and I was disappointed with its performance. I thought that it being faster than my Tokina 500/8, it might be more usable. But it was less sharp, so it didn't matter it was faster - I couldn't get any keepers with it. I would skip it. It would probably be a better idea to get the Samyang 500/6.3 instead.

Yeah, I forgot about the Samyang. You're absolutely right, that's probably a much wiser course of action.

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Last edited by jstevewhite; 05-14-2011 at 10:56 PM. Reason: correction

[gibikote]

Thanks for that; shall let this one pass.
I shall be looking for the Samyang.. and Rokinon too?

[Laurentiu Cristofor]

Thanks for that; shall let this one pass.
I shall be looking for the Samyang.. and Rokinon too?

Yes, the Samyang is available under a lot of brands - Rokinon is one of them. Just make sure you don't get the 500/8 version - that is poor. The 500/6.3 seems to be much better - no direct experience, but I've seen some full size shots taken with it and it looked very sharp (see this thread).