Linos Inspec lens (105mm macro) - fungus or dust?

[daz7]

Hi guys,

I have recently bought a Linos Inspec.x L 105mm macro lens from China. This is an industrial lens, basically the same as Rodenstock macro 105mm float, but with the floating element set at a rigid 1:3 scale.
The price was excellent, the delivery took ages, but now, when it finally arrived I do not know if I should even keep it.

The glass looks clean but there is a lot of white spots on internal metallic surfaces. At first I thought that would be a case of "schneideritis" and just black paint flaking, however there are also white spots on silver internal rings - is it a lot of internal dust or fungus?

I have never had any such dusty/fungi lenses and I am wondering if I should send it back or try to clean it somehow. Is it even doable, considering how advanced this lens' construction is.
Any help appreciated.

 

[Paul Spinnler]

Not ideal. Not sure if this can be fixed.

Was it disclosed and did you check whether it affects performance?

You won't get a lot down the line given it is the Linos fixed mag variant with these spots – so the only reason to keep it would be IMHO if it has no performance impact and if you are fine with the fact that it won't be an easy sell, should you want to part with it, at one point.

Unfortunately the reason for the low price seems to have been based on the condition as well, a bit?

Its a niche lens, so I guess it could make sense if it is a bargain and if you are fine as long as optical performance is intact.

 

[4x5Australian]

Hi daz7. That's disappointing. Rather than fungus, the speckling visible on the surfaces this side of the iris resembles pitting corrosion.

Corrosion of anodized aluminium - if that is what the spots are - might have been caused by stray electrical currents within the lens's former industrial environment.

In its new environment, the corrosion is probably stable. However, it's not something that will be possible to remove by cleaning.

Do you see any image degradation, such as flare?

If the lens is hard to find, and the price was really excellent, and it performs well, then I think I would be happy to keep it.

Rod

 

[Paul Spinnler]

If I remember correctly the Linos variant is like half the photo variant – so it would need to be a hefty discount on the Linos variant to justify it.

Before buying my Alpa variant I checked pricing on the Linos variant and it was super cheap – but with fixed ratio and a lower level of quality control apparently.

All depends on the IQ impact and your tolerance for cosmetic defects / price acquired.

 

[daz7]

Thanks guys.

I have taken a good look at the glass and it seems to be clear, so hopefully that's not fungus but metal corrosion as @4x5Australian suggested.
By the way, is it even possible for fungi to live on metal only, not on glass?

I have decided to keep the lens and the seller (who did not mention any corrosion in his listing) offered me a small rebate to keep the lens.
The price was good enough (under $300 after discounts) to justify keeping it even if no-one would buy it from me in the future.
I am guessing it makes this lens a possible candidate for the "bang for the buck" category.

The lens flares quite easily but it could be due to the very short distance of the rear element to the sensor - the Linos industrial version's lens barrel is quite long, so if used for its intended scale it gives around 5-6 cm of space between the lens and the sensor. Most of that space is then taken by the behind the lens shutter and sensor mount, so my Sinar's frames are maybe 20mm apart.
Also, the lens board that I have used is not optimal as it's got a some sort of shine to it, further contributing to flaring.

I think I will need to work out some way of mounting a shutter in front of that lens and find a better mounting board or paint the existing one.
To temporarily deal with the flaring, I have used a short and wide lens shade it seemed to help with flaring a bit.

What I like with the Linos optics is the lack of distortion, nice microcontrast and good colour representation.
It is hard to tell how much the resolution differs from the Rodie's photo lens equivalent but it seems to be OK, at least on par with Rodie's macro 120mm, which is a compliment for the supposedly less carefully checked and oftentimes mis-treated industrial optics.
Also, the usable image circle seems to be much (far much) bigger that the stated 83mm and is probably closer to 100-110mm.
@Paul Spinnler I am guessing that the photographic variant with a floating element must be even better but then I wouldn't be able to get it for $300, unfortunately.


I have just taken a quick and dirty test shot (at f11, so well away of the lens' optimal aperture of 5.6). Speaking about dirt - I have also discovered that my sensor needs to be cleaned, soon:


And here is a 100% view form my 50mpx back:

and another one:


At f5.6 resolution is improved but then the depth of focus is hair-thin:


And here is how it looks mounted in front of the Sinar shutter:

 

[rdeloe]

That's a bargain for a really nice lens. Well done.

This may or may not be relevant, but if you can't get on top of your flare problems with the solutions you described, consider a baffle at the rear. It's a simple and inexpensive solution that might be all you need.

I had some long enlarger lenses I was using as taking lenses a few years ago that had what I thought was unsolvable veiling flare. Lens hoods of any length did not make a difference. The solution was a rear-mounted baffle; it eliminated the flare. Here's a post I put up that illustrates the problem and the solution: https://www.dpreview.com/forums/thread/4557688#forum-post-64897184

 

[daz7]

Thanks, @rdeloe - great idea and I will try to make a rear baffle for that lens soon.
By the way, how do you calculate the needed rear diameter for the baffle so it would not obstruct the image circle?
Am I right to think that to calculate I should take the optical centre of the lens, calculate the distance to the rear edge of a baffle ring and then calculate the needed diameter based on the lens angle of view?

Oh, silly me, I thought that your baffle was all that metal thing in the back and it turns out to be just a flocking rectangular shape inside.
Nice one. I will do that much quicker then. Thanks.

Can you tell me, what material you've made your baffle from? Was it a telescope flocking paper / velour?

 

[rdeloe]

Right in one. It was telescope flocking paper attached to a circular disc of stiff plastic that I cut from an old report cover. I made trial ones using black construction paper and they worked as well.

 

[Paul Spinnler]

Wouldn't complain for 300 bucks!

 

[cunim]

That's a bargain for a really nice lens. Well done.

This may or may not be relevant, but if you can't get on top of your flare problems with the solutions you described, consider a baffle at the rear. It's a simple and inexpensive solution that might be all you need.

I had some long enlarger lenses I was using as taking lenses a few years ago that had what I thought was unsolvable veiling flare. Lens hoods of any length did not make a difference. The solution was a rear-mounted baffle; it eliminated the flare. Here's a post I put up that illustrates the problem and the solution: https://www.dpreview.com/forums/thread/4557688#forum-post-64897184

Interesting. My Kipon Phase/GFX adapter flares badly with the P1 lenses, particularly the 120 macro. Do you think sticking a baffle in the back of that would help. The IC is only just big enough to fill the sensor, with no movement, so I suspect the answer is "no".

 

[rdeloe]

Interesting. My Kipon Phase/GFX adapter flares badly with the P1 lenses, particularly the 120 macro. Do you think sticking a baffle in the back of that would help. The IC is only just big enough to fill the sensor, with no movement, so I suspect the answer is "no".

It's worth a try. If you look at the link I posted, you'll see that the baffle is a fairly small hole. Nonetheless, it did not restrict movements at all. Now that was in the case of a lens designed to enlarge 5x7 negatives, so huge image circle. Your P1 lens will have a tighter circle.

A rectangular hole seems to be important. I tried it with a circular hole and it wasn't as effective. The downside is the rectangular hole may be an issue if the shape of the baffle hole does not line up with the senor orientation. Even that won't be an issue unless you're making big movements.

My super scientific approach to sizing the hole was to make it small and then enlarge only as much as needed to allow the full range of movement I was seeking.

Edit: I just looked at a picture of the lens you mentioned. I would think it has the right baffles in place already. If not, it will be trickier to mount your own.