Used Canon EF 200mm f/2.8l ii usm .. internal spots

[migEOSRP]

I bought a used Canon 200mm f/2.8l ii usm lens very recently for my EOS RP camera (already that the Canon adapter) from an online retailer with excellent return policy. My question is about internal spots visually evident by looking through the lens. There are no scratches or smudges on the outer exposed lens surfaces and the functionality tested so far seems fine. I'm testing this lens mainly for astrophotography (star field photos etc) and with prelim testing at wide open f/2.8 the stars are reasonably pin-sharp up to the edges. I'm thinking of returning the lens as I think there should be absolutely no internally visible spots of any sort. Any suggestions on helping my decision process?

Also, any suggestions on a Canon RF prime lens in the range 200 to 400mm (but not zoom)? 

[shadowsports]

Greetings,

Over time it is possible for some lenses to ingest dust that is often visible looking through the lens, but has no effect on your pictures. 

Spots can also be present and not affect images, but it might be important to understand what they are.   Mold or fungus may continue to grow and might also compromise a lens coating.  At some point this may cause some type of visible anomaly in your images.  

If these spots are on the inside of the lens, we have to assume it's something environmental, likely mold or fungus.  

This is where you have to make a decision.  Me personally, I could never own something with this type of defect.  Other people are totally fine with this and use the lenses for many years without issues.  Spots like these can also impact resale value even if the lens works normally.  I have very high standards, so I'm not the right person to ask.  I wouldn't even consider a lens that had spots or blemishes.  Dust is okay but not spots.  

You need to decide if the lens performs to your expectations.

[ebiggs1]

What Rick says is mostly true. And some dust inside a lens is probably OOF so it doesn't effect the images. However like anything else what is too much dust. Even though dust particles are OOF at some point enough dust will interfere with the IQ. Without seeing it we can not tell with any authority.

Now mold or fungus is a whole other story I would not want any fungus or mold in  any of my lenses that I intend on using. For the most part it can not be removed and most likely will only get worse.

This becomes a cost vs benefit ratio. What did you pay and what does a lens without issues cost? This is not an inexpensive lens and the lens you have is always better than the lens you wish you have.

[migEOSRP]

thank you both (above) for the insightful comments. Here are two photos (taken looking through the lens at a clear sky). The larger 2 dark spots are my main concern. I've contacted to seller to get his comments on this. The spots are definitely internal. Since this used was ~ CAN$1000 used, I am not willing to risk that this is a fungus/mould issue but without taking apart, I imagine it is impossible to tell. I'm looking for a super razor sharp Canon lens in the 200mm f range for astro and that prime lens has good reports. If I decide to bail on this used prime lens, I might get the Canon RF 70-200mm F2.8L IS USM lens (~ $3.k plus). The light weight (of either lens) is a big consideration ... nothing heavier than ~ 1.5 kg.  

[ebiggs1]

That does look like dust but I would rather look at the lens in person to be sure. Dust can be removed or cleaned. Fungus or mold attacks the lens coating so even if it could be removed or cleaned the lens coating would be destroyed. And that would severely effect to lens IQ, but again to a degree so that's your decision.

You mentioned you have an R series camera and are considering the Canon RF 70-200mm F2.8L IS USM lens which I would very much prefer if it was my decision.

[migEOSRP]

I'm certain those larger spots aren't dust on the outer surfaces .. maybe fragments of inside barrel of lens on inner lens components?

The RF zoom (and the more expensive Z version) are tempting but I need to see evidence that these are really exceptional lenses .. particularly at 200mm zoom for adtro use. I wish there was a Canon RF 200mm prime lens which is f range I'd spend most of my astro-time.

[normadel]

Dust, dirt, fungus, other particles INSIDE of a lens, or on the SURFACE of a lens, do not show up distinctly in images, if they can be discerned at all.

Have you taken a look at your sensor to see if it has any contamination on it?

[migEOSRP]

Camera sensor is spotless (very new)

[migEOSRP]

Received a response from the camera distributer:

 " ... Do you see the spot when mounted on a camera? Also, do they appear in pictures? If they only show up to the naked eye, then it is totally normal"

I had asked the distributer if I asked for a replacement (they have 2 more of these lenses), could they visually check (and maybe send a simple photo) and guarantee that there are no such noticeable spots. However the distributer didn't respond to that question.

Is there a way to date the lens given the SN?

[ebiggs1]

"...  do not show up distinctly in images, if they can be discerned at all."

And of course that is totally wrong. Fungus and/or mold inside a lens can affect image quality of a lens. Fungus grows, key word here is grows, on lens elements. Over time, this can lead to various issues, including decreased contrast, shadows, increased flare, and permanent damage to the lens coatings.