It's probably a bit too late to ask the above question.. because I already bought it on Ebay for ~1k.
However, I would still like to know what exactly to expect when the lens arrives in a week or two.
I was reasonably happy with my (converted to EOS) Canon 300mm F4, but with this larger (and "L") cannon I expect much less colour fringing and better resolution, judging by Avandonk's work with his 300m mF2.8.
Last edited by bojan; 02-09-2015 at 03:14 PM.
Reason: better title
This link is for the Canon FD 400mm F/2.8 L EF converted, dont know how different it is for your lens, i'm a Nikon kind of guy, but search around on Astrobin to see what gear is capable of (bear in mind processing differences)
Hi Sil, Thanks.
Yes, this lens is quite good, however the images on astrobin are rescaled.. so not quite what I wanted to see.
Anyway, I will know soon enough ;-)
Today, after a lot of anticipation, the lens arrived....
But it was a disappointment.
I didn't mind the external cosmetics, neither the interface to camera (which was stuck BTW). I intended to use it for astrophotography only, so modification to EOS was on my mind from the start.
When I had a look inside against the sunlight I saw the lens have extensive damage caused by fungus and moisture on the back of focussing element. Ouch..
And then I made a biggest mistake of all: I started to dismantle it to see if this fungus can be cleaned...
And then I found out someone attempted to clean it before me and even did not properly assembled the affected element so it was loose inside. Retaining ring was loose and visible as that from the start.
The lens was not really functional when arrived, but I can't prove it now..
Focussing element (7-th from the left on attached optical schematic) needs polishing on back side, it is negative doublet, 70mm dia and 18mm thick.
So, question: where can I polish this surface, or, where can I obtain cerium oxide to do that myself? Are there any mirror-makers left around?
I did polish mirrors in the past, so.. maybe I can do it again?
The front group looks OK (just a tad of fungus on the back of the meniscus, 6-th element from the left), and this can be probably cleaned with windex and dishwashing detergent, no big deal at all.
Oh man, really feel for you Bojan. What a disappointment, let alone the problems from looking more closely at it. I hope there's a Canon lens guru here, or at least a recommendation for someone that could help.
If you're only doing astrophotography you may not even need the iris mechanism? Could be better to stop down externally with rings or something else, assuming you can safely reach the fungus and deal with it satisfactorily.
The probability of finding this particular glass element is pretty slim, but I will certainly ask Canon about it, just in case..
Anyway, I think the affected surface is definitely worth re-polishing, considering the condition of the rest of the glass.
Even without SSC coating, there will be a very small amount of visible inside reflections (because the icoming light beam will be reflected back and diverged on the convex surface of the element).
I should be able to help you if you can trust me with it. Perhaps you can drop in one day so that I can take a good look at it. My guess is that it will need to be reground before polishing. That could be done with minimum thickness loss of perhaps a few hundredths of a mm. I can't resist such a challenge so I would do it free of charge.
I should be able to help you if you can trust me with it. Perhaps you can drop in one day so that I can take a good look at it. My guess is that it will need to be reground before polishing. That could be done with minimum thickness loss of perhaps a few hundredths of a mm. I can't resist such a challenge so I would do it free of charge.
While the problem with the glass surface is being expertly sorted out by Stefan, I was working on modification to EOS..
I removed the iris and all mechanics around it (it will be a spare part in case someone needs it in the future), and designed the necessary parts to fit the EOS adapter..
I have two of them, one is with T-thread , another with M42x1mm.
The one with t-thread has necessary thickness to ensure the camera sensor is in the focal plane of the optical system, so I designed the fitting around it.
The printed plastic part turned out so well I decided to leave it as is.. I only need to slightly reduce the diameter of the section where thread is supposed to be.. so the metal ring of the adapter can be force-screwed on the plastic (unfortunately, my 3D printer is not capable of producing threads with such a small pitch (0.75mm.. or is it?) .. and I need to paint it black inside (or re-print it with black ABS).
any sort of reworking is going to cost you a multicoat bojan, you know that right?
depending upon the refractive index of the glass you are going to lose 6% off each surface, not a trivial amount!
pat
any sort of reworking is going to cost you a multicoat bojan, you know that right?
depending upon the refractive index of the glass you are going to lose 6% off each surface, not a trivial amount!
pat
Pat, I am aware of that..
but it is only one surface affected.. so 6% is not a big deal. I can absorb that.
This is equivalent to reduction in aperture from 140mm down to 135.7.. negligible.
I am pretty sure the loss due to current scattering on the damaged surface is worse.. not to mention the loss of contrast.
ah just re read your post, only on one surface then?
pat
Yep, only one..
BTW, for 2 surfaces the attenuation is 11.64%.. or transmission is 100% - 6% = 94%, and minus additional 6% of 94%, total is 88.36%..
11.64% in total
Canon 400mm F2.8 L FD (non-IS, manual)
