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Minolta MC Rokkor SI 28mm 2,5
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PostPosted: Mon Nov 22, 2021 8:28 pm    Post subject: Minolta MC Rokkor SI 28mm 2,5 Reply with quote

I keep storing this lens because it is not so good wide open at the corners and edges and it is quite heavy.

I happily use Canon FD 28 2,8 and Minolta MD 28 2,8 and 3,5 but I periodically come back to the Rokkor SI because I miss the extra crispness at about f5,6. At this setting I think nothing competes (at least in my equipment).

Let me know your thoughts.

[img]L'Arche de la Défense by lumens pixel, sur Flickr[/img]


PostPosted: Mon Nov 22, 2021 9:07 pm    Post subject: Reply with quote

I wouldn't expect much from that lens at least when it's directly compared to some others (including the Canon FD 28mm F2.8 you've mentioned), but this image definitely looks crispy indeed. Nice work! It's all about the end result and how we like it rather than pixel peeping or what have you. At the moment I prefer using Zuiko 28mm F3.5 which is pretty sharp even wide open, but I'd normally stop it down anyway. I like the rendering it gives. I enjoy using SMC Pentax 28mm F2 too, but it's a bit larger and heavier, so I rather use it for wide angle close ups, ever since I got the Olympus.


PostPosted: Mon Nov 22, 2021 9:11 pm    Post subject: Reply with quote

Nice picture, looks very crispy indeed. I recently acquired this very lens and will try it out soon.


PostPosted: Tue Nov 23, 2021 1:16 pm    Post subject: Reply with quote

It has been UV light treated?


PostPosted: Tue Nov 23, 2021 3:29 pm    Post subject: Reply with quote

Yes and very successfully. I have two of these lenses, one has been exposed three months to an Ikea Janso lamp, the other, three days to an UV led lamp with same result... UV led lights are so cheap I would recommend to buy one.


PostPosted: Tue Nov 23, 2021 3:49 pm    Post subject: Reply with quote

lumens pixel wrote:
Yes and very successfully. I have two of these lenses, one has been exposed three months to an Ikea Janso lamp, the other, three days to an UV led lamp with same result... UV led lights are so cheap I would recommend to buy one.


I have two, both former mosquito killer UV lamps with the right spectral output. The small fluorescent lamp one gets a bit too hot so I have to be careful, the LED one is fine but slower.

I wondered more whether edge definition could improve more with the treatment but as you already did it and still see some fall off ..........
Not that I notice it in the image.


PostPosted: Tue Nov 23, 2021 4:14 pm    Post subject: Reply with quote

There is some definition fall off towards the edge yes.

This lens works like the old ones (it is old indeed), sharp in the center, fuzzy outside unless you stop down. Modern lenses are designed for more even sharpness because this is what tests and markets are asking for. However I often noted that some old lenses stopped down have better average sharpness on the whole frame than some modern lenses.

And this what it is about with this lens. Accept f5,6 and you will be more than happy. If your subject is centered f4 and f4,5 will be perfect. F 2,5 only good in the center. Might nevertheless be useful in some cases.

In other words this lens is the worst compromise between weight, size and quality. Any MD 3,5 is better rounded. But none will reach the quality of the SI at middle aperture.

Choose your camp comrade.


PostPosted: Sun Nov 28, 2021 5:32 pm    Post subject: Reply with quote

lumens pixel wrote:
Yes and very successfully. I have two of these lenses, one has been exposed three months to an Ikea Janso lamp, the other, three days to an UV led lamp with same result... UV led lights are so cheap I would recommend to buy one.


It goes much quicker if you take the offending lens element out. The front cell comes out fairly easily, which in itself then comes apart fairly easily. It's been a while since I serviced these radioactive 28mm 2.5's, unfortunately my memory fails me as to which element in the front group is the radioactive one, but definitely NOT the front lens. I have a vague recollection it was the cemented doublet. No need to be worried about de-centering, all the lenses in the front group have been optically centre-edge-ground and fit the front cell mount precisely (common Minolta practice, very few Rokkors have centering set-screws in the cell mounts such as the early 100mm 2.5 and the 21mm 2.8

I thus managed to clear the element in a few days using a CFL UV terrarium lamp for reptiles (these animals need a daily amount UV exposure, which is in the desired wavelength). This was before UV led lights were cheap Wink