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35mm 3.5 versus 2.8

15 replies to this topic

#1 montanawildlives

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Posted 10 June 2021 - 20:55

OK, so I ordered a clone of the 35mm Kyoei Acall Kuribayashi 3.5 lens on ebay, along with a 2mm ZWB1 and 2.5mm BG39 (all in one kit touted as great for UV photography).

It arrived today, but there was a note that the seller was giving me a 35mm f/2.8 lens instead.

From what I can tell, the 2.8 lens is likely a newer version with "improved" coatings that would not work well for UV. If true, I'll be returning it.

Am I correct?

I will do some test shots too, but I trust this group more than my own lyin' eyes at this point.

Thanks!

#2 dabateman

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Posted 10 June 2021 - 21:02

Wait what did you order?
Was it the igoriginal 35mm lens?
I am surprised if thats it, that he gave you a f2.8.

#3 montanawildlives

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Posted 10 June 2021 - 21:49

View Postdabateman, on 10 June 2021 - 21:02, said:

Wait what did you order?
Was it the igoriginal 35mm lens?
I am surprised if thats it, that he gave you a f2.8.

The listing was:

"Kyoei Acall Kuribayashi (T-Mount) 35mm F3.5 Lens & Filter Set! UV Photography!"

"This is a variant/clone (the T-mount version) of the Kyoei Kuribayashi lens of UV photography fame!"

Then just before the lens arrived I received a message that he was sending the 2.8 lens instead. The only identifying information on the lens itself is that white plastic sticker which similarly specifies 2.8 as the maximum aperture.

I did see some information online that the 35mm 2.8 version was likely not good for UV because it was a newer lens and perhaps with "better" coatings.

Thanks.







#4 colinbm

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Posted 11 June 2021 - 01:36

Check with the seller, he is reliable.
The lens is a refurbished lens & is assembled from matching parts of these fabulous UV capable lenses.
The seller has probably assembled this lens from lenses from damaged casings, but good glass & used a faster aperture for yours. That is not a bad thing for UV photography where maximum light is needed.

#5 nfoto

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Posted 11 June 2021 - 09:12

I have yet to encounter an f/2,8 version in the 35mm class of lenses with UV performance to match the f/3.5 models. I'd love to be proven wrong of course.

#6 dabateman

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Posted 11 June 2021 - 10:58

These lenses from Igor aren't straight lenses. He does clean the elements, add seals and adjusts things.
Thus I call them igoriginal 35mm lens and nothing else.
A 35mm f3.5 lens should have a 10mm diameter open aperture when looking down from the front of the lens.
A 35mm f2.8 lens should have a 12.5mm diameter opening when looking down from the front of the lens.
That extra 2.5mm maybe possible and he may have swapped in a different body or aperture control on your version. I haven't measured the elements, but that might be possible. Just don't expect it to be sharp there. You still may need f5.6 or f8.

#7 montanawildlives

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Posted 11 June 2021 - 13:53

OK, thanks everyone. I will do some simple tests and post sample pics. I have the virgin PTFE sample so at least I should be able to set a reasonable white balance for testing now. I realize this is an entry-level kit with generic filters, so my expectations will be moderate; I just want something that is good enough to learn with (I want to be assured that it is ok to blame myself rather than my kit for bad pics!).

Thanks!

#8 Andrea B.

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Posted 11 June 2021 - 18:16

Make lots of photos with your new lens and filters. Long distance, medium distance, and close. Experiment with white balance both in-camera and out. Post photos in a "learning" thread and we will comment and try to help. :cool: :smile: :bee:

I'd like to say that it isn't so much what* gear you have, rather it is how well you learn to use it -- and also -- whether or not you are getting what *you* want from it.

It is sometimes useful also for a beginner to post a raw file to permit some experienced members to convert it to show the maximum which can be gained from a file. We have a wide range of converters in use across the membership.



*of course the gear must be at least minimally UV-capable.
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#9 Fandyus

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Posted 12 June 2021 - 17:20

There are way more knowledgeable people here but from what I know, I would suspect it to be worse as f/2.8 calls for thicker, bigger glass elements.

#10 Andy Perrin

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Posted 12 June 2021 - 18:21

View PostFandyus, on 12 June 2021 - 17:20, said:

There are way more knowledgeable people here but from what I know, I would suspect it to be worse as f/2.8 calls for thicker, bigger glass elements.
I don't think it works that way in practice. For example, the famous Cassar S is a 2.8, and it has fantastic bandpass.

#11 UlfW

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Posted 13 June 2021 - 11:45

View PostAndy Perrin, on 12 June 2021 - 18:21, said:

I don't think it works that way in practice. For example, the famous Cassar S is a 2.8, and it has fantastic bandpass.
That is an exception to the general behaviour, because the Cassar S likely is built with optical glass types that have a rather good UV transmission and that each element is thin.
Many lenses with higher speed often has more and thicker lens elements, giving them less UV-reach.
That is the same phenomenon that makes it difficult to make a wide angle lens with really deep UV-reach.
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#12 nfoto

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Posted 13 June 2021 - 14:51

For a given focal length, a "faster" lens means more elements and often thicker ones as well. One should only compare within a group not different groups of lenses.

#13 dabateman

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Posted 13 June 2021 - 15:09

Lets all remember we are talking about the Frankenstein igoriginal 35mm lens here.
If the 35mm f3.5 elements are 15mm or 13mm in diameter. Than it would be easy to use them in a lens frame or shell with an aperture that opens to 12.5mm.

You will have know idea until you test the subject lens. It might be the same or it might be very different than the igoriginal 35mm lenses that some of us own.


#14 nfoto

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Posted 13 June 2021 - 15:54

The diameteer of the lens is not the same as the (maximum) aperture.

It is the size of the entrance pupil that dictates the "speed" of a lens. And the pupil is an imaginary measure.

#15 dabateman

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Posted 14 June 2021 - 04:55

View Postnfoto, on 13 June 2021 - 15:54, said:

The diameteer of the lens is not the same as the (maximum) aperture.

It is the size of the entrance pupil that dictates the "speed" of a lens. And the pupil is an imaginary measure.

Yes true. But a lens element that is only 8mm can't be used infront of an aperture ring that needs to open to 10mmbto allow for a entrance pupil to dictate the aperture of the lens. But a 15mm element can. So it matters if your push as system beyond its original design because there is room to do so.

Many lenses can be used faster than orginally designed, because there is room to do so. There were quite a few Olympus four thirds lenses designed this way. The aperture would close down to the maximum opening setting. Thus people would focus, engage the lens release, and turn the lens out slightly to get the true maximum opening of the lens.

#16 nfoto

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Posted 14 June 2021 - 05:13

Still the lens will not be "faster" just because the elements are bigger. If there is a physical stop too small for the maximum aperture specified by the lens design you get vignetting. Not loss of "speed".