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white rear lens cap purpose?

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addy landzaat View Drop Down
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 17 April 2019 at 21:09
Originally posted by Miranda F Miranda F wrote:

Originally posted by addy landzaat addy landzaat wrote:

Originally posted by michelb michelb wrote:

My guess is they were cheaper to make and contained less chemicals (read petroleum) to make them black.
It has been a while since I was trained in Material Science, but plastics do not work like this.

I can't confirm the material of lens caps, but quite a lot of things have carbon black added to make them black. Arguable whether the carbon comes form fossil fuels or not.
Petroleum is not carbon.
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 17 April 2019 at 21:31
Originally posted by addy landzaat addy landzaat wrote:

Petroleum is not carbon.
You're right, petroleum isn't carbon, but it contains carbon atoms that can be turned into soot, carbon black and several other materials that contain (near) pure carbon.
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Post Options Post Options   Quote wesleysa Quote  Post ReplyReply Direct Link To This Post Posted: 17 April 2019 at 22:14
Originally posted by Photosopher Photosopher wrote:

White caps are made of fairy dust, and only appear in the lives of the most ardent A-Mount fans. You are very lucky to have one come across your path. The Mind of Minolta has smiled upon you. Hence forth, you will be seen as irresistible to the romantic. Traffic lights will shine green upon every journey. Your computer will never crash again. Keep an eye on your mailbox for that vacation giveaway sure to come.   If you're a gambling man, now is the time to lay it all on the table. From this day forth, your horse always wins.

Welcome to the club.




I have 4 white caps, 2 branded Minolta and 2 branded Konica Minolta. Whether they came with their original lens partners is anyone's guess, I only have 2 'original' Minoltas that must've been sold with the Minolta brand lens caps.

Unsurprisingly the older ones seem looser.
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Post Options Post Options   Quote Phil Wood Quote  Post ReplyReply Direct Link To This Post Posted: 17 April 2019 at 23:49
I have a mix of rear caps - the white ones are the ones I treasure most. They grip well and make aperture checking a doddle. Some black ones - 3rd party I suspect don't even have the lug to engage with the aperture lever.

In general I take cheap 3rd party into the field in case they get lost. Same with front caps, cheap centre pinch ones are the default.

Just looked at five white caps - all are branded Minolta, none KM.
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 05:13
Originally posted by pegelli pegelli wrote:

Originally posted by addy landzaat addy landzaat wrote:

Petroleum is not carbon.
You're right, petroleum isn't carbon, but it contains carbon atoms that can be turned into soot, carbon black and several other materials that contain (near) pure carbon.
Yes, but it all is besides the point. Black plastic is not black because of petroleum. It does not work like that.
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 07:20
Originally posted by addy landzaat addy landzaat wrote:

Originally posted by pegelli pegelli wrote:

Originally posted by addy landzaat addy landzaat wrote:

Petroleum is not carbon.
You're right, petroleum isn't carbon, but it contains carbon atoms that can be turned into soot, carbon black and several other materials that contain (near) pure carbon.
Yes, but it all is besides the point. Black plastic is not black because of petroleum. It does not work like that.
Well, I don't think it's totally besides the point. Most materials which are used to make polymers black are based on carbon black, which is produced from incomplete combustion of hydrocarbons, can be petroleum but usually heavier crude oil fractions like vacuum gasoil or the bottom residue from the crude oil fractionation. So I agree that it isn't petroleum that gives the black caps their colour but I can understand that someone without a chemical or refining background says something like that.   

But back on topic, I like the white caps because they open the aperture fully (the black caps only partially) and when mounted you can shine a flash-light through them and easily inspect the lens for dust or fungus.

Also all of my white caps are tight, some of my Minolta/Sony black caps are loose while others still remain tight. The black ones that I have the least faith in are the ones from Sigma, might be coincidence, but all Sigma end-caps I have are loose and easily fall off.

Edited by pegelli - 18 April 2019 at 07:24
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 09:11
Originally posted by pegelli pegelli wrote:

Originally posted by addy landzaat addy landzaat wrote:

Originally posted by pegelli pegelli wrote:

Originally posted by addy landzaat addy landzaat wrote:

Petroleum is not carbon.
You're right, petroleum isn't carbon, but it contains carbon atoms that can be turned into soot, carbon black and several other materials that contain (near) pure carbon.
Yes, but it all is besides the point. Black plastic is not black because of petroleum. It does not work like that.
Well, I don't think it's totally besides the point. Most materials which are used to make polymers black are based on carbon black, which is produced from incomplete combustion of hydrocarbons, can be petroleum but usually heavier crude oil fractions like vacuum gasoil or the bottom residue from the crude oil fractionation. So I agree that it isn't petroleum that gives the black caps their colour but I can understand that someone without a chemical or refining background says something like that.
Thank you! (though we apperantly have different definitions about what is and isn't besides the point )
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Post Options Post Options   Quote SnowFella Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 09:14
Seem to depend on what lens the Sigma caps slip on, only have one Sigma lens/cap to my name and it locks tight on the Sigma lens it came with but slips right off any Sony/Minolta lens I try it on.

Got a mad mix of white's and black caps plus a stack of 3rd party ones and don't really care what ones I use.
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Post Options Post Options   Quote owenn01 Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 09:18
Snowfella - I normally experience the reverse issue; Sigma rear lens caps sit happily on Sigma lenses but not on Sony/Minolta ones; perhaps it's a North:South Hemisphere thing!

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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 09:26
Originally posted by addy landzaat addy landzaat wrote:

though we apperantly have different definitions about what is and isn't besides the point
Probably the difference between a lawyer and an engineer
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Post Options Post Options   Quote SnowFella Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 09:32
Originally posted by owenn01 owenn01 wrote:

Snowfella - I normally experience the reverse issue; Sigma rear lens caps sit happily on Sigma lenses but not on Sony/Minolta ones; perhaps it's a North:South Hemisphere thing!

Best regards, Neil.


Think if you read again you will find we have the same experience
Though I also have a few black Sony ones that will fall off just about every lens I mount them to.
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Post Options Post Options   Quote owenn01 Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 10:15
Ah yes; a reflection of doing this over a coffee break at work!
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Post Options Post Options   Quote Bob J Quote  Post ReplyReply Direct Link To This Post Posted: 18 April 2019 at 12:35
Back in the early days of meetings - at least the type where we were all staying overnight at the same place, the evenings would tend towards 'stabilization' and kit (often with lots of kit arranged on the tables in front of us) - conversation one night in Southern Sweeden got onto rear caps (or as Manfred referred to them - 'Butt Plugs') and people expressed their preferences... and we all came away with the type we preferred...

Originally posted by Pyl Pyl wrote:



(Photo taken by Patrik Ylen 11 years ago! click the picture for more from that meet.)
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Post Options Post Options   Quote balacau Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2019 at 10:47
With regards to the rear lens cap fitting, the best fitting ones I've found so far are the newer Sigma and Tamron designs. Now this may be simply because they are new but they have a really nice and solid fit on any brand lens I put them on. I have two older Minolta rear lens caps and they are very loose. I won't use those when travelling as they'll gradually unscrew. Those are used when a lens is in the cabinet.

I've never seen a white lens cap before. That's something I've learned this morning.
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