[colonel00]

So I finally got my hands on a 16-85 and while I was showing it to the wife last night, she asked a question that I didn't have an answer for. I tried searching but perhaps I'm not using the correct name or description as I don't know what exactly this part is called. I assume it's there to reduce glare or reflections or something but I'd like to have a better understanding of why it's on some lenses and other lenses just have fully exposed round glass at the back.


Image borrowed from the internet.

[nitehntr]

So I finally got my hands on a 16-85 and while I was showing it to the wife last night, she asked a question that I didn't have an answer for. I tried searching but perhaps I'm not using the correct name or description as I don't know what exactly this part is called. I assume it's there to reduce glare or reflections or something but I'd like to have a better understanding of why it's on some lenses and other lenses just have fully exposed round glass at the back.


Image borrowed from the internet.

i don't have an answer but my tamron 70-200 f2.8 has the same type of rectangular opening opening. is the 16-85 a rebranded tamron perhaps?

[Adam]

So I finally got my hands on a 16-85 and while I was showing it to the wife last night, she asked a question that I didn't have an answer for. I tried searching but perhaps I'm not using the correct name or description as I don't know what exactly this part is called. I assume it's there to reduce glare or reflections or something but I'd like to have a better understanding of why it's on some lenses and other lenses just have fully exposed round glass at the back.


Image borrowed from the internet.

The shade helps reduce reflections, and is generally more common in crop lenses since the extremes of the image circle aren't visible.

On the DA* 60-250mm, for example, if you remove the shade the lens will cover the full frame image circle. The benefits of having it there are minor

[colonel00]

The shade helps reduce reflections, and is generally more common in crop lenses since the extremes of the image circle aren't visible.

On the DA* 60-250mm, for example, if you remove the shade the lens will cover the full frame image circle. The benefits of having it there are minor

Interesting. Did anyone remove the shade on the 16-85 and try it on the K-1?

[Paul the Sunman]

Interesting. Did anyone remove the shade on the 16-85 and try it on the K-1?

Interesting thought, though I'm very doubtful for the wide end at least. There's a 10-page thread on how to modify the 16-250. I do not know whether the same applies to the 16-85, but it's not trivial.

[Simen1]

It works like a lens hood. It makes a rectangular shadow around the sensor. If its removed then some light will reflect from parts around the sensor, and then reflect back towards the sensor again, reducing contrast. Its not replacing the hood, but supplementing it.

[stevebrot]

It works like a lens hood. It makes a rectangular shadow around the sensor. If its removed then some light will reflect from parts around the sensor, and then reflect back towards the sensor again, reducing contrast. Its not replacing the hood, but supplementing it.

Yep...The feature is fairly common and goes back many decades. In the past, having the rear mask was considered by some as an indication of quality.


Steve

[UMC]

Yep... In the past, having the rear mask was considered by some as an indication of quality.

Funny, the first example from the past that comes to my mind is not exactly what I would consider a quality lens of high rank: The Soligor MC Zoom-Auto F2.5/3.5 f=35-70mm can be found in 2 versions. With rectangular mask and without, but I'm sure the ones without are not lenses that have been tamereped with.

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[stevebrot]

Funny, the first example from the past that comes to my mind is not exactly what I would consider a quality lens of high rank: The Soligor MC Zoom-Auto F2.5/3.5 f=35-70mm can be found in 2 versions. With rectangular mask and without, but I'm sure the ones without are not lenses that have been tamereped with.

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I did not say the opinion of quality was true.


Steve

[Sagitta]

My lowly FA 28-90 has a variation of that. In that case its a rectangle with a circle in the middle.

EDIT: My Sigma 10-20 f3.5 sports a rectangle as well.

EDIT II: And my Pentax M-200.

[colonel00]

Thanks for the comments. So is "mask" the correct term then?

So I understand it's purpose I think but it leaves me wondering about something. There are lenses that will work for both a APS-C as well as a Full Frame sensor. When used with a crop sensor, aren't those lenses letting in all that "extra" light that could cause reflections leading to quality and contrast loss? I guess I'm just trying to now understand why it's something that Pentax felt this lens needed but not others as it seems that this would be a benefit to any lens, wouldn't it?

[Sagitta]

Thanks for the comments. So is "mask" the correct term then?

So I understand it's purpose I think but it leaves me wondering about something. There are lenses that will work for both a APS-C as well as a Full Frame sensor. When used with a crop sensor, aren't those lenses letting in all that "extra" light that could cause reflections leading to quality and contrast loss? I guess I'm just trying to now understand why it's something that Pentax felt this lens needed but not others as it seems that this would be a benefit to any lens, wouldn't it?

It might have something with the particular design of the lens. In my case, all three of mine are all over the map as far as length and purpose (and age). I'm thinking some designs by nature may let in a bit extra light around the edges, so they employ it, while others its apparently not an issue at all.

In the case of my FA 28-90, the image circle is actually cut out from the rectangle, which makes me wonder myself. Here is a shot of that lens's mount (not mine, but the same thing) just to give an idea.

[ScooterMaxi Jim]

Yeah, the SMC 200-m has the rear frame. I don't think it is as good a lens as the 75-150 from the same era that has no frame (I've had both for many years). So, ideas that it makes for more of a quality lens, or crop sensor related, or a Tamron product would pretty much qualify as alternative facts.

[UncleVanya]

This is related - but for reversed macro work. The point of all of these is to catch stray light.

https://www.flickr.com/photos/neekeeteen/7011812441