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Cinders · 01-25-2011, 10:20 PM

I have a Quantaray 100-300mm f4.5-6.7. When I used it on my K-x, the aperture would close up the more I zoomed in.

But now I've been using it on my ME Super. It has an aperture ring, but I can zoom in to 300mm and keep it on 4.5. Will it let me take a picture? Will it turn out weird?

I'm confused lol.

stevebrot · 01-25-2011, 10:53 PM

Originally posted by Cinders

I have a Quantaray 100-300mm f4.5-6.7. When I used it on my K-x, the aperture would close up the more I zoomed in.

But now I've been using it on my ME Super. It has an aperture ring, but I can zoom in to 300mm and keep it on 4.5. Will it let me take a picture? Will it turn out weird?

I'm confused lol.

The question is whether the meter reads the same. Your lens is not variable aperture per se...rather it is variable maximum relative aperture (f/stop). The absolute aperture stays the same, but the focal length increases resulting in a higher f-number and less light to the film/sensor/meter. Apparently the lens is able to communicate this fact to your K-x. The ME Super, on the other hand, has a much more simple mount and has no idea what focal length the lens is set at or even what the actual aperture is. All the camera is aware of is the offset of the aperture ring from maximum.

Steve

titrisol · 01-26-2011, 01:39 PM

Will work fine

stevebrot · 01-26-2011, 08:54 PM

Originally posted by titrisol

Will work fine

Yeah...that too!

Cinders · 01-26-2011, 09:21 PM

With no vignetting, or anything?

Weird, so why can't I shoot at f4.5 at 300mm on a DSLR?

stevebrot · 01-26-2011, 10:35 PM

Originally posted by Cinders

With no vignetting, or anything?

Weird, so why can't I shoot at f4.5 at 300mm on a DSLR?

Cuz at 300mm your lens is f/6.7...

The f-number formula goes like this: f(ocal length)/n = physical aperture diameter. The "slash" notation reflects this. This is the case regardless of what the aperture ring is set at.

Steve

(I know...the next question is why the DA* 50-135 is constant f/2.8...will let someone else answer that one...)

titrisol · 01-27-2011, 02:27 AM

Vignetting should be a problem in wide-angles
teles in general can cover areas way larger than 35mm.

You can shoot at 4.5 but it will be a different "effective" aperture (6.7) and the difference in luminosity will be metered by the camera.

Constant f/lenses are very special I guess.... some floating elements maybe?

Originally posted by Cinders

With no vignetting, or anything?

Weird, so why can't I shoot at f4.5 at 300mm on a DSLR?

Cinders · 01-27-2011, 02:53 PM

Ok, I think I get it now. Thanks guys.

01-25-2011, 10:20 PM	#1
Cinders Senior Member Join Date: Jun 2010 Location: Florida Posts: 118	Variable aperture, M-series film bodies question I have a Quantaray 100-300mm f4.5-6.7. When I used it on my K-x, the aperture would close up the more I zoomed in. But now I've been using it on my ME Super. It has an aperture ring, but I can zoom in to 300mm and keep it on 4.5. Will it let me take a picture? Will it turn out weird? I'm confused lol.

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01-25-2011, 10:53 PM	#2
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Cinders I have a Quantaray 100-300mm f4.5-6.7. When I used it on my K-x, the aperture would close up the more I zoomed in. But now I've been using it on my ME Super. It has an aperture ring, but I can zoom in to 300mm and keep it on 4.5. Will it let me take a picture? Will it turn out weird? I'm confused lol. The question is whether the meter reads the same. Your lens is not variable aperture per se...rather it is variable maximum relative aperture (f/stop). The absolute aperture stays the same, but the focal length increases resulting in a higher f-number and less light to the film/sensor/meter. Apparently the lens is able to communicate this fact to your K-x. The ME Super, on the other hand, has a much more simple mount and has no idea what focal length the lens is set at or even what the actual aperture is. All the camera is aware of is the offset of the aperture ring from maximum. Steve

01-26-2011, 01:39 PM	#3
titrisol Pentaxian Join Date: Dec 2007 Location: In the most populated state... state of denial Photos: Gallery \| Albums Posts: 1,854	Will work fine

01-26-2011, 08:54 PM	#4
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by titrisol Will work fine Yeah...that too!

01-26-2011, 09:21 PM	#5
Cinders Senior Member Join Date: Jun 2010 Location: Florida Posts: 118 Original Poster	With no vignetting, or anything? Weird, so why can't I shoot at f4.5 at 300mm on a DSLR?

01-26-2011, 10:35 PM	#6
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Cinders With no vignetting, or anything? Weird, so why can't I shoot at f4.5 at 300mm on a DSLR? Cuz at 300mm your lens is f/6.7... The f-number formula goes like this: f(ocal length)/n = physical aperture diameter. The "slash" notation reflects this. This is the case regardless of what the aperture ring is set at. Steve (I know...the next question is why the DA* 50-135 is constant f/2.8...will let someone else answer that one...)

01-27-2011, 02:27 AM	#7
titrisol Pentaxian Join Date: Dec 2007 Location: In the most populated state... state of denial Photos: Gallery \| Albums Posts: 1,854	Vignetting should be a problem in wide-angles teles in general can cover areas way larger than 35mm. You can shoot at 4.5 but it will be a different "effective" aperture (6.7) and the difference in luminosity will be metered by the camera. Constant f/lenses are very special I guess.... some floating elements maybe? Originally posted by Cinders With no vignetting, or anything? Weird, so why can't I shoot at f4.5 at 300mm on a DSLR?

01-27-2011, 02:53 PM	#8
Cinders Senior Member Join Date: Jun 2010 Location: Florida Posts: 118 Original Poster	Ok, I think I get it now. Thanks guys.

Variable aperture, M-series film bodies question

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