Pentax 645 FA 45-85 wide open

psychoanalyst · 08-30-2012, 07:26 AM

This could sound silly, but I want to dispel any doubts in my head.

Could someone post an image of the lens with its aperture at 4.5? For some reason I feel that wide open in my copy of the lens isn't really wide open (the aperture seems too small to me) and I just want to clarify that.

Sorry for the odd request. But I would appreciate your help.

I'll upload an image of what the wide open aperture on my lens looks like tonight.

Thanks.

Avi

JinDesu · 08-30-2012, 08:02 AM

Originally posted by psychoanalyst

This could sound silly, but I want to dispel any doubts in my head.

Could someone post an image of the lens with its aperture at 4.5? For some reason I feel that wide open in my copy of the lens isn't really wide open (the aperture seems too small to me) and I just want to clarify that.

Sorry for the odd request. But I would appreciate your help.

I'll upload an image of what the wide open aperture on my lens looks like tonight.

Thanks.

Avi

Do you have another lens? You can see if the exposure is correct - that would tell you if the aperture is correctly sized.

I.e. - 50mm F2.8, aim at a evenly lit and colored subject, ISO 100 or whatever, and see what shutter speed it suggest. Then take your 45-85 and do the same.

RonHendriks1966 · 08-30-2012, 09:44 AM

But transmission does vary from lens to lens, so these tests don't always give the same results.

Smolk · 08-30-2012, 10:55 AM

If your idea is based on just looking into the lens, it may well be normal: it looks relatively small indeed. My lens has always performed fine, but when I look at wide open from the back it seems smallish, in part because the front lens of course is no less than 77mm, otherwise I think it's just the design. Can't really upload it right now but can confirm if you do whether it looks any different.

JinDesu · 08-30-2012, 11:21 AM

Originally posted by RonHendriks1966

But transmission does vary from lens to lens, so these tests don't always give the same results.

Ah yeah, that's true. Could be worth a shot though, if it ends up being pretty similar.

psychoanalyst · 08-31-2012, 08:17 AM

thanks folks...yes...I did not do the meter tests for precisely those reasons.

I will upload a picture of my lens....that should be confimation enough.

Glad to know that the aperture is indeed "smallish" for others as well.

Yamanobori · 08-31-2012, 06:29 PM

At 45mm, the entrance pupil is 10mm. At 85mm, it is 19mm.

08-30-2012, 07:26 AM	#1
psychoanalyst New Member Join Date: Jul 2011 Location: Atlanta, GA Posts: 13	Pentax 645 FA 45-85 wide open This could sound silly, but I want to dispel any doubts in my head. Could someone post an image of the lens with its aperture at 4.5? For some reason I feel that wide open in my copy of the lens isn't really wide open (the aperture seems too small to me) and I just want to clarify that. Sorry for the odd request. But I would appreciate your help. I'll upload an image of what the wide open aperture on my lens looks like tonight. Thanks. Avi

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08-30-2012, 08:02 AM	#2
JinDesu Veteran Member Join Date: Jun 2011 Location: New York City Photos: Gallery Posts: 5,638	Originally posted by psychoanalyst This could sound silly, but I want to dispel any doubts in my head. Could someone post an image of the lens with its aperture at 4.5? For some reason I feel that wide open in my copy of the lens isn't really wide open (the aperture seems too small to me) and I just want to clarify that. Sorry for the odd request. But I would appreciate your help. I'll upload an image of what the wide open aperture on my lens looks like tonight. Thanks. Avi Do you have another lens? You can see if the exposure is correct - that would tell you if the aperture is correctly sized. I.e. - 50mm F2.8, aim at a evenly lit and colored subject, ISO 100 or whatever, and see what shutter speed it suggest. Then take your 45-85 and do the same.

08-30-2012, 09:44 AM	#3
RonHendriks1966 Banned Join Date: Jan 2009 Photos: Gallery Posts: 9,675	But transmission does vary from lens to lens, so these tests don't always give the same results.

08-30-2012, 10:55 AM	#4
Smolk Pentaxian Join Date: Feb 2010 Location: Eerbeek Photos: Gallery \| Albums Posts: 1,857	If your idea is based on just looking into the lens, it may well be normal: it looks relatively small indeed. My lens has always performed fine, but when I look at wide open from the back it seems smallish, in part because the front lens of course is no less than 77mm, otherwise I think it's just the design. Can't really upload it right now but can confirm if you do whether it looks any different.

08-30-2012, 11:21 AM	#5
JinDesu Veteran Member Join Date: Jun 2011 Location: New York City Photos: Gallery Posts: 5,638	Originally posted by RonHendriks1966 But transmission does vary from lens to lens, so these tests don't always give the same results. Ah yeah, that's true. Could be worth a shot though, if it ends up being pretty similar.

08-31-2012, 08:17 AM	#6
psychoanalyst New Member Join Date: Jul 2011 Location: Atlanta, GA Posts: 13 Original Poster	thanks folks...yes...I did not do the meter tests for precisely those reasons. I will upload a picture of my lens....that should be confimation enough. Glad to know that the aperture is indeed "smallish" for others as well.

08-31-2012, 06:29 PM	#7
Yamanobori Veteran Member Join Date: Feb 2011 Photos: Gallery Posts: 573	At 45mm, the entrance pupil is 10mm. At 85mm, it is 19mm.