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10-04-2015, 09:04 PM   #1
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A* 300mm/4 question?

Is the area between the aperture ring and the focus ring fixed, as in it does not move or turn? If so does anyone have the lens that could measure that area with calipers to get a mm measurement?

10-04-2015, 10:06 PM   #2
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Yes, it's fixed. I assume you want the diameter at that point, thinking to add a tripod foot? I don't have calipers, but eyeballing it with a ruler I'd put it at 70mm. If you mean longitudinally, along the lens axis, it's 39mm.
10-04-2015, 10:33 PM   #3
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If you are talking about the area with the DOF scale and the white bump, I believe that is part of the main lower mount assembly and is not removable, although that would require removal of the aperture ring to verify that it's not a separate piece held in by set screws. The aperture ring floats on an inset ring on the mount assembly and there is a slot through which is fed the tab for the cam to the aperture control. The focus ring actually travels up and down slightly as the helical slews in and out, so the distance between the aperture ring and the focus ring will vary ever so slightly depending on how far out you are focused. I can trek down to my basement and grab the calipers tomorrow morning if you need an exact measurement, but it would help if I knew exactly what you were trying to accomplish. If you do intend to add a tripod foot that is on a rotating ring, you are going to have to remove the white bump, and it would be best to lathe a channel into the ring so the foot doesn't slide up and down, since the fixed area is flush with the focus ring.
10-04-2015, 10:44 PM   #4
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Yes, I want to try to get something around it for some kind of tripod attachment. I have a couple ideas so the outside diameter would be the most helpful figure. I'd really appreciate the info if anyone has the ability to do so. I figured since the filter ring was 77mm and the diameter of the lens seems consistent down the length that it has to be around that measurement.

10-04-2015, 10:52 PM   #5
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??? Unless I am confused, the front of the lens we are talking about is much wider than the area down by the mount/focus ring:



This guy, right? If so, I estimate the area between the aperture and focus ring is somewhere between 25-35% smaller in diameter than the filter ring.



QuoteOriginally posted by littledrawe Quote
Yes, I want to try to get something around it for some kind of tripod attachment. I have a couple ideas so the outside diameter would be the most helpful figure. I'd really appreciate the info if anyone has the ability to do so. I figured since the filter ring was 77mm and the diameter of the lens seems consistent down the length that it has to be around that measurement.
10-05-2015, 05:55 AM   #6
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@dcshooter, it is the 645 A*300mm that I am looking at for this application. I should have clarified that in the first post, I apologize!
10-05-2015, 07:27 AM   #7
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Ah, that clears things up. I don't have the 645 lens, so I'll bow out of this conversation. (I suppose looking at the thread tree up above would have told me as well - I had accessed this thread from teh "new posts" section on the front page.)

QuoteOriginally posted by littledrawe Quote
@dcshooter, it is the 645 A*300mm that I am looking at for this application. I should have clarified that in the first post, I apologize!

Last edited by dcshooter; 10-05-2015 at 09:30 AM.
10-05-2015, 09:11 AM - 1 Like   #8
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As luck would have it, I received a copy of the SMC Pentax-A* 645 1:4 300mm ED(IF) from KEH this past Saturday. I think I'm going to like this one on the 645Z.

The measurement you're looking for is 2.9755 Inches = 75.578 mm, and it is fixed.

If you find a tripod mount for it, please let me know, I might be interested in getting one myself.

Good luck.

10-05-2015, 12:49 PM   #9
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I have an idea, thanks for the measurement, that should help me figure it out.
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