Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-19-2016, 11:13 PM   #16
Junior Member
Mahaku's Avatar

Join Date: Oct 2016
Location: Rayong, Thailand
Posts: 46
Original Poster
QuoteOriginally posted by Quartermaster James Quote
Okay, I'll bite: what is an "f-stop tube?"

Hi Quartermaster James

Can you try this f-stop tube. You will wake up and enjoy it.....

10-19-2016, 11:34 PM   #17
Loyal Site Supporter
Loyal Site Supporter
Quartermaster James's Avatar

Join Date: Oct 2014
Location: Anchorage, Alaska
Posts: 653
QuoteOriginally posted by Mahaku Quote
Hi Quartermaster James

Can you try this f-stop tube. You will wake up and enjoy it.....
I am thoroughly confused.
10-20-2016, 10:53 AM - 1 Like   #18
Veteran Member




Join Date: Dec 2010
Location: Ontario
Photos: Gallery
Posts: 3,332
QuoteOriginally posted by Quartermaster James Quote
Okay, I'll bite: what is an "f-stop tube?"
I'll take a stab at explaining-


Take an "A" series lens, remove the glass but leave the aperture mechanism intact. Attach this to the camera as per normal. This is now an extension tube with a built in aperture the camera can control.

Attach some length of cheap extension tubes to the filter threads of this lens.

Attach some other lens to the end of these extension tubes, leave this lens wide open.

You now have high magnification that you can focus and compose wide open, but the camera will automatically close the aperture for you at the time of shooting.


Why do this?
  1. It's cheap.
  2. At macro magnifications, you most likely want to be able to stop down.
  3. If you're shooting moving subjects and/or hand holding your camera, it's about a zillion times nicer to do it wide open and have the camera stop down when you press the shutter than it is to have to manually close down your aperture before the exposure.This will be a step up from cheap extension tubes on their own.

See also the earlier link provided by Nass: Control aperture of a reversed lens with an empty lens
10-20-2016, 04:10 PM   #19
Loyal Site Supporter
Loyal Site Supporter
Quartermaster James's Avatar

Join Date: Oct 2014
Location: Anchorage, Alaska
Posts: 653
So, it's just another term for extension tube then?

10-20-2016, 05:05 PM - 2 Likes   #20
Veteran Member
Nass's Avatar

Join Date: Aug 2009
Location: The British Isles
Photos: Gallery
Posts: 2,402
QuoteOriginally posted by Quartermaster James Quote
So, it's just another term for extension tube then?
No, extension tubes don't have a diaghraphm. Think extension tube with f/stops. The reason for it is to have f/stop control on the body for reversed lenses or other lenses for which it's not possible to use an auto extension tube (ie extension tube with the lever inside that communicates between lens and body)
10-20-2016, 05:59 PM   #21
Junior Member
Mahaku's Avatar

Join Date: Oct 2016
Location: Rayong, Thailand
Posts: 46
Original Poster
QuoteOriginally posted by Nass Quote
No, extension tubes don't have a diaghraphm. Think extension tube with f/stops. The reason for it is to have f/stop control on the body for reversed lenses or other lenses for which it's not possible to use an auto extension tube (ie extension tube with the lever inside that communicates between lens and body)

Hi BrianR , Nass , Quartermaster James

It is the right thing
Thank you for your consideration and clarification...

Ps. English is not my strong Trying to learn And looking for friends to conversation about group Pentaxian. .....
10-21-2016, 12:13 AM   #22
Senior Member




Join Date: Feb 2011
Location: Queens, New York
Posts: 122
My turn to bite. How do you this?>
QuoteOriginally posted by BrianR Quote
Attach some length of cheap extension tubes to the filter threads of this lens.


10-21-2016, 06:07 AM   #23
Veteran Member




Join Date: Dec 2010
Location: Ontario
Photos: Gallery
Posts: 3,332
QuoteOriginally posted by Achromatter Quote
My turn to bite. How do you this?>
I have a set of the cheap tubes similar to the ones shown, the sections screw together but the thread size does not match a standard filter, so I don't have adapter rings that would fit (and none may exist). Depends on the specific tubes of course. Looks like the OP may have used electrical tape?

My tubes used this way form a tight fit with either my A 50/1.7 or M 50/2 (I'm not de-glassing either though), so alignment shouldn't be a big issue and you could confidently epoxy one of the short tube sections to your deglassed lens for more permanence (what else are you going to use it for?).

Skipping the tubes and reversing the attached lens (as Nass has mentioned), would take a standard reverse coupling ring.
10-21-2016, 09:41 AM   #24
Loyal Site Supporter
Loyal Site Supporter
Quartermaster James's Avatar

Join Date: Oct 2014
Location: Anchorage, Alaska
Posts: 653
QuoteOriginally posted by Nass Quote
No, extension tubes don't have a diaghraphm. Think extension tube with f/stops. The reason for it is to have f/stop control on the body for reversed lenses or other lenses for which it's not possible to use an auto extension tube (ie extension tube with the lever inside that communicates between lens and body)
Thanks!
10-21-2016, 04:10 PM   #25
Senior Member




Join Date: Feb 2011
Location: Queens, New York
Posts: 122
QuoteOriginally posted by BrianR Quote
My tubes used this way form a tight fit with either my A 50/1.7 or M 50/2 (I'm not de-glassing either though), so alignment shouldn't be a big issue and you could confidently epoxy one of the short tube sections to your deglassed lens for more permanence (what else are you going to use it for?).
I thought maybe there was some adapter, or method, that was a bit more......elegant, or stable. as opposed to jerry-rigged.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
50mm, diy f-stop tube, lens, lenses, macro, picture, sample, step, technic diy f-stop, tip & technic
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
645Z + FA 645 55mm: Sharpest f-stop at f8 or stop down? Hyperfocal issues.... steve645z Pentax Medium Format 31 01-09-2017 08:08 AM
For Sale - Sold: Pentax-M 100mm f/4 Macro with 2x Extension tube (Full Frame Compatible) Newtophotos Sold Items 15 02-09-2016 03:11 PM
f-stop & ss not matching using flash amp Flashes, Lighting, and Studio 8 12-17-2015 05:44 PM
Stop Down Metering in K30 (with Extension Tube & Lens Reversed) rp_dxn Pentax K-30 & K-50 5 09-23-2013 11:43 PM



All times are GMT -7. The time now is 03:06 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top