Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Focus instability & support: Nikkor 180mm f/2.8 ED

  • Please log in to reply
12 replies to this topic

#1 Axunator

Axunator

    Viking 1

  • *****
  • topic starter
  • Posts: 708
  • Joined: 23 May 2015
  • Loc: Helsinki, Finland

Posted 03 January 2017 - 08:45 AM

I've had the old Nikkor 180 mm f/2.8 ED manual (AIS) lens (the one with the golden ring) for almost 30 years and used it without problems for landscape and general photography. Only recently I tried it for the first time for long-exposure AP (with SW Star Adventurer and AP-modded Nikon D7000). To my frustration I realized that when pointed up (higher than appr. 45-50 degrees), the lens rotates the focusing ring past infinity almost immediately, sliding down under its own weight! I know it's supposed to focus past infinity, that's not the problem, but the slippery nature of the focusing ring. Obviously, for general photography the lens is never in such a steep vertical position, so I have never noticed it before.

 

I took the lens to authorized Nikon repair shop (the most experienced one in these corners of the world), and they told me that the only thing they could do is to play with the amount of lubricant inside the lens. They definitely did not not want to do it and strongly advised against it, because the focusing works so beautifully and smoothly otherwise.

 

Anyone else had this problem? Ideas? Just taping the focusing ring after finding perfect focus?

 

Another question related to the same lens (do not want to start another thread): On some CN threads and blogs (e.g. in this one http://www.astropix....NIKON_180MM.HTM by Jerry Lodriguss) people have recommended guidescope rings to support the lens (since it does not have a mounting collar). Is this really necessary? If the weight of the lens would cause too much flexure on the bayonet, I would presume that Nikon would have put a collar on it to begin with? Again, for general photography, with just the camera body mounted on tripod I've never had any problems. FWIW, I do use it only with Nikon bodies, so I do not need a Nikon-to-Canon adapter between the lens and the body, which obviously might make the combination more flexure-prone and stressful for the bayonet with the rather heavy, unsupported lens.

 

Thanks!

Aki


Edited by Axunator, 03 January 2017 - 08:48 AM.


#2 MikeK5117

MikeK5117

    Explorer 1

  • *****
  • Posts: 95
  • Joined: 20 Sep 2016
  • Loc: Kansas City, Kansas

Posted 03 January 2017 - 08:56 AM

I have seen wide rubber bands, such as cutting a piece from an inner tube, used to stabilize slippery push-pull zoom rings, can't see why that won't work for your focus ring as well.

 

This is a non-auto focus lens, right?

 

Just put the rubber band over the rear 1/2 inch of the focus ring so that the other half of the rubber band contacts the lens body. This will provide enough friction to hold the focus in place, but still allow you to focus manually.

 

Regarding the lens and camera mounting, I am puzzling out the same concerns. My gut tells me just mounting the camera body with a heavy lens out front is not best. 

 

In cinema mounts they do have adjustable saddles that will cradle the front of a long lens. I am looking in that direction for something that will let me support the front of my longer lenses.


  • Axunator likes this

#3 Marco1968

Marco1968

    Mariner 2

  • -----
  • Posts: 206
  • Joined: 23 Apr 2010

Posted 03 January 2017 - 09:40 AM

Hello Aki,

 

I am sure there is nothing wrong with your lens behavior, consider that a buttery-smooth and fingertip-light focus ring actuation was desirable for daytime shooting in the time of manual focus lenses (ad still is today).

 

I am regularly using the Nikkor 180 mm f/2.8 ED manual (AIS) lens for astrophotography, along with 2 other vintage manual focus telephoto lenses (Nikon 300 mm f/4.5 ED non-IF, and Tamron 300 mm f/2.8 mod.107b adaptall-2) on Canon EOS 60Da body.

 

At the beginning, I had exactly your same problem and solved buying from 'Teleskop-Express.de' an ingenuos device they call 'TeleFokus', it is basically formed by two metal rings that allow to finely adjust and lock the focus when using telephoto lens for astrophotography.

 

Just Google search for "teleskop express telefokus", the first link shown will bring you to the product description page.

Disclaimer: I am not affiliated in any way with 'Teleskop-Express.de'.

 

I agree that a rubber band will keep the focus ring from rotating below the front lens weight, personally I think the two-rings 'TeleFokus' system allows more precise adjustment of the focus by rotating the side-to-side knobs.

 

About the camera mounting, with the Nikon 180 ED I do not use guidescope rings, nor with the 300mm telephoto lenses as these have both mounting collars. The Nikon 180 ED is short and lightweight and I think it does not apply much flexure (if not at all) on the camera bayonet. I will suggest to try it without rings before making the buy.

 

What I have found is that telephoto lenses with manual internal-focus mechanisms may not be so good for astrophotography as the internal focusing elements may not stay critically collimated as required to have a flat star field (a minimum tilt will ruin the shots).

 

Fortunately, this is not the case for the 180 ED and that is the reason I searched for the other telephoto mentioned above, all of them have external focusing mechanisms and are capable to deliver even and flat star fields.

 

Hope this helps,

 

Marco


  • Axunator and GoFish like this

#4 Steve OK

Steve OK

    Surveyor 1

  • -----
  • Posts: 1,639
  • Joined: 22 Sep 2007
  • Loc: OKC, OK

Posted 03 January 2017 - 10:52 AM

I was trying to remember where I got the idea for the device that Marco describes!  Thanks, Marco.  I made one for my 180mm ED out of some 1/2" x 1/8" aluminum.  It is not very pretty, but is is certainly functional.  Not only does it hold the focus position, it also allows for very fine focus adjustment.  Here are a couple of photos of my home-made device: 

 

Focuser-CN1.jpg

 

Attached to the lens:

Focuser-CN2.jpg

 

This seems like it would be a good 3-D printer project...

 

Steve

 


  • Traveler, calypsob and Axunator like this

#5 Axunator

Axunator

    Viking 1

  • *****
  • topic starter
  • Posts: 708
  • Joined: 23 May 2015
  • Loc: Helsinki, Finland

Posted 03 January 2017 - 12:52 PM

At the beginning, I had exactly your same problem and solved buying from 'Teleskop-Express.de' an ingenuos device they call 'TeleFokus', it is basically formed by two metal rings that allow to finely adjust and lock the focus when using telephoto lens for astrophotography.

 

Just Google search for "teleskop express telefokus", the first link shown will bring you to the product description page.

Disclaimer: I am not affiliated in any way with 'Teleskop-Express.de'.

Marco - excellent tip, thanks! Found it from the TS website, and it looks exactly like the gadget that solves my problem in an elegant fashion  :bow:

 

Steve - well done  :waytogo:



#6 premk19

premk19

    Viking 1

  • *****
  • Posts: 725
  • Joined: 19 Apr 2015

Posted 03 January 2017 - 04:34 PM

Marco, what diameter rings did you get from TS for this lens?



#7 t_image

t_image

    Gemini

  • -----
  • Posts: 3,390
  • Joined: 22 Jul 2015

Posted 03 January 2017 - 05:14 PM

I have an old Nikkor 70-200mm F/2.8 that I love to use for AP and EAA.

I use aluminum foil tape(removes easy like gaffers tape) for the zoom dial to hold it in place v. gravity/ although I usually zoom to 200 most of the time.

 

Here's a CN forum about mounting such lens,

my post with what I use:

http://www.cloudynig...r/#entry7377452

I often use a large wiretie to snug the lens to the mounting bar as well.
 

 

support the lens (since it does not have a mounting collar). Is this really necessary? If the weight of the lens would cause too much flexure on the bayonet, I would presume that Nikon would have put a collar on it to begin with?

Regarding the lens and camera mounting, I am puzzling out the same concerns. My gut tells me just mounting the camera body with a heavy lens out front is not best...........

 

#1 Nikon never consider AP'ers would be using it to the precision needed for AP.

#2 solutions to avoid flexure are not costly and shouldn't be too troublesome, so why not?

#3 effects of flexure may not be noticeable on your Star adventurer tracking mount,

because you probably aren't taking AP images going so deep with such precision and length of exposure,

(if you're even guiding in the first place).

[i.e. you probably have other larger variables that will prevent you from going too long/deep].

Imagers that have expensive precision tracking mounts with guiding set-ups have learned,

it is better to mount all optics appropriately to avoid any flexure...

You would never notice the small amount with terrestrial,

and as you noticed with focus drift due to gravity, you were not pointing it at angles most don't as well, yes?

Maybe someone wants to do the math and calculate based on size of sensor pixels and 180mm FL what the spatial resolution would be and how much flexure would be necessary to offset the image 1 pixel or more.....

However, as I said,

if one is looking to keep pinpoint starts with fine accuracy across the night with long subs, say 10 minutes+,

flexure can upset things. So "too much flexure" is not the question. "Should I take easy measures to eliminate any potential flexure" is more likely the question.

Especially if you've paid $$$$ to get a tracking mount and guiding setup so you can take precision long exposures.....

Eliminate all possible areas of deviation in your system

and you can both troubleshoot easier

and positively effect the performance of your guiding more efficiently.....

#4 as noted in the thread link above, the utility of some mounting solutions to allow one to rotate the camera to better frame a shot is also very helpful!

FWIW......


  • Axunator likes this

#8 Axunator

Axunator

    Viking 1

  • *****
  • topic starter
  • Posts: 708
  • Joined: 23 May 2015
  • Loc: Helsinki, Finland

Posted 03 January 2017 - 06:40 PM

Good points, t_image... 



#9 Marco1968

Marco1968

    Mariner 2

  • -----
  • Posts: 206
  • Joined: 23 Apr 2010

Posted 22 January 2017 - 06:10 AM

Hello premk19,

excuse me for being so late in answering your question, I did not come back to this thread for a while...

The diameter of the rings I bought from TS for the Nikkor Ai-S 180mm ED is 105mm.

They fit very nicely, one will be set on the focuser rotating section, the other one on the fixed, narrow section just before (that in silver color with the depth-of-field and IR dot engravings).

The narrow section is... yes, narrow, but it is just wide enough for the tips of the three radial screws to securely lock on it.

Hope this helps,
Marco
  • premk19 likes this

#10 premk19

premk19

    Viking 1

  • *****
  • Posts: 725
  • Joined: 19 Apr 2015

Posted 22 January 2017 - 04:32 PM

Thank you, Marco. After contacting the nice folks at TS I went with the 75mm version, as I have very little space between the lens barrel and the dovetail it's mounted on. It arrived a couple of days ago and it fits! I placed the two rings exactly as you described and I'm able to make very fine focus adjustments and lock it in place. A very handy add on!


  • GoFish likes this

#11 maxsid

maxsid

    Vostok 1

  • *****
  • Posts: 167
  • Joined: 11 Sep 2018
  • Loc: Sunnyvale, CA

Posted 16 October 2018 - 02:11 AM

I was trying to remember where I got the idea for the device that Marco describes!  Thanks, Marco.  I made one for my 180mm ED out of some 1/2" x 1/8" aluminum.  It is not very pretty, but is is certainly functional.  Not only does it hold the focus position, it also allows for very fine focus adjustment.  Here are a couple of photos of my home-made device: 

 

attachicon.gif Focuser-CN1.jpg

 

Attached to the lens:

attachicon.gif Focuser-CN2.jpg

 

This seems like it would be a good 3-D printer project...

 

Steve

Hello,

I realize this is an old thread but maybe you'll answer me. 

How did you make those rings? Aluminum pipe? Brackets glued on?

Thanks!



#12 calypsob

calypsob

    Fly Me to the Moon

  • *****
  • Posts: 5,445
  • Joined: 20 Apr 2013
  • Loc: Virginia

Posted 16 October 2018 - 01:01 PM

Hello,

I realize this is an old thread but maybe you'll answer me. 

How did you make those rings? Aluminum pipe? Brackets glued on?

Thanks!

the aluminum looks like it was brazed not glued. 



#13 Marco1968

Marco1968

    Mariner 2

  • -----
  • Posts: 206
  • Joined: 23 Apr 2010

Posted 16 October 2018 - 02:50 PM

Greetings,

 

the "teleskop express telefokus" rings are made in aluminum machined from solid, except for the 'finger' that serves as reaction to the pair of opposed setting screws.

The 'finger' is bolted as shown in the photo below.

 

Hope this helps,

 

Marco

 

Attached Thumbnails

  • 20181016_214402-1389x1686.jpg

  • calypsob and GoFish like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics