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

Secondary support for heavy telephoto lens

  • Please log in to reply
6 replies to this topic

#1 sumitshrestha

sumitshrestha

    Sputnik

  • -----
  • topic starter
  • Posts: 27
  • Joined: 04 Nov 2021

Posted 13 August 2022 - 03:48 PM

I have nikon af-s 300mm 2.8 and flat dovetail. I can attach it to the dovetail using single screw. I am thinking of adding secondary support at front of lens. What would be better options for me? 3D printing a ring or buying off the shelf telescope ring? I am really confused as to what I should do. IMG_9170.jpg IMG_9167.jpg



#2 MitchAlsup

MitchAlsup

    Fly Me to the Moon

  • -----
  • Posts: 6,586
  • Joined: 31 Aug 2009

Posted 13 August 2022 - 06:01 PM

For your purposed, wood would be good.



#3 KLWalsh

KLWalsh

    Surveyor 1

  • *****
  • Posts: 1,520
  • Joined: 19 Feb 2014
  • Loc: North Georgia, USA

Posted 13 August 2022 - 08:35 PM

Yes, you definitely need not only to support the lens, but you need a method to keep the lens from yawing to the left or right as the lens is oriented towards different parts of the sky. A single-point threaded connection can be torqued loose by the weight of the lens.

The method of support will depend on where the support touches the lens. If the support touches a rotating part of the lens, you might need a rotating ring, a V block with roller contacts, or a V block made from a low-friction plastic like delrin.
If the support touches a non-rotating part of the lens, then almost any simple V block could be used.
If you use a V block, a stiff bungee cord could then be used hold the lens against the block.
  • sumitshrestha likes this

#4 sumitshrestha

sumitshrestha

    Sputnik

  • -----
  • topic starter
  • Posts: 27
  • Joined: 04 Nov 2021

Posted 14 August 2022 - 12:02 PM

For your purposed, wood would be good.

Any specific wood designs that comes to your mind? I am not a carpenter or have done any wood work in past so totally new to this. Thanks for suggestion.



#5 sumitshrestha

sumitshrestha

    Sputnik

  • -----
  • topic starter
  • Posts: 27
  • Joined: 04 Nov 2021

Posted 14 August 2022 - 12:34 PM

Yes, you definitely need not only to support the lens, but you need a method to keep the lens from yawing to the left or right as the lens is oriented towards different parts of the sky. A single-point threaded connection can be torqued loose by the weight of the lens.

The method of support will depend on where the support touches the lens. If the support touches a rotating part of the lens, you might need a rotating ring, a V block with roller contacts, or a V block made from a low-friction plastic like delrin.
If the support touches a non-rotating part of the lens, then almost any simple V block could be used.
If you use a V block, a stiff bungee cord could then be used hold the lens against the block.

 Yellow line is rotating part and light blue is non rotating part. So basically front section does not rotates and has huge ed objective lens. So a support there would be perfect. I was just wondering what kind of support design would work best. I was thinking of using some kind of cord but was worried it might slip under extra pressure. I am fine with investing some money on decent support as long as it gives me peace of mind. Thanks.

Attached Thumbnails

  • 300_1mm.jpg


#6 Jaylab

Jaylab

    Explorer 1

  • *****
  • Posts: 89
  • Joined: 15 Sep 2013

Posted 14 August 2022 - 12:59 PM

I often use this same lens and have never found it to need support with time exposures. This stock lens foot is prone to resonance at shutter speeds from 1/100th to 1/4 second but I have never encountered a problem with longer times.

 

If you still wanted to support the front I would suggest a tapered wood wedge between the region just to the left of your white line and the aluminum foot.

 

-Jay-



#7 MitchAlsup

MitchAlsup

    Fly Me to the Moon

  • -----
  • Posts: 6,586
  • Joined: 31 Aug 2009

Posted 14 August 2022 - 04:24 PM

Any specific wood designs that comes to your mind? I am not a carpenter or have done any wood work in past so totally new to this. Thanks for suggestion.

Prior to the Russian invasion I would have suggested Baltic Birch. Strong, light, out-door grade, beautiful, not-that-expensive, easy to work with standard tools.

 

Also note: with respect to the picture of the lens, there is no <known> reason the holder could not be on the light shroud (forward of the blue non rotating ring.)




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