Tripod mounting long lenses and vibration problems.
 

Having swapped my 80-200 zoom for an old AIS manual focus 400mm lens. sorting possible tripod mounted vibration problems was todays mission. I had read Bjørn Rørslett's review, and although he gives it a good score for image quality, he does note that as it is a light lens, 1200 grams, it is prone to vibration when tripod mounted. As for image quality I was very impressed with performance when used on a monopod yesterday but had concerns over the tripod mounting bit.

With dismal light again today I decided to measure ( clock it ), when mounted on the Manfrotto sliding plate for the 501 fluid head. This was done by clamping it in a machine vice on the milling table so a very solid clamp. Although the lens has a good clamshell collar the pliable rubber on the sliding mounting plate allowed for a deflection of 50 thousands of an inch. I made a intermediate plate of significantly greater surface area that could be mounted on the lens then screwed using 2 screws to the sliding plate so compressing the rubber better and over a greater area. Back in the machine vice and the set up was reclocked. The maximum deflection under a load has been reduced from 50 to 2 thousands of an inch. The plate has effectively added 500grams of mass to the lens. Hopefully this will counter vibration problems noted by Bjørn. The clocks do not register mirror up or shutter movement, but mirror down gives about a thou of movement. Still the shutter has closed then so it should not be a problem.

When we get some decent light I will give it a proper test.

I knew Rob would have a good laugh, so I took a pic of the final clocking and have attached it.

Don

LOL - Yes Don I love it. I'll be interested in your findings.

Hi Don

It's interesting to read your very methodical and engineering approach to the problem of vibration in long lenses.

Mine is more Heath Robinson, my longest lens is the AFS 300 f4, which I use in conjunction with the TC 1.7. The lens collar on that lens is useless, so much so that I almost gave up on it, just could not get a sharp image due to vibration.

I bought a Manfrotto 501head and the images improved somewhat but were still a bit fluffy.

I read one thread on the net, where the responder had lodged a canister from an asthma inhaler between the collar foot and the lens barrel and had found a marked improvement in the quality of his images.

I improvised using a plastic cork from a wine bottle, around which I super glued a covering of 3mm thick rubber sheet, cut to size, and with that lodged in the gap between the barrel and foot plus the 501 have been very happy with the results.

Best of luck with your lens.

Brian

I have read somewhere that putting a bean bag on top of the lens when mounted on a tripod helps a lot with vibrations although I have not tried this myself.

Brian,

I found as much of the problem in the spongy nature of the rubber on the sliding foot hence the longer base I made.

I will take some close ups of the mount and test pics using Robs bar code tests. Trouble is this lens has turned into a cloud magnate. :( :(

I have managed to sneak a moon shot in the dark but have never managed more than 2 shots before the cloud mysteriously appears.:rolleyes:

A bean bag would certainly help as Roy has suggested but that does require the lens to be at less than 45 deg. I did a test with a bag of sunflower kernals and another with a sheet of lead ( same thing but not so handling friendly ) and it did absorb vibrations.

Don

Not a good day for the bar code test even though it is fairly bright. I have just put it on hold as windspeed is 24mph gusting 39mph. :(

Don

All amateur astronomers have this problem, especially if their telescope is new:D

Dave

Brian,

A bit off track but out of personal interest, and for the possible benefit of others, have you had an opportunity to try the 300 f4 AFS on a monopod for comparison. I am wondering if because in that situation you are holding the lens and camera, any vibrations would be to a degree damped.

Neat idea to overcome your problem. Your foot is obviouly of greater area than mine to overcome the spongy rubber on the sliding foot. When I see a suitable bit of thin cork I will use that to replace the rubber on mine.

Don

Extremely sturdy-looking tripod mount, Don, but looks a bit heavy to lug around and the dials are confusing.

The dials are to test deflection in various planes. The lens itself is very light, 1200gms so even with a bit of weight added it does not compare with what I would really like but could not afford, the f3.5 version at 2.8kg. I might baulk a bit at the f2.8 as thats 5.15kg.

In this case weight = image sharpness when on a tripod. For monopod use the additional foot I have made is not necessary as any vibration is damped by the weight of the hand on top of the lens barrel as tested by my gallery Starling pic.

Note I also added a bit of foam to the barrel for hand comfort in the cold. :D

Don