Fork mounted 250mm f1.7 /SPC900 yesyes style camera

[DIYASTRO]

I am posting these images here as not to mess up Gina's thread for widefield rig.

'Experiment ' to find decent focus mechanism avoiding crayford type focus.

Using threaded rod and timing belt / pulley driven by R/C servo which has been modded to give continual rotation, via a 50;1 worm gear set.

This gives a movement of the 'camera / filter wheel' attached to the acylic center plate equating to .016mm or .0006" per one rev of the servo.

By using a dc motor drive eg DCUSB (Shoestring astro) or even simple PWM circuit quite acurate and sensitive movement can be acheived.

I have made simular drive systems for std 50mm camera lenses and larger which I will attempt to post photos of later in different thread.

Hope this is usefull to Gina and others.

Boyd

[michael.h.f.wilkinson]

That looks impressive, but also like quite a tricky system to set up. Once set up, does it hold good collimation well?

[DIYASTRO]

Michael,

You are quite right.... the system is tricky to initially set up since all the plates must be 90 deg to the lead screws and the drive pulleys locked when in accurate position. Once this is done the focus plate holding the camera and filter wheel move very smooth and very accurate. The bearings on the leadscrews take the brunt of the work and although the servos I use are metal geared with integral bearings they do sound out a bit.

When focus needs to be altered the speed of the system I contol with PWM circuit and so can get far better accuracy than with a 10:1 crayford.

Suspect that this system wont be for everyone since it will require a bit of TLC regarding its upkeep. Glad you find it interesting.

Hope to post a new thread latter today showing a variety of this type of mechanism in my latest toy which is a multi camera GOTO in forks and is quite heavy!

Boyd

PS. The camera was constructed some 18 months ago and some pics of its construction are to be found on the Yesyes thread SPCLXMOD yesyes style ( page 10 or 12 I think!) Thanks to Chris for that wonderfull thread!

[DIYASTRO]

Gina,

Thanks for you PM.

Actually, its not that complecated at all.

Its simply 4 leadscrews supported on bearings with a worm drive to one shaft coupled together by pulleys and a drive belt.

Admit, tricky to initialy get all in alignment but once done and the 4 pulleys locked on to the leadscrews wonderfull smooth movement and with .0006" per servo rev its usable!

You may see that I have posted another thread 'Multi lens Astro GOTO camera', you will see smaller versions of the camera focus system using simular lenses to what you plan to use i.e. 50mm Pentax Tak etc.

Anyway I am sure you will come up with your own solutions but just thought it worth sharing .

Boyd

[Gina]

Yes, thank you for sharing

[DIYASTRO]

Gina,

you're welcome. I believe that when we see something that is not too far away from what we are trying to do, although not what we may have in mind , however it is presented to us, it somehow stimulates a seperate train of thought and culminates in solutions that we are happy with.

That is why I still look , and although time may pass quickly without posting frequently, I still try to do so through the SGL boards.

Kind regards

Boyd