Multi refractor

[DIYASTRO]

This has been my project over the Winter.

A multi refractor constructed within an old Celestron 8" tube Fork mounted.

Lots to say about it but thought I would share a couple of pics first.

This is a "prototype" so to speak for something I wish to build in the future. I would like to build a multi reflector with three 200mm mirrors fork mounted and goto. Big project and will be asking lots of questions soon for all the people who obviously like to tinker and think!

Boyd

[DIYASTRO]

Just for the record,

I have to thank Blinky (Craig) for his time and effort in instruction on how to post images on the SGL page Thanks Craig

Boyd

[DIYASTRO]

Ok.

A little explanation as to the idea.

simply a lunar / solar scope

It has two 80mm short f/l objectives and a 90mm f/l obj. the 90 at the top for dslr and visual. The two 80mm have webcam (SPC900nc) in the crayfords. the left scope is for PHD tracking (When used for DSLR) the right for imageing.

The imaging scope has an integral filter wheel built inside which is motor driven, and can be indexed via control panel. (shown in second image with focus plate removed) The filter wheel has two limit switches to indicate on control panel what the current filter position is and that it is located in position.

The short focal length of the 80mm lenses is to capture full disk on webcam although each of the cameras can have a 5x powermate attached also.

Focus is either manual or via stepper motors from control.

The bits on top of main tube are a Mintron video camera with a pentax 50mm f1.4 lens to show what you are looking at (finder) the gridded tube is a solar finder, giving little light dot on grid when in position.

The fork mount (Meade lx50) has had all the little motors and drive circuit removed and replaced by larger stepper geared motors.

The base has an integral 24Ah batt. with charge circuit, three PWM circuits for dew bands on objective lenses and all the control circuits for the drive motors.

Try to remember that this is a trial config but your constructive crit is very welcolm.

Boyd

[blinky]

It does look the business Boyd! What weight is all that?

[DIYASTRO]

Hi Craig,

Not too sure but when it sits on it leveling cradle outside it doesnt move in a gale!

[ncjunk]

Looks like a great setup and the steppers, cnnectors etc all look very tidy.

Neil c

[Darren B]

What lenses are you using with that?

Looks very inovative and different to anything I've seen.

[Peter Drew]

very interesting set-up Boyd, I like the idea of using mounts for multiple purposes. I have a redundant LX50 mount so this has got me thinking, seemed a bit retrograde just to get another OTA for it! On a similar tack, I have a slowly ongoing project fitting a 18" F3.5 lightweight reflecting system into a "stretched" 12" LX200 mount. The hope is to use it without a secondary diagonal and instead place a Stellacam 11 at the focus as an astrovideo instrument. The Mintron/camera lens finder idea works very well.

[DIYASTRO]

Peter,

thanks for your reply

your idea of mounting a camera at focal plane of primary is exactly what I want to do with a multi reflecter project using three 200mm reflectors.

My thinking however is more to do with reducing the obstruction of the secondary.

Correct me if I am wrong, but I think that contrast gets lower with increased obstruction.

A skywatcher 200m scope for example has a 52 mm secondary (Obstruction) By using a SPC900nc webcam I could get this down to about 48mm, not much of a saving.

However, if it where possible to issolate the ccd chip from the webcam and run screened fine cable to the electronics outside the 200mm primary I think I could get the obstruction down to about 25- 30mm which doesnt sound much but I think it would make quite a bit of difference to contrast as well as extra light gathering.

Problem how much electronic noise will the isolated / extended ccd give?!

Let me have those thoughts!

Boyd

[Peter Drew]

Hello again Boyd. I wouldn't worry too much about the obstruction within reason, video work is relatively insensitive to this. The camera I am proposing to use is based on the Watec 120n which is only around 1.5" square, negligable on a 18" aperture. My reasoning was simplicity, ease of collimation, reduction of light loss due to a second reflection and the lack of need to get up to an eyepiece. I don't know if you have tried a 120n but the images at around 10 seconds integration on my 12" SCT in near realtime exceed anything I have seen visually in my 30" Dob.

[DIYASTRO]

Peter

No, have never had the chance to see 120n but have read some good reports etc about it.

Maybe I should not get too fixated with obstruction reduction then!

Would like to have a 30" Mirror to play with myself! What f/l is it?

I shall go back to the Dwg board and have a re-think.

Boyd

[Astro_Baby]

It looks really wonderful stuff and I am always in awe by people who can make this kind of stuff.

[Peter Drew]

Boyd. The 30" is f4.1, 1.5" thick plate glass made by Astronomical Equipment when in Luton in the late 70's.

[DIYASTRO]

I have begun work on the bigger brother.

Again a multi refractor housed in a ten inch Meade tube and mounted in modded lx 50 forks.

This one has a 5 inch doublet as the main image scope which has an integral 45 deg mirror sending the image up through the top of the tube via a filter wheel and then to helical focuser for dslr.

The two smaller lenses are both 80mm one for guidecam the other for finder / imaging.

Thought some one may like to see it it in progress.

Third pic, shows the first multi scope in the 8" and a 10" SCT in background. Need a bigger room!

Boyd

[jgs001]

Very clever, and very interesting setups Boyd... They look like monsters and bet they weigh a huge amount. As for a trio of 200mm newts... I dread to think exactly how big that's gonna get....

[DIYASTRO]

Thanks for reply and nice comments John.

Its quite odd but the 10" multi unit is less weight than the 10" sct. Although I agree they do look much heavier.

The stuff that I am building at the moment is not what you would call grab and go!

It is really just to get the experience back after years of non engineering. As I say, ultimately I would like to do this type of fabrication with larger reflectors and yes, they will be large and heavy, but perfect for perm. set up in obsey.

Boyd