Article: Modifying a Newtonian Tube for DSLR Photography

iceman (Mike) · #1 06-11-2007, 09:19 AM

Hi all

Alchemy has kindly written an article on Modifying a Newtonian Tube for DSLR Photography.

You can read the article on the IceInSpace Projects & Articles page, or directly by clicking on the link below:

Modifying a Newtonian Tube for DSLR Photography

Thanks to Alchemy for writing the article. If you'd like to submit a review or article to IceInSpace, please Contact Me.

iceman (Mike) · #2 07-11-2007, 01:19 PM

Article uploaded.

erick (Eric) · #3 07-11-2007, 01:31 PM

Slow down!! You are uploading them faster than I can read them all!!

Gargoyle_Steve (Steve) · #4 10-11-2007, 05:28 AM

I think it's all the cloudy weather Eric, folks can't do any observing / imaging so their creative minds have found other outlets. All the better for those of us looking for solutions to problems that others have already solved!

Tilt (Michael) · #5 29-10-2008, 08:00 PM

Seems fairly straight forward.

I would really like to image through my GSO 10" with a DSLR, anyone else modified their Newt?

Michael

AdrianF (Adrian) · #6 06-05-2010, 05:18 PM

Instead of cutting the tube could you maybe make up some gadget to move the primary up the tube? Maybe longer screws/springs?
That way if its decided to sell the scope later it would be an easy reversal.
Anyone tried this?
Over this weekend I will have a look to see if possible.

Adrian

adman (Adam) · #7 08-05-2010, 07:23 PM

Quote:

Originally Posted by AdrianF

Instead of cutting the tube could you maybe make up some gadget to move the primary up the tube? Maybe longer screws/springs?
That way if its decided to sell the scope later it would be an easy reversal.
Anyone tried this?
Over this weekend I will have a look to see if possible.

Adrian

Yep - works well - longer bolts, but you will also need stiffer springs. Bunnings has an assortment of compression springs, you will probably have to cut them to size and file the ends flat.

Adam

Benno85 (Ben) · #8 06-07-2010, 03:40 PM

Ok, sliiiightly off topic, but....

I'm looking at using a low profile focuser as opposed to cutting the tube. The focuser I'm looking at is 32mm racked in height with a draw tube travel of 38mm, giving a total of 70mm maximum "out" distance.

The article says to subtract distance A from distance B to arrive at the "sweet spot distance" which I'll call distance X. Given the 70mm total distance a low profile focuser will allow me, if distance X on my setup falls within 70mm then am I right in my assumption that I should be able to reach focus without having to cut the tube?

My apologies if that was a bit long winded and complex, believe me I had a brain burnout whilst writing this reply!!

Cheers,

Ben.

JD2439975 (Justin) · #9 06-07-2010, 03:54 PM

Not sure on the maths Ben but if you're thinking of a GSO low profile focuser I would NOT recommend it.

I had one, it was rubbish for more than a light eyepiece & certainly can't support the weight of a DSLR, flexure would be your bane.

On my GSO 10" it turned out I had to cut the tube anyway...live & learn.

Justin.

Benno85 (Ben) · #10 06-07-2010, 04:08 PM

Thanks for thoughts Justin, this isn't the first time I've heard of the GSO focusers not handling a DSLR too well. A Moonlight or Feathertouch is out of the question for a while so I guess I'll bite the bullet and cut the tube. Did you change your secondary mirror to accommodate for the change in the light cone?

Cheers,

Ben.

JD2439975 (Justin) · #11 06-07-2010, 04:46 PM

No, no need to, I still had full mirror clips showing & beyond.

bmitchell82 (Brendan) · #12 06-07-2010, 05:38 PM

hey fellas, your already asking the questions that i have answered and shown to work.

Justin just because you can "see the mirror" doesn't mean anything really, you are loosing a lot of your light cone with the standard Minor axis secondary being sub 60mm in a 10" your losing out before you start.

My flats show the big difference and I know that i need to go to the 88mm MA secondary if i want to fully illuminate my 40d sensor minus the vignetting due to the MPCC. For example a VC200L has a 46% Central obstruction where as the SW Dob has a 26% central obstruction, difference is one is made for photography and has a fully illuminated and corrected where as the dob is tuned for visual.

Most of the factory large mirror newts are generally not designed for photography and it shows in the GSOs with them not coming to focus with DSLRS let alone CCD's with Filter wheels and Active optics.

http://www.iceinspace.com.au/forum/s...ad.php?t=59178

I have done a lot of upgrades now to the 10" with the only things left in it that are Sky watcher being the Tube, Mirror, dob mountings, quick release foot and the finder scope itself. Bugger all really.

If you want to do it do it right straight up don't fiddle around with long primary bolts. if they where good then you would see them on places like Gemini and Mt Palomar ect ect. they introduce flexure and a whole heap of other nasties unless you go stupid and put massive bolts in there ect ect. thats just my 2 cents worth.

JD2439975 (Justin) · #13 06-07-2010, 06:55 PM

Damn it Brendan, not another expense!

I still owe for the Moonlite...this hobby is sucking me dry mate, could have supported half a dozen girlfriends at this rate.

bmitchell82 (Brendan) · #14 06-07-2010, 08:07 PM

... im a uni student

...

Benno85 (Ben) · #15 06-07-2010, 08:14 PM

Confirming my fears there B-Man, now I'll have to start petitioning SWMBO for some parts for Christmas. I'm thinking that maybe a JMI focuser might be enough for my needs, I've just gotta work out how much closer I need to be to the secondary in order to reach focus.

bmitchell82 (Brendan) · #16 06-07-2010, 09:40 PM

for 50 bucks you can sort your fears out 100%... that and a bit of silicone and everything is all better!

a 2 inch focuser is alright try to get 2.5 or 3" is the best.

Benno85 (Ben) · #17 06-07-2010, 10:12 PM

Hmmm now you've got me intrigued...where would my hard earned fiddie be spent? Longer bolts and stiffer springs perhaps??

bmitchell82 (Brendan) · #18 06-07-2010, 11:02 PM

cut the tube be done with it!

take your 50 bucks to either bintel/andrews depending on which one is cheaper get yourself a new 70mm secondary. get some silicone, take the old secondary off, stick the new secondary on. don't be scared

i just pulled mine off for the second time and re collimated the whole kit from complete pull down within 5 minutes

.

win win bigger full illumination, giving you fainter nebulosity from the center out to the edge

nice and cheap uni student style!

Ian Robinson · #19 10-07-2010, 12:19 PM

Quote:

Originally Posted by Benno85

Hmmm now you've got me intrigued...where would my hard earned fiddie be spent? Longer bolts and stiffer springs perhaps??

Neither - just move the mirror cell up the tube and closer to the focusor and invest in a 1-2" long extension tube for when you want use to eyepieces that need the extra backfocus.

stephenb (Stephen) · #20 10-07-2010, 07:32 PM

Quote:

Originally Posted by Ian Robinson

Neither - just move the mirror cell up the tube and closer to the focusor and invest in a 1-2" long extension tube for when you want use to eyepieces that need the extra backfocus.

Cut the tube, cut the tube, cut the tube!!!

I agree with Ian, Brendan and everyone else from now until the end of time who will give the same advice

I've been through this and you will not regret it.

Forget the focuser method, just cut the tube using the terrific article by Alchemy.

And then go and buy an extention tube to bring your eyepiecees into focus.

And there is absolutely nothing wrong with using silicone to adhere the secondary mirror to that GSO holder. I did this for my first 6" newtonian I build 25 years ago, and seriously, it never moved 1 millimetre in 15 years!