Quattro conversion.

[Earl]

If you were going to attach the trunions off a 250px onto a 250 quatro to make a f4 dob, where would you drill holes in the ota? or better still how would you work out where?

[Thalestris24]

Hi Earl

Are you sure you want to do that?!! I've no experience of dobs etc. but just thinking about it analytically, I'd start by doing scale drawings of both and take it from there.

Louise

Edit: you can probably compare the balance points by just laying the ota's horizontally on a suitable piece of dowel. I imagine the 250px is balanced around or close to the trunions but I may be wrong!

[DrRobin]

I don't think there would be too much to be gained from mounting a Quattro (F/4) on a dob base.  Visually, you wouldn't really see much difference (any at all?) between a F/4 or a F/5 and imaging wise you would gain about 25% FoV for the same camera and reduce your exposure times to three quarters, but would this be enough of a difference?

A dob base is not going to be the best for DSOs, you will get field rotation and won't track as well as an EQ mount.  I don't think you can guide an Alt/AZ very well either.

Sorry if I have missed the point and to be a little negative, but I can't really see why?

If you really want to do it, a suggestion;

Put a broom handle on the floor, put the Quattro on top and move it backwards and forwards until it balances.  This is going to be the point you drill and mount the dob fixing points.  You might want to put you fav eyepiece/camera in first.

Robin

[Earl]

It would not be for imaging and its more of a why not than any other reason, I hear there visually is quiet a difference in nebulosity in the quattro a few have reported it.

Imaging wise, id not be using a newt im not that brave

[DrRobin]

Nothing wrong with using a Newt for imaging. My 8" Quattro works very well, but you do need to add a decent coma corrector.

As regards visual I couldn't say if it would be any better than say your F/5.

Good luck

Robin

[Macavity]

WIBBLE WARNING?

The "collimation challenge" goes as inverse cube of f-number, so you might not necessarily buy an f/4 Newt in preference to f/5 - At least In the "smaller" 8-12" Dob range? An f/4 Dob is "twice as hard" to collimate as an f/5. The "sweet spot" is 1.4 mm, rather than 2.8mm (yada yada) - But the latter [imo] is about the limit of the "mechanics" in *non-customised* budget Newts? Once into BIG Dobs (>=14") you might need f/4 (faster) optics to reach the eyepiece at zenith! Standard Newts are often f~1250mm - Perhaps as much to "human sized" as anything?

The requirement of coma correction is mentioned above. Moreover, f/4 "imaging Newts" are designed to have significant in-focus. This to get the focal plane outside the OTA for use with a DSLR. To use my GSO f/4 photo-newt *visually*, I need an 80mm 2" extension with some eyepieces! It all gets a tad awkward... ugly? The f/4 need for a larger than standard secondary mirror casts a bigger *secondary shadow* in the middle of field. You can use typical 32mm eyepieces for low power use in an f/5 Newt, but I find the shadow limits me to 20mm at f/4. Ironically f/4 has no advantage in visual field of view.

That said, I am a big fan of budget f/4 photo-Newts... Hey, I could afford one! The 8" f/4 is significantly smaller & lighter... It FITS my small observatory better, is not too heavy for my HEQ5. Collimation is a challenge. But with some mods (thanks to inspiration here) I've got it (mostly!) licked... Or as much as I NEED. But I am using my Newt as a Video Astronomy "light bucket". I am not aiming for "Magazine Quality" images. Video camera chips have a small ~8mm diagonal, coma is "not too bad" etc. etc.

It might be FUN to build a Dob base for an f/4 Newt. Or, as I did, use a "Giro" Type mount!

People do get (to my mind) great imaging results with them. But (as anecdote suggests?),

I don't think I would specifically buy a smaller f/4 imaging Newt *purely* for visual use.

[Earl]

I have decided to get a Orion Dob base for it, not the cheapest option but will be great.

[ollypenrice]

I would just insert the standard tube into a traditional Dob structure. I think David Lukehurst makes these as well as OO. There would be no need to go for a truss since tubed Dobs are perfectly common.

On the wisdom of the idea the only advantage I can see would be in wider FOV, but will it have a lot of coma? It will certainly be harder to collimate and it will, in my view, be inferior to the F5 because of the larger central obstruction which mainly impacts upon contrast. As other have said, F ratio does not work in visual observing as it does in imaging. I'd stick with the F5 any day.

Olly

[DrRobin]

Chris is right about the focus range.  My 8" Quattro has a very short travel on the focuser, it is fine for a DSLR (probably what it was really designed for), needed a small extension for a CCD and a massive extension for an eyepiece, probably about 50 - 60mm which got a bit flexible.  Since I only image, the only time an eyepiece goes in is for basic star alignment.

I know these scopes have a reputation for needing precise collimation and frequent checking but I have found that my Quattro (Carbon tube might help here) keeps it's collimation very well and is no harder to collimate than any other Newt and a whole lot easier than a SCT.  Due to the shorter focal length they are quite a bit shorter than the F/5 and like Chris my 8" Quattro just fits in my small obs, the F/5 wouldn't.

The secondary mirror wasn't central on mine when it arrived (it was second hand, but reasonably well collimated on arrival through the post, so it might have been like that at supply).  To centralise it I had to remove the spider and reset everything.  Astrobaby's guide came in very handy, as did a webcam and Mir d collimation to get it central in the focus tube.

I noticed a 10" Quattro sold on ABS the other day, guess it is making it's way to you as I type this?

Robin

[Earl]

Chris is right about the focus range.  My 8" Quattro has a very short travel on the focuser, it is fine for a DSLR (probably what it was really designed for), needed a small extension for a CCD and a massive extension for an eyepiece, probably about 50 - 60mm which got a bit flexible.  Since I only image, the only time an eyepiece goes in is for basic star alignment.

I know these scopes have a reputation for needing precise collimation and frequent checking but I have found that my Quattro (Carbon tube might help here) keeps it's collimation very well and is no harder to collimate than any other Newt and a whole lot easier than a SCT.  Due to the shorter focal length they are quite a bit shorter than the F/5 and like Chris my 8" Quattro just fits in my small obs, the F/5 wouldn't.

The secondary mirror wasn't central on mine when it arrived (it was second hand, but reasonably well collimated on arrival through the post, so it might have been like that at supply).  To centralise it I had to remove the spider and reset everything.  Astrobaby's guide came in very handy, as did a webcam and Mir d collimation to get it central in the focus tube.

I noticed a 10" Quattro sold on ABS the other day, guess it is making it's way to you as I type this?

Robin

Indeed it is

Its an experiment more than anything else, i do like the idea of it been smaller than the normal, the F3 10inch I found on he net was dinky and looked amazing, of course it would be very puninishing on the eyepieces etc, but bah why not.