Fast Newton

[Darth Takahashi]

Well it finally happened, I have gone over to the dark side of imaging using a FAST NEWTON. I managed to pick up a nice Orion Optic DX300 F4 Newton last weekend.

The weather is holding so tonight's its debut. I have already had first light and the collimation was way off. Its now bang on and ready to image, so lets see how it goes...

Most people will be wondering why am I going down this route being an avid Takahashi fan / collector?

Well like most I have seen the great result people achieve with these scopes but most of all its the SPEED that attract me. I have nothing approaching F4. The best I can get to right now is F6 with a focal reducer.

Keeping the image scale at F4 is what attracts me most (1200mm and F4) My TOA130F is about 800mm at F6, well actually F5.8!!!

Here are some pictures of my newest and cheapest telescope todate!!! Mind you, if it works I will be modding this system and the first thing that's going is the old VIXEN focuser.

Any tips or guidance on getting the most out of this scope are of course welcome because I'm a new NEWTON user.

[andrew s]

Neil - Nice scope, I suspect you will need a coma corrector for full field imaging. Aslo collimate it to perfection, which is not easy at F4. Andrew

[ollypenrice]

Easy to see the attraction and Mikes images speak very loudly for themselves. I think you will need a coma corrector for a larger chip, for sure. Orthognoality, balance and focus will need to be dead right and, I think, regular focus checks will be in order. Refractors are easier but you can't have F4 and over a metre of FL that way and that's that!

Olly

[NickK]

N****N? Wash your telescope out with soap for saying that!

Seriously, it looks intriguing - looking forward to the photos. Also explains why it's cloudy..

[Darth Takahashi]

My initial impression is not great sort of so so!! but remember I'm coming at this from high end refractors. These things seem to have a real hot spot in the center and thats on my ST-10 chip. I suppect the secondary is a little small for imaging, especially for a full frame chip.

Collimation seems to also shift with temperature but I'm still learning and playing so probably a mixture of my errors componding the original errors.

I can easily see that a new focuser and more sturdy spider for a bigger secondary would improve things greatly...

Advise from others regarding their mods would be appreciated, weather permitting I'm going to try M51 this weekend with it.

[MikeD]

I would rotate the OTA 180 in the rings so the Cam is pier side that way you will need less counter weight to balance.

How do you plan to guide?

Mike.

[MikeD]

Scratch that last Q I see you have an SBig.

Mike.

[Darth Takahashi]

Thanks Mike, I'll give that a try.

My biggest issue at the moment is that the collimation is drifting.

I collimated it when mounted, then slewed around the sky to some star fields to check the coma etc... but at the end of the night when I checked the collimation once more it was way off again. Thinking about it now I had to adjust the primary to bring it back!

At F4 holding collimation seems to be difficult!!! This seems to be my main challenge at the moment.

[andrew s]

Neil - If the collimation is off after a slew around the sky then something is loose. With out knowing all the details I would ensure the main and secondary mirrors cells & supports are good and solid and wont move with slight hand pressure. (The main mirror should be slightly loose and be back on it's supports.) It's easy to loosen things too much when collimating. I can move my F5.4 Newt 180 deg with only the autocollimator showing a slight shift. Andrew

[MikeD]

Thanks Mike, I'll give that a try.

My biggest issue at the moment is that the collimation is drifting.

I collimated it when mounted, then slewed around the sky to some star fields to check the coma etc... but at the end of the night when I checked the collimation once more it was why off again. Thinking about it now I had to adjust the primary to bring it back!

At F4 holding collimation seems to be difficult!!!

Could the collimation problem be movement in the focuser?

Mike.

[Marmite]

Did you look at the f/2.8 Takahashi Epsilon-180ED newtonian astrograph?

[Darth Takahashi]

Did you look at the f/2.8 Takahashi Epsilon-180ED newtonian astrograph?

Of course I did!!! and then fell off my chair .

Besides, I thought it would be more rewarding to achieve something special with a more assessable telescope like the Orion Optics. The whole reason for selecting it was in the worst case I brought a nicely figure mirror.

Also I wanted more BANG for my buck 180@F2.8 versus 130@F5.6 or 300@F4 . If the Epsilon had been 250@ F2.8 for 3.5k I would have definitely thought twice about buying it.

[Darth Takahashi]

Could the collimation problem be movement in the focuser?

Mike.

The focuser is a rack and pinion VIXEN type and its very solid, in fact that's its problem, with the right force to ensure it stay engaged its difficult to focus with it, let alone fine focus!

I have checked the draw tube and it also fine, no movement etc...

I'm wondering if the weight of the camera and filter wheel are causing some sort of deflection / bending. But I'd expect it to spring back when its removed?

[Darth Takahashi]

Neil - If the collimation is off after a slew around the sky then something is loose. With out knowing all the details I would ensure the main and secondary mirrors cells & supports are good and solid and wont move with slight hand pressure. (The main mirror should be slightly loose and be back on it's supports.) It's easy to loosen things too much when collimating. I can move my F5.4 Newt 180 deg with only the autocollimator showing a slight shift. Andrew

Sounds very possible, so what I'm I looking for? How do I check this / what adjustments can I make?

[ollypenrice]

Very interesting thread. Keep going!!

Olly

[andrew s]

Neil - I would, with clean hands, try the various cells etc. to see if I can move them with a "finger tight" force. Push or pull on the cell spider etc. If possible get someone to monitor the collimation as you do it. Typically the main mirror cell will have springs and these need to be compressed quite tightly if there are no locking screws. Collimate with the tube horizontal then flip 180 and see the effect etc. It is difficult to be exact as the designs vary so much. You have to develop a feel for your scope and its ways. Andrew

PS In addition to my home made 300mm F5.4 Newt with OO mirrors, I have an Epsilon 180 and it's a dream!

[Astroscot2]

Neil im following the thread with interest, newts make excellent astrographs when everything works together, The biggest worry I day was flexure and opted for a carbon tube Newt, so far ive really only imaged with a DSLR and coma corrector with OK results, I have tried a full frame CCD Starlight H35 on the focuser and the results were so so. problem is the weight on the camera on the focuser - still need to try a few more shots this way. an option for me is a smaller lighter camera. will see?

http://stargazerslounge.com/imaging-deep-sky/115737-elephant-trunk-ha.html

[Darth Takahashi]

Neil - I would, with clean hands, try the various cells etc. to see if I can move them with a "finger tight" force. Push or pull on the cell spider etc.

Thanks Andrew,

I clean my hands very well and gently try to move the primary mirror in the mirror cell. To my surprise it was easy to lift it about 2 to 3mm. I plucked up courage and remove the mirror and cell together. After peeling back the black tape I could locate three Teflon grub screws. I have adjusted two of them to slightly pinch the mirror sides, adjust enough force to hold it in place etc...

After reassembling it I performed a new collimation and check it by moving the scope though 180 deg, to the other side of the mount. The collimation shifts but only by a very small amount, it stays within the first circle of the collimators rectal.

Now to get some images!!!