I need help trying to decide frac vs newt for imaging

[laser_jock99]

On 05/12/2017 at 14:19, Orion1 said:

I'm upgrading from a Canon 200mm f2.8L lens. I have a Skywatcher EQ5 Synscan mount and a Canon 600D full spectrum with a Astronomik CLS-CCD) camera.

I need help because I'm stuck trying to decide whether to buy the TS 80mm triplet with reducer or the Skywatcher 130PDS with coma corrector.

I love the nimble form factor of the 80mm triplet but the price/performace ratio of the 130PDS is giving me a headache...

Neither of the above........the GSO 6" F4 astrograph would be okay with a full spectrum DSLR and EQ5.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p4762_GSO-6--Imaging-Newtonian---6--f-4---2--Monorail-focuser.html

At F4 collimation needs to be spot on. Not a difficult proceedure in itself (with the correct tools) but something you don't have to do with a frac. Then again there are few F4 fracs......(you could even get F2.9 if you add one of these) not reccomened for non tweakers though!!!

NGC7000 159 second single sub with a 6" F2.9 GSO Newtonian

[alacant]

41 minutes ago, laser_jock99 said:

6" F4

Absolutely and 100%ly +1. I've a 130pds and had the fortune of having a go with a 150 f4 a bit back; same data, half the time.

50 minutes ago, laser_jock99 said:

F4 collimation needs to be spot on. Not a difficult proceedure

I'm still a bit confused about this. I find the procedure exactly the same no matter what f-ratio is being collimated. 

Cheers, clear skies and good luck with whatever you go with. 

[laser_jock99]

15 minutes ago, alacant said:

I'm still a bit confused about this. I find the procedure exactly the same no matter what f-ratio is being collimated.

Correct - I'd be using the same tools/proceedure collimatiing at F8 or F2.9 

At F8 I could get away with not being as precise.

[Stub Mandrel]

On 06/12/2017 at 21:11, ollypenrice said:

Don't obsess about load capacity. What experience will tell you is that the resolution of your imaging setup in arcseconds per pixel is what tests the limits of your mount. The fewer arcsecs per pixel at which you're imaging, the more accurate your mount has to be. It is this which is the most important thing.

Olly

I think this is very true... I'm not sure how mount/tripod capacities are calculated, but knowing enough to judge the load bearing capacities of various bearings I think with a well lubricated and adjusted mount the rigidity of the tripod is the limiting factor for weight, not the mount, as long as you don't overload motors and gears (which mostly means good balance and not whirling the scope around like a tree-legged fencing match).

I keep being tempted by an EQ5 or HEQ5... but at the moment I am (finally) getting consistent guiding at around 1.7" RMS with an imaging scale of 1.84" per pixel (EQ3-2 with 130P-DS) and I'm not sure I have anything to gain from a 'better' mount without more demanding optics.

As always I stand to be corrected...

<edit> I'll correct myself, just went out to change camera batteries and PHD2 says its managing 0.63", not bad for an overloaded EQ3-2!

Does this mean I need a camera with smaller pixels Olly?

[Orion1]

11 hours ago, laser_jock99 said:

Neither of the above........the GSO 6" F4 astrograph would be okay with a full spectrum DSLR and EQ5.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p4762_GSO-6--Imaging-Newtonian---6--f-4---2--Monorail-focuser.html

At F4 collimation needs to be spot on. Not a difficult proceedure in itself (with the correct tools) but something you don't have to do with a frac. Then again there are few F4 fracs......(you could even get F2.9 if you add one of these) not reccomened for non tweakers though!!!

NGC7000 159 second single sub with a 6" F2.9 GSO Newtonian

Oh no, yet another option  thanks for the tip! No doubt I’ll choose this over the 130PDS. Still not sure about newt. I like the fov and the convenience of a small frac...

[ollypenrice]

12 hours ago, alacant said:

Absolutely and 100%ly +1. I've a 130pds and had the fortune of having a go with a 150 f4 a bit back; same data, half the time.

I'm still a bit confused about this. I find the procedure exactly the same no matter what f-ratio is being collimated. 

Cheers, clear skies and good luck with whatever you go with. 

The procedures are indeed independent of F ratio but the tolerances are not. If you're lucky the mechanical tolerances on your particular copy of the scope will be fine and collimation will be easy enough. But there are lots of opportunities for a manufacturer to make life hard for us! One of my very experienced guests uses a Tak Epsilon which, he said, took him quite a long time to get to 'almost perfect.' It still isn't quite there because, he suspects, his modded camera may have a tiny amount of chip tilt which would't show up in a slower system.

Olly

[Stub Mandrel]

29 minutes ago, ollypenrice said:

his modded camera may have a tiny amount of chip tilt which would't show up in a slower system

When I 'cooled' my 450D one of the shims fell out. I was fairly confident I knew which one as shims in the other two would probably not have been able to slip off as easily. I figured fitting it in the wrong place would create a double error which would be quite obvious; by luck or judgement I got it right, a relief as camera dismembering/re-membering is a tad stressful!

[ollypenrice]

2 minutes ago, Stub Mandrel said:

 by luck or judgement I got it right, a relief as camera dismembering/re-membering is a tad stressful!

...so much so that, in my case, it will be scrupulously avoided!!

lly

[Gerry Casa Christiana]

18 hours ago, ollypenrice said:

The debate is undecided, Gerry. I have an open mind, having taken images which I have enjoyed processing at anything between 0.66 and 3.5 arcseconds per pixel. To be honest, If I could find a camera with the chip size of the Atik 11000 (3.5"PP for me) that gave me 2"PP I'd sell someting precious and buy it! But it doesn't exist...

3.5"PP...

1.8"PP...

0.9"PP...

They're all pictures...

Olly

Oh yes I can see those are pictures! Awesome! I just love that NGC 1499 I've been photographing it too but I imagine you had a lot of data there? I'm really glad you said the debate is still open.  I prefer it that way but I'm guessing though for you that 2PP is what you would like as a ideal. Looking at those pictures it's hard to tell the difference in any quality. A friend and I have just built a observatory I read somewhere you have 6! Anyway we are still in the very early stages and still using dslr and cheaper equipment. Thanks for the inspiring pictures. 

Olly can I ask another question  what do you think of RC's I was toying with getting a RC8 so I could go a little deeper with my fov. I'm used to Newtonians so I'm well up on collimation. Tough setting them up? Or better to go with larger pixel frame and crop more?

Thanks

Gerry

[ollypenrice]

26 minutes ago, Gerry Casa Christiana said:

Oh yes I can see those are pictures! Awesome! I just love that NGC 1499 I've been photographing it too but I imagine you had a lot of data there? I'm really glad you said the debate is still open.  I prefer it that way but I'm guessing though for you that 2PP is what you would like as a ideal. Looking at those pictures it's hard to tell the difference in any quality. A friend and I have just built a observatory I read somewhere you have 6! Anyway we are still in the very early stages and still using dslr and cheaper equipment. Thanks for the inspiring pictures. 

Olly can I ask another question  what do you think of RC's I was toying with getting a RC8 so I could go a little deeper with my fov. I'm used to Newtonians so I'm well up on collimation. Tough setting them up? Or better to go with larger pixel frame and crop more?

Thanks

Gerry

Around 2"PP is nice, certainly, but for galaxies (other the than M33, M31 and a handful of other big ones) you need to go below that. You can do this by using smaller pixels or a longer focal length. DSLRs already have small pixels so you probably don't need a FL of much more than a metre to get to a galaxy resolution. DSLRs do like a fast F ratio though.

The California did have a lot of data. HaOIIILRGB. Ha 11.5 Hrs, OIII 7 hours L 1.5 Hrs, colours an hour each. 22 hours all in, but done with a dual rig in a couple of nights. The narrowband data is doing most of the work in that image.

People do get good results from the GSO or GSO-based RCs but, equally, some people really struggle to set them up. I tried to help a guest with one once and we simply went round in circles. One adjustment threw another out until we gave up. They are considerably harder than Newts since they have two parabolic mirrors. I like using refractors, which just work! But I'm lazy. 

Good to hear you've an observatory now. There are indeed 6 observatories here but one I only host, one I rent out and the others are for our scopes. This is my job though. An excellent excuse!

Olly

 

[emyliano2000]

30 minutes ago, ollypenrice said:

This is my job though

What a great job to have.