The joys of an F5 newt instead of an F4......

[gazza]

Hi,

I've spent 2 years and countless hours trying to get consistent images on my 8" CF Quattro. There have been many mods, and many hours of trials. I finally managed to get a nice field across an APSC chip that did not require cropping. My remaining issue was that the scope required tweaking collimation in the position it was imaging, and also tweaking before the beginning of each nights imaging run. I could probably have fixed this by building a new primary mirror cell, but I'd basically had a gut full....

I then borrowed a friends F5 200PDS, collimated it on the bench, fitted it to the mount, rotated it in the rings, fitted the camera/coma corrector assembly. Focused with a Bahtinov mask and took an image. What do you know? Perfect to the edge!!! No re build, no swearing, just a proper collimation and it worked. It also did not require re collimation the next night I tried it......

I was so impressed with the difference in ease of use of the F5 that tomorrow I pick up a 300PDS to mount on my Mesu. I'm now convinced that F4 in a newt is an exercise in frustration unless one has the dollars to spend on a top of the range OTA. The affordable F4's are not built to the mechanical tolerances that are required to achieve/maintain excellent collimation. They seem OK with a small chip, but if you go APSC, be prepared for a world of pain. The tolerances at F4 are just so small that a scope with a basic build just won't consistently cut it.

You know you have a problem when your partner tells you you need a new hobby because the current one doesn't give you any joy ! That was my Quattro....

BTW, my Esprit is a magnificent, scope that gave perfect images from day one....it's just no good for galaxies :-)

cheers

Gary

[pipnina]

I got a 130-PDS on Thursday. I haven't used it yet had the chance to use it yet but your appraisal for the lineup gives me a good feeling

How tightly do you tighten the primary locking screws? How close to perfect do you strive for with primary and secondary adjustment?

I had thought of a Skywatcher F4 quattro at one point - you kinda make me glad I didn't go for one! I'm certainly not as good at collimation as many here, so an F4 is likely an exercise in disaster for me anyway.

 

Glad you are getting along with your kit now

[Whistlin Bob]

4 minutes ago, pipnina said:

I got a 130-PDS on Thursday. I haven't used it yet had the chance to use it yet but your appraisal for the lineup gives me a good feeling

How tightly do you tighten the primary locking screws? How close to perfect do you strive for with primary and secondary adjustment?

I had thought of a Skywatcher F4 quattro at one point - you kinda make me glad I didn't go for one! I'm certainly not as good at collimation as many here, so an F4 is likely an exercise in disaster for me anyway.

 

Glad you are getting along with your kit now

I bought a 130-pds back in September to get into AP. The collimation was almost bang on out of the box. I tightened the screws finger tight and no more, having damaged other astro gear being too heavy handed. I've checked it a couple of times since and it hasn't changed so I've not touched it again. 

With our weather it gets out about twice a month on average, but has been excellent. For an astro graph it's quite a crude bit of kit really, but I get why people love them- they work really well and are pretty simple.

[gazza]

The 130pds is like most F5's - easy to collimate. You just have to make sure the secondary is positioned correctly. If it is, then a laser align of the secondary pointing, followed by the use of a cheshire, and you should be good to go...... 

cheers

Gary

[ollypenrice]

This makes perfect sense to me. Fast and cheap just don't go together and probably never will. You can also be lucky or unlucky, of course.

A slightly larger Esprit ought to be great for galaxies, too, but of course big refractors are expensive.

Olly

[Macavity]

I think the budget (steel tube) f/4 Newts work well enough as a "light bucket" for
e.g. visual astronomy. They are "twice as difficult" to collimate as an f/5 (theory)! 
Ya pays yer money? Some folks like to tinker, some don't? Few *illusions* here... 
I am indebted to a spread of views and useful upgrade ideas for budget things.

I often wonder how many folk are *really* getting the best out of <=f/5 scopes?
Outside of the connaisseur range, some refractors can be quite "out of whack".

[pipnina]

11 minutes ago, Macavity said:

I think the budget (steel tube) f/4 Newts work well enough as a "light bucket" for
e.g. visual astronomy. They are "twice as difficult" to collimate as an f/5 (theory)! 
Ya pays yer money? Some folks like to tinker, some don't? Few *illusions* here...

if you're going to be siting the scope on a fixed mount in an observatory, where it only gets to move when the mount moves you probably get the most out of an f4. No bumps from car travel or being carried in and out the house. Collimation would probably go out only rarely and you would probably only need to adjust the secondary once in its lifetime, leaving only the easy part of collimation to do.

[dph1nm]

Bah - I have the 12" Quattro f4 (+Skywatcher Aplanatic CC), only use it for imaging. It's a great scope. I have never touched the secondary since I opened the box, and only collimated the primary twice on sky in 6 months. Are the stars at the edge absolutely  perfect. Probably not. Do I care? No, it still takes an excellent photo. Would I buy it again - yes, absolutely!

NigelM

[Martin Meredith]

I love my Quattro 8" f4 and would definitely buy it again, but have only used it for EAA with a small sensor (and without needing a CC) where speed is of the essence and the edges of the field don't much matter. As a galaxy person I occasionally wish for a slightly longer FL, and then the issue would be whether to go for a 10" f4 or a 8" f5. Again, for EAA I'd probably opt for the former, but I can understand that ease of use points towards the f5 for AP. If I had an observatory I'd be thinking along the same lines as Nigel.

Martin 

[gazza]

7 hours ago, dph1nm said:

Bah - I have the 12" Quattro f4 (+Skywatcher Aplanatic CC), only use it for imaging. It's a great scope. I have never touched the secondary since I opened the box, and only collimated the primary twice on sky in 6 months. Are the stars at the edge absolutely  perfect. Probably not. Do I care? No, it still takes an excellent photo. Would I buy it again - yes, absolutely!

NigelM

What chip are you using Nigel? A small chip and/or larger pixels can hide the problems I experienced. I admit I am a bit OCD about getting a perfect field :-)  I can't see the point of buying a larger chip and then having to crop your images to get rid of less than round stars.....

cheers

Gary

[Adam J]

APS-C is pushing it. Something the size of a ASI1600 or a 183 is perfectly doable, doubly so if it's in an obsy. Having said that F5 is easier, so you are not wrong about that. Have been wondering if my HEQ5 can handle a 6 inch  f6 recently, for galaxies. 

[pete_l]

18 hours ago, dph1nm said:

Are the stars at the edge absolutely  perfect. Probably not. Do I care? No, it still takes an excellent photo. Would I buy it again - yes, absolutely!

NigelM

A very good, very realistic attitude.
ISTM that cropping an image to remove "imperfections" is a very practical, very quick way of dealing with them. Most people's astro photos feature the object of their desire in the centre and loads of Little White Dots (stars!) covering the majority of the field out to the edges.
IMHO most of those LWDs add nothing to the photo and their removal is neither noticed nor missed.

Clearly this is not the case for very large astronomical features that extent to (or past) the size of the field. But for the vast majority of images, that feature some interesting stuff in the centre and mostly just star fields past that there is nothing to be gained from including them.

[ollypenrice]

5 hours ago, pete_l said:

A very good, very realistic attitude.
ISTM that cropping an image to remove "imperfections" is a very practical, very quick way of dealing with them. Most people's astro photos feature the object of their desire in the centre and loads of Little White Dots (stars!) covering the majority of the field out to the edges.
IMHO most of those LWDs add nothing to the photo and their removal is neither noticed nor missed.

Clearly this is not the case for very large astronomical features that extent to (or past) the size of the field. But for the vast majority of images, that feature some interesting stuff in the centre and mostly just star fields past that there is nothing to be gained from including them.

Ironically I find that having a large chip (full frame) and short focal length leads me into the constant temptation to do mosaics. The trouble is that the large objects tend to be far larger than you think and also tend to connect with one another. Anyone thinking about this from scratch might think that a large format would remove the need for mosaics. Unfortunately for my sanity I find the reverse! (For example, it seems that the two small IC nebulae around gamma Cass actually connect with the Monkey head - at least in line of sight and possibly in fact as well.)

Olly

[glowingturnip]

I've certainly no complaints with my new-ish f5 200pds.  Out of the box it wasn't very well collimated, the secondary was longitudinally out of place in the tube and a bit squint too (but I did buy it in Spain - maybe they dropped it), but after an extended session with the cheshire lining it all up it keeps collimation well now.  I set up and tear down each session, and only need a quick laser collimate to get it all back in line again.

My coma corrector MPCC III spacing was a headache though, I've ended up a full mm longer than the recommended 57.5mm spacing for M48 threads and it's nearly all gone, just a tiny bit of coma left along one of the edges, but any more spacing and I wouldn't be able to screw it all together.

[gazza]

Hi,

I'm with Olly regarding mosaics, can't do them if you have crappy stars at the edge. Also if I had been happy with cropping I would have bought a small chip camera instead :-) .I like to see objects in their context as well, this means seeing things with the stars around them, not cutting off stuff that is distorted. Others may have different aims, but I just wanted to warn people that using these cheap F4 scopes is not easy and much depends on the luck of the draw when buying, your ability to collimate, your chip size, your tolerance to twiddling, whether you are happy to crop, and whether your partner can tolerate your frustrations........ Me? I find F5 a doddle by comparison - just picked up my 300pds and awaiting a friends help to lift it onto the mount.

YMMV

Gary

[dph1nm]

On 30/04/2018 at 21:38, gazza said:

What chip are you using Nigel? A small chip and/or larger pixels can hide the problems I experienced. I admit I am a bit OCD about getting a perfect field :-)  I can't see the point of buying a larger chip and then having to crop your images to get rid of less than round stars.....

cheers

A 1000D, which means pretty close to 1" pixels and a 1deg field. But my seeing is rarely any better than 3", so I admit I am not trying for sub-arcsec round stars! It is also permanently mounted in an observatory, which may help. I think the point I am trying to make is that you see a lot of criticism of these f4 Newts (and I worried about this before getting one last year), but I have found it no harder to deal with than my old 8.5" f6 which I used to use. Maybe the 12" is somewhat better built than the smaller ones, of course, I wouldn't know about that. It is certainly heavy!

NigelM