Help with multi-purpose 'scope for a beginner

[Greybeard]

Hi there,

I'm thinking of getting my first telescope in almost 25 years. Ages ago I used to own a Russian "Mizar" (it's now called TAL-1) 110 mm Newtonian on equatorial (not-motorised) mount, heavy as hell but I had loads of fun then.

Now my daughter asked me many times for a telescope and I finally decided to get one.

I tried to get my head around what are my real requirements and what are just nice-to-have features, but I really need some advice on this

1. Weight, portability and general compactness is an important concern for me, but I want to have a step-up in image quality in comparison to that 110mm - I couldn't then resolve the Cassini divide or see Mars polar caps!

2. I'm an amateur photographer and my previous job was related to image processing so I'm a bit of a pixel-peeper I really would like to do imaging as well as observations (DSO/planetary/terrestrial).

3. Tracking mount is a must, GoTo is nice to have.

4. Budget is three-digits in British pounds I will probably invest in a high-quality eyepiece or two later on.

5. I don't like long tubes of refractors, and I don't like Newtonians in general as observing at 90 degrees angle (esp. terrestrial) is awkward for me. Although this is not critical.

After couple of days of intensive reading I have many more questions than I had before my research. 

My initial choice is GSO RC 6" but I have doubts as it's f/9. Also I have no idea about what mount should I want.

My questions are:

1a. Is there a light-weight and cheap 7-8" option, or 6" is the only way?

1b. Does that 6" Ritchey–Chrétien really have an edge over a typical 6" Schmidt-Cassegrain/Mak photography wise?

2a. Photography implies low(ish) f-number, but how low should I aim for? I read that shallow DOF and field curvature could be a problem - should I be worried?

2b. I use  micro Four-Thirds camera with smaller image circle than 35mm, which means using reducer shouldn't cause any vignetting. But does reducer/corrector make sense with Ritchey–Chrétien scope, or "corrector" bit only applicable to Newtonians/CSTs/Maks?

2c. What are pros and cons of having a f/5 astrograph vs f/10 tube + reducer? I think the less glass in the way of light the better?

2d. Using as occasional spotting scope / terrestrial photo lens - do I need anything else except 45 erect diagonal?

3a. All I know about mounts just that Alt-Az not suitable for long exposure photography due to field rotation. What sort of tracking mounts are there, given I want whole setup to be less than 15kg?

3b. Is it true that mount should be about 2x heavier than the tube?

4. I think just a couple of Plossl EP is fine for starters, but ideally wanted a super-wide-field EP - is it true that they only exist for 2" not 1.25"? (By the way that 15mm Kelner that came with TAL was rubbish - had small apparent field and tiny eye relief - in contrast the 25mm Plossl view was amazing!)

I really hope some kind souls could answer these

Kind regards,

George Greybeard.

[ronin]

Your "requirements" seem to exclude a refractor, newtonian and as DSO imaging comes into it then that excludes an SCT or Mak.

So that is in effect all types of scope excluded. :grin:

Amateur photography is far removed from astrophotography.

When with a DSLR in your hand did you last have to track an object for say 120 seconds such that the image on the sensor did not move by a pixel. Then do that a total of 10 times then stack those ten 120 second exposures on top of one another?

Budget, consider the cost of a good 500mm f/2.8 lens for a camera, that is the budget required for a scope. A Sigma 500mm f/4.5 for a camera is £4800 as a guide.

I have 2 scopes usable for astro photography and each new are £1000 (neither are great AP scopes), a reasonable mount like the iOptron ZEQ25 is £850 and the Skywatcher AZEQ5 is £930. Both would be about right for a smallish setup.

If you are intending to use a DSLR I assume you have one, however a reasonable astro ccd like the Atik 450 is about £1400-£1500, 5 Mpixels. A full frame Atik is around £3500 but mono only, not colour. For a DSLR you will need a flattener, the one I have was £135 and that was less then expected.

The reality is not stick camera on scope and go click, click, click and look at the pretty pictures.

Consider the following:
Visual astronomy is different to imaging, and within imaging DSO imaging is different to planetary imaging.

DSO imaging is with multiple long exposures with a short fast scope whereas planetary is with a webcam and a video on a slow long scope.

There is not a great deal of overlap, some but not much.

What often occurs is someone goes imaging DSO's and has a small inexpensive visual kit to do some observing while the AP kit is getting images. 2 kits.

Take tripod and DSLR, set DSLR to fully manual, set ISO to say 4000, aperture to one or two stop down from max, set exposure to 20 seconds, aim at sky Casseiopia as the milky way is there, set the focus and take an exposure, have the NR facility set On. See what comes out. You likely cannot use the live view as the general light level may be too low for it to kick in and display anything. All camera setting must be overridden and manually set.

That allows you to up the ISO, open the aperture, extend the exposure period a bit.

That is no cost, if it is the stock supplied zoom then result may be not too good, a prime lens of 30mm-50mm would be better.

[jonathan]

As ronin pointed out, you'll be wanting two scopes for your requirements as I guarantee you will not want to be using several thousand pounds worth of kit with a young one or for casual spotting scope duties - for spotting scope you want a spotting scope on an Alt-Az mount.  The photography set up will be either a Dob with goto or more likely a very large and heavy EQ with wires and other bolt-on scopes and bits, something that you set up and leave to run.

If I were you and knowing what I know now, and if money was almost no object, I would start off with a nice small mount for visual, something like my favourite the Celestron Omni CG-4 which you can buy with scope if you like or on its own (single or dual axis motor drive an optional extra), but I prefer to put something better on such as the Skywatcher 150P newtonian or Altair Astro triplet 102 or 120 refractor.

Then I would be buying a copy of Making Every Photon Count and following ronin's advice regarding mounts and cameras along with what is suggested in the book.  I have an NEQ6 Pro Syntrek currently collecting dust because it's just too much of a chore for me to get out compared to my nice simple, fairly light Omni CG-4, and the views are arguably better through my 102 refractor than my 8SE SCT.  If I put my mind to it I could do some short exposure photography with the 102 on CG-4 mount as well.

Getting it right can be very complicated when first starting out, you'll probably benefit a lot from learning with a smaller rig first that you out-grow, which could then be put to visual duties as you move on to bigger and more complex kit.

[Greybeard]

Many thanks for the replies guys.
 

Your "requirements" seem to exclude a refractor, newtonian and as DSO imaging comes into it then that excludes an SCT or Mak.

So that is in effect all types of scope excluded. :grin:

Well, as I said it's not critical, it's a preference - if I could get 6" RC f/5 this would tick most of my boxes.
Minor point - I never liked that tube opening in Newt - gathers dust and I had people dropping things down the tube on the main mirror. From that perspective, refractor/SCT/Mak is safer.
 

ronin, you explained well why I shouldn't expect an observation scope to do well with astrophotography.

In fact, I did a bit of astrophotography (no digital then - we used slides!) on our university's 300 mm refractor, but this all seems like the Stone Age now. But I know a bit about image stacking, even wrote denoising software mysefl, so image processing isn't a massive issue for me.

It's funny you mentioned taking pictures of Milky Way with DSLR - I tried it with my camera (Olympus E-M5) and a 20 mm Panasonic f/1.7 (40mm equivalent) lens but the result was barely satisfactory, mainly due to the known bug (band noise)  that my camera suffers from with this particular lens, and the contract was quite low due to light pollution.

...and the views are arguably better through my 102 refractor than my 8SE SCT.  

This is really interesting - what would be the conditions where 4 times more light (8" vs 102 mm) wouldn't make it for a better picture?

I totally agree with you though - I shall start with a relatively small scope/mount for observation only, and see where I get from there.
 

[Greybeard]

Again thanks for advice - just purchased SkyWatcher SkyMax-127 on GoTo mount, and can't wait!



 

[jonathan]

This is really interesting - what would be the conditions where 4 times more light (8" vs 102 mm) wouldn't make it for a better picture?

I totally agree with you though - I shall start with a relatively small scope/mount for observation only, and see where I get from there.

I think it really has to do with the difference in speed and quality of the scopes, the refractor is a high quality f7 triplet, while not the fastest it is certainly of decent quality so I can use high quality eyepieces, giving sharp and steady views.  It is also a lighter scope than the 8SE so I can mount it on a smaller tripod, easier for me to handle and precisely point.  The 8SE is a slow f10 SCT which can't really make good use of the same high quality eyepieces so the previous gains of the better glass are lost.  True enough, the image should be larger and thus better in the 8SE but in my practical experience with the eyepiece difference it just isn't the case.  There is also the thing of the narrower field of view with the SCT which means that finding those faint DSOs is rather difficult.

The refractor is better on planets because of the sharper views, even if those views may not be as large in the eyepiece (they are large enough on a clear night to see plenty of sharp details).  A small sharp view is better than a big fuzzy view.

The 8SE excels at lunar and other large object observing such as the Orion nebula, and would possibly also be excellent at solar observing too with a suitable objective filter (would probably need to buy the larger Baader solar film option or a pre-made one for 8" - considerably more expensive than for the 102 refractor).

I need to have both scopes out at the same time to do a proper comparison, seeing conditions can be very different from one night to the next, this is just how I remember it.