Help requested in choosing a telescope to image with please

[inFINNity Deck]

On 30/12/2021 at 22:45, Roog said:

I trusted family friend has suggested that I select an 80mm triplet APO, of relatively short focal length, SLR imaging camera plus HEQ5 mount and modest tracking scope.

And yet I see that others aim for 100mm and 120mm aperture triplet APO’s with dedicated Astro cameras and even bigger mounts! (Yes this is going to be loads of money) 
So is an 80mm APO with modest focal length enough for a reasonable selection of deep space targets?

Hi Paul,

most important points have already been mentioned above, and I agree that the mount is key, so do not economise on that.

Regarding the various APOs: I started out imaging using a SkyWatcher Esprit 150ED. A few months ago I added a SkyWatcher Esprit 80ED to the set-up as I noticed that the 150ED is a fine scope, but with very limited FOV (Field Of View). Here is the difference:

M13 using SW 150ED and ZWO ASI1600MM Pro Cool: https://www.dehilster.info/astronomy/deep-sky-objects/M13-colour.jpg

M13 using SW 80ED and ZWO ASI1600MM Pro Cool: https://www.dehilster.info/astronomy/deep-sky-objects/M13_210823.jpg

When I started looking for a smaller scope I used Stellarium to make my decision. In Stellarium it is possible to define a camera and all the scopes you possibly want. Then Stellarium will show what will fit the sensor, so you get an idea of what you can/cannot achieve with the combination. At the time I made myself the following comparison-grid with the 150ED at the upper left as reference, the red rectangle represents the imaging chip of the ZWO ASI1600MM:

HTH

Nicolàs

Edited January 1, 2022 by inFINNity Deck
typo

[inFINNity Deck]

11 minutes ago, teoria_del_big_bang said:

• Guiding scope and CCD - not actually essential to start with but you will want this eventually.

This of course depends on the mount that is used. So far I have not been guiding (10Micron GM3000HPS), although I have to admit that I will try guiding for the first time coming months to see if that is beneficial to star size. My subs are usually between 30s and 420s, here is one consisting of 60 x 420s subs (7 hours data) in H-alpha, O-iii and S-ii: https://www.dehilster.info/astronomy/deep-sky-objects/NGC7380_211028.jpg

Nicolàs

[Roog]

5 hours ago, iantaylor2uk said:

A William Optics 81 mm triplet is a good choice (I have the 81 GT IV). You will still need a flattener, you can either use a dedicated WO flattener/reducer (which will give you a focal length of about 380 mm) or a general purpose flattener (I use a Hotech 1x flattener, which gives a focal length of 478 mm). This gives good round stars right out to the edge of an APS-C sized sensor, and at 478 mm focal length, the field of view is 2.8 x 1.9 degrees, with a resolution of about 2.1" per pixel, so autoguiding should be pretty straightforward. A larger refractor will usually have a longer focal length, so a smaller field of view, which can be good for some targets, like galaxies. 

Hi @iantaylor2uk thank you for your help, the Williams optics is one on my list of APO’s to consider. Can I ask, what is a flattener, why do I need one and why does it affect the focal length?

[teoria_del_big_bang]

46 minutes ago, Roog said:

Hi @iantaylor2uk thank you for your help, the Williams optics is one on my list of APO’s to consider. Can I ask, what is a flattener, why do I need one and why does it affect the focal length?

A good explanation HERE

Steve

[ollypenrice]

80mm aperture is tiny?

85mm gave me the image below. It was many years ago that I used this 85mm scope and I'm fairly horrified by the processing of this image when I look at it with hindsight. However, that's not the scope's fault. The key point about an imaging rig is that, unlike a visual rig and the human eye, it can collect light over time. The eye cannot. With the eye it's light in, light out.

My imaging rig priority order is, without any doubt whatever, mount-camera-optics.

Olly

 

[Swillis]

Looks like you've had plenty of great advice here. As mentioned by many above, with so much to learn it is a good idea to keep it simple. With that in mind you could go even simpler than suggested, if you have a DSLR and lens you could start with that and add a mount. Either something simple such as a star adventurer (or similar), or as you mentioned you preferred to 'buy once' then get the mount you want to run your intended equipment on and learn the basics before moving onto something bigger/more demanding/complicated. There is lots to learn from setting up, through taking images, guiding and processing if you can smooth the learning curve out a little that should go a long way to keeping your interest going. 

When you talk to your family friend it may be a good idea to ask for their story of how they got into AP and what gear they started with. 

Best of luck

[Roog]

Cheers @inFINNity Deck the app looks helpful, I can see me tinkering with that.

[Roog]

2 hours ago, teoria_del_big_bang said:

A good explanation HERE

Steve

Thanks Steve, that’s the best explanation I have seen and explains why I have seen people talk about spacers and cameras!

[rickwayne]

A ways back in the thread, in the context of mounts, you noted that you would rather "buy once, cry once". This is an excellent attitude to have toward your first mount. It is possible to get a mount which is too heavy or too awkward to set up (assuming, like most of us, you  can't do a permanent installation), but it's almost impossible to get one that is too good. My CEM70 works beautifully with a DSLR and a 50mm lens, and also with the longest scope available to me, a filter wheel, and a cooled astro camera. It is every bit as simple to set up and  get running as my first mount was -- in fact, a lot easier, since it has through-mount cabling and much higher-quality adjustment mechanisms.

The same can't be said of a scope. Tale as old as time: Beginning astrophotographer, logically enough, assumes that optical quality and focal length are the primary determinant of high-quality images, buys a long-reach scope with huge aperture. Surprise! Long reach and big aperture mean even bigger challenges for mount  and for  technique. Endless frustration, rage-quits the hobby.

Blowing almost all of your initial budget on a mount and imaging with a DSLR and telephoto prime is an excellent way to start, actually (assuming you can work out an autoguiding rig).

[ONIKKINEN]

On 31/12/2021 at 21:14, ollypenrice said:

My imaging rig priority order is, without any doubt whatever, mount-camera-optics.

Olly

I ignored the mount part when building my setup and hate myself for it. I thought "well the manufacturer says 10kg is fine so why would a 0.1kg telescope be any better than a 9.9kg one". Well its not that simple and that's the markets fault for accepting the blatant lies from manufacturers. We really do need manufacturers to state AT WHAT FORM do the payload limits and FOR WHAT USAGE they apply. For imaging and for long OTAs, like long refractors and especially Newtonians the limits are probably closer to 50% of the stated "max payload". Shame it has to be this way really as i believe the overwhelming majority of the userbase is budget limited and must choose which evils to pick from, and the mount should absolutely not be one of them.

If i had a time machine i would go back in time and pour almost all of my budget in the mount. Nothing else in the setup matters at all if the mount underperforms.

[inFINNity Deck]

13 hours ago, rickwayne said:

It is possible to get a mount which is too heavy or too awkward to set up (assuming, like most of us, you  can't do a permanent installation), but it's almost impossible to get one that is too good.

Mind you that the larger mounts also have a minimum payload, even though it is never specified. I once wanted to do some tests with only a single scope on my GM3000HPS, but found out that the 15kg SkyWatcher Esprit 150ED was not heavy enough to get my mount balanced, it required at least 5kg of additional weight to be able to use a counterweight on the counterweight shaft. The shaft alone was just too light to balance the scope and the counterweights I have are 20kg each... (as far as I am aware there are no lighter ones for the GM3000).

Nicolàs

 

[Roog]

Thank you all for your advice, I appreciate the importance of a good mount and tripod, not to mention a firm surface on which to place it. I am naturally  a sceptic when it comes to performance specs, but I guess you have to start somewhere. 
 

[edarter]

Maybe I'm a bit different to most, but I haven't found getting mount, camera, computer, and software for imaging etc talking to each other much of a challenge really. Yes a few niggles but that's all. The far bigger challenge for me has been (and still is) the image processing once the capture is done.

I would advise you set yourself an initial budget and work from that to identify potential purchases, you can then decide whether you want to exceed that budget to upgrade parts of the setup or not. Like everyone else here advises, spend the money on the mount! If that means your scope is a 130pds rather than an apo triplet then so be it, the 130pds still gives plenty of bang for your buck. Newtonians give more light gathering capability for £ spent but need collimation, again not something that has particularly troubled me and if you already have a dob I guess you are already used to that. Refractors don't have that problem but a good one is a lot more money and will likely need more integration time.... which is the next point, where are you? If you live somewhere that has reasonable weather it may not be a problem, but if in the UK then every second counts as we get about 10 minutes clear skies per year!

Do factor in other costs though, you will need a field flattener or coma corrector very quickly, most post processing software costs something and you're going to need a laptop or similar to control the mount and do image acquisition.

If I were to start again there isn't much I would change tbh: eq6, 2nd hand modded DSLR, SW 130pds and coma corrector. Since then I have added guide scope and camera and my next upgrade will be to a dedicated astro camera.

[Roog]

Thank you @edarteroh I am in total agreement with you, my biggest fear by far is in processing data. I am not at all comfortable with computer based applications, this is one of the the reasons why i opted for a visual rig.

As per my original post , I am itching to give astrophotograpy a go, I would like to give it my best shot without needing to win the lottery, I don't mind saving for some thing if the result is that I enjoy the experience. Equipment that can't gather reasonable images and software that i cannot fathom would be a terrible outcome.  

I am currently aiming  for a CEM 40 with a modest refractor, say 80mm, I need to look at the weight of all of the bits to see how close I get to the payload capacity of the mount, which I propose to consider very conservatively.

I shall return.

[rickwayne]

You're probably going to be well within a CEM 40's happy range. For example my 70mm Stellarvue with a cooled astro cam, filter wheel, autofocus motor, and Raspberry Pi came to about 17 pounds (I think that was with the off-axis guider instead of a guidescope). That worked OK on a CEM 25P, a 40 would be laughing.