8” Aperture

[BigMisterP]

For sum reeson i have it in my head that 8” if a good apature for a reflector.

I’ve seen Schmitt Cassegrain, Ritchie Chretiene, Rowe Atkinson, Maksutov and Newtonian which all seem to qualify because they have mirrors.

Main use would be Galaxys and emission nebula, whirlpool, bods nebula, vile and pelican

Any recomendashions?

 

[Stu]

18 minutes ago, BigMisterP said:

For sum reeson i have it in my head that 8” if a good apature for a reflector.

I’ve seen Schmitt Cassegrain, Ritchie Chretiene, Rowe Atkinson, Maksutov and Newtonian which all seem to qualify because they have mirrors.

Main use would be Galaxys and emission nebula, whirlpool, bods nebula, vile and pelican

Any recomendashions?

 

Probably a good bet would be to read this book before doing anything....

https://www.firstlightoptics.com/books/making-every-photon-count-steve-richards.html

[iapa]

+1 for Steve’s book.

[alacant]

1 hour ago, BigMisterP said:

Any recomendashions

Hi

As soon as you're allowed to do so, go along to an astro club, see all the mirrors first hand and get a free demonstration:) 

Cheers

[Stu Wilson]

Ts optics instead of skywatcher.

[ollypenrice]

If you're thinking about taking up imaging, don't begin with a pre-conceived idea of a preferable mirror size. It really does not work like that. You can take good, bad or indifferent images with any size of mirror. Mirror size is about as important as the colour of the socks you wear during the capture.

Olly

[Jonny_H]

On 07/05/2021 at 20:33, ollypenrice said:

Mirror size is about as important as the colour of the socks you wear during the capture.

Olly

And here was me thinking that wearing my lucky blue socks whilst imaging dramatically improves my images 😩 😜

[ollypenrice]

2 hours ago, Jonny_H said:

And here was me thinking that wearing my lucky blue socks whilst imaging dramatically improves my images 😩 😜

At night all socks are grey...

lly

[johninderby]

9 minutes ago, ollypenrice said:

At night all socks are grey...

lly

Not allways 😁😁😁

[gorann]

My guess is that 8" reflectors are rather popular because they can be carried by budget mounts like SW NEQ6 and similar. Bigger relectors demand more expensive mounts. Still, most 8" refelctors (except things like  RASA8) have rather long focal lengths (usually 1500 - 2000 mm) and are therefore really not beginner scopes since they demand good off-axis guiding, good seeing, and good collimation. The usual recommendation is to start imaging with a 3 - 5" refractor, which is much more forgiving and can be guided with a guide scope and should not demand collimation. They can rapidly give quite rewarding results.

Edited May 9, 2021 by gorann

[alacant]

9 minutes ago, gorann said:

long focal lengths (usually 1500 - 2000 mm)

Hi

Our f4.something Newtonian reflector has a 203mm diameter mirror and 1000mm focal length. It's fine even on our abused eq6s. 

I wish someone had suggested it rather than a miserable 80mm refractor with which to begin imaging!

@gorann May we take this opportunity to congratulate you upon the images you produce using modern cameras upon your RASA? They should help convince the OP one way or the other. Most likely one way. They have certainly helped us in deciding that that's the way things are heading.

Cheers

[ollypenrice]

5 hours ago, johninderby said:

Not allways 😁😁😁

Mods! Mods! This man is promoting light polluting smalls on SGL!

2 hours ago, alacant said:

 

I wish someone had suggested it rather than a miserable 80mm refractor with which to begin imaging!

Nobody's suggesting miserable ones. If 80mm scopes are miserable then the Samyang lenses must be positively suicidal... only they don't seem to be. Please explain!

Olly

 

[alacant]

18 minutes ago, ollypenrice said:

Samyang lenses must be positively suicidal..

No no. They're f2. So much faster.

See here for a full explanation. LOL!

 

Edited May 9, 2021 by alacant

[ollypenrice]

28 minutes ago, alacant said:

No no. They're f2. So much faster.

See here for a full explanation. LOL!

 

You're the one knocking small aperture imaging. I'm not. I'm perfectly well aware of the advantage of aperture but I'm a pragmatist and put practice first. When your Newt images are as good as Sara Wager's Baby Q images I'll be really interested, I really will... LAZ. *

Olly

*Apparently it's fashionable to end posts with three meaningless capital letters so there you go.

 

 

Edited May 9, 2021 by ollypenrice

[rickwayne]

To the original poster: Mirror size, or aperture generally, matters a lot for visual observing. Your eye can only integrate over fractions of a second, so you want to hit it with a flood of photons at once. Aperture also determines the theoretical size of the smallest detail a scope can resolve.

For photography, we can literally take our time -- the sensors will patiently accumulate photons over long exposures, and more to the point the computers can integrate the photons received over many exposures. (A bucket of math there -- for now, just take my word for it, lots of exposures are good).

Because the atmosphere wobbles and our mounts aren't perfect, no one ever achieves the theoretical resolution for a given aperture. And, as noted above, wider scopes tend to magnify more, amplifying those problems. So on the same mount, the photographer with a smaller, lighter scope just shrugs and adds more exposures, winding up  with a better final product than the big-scope guy.  Since smaller, lighter scopes are cheaper, for the same total budget she'll have a better mount and  be getting even better pictures still.

Alacant is exceptional -- most beginners struggle more with a bigger, longer scope. Once you're learned the techniques, a little refractor can be limiting, but learning is not the same as doing.

[vlaiv]

I would actually recommend 5-6" F/5 newtonian as bigger starter scope with mirrors.

There are two popular models Skywatcher 130PDS and 6" F/5 by different vendors. Someone recommended TS Photon newtonians instead - these are made by GSO rather than Synta and are quite fine.

More important "metric" than telescope size is something called sampling resolution. It depends on both used camera and selected focal length of telescope.

I'm assuming you'll start with DSLR type camera with APS-C sized chip. Most such cameras nowadays have pixel sizes that are good match for ~600-700mm of FL.

130PDS is F/5 instrument and has 650mm of focal length. 6" F/5 telescope will have 750mm of focal length - so both are good matches for DSLRs and general working resolution of about 1.5"-2"/px

You can get 6" F/4 telescope - which has 600mm of FL or even 8" F/4 instrument with 800mm FL - but those are fast telescopes and collimation and keeping everything squared is going to be problem for a beginner.

Newtonians are going to require coma corrector - so factor that in and coma corrector needs to be placed at certain distance to camera so you'll need proper adapter to connect it together.

Exception to above is nice imaging scope (more expensive) that has built in corrector:

https://www.teleskop-express.de/shop/product_info.php/info/p12005_Explore-Scientific-MN-152-f-4-8-Maksutov-Newtonian-Telescope-with-Field-Correction.html

That is Maksutov Newtonain telescope. It ha 730mm of focal length and you don't need to purchase coma corrector for it. It has big meniscus lens that makes nice flat field suitable for astrophotography.

[gorann]

1 hour ago, vlaiv said:

I would actually recommend 5-6" F/5 newtonian as bigger starter scope with mirrors.

There are two popular models Skywatcher 130PDS and 6" F/5 by different vendors. Someone recommended TS Photon newtonians instead - these are made by GSO rather than Synta and are quite fine.

More important "metric" than telescope size is something called sampling resolution. It depends on both used camera and selected focal length of telescope.

I'm assuming you'll start with DSLR type camera with APS-C sized chip. Most such cameras nowadays have pixel sizes that are good match for ~600-700mm of FL.

130PDS is F/5 instrument and has 650mm of focal length. 6" F/5 telescope will have 750mm of focal length - so both are good matches for DSLRs and general working resolution of about 1.5"-2"/px

You can get 6" F/4 telescope - which has 600mm of FL or even 8" F/4 instrument with 800mm FL - but those are fast telescopes and collimation and keeping everything squared is going to be problem for a beginner.

Newtonians are going to require coma corrector - so factor that in and coma corrector needs to be placed at certain distance to camera so you'll need proper adapter to connect it together.

Exception to above is nice imaging scope (more expensive) that has built in corrector:

https://www.teleskop-express.de/shop/product_info.php/info/p12005_Explore-Scientific-MN-152-f-4-8-Maksutov-Newtonian-Telescope-with-Field-Correction.html

That is Maksutov Newtonain telescope. It ha 730mm of focal length and you don't need to purchase coma corrector for it. It has big meniscus lens that makes nice flat field suitable for astrophotography.

First Vlaiv, I got a bit irritated when you try to talk a beginner into buying a Newton for AP rather than a refractor, but that Maksutow Newtonian from TS you suggest looks like something that could be very rewarding for a beginner. A nice amount of aperture, no coma corrector needed and no sensor distance to worry about - just a bit of collimation. Sounds like a good choice, and it is not on back order right now.

[vlaiv]

1 minute ago, gorann said:

First Vlaiv, I got a bit irritated when you try to talk a beginner into buying a Newton for AP rather than a refractor

I based my recommendation on the fact that OP wanted to start of with mirrored system. Wasn't really trying to talk anyone into anything.

Out of all mentioned scopes that have mirrors - I still think that 5" or 6" F/5 newtonian - or that Maksutov Newtonian are the best - although MN is more expensive.

I also think that we should present people with all options. I know that most people would be more comfortable with refractor scopes to start off with - but that does not mean that there are no people that would manage newtonian to start with. I took some of my first images with F/6 8" newtonian.

Yes, they were poor images - but I don't think I would be able to produce better images with 4" APO at that stage .

 

[iapa]

I’m in the reflector “family”.

Basically as I started with an F5, 5” (650mm fl) reflector, then to f5, 8” (1000mm).

I’ve since collected an f10, 8” SCT (2000mm+ fl) and f4,10” (1000mm fl) reflector.

I just like reflectors :), and fiddling 🔨🔧

[iapa]

I should also say that I have a pier up, rarely travel, and when I do it is to self catering cottages so I take the biggest heaviest mount and tripod with me.

Then it sits while it rains all day and all night 

[rickwayne]

Even those of us who recommend small refractors to beginners recognize that there are other valid paths -- or at least we ought to! It's just that such scopes tend to give adequate results with the least amount of trouble and fiddling. In fact I often recommend that folks start with DSLR/lens combos with which they're already familiar.

If someone decided that they wanted to grind their own half-meter f/11 mirror, machine their own mount, and assemble The Newtonian Astrograph of The Gods for their very first imaging experience, more power to 'em, I say. But it's not the route I'd advise for most people. Many of us find more than sufficient challenge trying to get things working the easy way.

[PXR-5]

I generally recommend an 8" to start.

Providing it can be easily moved and stored.

 

Right now everything is backordered, so I recommend just about anything to get started, of course do not over look binoculars

I use my binos more than my scopes

 

 

[vlaiv]

8 hours ago, PXR-5 said:

Right now everything is backordered, so I recommend just about anything to get started, of course do not over look binoculars

I use my binos more than my scopes

How do you image with binoculars? Afocal method?

Do you have side by side setup with two cameras to exploit both lenses?

[PXR-5]

16 hours ago, vlaiv said:

How do you image with binoculars? Afocal method?

Do you have side by side setup with two cameras to exploit both lenses?

I don't do imaging at all.

 

But you ask a good question, I saw someone post some solar images with binoculars.

 

Like, how the heck did you do that?

[Stu]

2 hours ago, PXR-5 said:

I don't do imaging at all.

 

But you ask a good question, I saw someone post some solar images with binoculars.

 

Like, how the heck did you do that?

Let’s keep the thread on topic please, which was about starting imaging with an 8” reflector.

Thank you 👍