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parallaxerr

Considering one of those reflecty things, but how big?

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Over recent months I seem to have come around to the idea of a reflector. I've previously resisted having just accepted that I like fracs, but I am guilty of never having owned a newt (I did once have an SCT though).

Maybe it's the realisation that large refractors are just too much of a compromise or that having recently collimated a refractor, realising that it's not really a big deal. Ironic that I had to do that when it was collimation that put me off reflectors for so long. Also, there's no arguing with the £/inch of aperture equation!

I also now have a capable mount in the form of the AZ100 so I've been looking at OTA sizes and weights whilst trying to keep aperture fever at bay! 

It would appear that both 8" and 10" newts are being used on similar mounts, such as skytee II's, but the 10" don't half look big! It's so difficult to tell from some images where there's nothing to scale against though, as people often take photos of their kit in isolation. I have used the threads below for comparison...

This is purely a DSO venture, though I'm sure both would perform admirably on planets. My winter targets typically being the Veil Nebula, Orion, Andromeda, the Ring nebula, etc. I'm really interested to see how much deeper I can go with a larger scope and to find some new targets, having not ventured beyond 120mm aperture before (apart from the 8" sct but that only really got used on Jupiter at the time).

Can anyone comment on whether the additional size and weight of the 10" is worth it over the 8" for the extra light gathering ability? A subjective question I agree, but I'd be interested to hear anyway, e.g. "the 10" doesn't offer much more but is a beast to handle", or "the extra 2" makes a HUGE difference to what you can see".

Also, I wonder if the 10" is going to offer any more from my home location with moderate LP, or if it's just going to collect more of the wrong light? Is there a point where this becomes an issue with respect to aperture?

 

 

 

 

 

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One thing I have noticed which may sway the decision: 

When considering what I know to be a good exit pupil for observing from my location, the extra focal length of the 10" does offer a larger image but also starts to really draw in the FoV available with my current EPs......that could get expensive not only in wider field EP's but a coma corrector too.

Am I right in saying that using moderate 55°-68° EP's with the 8" would not necessitate the requirement for a coma corrector?

 

astronomy_tools_fov.png

Edited by parallaxerr

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I did experiment with using the OTA from my Bresser 10” dob on a Skytee  and actually it worked quote well. A right pain to fit it to the mount though holding the OTA with one hand while tightening the saddle clamp.

2D283939-493F-4C6D-B54E-2BEB8EDA24DB.jpeg

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I've run an Orion Optics 10 inch F/4.8 on a Giro-type alt-azimuth mount. That was a nice rig and easy to set up and use but the OO tubes are lighter than their chinese counterparts. The AZ100 would certainly cope with it easily. If you are after DSO's the additional light gathering of the 250mm over the 200mm is worth having I feel.

I have owned a Skywatcher 250PX dob but never used that OTA on an alt-az mount.

 

https://stargazerslounge.com/uploads/monthly_06_2011/post-12764-133877625165.jpg

 

 

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Thanks John & John. The different perspectives of those pictures really help.

@johninderby, is that a Uni or a Planet? Planet I suspect. That's another consideration, I'm currently on a 1.75" steel tripod which is fine for the frac, but I wonder if it would struggle with a 10" on the AZ100? I do use it all but fully collapsed, only extending an inch or so of one or two legs to level, so may be OK.

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46 minutes ago, parallaxerr said:

 

Am I right in saying that using moderate 55°-68° EP's with the 8" would not necessitate the requirement for a coma corrector?

 

 

In my opinion you do not require a coma corrector for visual if you are using well corrected eyepieces (including the TV and ES 82 degree eyepieces) for scopes down to around f5, unless you are a fanatic  about the view being aberration free right to the edge of the field. You also need to be aware that some coma correctors are quite heavy as well and will potentially affect the balance of your scope, and partly for this reason don't usually bother using my ES Coma Corrector with my 14in f5 Newtonian. 

For photography however this is a different matter.

John 

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Just now, johnturley said:

In my opinion you do not require a coma corrector for visual if you are using well corrected eyepieces (including the TV and ES 82 degree eyepieces) for scopes down to around f5, unless you are a fanatic  about the view being aberration free right to the edge of the field. You also need to be aware that some coma correctors are quite heavy as well and will potentially affect the balance of your scope, and partly for this reason don't usually bother using my ES Coma Corrector with my 14in f5 Newtonian. 

For photography however this is a different matter.

John 

Thanks John, good info. I'd be using ES 68° EP's and don't typically obsess over edge of field performance.

I must have inadvertently denoted this thread for comment from John's only!? 😂

 

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13 minutes ago, parallaxerr said:

Thanks John & John. The different perspectives of those pictures really help.

@johninderby, is that a Uni or a Planet? Planet I suspect. 

It’s a Uni tripod. Now used with my AZ100.

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2 minutes ago, johninderby said:

It’s a Uni tripod. Now used with my AZ100.

Ah, I'm surprised as the tripod looks quite beefy compared to the skytee II. I've seen your images of the AZ100 on the Uni, obviously it's a fair bit chunkier.

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......as the pictures in one of John's post confirms

 

 

P1090261.JPG.69f80a6460e6b766fcc0ff7c2f58f529.jpg

Edited by parallaxerr

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You can use an EQ6 tripod with the 2” legs with the Skytee if you get a Geoptik HEQ5 to EQ6 adaptor. The CG5 tripod with the 2” legs  is a direct fit but hard to find nowadays.

A5422E9D-E9E8-49D4-8807-775F145F9E61.jpeg

Edited by johninderby

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Yes, a shame I sold my black version (for CG5) a few years back. Not sure I could stand a white tripod with the AZ100 on top!

Edited by parallaxerr

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Hi Jon,

I've been having similar thoughts about adding a reflector option on to my own alt-az mount set up.

I too, like my refractors, but miss that extra bit of aperture when looking at the deep sky.

I'm also at an age now, and Tuesday nights session at our EMS darksite reminded me of it.......that its rather a struggle at looking at anything

high up in the sky with a longish refractor. My 140mm scope is nearly a metre of focal length, which leaves the eyepieces rather low down when chasing anything high up.

My days of observing on my knees on damp ground are over. Even using binocs is tricky if i pan too high : i have an arthritis issue in my neck, and it doesn't take too long before discomfort and pain sets in.

"So why not get a Newt....??!! " i asked myself, having had to give up on Andromeda and the double cluster as they were so high......and observe seated in comfort with the eyepieces in a good place.....

 

My DM-6 has a 40 lb capacity, and i have the digital setting circle computer thing there ready to go.

I've had 3 Newtonians before. A fairly recently sold OO 12" F4.  This was a nice scope, but i didn't really get on with the OO Dob mount too much. Too many balance issues with binoviewers !

And the same problem in reverse.......low down objects are tricky to view with a Dob mount. 

Before the OO VX12 i had a OO VX10 F6.3 with the long 1600mm tube which made the same issues worse from a balance point of view.

20 years before this, my first serious scope was an OO 10" Europa F4.7 on a rather dodgy German equatorial mount. It actually handles the big tube reasonably well, and it showed me what a 10" scope was capable of.

 

So, why not try and mount a Newtonian on my alt-az ?

My own choice would be between a 10" tube and an 8" but i'm leaning toward a 10" (in for a penny, in for a pound, right ?)   with an F4.5 - F5 ratio. A 10" hit a good sweetspot here in the UK i think.

I actually tried my old 12"F4 out indoors on the DM-6, and while it was ok, it was certainly a bit precarious, probably warranting a tripod upgrade. (i have the BB Uni 18 as well, but the Planet would be a better bet with this idea)

And its not so much the tube weight thats the issue (and yes OO tubes are lightish for their aperture) but the size + mass itself. A 12" solid tube is a big old scope, no doubt about it. And the wind is the main enemy when out in the field,

and a large solid tube telescope and any sort of wind gusts are a toxic combination.

My current alt-az workhorse is on the right (The one on the left is a grab / go which i use with a small 4" refractor)

Let us know how you get on with whatever option you choose.....🙂

50071672846_f2d38d590b_c.jpg

Edited by Space Hopper

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Hey Rob, it sounds like your thoughts are very much aligned with my own. It's interesting what you say about the larger scope in the wind, definitely something to consider especially with my less than ideal tripod. I feel a 10" would also require the addition of a Berlebach so the cost is doubled, say £800-£1000 for 10" OTA + BB vs <£300 for just an 8" OTA. 

I'm probably leaning towards an 8" right now, especially as it will provide a wider FoV without upgrading EP's and is a modest introduction to reflectors. A 200p is cheap enough and could be upgraded at a later date.

 

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Yes, an 8" tube is probably a better bet with a standard sort of tripod, and will still show you alot.

For me though, an obstructed 8" is not that big a leap from my own unobstructed 5.5" refractor, so i'm thinking a 10" would be better.

I've considered a C9.25 or C11 SCT (i've also had an 8" in the past) an while they have alot of aperture in a fairly compact  sized scope,

you are still tied into a long focal length, and what i really want, is low power, wide angle, rich field views in a fast F4 - F5 Newtonian.

There are other tripod options as well. For a 10" tube (or bigger) a Losmandy FHD is a better bet perhaps, and while it is pretty much bombproof they are a step up in price.

I've been looking for a used one to come up, but they very rarely do........

 

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Aside from already owning an AZ100, is there any reason why you're looking to mount a Newtonian on an alt/az tripod mount rather than buying a Dobsonian? Holding either an 8" or 10" tube with one hand while tightening the clamp with the other seems like quite a difficult prospect compared to simply placing the OTA onto a dob mount. Of course the Bresser dobs have tube rings so there is the possibility of trying both mounting options if desired. 

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2 hours ago, Ricochet said:

Aside from already owning an AZ100, is there any reason why you're looking to mount a Newtonian on an alt/az tripod mount rather than buying a Dobsonian? 

Yes, my garden! It's really not astro-friendly and is made up of tiers and what tiers there are aren't flat. The tripod allows me to get the AZ100 level but I fear a dob would rock and roll all over the shop.

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4 minutes ago, parallaxerr said:

Yes, my garden! It's really not astro-friendly and is made up of tiers and what tiers there are aren't flat. The tripod allows me to get the AZ100 level but I fear a dob would rock and roll all over the shop.

Fair enough! My garden isn't perfectly flat and the dob copes with being a small amount out of level but if you've got serious changes I can see where the built in adjustment of a tripod will come into its own. I would definitely factor in getting a handle to the purchase cost and would probably err on the side of smallness as extra weight and difficulty will dissuade you from getting a telescope out (or rather, you'll just get a smaller frac out instead of the newt). 

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It looks to me like these various Alt-Az mounts are putting the OTA's at about the same height as my NEQ6 puts my 250PDS.

If that is the case it's worth considering the height of the eyepiece at high elevations. With my big Newt I need a couple of steps to see things towards the zenith. I'm a very boring 5' 9" and the eyepiece isn't "just" out of reach, it's over a foot out of reach! 

My home viewing area is on grass so I then need to put a board down to stand the steps on. 

This, along with my sight not being as youthful as it once was and increasing light pollution, is part of the reason I've started using a camera instead of an eyepiece!

Having said that, the 250PDS is a lot of scope for the money and I love mine. It does catch the wind but for visual it really isn't a problem. Indeed, I've been thinking about either a Dob or Alt-Az mount for purely visual away days, just me and the Big Gun under a dark sky...

Edited by Paul M
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10 hours ago, Paul M said:

It looks to me like these various Alt-Az mounts are putting the OTA's at about the same height as my NEQ6 puts my 250PDS.

If that is the case it's worth considering the height of the eyepiece at high elevations.

Yep, that is very much on my mind Paul, especially with the uneven nature of my garden, I don't really want to be standing on a box/steps! It's a bit more weight to the 8" argument..

 

A bit of evening research and I discovered the TS optics PHOTON line of newtonians, they look rather nice and have better focusers than the SW equivalents. The 8" is particularly well priced, but the 10" F4 also caught my eye as the shorter tube goes some way to combat the issues discussed above and provides a larger FoV. 

But, will an F4 be suitable? I'm aware it will require more precise collimation, but have some other questions:

1. Will I need a coma corrector @ F4 with 68° EP's?

2. Will the larger central obstruction really be noticeable, especially considering the faint fuzzies?

 

 

Edited by parallaxerr
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I don't think the larger CO will be a problem for deep sky observing.

F/4 is a fast newtonian though. I think coma will be apparent in 68 degree AFoV eyepieces, provided that they are well corrected enough that their astigmatism does not mask it.

 

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3 minutes ago, John said:

I don't think the larger CO will be a problem for deep sky observing.

F/4 is a fast newtonian though. I think coma will be apparent in 68 degree AFoV eyepieces, provided that they are well corrected enough that their astigmatism does not mask it.

 

Thanks John,

I did some more calcs and realised the exit pupil was getting too large with the 10" F4, requiring shorter EP's. Great for mag but FoV was suffering. Not a problem if I wanted to invest in Ethoi and a paracorr, but that's not on the cards right now.

The 8" really is looking like a solid option.

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I've had a couple of the Skywatcher 200mm F/5's in the past (actually mine were branded Celestron and Helios but they were the same thing) and I've been impressed how well they performed. You can get clean and tidy used ones for £130 or so and they deliver a lot of observing potential for not many £'s IMHO.

 

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A little update. Having sold my CG5 2" tripod some time ago, I'd lived to really regret the move. Searches for a replacement turned up nothing but I stumbled upon stock on David Hinds' website over the weekend, don't know why I didn't look their before.

Anyway, order placed and shipment notification received today.

I think a 10" is back on the cards.

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