20 replies to this topic

[Milos1977]

I have actually never looked at the Orion Nebula with any telescope. Only with about 30 different binoculars over the years. Now I would like to take a closer look.

I am gearing up to look at it as well as planets and the moon this winter. I got the Skywatcher 180m Mak with 2" dielectric mirror diagonal. Mak is of the newer kind with 33mm baffle opening and oversized primary. I have 8.8mm, 11mm, 14mm, and 25mm eyepieces of 70°-82° kind. 

 

My question is:

Considering the shape/size of nebula is so broad,  and my seeing from the city is rarely good (but it ok sometimes and I do go for it) and the scope has pretty narrow field of view, where does it leave me for maybe best view of it? 

 

Which is the widest 2" eyepiece that will take most advantage of the baffle without getting waisted in vignetting?

 

I gathered this much so far but im not sure if they are too wide for my scope. 

 

- Williams Optics SWAN 40mm 72°

- Agena SWA 38mm 70°

 

Any thoughts or specific recommendations from your experience? S

Should I consider a filter?

 

Thanks

 

p.s.

Budget is between $100-$200 in new or good used selections. 

Edited by Milos1977, 29 September 2020 - 10:07 AM.

[havasman]

I really think your best view is still going to be via your image stabilized binoculars or maybe the 70mm binos. The nebulous area is so huge and extends so incredibly far beyond the commonly considered boundaries that an f15 instrument is going to present challenges. Contrast can be difficult to see if there is no edge to the object in the field. The figure/ground relationship is diminished. You should get tremendous views of the Trapezium with your scope and are fully equipped for it. I don't think buying another widefield eyepiece is going to get you a lot at f15.

 

No scope can do it all.

Edited by havasman, 29 September 2020 - 07:37 PM.

[Peter Besenbruch]

I have actually never looked at the Orion Nebula with any telescope. Only with about 30 different binoculars over the years. Now I would like to take a closer look.

I am gearing up to look at it as well as planets and the moon this winter. I got the Skywatcher 180m Mak with 2" dielectric mirror diagonal. Mak is of the newer kind with 33mm baffle opening and oversized primary. I have 8.8mm, 11mm, 14mm, and 25mm eyepieces of 70°-82° kind. 

 

My question is:

Considering the shape/size of nebula is so broad,  and my seeing from the city is rarely good (but it ok sometimes and I do go for it) and the scope has pretty narrow field of view, where does it leave me for maybe best view of it? 

 

Which is the widest 2" eyepiece that will take most advantage of the baffle without getting waisted in vignetting?

 

I gathered this much so far but im not sure if they are too wide for my scope. 

 

- Williams Optics SWAN 40mm 72°

- Agena SWA 38mm 70°

 

Any thoughts or specific recommendations from your experience? S

Should I consider a filter?

The William Optics eyepiece is trying a little too hard in its claims; both will have the same field of view. Both will vignette, and, yes, you can see it, but it's not too bad.

 

Another eyepiece that will produce very good views is the 28mm LET that was bundled with the scope.

[luxo II]

Having had one of these scopes I tried quite a few low-power eyepieces with it, but the two I like most are:

- 2" 38mm SWA 70-degree UWA, this is available under many badges, very comfortable;

- 2" APM 30mm ultraflat, this is available from APM or from Agena Astro, or Altair Astro (UK).

[Tropobob]

I have actually never looked at the Orion Nebula with any telescope. Only with about 30 different binoculars over the years. Now I would like to take a closer look.

I am gearing up to look at it as well as planets and the moon this winter. I got the Skywatcher 180m Mak with 2" dielectric mirror diagonal. Mak is of the newer kind with 33mm baffle opening and oversized primary. I have 8.8mm, 11mm, 14mm, and 25mm eyepieces of 70°-82° kind. 

 

My question is:

Considering the shape/size of nebula is so broad,  and my seeing from the city is rarely good (but it ok sometimes and I do go for it) and the scope has pretty narrow field of view, where does it leave me for maybe best view of it? 

 

Which is the widest 2" eyepiece that will take most advantage of the baffle without getting waisted in vignetting?

 

I gathered this much so far but im not sure if they are too wide for my scope. 

 

- Williams Optics SWAN 40mm 72°

- Agena SWA 38mm 70°

 

Any thoughts or specific recommendations from your experience? S

Should I consider a filter?

 

Thanks

 

p.s.

Budget is between $100-$200 in new or good used selections. 

Take a peep at the nebulae with your existing 25mm EP; it will be amazing.  Then use that experience/feedback to proceed from there. 

[CQDDEMGY]

The orion nebula is a treat as it is fantastic at high or low magnification, and your instrument is ideal for high magnification study

https://skyandtelesc...ions-trapezium/

[Redbetter]

 

I am gearing up to look at it as well as planets and the moon this winter. I got the Skywatcher 180m Mak with 2" dielectric mirror diagonal. Mak is of the newer kind with 33mm baffle opening and oversized primary. I have 8.8mm, 11mm, 14mm, and 25mm eyepieces of 70°-82° kind. 

 

 

Which is the widest 2" eyepiece that will take most advantage of the baffle without getting waisted in vignetting?

 

I wouldn't worry about vignetting as being a significant concern for visual.  The supposed "rule" about not exceeding the rear baffle diameter is a myth that propagates primarily because folks haven't tried it much.   My experience has been that even the ~27mm rear baffle opening of an ES 127 f/15 Mak is not really an issue with the widest possible field stop in 2", 46mm.  I am actually finding that I like the 55 Plossl with this set up because at f/15+ with 2" diagonal, I need all of the exit pupil I can get for nebulae.    One could just as well use a 41 Panoptic or similar for other types of targets.  

 

With such a long focal length, 2700mm, what you will find you need for large targets--particularly large nebulae--is true field of view.  The edge might have some vignetting, but it is inconsequential compared to getting some useful field of view that aids in framing/panning/etc.  For the SW 180 are looking at a max with a 46mm field stop of about 1.02 degrees.  

 

A lot depends on where you intend to observe and if the Orion Nebula is all you are really after.  It is so bright that when folks ask what filter they will need for it I mostly respond, "sunglasses."  Few other large nebulae even come close. 

 

Rural viewing and suburban viewing are much different and urban viewing would be different still.  I am not terribly keen on nebula viewing even in the suburbs, so I don't limit my eyepieces to what I would tend to use for light polluted conditions.

[Milos1977]

Thank you all for very useful answers. I guess the next is to get some experience in that range EPs myself. 

I do have Meade 8" SCT which I will also use to compare. I cant afford to keep both so one will have to go. 

Thanks again. 

[whizbang]

I loved my WO 40mm SWAN with a 127mm Mak.  Maks are slow scopes and the WO does a good job, cheap!

[kjkrum]

I'd suggest basing your choice on exit pupil, but you'll have to figure out what's best for your own environment. I have a f/12 Mak, and my backyard NELM is 5.1 on a very good night. Between my 15, 25, and 32mm EPs, I seem to get the best contrast on M42 with the 25mm, or 2.1mm exit pupil. The sky is too bright in the 32. This aligns with what I've read here about people preferring 2-3mm exit pupils for DSOs.

[SeattleScott]

You won’t be able to fit all of it in so just go as wide as you can. The WO or Agena are excellent options at F15. Get whichever is cheaper. My only complaint was that 43mm eye lens has a tendency to fog up some nights after an hour or so. But big eye lenses are hard to avoid on 40mm SWA eyepieces.

Scott

[jmillsbss]

I really think your best view is still going to be via your image stabilized binoculars or maybe the 70mm binos. The nebulous area is so huge and extends so incredibly far beyond the commonly considered boundaries that an f15 instrument is going to present challenges. Contrast can be difficult to see if there is no edge to the object in the field. The figure/ground relationship is diminished. You should get tremendous views of the Trapezium with your scope and are fully equipped for it. I don't think buying another widefield eyepiece is going to get you a lot at f15.

 

No scope can do it all.

Okay. It's not a widefield scope.  Lots of power.  Vignette issues.  No background reference diminishes the perceived contrast.  But what if he uses a focal reducer?  Why not get the scope down to say, f/7.5 with a 0.5 reducer?  It might be a bugger, but OP's got a 2" diagonal and likely a 2"/1.25" adapter.... so what about a TV55 and a $40 0.5x reducer?  I doubt he's gonna see much DARK sky where he's located, but then again, going to a darkER site might still not be dark ENOUGH skies to see the finest filaments at the edges.  Now, I've no experience whatsoever with a TV55 OR a decent focal reducer.  I'm just asking.

 

For context, I got a revo imager some time back and it included a 0.5 reducer, not a great one, but, I was messing around on my C8 and could ALLLLLLMOST get it all in the field with a ES68/24.  It was hard to stay on the focal point, but after a little practice it was decent.  Really not the right way to do it, I guess, but it worked.  I almost always agree with, and learn from, your counsel, however, you suggested binos, but the OP said he'd already seen M42 in 30 pair of binos.  I understood he wanted to use the Mak.  Again, I'm just curious..... J

[Milos1977]

@jmillsbs

Thanks for bringing this up. I will find out in few weeks first hand how it works as I have one of the Meade f/6.3 Focal Reducer & Field Flattener LX already.

 I got it with my 8" SCT but never used it.

https://www.bhphotov...r.html/overview

 

 

"The Meade 07049 f/6.3 Focal Reducer & Field Flattener is a 4-element multicoated 41mm lens in a metal cell which threads upon the 2.00"-18 rear cell thread of any 8.0-16.0" Meade Schmidt-Cassegrain or Ritchey-Chrétien telescope.  It also is compatible with Meade's lineup of APO refractors, and 7.0" Maksutov-Cassegrains (though not ideal for either, because they don't benefit from the field-flattening influence)."

 

 

Has anyone tried it on these Maks?

 

This below is (on paper) comparing f/6.3 reducer paired with 25mm 70° EP against solo 38mm 70°eyepiece

Attached Thumbnails

• 

Edited by Milos1977, 01 October 2020 - 08:28 PM.

[havasman]

 But what if he uses a focal reducer?  Why not get the scope down to say, f/7.5 with a 0.5 reducer?   I doubt he's gonna see much DARK

For context, I got a revo imager some time back and it included a 0.5 reducer, not a great one, but, I was messing around on my C8 and could ALLLLLLMOST get it all in the field with a ES68/24.  It was hard to stay on the focal point, but after a little practice it was decent.  Really not the right way to do it, I guess, but it worked.  

Your idea could be worth a shot. I failed to note the observer's location and that is a critical component of the matter here.

[Peter Besenbruch]

Okay. It's not a widefield scope.  Lots of power.  Vignette issues.  No background reference diminishes the perceived contrast.  But what if he uses a focal reducer?  Why not get the scope down to say, f/7.5 with a 0.5 reducer?  It might be a bugger, but OP's got a 2" diagonal and likely a 2"/1.25" adapter.... so what about a TV55 and a $40 0.5x reducer?

The OP could certainly get lower power that way, but the baffle tube opening doesn't change, and the vignetting would likely be ferocious, or there would be a complete cutoff well before the field stop. Has anyone tried this?

[SeattleScott]

I have used the Antares 0.63 with my 6” Mak. The baffle causes a hard stop at about 1.8-1.9 degrees. Keep in mind the 180 Mak has 50% more focal length, and at least the older models had a smaller baffle tube. I think the newer models have 34mm or something, more like my Mak.

Scott

[Redbetter]

I have used the Antares 0.63 with my 6” Mak. The baffle causes a hard stop at about 1.8-1.9 degrees. 

Did you determine the field width via drift timing?  That is one of the things I am curious about with given scopes, putting some more precise numbers down for observed cut offs with the extreme cases of using reducers.  Unfortunately, with Maks and SCT's the true field is not something we can determine from specs a lone because of the moving primary focus system.  Length added (or subtracted) by different diagonals/adapters, eyepiece focal planes, and reducers/correctors each significantly alter the operating focal length of the system.  Fortunately, by drift timing one can determine the true field of view. 

 

A person can also get a measurement of the focal length and change in focal length of a scope with a given configuration.  To do this one needs to employ a short or moderate focal length eyepiece with known field stop diameter, then do a set of timings at the normal/native configuration of the scope, then repeat with the same eyepiece in the new configuration.  As long as a short enough focal length was chosen that the new configuration doesn't risk full cut off, this test will reveal the change in focal length of the scope. 

 

This works well for later comparisons of eyepieces with focal planes all in the same approximate position.  One has to do some extrapolation for eyepieces with focal planes that are far way from this:  e.g. the 55 Plossl, 40 Plossl, some longer focal length Delos, longer Naglers (e.g. 31 and 22), and many Ethos.  These extrapolations for non-reducer system can used fixed factors for simply changing diagonal types, but the reducers are going to result in a different factor.

[SeattleScott]

I determined the size by observing the Pleiades, which is 1.9 degrees wide. It just about fits the entire thing with no framing.

Scott

[Redbetter]

Scott,

 

Did you use specific stars for the metric?  The confusion for me is in determining where to say the Pleiades end.  The primary stars can be framed in a 1.2 degree field, but beyond that it becomes more challenging to determine where to cut things off.  If I can find specific pairs of stars that are right at the widest part of the field stop then I can use Stellarium's angle tool to measure the distance. 

 

The method above isn't as accurate as drift timing can be, but it doesn't take as long to measure wide fields...especially since it often takes multiple tries to be certain the star is traversing the widest possible path.  Generally, the largest number determined by drift timing is the most accurate one...unless I made some sort of timing error (starting the stopwatch too soon and/or stopping it too late) or the scope was somehow bumped, etc.  I imagine it could be difficult to see exactly where full cutoff is starting and ending, complicating things compared to vignetted cases at the field stop.

[jmillsbss]

The OP could certainly get lower power that way, but the baffle tube opening doesn't change, and the vignetting would likely be ferocious, or there would be a complete cutoff well before the field stop. Has anyone tried this?

Yeah I never tried it in a proper "as designed for" situation either. But just messing about with the piddly reducer I had, it was obvious there was difficulty staying on the image. Vignetting from the baffle I suppose. Its not really the right way to do it I suppose.

[Jon Isaacs]

My two cents:

 

Don't worry about "framing" the Orion nebula.  It's got so much structure and detail that it's interesting at any magnification and field of view.  I calculate the maximum possible field of view with a 180mm F/15 is 0.98 degrees, that's plenty.  

 

As Bob said, try it in your existing 25mm wide field, that's 108x with a 1.7mm exit pupil.  That's a good place to be. 

 

Jon